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Home My WebLink About1.02 Soils & Geology• NINoup ri COLORADO NommaRIVER ENGINEERING, INC. P.O. Box 1301 Rifle, CO 81650 Tel 970-625-4933 Fax 970-625-4564 June 29, 2000 Ms. Gaye Leo PO Box 986 Silt, CO. 81652 RE: Leo Subdivision — Soils & Geology/Hazards Evaluation Dear Gaye: As Requested, Colorado River Engineering, Inc. has completed a soil and geologic hazard evaluation for the proposed Leo Subdivision on Taughenbaugh Mesa. Our review has indicated that no hazards or soil constraints exist that would impair the development of the property. However, we recommend that site-specific soils test and an engineered foundation be required for the two undeveloped parcels prior to issuance of a building permit. We have prepared this letter report to summarize our review. Background The proposed Leo Subdivision is located on Taughenbaugh Mesa in Garfield County, Colorado. The size of the property is about 52 acres situated in the western half of the SW/4 of Section 20, Township 6 South, Range 93 West, of the 6th P.M. as illustrated on the attached General Location Map (Figure 1). Taughenbaugh Mesa overlooks the Colorado River to the North and is bordered on the west and east by Beaver Creek and Helmer Gulch, respectively. The mesa and subject property consists of sloping (6%) pastures and historically irrigated hay crops with water diversions originating from Beaver Creek. The proposed subdivision will create 3 lots total with 2 undeveloped lots of approximately 5 acres each and the remaining 42 -acre lot to occur with the existing home, as shown on Figure 1 Geology Taughenbaugh Mesa is a gently sloping fan shaped, geomorphic surface comprised of a debris flow situated on top of the Wasatch formation according to the USGS preliminary report "Geologic Map of the Rifle Quadrangle, Garfield County, Colorado by Ralph Shroba and Robert B. Scott, 1997, OFR 97-852". Figure 2 shows the mapped geologic units, which consist of the bedrock Wasatch formation (Tws), covered by colluvium debris -flow (Qdi) deposits (middle Pleistocene), C \pto • • Geotechnical Constraints It is our opinion that there are not any geotechnical constraints that would limit construction of homes on the two 5 -acre lots based on our field investigations and available soils/geology reports. This is supported by construction of the existing home on the larger parcel and by other residences constructed on the mesa. However, the possible existence of localized areas of clay - loam lenses with shrink/swell properties warrants future considerations. We recommend that site specific soil samples be collected for each building footprint prior to building permit issuance for the two undeveloped parcels. A geotechnical engineer should examine the soils and prepare an engineered foundation. If you have any questions, please do not hesitate to call 970-625-4933. Sincerely, Christopher Manera, P.E. CM:cm Encl: CC: Caloia & Houpt, P.C. SoilsGeology.doc • y JAY r• ti• J: t • 't r �•�/! ? /kt • N, m z €F o W o z .28. gc 5 h o }z 0,e _1 W m • • CCo� m U a tocn a 00 tn O vri oo n (-4 ,C 0 `Q X U O CO a)" os a�Hw 0 • • Appendix A Soil Survey Attachments United.States Department of Agriculture Soil Conservation Service • In Cooperation with the Colorado Agricultural Experiment Station • Soil Survey of Rifle Area, Colorado Parts of Garfield and Mesa Counties 32 " SOIL SURVEY 55—Potts loam, 3 to 6 percent slopes. This deep, well drained, moderately sloping soil is on mesas, bench- es, and sides of valleys. Elevation ranges from 5,000 to 7,000 feet. This soil formed in alluvium derived from sandstone, shale, or basalt. The average annual precipi- tation is