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Home My WebLink About1.23 Aquifer Sustainability Study 1 TABLE OF CONTENTS INTRODUCTION ......................................................................................................................................................... 2 BACKGROUND ........................................................................................................................................................... 2 AQUIFER CHARACTERISTICS ................................................................................................................................. 2 PRECIPITATION INFILTRATION ............................................................................................................................. 3 AQUIFER RECHARGE ............................................................................................................................................... 4 ANTICIPATED DIVERSIONS & DEPLETIONS ....................................................................................................... 5 TOTAL SPRING VALLEY AQUIFER DEMANDS ................................................................................................... 7 SUMMARY .................................................................................................................................................................. 8 FIGURE 1: SPRING VALLEY RANCH VICINITY MAP…………………………………………………………………………………………………….ATTACHED FIGURE 2: SPRING VALLEY RANCH GEOLOGY MAP…………………………………………………………………..……………………………...ATTACHED FIGURE 3: SPRING VALLEY RANCH 1991-2020 AVERAGE PRECIPITATION MAP…………………………….……………………………….ATTACHED FIGURE 4: SPRING VALLEY RANCH NATIONAL LAND COVER MAP…………………………….………………………………………………….ATTACHED TABLE 1: ESTIMATED PRECIPITATION AND INFILTRATION INTO THE SVA. *..................................................................................... 4 TABLE 2: ESTIMATED LOSSES TO FROM EVAPOTRANSPIRATION BY VEGETATION TYPE. ....................................................................... 5 TABLE 3: POTABLE WATER DEMANDS AND DEPLETIONS…………………………………………………………………………………………….ATTACHED TABLE 4: NON-POTABLE WATER DEMANDS AND DEPLETIONS…………………………………………………………………………………….ATTACHED TABLE 5: TOTAL POTABLE AND NON-POTABLE WATER DEMANDS AND DEPLETIONS…………….………………………………………….ATTACHED TABLE 6: MONTHLY DEPLETION AND DELAYED RETURN FLOW FACTORS DECREED IN CASE NO. 87CW155 ........................................ 5 TABLE 7: TOTAL DIVERSIONS AND DEPLETIONS FOR SPRING VALLEY DEVELOPMENTS BASED ON DECREED PLANS FOR AUGMENTATION .... 8 2 INTRODUCTION This report has been prepared to update previous engineering evaluations related to the sustainability of the Spring Valley Aquifer (SVA) located approximately 6 miles southeast of Glenwood Springs, CO (Figure 1). The SVA is identified as a major alluvial aquifer resource in the Colorado Groundwater Atlas prepared by the Colorado Geological Survey. The purpose of this updated study is to incorporate more modern datasets into the analysis and determine if recent changes to precipitation, temperature, and resultant hydrology have altered the results of previous analyses, all of which found the aquifer to have sufficient water in aquifer storage and recharge to support Spring Valley Ranch (SVR) and other planned developments. BACKGROUND Colorado River Engineering (CRE) has reviewed previous studies related to the SVA.1 2 3 These studies were undertaken in the early 2000’s to quantify the water availability and compare it to the water demands associated with the SVR development as well as other planned developments which were all contemplated to rely on the SVA. Gamba (2000) determined the probable amount of annual recharge to the Spring Valley Aquifer (SVA) to be 10,059 acre-feet per year on average based on average annual precipitation (1951-1980) of 19,908 acre-feet, evapotranspiration (ET) losses of 9,249 acre-feet, and estimated surface flow losses down Landis Creek of 600 acre-feet. The probable annual recharge was quantified to be well above the expected total development groundwater diversions, which are not completely consumptive to the aquifer, of 1,100 acre- feet which included 600 acre-feet from SVR and 500 acre-feet from other developments. HRS provided review of the Gamba analysis with a resultant recharge estimate of 4,700 acre-feet, which estimated crop ET from free surface water evaporation. The results of these studies have been updated by CRE utilizing more modern datasets considering recent changes in precipitation, satellite derived vegetation types, and more detailed consumptive use estimates. The Gamba analysis quantified the total water in storage in the aquifer to be 68,000 to 105,000 acre-feet of which 38,000 to 46,000 acre-feet is stored in the SVA and 30,000 to 60,000 acre-feet are available in the upland volcanic materials tributary to the SVA. The HRS analysis included a similar estimate of 82,000 acre-feet of water available in storage in the SVA. The aquifer serves as an underground reservoir to offset dry years with lower than normal recharge and to store water in above normal recharge years. AQUIFER CHARACTERISTICS The cited Gamba report provides a detailed explanation of the geologic conditions that formed the Spring Valley Hydrologic System, which is briefly summarized herein. The SVA tributary area 1 Gamba, J. 2000. The Spring Valley Hydrologic System. Prepared for Bill Peacher. 2 HRS Water Consultants, Inc, 2000. RE: Spring Valley Ranch – Review of Jerome Gamba & Associates, Inc. Report, The Spring Valley Hydrologic System. 3 Wright Water Engineers, Inc. 2000. Water Requirements, Water Resources, and Spring Valley Area Water Balance. Prepared for Spring Valley Development, Inc. 3 which contributes to recharge is approximately 15.4 square miles (Figure 1) and varies in elevation from 6,870 to 9,400 feet. The aquifer was formed as soluble salts present in the underlying Eagle Valley Evaporite formation were dissolved by groundwater resulting in collapse, deformation, shear fracturing, and faulting of the overlying Maroon formation and volcanic rocks. These processes resulted in the high infiltration rate and water bearing capacity of the volcanic rocks. Millions of years of erosion have resulted in removal of softer, unconsolidated cinders and ash from the surface and exposed the weather resistant basalt rocks. The ash and cinder lenses that remain below the basalt provide pockets of highly porous materials that detain groundwater, also called “hanging aquifers”. Water is channeled into these pockets via fractured and rubblized basalt on the surface. These areas are interconnected by subsurface fractures that slowly transmit water from higher elevations to lower elevations. The upland areas are the primary area of recharge. The SVA, which is a portion of the full contributing area of the aquifer, is a composite of a series of confined aquifers within the sediments overlaying bedrock which produce artesian wells. The confined aquifers in the lakebed sediments are comprised of sand and sandy gravel horizons confined between layers of clay or sandy, gravely clays. The bedrock form of the lake basin is a “half graben” with a fault on the south side of the basin. The blue gray clay layer acts as a seal between the lake sediments and underlying volcanic rock materials. PRECIPITATION INFILTRATION There have been several updates to Colorado’s annual average precipitation analysis since the 1951-1980 dataset utilized by Gamba. Climate normals are updated every 10-years to reflect the most recent 30-year period; the 1991-2020 climate normals were recently released. These data are available at a station scale but are also available as a gridded dataset produced by the PRISM Climate Group on an 800-meter resolution grid. This gridded data was overlain on the geologic unit map within the SVA tributary area as defined on Figure C-1-E of the Gamba report. A geology map is attached as Figure 2. The 1991-2020 average annual precipitation (Figure 3) was calculated for each geologic unit which include: PPM – Pennsylvanian/Permian Maroon Formation, Tb – Tertiary Volcanic Materials, and Ql – Quaternary Lake Sediments (aka SVA). The average annual precipitation over the SVA tributary area was calculated to be 18,384 acre-feet compared to the 19,908 acre-feet utilized by Gamba. This is a reduction of 1,524 acre-feet or 7.7%. 4 Table 1: Estimated Precipitation and Infiltration into the SVA. * *Note minor discrepancy in total acreage based on digitization of boundaries from Gamba, 2000. The infiltration rates by geologic unit utilized in the Gamba analysis were also utilized in the CRE analysis, as they were deemed to be appropriate, and are included in Table 1. The local geology exhibits relatively quick infiltration rates. Based on the assumed infiltration rates of the geologic units, the estimated infiltration has been quantified to be 9,318 acre-feet compared to the 10,314 acre-feet calculated by Gamba. This is an infiltration reduction of 996 acre-feet or 9.7% and is largely attributed to the reduced precipitation inputs. The full annual amount of ET was assumed to deplete the available precipitation inputs, regardless of whether water was available in soil moisture and available to plants or not, which bases the analysis on a conservative aquifer recharge amount. AQUIFER RECHARGE The total amount of infiltration is not realized as recharge to the aquifer due to losses from ET and surface runoff. Using the Gamba methodology, the probable recharge was determined using the following formula: Recharge = Precipitation – Evapotranspiration - Landis Creek surface flows Eq 1.1 Evapotranspiration was quantified by overlaying the National Land Cover Dataset (NLCD) (Figure 4), a satellite derived depiction of land cover, on the SVA Tributary area boundary and quantifying the area of various vegetation types. The NLCD was cross-checked with aerial photos to ensure accurate depiction of land cover types. If discrepancies were found, the area was included with other vegetation types supported with aerial photography. Native vegetation ET rates were obtained from the book values from the Handbook of Applied Hydrology, however, there are also large, irrigated pastures located within the SVA aquifer. The potential evapotranspiration (PET) from these irrigated pastures was updated using the Lease-Fallow Tool and ASCE standardized methodology for pasture grass using the study period 2000-2019, which was conservatively quantified to be 30-inches per year. Other vegetation types are shown in Table 2, below. Shrub/Scrub utilized high range values for sagebrush in western regions of 10-inches. Deciduous forest utilized the value for aspen of 23-inches. Evergreen forest utilized the average of the values Geologic Unit Area (ac)Infiltration Rate Mean Precip (mm) Mean Precip (in) Average Annual Precipitation Volume (AF) Estimated Infiltration (AF) PPM 2132 20% 612 24 4281 856 Tb 6290 60% 570 22 11763 7058 Ql 1453 60% 491 19 2341 1404 Total 9875 18384 9318 5 for lodgepole and Engelmann spruce-fir of 17-inches. Mixed forest utilized the average value of the deciduous and evergreen forests which is 20-inches. All of these values are greater than those in the Gamba analysis and represent an increase in demands due to changes in climate as well as more spatial detail to refine the vegetation types. The total annual potential ET was quantified to be 13,842 acre-feet/year and represents a conservative value which assumes water is always available to meet the demands of the various vegetation types. Table 2: Estimated losses to from evapotranspiration by vegetation type. Utilizing the Equation 1.1 results in the following estimated recharge: Recharge = 18,384 – 13,842 - 600 = 3,942 acre-feet These values represent average recharge conditions using conservative depletion assumptions. This is water available for groundwater withdrawals without creating an aquifer deficit, i.e., “mining”, since it will be replenished on an average annual basis. The CRE estimated recharge is 6,117 acre-feet less than what was estimated by Gamba due to decreased precipitation inputs and increased demands from evapotranspiration which are partly due to temperature and partly due to increased spatial representativeness. The estimated annual recharge is similar to the HRS results which quantified 4,700 acre-feet of recharge on average. ANTICIPATED DIVERSIONS & DEPLETIONS The development water demands for Storied Development’s amended SVR PUD plan (currently being reviewed by Garfield County) will be less than the previously approved SVR PUD demands; and less than the demands already decreed and covered by existing court approved augmentation plans in Case Nos. 87CW155 and 98CW254, the latter being the operative plan for augmentation. Basalt Water Conservancy District (BWCD) augments the structures, including wells, surface and storage structures, which will supply water for the development. In sum, the 98CW254 augmentation plan allows for an annual water demand of 1457 acre-feet of diversions, a total annual consumptive use of 974 acre-feet in a dry year, and an overall augmentation requirement of 420 acre feet. The 98CW254 decree allows for modifications and reconfigurations of the number of EQRs and amounts of irrigated acreage so long as the overall SVR PUD consumptive use does not exceed 974 acre-feet annually. Tables 3-5 (attached) provide details Vegetation Type Acreage (ac)ET (in/yr) ET Losses (AF/yr) Hay/Pasture/Herbaceous 756 30 1904 Shrub/Scrub 5031 10 4192 Deciduous Forest 3872 23 7421 Evergreen Forest 139 17 197 Mixed Forest 77 20 129 Total 9875 100 13842 6 of the potable, non-potable, and total diversions and depletions that are augmented pursuant to the BWCD contracts, as incorporated and approved in Case No. 98CW254. Potable diversions, which are attributed solely to groundwater sources, total 473.1 acre-feet with associated depletions of 177.5 acre-feet and include domestic in-house and irrigation uses associated with 695 EQR’s and 90 acres of domestic irrigation. The non-potable diversion, of which a portion will be satisfied by senior surface water rights, total 983.9 acre-feet with associated depletions of 796.96 acre-feet which includes uses of non-domestic irrigation for 420 acres and 24 acres of open surface water evaporation. Overall, the total project diversion demands are 1,457 acre-feet with associated depletions of 974 acre-feet. Again, Case No. 98CW254, paragraph 10.c. allows for modification to the number of EQRs and irrigated acreage if the depletions do not exceed 974 acre-feet. In contrast, Storied Development’s amended SVR PUD proposal seeks to modify certain components of the previously approved PUD including the type and number of development units, irrigation requirements, and to add snowmaking as a use of its non-potable water system. CRE has calculated the water requirements for the revised PUD plan and in sum, the total water demand for the revised PUD plan is 1,221 acre-feet/year, with total consumptive use of 688 acre- feet/year. This is less than the contemplated and approved water demand associated with the currently approved PUD; however, for purposes of this report and aquifer sustainability analysis, CRE utilizes the larger acre foot demands and depletions described above and approved in the 98CW254 case. Because most of the lands to be irrigated are located within the SVA tributary area, irrigation return flows will accrue to the aquifer and will not be totally consumptive to the aquifer. It is also anticipated, based on land use approvals and engineering related to the expansion of the Spring Valley Sanitation District, that treated wastewater effluent will also be returned within the SVA tributary area. It was estimated that approximately 25% of the treated effluent would return to the SVA by infiltration from the discharge point(s) along the Spring Valley Drainage basin minimizing adverse impacts to the Spring Valley environment.4 In addition, Storied Development will have rights to use the Spring Valley Sanitation District Pipeline decreed in Case No. 00CW21 in the amount of 3.48 c.f.s., conditional, for irrigation within the Spring Valley Sanitation District service area which encompasses the SVA tributary area. The direct use of treated effluent for irrigation will reduce the demand for groundwater and will supplement aquifer recharge. Lagged well depletions will be calculated pursuant to the BWCD decree (Exhibit F, Case No. 87CW155) based on the locations of the constructed wells. The well location will determine the lagged depletion zones which are used to quantify the timing of depletions to the stream from well pumping. Case Nos. 87CW155 and 98CW254 classified the Spring Valley wells in Groups F1 (SVA) and F2 (Upland Aquifers). The monthly depletion percentages by Well Group are shown in 4 Wright Water Engineers, Inc. March 24, 1999. RE: Spring Valley Sanitation District Service Plan Amendment (Exhibit 4.3 to Spring Valley Sanitation District Engineering Report for Application for site approval for modification or expansion of an existing domestic wastewater treatment plant and application and certification procedures for lift station and interceptors dated September 1999) 7 the following table which was attached as an exhibit in Case No. 87CW155. The timing of depletions dictates the monthly augmentation replacement requirements during periods of downstream call. Table 6: Monthly Depletion and Delayed Return Flow Factors Decreed in Case No. 87CW155 TOTAL SPRING VALLEY AQUIFER DEMANDS In addition to the demands associated with Spring Valley Ranch, several other subdivisions and individual properties rely upon the Spring Valley Aquifer for all or a portion of their overall water supplies. The following developments and associated plans for augmentation were reviewed and are summarized in Table 7. The demands include Spring Valley Ranch, Los Amigos (Elk Springs/Pinyon Mesa), Colorado Mountain College, Berkeley/Lake Springs Ranch, Lookout Mountain Ranch, and individual lot owners. It is not known if Lookout Mountain Ranch relies on the SVA for a portion of their water supplies because well construction logs and accounting are unavailable; however, the total demand was included in the interest of being conservative. There are approximately 30 individual properties with wells (or future wells) accessing the SVA area with an estimated annual diversion of 30 acre-feet and an estimated depletion of 10 acre-feet, which is based on engineering judgment. The total diversion from all developments relying on the SVA totals approximately 1,920 acre-feet while the total depletions are approximately 1,263 acre-feet. The total diversions represent 49% of the anticipated recharge while the total depletions represent only one third of the anticipated annual recharge to the SVA. The analysis illustrates that the anticipated uses, based on conservative assumptions, do not result in long- term mining of the groundwater aquifer as the average annual demands of the developments 8 are met by the average annual recharge to the aquifer. In addition, these demands do not consider the fact that a portion of the SVR irrigation demands will be met with senior, surface water rights, which results in irrigation return flows that deep percolate and recharge the SVA. The sustainability analysis is conservative and supports the conclusion that there is adequate groundwater supplies for all users of the SVA. This analysis, in conjunction with a groundwater monitoring plan, allows all SVA water users to manage the water resource in a sustainable manner. Table 7: Total Diversions and Depletions for Spring Valley Developments Based on Decreed Plans for Augmentation SUMMARY The estimated average annual recharge of 3,942 acre-feet is more than three times the estimated depletion of 1,263 acre-feet for all users of the SVA. Under the proposed amended PUD plan, groundwater withdrawals for irrigation will be less than calculated due to utilization of Landis Creek surface water rights, which have historically been used to irrigate the property, and only using groundwater for supplemental irrigation supplies. In addition to the annual recharge, it has been estimated by Gamba that there is 68,000 to 105,000 acre-feet of water in storage in the SVA and upland areas which essentially serve as an underground reservoir to balance extreme dry year and extended drought-year recharge with water demands. As was found in previous studies, there is sufficient water in storage in the SVA and available from annual recharge to serve all the proposed uses without injuring the groundwater resource. The groundwater levels in the SVA will experience seasonal and year to year fluctuations due to variability in precipitation and snowpack inputs. Each of the subdivisions that pump water from the SVA have a long term vested interest in a comprehensive groundwater monitoring plan to understand baseline and future groundwater conditions. A groundwater monitoring plan is currently being developed for implementation by these water users. Development Case No. Annual Diversion (AF) Annual Depletion (AF) Spring Valley Ranch 98CW256 1457.0 974.0 Los Amigos (Elk Springs and Pinyon Mesa)98CW312 159.8 117.0 Colorado Mountain College 99CW99 132.3 53.1 Lake Springs Ranch/Berkeley W-3571 105.2 97.6 Individual Lot Owners N/A 30.0 10.0 Lookout Mountain Ranch 84CW100 36.0 11.0 Grand Total 1920.3 1262.8 !( !(!( !( !( !( !( !( !( !( !(!( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !(!( !( !( !( !( !( !( !(!( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !(!( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !(!( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !(!( !( !( !(!( !( !( C a ttl e Creek LandisCreek LandisC reek F i s h e r Creek D e v i l s H o l e C r e e k Ca t t le Creek D eadmansCreek Me s a C r e e k Bear Creek Grindsto n e C r e e k Old H i g h w a y 8 2 C M C CM C Cottonwood Pass Old Dump C o r y e l l Fis h e r Ce m e t e r y Kin d a l l Cottonwood Pass H a r d w i c k B r i d g e Fi s h e r C r e e k Loo k o u t M o u n t a i n R e d C a n y o n Source: Esri, Maxar, Earthstar Geographics, and the GIS UserCommunity4 Legend Yield (gpm) Yield !(0 - 10 !(11 - 25 !(26 - 75 !(76 - 200 !(201 - 400 Spring Valley Aquifer SVA_Tributary_Area CountyRoads040711 Spring Valley Holdings LLCAll_Named_NHDFlowline FType Rivers Ditches Connector Pipeline Streams Document Name: SpringValleyRanchAquifer.mxd Drawn by: WR Approved by: WR Date: 4/5/2024 PO Box 1301Rifle, CO 81650Tel 970-625-4933 1, 4 0 0 2, 8 0 0 0 Graphic Scale in Feet Client: Figure:Spring Valley Aquifer and Wells Vicinity Map 1 1273: Spring Valley Ranch C a ttl e Creek LandisCreek LandisC reek F i s h e r Creek D e v i l s H o l e C r e e k Ca t t le Creek D eadmansCreek Me s a C r e e k Bear Creek Grindsto n e C r e e k Old H i g h w a y 8 2 C M C CM C Cottonwood Pass Old Dump C o r y e l l Fis h e r Ce m e t e r y Kin d a l l Cottonwood Pass H a r d w i c k B r i d g e Fi s h e r C r e e k Loo k o u t M o u n t a i n R e d C a n y o n Source: Esri, Maxar, Earthstar Geographics, and the GIS UserCommunity4 Legend Spring Valley Aquifer SVA_Tributary_Area CountyRoads040711All_Named_NHDFlowline FType Rivers Ditches Connector Pipeline Streams Ql Tb PPM Document Name: SpringValleyRanchAquifer.mxd Drawn by: WR Approved by: WR Date: 4/4/2024 PO Box 1301Rifle, CO 81650Tel 970-625-4933 1, 4 0 0 2, 8 0 0 0 Graphic Scale in Feet Client: Figure:Spring Valley AquiferGeologic Units 2 1273: Spring Valley Ranch 20-25" >25" <20" C a ttl e Creek LandisCreek LandisC reek F i s h e r Creek D e v i l s H o l e C r e e k Ca t t le Creek D eadmansCreek Me s a C r e e k Bear Creek Grindsto n e C r e e k Old H i g h w a y 8 2 C M C CM C Cottonwood Pass Old Dump C o r y e l l Fis h e r Ce m e t e r y Kind a l l Cottonwood Pass H a r d w i c k B r i d g e Fi s h e r C r e e k Loo k o u t M o u n t a i n R e d C a n y o n Source: Esri, Maxar, Earthstar Geographics, and the GIS UserCommunity4 Legend Spring Valley Aquifer SVA_Tributary_Area CountyRoads040711 All_Named_NHDFlowline FType Rivers Ditches Connector Pipeline StreamsPrecipitation inches 20 25 30 Document Name: SpringValleyRanchAquifer.mxd Drawn by: WR Approved by: WR Date: 4/4/2024 PO Box 1301Rifle, CO 81650Tel 970-625-4933 1, 4 0 0 2, 8 0 0 0 Graphic Scale in Feet Client: Figure:Spring Valley Aquifer1990-2020 Normal Precipitation (in)3 1273: Spring Valley Ranch C a ttl e Creek LandisCreek LandisC reek F i s h e r Creek D e v i l s H o l e C r e e k Ca t t le Creek D eadmansCreek Me s a C r e e k Bear Creek Grindsto n e C r e e k Old H i g h w a y 8 2 C M C CM C Cottonwood Pass Old Dump C o r y e l l Fis h e r Ce m e t e r y Kin d a l l Cottonwood Pass H a r d w i c k B r i d g e Fi s h e r C r e e k Loo k o u t M o u n t a i n R e d C a n y o n Source: Esri, Maxar, Earthstar Geographics, and the GIS UserCommunity4 Legend Spring Valley Aquifer SVA_Tributary_Area CountyRoads040711All_Named_NHDFlowline FType Rivers Ditches Connector Pipeline Streamsnlcd_co_utm13_Clip NLCD_Land Open Water Developed, Open Space Developed, Low Intensity Developed, Medium Intensity Developed, High Intensity Deciduous Forest Evergreen Forest Mixed Forest Shrub/Scrub Herbaceous Hay/Pasture Cultivated Crops Woody Wetlands Emergent Herbaceous Wetlands Document Name: SpringValleyRanchAquifer.mxd Drawn by: WR Approved by: WR Date: 4/4/2024 PO Box 1301Rifle, CO 81650Tel 970-625-4933 1, 4 0 0 2, 8 0 0 0 Graphic Scale in Feet Client: Figure:Spring Valley AquiferNational Land Cover Data 4 1273: Spring Valley Ranch In‐House Domestic Irrigation Total Diversion In‐House Domestic Irrigation Total Depletion Jan 100% 23.1 0.0 23.1 1.5 0.0 1.5 Feb 100% 21.1 0.0 21.1 1.3 0.0 1.3 Mar 100% 23.1 0.0 23.1 1.5 0.0 1.5 Apr 100% 22.4 16.9 39.3 1.4 13.5 14.9 May 100% 23.1 27.0 50.1 1.5 21.6 23.1 Jun 100% 22.4 41.6 64.0 1.4 33.3 34.7 Jul 100% 23.1 47.3 70.4 1.5 37.8 39.3 Aug 100% 23.1 39.4 62.5 1.5 31.5 33.0 Sep 100% 22.4 24.8 47.2 1.4 19.8 21.3 Oct 100% 23.1 3.4 26.5 1.5 2.7 4.2 Nov 100% 22.4 0.0 22.4 1.4 0.0 1.4 Dec 100% 23.1 0.0 23.1 1.5 0.0 1.5 Total 272.7 200.4 473.1 17.2 160.3 177.5 EQR 695 Gal/EQR/day 350 Domestic Irrigation (ac)90 Lawn/Golf/Open Space Unit Irrigation Diversion (AF/ac)2.24 Lawn/Golf/Open Space Unit CU (AF/ac)1.79 Lawn/Golf/Open Space Efficiency %80% Domestic Depln (%)6.3% Table 3: Potable Demands Diversions (AF)Depletion (AF) % Occupancy Month Diversions_Depletions Jan 0.0 0 0.0 0 0 0 Feb 0.0 0 0.0 0 0 0 Mar 0.0 1.9 1.9 0 1.9 1.9 Apr 78.8 4.1 82.9 63.04 4.1 67.14 May 126.0 7 133.0 100.8 7 107.8 Jun 194.3 9.6 203.9 155.44 9.6 165.04 Jul 220.5 9.8 230.3 176.4 9.8 186.2 Aug 183.8 7.2 191.0 147.04 7.2 154.24 Sep 115.5 5.5 121.0 92.4 5.5 97.9 Oct 15.8 3.1 18.9 12.64 3.1 15.74 Nov 0.0 1 1.0 0 1 1 Dec 0.0 0 0.0 0 0 0 Total 934.7 49.2 983.9 747.76 49.2 796.96 Irrigated Area (ac)420 Evaporation Area (ac)24 Table 4: Non‐Potable Demands Month Pond Evaporation Non‐Domestic Irrigation Total Diversions (AF) Non‐ Domestic Pond Evaporation Total Depletions (AF) Diversions_Depletions In‐House Irrigation Evap Total In‐House Irrigation Evap Total Jan 23.1 0.0 0 23.1 1.5 0.0 0 1.5 Feb 21.1 0.0 0 21.1 1.3 0.0 0 1.3 Mar 23.1 0.0 1.9 25.0 1.5 0.0 1.9 3.4 Apr 22.4 95.7 4.1 122.2 1.4 76.6 4.1 82.1 May 23.1 153.0 7 183.1 1.5 122.4 7 130.9 Jun 22.4 235.9 9.6 267.9 1.4 188.7 9.6 199.7 Jul 23.1 267.8 9.8 300.7 1.5 214.2 9.8 225.5 Aug 23.1 223.2 7.2 253.5 1.5 178.6 7.2 187.2 Sep 22.4 140.3 5.5 168.2 1.4 112.2 5.5 119.2 Oct 23.1 19.2 3.1 45.4 1.5 15.4 3.1 19.9 Nov 22.4 0.0 1 23.4 1.4 0.0 1 2.4 Dec 23.1 0.0 0 23.1 1.5 0.0 0 1.5 Total 272.66 1135.10 49.20 1456.96 17.18 908.08 49.20 974.46 Table 5: Total Potable and Non‐Potable Demands Month Total Diversion Total Depletion Diversions_Depletions Page 1 of 7 Colorado River Engineering P.O. Box 1301 Rifle, CO 81650 (970) 625-4933 November 27, 2024Storied Development LLCc/o Jeff Butterworth Via: JButterworth@storiedliving.com RE: Spring Valley Ranch – Response to Matrix Design Group, Inc. Review Letter – Aquifer Sustainability and Well Yield Physical Water Supply Dear Jeff: At the request of Storied Development, LLC, this letter presents the technical response to questions and comments provided by Matrix Design Group, Inc. (“Matrix”) in its September 6, 2024 review letter for Garfield County. Colorado River Engineering, Inc. (“CRE”) is addressing comments 1, 2, 3, and 5. Comments 4, 6, and 7 are addressed by Roaring Fork Engineering (“RFE”) in a separate response. SUMMARY The responses below provide information on 15 wells that have been drilled on the Spring Valley Ranch project property. Pumping tests on 9 wells demonstrate that Spring Valley Ranch has an adequate physical water supply for the project and 18 additional wells can be developed on the property. In addition, the Spring Valley Aquifer is a known groundwater resource specifically recognized by theColorado Division of Water Resources. The Spring Valley Aquifer has been characterized by private consultants, the Colorado Geological Survey, and the US Geological Survey. The sustainability of the aquifer has been analyzed and peer reviewed by numerous consultants. CRE has provided a current analysis with more refined data and analysis incorporating drier and hotter climate conditions that demonstrates the groundwater resource can supply the anticipated future demands of the Spring Valley Project and other existing/future projects. Spring Valley Ranch owns all of the water rights on Landis Creek. There is no local call from senior water rights on Landis Creek or Red Canyon CreekSpring Valley Ranch is in BWCD Contract Service Area A and is subject only to a downstream call on the Roaring Fork or Colorado Rivers. Releases from Ruedi Reservoir pursuant to BWCD Contract Nos. 43 and 328 and the decrees in Case Nos. 84CW212, 98CW255, and 22CW3009 will augment downstream depletions on the Roaring Fork or Colorado Rivers. Spring Valley Ranch has demonstrated an adequate legal and physical water supply for the project. Page 2 of 7 Colorado River Engineering P.O. Box 1301 Rifle, CO 81650 (970) 625-4933 Comment 1 – Spring Valley Aquifer Physical Water Supply The Matrix comment seeks additional information on the geology and characterization of the Spring Valley Aquifer (“SVA”) groundwater resource. Matrix also makes an observation that the area is dry arid climate with limited surface streamflows and Consolidated Reservoir in the adjacent drainage has very little storage throughout the year. In response, it should be noted that the annual precipitation for the tributary area for the SVA ranges from 16 inches to 30 inches. The surface soils and geology have a high infiltration rate. Consolidated Reservoir is an irrigation reservoir that is full or could be full, usually at the start of the irrigation season, but then continually drops in storage due to evaporation, seepage, and irrigation releases. Thus, it is not an indicator of “limited streamflows” in the area.” The SVA has been studied and characterized by Jerome Gamba and Associates in its March 10, 2000 report titled The Spring Valley Hydrologic System and by the Colorado Geological Survey/US Geological Survey in the Geological Society of America Special Paper 366, 2002 titled Evaporite Tectonism in the Lower Roaring Fork Valley, West Central Colorado.(Copies attached in Appendix A). The Gamba study is summarized in the April 11, 2024 CRE report titled Spring Valley Aquifer Sustainability Study. The CGS/USGS report utilizes data from the Spring Valley Ranch wells and confirms the geological characterization presented by Gamba. The SVA is located in a closed basin created by a collapse in the underlying Eagle Valley Evaporite which caused the Maroon formation bedrock to shear at a fault line on the west side of the valley. The CGS/USGS report also provides an alternative theory that a large block of the Maroon formation “rafted” toward the Roaring Fork River Valley, leaving behind a closed basin. In both scenarios, the closed basin was a lake that filled with alluvial, lacustrine (lake), and colluvial deposits creating a groundwater resource. The CGS/USGS report states that “When early settlers first homesteaded this region, Spring Valley was a closed depression and a lake occupied much of the valley floor (Calvin Cox, 1994, personal commun.). The presence of lacustrine sediments beneath much of the valley supports this conclusion. The settlers hand dug a drain ditch at the north end of the valley shortly before the end of the 19th century, drained the lake, and turned the valley floor into agricultural land.” The characterization of the SVA is visually presented in the attached Figures 1 and 2 from the two reports. Due to the collapse or rafting of the bedrock, the land surrounding the basin became over-steepened and experienced landslides. The resulting landslide deposits with large scarps or benches are unconsolidated material containing large blocks of basalt and bouldery basalt rubble. The landslide deposits and underlying fractured Maroon formation provide “upland aquifers” that are tributary to the SVA. The surface and subsurface flow of water is towards the SVA. This conclusion, visually shown on Figures 1 and 2, is supported by springs that emerge from the hillside to the east, wells drilled into these “upland aquifers”, and a groundwater ridge to the west on Los Amigos Mesa and to the north on Lookout Mountain. A continuous groundwater gradient to the southwest towards CMC, and to the northwest towards Red Canyon, appear to be the discharge areas out of the SVA, into the Maroon Page 3 of 7 Colorado River Engineering P.O. Box 1301 Rifle, CO 81650 (970) 625-4933 formation, and ultimately to the Roaring Fork River. The aquifer deposits appear to seal the fault on the west end of the SVA. The SVA and the adjacent upland aquifers to the east have a significant amount of pore space storage of groundwater. Gamba conservatively estimated that the SVA has between 38,000 and 46,000 acre feet of storage and the upland aquifers have between 30,000 and 60,000 acre feet of storage. HRS Water Consultants, Inc. peer reviewed the Gamba report in a March 10, 2000 letter (see Appendix A) and estimated there is a total of 82,000 acre feet of storage in the Spring Valley area aquifers. HRS also analyzed soils data and determined that the soils have high infiltration rates and low soil moisture holding capacity, supporting the conclusion that a significant amount of the precipitation infiltrates the soils and reaches the groundwater. Water is not tied up and trapped in the soil on a cumulative basis year after year. HRS concluded that the average aquifer recharge rate is estimated at 4,700 acre feet per year. The CRE aquifer sustainability report estimated the annual recharge at approximately 3,950 acre feet per year. This analysis includes several conservative assumptions. First, the full annual amount of ET from vegetation was assumed to deplete the available precipitation inputs, regardless of whether water was available in soil moisture and available to plants or not. Based on the low soil moisture holding capacity and the distribution of precipitation throughout the year, adequate soil moisture would not be available throughout the growing season. This assumption can account for water tied up in the soil that is ultimately lost from the system. Second, the surface water runoff in Landis Creek that leaves the basin down Red Canyon (600 acre feet apparently based on the WWE observations) is significantly overstated and likely includes runoff from the Red Canyon Creek basin not tributary to Spring Valley. In addition, any surface water flowing through Spring Valley to the northwest is diverted and used to flood irrigate hay and pasture land. A portion of this surface flow will return to the groundwater after application to the ground for irrigation. In addition, the ET depletions from the ground cover within the tributary basin includes irrigation that occurs with the surface water flow. The CRE aquifer sustainability study (and prior studies) do not include an estimate for discharge from the aquifer in the comparison of water demands and annual recharge because the aquifer is a flow through system with significant storage. The rate of discharge to the Roaring Fork River is likely a function of the aquifer elevation, the higher the elevation the larger the ground water gradient controlling the flow of groundwater. Comment 2 – Existing Well Yield The Matrix comment questions whether the pumping tests conducted by LRE Water demonstrate firm yields as presented in the January 25, 2023 LRE Water report titled Spring Valley Ranch Physical Water Supply Report. Matrix identified a concern with large drawdown of 340 feet in one of the wells. In Page 4 of 7 Colorado River Engineering P.O. Box 1301 Rifle, CO 81650 (970) 625-4933 response, the actual drawdown in SVH Well No. 10 was 245 feet, the 340 foot number was the depth to groundwater. The large drawdown was due to the initial pumping rate of 40 gpm and the average pumping rate of 11 gpm in a well that produces about 5 gpm. Regardless, SVR Well No. 10 will not be used as a production well for the project. The proposed water supply plan for the potable water system outlined by RFE is to develop at least 315 gpm from wells on the Middle Bench and on the mountain. The 315 gpm represents the maximum peak day demand in June and July. During this time frame, the aquifer recharge from snowmelt is at higher rates and well yields are anticipated to be higher than during the winter months when pumping tests have been conducted on the wells. As described below, there are five existing wells drilled on the Middle Bench with a long term yield estimated at 205 gpm. There is an existing well on the mountain below Hopkins Reservoir with a yield of 75 gpm for a total of 280 gpm. Spring Valley Ranch can develop two additional decreed wells on the Middle Bench, and has the right to develop up to 18 additional wells on the property. The additional capacity can be added in the future when the project builds out and the water demand requires additional supply. In addition, there are three high capacity SVA aquifer wells. The three wells have been tested with a combined long term yield of approximately 600 gpm. Additional high capacity wells can be developed in the SVA. It is proposed to use the SVA wells to provide supplemental irrigation water for open space and golf course areas, and to supply the snowmaking demand. Fifteen wells have been drilled on the Spring Valley Ranch property to characterize the sub surface geology and to evaluate the yield of wells in the SVA and the adjacent upland aquifers. The locationsof the wells are shown on the attached Figure 3. Pumping tests of these wells have occurred during winter months when the seasonal groundwater elevations are lowest and the recharge is low. LRE Water conducted pumping tests in the winter of 2022/2023 on eight of the wells, including one in the SVA, five on the Middle Bench, and two in the upper mountain. RFE conducted pumping tests on one Middle Bench well and one SVA well in 2021. WWE conducted pumping tests on three Middle Bench wells in 1998, 1999 and 2000, and one SVA well in 2000. A summary of the well permits, well construction data, and pumping tests is provided on the attached Table 1. WWE conducted a 2 week pumping test on SVR Well No. 6 from February 29, 2000 – March 13, 2000. The results are summarized in the attached March 21, 2000 letter and indicate a 250 gpm plus yield from the SVA with pumping effects observed in a well 500 feet away, but not in a well 700 feet away. WWE conducted several 24-hour tests in 1998 and 1999 on Middle Bench wells SVR Well No. 20 (Gamba No. 1), ASR Well No. 13 (Gamba No. 3), and ASR Well No. 14 (Gamba No. 4). WWE then conducted testing in winter of 2000 for 11 days on SVR Well No. 20, for 36 days on ASR Well No. 13, Page 5 of 7 Colorado River Engineering P.O. Box 1301 Rifle, CO 81650 (970) 625-4933 and for 16 days on ASR Well No. 14. WWE opined that the wells had reliable yields of 30 gpm, 75 gpm, and 30 gpm respectively for a total of 135 gpm. RFE conducted 24-hour pumping tests on SVR Well No. 17 and SVR Well No. 20 in the fall of 2021. SVR Well No. 17 is in the SVA, was pumped at 95 gpm, and can reliably yield at least 95 gpm. SVR Well No. 20 is on the Middle Bench, was pumped at 65 gpm, and can reliably yield at least 30 gpm as indicated in the WWE testing. LRE Water conducted 24-hour pumping tests on 8 wells as described in the January 25, 2023 report submitted with the current application to Garfield County. The SVA well tested by LRE Water was Spring Valley Well No. 1. The LRE Water report indicates that this SVA well can reliably yield at least 250 gpm. Well 36569-MH located on the mountain below Hopkins Reservoir was pumped at 100 gpm and could reliably yield at least 75 gpm. The Middle Bench wells have estimated yields as follows. SVR Well No. 10 was pumped at an average rate of 11 gpm and could reliably yield approximately 10 gpm. SVR Well No. 14 was pumped at an average rate of 10 gpm and has a reliable yield of at least 30 gpm as indicated in prior testing by WWE. SVR Well No. 15 was pumped at an average rate of 79 gpm and has a reliable yield of at least 50 gpm. ASR Well No. 16 was pumped at an average rate of 54 gpm and appears to have a reliable yield of approximately 20 gpm. SVR Well No. 20 was pumped at an average rate of 52 gpm and confirms a reliable yield of at least 30 gpm. The above pumping tests indicate that the SVA wells yield approximately 600 gpm. The current wells on the Middle Bench have a reliable yield estimated at approximately 205 gpm. In addition, the mountain well below Hopkins Reservoir adds another 75 gpm for a total of 280 gpm for the central potable water system. The Spring Valley Ranch can develop one or two additional wells on the Middle Bench at some point in the future when the potable water system demand requires additional supplies. In the event the Middle Bench wells do not provide the full buildout potable water supply, one of theSVA wells can be added to the potable water system. The pumping tests demonstrate that the groundwater resources on the property are adequate to provide the physical water supply for the project. Additional high capacity SVA wells can be developed and up to 18 additional wells can be drilled on the property. Spring Valley Ranch has demonstrated an adequate physical water supply for the project. Page 6 of 7 Colorado River Engineering P.O. Box 1301 Rifle, CO 81650 (970) 625-4933 Comment 3 – Irrigation Demand The Matrix comment is that the annual consumptive use rate of 1.79 AF/acre stated in the Legal Water Supply Report is low. There appears to be a consumptive use rate of 2.13 AF/acre in one report, there is an apparent inconsistency in irrigation efficiency (67% vs 80%), an inconsistency in the peak daily application rate (0.12 inch vs 0.22 inch), and an inconsistency in the golf course acreage (100 acres vs 124 acres). The Legal Water Supply Report presents the decreed consumptive use rate of 1.79 AF/acre as decreed in Case No. 98CW254 for the project and the value was based on the cooler and wetter climate data in the 1990’s. The engineering tables are based on a consumptive use rate of 2.13 AF/acre (calculated using climate data through 2020) and an irrigation efficiency of 80%. The Golf Course can have up to 124 acres of irrigation, which equates to a demand of 329 AF using 2.13 AF/acre and 80% irrigation efficiency. The 100 acres in the RFE report was a typo and Matrix back calculated an efficiency of 67% based on 100 acres of irrigation. The application of 0.12 inch in July in the RFE report appears to be a typo. CRE agrees that the estimated water demand is 0.22 inch per day in July. Comment 5 – Legal Water Supply The Matrix comment raises questions about a local water rights administrative call on Landis Creek and the flow of water in Landis Creek downstream from the project. Landis Creek terminates in Spring Valley. The potential flow of water to the north is a ditch that could convey high flows from runoff into Red Canyon Creek. Red Canyon Creek only flows during snowmelt and rainstorm runoff events. Spring Valley Ranch owns all of the water rights on Landis Creek. There is no local call from senior water rights on Landis Creek or Red Canyon Creek. Spring Valley Ranch will sweep the flow in Landis Creek at its historic headgate consistent with historic irrigation practices. Spring Valley Ranch is in BWCD Contract Service Area A and is subject only to a downstream call on the Roaring Fork or Colorado Rivers. Releases from Ruedi Reservoir pursuant to BWCD Contract Nos. 43 and 328 and the decrees in Case Nos. 84CW212, 98CW255, and 22CW3009 will augment downstream depletions on the Roaring Fork or Colorado Rivers. Spring Valley Ranch has demonstrated an adequate legal water supply for the project. Page 7 of 7 Colorado River Engineering P.O. Box 1301 Rifle, CO 81650 (970) 625-4933 Please call if you have any questions or need additional information. Sincerely, Colorado River Engineering, Inc. Michael Erion, P.E.Principal Water Resources Engineer 1273MJE/mje Cc: Scott Miller, Esq. Jon Fredericks Michaela Craig Attachments:Figures 1-3Table 1Appendix A Reference Documents Evaporite tectonism in the lower Roaring Fork River valley, west-central Colorado 91 Figure 16. Schematic cross sections (E–E) showing two possible interpretations of the subsurface geology through Spring Valley. Upper cross section depicts the Spring Valley structure as a half graben chiefly due to removal of evaporite from beneath the valley by dissolution. In the lower cross section, the Spring Valley structure is shown as a pull-apart feature caused by evaporite flow toward the Roaring Fork River valley. Location of cross section shown on Figure 2. model, the sediment deposited in the Spring Valley structure would directly overlie evaporite. Strain along the southern margin of thehypothesizedrafted block may be largely lateral shearing. The strain would occur as sinistral-strike slip or oblique slip along a narrow, arcuate fault zone that starts in the southeast corner of the structure, bends to a nearly west trend, and disappears into the evaporitic rocks that crop out beneath the volcanic rocks on the east wall of the river valley (Fig. 2). Lateral strain on thenorthernmargin of a rafted Spring Valley structure would in part be accom- modated by thenarrow grabenthatextendsnorthwestwardfrom Spring Valley and in part by the complex fault swarm between the graben and the river valley. Minor structures.Several small synclinal sags deform the Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user ),*85( C a t t l e Creek LandisCreek Landis C r e e k F i s h e r Creek D e v i l s H o l e C r e e k Ca t t le Creek D e a d m ansCreek Me s a C r e e k Bear Creek Grindsto n e C r e e k Old H i g h w a y 8 2 C M C CM C Cottonw ood P ass Old Dump C o r y e l l Fis h e r Ce m e t e r y Kin d a l l Cottonwood Pass H a r d w i c k B r i d g e Fi s h e r Cr e e k Loo k o u t M o u n t a i n R e d C a n y o n Source: Esri, Maxar, Earthstar Geographics, and the GIS UserCommunity4 Legend Spring Valley Aquifer SVA_Tributary_Area CountyRoads040711 All_Named_NHDFlowline FType Rivers Ditches Connector Pipeline Streams Ql Tb PPM Document Name: SpringValleyRanchAquifer.mxd Drawn by: WR Approved by: WR Date: 4/4/2024 PO Box 1301Rifle, CO 81650Tel 970-625-4933 1, 4 0 0 2, 8 0 0 0 Graphic Scale in Feet Client: Figure:Spring Valley AquiferGeologic Units 2 1273: Spring Valley Ranch PPM Tb Ql Spring Valley RanchMap Key Garfield County ParcelsProperty LineSpring Valley Holdings LLC Well Location Source !(Alta Survey 2022 !(LRE GPS 2022 !(WWE Well Map 2001 !(Not Drilled (Decreed) Data Sources:U.S. Bureau of Land ManagementU.S. Census BureauU.S. Department of AgricultureU.S. Geological SurveyCO Department of Water ResourcesCO Department of Transportation !