about 14 inches, the average annual air tem- perature is about 46 degrees F, and the average frost - free period is about 120 days. Typically, the surface layer is brown loam about 4 inches thick. The subsoil is reddish brown clay loam about 24 inches thick. The substratum is pinkish white loam to a depth of 60 inches. Included with this soil in mapping are small areas of Olney, Kim, and Ildefonso soils that have slopes of 3 to 6 percent. These areas make up 10 to 15 percent of the map unit. Permeability is moderate, and available water capacity is high. Effective rooting depth is 60 inches or more. Surface runoff is slow, and the erosion hazard is moder- ate. This soil is used mainly for irrigated crops and hay and for dryland farming (fig. 10). Alfalfa, small grains, and grass -legume hay are grown. Small areas are used for grazing. These soils are usually irrigated by flooding. Drop structures in irrigation ditches, grassed waterways, and minimum tillage prevent serious erosion. Irrigation water should be carefully managed to avoid piping and erosion. Cover crops or stubble mulching also help to limit ero- sion in dryfarmed areas. The native vegetation on this soil is mainly wheat - grass, needleandthread, and sagebrush. When range condition deteriorates, forbs and shrubs increase. When the range is in poor condition, undesira- ble weeds and annual plants are numerous. Properly managing grazing maintains and improves range condi- tion. Reducing brush improves the range. Seeding im- proves range in poor condition. Crested wheatgrass, western wheatgrass, and Russian wildrye are suitable for seeding. Preparing a seedbed and drilling the seed are good practices. Pheasant, mourning dove, cottontail rabbit, some mule deer, and squirrel find habitat on this soil. Community development and recreation are limited by low strength and the shrink -swell potential. Dwellings and roads can be designed to overcome these limita- tions. Community sewage systems will be needed if the population density increases. This soil is in capability subclasses Ille, irrigated, and IVe, nonirrigated. 56—Potts loam, 6 to 12 percent slopes. This deep, well drained, moderately sloping to rolling soil is on mesas, benches, and sides of valleys. Elevation ranges from 5,000 to 7,000 feet. This soil formed in alluvium derived from sandstone, shale, or basalt. The average annual precipitation is ahnut 14 innhns. the aVr'r-jq annual air temperature is about 46 degrees F, and the average frost -free period is about 120 days. Typically, the surface layer is brown loam about 4 inches thick. The subsoil is reddish brown clay loam about 24 inches thick. The substratum is pinkish white loam to a depth of 60 inches. Included with this soil in mapping are small areas of Kim, Olney, and Ildefonso soils that have slopes of 6 to 12 percent. These areas make up 10 to 15 percent of the map unit. Permeability is moderate, and available water capacity is high. Effective rooting depth is 60 inches or more. Surface runoff is medium, and the erosion hazard is severe. This soil is used mainly for grazing, wildlife habitat, and some dryland farming (fig. 10). Wheat, barley, and oats are grown. Minimum contour tillage and stubble mulching help to prevent excessive erosion. The native vegetation on this soil is mainly wheat - grass, needleandthread, and sagebrush. When range condition deteriorates, forbs and shrubs increase. When the range is in poor condition, undesira- ble weeds and annual plants are numerous. Properly managing grazing improves and maintains range condi- tion. Reducing brush improves range. Seeding improves range in poor condition. Crested wheatgrass, western wheatgrass, and Russian wildrye are suitable for seed- ing. Preparing a seedbed and drilling the seed are good_ practices. Community development and recreation are limited by low strength, shrink -swell potential, and slope. Dwellings and roads can be designed to overcome these limita- tions. Community sewage systems will be needed if the population density increases. This soil is in capability subclass IVe, irrigated and nonirrigated. 