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( 36567-MH(Gamba #5) 36569-MH(Gamba #6) 36760-MH ASR Well No. 15(Gamba #1A) 51363-F Spring Valley Ranch Well No. 2 56722-F SVH Well No. 10 86627-F SVR Well No. 17(WELL #03-2A) 86628-FSVR Well No. 20(Gamba #1) 86629-F ASR Well No. 16(Gamba #8) 86630-FSpring ValleyWell No. 1 86631-F Spring Valley RanchWell No. 3 76874-F SVR Well No. 21 66298-F ASR Well No. 13(Gamba #3) 66299-F ASR Well No. 14(Gamba #4) 56717-F SVH Well No. 5 56719-F SVH Well No. 7 56720-F SVH Well No. 8 56721-F SVH Well No. 9 68886-F SVR Well No. 19 68887-F SVR Well No. 18 251164-WELL #03-1251165-WELL #03-2 251166-WELL #03-3 35164-MHGamba #2 68889-F SVH Well No. 6 Source: Esri, Maxar, Earthstar Geographics, and the GIS User Community Document Name: Figure 3 - SVR Well Inventory.mxdDrawn by: JT Figure: PO Box 1301Rifle, CO 81650Tel 970-625-4933 Client:Date: 11/21/2024Approved by: MG 3 1273 Well Inventory : 1, 0 0 0 2, 0 0 0 0 Graphic Scale in Feet Legal Name Shown on Maps by 1,2,3,4,5,6 Permit No. Associated Permit Associated Case Status UTMX UTMY Applicant Well Depth (ft) Yield (gpm) Static Water Level (ft) Total Depth (ft)Yield (gpm)Static Water Level (ft)Yield (gpm)Static Water Level (ft) Field Well Depth (ft) Static Water Level (ft) Top of Casing (in) Spring Valley Well No. 1 LRE, WWE, CRE, Alta Survey 86630-F 23334-F, 28959-F, 324058-, 56716-F, 51362-F 82CW0075, 84CW0212, 87CW0155, 98CW0255, 98CW0254, W3298, 22CW3009 Well Constructed 307104.8 4375360.0 SPRING VALLEY HOLDINGS LLC (ARDENNE, MARTIN V.)305 300 18 300 22 360 18.8 17 Spring Valley Ranch Well No. 2 LRE, WWE, CRE, Alta Survey 51363-F 12722-AD, 28960-F, 23679- F 82CW0075, 84CW0212, 87CW0155, 98CW0255, 98CW0254, W3298, 22CW3009 Well Constructed 307215.3 4375575.2 SPRING VALLEY DEVELOPMENT INC 00 0 20 6 207 4.6 4 Spring Valley Ranch Well No. 3 LRE, WWE, CRE, Alta Survey 86631-F 96896-, 23518-F, 28961-F, 52185-F 82CW0075, 84CW0212, 87CW0155, 98CW0255, 98CW0254, W3298, 22CW3009 Well Constructed 306850.4 4375444.8 SPRING VALLEY HOLDINGS LLC (ARDENNE, MARTIN V.)111 20 25 10 44 69.4 39.7 17.5 SVR Well No. 17 LRE, Alta Survey 86627-F 66297-F, 251755-, 324057- 22CW3009 Well Constructed 307746.9 4374255.8 SPRING VALLEY HOLDINGS LLC (ARDENNE, MARTIN V.)320 100+ 9 75 - 300 0 and flowing out 30 SVR Well No. 21 LRE 76874-F 67700-F, 276909- 22CW3009 Well Constructed 307176.5 4375951.5 LAGIGLIA LOUIS & DONNALYNE 80 10 43 -- - 52 - SVR Well No. 20 (Gamba #1) LRE, WWE, Alta Survey 86628-F 68885-F, 34995-MH, 324055-, 66562-F 22CW3009 Well Constructed 310198.7 4375286.2 SPRING VALLEY HOLDINGS LLC (ARDENNE, MARTIN V.)223 95 105 220 30 107 51.69 113 250.3 110.8 13.5 ASR Well No. 13 (Gamba #3) LRE, WWE, CRE, Alta Survey 66298-F 35174-MH 82CW0075, 84CW0212, 87CW0155, 98CW0255, 98CW0254, W3298, 22CW3009 Well Constructed 309141.1 4376515.5 SPRING VALLEY HOLDINGS LLC 200 90 140 202 75+ 138 -- 212 143.1 32 ASR Well No. 14 (Gamba #4) LRE, WWE, CRE, Alta Survey 66299-F 35175-MH 82CW0075, 84CW0212, 87CW0155, 98CW0255, 98CW0254, W3298, 22CW3009 Well Constructed 309490.1 4376213.5 SPRING VALLEY HOLDINGS LLC 180 90 134 182 30-50 137 10 143.6 181.5 114 28 ASR Well No. 15 (Gamba #1A) LRE, WWE, CRE, Alta Survey 36760-MH -82CW0075, 84CW0212, 87CW0155, 98CW0255, 98CW0254, W3298, 22CW3009 Well Constructed 310264.6 4375236.5 SPRING VALLEY DEV INC 220 100 105 100 112.8 209.6 111.5 18.5 ASR Well No. 16 (Gamba #8) LRE, CRE, Alta Survey 86629-F 245477-, 66563-F, 68888-F, 324056- 82CW0075, 84CW0212, 87CW0155, 98CW0255, 98CW0254, W3298, 22CW3009 Well Constructed 308943.8 4377148.5 SPRING VALLEY HOLDINGS LLC (ARDENNE, MARTIN V.)260 50 23 60 20.25 152 18.9 21 35164-MH (Gamba #2) LRE, Alta Survey 35164-MH 251166-, Possibly 31598- - Well Constructed 311097.7 4374426.6 ASPEN SPRINGS RANCH 455 55 330 - - 364 320.6 18.5 36567-MH (Gamba #5) LRE, WWE, Alta Survey 36567-MH --Well Constructed 310413.6 4378043.2 SPRING VALLEY DEV INC 250 6 70 7.7 89 36569-MH (Gamba #6) LRE, WWE, Alta Survey 36569-MH 35171-MH - Well Constructed 310020.7 4378457.2 SPRING VALLEY DVLP INC 163 70 10 100 20 175 8.9 - SVH Well. No 6 WWE, CRE, Alta Survey 68889-F 51365-F, 28963-F, 56718-F, 12725-AD 82CW0075, 84CW0212, 87CW0155, 98CW0255, 98CW0254, W3298, 22CW3009 Permit Issued 306963.3 4375306.4 SPRING VALLEY HOLDINGS LLC 400 250 125 470 0 4.4 SVH Well. No 10 LRE, CRE, Alta Survey 33819-MH 28967-F, 51369-F, 10102- AD, 12729-AD, 56722-F 82CW0075, 84CW0212, 87CW0155, 98CW0255, 98CW0254, W3298, 22CW3009 Well Constructed 309862.5 4375250.1 SPRING VALLEY RANCH 360 15 90 11.4 95.7 346 121.4 - SVH Well. No 5 CRE, Alta Survey 56717-F 28962-F, 51364-F 82CW0075, 84CW0212, 87CW0155, 98CW0255, 98CW0254, W3298, 22CW3009 Permit Issued 307250.7 4375474.5 SPRING VALLEY DEVELOPMENT INC SVH Well. No 7 CRE, Alta Survey 56719-F 28964-F, 51366-F 82CW0075, 84CW0212, 87CW0155, 98CW0255, 98CW0254, W3298, 22CW3009 Permit Issued 307359.8 4375712.9 SPRING VALLEY DEVELOPMENT INC SVH Well. No 8 CRE, Alta Survey 56720-F 28965-F, 51367-F 82CW0075, 84CW0212, 87CW0155, 98CW0255, 98CW0254, W3298, 22CW3009 Permit Issued 309498.0 4375620.9 SPRING VALLEY DEVELOPMENT INC SVH Well. No 9 CRE, Alta Survey 56721-F 28966-F, 51368-F, 10101- AD 82CW0075, 84CW0212, 87CW0155, 98CW0255, 98CW0254, W3298, 22CW3009 Permit Issued 309600.8 4375527.3 SPRING VALLEY DEVELOPMENT INC SVR Well No. 18 Alta Survey 68887-F 66560-F 22CW3009 Permit Issued 307602.9 4374224.2 SPRING VALLEY HOLDINGS LLC SVR Well No. 19 Alta Survey 68886-F 66561-F 22CW3009 Permit Issued 307633.3 4374072.8 SPRING VALLEY HOLDINGS LLC SVR Ranch House DWR only 274091---Well Constructed 307133.0 4375953.7 SPRING VALLEY HOLDINGS LLC 80 15 46 Well #03-1 Alta Survey 251164---Well Constructed 308523.6 4373784.9 SPRING VALLEY DEVELOPMENT INC 280 50 92 Well #03-2 Alta Survey 251165---Permit Expired 307792.6 4373967.2 SPRING VALLEY DEVELOPMENT INC Well #03-3 Alta Survey 251166---Permit Expired 310496.7 4374895.5 SPRING VALLEY DEVELOPMENT INC Gamba #7 WWE ------- Data references: 1.)WWE - Report w/ Map "Spring Valley Upland Aquifer Pumping Tests - 2000" (2000-03-10) by Wright Water Engineers, Inc (Gamba Wells #1, 3, and 4 tested Jan/Feb 2000) 2.)WWE - Report w/ Map "Spring Valley Ranch Well No. 6" (2000-03-21) by Wright Water Engineers, Inc (SVR Well No. 6 tested Feb 29, 2000) 3.)LRE - Map "Spring Valley Ranch Well Locations and Pumping Test Rates", (2022-10-10) by LRE Water. Map shows Yield and Static Water Level of tested wells 4.)CRE - Map "Water Rights Summary Map", (2022-12-06) by Colorado River Engineering 5.)Alta Survey - Map obtained from Roaring Fork Engineering (data collected in 2022) 6.)DWR - Colorado Division of Water Resources data from well attribute tables and Well Construction Reports (data accessed October 2024) 7.)RFE - Table provided by Roaring Fork Engineering summarizing Static Water Level, Field Depth, and Top of Casing of tested wells (2024-10-22) Table 1 Spring Valley Ranch Well Inventory No Well Completion Report RFE Measurement 2024 7 Not located - due to snow Not Located - DNE Possible duplicate of SVR Well No. Well Description LRE Measurement 2022 3DWR Well Data 5 WWE Measurement 2000 1,2 Colorado River Engineering 11/21/2024 Geological Society of America Special Paper 366 2002 73 Evaporite tectonism in the lower Roaring Fork River valley, west-central Colorado Robert M. Kirkham Colorado Geological Survey, 5253 County Road 1 South, Alamosa, Colorado 81101, USA Randall K. Streufert Summit Geology and Consulting, Silverthorne, Colorado USA Michael J. Kunk James R. Budahn Mark R. Hudson William J. Perry Jr. U.S. Geological Survey, Box 25046, Denver Federal Center, Denver, Colorado 80225, USA ABSTRACT Evaporite tectonism in the lower Roaring Fork River valley in west-central Col- orado has caused regional subsidence of a differentially downdropped area in the southern part of the Carbondale collapse center during the late Cenozoic. A promi- nent topographic depression coincides with this collapse area, and drainage patterns within the collapse area contrast sharply with those outside of it. Miocene volcanic rocks are downdropped asmuchas 1220 min the collapsearea.Muchofthestructural lowering occurred along the margins of the collapse area. Major Laramide-age struc- tures bound the east and west sides of the collapse area, but movement on these structures during late Cenozoic collapse was in an opposite direction to their Lar- amide movement. Within the interior part of the collapse area faults and folds have as much as 300 m of structural relief. Large blocks of rock may be rafting into the Roaring Fork River valley as underlying evaporite ﬂows toward the valley. Sinkholes are common in thecollapsearea,asareclosed,ornearlyclosed,structurallycontrolled topographic depressions that are formed in both surﬁcialdepositsandbedrock.Upper Cenozoic deltaic and lacustrine deposits preserved on ridgelines and mesas document the positions of former structural depressions that were initially ﬁlled with sediments and later breached by erosion. At least 450 m of syn-collapse sediments accumulated in a collapse depression on the north side of Mount Sopris. Complexly deformed and brecciated deposits in the interior parts of the collapse center are interpreted as col- lapse debris. Evaporite ﬂow is an important element in the collapse process, and during early stages of collapse it was perhaps the primary means of deformation. Flow by itself, does not remove evaporite from the collapse area. Dissolution and accompanying transport of dissolved constituents by groundwater and surface water are the ultimate means by which evaporite exits the collapse area. Collapse continues today, as evidenced by historic sinkholes and modern high-salinity loads in rivers and thermal springs. Thick evaporite deposits still underlie much of the collapse area, so collapse will likely continue in the future. Kirkham, R.M., Streufert, R.K., Kunk, M.J., Budahn, J.R., Hudson, M.R., and Perry, W.J., Jr., 2002, Evaporite tectonism in the lower Roaring Fork River valley, west-central Colorado,in Kirkham, R.M., Scott, R.B., and Judkins, T.W., eds., Late Cenozoic evaporite tectonism and volcanism in west-central Colorado: Boulder, Colorado, Geological Society of America Special Paper 366, p. 73–99. Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user R.M. Kirkham et al.74 Figure 1. Location map of the southern part of the Carbondalecollapse center, lower Roaring Fork River valley (modiﬁed from Kirkham et al., 2001b). Queries indicate locations where the collapse area bound- ary is poorly constrained. INTRODUCTION Dissolution and ﬂow of evaporitic rocks in the Pennsyl- vanian Eagle Valley Evaporite during late Cenozoic time have caused as much as 1220 m of differential subsidence in rocks that overlie the evaporite. This structurally downdropped block forms the southern part of the 1200 km 2 Carbondale collapse center in the lower Roaring Fork River valley between the towns of Glenwood Springs and Basalt (Fig. 1). Kirkham and Scott (this volume) describe the conceptual model of evaporite collapse and its relationships with surface water and ground- water. Evaporite ﬂow plays a major role in the collapse, and it is responsible for lateral movement of large massesofevaporite and causes subsidence in upland areas. However, dissolution is the ultimate mechanism that removes evaporite from the col- lapse area. Modern high salinity loads in rivers and springs indicate that dissolution is active (Chaﬁn and Butler, this vol- ume; Kirkham and Scott, this volume). Evaporitic rocks were ﬁrst recognized in the region in the late 1800s (A.R. Marvine in Peale, 1876). Subsequent geologic investigations in the region reported on various aspectsofevap- orite stratigraphy, depositional setting, and evidence of local- ized evaporite tectonism and deformed upper Cenozoic rocks and deposits. Kirkham and Scott (thisvolume)summarizethese previous studies. Evaporite tectonism, which includes the effects of both ﬂow and large-scale dissolution, has affected depositional pat- terns and drainage systems in this area since shortly after the evaporitic rocks were deposited (Freeman, 1971, 1972; Tweto, 1977). Kirkham and Streufert (1996)ﬁrst reported regional late Cenozoic collapse due to evaporitetectonisminthelowerRoar- ing Fork River valley downstream of the town of Basalt (Fig. 1). The discovery of this regional collapse resulted from a 1:24000-scale geologic mapping program initiated by the Col- orado Geological Survey (CGS) in 1993 and supported by geo- chronologic, geochemical, and paleomagnetic studies by the U.S. Geological Survey. Geologic mapping provided the structural andstratigraphic background needed to recognize and understand the major ele- ments of the collapse. Accurate correlation of upper Cenozoic volcanic rocks in west-central Colorado was essential to char- acterize many details of the collapse process and to constrain the timing of the deformation. 40Ar/39Ar geochronologic dating of 80 volcanic ﬂows by Kunk and Snee (1998), Kunk et al. (2001), and Kunk et al. (this volume) and geochemical and isotopic studies of 220 samples by Unruh et al. (2001), fa- cilitated the correlation of these rocks by Budahn et al. (this volume). Average La/Yb and Hf/Ta ratios and preferred ages for the compositional geochemical groups discussed in this pa- per are listed in Table 1. GEOLOGIC SETTING The southern part of the Carbondale collapse center is de- ﬁned on at least three sides by major Laramide-age (Late Cre- taceous to early Eocene) structures. The northern margin of the collapse area is on the southern ﬂank of the White River uplift, the Basalt Mountain fault marks the eastern edgeofthecollapse area, and the Grand Hogback monoclineformsthewesternside. A long and narrow extension of the Carbondale collapse center follows the monocline northwestward from near Glenwood Springs (Scott et al., this volume). The southern margin of the collapse center is poorly understood (Kirkham and Scott, this volume), but is placed north of Mount Sopris. The Middle and Upper Pennsylvanian Eagle Valley Evap- orite crops out or underlies surﬁcial deposits in the lower Roar- ing Fork River valley downstream of Basalt, in the lower Crys- tal River valley, in lower Cattle Creek, and on the south wall of Glenwood Canyon upstream of Glenwood Springs (Fig. 1). This formation, which consists of halite, gypsum, anhydrite, clastic rocks, and carbonate rocks, was deposited in the Eagle basin part of the Central Colorado trough. Thick sequences of evaporite within the Roaring Fork diapir underlie the lower Roaring Fork River valley. Mallory (1971) and De Voto et al. (1986) reported the evaporite was as much as 2.7 km thick. Perry et al. (this volume) estimate a maximum evaporite thick- ness of 1.5 km based on interpretations of seismic reﬂection data from lines that cross only the ends, but not the center part, of the diapir. Most outcrops of the Eagle Valley Evaporite within the southern Carbondale collapse center include thick Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user Evaporite tectonism in the lower Roaring Fork River valley, west-central Colorado 75 TABLE 1. AVERAGE CHONDRITE-NORMALIZED TRACE-ELEMENT RATIOS AND PREFERRED 40Ar/39Ar AND LASER-FUSION AGES OF SELECTED COMPOSITIONAL GEOCHEMICAL GROUPS OF BASALTIC ROCKS IN THE LOWER ROARING FORK RIVER VALLEY Geochemicalgroup Average chondrite-normalized La/Yb Average chondrite-normalized Hf/Ta Preferred age or age range(Ma) 1b 5.490 0.759 9.75 0.06 to 10.84 0.061c8.005 0.754 10.60 0.072b8.270 0.615 9.68 0.03 to 10.70 0.153a7.926 0.474 No dates4a11.000 0.530 No dates4b11.659 0.541 9.68 0.03 to 10.49 0.075a10.474 0.388 7.75 0.035b10.312 0.440 7.75 0.046b12.829 0.329 3.97 0.086b12.118 0.285 2.90 0.016b11.681 0.364 3.17 0.026c12.389 0.377 3.05 0.0410a21.483 0.444 22.56 0.1312a11.959 0.765 13.29 0.2812b12.349 0.787 13.38 0.0613a13.593 0.928 13.57 0.05 Note:From Budahn et al. (this volume); Kunk and Snee (1998); Kunk et al. (2001, this volume). beds of gypsum that are often highly deformed, but halite and anhydrite are present only in the subsurface. A lithologic log of the 933-m-deep Shannon Oil Rose #1 well, provides the best subsurface information in the southern part of the Carbondale collapse center (unpublished lithologic log by American Strati- graphic Company, now held by the Denver Earth Resources Library). This well, drilled near the mouth of Cattle Creek(Fig. 2), penetrated 18 m of alluvial gravel, then 915 m of gypsum, anhydrite, halite, and clastic and carbonate rocks. The lower 285 m of the well was predominantly halite, and the well did not reach the base of the evaporite sequence. The Champlin Oil and Reﬁning Blue #1 well was drilled in the center ofthe collapseareaonthenorthsideoftheRoaring Fork River between Carbondale and El Jebel (Fig. 2). The well encountered evaporitic rocks to a depth of 707 m, but had to be abandoned. The Mobil Oil Elk Camp Federal #F23X-22P, located in the Grand Hogbackmonoclineonthesouthwest ﬂank of the White River uplift 22 km west of Glenwood Springs, penetrated 4810 m of steeply dipping post-evaporite sedimen- tary rocks before reaching the Eagle Valley Evaporite (unpub- lished lithologic log by G.E.O., Inc.). Halite was encountered at a depth of 5311 m and immediately began ﬂowing into the borehole (J.L. White, 1998, personal commun.). None of these wells penetrated the entire evaporite sequence, because halite caused drilling problems. The unusually thick section of evaporitic rocks underlying the lower Roaring Fork River valley may be related to tectonic thickening or ﬂow of evaporite beneath and adjacent to the Grand Hogback monocline. When the monocline formed dur- ing the Laramide orogeny, evaporite may have ﬂowed toward the point of greatest curvature of the monocline (Perry et al., this volume). Late Cenozoic ﬂow from beneath adjacent up- lands to the valley also thickened the evaporite beneath the valley (Kirkham and Scott, this volume). CHARACTERISTICS OF THE COLLAPSE AREA Topography The southern part of the Carbondale collapse center is a roughly square-shaped topographic depression within an oth- erwise mountainous region. The topographic depression is readily apparent in an oblique shaded relief image of the region (Fig. 3). The land surface within the collapse area is as much as 1220 m lower than surrounding upland areas. Conspicuous escarpments that descend rapidly intothecol- lapse area mark the northern and easternmarginsofthecollapse center (Fig. 3). Prominent, parallel, northwest-trending valleys and ridges west (left) of the conﬂuence of the Roaring Fork and Crystal Rivers are related to differential erosion of Mesozoic and Paleozoic sedimentary rocks within the Grand Hogback monocline. Gently east-sloping, basalt-capped Sunlight Mesa is north-northwest of these prominent valleys and ridges. A broad, bowl-like depression superposedonthemesaisprobably a result of differential collapse of the monocline. Northwest- trending, parallel, relatively shallow valleys and low ridges cross Sunlight Mesa. These landforms are associated with bedding-plane faults caused by ﬂexural slip of the collapsing Grand Hogback monocline. Broad ﬂat valleys, such as Spring Valley and Cottonwood bowl, gently sloping basalt-cappedme- sas like Los Amigos Mesa, which is the landform between Spring Valley and the Roaring Fork River, and the rolling hills of Missouri Heights typify the interior parts of the collapsearea (Fig. 3). Los Amigos Mesa and the block of rock northeast of the conﬂuence of the Crystal and Roaring Fork Rivers jut far out into the valley ﬂoor. These blocks may be rafting into the valley as the underlying evaporite ﬂows toward the river. The land surface, particularly in the northeastern and cen- tral parts of the collapse area, is hummocky. Drainagesof many Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user Figure 2. Geologic features of the southern part of the Carbondale collapse center (modiﬁed from Kirkham et al., 2001b). BCT—Blue Creek trough; BGT—Barbers Gulch trough; BP—Buck Point; CCB—Cattle Creekbowl; CB—Cottonwoodbowl;CT—Crystalterracetrough;DRF— doubly recumbent fold; LAS—Los Amigos sag; LBP—Little Buck Point; LM—Lookout Mountain; LT—Leon trough; PS—Polarissag;SBS— Shippes Bowl sag; SDS—Shippes Draw sag; SPR—Spring Park Reservoir; TKK—Ti-Ke-Ki sag. Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user Evaporite tectonism in the lower Roaring Fork River valley, west-central Colorado 77 WHITE RIVER PLATEAU MH R o a r i n g Fork Riv e rRiv e r Cry s t a l BM LGM LAM SV SM RTM ? ??? MS Figure 3. Oblique shaded-relief digital elevation model of the lower Roaring Fork River valley, showing major geographic features (100 m DEM provided by David Catts, 2001, U.S. Geological Survey). View is to north. Dashed line with hachures marks boundary of collapse area. BM—Basalt Mountain; LAM—Los Amigos Mesa; LGM—Little Grand Mesa; MH—Missouri Heights; MS—Mount Sopris; RTM—RedTable Mountain; SM—Sunlight Mesa; SV—Spring Valley. At the west edge of Little Grand Mesa, the collapse margin drops down into Glenwood Canyon and is not visible in this perspective. of the tributary streams within the collapse area are irregular, poorly integrated, and sometimes interrupted by swallowholes. The tributary streamsareincisedlittleandhaverelativelygentle valley walls compared to the well-integrated and deeply and sharply incised streams outside of the collapse area (Fig. 3). Sinkholes are common in the area (Fig. 2) (Mock, thisvolume). Several closed or nearly closed depressions lie within the col- lapse area; they include broad, downwarped river terraces(sub- sidence troughs) and shallow synclines formed in volcanic rocks (synclinal sags) (Fig. 2). Margins of the collapse area We depict our preferred positions of the collapse area mar- gins in Figures 1, 2, and 3. These boundaries are best deﬁned where upper Tertiary volcanic rocks are preserved. Upper Ter- tiary basaltic ﬂows immediately outside of the collapse center are generally ﬂat lying, whereas in the structural zones along the margins of the collapse areas, these same ﬂows dip as much as 52 into the collapse center. Western margin.The Grand Hogback monocline, a major down-to-the-west fold created near the end of the Laramide orogeny (Tweto, 1977), forms the western margin of the col- lapse center in the lower Roaring Fork River valley (Fig. 2). Lower Tertiary and older rocks within the monocline generally dip 40 –60 westward (Murray, 1966; Kirkham et al., 1996, 1997). A subhorizontal erosion surface was cut across the sharply folded lower Tertiary and older rocks during or prior to the middle Miocene. A sequence of basaltic lava ﬂows erupted onto this erosion surface ca. 10.6–9.9 Ma (Kirkham et al., 2001b; Kunk et al., this volume). Individual ﬂows are as much as 10 to 15 m thick. Many ﬂows maintain fairly constant thick- nesses across large areas and show no evidence of thickening in the collapse area; some have pahoehoe ﬂow structure. Such Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user R.M. Kirkham et al.78 Figure 4. Cross section A–A through Sunlight Mesa. Location of cross section shown on Figure 2. characteristics indicate that the lava ﬂows were originally erupted onto the subhorizontal erosion surface (KenHon,1995, written commun.). Geologic relationships along the western margin ofthecol- lapse center demonstrate that the Grand Hogback monocline underwent down-to-the-east relaxation or unfolding during late Cenozoic time. This movement of the monocline is opposite in direction to its Laramide movement and is interpreted to result from removal of evaporite from beneath the monocline, either by ﬂow and/or dissolution (Unruh et al., 1993; Kirkham et al., 2001b). This relaxation or unfolding caused the overlying, sub- horizontal basaltic caprock to tilt eastward into the Carbondale collapse center, while simultaneously reducing the dips of the lower Tertiary and older rocks within the monocline.Prominent bends are apparent in the hogback ridge along the monocline west of the conﬂuence of the Crystal and Roaring Fork Rivers where the ridge crosses the margin of the collapse area (Fig. 3). The ﬂattening of dip that was caused by late Cenozoic relaxa- tion or unfolding of the monocline is responsible for the promi- nent bends in the hogback ridge. As the monocline relaxed,ﬂexural slip occurredalongbed- ding planes in the sedimentary rocks within the monocline, much like the movement of a deck of cards as it topples over. This slip formed a series of subparallel, down-to-the-west ﬂexural-slip faults (Murray, 1966, 1969; Stover, 1986) that rup- tured the basalt ﬂows and some overlying surﬁcial deposits (Figs. 2 and 4). The ﬂexural-slip faults have normal displace- ment and, because they follow bedding planeswithinthemono- cline, probably become listric in the lower or synclinal limb of the monocline. A large remnant of ca. 10 Ma volcanic ﬂows is preserved on Sunlight Mesa southwest of Glenwood Springs. The ﬂows are broken by numerous northwest-striking, parallel,ﬂexural- slip faults and are tilted eastward into the collapse area (Figs. 2 and 4). Within the blocks bounded by the faults, the ﬂows typically dip 10 –20 east and locally have dips 40 .The ﬂexural-slip faults are recognizable only where lava ﬂows and certain surﬁcial deposits unconformably overlie the folded older sedimentary rocks. A prominent series of northwest- striking, fault-controlled valleys and ridges that trend parallel to the monocline are developed in the basalt cap (Figs. 5 and 6). These parallel ridges and valleys form a fault-controlled trellis drainage pattern. Faultsthatcutthe volcaniccaponSunlightMesaaredown- thrown to the west, opposite in direction to the overall east tilt of the basalt cap and to the east dip of ﬂows within the fault blocks (Kirkham et al., 1996, 1997). Flexural-slip faults are widely spaced in areas where the basalt cap is underlain by the Upper Cretaceous Mancos Shale and have greater displace- ments than faults in areas underlain by the Upper Cretaceous Mesaverde Group or lower Tertiary Wasatch Formation. A few northeast-trending cross faults cut the basalt cap near the north end of Sunlight Mesa (Figs. 2 and 5). A fault scarp in upper Quaternary deposits along one of these faults (marked by “A” in Figure 5) suggests latest Pleistocene or Holocene movement (Kirkham et al., 1997). A structurecontourmaponthetopoftheca.10Mabasaltic rocks on Sunlight Mesa (Fig. 7) indicates this formerly ﬂat- lying basaltic cap now has an overall eastward slope of 6 –10 into the collapse center. This map conﬁrms that the bowl-like Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user Figure 5. Vertical aerial photograph of the Sunlight Mesa area (National Aerial Photography Program [NAPP] photo 6716–41), where ﬂexural-slip faults cut Miocene volcanic rocks that overlie an angular unconformity eroded acrosswest-dippingsedimentary rocks in the Grand Hogback monocline. Note the prominent, parallel, northwest-striking, light-colored lineaments that are linear grassy valleys (some are marked by arrows). Each valley is underlain by a west-dipping normal fault related to relaxation of the monocline. The linear dark areas between the valleys are ridges formed by fault blocks capped by east-dipping volcanic rocks. Arrows labeled “A” indicate ends of a cross fault that cuts upper Quaternary deposits. Bershenyi terrace has been folded by Pleistocene diapirism. Town of Glenwood Springs in upper right. Scale and north arrow are approximate. Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user R.M. Kirkham et al.80 Kd Figure 6. Oblique aerial photograph of the northern end of Sunlight Mesa looking northwest. Prominent fault-controlled ridges and valleys are formed in the ca. 10 Ma basalt ﬂows that cap the mesa. Arrows denote some of the valleys. Note steep westward dip of Dakota Sandstone (Kd) in Grand Hogback monocline. depression on the mesa has a structural origin and is likely related to differential collapse of the monocline. Late Miocene volcanic ﬂows drop 1040 m in elevation from the top of Sun- light Peak to the lowest exposure of correlative ﬂows on the west side of the Roaring Fork River. This elevation difference is the minimum amount of post–10 Ma collapse on the western margin of the collapse center. Equivalent-age volcanic rocks are 180 m lower in elevation on the east side of the river, which suggests 1220 m of collapse since eruption of the ca. 10 Ma ﬂows. The average slope of the ground surface varies acrossSun- light Mesa (Fig. 3). On the western side of the mesa, near and east of Sunlight Peak, the surface slopes as much as 40% to the east. The surface of the mesa ﬂattens east of the zone of steep slope and remains fairly ﬂat until reaching the subcrop of the Dakota Sandstone beneath the volcanic ﬂows (Fig. 4). Rem- nants of the basalt cap extend eastward beyond the Dakota sub- crop in three areas (Kirkham et al., 1996, 1997), and in all three locations the dip of the ﬂows sharply increases east of the Da- kota subcrop. Paleomagnetic measurements at three sites in the basaltic ﬂows in the wedge-shaped remnant east of the Dakota subcrop along cross section A–A (Fig. 4) are consistent with an interpretation of eastward tectonic tilting (Hudson et al., this volume). Flexural-slip faults associated with the Grand Hogback monocline also offset upper Tertiary to lower Quaternary basalt-rich gravel deposits west of Carbondale (Figs. 2 and 8). Light-colored linear features in Figure 8 mark grassy swales underlain by the faults, and the darker areas are the upthrown blocks that are vegetated with sagebrush and/or gambel oak. Prominent uphill-facing scarps mark the down-to-the-west ﬂexural-slip faults in the basalt-rich gravel deposits (Fig. 9). Three of these faults offset upper Quaternary deposits that ﬁll one of the valleys between the mesas (Stover, 1986; Kirkham et al., 1996). Individual ﬂexural-slip faults offset the Miocene basalt Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user Evaporite tectonism in the lower Roaring Fork River valley, west-central Colorado 81 Figure 7. Structure contour maps on the top of the 7.75 Ma volcanic ﬂows in geochemical groups 5a and 5b and on the top of the ca. 10 Ma rocks of groups 1b, 2b, 4a, and 4b (Table 1). Adapted from Kirkham et al. (2001b). Geochem- ical correlations are by Budahn et al. (this volume). Dashed line indicates ap- proximate location of generalized cross section F–F (Fig. 22). ﬂows as much as 92 m. The upper Tertiary to lower Quaternary gravel deposits are displaced a maximum of 30 m, whereas the fault throw in the upper Quaternary deposits is only an estimated 3 m. The increasing displacement in successively older deposits indicates the ﬂexural-slip faults associated with the Grand Hogback monocline have experienced recurrent or continuous movement during the late Cenozoic. Northern margin.East of Glenwood Springs, near Look- out Mountain (Fig. 2), the northern margin of the collapse cen- ter is poorly constrained. The margin is arbitrarily placed at the northern limit of evaporite on the south wall of Glenwood Can- yon. Evaporitic rocks were probably once present north of their modern outcrop, and late Cenozoic or older evaporite defor- mation may have occurred there prior to removal of the evap- orite by erosion. Faulted remnants of ca. 10 Ma group 2b volcanic rocks (Table 1) crop out on the south side of Lookout Mountain at substantially lower elevations than other age-equivalent ﬂows that are widely distributed across the White River Plateau (Lar- son et al., 1975; Kunk et al., this volume). The upper Miocene ﬂows on Lookout Mountain and those to the south and east (Fig. 2) are within the collapse area. Deformation along the collapse margin in the Lookout Mountain area appears to be spread across a broad belt, with the collapse being accommo- dated by several small faults and by tilting. Elevation differ- ences between the group 2b rocks preserved on the WhiteRiver Plateau and those on the northern margin of the collapse area indicate a minimum vertical displacement of 680 m (Fig. 7). The maximum amount of post–10 Ma collapse along the north- ern margin is 1060 m, based on the elevation of ca. 10 Ma ﬂows on the east valley wall of the Roaring Fork River. East of Lookout Mountain is a 13-km-long basalt-capped mesa called Little Grand Mesa or Dock Flats. A stacked se- quence of thick ﬂows caps the mesa, which is up to 5 km wide. Group 5b ﬂows (Table 1) crop out in the western part of Little Grand Mesa, whereas group 5a rocks are found in the eastern end. Both groups are ca. 7.75 Ma (Table 1). The volcanic ﬂows that cap Little Grand Mesa are not noticeably folded or faulted Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user A B B N 0 .5 1 Km Figure 8. Vertical aerial photograph of an area west of Carbondale (NAPP photograph 6717-8). Flexural-slip faults related to relaxation of the Grand Hogback monocline underlie the light-colored, grassy meadows in upper Tertiary to lower Quaternary basalt-rich gravel deposits that cap the mesas (some of the faults are marked with arrows). Three faintly visible faults (in box labeled “A”) cut upper Quaternary valley-ﬁll deposits. Faults shown in Figure 9 are labeled “B.” Scale and north arrow are approximate. Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user Evaporite tectonism in the lower Roaring Fork River valley, west-central Colorado 83 LITTLE GRAND MESA Figure 9. Photograph of ﬂexural-slip fault with prominent uphill-facing scarp in upper Tertiary-lower Quaternary gravel deposits that cap a mesa west of Carbondale. Arrows denote the scarp, which faces to the left. Other more subtle scarps are visible in front of and behind the prominent scarp. View is to northeast, with Little Grand Mesa forming part of the skyline. See Figure 8 for location of photograph. even though evaporite may occur in the subsurface beneath much of the mesa. In several good exposures, stacked se- quences of ﬂows can be traced for hundreds of meters with no apparent deformation. The ﬂows on Little Grand Mesa occur at the highest elevation of any 7.75 Ma ﬂows in the region. We conclude that differential collapse has not occurred be- neath Little Grand Mesa during the past 7.75 m.y., but recog- nize that the entire basalt-capped mesa may be an intact block that uniformly lowered as underlying evaporite was removed from beneath it. The northeastern margin of the collapse center is placed at the top of a sharp monoclinal drape fold called the Cottonwood monocline, which forms the southern edge of Lit- tle Grand Mesa. If the intact block of Little Grand Mesa was lowered by evaporite collapse, then the margin of the collapse center probably follows the evaporite outcrop on the southern wall of Glenwood Canyon, north of Little Grand Mesa (Fig. 1). Evidence of evaporite tectonism, such as complex recumbent folds (Fig. 10), unusual fault patterns in rocks overlying the evaporite, and sinkholes, is present northeast of Little Grand Mesa (Streufert et al., 1997). These features suggest evaporite tectonism has affected this area, but this deformation may pre- date the late Cenozoic. Cottonwood monocline (Fig. 2) is a narrow and sinuous fold with severalnearlyright-anglebends(Streufertetal.,1997; Kirkham et al., 1995). The ﬂat-lying, 7.75 Ma group 5a vol- canic rocks (Table 1) capping Little Grand Mesa are abruptly deformed by the monocline (Fig. 11). Within the monocline, these volcanic rocks are moderately well exposed in a small valley cut across the monocline (valley is left of symbol “CM” in Figure 11). Cross section B–B (Fig. 12) is drawn perpen- dicular to the monocline at the location of symbol “CM” on Figure 11. Both the top and bottom limbs of the monocline are sharp. Group 5a basalts dip as much as 44 into the collapse center. They are lowered 180 m by Cottonwood monocline (Figs. 6 and 12). A few very small displacement faults cut the ﬂows within the monocline, but folding accommodates most of the monocline’s structural relief. Cottonwood bowl lies at the bottom of the monocline. A veneer of upper Tertiary to lower Quaternary sediments as much as 35 m thick (unit QTs in Fig. 2; unit QTc in Fig. 12) Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user R.M. Kirkham et al.84 Figure 10. Photograph of a complex recumbent fold formed in the Eagle Valley Evaporite on the northeast side of Cottonwood Creek. View is to northeast. Fold located northeast of Cottonwood monocline (“DRF” in Figure 2). Photograph by Beth L. Widmann. blankets much of the ﬂoor of Cottonwood bowl. These locally derived alluvial and colluvial sediments were mostly eroded from the face of the monocline as it formed, accumulated in the topographic depression of Cottonwood bowl at the toe of the monocline, and have since been slightly dissected by ero- sion. The low hills visible on the ﬂoor of Cottonwood bowl (Fig. 11) are capped by these sediments, which overlie the downdropped 7.75 Ma group 5a volcanic rocks. Although poorly exposed, the volcanic rocks beneath the ﬂoor of Cotton- wood bowl appear to be subhorizontal with an overall gentle southward dip. This structural bench continues southward until reaching a west-northwest-striking, broad monoclinal structure on the north side of Cattle Creek. Eastern Margin.The Basalt Mountain monocline forms the eastern margin of the Carbondale collapse center (Fig. 2). It merges with the Cottonwood monocline at the northeast corner of the collapse center near Cottonwood Pass. The Basalt Mountain monocline coincides with the Basalt Mountain fault, a high-angle, Laramide-age fault with 3000 m of down-to- the-east throw (Streufert et al., 1997; Kirkham et al., 1998). Where the Eagle Valley Evaporite is at or near the ground sur- face on the west side of the fault there is widespread evidence of major collapse. On the east side of the fault, where the evap- orite is overlain by as much as 2500 m of sedimentary and volcanic rocks, there is no known evidence of collapse (Fig. 13). During the late Miocene, multiple group 4b ﬂows (Table 1) erupted from the Basalt Mountain shield volcano on the east side of the Basalt Mountain fault (Fig.2)ca.10.5–9.7 Ma. Flows from the Basalt Mountain volcano extend nearly to Car- bondale,14 km west of the crater (Fig. 7). As on the western side of the collapse area, these ﬂows were erupted onto a land- scape with low topographic relief prior to any signiﬁcant late Cenozoic collapse (Kirkham et al., 1998). These late Miocene, formerly ﬂat-lying ﬂowsare nowsharplytiltedwestwardwithin the Basalt Mountain monocline, which is a broad hinge zone with average width of 1.6 km. Although the group 4b ﬂows within the monocline are very broken and jumbled, they dip on average 14 to the west. In the Missouri Heights area west of the monocline, group 4b volcanic ﬂows are broken by faults and fractures, but generally are subhorizontal with only gentle west and southwest dip. The minimum amount of post–10 Ma Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user Evaporite tectonism in the lower Roaring Fork River valley, west-central Colorado 85 CB LGM LGM CM CP CB LGM Figure 11. Oblique aerial photograph looking east across Cottonwood bowl (CB) and Cottonwood monocline (CM). Syn-collapse sediments underlie the rounded low hills in Cottonwood bowl. The dashed line with hachures marks top of Cottonwood monocline, which here forms the margin of the Carbondale collapse center. The steep hillside that coincides with the monocline is a dip slope formed by tilted 7.75 Ma basaltic ﬂows. Little Grand Mesa (LGM), the ﬂat surface in the upper left and in the foreground, is capped by nearly horizontal 7.75 Ma basaltic ﬂows. Cottonwood Pass (CP) is in the upper right. Cross section B–B (Figs. 2 and 12) crosses the monocline approximately at the location indicated by CM. collapse on the eastern margin ofthe collapsecenteris 580 m, based on elevation differences between group 4b rocks at the base of Basalt Mountain shield volcano and those exposed in Missouri Heights. If Basalt Mountain was lowered by collapse as a large intact block, a hypothesis discussed by Kirkham and Scott (this volume), then the margin of the collapse center is east of Basalt Mountain and the amount of structural relief re- ported above represents only a portion of the total vertical sub- sidence along the eastern margin. A small cinder deposit and related ﬂow near the southeast end of Spring Park Reservoir (geochemical group 6b ) are pre- served within the Basalt Mountain monocline and immediately west of it (unit Tvp on Fig. 2). The cinders and ﬂow have a preferred age of 2.90 0.01 (Table 1). The lava from this volcano originally ﬂowed downhill awayfromtheeruptivecen- ter. However, the northeastern and most distal end of the pre- served ﬂow is now as much as 73 m higher in elevation than the cinder cone from which it was probably erupted. The ﬂow is tilted westward into the collapse center at an estimated 13 , which is similar to the tilt in the ca. 10 Ma Basalt Mountain ﬂows folded by the Basalt Mountain monocline (Kirkham et al., 1998, 2001b). This suggests that much of the collapse ac- commodated by the Basalt Mountain monocline occurred dur- ing the past 3 m.y. On the east side of the Basalt Mountain fault, where evap- oritic rocks are deep in the subsurface, no evidence of evaporite tectonism is recognized. Basalt Mountain shield volcano and the ﬂows from it appear to be intact and are not noticeably deformed on the east sideof the fault.However,withthegreater depth to the evaporite, overlying strata may have absorbed strain, so that collapse could have occurred on the east side of the fault without forming obvious structural features visible at the ground surface. In such a scenario, the shieldvolcanowould collapse as an intact block of rock. The ca. 10 Ma ﬂows on Basalt Mountain are at somewhat lower positions in the land- scape than are other age-equivalent rocks at other locations in Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user R.M. Kirkham et al.86 Figure 12. Cross section B–B through the Cottonwood monocline on the northeast side of Cottonwood bowl, northern margin of collapse center. Location of cross section shown in Figures 2 and 11. Figure 13. Schematic cross section C–C through the Basalt Mountain monocline on the eastern margin of the collapse center. Approximate location of cross section shown in Figure 2. west-central Colorado (Kirkham et al., 2001a). Thus, the Basalt Mountain volcano either was lowered by collapse as an intact block, or the late Miocene landscape had several hundred me- ters of relief. Flows from Basalt Mountain volcano are the only ca. 10 Ma eruptions in the study area known to have ﬂowed into and blocked a late Miocene paleovalley, so perhaps there was appreciable topographic relief during the late Miocene. Southern margin.The southern margin of the collapse center is more poorly deﬁned than the other sides, largely be- cause upper Cenozoic volcanic rocks are scarce (Fig. 2). Thick Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user Evaporite tectonism in the lower Roaring Fork River valley, west-central Colorado 87 deposits of middle(?) and late Tertiary ﬂuvial gravel are pre- served on the drainage divide between the Roaring Fork and Crystal Rivers and on the west side of the Crystal River. We conclude that these gravels accumulated in a gradually subsid- ing basin related to evaporite tectonism. Therefore the margin of the collapse center lies south of these deposits. Fluvial gravels on Light Ridge south of Basalt abruptly thicken where they cross the postulated margin of the late Ce- nozoic collapse area (Fig. 2). A group 13a basalt ﬂow dated at 13.57 0.05 Ma (Kunk et al., 2001) is interbedded with the ﬂuvial gravels at the north end of Light Ridge. This ﬂow is lowered by collapse at least 730 m, based on its elevation rela- tive to age-equivalent ﬂows outside the collapse area (Larson et al., 1975). To accommodate the basalt ﬂow and align with the abrupt thickening of gravel on Light Ridge, the margin of the collapse center, which trends north-northeast on the west side of Basalt Mountain, must ﬁrst bend 110 to aneaststrike, then swing sharply southward (Fig. 2). The late Cenozoic col- lapse margin probably turns to the west just south of Light Ridge, and then runs generally west or northwest along the north side of the Mount Sopris pluton until rejoining the Grand Hogback monocline southwest of Carbondale. A 35.21 0.03 Ma ash-ﬂow tuff (Kunk et al., 2001) on the northeast side of Mount Sopris (Fig. 2) also provides evi- dence of the amount of subsidence on the southern margin of the collapse center. The top of an age-equivalent intrusivestock crops out at the summit of the nearby Mount Sopris (Streufert, 1999), therefore the land surface at the time of intrusion must have been equal to or higher than the top of the stock. It is unlikely that a deep paleovalley existed in close proximity to the stock at the time of its emplacement. We conclude that the ash-ﬂow tuff was originally erupted onto a ground surface that was probably equal to or perhaps even higher than the top of the Mount Sopris stock and was subsequently lowered by col- lapse. The tuff now crops out 1290–1460 m lower than the top of the stock. Where last observed, the tuff disappears beneath the Tertiary sediments that ﬁll Sopris bowl and probably con- tinues into the subsurface for some unknown depth beneath its lowest outcrop. If the tuff was erupted onto a surface equal to or higher than the top of the Mount Sopris stock, then the total amount of post–35 Ma collapse probably exceeds 1460 m. Structures within the interior of the collapse area Structural deformation within the interior of the collapse center involves both major and minor structures that affect rocks and surﬁcial deposits that overlie the evaporite. The style and amount of deformation in the volcanic rocks, which were erupted onto a low-relief surface prior to collapse, vary greatly. Locally the volcanic rocks are nearly ﬂat lying, even though they were lowered a thousand metersormoreinelevation.Else- where, well-deﬁned major structures, some with 300 m of local structural relief, disrupt the volcanic rocks. The ﬂows are near vertical and perhaps overturned in at least one structure (Hudson et al., this volume). We call elongate structural de- pressions formed in volcanic rocks overlying the evaporitesyn- clinal sags. Basin-like structural depressions in bedrock are re- ferred to as bowls. Locally within the collapse center the basaltic rocks are highly broken, fractured, and jostled; in these areas individual structures are difﬁcult to map at a scale of 1:24000. These intensely deformed deposits are mappedascol- lapse debris.MinorstructuraldepressionsformedinPleistocene terraces are called troughs. Sinkholes are prevalent throughout the collapse area (Mock, this volume) and common in some troughs. Heuschkel Park sag.Heuschkel Park sag is a generally east-west-trending, major synclinal structure in volcanic rocks north of Carbondale (Fig. 2). This structure, along with the faulted and tilted basalt-capped mesa north of it, form promi- nent landformsreadilyapparentonaerialphotographs(Fig.14). The axis of the Heuschkel Park sag underlies the broad and ﬂat ﬂoor of Heuschkel Park. East of the park, the axis of the sag gradually bends northward and eventually turns back to west, creating a ﬁshhook type of map pattern for the fold axis. To the west, the sag axis appears to transition into a faulted structure. Group 1b ﬂows are widely distributedacrossthearea(Figs. 6 and 15). These 9.7–10.9 Ma ﬂows (Kunk et al., this volume) characterize the structural deformation of the Heuschkel Park sag. Paleomagnetic studies at seven sites in and adjacent to the Heuschkel Park sag indicate the ﬂows on the north limb of the sag may be strongly draped over the limb (Hudson et al., this volume). These data demonstrate south tilts as steep as 53 , which exceeds the slope of the north valley wall. Beneath the ﬂoor of Heuschkel Park, surﬁcial deposits conceal the ﬂows, but they are essentially ﬂat lying where they crop out on the east end of the park, an interpretation supported by paleomag- netic studies. The low ridge south of Heuschkel Park (Fig. 15) is capped by group 1b ﬂows in the southern limb of the sag. These ﬂows dip north, into the axis of the sag. The only other volcanic rocks preserved on the south side of Heuschkel Park are on Red Hill, where three samples of the 10.6 Ma group 1c rocks (Table 1) were collected. Although these ﬂows cannot be used to precisely characterize the structure of the south limb of the sag, their age and position in the landscape indicate the structural relief on the south limb of the sag is much less than that on the north limb. North of the north valley wall is a gently to moderately northward-sloping mesa that is capped by a stacked sequence of basalt ﬂows. The upper three ﬂows in an outcrop on the rim of the mesa north of the east end of the park are group 1b rocks. A small-displacement, east-west-striking fault probably sepa- rates the north-dipping ﬂows beneath the mesa from the south- dipping ﬂows on the valley wall of the park. Total structural relief in the group 1b volcanic rocks between the axis of the sag and the north-sloping basalt-capped mesa is 300 m. The north-sloping basalt-capped mesa is broken by 20 faults that trendeitherabout N35 –55 EorN10 –45 W.Manyofthefaults abut or intersect at nearly right angles. Grassy meadows are Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user R.M. Kirkham et al.88 Carbondale Fork Crystal Trough Ro a r i n g River Creek Cattle Heuschkel Park QTcd Ri v e r Cr y s t a l Sag QTcd DiapirMargin N 0 .5 1 Km Figure 14. Vertical aerial photograph of the Carbondale to Cattle Creek area (NAPP photograph 6717-236). Axis of Heuschkel Park sag trends approximately east-west through the grassy meadow of Heuschkel Park, which is underlain by nearly horizontal ca. 10 Ma group 1b basaltic ﬂows (Table 1). Steeply south-dipping ca. 10 Ma ﬂows are preserved on the tree-covered slope north of the park. Farther north is the north- tilted mesa capped by ca. 10 Ma basalt, which is cut by several prominent faults (some marked by arrows) that intersect to form a rectilinear pattern. This faulted basalt cap grades northeastward into collapse debris (QTcd) that underlies the hummocky topography in the right side of the photograph. Scale and north arrow are approximate. Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user Figure 15. Geologic map of Heuschkel Park sag and cross section D–D (adapted from Kirkham and Widmann, 1997). Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user R.M. Kirkham et al.90 present along many of the faults, and they contrast sharplywith the adjacent pine-covered hills between the faults, creating quasi-rectilinear vegetation patterns on the mesa (Fig. 14). The Heuschkel Park sag may simply be an asymmetrical syncline due to removal of evaporite from beneath it. However, the block of rock that includes the sag protrudes into and some- what restricts the valley ﬂoor of the Roaring Fork River (Fig. 3). This block of rock may be rafting southward on underlying evaporite, as the evaporite ﬂows toward the river. Spring Valley structure.Spring Valley is a nearly 6-km- long, broad,ﬂat, arcuate valley between Glenwood Springsand Carbondale on the east side of the Roaring Fork River (Figs. 2 and 3). It is 300 m higher than the ﬂoor of the river valley, and its orientation and position suggested Spring Valley was a former paleovalley of the Roaring Fork River. However,ﬂuvial gravel deposits related to an ancestral Roaring Fork River have not been found in or near Spring Valley. When early settlers ﬁrst homesteaded this region, Spring Valley was a closed de- pression and a lake occupied much of the valley ﬂoor (Calvin Cox, 1994, personal commun.). The presence of lacustrine sed- imentsbeneath muchofthe valleysupportsthisconclusion.The settlers hand dug a drain ditch at the north end of the valley shortly before the end of the 19th century, drained the lake, and turned the valley ﬂoor into agricultural land. The oldest upper Tertiary volcanic rocks within the col- lapse area crop out at the northern end of Spring Valley. These group 10a rocks (Table 1), which are 22.56 0.13 Ma, are only 300 m above the ﬂoor of the Roaring Fork River valley and are 1200 m lower in elevation than age-equivalent ﬂows in the White River Plateau (Larson et al., 1975). Some of the best outcrops of these early Miocene ﬂows are within a narrow graben at the northwest end of the Spring Valley structure (Fig. 2). Paleomagnetic studies of the early Miocene ﬂows at three sites within the graben indicate these rocks are strongly tilted (Hudson et al., this volume). A model tilt of 100 15 south- west was calculated for the ﬂow on the east side of the graben, suggesting it is overturned or nearly vertical. The Spring Valley structure is concealed beneath the sur- ﬁcial deposits that ﬁll the valley ﬂoor, and subsurface data are limited, so the structure is poorly understood. Los Amigos Mesa, which is capped by 7.75 Ma ﬂows (group 5b) and ca. 10 Ma ﬂows (groups 1b, 2b, and 3a), lies between Spring Valley and the Roaring Fork River valley. Volcanic ﬂows in the northern end of this mesa are deformed by several small- displacement faults, and at least one synclinal sag occurs on the edges of the mesa (Fig. 2), but overall the mesa is little de- formed. Along the western edgeofthe mesa,theupperMiocene volcanic rocks dip away from the river valley as much as 13 . The underlying Maroon Formation dips more steeply away from the river valley than do the overlying ﬂows, indicating pre–middle Miocene movement on the Cattle Creek anticline and/or Roaring Fork diapir. Much of the mountain side east of Spring Valley is under- lain by broken, jumbled blocks and boulders of basalt in a large landslide complex. This landslide complex developed in re- sponse to the collapse of the Spring Valley structural depres- sion, which removed the rock that supported the hillslope east of the valley, effectively oversteepening the east valley wall. This triggered movement of the hillslope toward the valley as a large landslide complex. Large blocks of relatively intact ba- salt are preserved within the landslide, but much of the basalt was broken into bouldery rubble. Large scarps, which were mapped as down-to-the-west faults by Kirkham et al. (1995) and Kirkham and Widmann (1997), cut both the landslide de- posits and adjacent bedrock. These structures may be majorslip planes related to massive failure of the entire rock mass and overlying surﬁcial deposits on the east side of Spring Valley. A 174-m-deep groundwater exploration test hole (“SVR6” in Figure 2) in the middle of the valley failed to reach bedrock (Robin VerSchneider, 2001, personal commun.). Most material penetrated by the well was ﬁne-grained silt and clay, and no basalt ﬂowswereencountered.Theabundantclayandsiltfound in thewell suggestsalacustrineenvironmentpersistedinSpring Valley for much of the time interval represented by the beds penetrated in the drill hole. A thick sequence of reworked vol- canic ash and clastic sediments eroded from adjacent hillslopes was present at depths of 75–91 m in the drill hole. A.M. Sarna-Wojcicki (2002, written commun.) geochemically cor- related the ash with the Lava Creek B ash, which was recently dated at 639 ka by Lanphere et al. (2002). The depth of burial of the ash indicates the average sedimentation rate in the valley since the middle Pleistocene was 140 mm/k.y. This rapidsed- imentation rate suggests the Spring Valley structure had a high rate of deformation during the past 639 ka. Kirkham et al. (1995, 1997) and Kirkham and Widmann (1997) considered the Spring Valley structure to be a half gra- ben whose ﬂoor was tilted to the west (Fig. 16, upper diagram). In this model, a large normal fault forms the western margin of the structure, and Spring Valley is a structural low on the down- dropped eastern side of the fault. Basaltic ﬂows would underlie the valley-ﬁll deposits and overlie red beds of the Maroon For- mation, if the structure is a half graben. As the valley tilted westward, the hills east of the valley gradually became over- steepened and eventually slid toward the valley. An alternative model for the Spring Valley structure is pre- sented in the lower diagram in Figure 16. In this model, the large block of relatively intact basalt and underlying post- evaporite Paleozoic sedimentary rocks between Spring Valley and the Roaring Fork River valley is being rafted into the river valley along an average travel path of S60 –70 W, as the un- derlying evaporite ﬂows toward areas with lower lithostatic loads. The release zone for the structure coincides with the to- pographic outline of the valley, which is a roughly north-south- oriented valley with ends that ﬂare back to the west. The west- ern side of the rafted block would have slowly advanced into the Roaring Fork River valley. As shown in Figure 3, this block of rock does protrude into the river valley. In the rafted-block Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user Evaporite tectonism in the lower Roaring Fork River valley, west-central Colorado 91 Figure 16. Schematic cross sections (E–E) showing two possible interpretations of the subsurface geology through Spring Valley. Upper cross section depicts the Spring Valley structure as a half graben chieﬂy due to removal of evaporite from beneath the valley by dissolution. In the lower cross section, the Spring Valley structure is shown as a pull-apart feature caused by evaporite ﬂow toward the Roaring Fork River valley. Location of cross section shown on Figure 2. model, the sediment deposited in the Spring Valley structure would directly overlie evaporite. Strain along the southern margin of thehypothesizedrafted block may be largely lateral shearing. The strain would occur as sinistral-strike slip or oblique slip along a narrow, arcuate fault zone that starts in the southeast corner of the structure, bends to a nearly west trend, and disappears into the evaporitic rocks that crop out beneath the volcanic rocks on the east wall of the river valley (Fig. 2). Lateral strain on thenorthernmargin of a rafted Spring Valley structure would in part be accom- modated by the narrow grabenthatextendsnorthwestwardfrom Spring Valley and in part by the complex fault swarm between the graben and the river valley. Minor structures.Several small synclinal sags deform the Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user R.M. Kirkham et al.92 Figure 17. Oblique aerial photograph of Shippes Bowl sag (SBS), looking south. Basalt Mountain forms the skyline on the left side of the photograph, and Spring Park Reservoir is in the middle distance between the sag and the base of Basalt Mountain. Margin of collapse center, immediately below the top of Basalt Mountain, shown by dashed line with tick marks. volcanic bedrock in the Carbondale collapse center (Fig. 2). They include the Los Amigos sag, Polaris sag, Shippes Bowl sag, Shippes Draw sag, and Ti-Ke-Ki sag (Kirkham etal.,1996, 1998, 2001b). The previouslydescribedHeuschkelParksaghas sharp walls and considerable structural relief, but others have broad, relatively ﬂat limbs with only meters or tens of meters of structural amplitude. Los Amigos sag is a 1500-m-long, slightly arcuate, north- west-trending feature adjacent and parallel to the Roaring Fork River valley. Polaris sag, Shippes Bowl sag, and Shippes Draw sag are 1.6- to 2.6-km-long, northeast- or east-trending struc- tures in the northeastern part of the collapse area (Fig. 2). They lie on a nearly horizontal structuralbenchunderlainbyMiocene volcanic rocks between Cottonwood monocline and Cattle Creek (Fig. 7). Topographically, the Polaris sag and Shippes Draw sag are broad, shallow depressions, but a prominent,240- m-deep, nearly circular topographic depression is associated with Shippes Bowl sag (Fig. 17). Basalt ﬂows are drapedacross the eastern, northeastern, and perhaps western ﬂanksofShippes Bowl sag, but are absent on other ﬂanks. The 2.4-km-long Ti- Ke-Ki sag formed in basalt ﬂows on the interﬂuve between the valleys of the Roaring Fork and Crystal Rivers. Within the east-central part of the collapse center the ba- saltic ﬂows are highly broken, fractured, and jostled. Kirkham and Widmann (1997) described these deposits as collapse de- bris. Individual structures within the collapse debris are typi- cally too complex to map at a scale of 1:24000. Collapsedebris locally includesvaryingamountsofunconsolidatedsurﬁcialde- posits that have collected over or between the blocks of broken, locally rubbly bedrock. Much of the Missouri Heights area is underlain by collapse debris (Fig. 2). Ten closed, or nearly closed, linear topographic depres- sions were identiﬁed in Pleistocene terraces along the Roaring Fork and Crystal Rivers (Fig. 2). These depressions, whichpar- allel the subjacent river channels, are interpreted as subsidence troughs resulting from bending due to roof collapse into dis- solution cavities formed in evaporite beneath the terraces.Sink- holes are associated with many of the troughs. The Barbers Gulch trough southwest of Carbondale (Fig. 2), which formed in a middle Pleistocene terrace west of the Crystal River, is 3.5 km long, 0.6 km wide, and 12 m deep; it is the largest subsidence trough in the area. In addition to locally derived alluvium and colluvium, the trough contains a bed of Lava Creek B ash that lies 73 m above the Crystal River (Kirkham and Widmann, 1997). A subsidence trough likely existed at this location prior to deposition of the 0.64 Ma ash (Lanphere et al.,2002),astopographicdepressionsaregood environments in which to preserve tephra deposits. The ash bed appears to be slightly tilted (Kirkham and Widmann, 1997), which suggests trough subsidence also postdates tephra depo- sition. Other notable subsidence troughs include the Crystal ter- Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user Evaporite tectonism in the lower Roaring Fork River valley, west-central Colorado 93 Figure 18. Distribution and minimum preserved thickness of late Ce- nozoic syn-collapse sediments. Contour interval 100 m. race trough, Blue Creek trough, and Leon trough along the Roaring Fork River (Fig. 2). Crystal terrace trough is a well- preserved, symmetrical depression on a late Pleistocene terrace east of Carbondale. The axis of the trough is 10 m lower than the edges of the terrace. Blue Creek trough is a narrow depres- sion formed on the outerorvalley-wall sideofalatePleistocene terrace north of El Jebel. Blue Creek makes a sharp, nearly right-angle bend as it enters the trough and ﬂows roughly par- allel to the Roaring Fork River for nearly 1700 m. Leon trough is south of El Jebel. Collapse of this nearly circular depression involves a latest Pleistocene terrace that was dropped to the level of the Holocene valley-ﬁll deposits. Holocene ﬂuvial sed- iments may partially ﬁll Leon trough. A slightly smallertrough, adjacent to and northeast of Leon trough, lies on the outer edge of the valley ﬂoor. This trough, in which a lake for water skiing was recently built, is separated from the Leon trough by a to- pographic high that likely is a narrow remnant of the original terrace tread. Sinkholes are prevalent throughout the collapse area (Mock, this volume). They occur in outcrops of evaporite and in bedrock and surﬁcial deposits that overlie evaporite. Sink- holes are most numerous along the Roaring Fork diapir, where on average there is one known sinkhole every 3.9 km 2.The sinkholes provide direct evidence of evaporite dissolution. Some sinkholes may be thousands of years old, but dozenshave disrupted the ground surface during the past few years or de- cades. Most known sinkholes that formed during historic time are associated with irrigated ﬁelds, irrigation ditches, ponds, and lakes. This coincidence may be due to the relatively abundant supply of fresh water found in these areas, which can cause or enhance sinkholes by evaporite dissolution and can induce roof collapse of underground voids by piping. Also, the close atten- tion paid to agricultural ﬁelds and water-supply systems could account formore complete reportingofsinkholesinthoseareas. Spring Park Reservoir, an irrigation reservoir between Carbon- dale and Basalt Mountain (Fig. 2), was rapidly drained twice during the twentieth century when sinkholes developed in the ﬂoor of the reservoir (Steve Callicotte, 1996, personal com- mun.). Open, sinuous voids are present in many exposures of evaporite. Sinkholes and open voids may be interconnected, forming groundwater ﬂow paths with very high transmissivity. A spring with high discharge ﬂows from an open void 1.3 km north of El Jebel. Individual sinkholes may be very large; one in a basalt ﬂow that overlies evaporite near Colorado Mountain College (Fig. 1) is 70 m wide. COLLAPSE-RELATED SEDIMENTARY DEPOSITS Syn-collapse sedimentary deposits accumulated in four major structural depressions formed in bedrock: The previously described Spring Valley structure and Cottonwood bowl, the Sopris bowl on the north side of Mount Sopris, and the Cattle Creek bowl along the east-central part of the collapse area (Fig. 2). Both the Spring Valley structure and Cottonwood bowl are topographically well expressed, but Sopris bowl and Cattle Creek bowl were recognized chieﬂy by the preserved remnants of sediments originally deposited within them. The thickest and laterally most extensive syn-collapsesed- imentary deposits ﬁll Sopris bowl (Kirkham and Widmann, 1997; Kirkham et al., 1998; Streufert et al., 1998; Streufert, 1999). Large remnants of these deposits are found on the in- terﬂuve between the Roaring Fork and Crystal Rivers and in the hills on the west side of the Crystal River (Fig. 18). The sediments include gravelly clast-supported ﬂuvial deposits and matrix-supported debris-ﬂow deposits. Clast lithologies indi- cate an ancestral Crystal River provenance for deposits in the western part of the basin and an ancestral Roaring Fork River provenance in the eastern part. The paleovalley exposed on Light Ridge (Figs. 2 and 18) probably accommodated the an- cestral Roaring Fork River. The exposed thickness of syn-collapse deposits in Sopris bowl exceeds 450 m in the central part of the bowl (Fig. 18). Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user R.M. Kirkham et al.94 Figure 19. Map of the Roaring Fork diapir, Quaternary depositsfolded by evaporite diapirism, and seismic reﬂection lines used to interpret the diapir and collapse center (modiﬁed from Kirkham et al., 2001b). Refer to Perry et al. (this volume) for interpretation of the seismic lines. BT—Bershenyi terrace. The base of the syn-collapse deposits is concealed beneath the ground surface in most of the bowl. Where exposed west of Basalt, the basal contact of the syn-collapse sediments slopes into Sopris bowl with an apparent dip of 9 to the northwest (Streufert et al., 1998). This suggests the maximum preserved thickness of these syn-collapse deposits greatly exceeds 450 m. Seismic reﬂection data collected from the southwestern part of Sopris bowl suggest the syn-collapse depositsattainapreserved thickness of 1100 m (Perry et al., this volume). An ash-ﬂow tuff underlies the syn-collapse sediments in the southeast corner of Sopris bowl (Fig. 2). The tuff dips 20 to the northeast (Streufert et al., 1998) and contains sanidine dated at 35.21 0.03 Ma (Kunk et al., 2001). Deformation associated with Sopris bowl must have begun sometime after eruption of the ash-ﬂow tuff. Basalt ﬂows west of El Jebel (groups 12a and 12b) with an average age of 13.3 Ma (Table 1) are stratigraphically at or near the top of the syn-collapse sedimentary sequence, which indicates Sopris bowl continued to ﬁll with sediments until near the end of the middle Miocene. Since the 13.3 Ma ﬂows are tilted and are at elevations sub- stantially lower than other middle Miocene ﬂows found outside the collapse area, major subsidence continued in Sopris bowl after 13.3 Ma. The proximity of Sopris bowl to Mount Sopris stock, and age relationships between the formation of the bowl and emplacement of the stock, suggest increased geothermal gradients and other hydrologic changes associated with the stock may have caused or enhanced evaporite dissolution. A laterally extensive but relatively thin remnant of syn- collapse sediments deposited in Cattle Creek bowl is preserved on the drainage divide between Cattle Creek, MissouriHeights, and Spring Park Reservoir (Fig. 18). A west-ﬂowing stream deposited these sediments in ﬂuvial, deltaic, and lacustrine en- vironments. Coarse-grained, sandy, silty, cobble and pebble gravel eroded from the mountains east of the collapse area was deposited in the eastern and central parts of Cattle Creek bowl. Fine-grained sediments found farther west in the bowl suggest that collapse created closed topographic depressions favorable for lacustrine and deltaic deposition. The syn-collapse sediments in Cattle Creek bowl uncon- formably overlie ca. 10 Ma group 1b volcanic rocks, although in places the group 1b volcanic rocks crop out in hills that are topographically higher than adjacent syn-collapse sediments. As the syn-collapse sediments were ﬁrst deposited, these hills of volcanic rock formed islands that rose above the streamsand lakes in which the sediments accumulated. The sediments in Cattle Creek bowl also locally overlie 7.75 Ma volcanic rocks, but stratigraphic relationships with the Pliocene (3.05 0.04 Ma) group 6c rocks are equivocal. EVAPORITE FLOW Evidence of evaporite ﬂowinthelowerRoaringForkRiver valley includes valley-centered anticlines, diapiric contacts be- tween evaporite and overlying rocks, and folded Quaternary deposits. The Cattle Creek anticline,ﬁrst described by Mallory (1966),underliesthe RoaringForkRivervalleyfromGlenwood Springs to near Carbondale (Fig. 1). Evaporite in the core of this anticline is at least locally diapiric (Figs. 4 and 19). This structure coincides with the upper limb of the Laramide Grand Hogback monocline in much of the lower Roaring Fork River valley. Evaporite ﬂowed toward the upper limb of the mono- cline during the Laramide orogeny (Perry et al., this volume). The valley-centered anticline was enhanced by subsequent late Cenozoic evaporite ﬂow and diapirism related to the Roaring Fork diapir. Over 100 m of diapiric piercement by the Eagle Valley Evaporite into overlying beds in the Middle and Upper Pennsylvanian Eagle ValleyFormationisapparentinthepromi- nent exposure on the east valley wall of the Roaring Fork River immediately south of Cattle Creek (Fig. 20). Quaternary outwash terraces are deformed by evaporite ﬂow at four locations in the lower Roaring Fork River valley between Glenwood Springs and Carbondale (Fig. 19). These tilted deposits dip away from the axis of the valley, even where the deposits are adjacent to the valley wall. This folding prob- Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user Evaporite tectonism in the lower Roaring Fork River valley, west-central Colorado 95 RED TABLE MOUNTAIN CATTLE CREEK BOWL Diapir Margin ROARING FORK DIAPIR Figure 20. Photograph of Roaring Fork diapir. View is to east. Note diapiric contact between the Eagle Valley Evaporite and overlying Eagle Valley Formation (shown by arrows). Outcrop is on east side of the Roaring Fork River valley between Cattle Creek and the town of Carbondale. ably resulted from upward evaporite ﬂow in the Roaring Fork diapir during or after the middle Pleistocene, because Quater- nary deposits that sag or collapse into subsidence troughs al- ways dip into the subsided area. Unruh et al. (1993) described terraces deformed by evaporite ﬂow along the west wall of the Roaring Fork River valley southwest of Basalt. These deposits appear to be uparched in an anticlinal structure that is oblique to the valley axis, which also is suggestive of deformation by upwelling evaporite. At Bershenyi terrace, near the northern end of the Roaring Fork diapir (Figs. 5, 19, and 21), a Quaternary terraceandover- lying deposits are deformed by evaporite ﬂow. The middle Pleistocene Bershenyi terrace (Piety, 1981) is overlain by a wedge-shaped layer of debris-ﬂow deposits that is thickest at the fan head (Kirkham et al., 1996, 1997). Where closest to the river, these deposits are folded upward and dip away from the river. The downstream (northern) end of the terrace is uparched such that debris-ﬂow deposits at the distal end of the fan are now 30 m higher in elevation than correlative deposits at the original fan head. The adjacent late Pleistocene airport terrace (“AT” on Fig. 21), is not visibly affected by evaporite tecton- ism. Measurable evaporite ﬂow last occurred at this location after deposition of the middle to upper Pleistocene debris-ﬂow deposits and prior to deposition of the undeformed, adjacent upper Pleistocene terrace deposits. Seismic reﬂection data interpreted by Perry et al. (this vol- ume) support our conclusion that evaporite ﬂow and diapirism locally created evaporite-cored valley anticlines and uparched Quaternary terraces and associated deposits along the valley axis. The interpreted seismic lines suggest the evaporitic strata are thin beneath the Grand Hogback monocline and in the area east of the Roaring Fork River valley but up to 1.5 km thick in the ends of the intrusive diapir under the valley. The evaporite apparently withdrew from the adjacent upland areas and ﬂowed into the valley-centered diapir. The interpretation of Perry et al. (this volume) suggests that the Roaring Fork diapir may locally pierce as much as a kilometer of overlying strata. Evaporite ﬂow may also be responsible for the Spring Val- ley structure and Heuschkel Park synclinal sag, which were previously described. Large, relatively intactblocksofrockthat Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user R.M. Kirkham et al.96 BT AT Figure 21. Photograph of Bershenyi terrace (BT, in the left center of photograph) looking north. The downstream end of this middle Pleistocene outwash terrace and the distal (northern) end of an overlying debris-ﬂow fan are upwarped by evaporite ﬂow. The adjacent late Pleistocene airport terrace (AT) is not deformed by evaporite ﬂow. Location of terraces shown in Figures 5 and 19. overlie the evaporitic strata between these structures and the river valley may be rafting into the valley as the underlying evaporite ﬂows toward the valley. TIMING OF COLLAPSE Available data indicate that the rate of evaporite-related collapse has varied temporally and spatially. The earliest rec- ognized evidence of post-Laramide evaporite collapseoccurred between 35.21 Ma and 13.3 Ma when a deep, but localized dissolution basin formed immediately north of Mount Sopris. Collapse during this time period apparently was restricted to the area north of Mount Sopris. Major subsidence across the entire collapse center began sometime after 10 Ma (Fig. 22), but its precise initiation is poorly constrained. In some areas, ca. 10 Ma volcanic rocks are downdropped more than the 7.7 Ma ﬂows, suggesting some of the regional collapse occurred between ca. 10 Ma and 7.7 Ma. Deﬁnitive evidence of collapse during this time, such as greatly deformed older ﬂows overlain by less-deformed ﬂows, how- ever, was not observed. Rates of river incision probably in- creased ca. 10-8 Ma, and greatly accelerated during the past 3 m.y. (Kirkham et al., 2001a). This incision in turn decreased lithostatic pressures on the evaporitic rocks beneath the valleys and triggered or enhanced evaporite ﬂow. As the rivers cut deeper, fresh groundwater circulated to greater depths in the evaporite and promoted dissolution and collapse. Along the eastern margin of the collapse area, near Spring Park Reservoir, a 2.90 Ma cinder cone and associated volcanic ﬂow (group 6b ) are tilted approximately the same amount by the Basalt Mountain monocline as are nearby ca. 10 Ma group 4b basaltic rocks. Therefore most of the collapse of the Basalt Mountain monocline occurred after ca. 3 Ma (Kirkham et al., 2001b). Major Pliocene and younger collapse can also be in- ferred from data in the northeastern part of the collapse area. Preserved remnants of the 3.17 0.02 Ma eruptive center at Buck Point (group 6b ) are at an altitude of 2680 m (Streufert et al., 1997), and the 3.97 0.08 Ma eruptive center at Little Buck Point (group 6b) is at 2620 m (Kirkham et al., 1995). Both of these Pliocene eruptive vents are within the collapse Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user Figure 22. Schematic east-west cross sections (F–F) showing the generalized evolution of the Carbondale collapse center in the lower Roaring Fork River valley (adapted from Kirkham et al., 2001b). Approximate line of section (shown by dashed line in Figure 7) follows an irregular path from Sunlight Peak to Basalt Mountain. Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user R.M. Kirkham et al.98 center, yet they are only slightlylowerthanorequalinelevation to the 7.75 Ma ﬂows on Little Grand Mesa, which are at an altitude of 2680–2745 m and are outside of the Carbondale collapse center. If signiﬁcant collapse occurred between 7.75 and ca. 3 Ma, then these younger eruptive vents would have been constructed on a ground surface that was lower in the landscapethanLittleGrandMesa.Thesedatasuggestthatmuch of the evaporite collapse in the lower Roaring Fork Rivervalley occurred during the past 3 million years, which closely mirrors incision rates (Kirkham et al., 2001a; Kunk et al., this volume). Historic sinkholes and high salinity loads in rivers and thermal springs document active dissolution and deformation.Thepres- ence of thick evaporite beneath much of the collapse area por- tends continuing collapse. Future collapse rates likely will ﬂuc- tuate as climate and rates of incision and uplift vary. SUMMARY Dissolution and ﬂow of Pennsylvanian evaporitic rocks during the late Cenozoic have created a regional collapse area in the lower Roaring Fork River valley in west-central Colo- rado. Abundant and well-preserved evidence of this evaporite tectonism is widespread in the collapse area. The lateral extent and amount of vertical collapse, as well as the timing and style of deformation, are well constrained by upper Cenozoic vol- canic rocks that were correlated using ﬁeld mapping, 40Ar/39Ar geochronology, geochemistry, and paleomagnetism. These vol- canic rocks are downdropped as much as 1220 m in thecollapse area. Syn-collapse sedimentary deposits accumulated in struc- turally controlled topographic depressions along the margins of the collapse center and within its interior. Local collapse initiated during the Oligocene or early Mio- cene. Collapse became widespread between ca. 10 Ma and 7.7 Ma, and it greatly accelerated during the past 3 million years, largely in response to river incision. When the Roaring Fork River began to downcut through a broad, low-relief erosion surface during the late Miocene, rocks overlying the evaporite beds were eroded from the valley. This created differentiallith- ostatic pressures, which triggered ﬂow of the evaporite from beneath adjacent upland areas where pressures remained high, toward the Roaring Fork River valley where the pressureswere reduced. River incision also allowed relatively fresh ground- water to circulate to progressively greater depths, a processthat increased dissolution rates. Since thick evaporite still underlies much of the collapse area, continued subsidence is likely. ACKNOWLEDGMENTS The National Cooperative Geologic Mapping Program sup- ported most of our geologic mapping; the U.S. Forest Service and Bureau of Land Management also provided ﬁnancial and logistical support. Nancy Bauch, Bruce Bryant, Chris Carroll, Jim Cappa, Paul Carrara, Nancy Driver, Francisco Gutie´rrez, Ken Hon, Karl Kellogg, Dave Lidke, Bill Lorah, Dave Merritt, Ralph Mock, Bob Scott, Ralph Shroba, Tom Steven, Dan Un- ruh, Robin VerSchneider, Paul Von Guerard, and Beth Wid- mann shared information and ideas that contributed to our study. Kenneth S. Johnson and James T. Neal reviewed the manuscript for the Geological Society of America; William Pat Rogers, Ren Thompson, Francisco Gutie´rrez, Bruce Bryant, and Vince Matthews reviewed earlier versions of this manu- script. We appreciate their thorough and insightful reviews. Larry Scott prepared the digital graphics. REFERENCES CITED De Voto, R.H., Bartleson, B.L., Schenk, C.J., and Waechter, N.B., 1986, Late Paleozoic stratigraphy and syndepositional tectonism, northwestern Col- orado,in Stone, D.S., ed., New interpretations of northwest Colorado geology: Denver, Colorado, Rocky Mountain Association of Geologists, Symposium, p. 37–49. Freeman, V.L., 1971, Permian deformation in the Eagle Basin, Colorado: U.S. Geological Survey Professional Paper 750-D, p. D80–D83. Freeman, V.L., 1972, Geologic map of the Woody Creek quadrangle, Pitkin and Eagle Counties, Colorado: U.S. Geological Survey Geologic Quad- rangle Map GQ-967, scale 1:24000. Kirkham, R.M., and Streufert, R.K., 1996, Neogene deformation in the Glen- wood Springs-Carbondale-Gypsum area, Colorado: Geological Society of America Abstracts with Programs, v. 28, no. 7, p. A-517. Kirkham, R.M., and Widmann, B.L., 1997, Geologic map of the Carbondale quadrangle, Garﬁeld County, Colorado: Colorado Geological Survey Open-File Report 97-3, scale 1:24000. Kirkham, R.M., Streufert, R.K., and Cappa, J.A., 1995, Geologic map of the Shoshone quadrangle, Garﬁeld County, Colorado: Colorado Geological Survey Open-File Report 95-4, scale 1:24000. Kirkham, R.M., Streufert, R.K., Hemborg, H.T., and Stelling, P.L., 1996, Geo- logic map of the Cattle Creek quadrangle, Garﬁeld County, Colorado: Colorado Geological Survey Open-File Report 96-1, scale 1:24000. Kirkham, R.M., Streufert, R.K., and Cappa, J.A., 1997, Geologic map of the Glenwood Springs quadrangle, Garﬁeld County, Colorado: Colorado Geological Survey Map Series 31, scale 1:24000. Kirkham, R.M., Widmann, B.L., and Streufert, R.K., 1998, Geologic map of the Leon quadrangle, Eagle and Garﬁeld Counties, Colorado: Colorado Geological Survey Open-File Report 98-3, scale 1:24000. Kirkham, R.M., Kunk, M.J., Bryant, B., and Streufert, R.K., 2001a, Constraints on timing and rates of incision by the Colorado River in west-central Colorado: A preliminary synopsis,in Young, R.A., and Spamm, E.E., eds., The Colorado River: Origin and evolution: Grand Canyon, Arizona, Grand Canyon Association Monograph 12 (in press). Kirkham, R.M., Streufert, R.K., Budahn, J.R., Kunk, M.J., and Perry, W.J., 2001b, Late Cenozoic regional collapse due to evaporite ﬂow and dis- solution in the Carbondale collapse center, west-central Colorado: The Mountain Geologist, v. 38, no. 4, p. 193–210. Kunk, M.J., and Snee, L.W., 1998, 40Ar/39Ar age-spectrum data of Neogene and younger basalts in west-central Colorado: U.S. Geological Survey Open-File Report 98-243, 112 p. Kunk, M.J., Winick, J.A., and Stanley, J.O., 2001, 40Ar/39Ar age-spectrum and laser-fusion data for volcanic rocks in west-central Colorado: U.S. Geo- logical Survey Open-File Report 01-472, 94 p. Lanphere, M.A., Champion, D.E., Christiansen, R.L., Izett, G.A., and Obra- dovich, J.D., 2002, Revised ages for tuffs of the Yellowstone Plateau volcanic ﬁeld: Assignment of the Huckleberry Ridge Tuff to a new geo- magnetic polarity event: Geological Society of America Bulletin (in press). Larson, E.E., Ozima, M., and Bradley, W.C., 1975, Late Cenozoic basic vol- Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user Evaporite tectonism in the lower Roaring Fork River valley, west-central Colorado 99 Printed in the U.S.A. canism in northwest Colorado and its implications concerning tectonism and origin of the Colorado River system,in Curtis, B.F., ed., Cenozoic history of the southern Rocky Mountains: Boulder, Colorado, Geological Society of America Memoir 144, p. 155–178. Mallory, W.W., 1966, Cattle Creek anticline, a salt diapir near Glenwood Springs, Colorado: U.S. Geological Survey Professional Paper 550-B, p. B12–B15. Mallory, W.W., 1971, The Eagle Valley Evaporite, northwest Colorado—A regional synthesis: U.S. Geological Survey Bulletin 1311-E, 37 p. Murray, F.N., 1966, Stratigraphy and structural geology of the Grand Hogback monocline, Colorado [Ph.D. thesis]: Boulder, Colorado, University of Colorado, 219 p. Murray, F.N., 1969, Flexural slip as indicated by faulted lava ﬂows along the Grand Hogback monocline, Colorado: Journal of Geology, v. 77, p. 333– 339. Peale, A.C., 1876, Report on the valleys of Eagle, Grand, and Gunnison Rivers, Colorado: Annual Report of the United States Geological and Geograph- ical Survey of the Territories, 8th Annual Report, p. 73–180. Piety, L.A., 1981, Relative dating of terrace deposits and tills in the Roaring Fork valley, Colorado [M.S. thesis]: Boulder, Colorado, University of Colorado, 209 p. Stover, B.K., 1986, Geologic evidence of Quaternary faulting near Carbondale, Colorado, with possible associations to the 1984 Carbondale earthquake swarm,in Rogers, W.P., and Kirkham, R.M., eds., Contributions to Col- orado seismicity and tectonics—A 1986 update: Colorado Geological Survey Special Publication 28, p. 295–301. Streufert, R.K., 1999, Geologic map of the Mount Sopris quadrangle, Garﬁeld and Pitkin Counties, Colorado: Colorado Geological Survey Open-File Report 99-7, scale 1:24000. Streufert, R.K., Kirkham, R.M., Widmann, B.L., and Schroeder, T.J. II, 1997, Geologic map of the Cottonwood Pass quadrangle, Eagle and Garﬁeld Counties, Colorado: Colorado Geological Survey Open-File Report 97- 4, scale 1:24000. Streufert, R.K., Widmann, B.L., and Kirkham, R.M., 1998, Geologic map of the Basalt quadrangle, Eagle, Garﬁeld, and Pitkin Counties, Colorado: Colorado Geological Survey Open-File Report 98-1, scale 1:24000. Tweto, O., 1977, Tectonic history of west-central Colorado,in Veal, H.K., ed., Exploration frontiers of the central and southern Rockies: Denver, Colorado, Rocky Mountain Association of Geologists, Symposium, p. 11–22. Unruh, D.M., Budahn, J.R., Siems, D.F., and Byers, F.M., 2001, Major- and trace-element geochemistry; lead, strontium, and neodymium isotopic compositions; and petrology of late Cenozoic basaltic rocks from west central Colorado: U.S. Geological Survey Open-File Report 01-477, 90 p. Unruh, J.R., Wong, I.G., Bott, J.D., Silva, W.J., and Lettis, W.R., 1993,Seismo- tectonic evaluation, Riﬂe Gap Dam, Silt Project, Ruedi Dam, Fryingpan– Arkansas Project, northwestern Colorado: Report prepared by William R. Lettis and Associates and Woodward-Clyde Consultants for U.S. Bureau of Reclamation, 154 p. MANUSCRIPT ACCEPTED BY THE SOCIETY APRIL 12, 2002 Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user Downloaded from http://pubs.geoscienceworld.org/gsa/books/book/510/chapter-pdf/967736/i0-8137-2366-3-366-0-73.pdfby Colorado School of Mines user The purpose of this report is to examine geologic and hydrologic data related to the geographic area known as Spring Valley and, there from, prepare estimates of the potential specific yield of the water bearing horizons (aquifers) and estimates of amount of annual recharge to those water bearing horizons. A segment of the natural phenomenon that will be discussed in this dissertation is often referred to as the “Spring Valley Aquifer”. This is the approximate 1,500-acre area basin, flanked on the east by County Road 114 and on the north by County Road 115. It has been penetrated by a number of wells that serve Colorado Mountain College, the sod farm and most of the single-family homes along 114 road and 115 road. The small stream that drains the surface of the basin, discharges in Red Canyon. This basin, as noted above, represents only a segment of a dynamic hydrologic system comprised of highly favorable geologic conditions situated in a meteorological environment conducive to precipitation levels substantially greater than the adjacent lower valley areas. GEOLOGIC CONDITIONS The recharge area of the Spring Valley Hydrologic System is comprised of approximately 15.4 square miles. This area, illustrated on the attached map, varies in elevation from 6,870 to 9,400 feet. The surficial geology of this recharge area may be divided, for purposes of hydrologic consideration, into three petrographic types: x Siltstones, sandstones, clay stones and conglomerates of the Pennsylvanian/ Permian Maroon Formation; x Basalt flows, basalt talus, colluvium comprised predominantly of basaltic material, all of Tertiary and early Quaternary age; and x Quaternary lacustrine materials comprised predominantly of fine-grained products of the chemical and mechanical weathering of the older rock materials that were deposited in a lake. Samples from recent well drilling have been examined which indicate deposits of volcanic ash in the lower portions of the lake basin. Stratigraphically, the Maroon Formation under lays the basalt and alluvial materials. It overlays the Eagle Valley Evaporate Formation, sometimes referred to as the Paradox Formation. The Maroon formation, along with underlying sediments, was elevated and exposed by erosion in the course of the orogeny that created the White River uplift to the north. The Eagle Valley Evaporite formation contains beds of soluble salts such as Gypsum and Halite. The introduction of ground water into these salt beds resulted in the slow, but steady solution and removal of several thousand feet of this formation over a large section of a portion of the Roaring Fork River drainage area. The area of the Spring Valley Hydrologic System straddles the northern edge of this affected area. As the salts were removed, the overlaying rocks settled. This activity was, likely, very similar to the current mining of soluble minerals by hydrothermal water as demonstrated by the Glenwood Hot Springs and the other hot springs along the Colorado River. The solution and removal of salts was not uniform over the effected area and the collapse of the The Spring Valley Hydrologic System March 10, 2000 Page 2 of 11 overlaying rocks resulted in deformation, shear fracturing and faulting of the Maroon formation as well as the overlaying rock of volcanic origin. The intensity of this fracturing may be better understood by observing the Maroon Formation outcrops exposed along Highway 82 from Carbondale to Red Canyon. The sandstone beds which are interbedded with siltstones and shales are well-cemented, relatively hard rock. When they were originally deposited and lithified, they formed straight, flat, continuous unbroken layers of stone. Now they have the character of blocks of stone laid up in a dry stack wall constructed on an uneven surface. While a minor amount of this fracturing may be attributed to the White River Uplift activity, the vast majority is the result of irregular collapse due to the solution mining of the underlying Eagle Valley Evaporites. The volcanic materials were similarly fractured by this removal of the evaporite basement rock. The fracturing of relatively continuous lava flows may be observed in the cliffs along the lower reaches of Landis Creek and on the slopes northerly of county road 115. The high infiltration rate and water bearing capacity of the volcanic rock material is the product of the above noted, intense fracturing of the very brittle basalt coupled with the high porosity of the subsurface beds and lenses of volcanic ash, cinders and breccias. The strongest fault/fracture systems are indicated by geomorphologic evidence and are illustrated on the map. It appears that most of the fracturing of the volcanic materials is the result of bending and slumping of the rock layers which caused very little displacement from one side of the fault/fracture zone to the other. Some of the volcanic material outcrops and sub-outcrops are virtually rubblized while other outcrop sections appear to be rafted basalt blocks with horizontal dimensions of several hundred feet. Much of the land surface which slopes at 20% or greater has a very thin to virtually non- existent soil cover. Vegetation, in these areas, is sparse and small indicating that it survives with a minimal moisture supply, even though the area receives 25 to 30 inches of precipitation per year. Excavation in the course of constructing pioneer roads reveals areas of the subsoil rock, to be comprised primarily of medium sized to massive boulders wherein the “porosity” may be visualized as that which would result from the stacking of poorly sorted particles that range in size from basketballs to Volkswagens. The percolation rate in these areas is obviously, very rapid. In some areas of the surface, where the land slope is less than 15 percent, soil has accumulated to depths of as much as 20 feet over the rock. Percolation tests were conducted on soils of this type at 11 locations in the upland aquifer recharge area. The average of the percolation rates measured was 25.5 minutes per inch (2.35 inches per hour) with the range being from 3 to 64 minutes per inch. Of the 11 tests, 8 measured at 34 minutes per inch or less. The volcanic activity events of 3 to 4 +/- million years ago deposited 100 to 200 feet or more of interlayered basalt, cinders, ash, and breccias on a substantially more horizontal surface than is present in the area today. The intervening 3 million +/- years of erosion on that surface, which was slowly tilting southerly, has removed the softer, unconsolidated cinders and ash from the surface, exposing, hard, weather resistant basalt. The remaining, highly porous ash and cinder lenses below the hard basalt surface provide pockets or constricted basins of high porosity where ground water is detained. Surface The Spring Valley Hydrologic System March 10, 2000 Page 3 of 11 water is channeled into these detention basins or “hanging aquifers” via the fractured and rubblized surface basalt. Subsurface fractures interconnect the detention basins and act as restricted conduits that facilitate the slow, but continuous, transmission of water from those at higher elevations to the ones below. The segment of the system, which is referred to, as the Spring Valley Aquifer is in fact a composite of a series of confined aquifers in the sediments overlaying the bedrock, and the upper portion of the bedrock, underlying these sediments, which is itself, a confined aquifer capable of, and demonstrated to produce artesian wells. The confined aquifers within the lakebed sediments are comprised of sand and sandy gravel horizons confined between layers of clay or sandy, gravely clay. From previous drilling and data from Spring Valley Ranch well #6 drilled in February and March 2000, it appears that the lower 70 to 110 feet of the sediment section in the northwestern end of the basin is very fine-grained sand. Samples taken from this well drilling were tested and it was determined that the specific porosity of this material is approximately 30%. Microscopic examination of this material reveals that it is highly angular, with the appearance of shattered glass. The particles do not exhibit the characteristics of sand grains that have been subjected to significant transportation and attrition by either water or wind action. It is suspected that this sand is vitric volcanic ash, which was deposited in and adjacent, upslope of the lake basin during the creation of the basin by subsidence, as discussed below. The bedrock form of the lake basin is a “half graben” with the fault on the southerly side along County Road 119. The bedrock is comprised of Maroon Formation sediments, capped with 100 feet or more of volcanic material similar to that which may be observed on the north side of 115 road and in the cap rock on the south side of the valley. This bedrock block tilts, or more accurately “slumps” southerly From the divide between the Colorado and Roaring Fork river drainages, down the south facing slopes of Spring Valley and under the basin, to its termination at a fault that extends along the southern side of the valley. An additional feature has been observed in the aquifer basin. In many of the deep drill holes, the volcanic rock section below is separated from the overlaying lake sediments by a layer of blue gray clay as much as 40 feet thick. This is probably montmorillonite clay of the bentonite variety that is formed by the alteration of volcanic ash and tuff. Where present, this clay layer acts as a seal between the lake sediments and the underlying volcanic rock material. HYDROLOGIC CONDITIONS The conditions and events noted above created the geologic setting for the Spring Valley Hydrologic System. The other component of the system is the precipitation provided by the meteorological environment. Average annual precipitation in the Colorado Mountains increases substantially with elevation. This is illustrated on the Colorado Average Precipitation Map, 1951 to1980, prepared by Colorado State University in conjunction with Climatology Report 84-5, The Spring Valley Hydrologic System March 10, 2000 Page 4 of 11 published by the U.S. Geological Survey. This map indicates that the uppermost part of the recharge area of this hydrologic system receives an average of 30 inches of precipitation per year while the lowest portion of the recharge area receives 16 inches to 20 inches per year. PRECIPITATION INFILTRATION The effective introduction of this precipitation into the underground hydrologic system is largely dependent upon the character of the surface geology. Fractured basalt flows, basalt talus and colluvium comprised predominantly of granular soil and rock are highly permeable, wherein it is estimated that, at least 60% of the precipitation will enter the aquifer after evaporation, transpiration and surface run-off. This high rate of infiltration is graphically demonstrated by the drainage along County Road 115 within the Spring Valley Ranch. The Basalt hillside northerly of the road ranges in slope from 10 to 40 percent. The average annual precipitation received by this area is 20 to 25 inches per year. Drainage sub-basins above, discharge to these slopes, yet many of the natural drainage swales crossed by the road do not have culverts and do not have the appearance of areas that transport or pond water. It is reported, by longtime residents of the area, that only on occasions of extremely high snow melt or cloud burst, does flooding of the road occur. This condition has also been observed on the pioneer roads constructed on the higher portions of the Spring Valley Ranch that are underlain by fractured basalt or thin granular soils over basalt. The inability of the thin soils to retain moisture is demonstrated by the light vegetation cover. The topographic characteristics of the highly basaltic surfaces are further evidence of its high infiltration rate. This is an area that sustains an average precipitation of 20 to 30 inches per year on slopes of 10 to 50 percent. If the rate of infiltration of precipitation was not exceptionally high, the large volume of high velocity run-off would have eroded major drainage swales and gulches down the slopes, nearly perpendicular to the contours. The precipitation does occur, but the run-off does not. Instead, this precipitation enters the fractured and otherwise highly porous basaltic materials and is detained there in a series of cascading aquifers that are interconnected by shear fracture zones. These fracture zones function as control orifices and slowly release the gravity flow of water to springs and the aquifers below. Conversely, fractured Maroon formation overlain with silty, loam soils supporting moderate to heavy vegetation will result in the infiltration of approximately 20% of the precipitation with the balance being lost to evapotranspiration and surface runoff. Where this surface runoff must cross the basaltic areas noted above, much of it will enter the groundwater system. The conditions described above were applied to the map of the recharge area, prepared on the basis of published geologic mapping and personal observations. The following table was prepared which estimates the average precipitation amount in the recharge area and the potential infiltration amount entering the underground hydrologic system. The Spring Valley Hydrologic System March 10, 2000 Page 5 of 11 PERCIPITATION ZONE AND ESTIMATED INFILTRATION RATE AREA (ACRES) AVERAGE ANNUAL PRECIPITATION (A/F) ESTIMATED INFILTRATION TO AQUIFER (A/F) 16’ – 20” (18”) 20% 592 888.0 177.6 16” – 20” (18”) 60% 1,497 2,245.5 1,347.3 20” – 25” (22.5”) 20% 1,050 1,968.8 393.8 20” – 25” (22.5”) 60% 2,180 4,087.5 2,452.5 25” – 30” (27.5”) 20% 450 1,331.3 206.3 25” – 30” (27.5”) 60% 3,794.6 8,694.6 5,216.8 30” 75% 277 692.5 519.4 TOTAL 9,840.6 19,908.2 10,313.7 WET/DRY YEAR 11,345.07/8,250.96 As may be observed, the above calculations indicate that more than 50% of the system recharge occurs in the higher elevations. The possible amount of recharge to the aquifer may also be estimated by the following formula: recharge = precipitation – evapotranspiration – surface flow down red canyon. Observations made by Wright Water Engineers, indicate that the surface flow down Red Canyon will vary from 400 to 600 acre feet per year. As noted above, the estimated average precipitation for the total system recharge area is computed to be 19, 908.2 acre feet per year. The following table illustrates an estimate of the probable losses to evapotranspiration in the various precipitation zones and vegetation types. The evapotranspiration rate factors used in the calculations were taken from Handbook of Applied Hydrology by Chow, McGraw-Hill. PRECIPITATION ZONE WATERSHED AREA (ACRES) VEGETATION TYPE & EVAPOTRANSPIRATION FACTOR (INCHES/YEAR) POTENTIAL LOSS TO EVAPOTRANSPIRATION 16” –20” 2,089 GRASS, BRUSH & SHRUBS 5-10 (USE 7.5) 1,305.6 20” –25” 3,230 GRASS, BRUSH & SHRUBS 5-10 (USE 7.5) 2,018.8 25” – 30” 2,122,3 2,122.3 50%GRASS, BRUSH & SHRUBS 7.5 50% ASPEN/FIR 23 1,326.4 4,067.7 30’ 277 ASPEN/FIR 23 530.9 TOTAL 9,840.6 9,249.4 Appling the equation noted above: recharge = precipitation – evapotranspiration – surface flow down red canyon. Probable Recharge = 19,908.2 - 9,249.4 – 600 = 10,058.8 acre feet per year The section underlain by basaltic materials located easterly of Landis Creek accounts for the majority of the recharge and is believed to support the greatest detention volume in the system, which, in turn recharges the Spring Valley Aquifer. The Spring Valley Hydrologic System March 10, 2000 Page 6 of 11 This belief is supported by the presence of consistently flowing springs which surface in the upland area and the characteristics of the seven wells which have been drilled there and pump tested . One well was drilled in the Maroon formation and six in the volcanics. All of the wells were test pumped for 24 hours immediately following drilling and 3 were selected for extended pump tests. The extended pump tests are described in the Wright Water Engineers, Inc., report “Spring Valley Upland Aquifer Pumping Tests – 2000”. Peter Cabrinha has been closely associated with the Spring Valley Ranch for 37 years and has observed the performance of springs on the property. In a recent interview with Mr. Cabrinha, the following observations were related: x All of the springs appear to flow year around at relatively consistent rates with the exception of periods following extremely low winter and spring precipitation. x In his 37 years of observation, there were two occasions when the upper Landis Creek springs, at 9,100 ft elevation, stopped flowing. These stoppages occurred in the late summer or early fall of the year following the low winter and spring precipitation. The springs resumed flow the following spring. x The flows of the lower elevation springs do not appear to diminish following dry winter/spring seasons. ESTIMATE OF SPECIFIC YIELD OF SYSTEM AQUIFIRS In order to accommodate to the performance described above, the hydrologic system must receive a substantial portion of the precipitation, as indicated in the table above, and have a sufficient volume of specific yield to detain the infiltrated precipitation of several years. Information is available to compute a conservative estimate of the potential specific yield of the aquifers in the system. The following assumptions and parameters will be used in computing the estimated specific yield. 1. The upland area in the 20-inch to 30+-inch precipitation zone covered by volcanic materials contains approximately 5,975 acres. 2. The thickness of the volcanic materials intercepted by the six wells, drilled in volcanics, in the upland area ranged from 112 feet to 200 feet with an average of 168 feet. The depth of water in the wells (static level to bottom) ranged from 46 feet to 310 feet with an average of 135 feet. For conservative estimating purposes, a saturated thickness of only 50 feet will be used. 3. The porous volcanic materials will perform similarly to sand, gravel and cobbles for which the specific yield will range from 34% to 20% (from Figure 5-4 Bear Jacob. 1979 Hydraulics of Groundwater. McGraw-Hill). For conservative estimating purposes, a range of 10 to 20% will be used. 4. The surface area of the Spring Valley aquifer is approximately 1,500 acres. 5. Well log information indicates that the thickness of lake sediments may average from 250 to 300 feet. in thickness, comprised of 10 to 20 feet of gravel bed, 140 to 180 feet of sandy, clayey silt with some gravel and 70 to 110 feet of very fine sand (vitric volcanic ash). For conservative estimating purposes, the following will be used for the lake sediments: The Spring Valley Hydrologic System March 10, 2000 Page 7 of 11 Sandy, clayey silt = 140 feet; gravel = 10 feet; very fine sand = 70 feet. 6. The specific yield of gravel beds in the lake sediments will range from 25% to 34%; the silty clay may range from 3% to 25%; the sand from 25% to 35% (from Figure 5-4 Bear Jacob. 1979 Hydraulics of Groundwater.) McGraw-Hill). For conservative estimating purposes, 25% will be used for the gravel beds and 3% will be used for the clayey sediments and 20% for the very fine sand. Bear Jacob. 