57—Potts-Ildefonso complex, 3 to 12 percent slopes. These gently sloping to rolling soils are on mesas and sides of valleys. Elevation ranges from 5,000 to 6,500 feet. The Potts soil formed in alluvium derived from sandstone, shale, or basalt. The Ildefonso soil formed in very strongly calcareous, basaltic alluvium and small amounts of eolian material. The average annual precipitation is about 14 inches, the average annual air temperature is about 46 degrees F, and the average frost -free period is about 120 days. The Potts soil makes up about 60 percent of the map unit, and the Ildefonso soils makes up about 30 percent. The Potts soil is on slightly concave positions, and the Ildefonso soil is on the breaks of steeper slopes. The Potts soil is deep and well drained. Typically, the surface layer is brown loam about 4 inches thick. The subsoil is reddish brown clay loam about 24 inches thick. The substratum is pinkish white loam that extends to a depth of Fr inrhp; TUNNE 3 2E R. 94 W -I R. 93 W. (Joins sheet 16) 106 TABLE 7. --BUILDING SITE DEVELOPMENT --Continued Soil name and Shallow map symbol excavations Dwellings without basements Dwellings with basements 55 Potts ;Slight ;Slight 56 ;Moderate: ;Moderate: Potts ; slope. ; slope. ;Slight :Moderate: 1 slope. Small commercial buildings ;Moderate: 1 slope. :Severe: slope. TABLE 8. --SANITARY FACILITIES --Continued SOIL SURVEY Local roads and streets 1i ;Slight. ;Moderate: slope. 1 Soil name and map symbol Septic tank absorption fields Sewage lagoon areas 54, 55 Moderate: Potts ; percs slowly. 56 ;Moderate: Potts : slope, 1 percs slowly. ;Moderate: : slope, : seepage. :Severe: : slope. Trench sanitary landfill ;Slight ;Slight Area 1 Daily cover sanitary ; for landfill landfill ; ;Slight ; !Good. :Moderate: ;Fair: : slope. : slope. TABLE 13. --ENGINEERING INDEX PROPERTIES --Continued 1 Classification 1Frag- 1 Percentage passing ' : Soil name and ;Depth; USDA texture ;ments ; sieve number-- :Li map symbol : : Unified ; AASHTO : > 3 : : ; ; : limit 1 ticity ' ' ; ;inches: 4 ; 10 1 40 1 200 : : index i i i i r 1 1 , 1 1 1 i i 1 1 1 0-4 :Loam ;ML IA -4 ; 0 175-100175-100165-90 :50-70 : 25-35 I NP -5 1 4-281Clay loam :CL 1A-6 I 0 175-100:75-100170-100155-80 : 25-35 1 10-15 :28-601Loam IML 1A-4 : 0 175-100175-100165-90 150-70 1 25-35 1 NP -5 54, 55, 56 Potts TABLE 14. --PHYSICAL AND CHEMICAL PROPERTIES OF SOILS --Continued rr T T T—Erosion 1 1 I I 1 Soil name and :Depth:Clay <2mn; Permeability ;Available: Soil :Salinity; Shrink -swell I factors snap symbol ; ; ; water :reaction: potential , 1 1 1 ;capacity 1 , ; 1 K : T 1 In : Pct : In/hr 1 In/in I p , :mmhos/cm _ I ; , 1 0-4 1 15-25 1 0.6-2.0 10.16-0..1816.6-7.8 ; (2 :Low 10.371 5 4-28; 20-35 1 0.6-2.0 ;0.19-0.21;6.6-8.4 1 <2 ;Moderate 10.431 :28-60: 15-25 1 0.6-2.0 ;0.16-0.1817.9-9.0 1 (2 •;Low ;0.551 54, 55, 56 Potts TABLE 15. --SOIL AND WATER FEATURES --Continued :Organ 1 matte Pct. 1-2 1 , , Flooding,1 High water table 1 Bedrock , 1 Risk of c Soil name and ;Hydro-: 1 : 1 ; I; Potential map symbol 1 logic; Frequency 1 Duration ;Months 1 Depth 1 Months 1 Depth 1 Hardness ; frost :Uncoated ;group 1 1 1 1 1 1 1 1 action steel : 1 ; 1 Ft 1 : In I ; 1 7 r r 1 1 r 1 r r , l4, 55, 56 1 B :None 1 ; --- ; >6.0 ; ; >60 1 ;Low :High Potts ; 1 : : ; : :