1979. Hydraulics of groundwater. McGraw-Hill. The following calculations of the specific yield of the aquifers in the hydrologic system are based on the assumptions and parameters stated above. Upland volcanic areas 5,975 acres x 50 feet thick x 0.10 or 0.20 specific yield = 29, 875 to 59,750 acre feet Spring valley aquifer gravel beds 1,500 acres x 10 feet thick x 0.25 specific yield = 3,750 acre feet Spring valley aquifer silty clay sediments 1,500 acres x 140 feet thick x 0.03 specific yield = 6,300 acre feet Spring valley aquifer very fine sand bed 1,500 acres x 70 feet thick x 0.20 specific yield = 21,000 acre feet Volcanics at base of Spring Valley aquifer 1,500 acres x 50 feet thick x 0.10 or 0.20 specific yield = 7,500 to 15,000 acre feet ESTIMATED TOTAL SPECIFIC YIELD OF AQUIFERS IN SPRING VALLEY HYDROLOGIC SYSTEM = 68,425 to 105,800 AF The Spring Valley Hydrologic System March 10, 2000 Page 8 of 11 Note: the above calculations do not include the volcanic areas in the 16” to 20” precipitation zone nor any of the Maroon formation area. ADDITIONAL AQUIFER CHARACTERISTICS Examination of the records of the State Engineer indicates that the majority of the domestic (single family home) wells in the Spring Valley are drawing water from the upper to middle, silty, clayey lakebed sediments. Although the specific yield of these materials is estimated to be only 3%, it is believed to be a viable segment of the aquifer because it can provide adequate supplies of water to small domestic wells in the valley bottom and probably not be effected by the pumping of large volume wells which draw from the higher yield sands and volcanics in the lower section of the aquifer. The large volume wells of CMC, Los Amigos and the sod farm are drawing water from the volcanic material horizon at the base of the Spring Valley aquifer. Intermediate test pumping of Spring Valley Ranch well #6 from the fine sand zone above the clay indicates that sustained production of at least 250 gpm is available from this material. The static head elevations of the CMC and Los Amigos wells, on the southeast end of the valley, is approximately 100 feet lower than the Spring Valley Ranch wells on the northwest end indicating a general flow of northwest to southeast. This would support the theory that the aquifer outflow generally follows the half graben fault fracture system to the roaring fork valley. SUMMARY AND CONCLUSIONS 1. The source of recharge for the Spring Valley Aquifer is predominantly from the volcanic material in the upland aquifers. 2. This writer believes the average annual precipitation entering the system as recharge and flowing through the series of aquifers, to be approximately 10,000 acre-feet. Peer review of this information by others who have not had the benefit of on-site observations, assign substantially higher volume to loss by evapotranspiration and therefore estimate the average annual recharge volume more conservatively at 4,700 acre-feet. Considering that the potential total annual depletion of the aquifer by existing and future land development is in the vicinity of 1,300 to 1,500 acre feet, the lower figure still assures viability of the aquifer. 3. The estimated specific yield volume of the aquifers in the hydrologic system is in the range of 68,000 to 105,000 acre feet, of which approximately 38,000 to 46,000 acre feet are contained in the Spring Valley aquifer and approximately 30,000 to 60,000 acre feet are available in the upland volcanic material aquifers to recharge the Spring Valley aquifer. These large volumes of stored water provide a leveling effect to the variations in annual precipitation over a period of 6 to 10 years, or more. 4. A substantial portion of the water that enters the system does not again surface in the system, but, leaks out through fracture systems associated with the half graben The Spring Valley Hydrologic System March 10, 2000 Page 9 of 11 fault on the south side of the Spring Valley aquifer and probably enters the Roaring Fork River valley gravel aquifer. 5. The most promising target zones for a large production well appears to be the volcanic ash layer in the lower sediments and the volcanic material horizon below the sediments in the Spring Valley Aquifer. 6. It is highly probable that water production from the lower volcanic ash layer in the sediments and the volcanic material horizon below the sediments in the Spring Valley Aquifer will reduce the leakage to the Roaring Fork River area, but will have little or no effect on the small domestic wells in the upper sediments or the surface discharge down Red Canyon. Respectfully, Jerome F. Gamba, P.E. & L.S. 5933 Enclosures: Exhibit 1, Map of Spring Valley Hydrologic System Exhibit 2, Generalized Geologic Section of Spring Valley and Upland Aquifers The Spring Valley Hydrologic System March 10, 2000 Page 10 of 11 REFERENCES Bass, N.W., and Northrup, S. A., 1963, Geology of Glenwood Spring Quadrangle and Vicinity, Northwestern Colorado: U.S. Geological Survey Bulletin 1142-J 74p. Colorado Average Precipitation Map, 1951 to 1980, prepared by Colorado State University in conjunction with Climatology Report 84-5, published by the U. S. Geological Survey. Colorado Geological Survey, 1974, Roaring Fork and Crystal Valleys-An Environmental and Engineering Geology Study, Environmental Geology No. 8. Kirkham, Robert, M. and others, 1995, Geologic Map of the Glenwood Springs Quadrangle, Garfield County, Colorado, Colorado Geologic Survey, Open File Report 95-3. Kirkham, Robert, M. and others, 1995, Geologic Map of the Shoshone Quadrangle, Garfield County, Colorado, Colorado Geologic Survey, Open File Report 95-4. Kirkham, Robert, M. and others, 1996, Geologic Map of the Cattle Creek Quadrangle, Garfield County, Colorado, Colorado Geologic Survey, Open File Report 96-1. Kirkham, Robert, M. and Beth L. Widmann, 1997, Geologic Map of the Carbondale Quadrangle, Garfield County, Colorado, Colorado Geologic Survey, Open File Report 97-3 Geologic Map of the Spring Valley Ranch, 1999, CTL/Thompson, Inc., Consulting Engineers. Report: Water Requirements, Water Resources, and Spring Valley Area Water Balance, 2000, Wright Water Engineers, Inc. The Spring Valley Hydrologic System March 10, 2000 Page 11 of 11 ROCKY MOUNTAIN | MIDWEST | SOUTHWEST | TEXAS 909 Colorado Avenue Glenwood Sp ring s , CO 81601 |Office: 970-945-6777 |LREWATER.COM SPRING VALLEY RANCH Physical Water Supply Report Prepared for: Roaring Fork Engineering Date 1/25/2023 Project Number 21667SVRD02 The following members of the LRE Water staff contributed to the preparation of this report. Angela Schenk, Senior Project Hydrogeologist January, 2023 – Project # 2167SVRD02 TABLE OF CONTENTS Section 1: Introduction ................................................................................................................. 1 Section 2: Background ................................................................................................................. 1 Section 3: Physical Water Supply ................................................................................................... 1 3.1 SV Well No. 1 ..................................................................................................................... 2 3.2 ASR Well No. 16 fka Gamba 8 ................................................................................................ 4 3.3 Well 36567-MH ................................................................................................................... 6 3.4 Well 36596-MH ................................................................................................................... 9 3.5 SVR Well No. 20 fka Gamba 1 .............................................................................................. 11 3.6 ASR Well No. 15 ............................................................................................................... 14 3.7 ASR Well No. 14 ............................................................................................................... 16 3.8 SVH Well 10 ..................................................................................................................... 19 Section 4: Water Quality Results .................................................................................................. 21 LIST OF FIGURES Figure 1: SVR Well 1 (86630-F) Pump Test .................................................................................................................. 3 Figure 2: SVR Well 1 (86630-F) Recovery ..................................................................................................................... 4 Figure 3: ASR Well No. 16 (86629-F) Pump Test .......................................................................................................... 5 Figure 4: ASR Well No. 16 (86629-F) Recovery Analysis .............................................................................................. 6 Figure 5: Well 36567-MH Pump Test ............................................................................................................................. 8 Figure 6: Well 36567-MH Recovery Analysis ................................................................................................................. 9 Figure 7: Well 36569-MH Pump Test ........................................................................................................................... 10 Figure 8: Well 36569-MH Recovery Analysis ............................................................................................................... 11 Figure 9: SVR Well No. 20 (86628-F) Pump Test ........................................................................................................ 13 Figure 10: SVR Well No. 20 (86628-F) Recovery Analysis .......................................................................................... 14 Figure 11: SVR Well No. 15 (MH-36760) Pump Test ................................................................................................... 15 Figure 12: SVR Well No. 15 (MH-36760) Recovery Analysis ...................................................................................... 16 Figure 13: SVR Well No. 14 (66299-F) Pump Test ...................................................................................................... 18 Figure 14: SVR Well No. 14 (66299-F) Recovery Analysis .......................................................................................... 19 Figure 15: SVR Well No. 10 (MH-33819) Pump Test ................................................................................................... 20 Figure 16: SVR Well No. 10 (MH-33819) Recovery Analysis ...................................................................................... 21 January, 2023 – Project # 2167SVRD02 LIST OF TABLES Table 1: Summary of Spring Valley Ranch Wells Pump Test Analysis .......................................................................... 2 Table 2: Regulated Water Quality Results ................................................................................................................... 23 Table 3: Additional Water Quality Parameters ............................................................................................................. 24 LIST OF ATTACHMENTS Attachment 1: Well Location and Current Production Rate Map Spring Valley Ranch Page 1 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 SECTION 1: INTRODUCTION LRE Water, Inc. (LRE) was retained to perform 24 hour well pumping test with 24 hour recovery period on the wells located on Spring Valley Ranch (SVR). In addition to the well pumping tests, water quality samples were collected and analyzed by a State of Colorado certified laboratory that follows accepted industry standards and quality assurance/quality control procedures. This report describes the results of the pumping test and physical groundwater supply; the water quality results; and provides recommendations for treatment. SECTION 2: BACKGROUND The Spring Valley Ranch Planned Unit Development (PUD) is an approximately 5,900 acre planned development. The property consists of four parcels located in the Roaring Fork Valley on the western end of Missouri Heights between the towns of Carbondale and Glenwood Springs in Garfield County. A location map is included in Attachment 1. SECTION 3: PHYSICAL WATER SUPPLY LRE conducted a constant-discharge pump test at eight wells located on SVR. A map of the well locations is included in Attachment 1. The pumps test were performed to evaluate the current pumping capacities of the wells under current aquifer conditions. Additionally, these tests were performed during the period of the year when groundwater is seasonally lower because there is minimal recharge occurring. All of the wells produce from unconfined aquifers, which largely recharge from snowmelt run-off, precipitation, and irrigation occurring on the ranch. Currently, only a small area of the lower valley is irrigated. Table 1 provides a summary of the current static water levels, pumping capacities, and drawdown of the wells evaluated. The individual well tests and results are described in more detail below. Spring Valley Ranch Page 2 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 Table 1: Summary of Spring Valley Ranch Wells Pump Test Analysis Well Production Rate, Static Water Levels, and Max Drawdown Well Name Permit/ Decreed Rate (gpm) Permit No. Pump Test Date Well Production Rate (gpm) Static Water Level (ft) Max Drawdown Measurement (ft) Max Drawdown (ft) SV Well No. 1 300 86630-F 9/29/2022 300 22 161.53 139.53 ASR Well No. 16 fka Gamba 8 100 86629-F 10/12/2022 60 20.25 231.42 211.17 36567-MH 100 36597-MH 10/18/2022 7.7 89 219.37 130.37 36596-MH 100 36596-MH 10/19/2022 100 19.55 91.01 71.46 SVR Well No. 20 fka Gamba 1 300 86628-F 10/31/2022 51.69 113 169.9 56.9 ASR Well No. 15 100 36760 MH 11/14/2022 100 112.8 149.58 36.78 ASR Well No. 14 100 66299-F 11/30/2022 10 143.6 154 10.4 SVH Well 10 40 33819 MH 12/14/2022 11.4 95.7 340.78 245.08 3.1 SV WELL NO. 1 LRE conducted a 24-hour constant discharge pumping test at SV Well No. 1 on September 29, 2022. The temporary well pump was set at 180 ft. The perforated portion of the well casing is from 85 ft to 285 ft below the ground surface. The pressure transducer was installed at 175 ft and was set to record pressure and temperature reading every minute. Barometric pressure can impact water levels in unconfined aquifers; therefore, all pressure values were corrected for changes in barometric pressure. LRE relied on this dataset to analyze drawdown within the well over the course of the pumping test. In addition, a turbine flowmeter was then connected between the outflow of the pump and the discharge line. This meter was used to establish and monitor the pumping rate and volume pumped. The static water level prior to the test was measured to be 22 ft below the top of the well casing (TOC). With the pump set at 180 ft below the ground surface, there was approximately 158 ft of available drawdown in the aquifer. The pump was initially set to 100 gpm increased to 300 gpm 36 minutes after starting the test. On average, LRE Water calculated a pumping rate of 298.4 gpm over the 24 hour pumping period, with a maximum pumping rate of 300 gpm. The pump was intentionally operated to run at or near this rate based on the permitted rate. Spring Valley Ranch Page 3 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 Throughout the pumping test, manual readings were collected in the field. In particular, the drawdown was monitored in order to determine if the pumping rate could be sustained. Once the pump test started the aquifer dropped 131 ft within 40 minutes (six minutes after achieving 300 gpm), then incrementally dropped over the 24-hour test. The maximum water level drawdown occurred at the end of the pump test with a water level depth of 161.53 ft below TOC (139.53 feet of drawdown compared to static water levels). Figure 1 graphically shows the water depth measurements that were taken both manually and electronically by the pressure transducer. Figure 1: SVR Well 1 (86630-F) Pump Test Depth from Top of Casing (TOC) In addition to monitoring the water level during the pumping test, it is equally important to monitor the recovery process. The pump and pressure transducer were therefore kept in place at the conclusion of the test. The water level in the well at the start of recovery rebounded within the first six minutes from a depth of 161.53 ft to a depth of 47.85 ft.Figure 2 depicts the water level recovery in the well and demonstrates the well recovered to 96% after 24 hours of the pump being shut off. Static Water Level (ft)Notes: 1.) Initial Water Level = 22.0 ft. below Top of Well CasingDepth of Water from TOC 2.) Final Water Level = 161.53 ft. below Top of Well CasingManual Measurements 3.) Well Depth =305 ft. from Top of Well CasingFlow Rate (gpm) 0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.00.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 1 10 100 1000 Fl o w Ra t e (g p m ) De p t h fr o m TO C (f e e t ) PumpingTime (minutes) StaticWaterLevel =22.0ft. AveragePumpingRate=300gpm Spring Valley Ranch Page 4 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 Figure 2: SVR Well 1 (86630-F) Recovery Depth from Top of Casing (TOC) The aquifer drawdown and recovery data support that SV Well No. 1 can currently produce 300 gpm and experienced a 96% recovery in 24 hours. Setting the pump at the deepest elevation in the well results in approximately 260 ft of allowable drawdown of the aquifer. 3.2 ASR WELL NO. 16 FKA GAMBA 8 LRE conducted a 24-hour constant discharge pumping test at ASR Well No. 16 on October 12, 2022. The temporary well pump was set at 240 ft. The perforated portion of the well casing is from 150 ft to 180 ft below the ground surface. The pressure transducer was installed at 235 ft and was set to record pressure and temperature reading every minute. Barometric pressure can impact water levels in unconfined aquifers; therefore, all pressure values were corrected for changes in barometric pressure. LRE relied on this dataset to analyze drawdown within the well over the course of the pumping test. In addition, a turbine flowmeter was then connected between the outflow of the pump and the discharge line. This meter was used to establish and monitor the pumping rate and volume pumped. The static water level prior to the test was measured to be 20.25 ft below the top of the well casing (TOC). With the pump set at 140 ft below the ground surface, there was approximately 120 ft of Static Water Level (ft)Residual Drawdown (ft) 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 1 10 100 1000 De p t h fr o m TO C (f e e t ) RecoveryTime (minutes) StaticWaterLevel =22.0ft. Spring Valley Ranch Page 5 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 available drawdown in the aquifer. The well has a permitted rate of 100 gpm, so the pump was initially set to 100 gpm. The pumping rate was decreased over the 24-hour pumping test due to the rate of drawdown and available water in the well. On average, LRE Water calculated a pumping rate of 54.3 gpm over the 24 hour pumping period. Throughout the pumping test, manual readings were collected in the field. In particular, the drawdown was monitored in order to determine if the pumping rate could be sustained. Once the pump test started the aquifer dropped 93.32 ft within 10 minutes and continued to decline at a steady rate until the flow rate was reduced to 82 gpm. The well recovered approximately 50 ft after the flow rate was reduced, but then the aquifer level began to steadily decline until the flow rate was reduced to a lower rate. A flow rate reduction was performed a couple more times throughout the test. The maximum water level drawdown occurred at the end of the pump test with a water level depth of 231.42 ft below TOC (211.17 feet of drawdown compared to static water level). Figure 3 graphically shows the water depth measurements that were taken both manually and electronically by the pressure transducer. Figure 3: ASR Well No. 16 (86629-F) Pump Test Depth from Top of Casing (TOC) Static Water Level (ft)Notes: 1.) Initial Water Level = 20.25 ft. below Top of Well CasingDepth of Water from TOC 2.) Final Water Level = 222.67 ft. below Top of Well CasingManual Measurements 3.) Well Depth =260 ft. from Top of Well CasingFlow Rate (gpm) 0.0 20.0 40.0 60.0 80.0 100.0 120.00.0 50.0 100.0 150.0 200.0 250.0 1 10 100 1000 Fl o w Ra t e (g p m ) De p t h fr o m TO C (f e e t ) PumpingTime (minutes) StaticWaterLevel =20.25ft. AveragePumpingRate=54.3gpm Spring Valley Ranch Page 6 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 In addition to monitoring the water level during the pumping test, it is equally important to monitor the recovery process. The pump and pressure transducer were therefore kept in place at the conclusion of the test. The water level in the well at the start of recovery rebounded within the first 10 minutes from a depth of 231.42 ft to a depth of 150.9 ft, equal to approximately an 80 ft rise in the aquifer level. Figure 4 depicts the water level recovery in the well and demonstrates the well recovered to 70% after 24 hours of the pump being shut off. Figure 4: ASR Well No. 16 (86629-F) Recovery Analysis Depth from Top of Casing (TOC) Using an average pump rate of 54.3 gpm and total drawdown of 211.17 ft, the specific capacity of the well was calculated to be 0.26 gpm per foot. This is a conservative estimate since the pump was pumped at higher rates for the first seven hours of the test, which could result in a higher amount of drawdown than if the pump had been set at 54.3 gpm throughout the 24-hour pumping period. Using the specific capacity of the well and 235 ft of available drawdown, LRE estimates ASR Well No. 16 can currently produce at 60 gpm. 3.3 WELL 36567-MH LRE conducted a 4-hour constant discharge pumping test at Well 36567-MH on October 18, 2022. The temporary well pump was set at 240 ft. The perforated portion of the well casing is from 180 ft to 250 ft below the ground surface. The pressure transducer was installed at 235 ft and was set to record pressure and temperature reading every minute. Barometric pressure can impact water Static Water Level (ft)Residual Drawdown (ft) 0.0 50.0 100.0 150.0 200.0 250.0 1 10 100 1000 De p t h fr o m TO C (f e e t ) RecoveryTime (minutes) StaticWaterLevel=20.25ft. Spring Valley Ranch Page 7 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 levels in unconfined aquifers; therefore, all pressure values were corrected for changes in barometric pressure. LRE relied on this dataset to analyze drawdown within the well over the course of the pumping test. In addition, a turbine flowmeter was then connected between the outflow of the pump and the discharge line. This meter was used to establish and monitor the pumping rate and volume pumped. The static water level prior to the test was measured to be 89 ft below the top of the well casing (TOC). With the pump set at 240 ft below the ground surface, there was approximately 151 ft of available drawdown in the aquifer. The pump was set to 8 gpm. On average, LRE Water calculated a pumping rate of 7.7 gpm over the 24 hour pumping period, with a maximum pumping rate of 8 gpm. Throughout the pumping test, manual readings were collected in the field. In particular, the drawdown was monitored in order to determine if the pumping rate could be sustained. Once the pump test started the aquifer dropped 130.86 ft within 10 minutes. A rise in the water level occurred in the well when the flow rate dropped to 6 gpm. When the flow rate was adjusted back to 8 gpm around minute 100 the aquifer steadily declined, but experienced brief periods of recharge. The maximum water level drawdown occurred at the end of the pump test with a water level depth of 219.37 ft below TOC (130.37 feet of drawdown compared to static water level). Figure 5 graphically shows the water depth measurements that were taken both manually and electronically by the pressure transducer. In addition to monitoring the water level during the pumping test, it is equally important to monitor the recovery process. The pump and pressure transducer were therefore kept in place at the conclusion of the test. The water level in the well at the start of recovery rebounded within the first 10 minutes from a depth of 219.37 ft to a depth of 191.79 ft. Figure 6 depicts the water level recovery in the well and demonstrates the well recovered to 91.5% after 4 hours and 100% after 16 hours of the pump being turned off. Spring Valley Ranch Page 8 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 Figure 5: Well 36567-MH Pump Test Depth from Top of Casing (TOC) Static Water Level (ft)Notes: 1.) Initial Water Level = 89.0 ft. below Top of Well CasingDepth of Water from TOC 2.) Final Water Level = 219.37 ft. below Top of Well CasingManual Measurements 3.) Well Depth =264 ft. from Top of Well CasingFlow Rate (gpm) 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.00.0 50.0 100.0 150.0 200.0 250.0 110100 Fl o w Ra t e (g p m ) De p t h fr o m TO C (f e e t ) PumpingTime (minutes) StaticWaterLevel =89.0ft. AveragePumpingRate=7.7gpm Spring Valley Ranch Page 9 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 Figure 6: Well 36567-MH Recovery Analysis Depth from Top of Casing (TOC) The aquifer drawdown and recovery data support that Well 36567-MH can currently produce 7.7 gpm and with 91.4% recovery occurring in 4hours and 100% recovery experienced in 16 hours. 3.4 WELL 36596-MH LRE conducted a 24-hour constant discharge pumping test at Well 36596-MH on October 19, 2022. The temporary well pump was set at 150 ft. The perforated portion of the well casing is from 80 ft to 150 ft below the ground surface. The pressure transducer was installed at 145 ft and was set to record pressure and temperature reading every minute. Barometric pressure can impact water levels in unconfined aquifers; therefore, all pressure values were corrected for changes in barometric pressure. LRE relied on this dataset to analyze drawdown within the well over the course of the pumping test. In addition, a turbine flowmeter was then connected between the outflow of the pump and the discharge line. This meter was used to establish and monitor the pumping rate and volume pumped. The static water level prior to the test was measured to be 19.55 ft below the top of the well casing (TOC). With the pump set at 150 ft below the ground surface, there was approximately 130 ft of available drawdown in the aquifer. The pump was set to 8 gpm, based on the expected yield of the well. On average, LRE Water calculated a pumping rate of 99.9 gpm over the 24 hour pumping period. Static Water Level (ft)Residual Drawdown (ft) 0.0 50.0 100.0 150.0 200.0 250.0 1 10 100 1000 De p t h fr o m TO C (f e e t ) RecoveryTime (minutes) StaticWaterLevel =89.0ft. Spring Valley Ranch Page 10 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 Throughout the pumping test, manual readings were collected in the field. In particular, the drawdown was monitored in order to determine if the pumping rate could be sustained. Once the pump test started the aquifer dropped 50 ft within 10 minutes, then incrementally dropped over the 24-hour test. The maximum water level drawdown occurred at the end of the pump test with a water level depth of 91.01 ft below TOC (71.46 feet of drawdown compared to static water levels).Figure 7 graphically shows the water depth measurements that were taken both manually and electronically by the pressure transducer. Figure 7: Well 36569-MH Pump Test Depth from Top of Casing (TOC) In addition to monitoring the water level during the pumping test, it is equally important to monitor the recovery process. The pump and pressure transducer were therefore kept in place at the conclusion of the test. The water level in the well at the start of recovery rebounded within the first 10 minutes from a depth of 91.01 ft to a depth of 36.74 ft, equal to approximately a 17.19 ft rise in the aquifer level. Figure 8 depicts the water level recovery in the well and demonstrates the well recovered to 97% after 24 hours of the pump being shut off. Static Water Level (ft)Notes: 1.) Initial Water Level = 19.55 ft. below Top of Well CasingDepth of Water from TOC 2.) Final Water Level = 88.75 ft. below Top of Well CasingManual Measurements 3.) Well Depth =163 ft. from Top of Well CasingFlow Rate (gpm) 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0 1 10 100 1000 Fl o w Ra t e (g p m ) De p t h fr o m TO C (f e e t ) PumpingTime (minutes) StaticWaterLevel =19.55ft. AveragePumpingRate=99.9gpm Spring Valley Ranch Page 11 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 Figure 8: Well 36569-MH Recovery Analysis Depth from Top of Casing (TOC) The aquifer drawdown and recovery data support that 36596-MH can currently produce 100 gpm and experience a 97% recovery in 24 hours. 3.5 SVR WELL NO. 20 FKA GAMBA 1 LRE conducted a 24-hour constant discharge pumping test at SVR Well No. 20 on October 31, 2022. The temporary well pump was set at 180 ft. The perforated portion of the well casing is from 110 ft to 219 ft below the ground surface. The pressure transducer was installed at 175 ft and was set to record pressure and temperature reading every minute. Barometric pressure can impact water levels in unconfined aquifers; therefore, all pressure values were corrected for changes in barometric pressure. LRE relied on this dataset to analyze drawdown within the well over the course of the pumping test. In addition, a turbine flowmeter was then connected between the outflow of the pump and the discharge line. This meter was used to establish and monitor the pumping rate and volume pumped. The static water level prior to the test was measured to be 113 ft below the top of the well casing (TOC). With the pump set at 180 ft below the ground surface, there was approximately 67 ft of available drawdown in the aquifer. The well has a permitted rate of 300 gpm. The pump was set initially to produce at a constant rate of 70 gpm with the intent to increase to 100 gpm shortly after the test began. The pumping rate was decreased over the 24-hour pumping test due to the rate Static Water Level (ft)Residual Drawdown (ft) 0.0 10.0 20.0 30.0 40.0 50.0 60.0 1 10 100 1000 De p t h fr o m TO C (f e e t ) RecoveryTime (minutes) StaticWaterLevel =19.55ft. Spring Valley Ranch Page 12 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 of drawdown and available water in the well. On average, LRE Water calculated a pumping rate of 51.6 gpm over the 24 hour pumping period. Throughout the pumping test, manual readings were collected in the field. In particular, the drawdown was monitored in order to determine if the pumping rate could be sustained. Once the pump test started the aquifer dropped 56.9 ft within 5 minutes, so the flow rate was reduced to and then increased to approximately 80 gpm. The aquifer level began to steadily decline until the flow rate was reduced to a lower rate. A flow rate reduction was performed a couple more times throughout the test. The maximum water level drawdown occurred within the first five minutes of the test with a water level depth of 151.44 ft below TOC occurring at the end of the 24-hour pumping period. Figure 9 graphically shows the water depth measurements that were taken both manually and electronically by the pressure transducer. In addition to monitoring the water level during the pumping test, it is equally important to monitor the recovery process. The pump and pressure transducer were therefore kept in place at the conclusion of the test. The water level in the well at the start of recovery rebounded within the first six minutes from a depth of 151.44 ft to a depth of 121.13 ft, equal to approximately an 30 ft rise in the aquifer level. Figure 10 depicts the water level recovery in the well and demonstrates the well recovered to 90% after 24 hours of the pump being shut off. Using an average pump rate of 51.6 gpm and total drawdown of 56.9 ft, the specific capacity of the well was calculated to be 0.91 gpm per foot. This is a conservative estimate since the pump was pumped at higher rates for the part of the test, which could result in a higher amount of drawdown than if the pump had been set at 51.6 gpm throughout the 24-hour pumping period. Using the specific capacity of the well and 105 ft of available drawdown, LRE estimates SVR Well No. 20 is capable of currently producing at 95 gpm if the pump was set at the deepest elevation in the well. Spring Valley Ranch Page 13 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 Figure 9: SVR Well No. 20 (86628-F) Pump Test Depth from Top of Casing (TOC) Static Water Level (ft)Notes: 1.) Initial Water Level = 113.0 ft. below Top of Well CasingDepth of Water from TOC 2.) Final Water Level = 151.44 ft. below Top of Well CasingManual Measurements 3.) Well Depth =223 ft. from Top of Well CasingFlow Rate (gpm) 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.00.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 1 10 100 1000 Fl o w Ra t e (g p m ) De p t h fr o m TO C (f e e t ) PumpingTime (minutes) StaticWaterLevel =113.0ft. AveragePumpingRate=51.6gpm Spring Valley Ranch Page 14 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 Figure 10: SVR Well No. 20 (86628-F) Recovery Analysis Depth from Top of Casing (TOC) 3.6 ASR WELL NO. 15 LRE conducted a 24-hour constant discharge pumping test at ASR Well No. 15 on November 14, 2022. The temporary well pump was set at 190 ft. The perforated portion of the well casing is from 110 ft to 220 ft below the ground surface. The pressure transducer was installed at 185 ft and was set to record pressure and temperature reading every minute. Barometric pressure can impact water levels in unconfined aquifers; therefore, all pressure values were corrected for changes in barometric pressure. LRE relied on this dataset to analyze drawdown within the well over the course of the pumping test. In addition, a turbine flowmeter was then connected between the outflow of the pump and the discharge line. This meter was used to establish and monitor the pumping rate and volume pumped. The static water level prior to the test was measured to be 112.8 ft below the top of the well casing (TOC). With the pump set at 190 ft below the ground surface, there was approximately 77 ft of available drawdown in the aquifer. The pump was set to 100 gpm, based on the expected yield of the well. The pumping rate was reported as decreasing over the 24-hour pumping test based on the flow meter, but was not manually decreased because there was still plenty of water level available in the well to maintain the 100 gpm pumping rate. Based on the reported flow rates, LRE Water calculated an average pumping rate of 79 gpm over the 24 hour pumping period. Static Water Level (ft)Residual Drawdown (ft) 50.0 70.0 90.0 110.0 130.0 150.0 170.0 1 10 100 1000 De p t h fr o m TO C (f e e t ) RecoveryTime (minutes) StaticWaterLevel =113ft. Spring Valley Ranch Page 15 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 Throughout the pumping test, manual readings were collected in the field. In particular, the drawdown was monitored in order to determine if the pumping rate could be sustained. Once the pump test started the aquifer dropped 30.36 ft within 5 minutes, then incrementally dropped over the 24-hour test. The maximum water level drawdown occurred at the end of the pump test with a water level depth of 149.58 ft below TOC (36.78 feet of drawdown compared to static water levels). It is worth noting that approximately 40 ft of water in the well was available for additional drawdown during the pump test. Figure 11 graphically shows the water depth measurements that were taken both manually and electronically by the pressure transducer. Figure 11: SVR Well No. 15 (MH-36760) Pump Test Depth from Top of Casing (TOC) In addition to monitoring the water level during the pumping test, it is equally important to monitor the recovery process. The pump and pressure transducer were therefore kept in place at the conclusion of the test. The water level in the well at the start of recovery rebounded within the first six minutes from a depth of 149.58 ft to a depth of 124.83 ft, equal to approximately a 25 ft rise in the aquifer level and then experienced an incremental rise throughout the monitoring period.Figure 12 depicts the water level recovery in the well and demonstrates the well recovered to 80% after 24 hours and 95% after seven days of the pump being turned off. Static Water Level (ft)Notes: 1.) Initial Water Level = 112.8 ft. below Top of Well CasingDepth of Water from TOC 2.) Final Water Level = 149.58 ft. below Top of Well CasingManual Measurements 3.) Well Depth =220 ft. from Top of Well CasingFlow Rate (gpm) 0.0 20.0 40.0 60.0 80.0 100.0 120.0Ͳ30.0 20.0 70.0 120.0 170.0 220.0 1 10 100 1000 Fl o w Ra t e (g p m ) De p t h fr o m TO C (f e e t ) PumpingTime (minutes) StaticWaterLevel =112.8ft. AveragePumpingRate=79gpm Spring Valley Ranch Page 16 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 Figure 12: SVR Well No. 15 (MH-36760) Recovery Analysis Depth from Top of Casing (TOC) Using an average pump rate of 79 gpm and total drawdown of 36.8 ft, the specific capacity of the well was calculated to be 2.15 gpm per foot. This is a conservative estimate since the pump was pumped at higher rates for the part of the test, which could result in a higher amount of drawdown than if the pump had been set at 79 gpm throughout the 24-hour pumping period. Using the specific capacity of the well and 105 ft of available drawdown, LRE estimates the well can currently produce at a maximum rate of 215 gpm if the pump was set at the deepest elevation in the well. This and the unutilized 40 ft of water column in the well during the pump test suggests that the well should be able to support a 100 gpm pump. 3.7 ASR WELL NO. 14 LRE conducted a 24-hour constant discharge pumping test at ASR Well No. 14 on November 30, 2022. The temporary well pump was set at 160 ft. The perforated portion of the well casing is from 140 ft to 160 ft below the ground surface. The pressure transducer was installed at 155 ft and was set to record pressure and temperature reading every minute. Barometric pressure can impact water levels in unconfined aquifers; therefore, all pressure values were corrected for changes in barometric pressure. LRE relied on this dataset to analyze drawdown within the well over the course of the pumping test. In addition, a turbine flowmeter was then connected between Static Water Level (ft)Residual Drawdown (ft) 90.0 100.0 110.0 120.0 130.0 140.0 150.0 160.0 1 10 100 1000 10000 De p t h fr o m TO C (f e e t ) RecoveryTime (minutes) StaticWaterLevel =112.8ft. Spring Valley Ranch Page 17 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 the outflow of the pump and the discharge line. This meter was used to establish and monitor the pumping rate and volume pumped. The static water level prior to the test was measured to be 143.6 ft below the top of the well casing (TOC). With the pump set at 160 ft below the ground surface, there was approximately 16.4 ft of available drawdown in the aquifer. The pump was set to 50 gpm based on the expected yield. The pumping rate was decreased over the 24-hour pumping test due to the rate of drawdown and available water in the well. On average, LRE Water calculated a pumping rate of 10 gpm over the 24 hour pumping period. Throughout the pumping test, manual readings were collected in the field. In particular, the drawdown was monitored in order to determine if the pumping rate could be sustained. Once the pump test started the aquifer dropped below the pressure transducer with in the first minute. The pumping rate was decreased to 10 gpm and the water level in the well rebounded to 146 ft within eight minutes. The rate was increased to 16 gpm at 10 minutes and the water level dropped approximately 4.5 ft in two minutes. 30 minutes after pumping began the rate was decreased to 10 gpm and remained constant throughout the test. The water level depth at the end of the pump test was 146.85 ft below TOC (3.25 feet of drawdown compared to static water levels). Figure 13 graphically shows the water depth measurements that were taken both manually and electronically by the pressure transducer. In addition to monitoring the water level during the pumping test, it is equally important to monitor the recovery process. The pump and pressure transducer were therefore kept in place at the conclusion of the test. The water level in the well at the start of recovery rebounded within the first 1 minute from a depth of 146.85 ft to a depth of 143.95 ft, equal to approximately a 2.9 ft rise in the aquifer level equating to 90% recovery. Figure 14 depicts the water level recovery in the well and demonstrates the well recovered to 100% after 18 hours of the pump being shut off. Spring Valley Ranch Page 18 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 Figure 13: SVR Well No. 14 (66299-F) Pump Test Depth from Top of Casing (TOC) Static Water Level (ft)Notes: 1.) Initial Water Level = 143.6 ft. below Top of Well CasingDepth of Water from TOC 2.) Final Water Level = 146.85 ft. below Top of Well CasingManual Measurements 3.) Well Depth =180 ft. from Top of Well CasingFlow Rate (gpm) 0.0 10.0 20.0 30.0 40.0 50.0 60.0142.0 144.0 146.0 148.0 150.0 152.0 154.0 156.0 1 10 100 1000 Fl o w Ra t e (g p m ) De p t h fr o m TO C (f e e t ) PumpingTime (minutes) StaticWaterLevel =143.6ft. AveragePumpingRate=10gpm Spring Valley Ranch Page 19 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 Figure 14: SVR Well No. 14 (66299-F) Recovery Analysis Depth from Top of Casing (TOC) The aquifer drawdown and recovery data support that ASR Well No. 14 can currently produce 10 gpm and experience a 100% recovery in 18 hours. 3.8 SVH WELL 10 LRE conducted a 24-hour constant discharge pumping test at SVH Well 10 on December 14, 2022. The temporary well pump was set at 350 ft. The perforated portion of the well casing is from 90 ft to 350 ft below the ground surface. The pressure transducer was installed at 345 ft and was set to record pressure and temperature reading every minute. Barometric pressure can impact water levels in unconfined aquifers; therefore, all pressure values were corrected for changes in barometric pressure. LRE relied on this dataset to analyze drawdown within the well over the course of the pumping test. In addition, a turbine flowmeter was then connected between the outflow of the pump and the discharge line. This meter was used to establish and monitor the pumping rate and volume pumped. The static water level prior to the test was measured to be 95.7 ft below the top of the well casing (TOC). With the pump set at 350 ft below the ground surface, there was approximately 254 ft of available drawdown in the aquifer. The pump was set to 50 gpm, based on the expected yield of the well. The pumping rate was decreased over the 24-hour pumping test due to the rate of Static Water Level (ft)Residual Drawdown (ft) 143.4 143.6 143.8 144.0 144.2 144.4 144.6 144.8 145.0 1 10 100 1000 De p t h fr o m TO C (f e e t ) RecoveryTime (minutes) StaticWaterLevel=143.6ft. Spring Valley Ranch Page 20 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 drawdown and available water in the well. On average, LRE Water calculated a pumping rate of 11.4 gpm over the 24 hour pumping period. Throughout the pumping test, manual readings were collected in the field. In particular, the drawdown was monitored in order to determine if the pumping rate could be sustained. Once the pump test started the aquifer dropped 184.78 ft within 5 minutes, so the flow rate was reduced to to 38 gpm. After 40 minutes of pumping the well had experienced 228.85 ft of drawdown and the water level was at 324.55 ft below the top of casing. The pumping rate was reduced to 16 gpm and the water level experienced a 32 ft rise and then the aquifer level began to steadily decline until the flow rate was reduced to a 12 gpm. A flow rate reduction was performed a couple more times throughout the test. The maximum water level drawdown occurred at the end of the pump test with a water level depth of 340.78 ft below TOC (245.08 feet of drawdown compared to static water levels). Figure 15 graphically shows the water depth measurements that were taken both manually and electronically by the pressure transducer. Figure 15: SVR Well No. 10 (MH-33819) Pump Test Depth from Top of Casing (TOC) In addition to monitoring the water level during the pumping test, it is equally important to monitor the recovery process. The pump and pressure transducer were therefore kept in place at the conclusion of the test. The water level in the well at the start of recovery rebounded within the Static Water Level (ft)Notes: 1.) Initial Water Level = 95.7 ft. below Top of Well CasingDepth of Water from TOC 2.) Final Water Level = 340.78 ft. below Top of Well CasingManual Measurements 3.) Well Depth =360 ft. from Top of Well CasingFlow Rate (gpm) 0 5 10 15 20 25 30 35 40 450 50 100 150 200 250 300 350 400 1 10 100 1000 Fl o w Ra t e (g p m ) De p t h fr o m TO C (f e e t ) PumpingTime (minutes) StaticWaterLevel =95.7ft. AveragePumpingRate=11.4gpm Spring Valley Ranch Page 21 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 first 5 minutes from a depth of 340.78 ft to a depth of 297.34 ft, equal to approximately a 43.44 ft rise in the aquifer level. Figure 16 depicts the water level recovery in the well and demonstrates the well recovered to 99% after 24 hours of the pump being shut off. Figure 16: SVR Well No. 10 (MH-33819) Recovery Analysis Depth from Top of Casing (TOC) The aquifer drawdown and recovery data support that SVH Well 10 can currently produce 11.4 gpm and experience a 100% recovery in 24 hours. SECTION 4: WATER QUALITY RESULTS Wells were sampled for a standard suite of parameters in accordance with CDPHE Regulation No. 11 – Colorado Primary Drinking Water Regulations. Samples were analyzed by a State of Colorado certified laboratory that follows accepted industry standards and quality assurance/quality control procedures. The water quality results are tabulated in Table 2 and Table 3.1 Overall, results indicate good water quality for potable consumption and use. The data indicate the only likely treatment required for the well will be chlorine disinfection if the water will be used for a community or non-community water system as defined by CDPHE. 1 As of the date on this report, not all water quality reports had been received from the laboratory. Water quality results will be supplemental once received. Static Water Level (ft)Residual Drawdown (ft) 0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.0 400.0 1101001000 De p t h fr o m TO C (f e e t ) RecoveryTime (minutes) StaticWaterLevel=95.7ft. Spring Valley Ranch Page 22 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 ASR Well No. 16 has elevated levels of iron and manganese. Results at Well 36567-MH also had elevated iron levels. Iron and manganese are secondary parameters, so no treatment will be required by CDPHE. Although treatment will not be required, removal of these contaminants from the water is recommended to maintain the service life of the water mains and service lines and to provide water to the users without taste and odor issues. Elevated levels of Toluene were present in ASR Well No. 16 and Well 36567-MH. Toluene is a volatile organic compound and is known to be toxic for human consumption. Retesting of these wells for toluene is recommended to confirm presence in the groundwater. If the presence of toluene is confirmed with retesting, treatment will be required to remove this compound and the method of treatment determined by a professional engineer. ASR Well No. 16 and Well 36596-MH are located approximately 110 ft and 20ft from Landis Creek, respectively. It is anticipated that CDPHE will require a that a Groundwater Under the Influence of Surface Water (GWUDI) evaluation be completed on both wells. The GWUDI occurs over six months and consists of weekly sampling from both the wells and creek. CDPHE will require additional treatment if the results of the evaluation indicate that Landis Creek has a direct influence on the wells. Spring Valley Ranch Page 23 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 Table 2: Regulated Water Quality Results Regulation 11 Constituents Name SV Well No. 1 ASR Well No. 16 fka Gamba 8 36567-MH SVR Well No. 20 fka Gamba 1 Permit No.86630-F 86629-F 36567-MH 86628-F Parameter Unit MCL Result Result Result Result Regulation 11 Constituents Total Coliform RuleTotal Coliform ----------E.coli MPN/100mL -------- Nitrate and Nitrite RuleNitrate - N mg/L 10 0.84 ND 0.68 0.53Nitrite - N mg/L 1 ND ND ND ND Inorganics RuleAntimony mg/L 0.006 ND ND ND NDArsenicmg/L 0.01 ND ND ND NDAsbestosfibers/L 7 mil fibs/L ND ND ND NDBariummg/L 2 0.36 0.12 0.085 0.16Berylliummg/L 0.004 ND ND ND NDCadmiummg/L 0.005 ND ND ND NDChromiummg/L 0.1 ND ND 0.0072 NDCyanidemg/L 0.02 ND ND ND 0.0057Fluoridemg/L 4 0.14 ND ND NDMercurymg/L 0.002 ND ND ND NDNickelmg/L ND ND 0.0036 NDSeleniummg/L 0.05 ND ND ND NDThalliummg/L 0.002 ND ND ND NDSodiummg/L 9.3 4.8 ND ND Secondary Parameters Secondary MCLAluminummg/L .05 - 0.2 ND ND 2.4 NDChloridemg/L 250 ND ND ND NDIronmg/L 0.3 ND 12.1 1.6 0.3Manganesemg/L 0.05 ND 0.18 0.011 0.002pH6.5-8.5 7.96 8.31 8.11 7.85Silvermg/L 0.1 ND ND ND NDSulfatemg/L 250 4.6 ND 1.4 NDTDSmg/L 500 331 115 248 204Zincmg/L 5 ND ND ND ND RadionuclidesGross Alpha pCi/L 15 ND ND ND NDGross Beta pCi/L 15 3.8 ND 1 NDCombined Radium pCi/L 5 0.910.8ND SOCs and VOCs (only noting detected compounds )Toluene mg/L 1 ND 4.2 6.7 NDDI(2-ethylhexyl)phthalate mg/L 0.4 ND 0.45 ND ND Spring Valley Ranch Page 24 of 24 Physical Water Supply January, 2023 – Project # 2167SVRD02 Table 3: Additional Water Quality Parameters Name SV Well No. 1 ASR Well No. 16 fka Gamba 8 36567-MH SVR Well No. 20 fka Gamba 1 Permit No.86630-F 86629-F 36567-MH 86628-F Parameter Unit MCL Result Result Result Result Corrosivity and Hardness Bicarbonate mg/L as CaCO3 253 91 151 176 Carbonate mg/L ND 5 ND ND Hydroxide mg/L ND ND ND ND Total Alkalinity mg/L as CaCO3 253 96 151 176 Total Hardness mg/L as CaCO3 66.7 137.0 140.0 Calcium mg/L 72.6 26.7 53.7 56.2 Magnesium mg/L 9.98 6.86 4.60 9.40 Additional WQ Paramters Specific Conductance umhos/cm 520 201 310 355 Phosphate - Ortho (as P)mg/L as P Phosphate - Ortho (as PO4)mg/L as PO4 Turbidity NTU 12.00 0.15 Sodium Adsoprtion Ratio Calc 4 0.271 0.215 0.105 0.146 Langelier Index --0.3 0.60 0.40 !. !. !. !. !. !. !. !.!.!. !. !. !. SV Well No 1300 gpm ASR Well No.1410 gpm ASR Well No.13 ASR Well No.16 fka Gamba 854 gpm SVR Well No. 2 ASR Well No. 1579 gpm SVR Well No. 20 fka Gamba 152 gpm SVH Well No. 1011 gpm SVR Well No. 17 SVR Well No. 21 SVR Well No. 3 36596-MH100 gpm 36567-MH8 gpm Landis CreekLandis Creek Attachment 1 Well Location and Current Production Rate Map Spring Valley Holdings, LLC ® 0 2,000 4,0001,000 Feet Date: 2023-01-20File: 2166702Drawn: ABSApproved: Source: USDA 2019 NAIP Garfield County Spring Valley Holdings, LLC Garfield County Parcels Streams Well Locations !.GPS !.Alta Survey