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HomeMy WebLinkAbout1.06 Impact Analysis North Hangs Mine February 2023 27 Impact Analysis Sections 7-1002 and 7-1003 of the Garfield County Land Use and Development Code (Code) address mitigation efforts required for permitted gravel mining operations in Garfield County. Garfield County requires adherence to Colorado State Statutes (CRS) §25-12, which establishes statewide standards for noise level limits for various time periods and areas. 1. General Impact Mitigation All impacts discussed in this section are primarily mitigated by two factors: 1) the inherent topographical differences between the mining operations onsite and 2) the surrounding land and groves of trees along the Colorado River that will be maintained. All mining activities will take place in an area of the site that sits below the existing grade, with the exception of topsoil stripping and initial stockpiling. Processing will occur several feet below ground level to reduce noise propagation. Topsoil stripping will be conducted in short term periods of the year, typically in the early spring or late fall. Trees will be planted to in-fill the existing vegetation along the Colorado River and along the south side of processing and stockpiling. These trees will mitigate the visual and noise impacts of the operation to the Town of Silt, Colorado and the I-70 corridor. Note that any reference to ‘Exhibits’ or ‘Maps’ refers to Exhibits and Maps contained within the attached Colorado Division of Reclamation, Mining, and Safety (CDRMS) application components for the North Hangs Mine unless specifically stated otherwise. 2. Adjacent Land Use The proposed Land Use Change would allow for the development of a gravel mine at the location. This use is consistent with the industrial/commercial aspect of adjacent land including an existing gravel mine 1000 feet southeast of the proposed North Hangs Mine and the I-70 corridor along the southern boundary of the property. To the west is agricultural land used as irrigated pasture for cattle. To the north is the Colorado River, with Colorado Parks and Wildlife open space across the river to the northeast. Across the river to the northwest is agricultural land consisting of rangeland and a single residence. 3. Site Features Map C-1 of the CDRMS permit application in Appendix 4 shows the site features including floodplain area, wetlands, water pathways, ditches, topography, vegetative cover, and more. 4. Soil Characteristics A soil report was generated using the United States Department of Agriculture’s NRCS Web Soil Survey (WSS) and is included in the CDRMS permit application in Appendix 4 as part of Exhibit I. The WSS provides soil data and information produced by the National Cooperative North Hangs Mine February 2023 28 Soil Survey. The majority of the site (89.6%) is split between three soil types, Wann, Halaquepts, and Torrifluvents (see Map C-1). Each of these primary soil types are described on the following pages. Suitability for Reclamation and Landscaping All three soil types provide an average of at least 12 inches of suitable material for revegetation. All three soils are listed as class VII without irrigation. Class VII are not suitable for cultivation and are restricted to grazing by domestic animals or wildlife; all are listed as climatically limited soils. Soil Type Descriptions Wann sandy loam, 1 to 3 percent slopes Map Unit Setting National map unit symbol: jnzc Elevation: 5,000 to 6,500 feet Farmland classification: Prime farmland if irrigated and reclaimed of excess salts and sodium Map Unit Composition Wann and similar soils: 85 percent Minor components: 15 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Wann Setting Landform:Terraces, valley floors Landform position (three-dimensional):Tread Down-slope shape: Linear, convex Across-slope shape: Linear, convex Parent material: Alluvium derived from sandstone and shale Typical profile H1 - 0 to 8 inches: sandy loam H2 - 8 to 60 inches: fine sandy loam, sandy loam, coarse sandy loam H2 - 8 to 60 inches: H2 - 8 to 60 inches: Properties and qualities Slope:1 to 3 percent Depth to restrictive feature: More than 80 inches Drainage class: Poorly drained Runoff class: Very low Capacity of the most limiting layer to transmit water (Ksat): High (2.00 to 6.00 in/hr) Depth to water table: About 0 inches Frequency of flooding: OccasionalNone Frequency of ponding: None Calcium carbonate, maximum content:10 percent Maximum salinity: Nonsaline to very slightly saline (0.0 to 2.0 mmhos/cm) Available water capacity: Very high (about 26.3 inches) Interpretive groups Land capability classification (irrigated): 4w Land capability classification (nonirrigated): 6w Hydrologic Soil Group: A/D Ecological site: R048AY265CO - Salt Meadow Hydric soil rating: Yes Custom Soil Resource Report 18 Minor Components North Hangs Mine February 2023 29 Torrifluvents Percent of map unit:5 percent Hydric soil rating: No Kim Percent of map unit:5 percent Hydric soil rating: No Arvada Percent of map unit:5 percent Hydric soil rating: No Halaquepts, nearly level Map Unit Setting National map unit symbol: jnxr Elevation: 5,400 to 7,400 feet Frost-free period: 101 to 135 days Farmland classification: Not prime farmland Map Unit Composition Halaquepts, nearly level, and similar soils:85 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Halaquepts, Nearly Level Setting Landform:Terraces, fans, valleys Landform position (three-dimensional):Tread Down-slope shape: Convex, linear Across-slope shape: Convex, linear Parent material: Alluvium Typical profile H1 - 0 to 8 inches: clay loam H2 - 8 to 24 inches: loam H3 - 24 to 60 inches: stratified very gravelly cobbly sand Properties and qualities Slope:0 to 6 percent Depth to restrictive feature: More than 80 inches Drainage class: Poorly drained Runoff class: Medium Capacity of the most limiting layer to transmit water (Ksat): Moderately high (0.20 to 0.60 in/hr) Depth to water table: About 0 inches Frequency of flooding: Occasional None Frequency of ponding: None Calcium carbonate, maximum content:10 percent Gypsum, maximum content: 5 percent Maximum salinity: Moderately saline to strongly saline (8.0 to 16.0 mmhos/cm) Sodium adsorption ratio, maximum:30.0 Available water capacity: Low (about 3.9 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 6w Hydrologic Soil Group: C/D Hydric soil rating: Yes Torrifluvents, nearly level Map Unit Setting National map unit symbol: jnz3 Custom Soil Resource Report 16 North Hangs Mine February 2023 30 Elevation: 5,000 to 7,000 feet Mean annual precipitation: 12 to 15 inches Mean annual air temperature: 46 to 48 degrees F Frost-free period: 90 to 120 days Farmland classification: Not prime farmland Map Unit Composition Torrifluvents and similar soils:85 percent Minor components:15 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Torrifluvents Setting Landform: Distributaries, rivers, flood plains Down-slope shape: Linear, convex Across-slope shape: Linear, convex Parent material: Alluvium Typical profile H1 - 0 to 36 inches: loam H2 - 36 to 60 inches: sand Properties and qualities Slope:0 to 6 percent Depth to restrictive feature: More than 80 inches Drainage class: Moderately well drained Runoff class: Low Capacity of the most limiting layer to transmit water (Ksat):Moderately high to high (0.60 to 2.00 in/hr) Depth to water table: About 12 to 36 inches Frequency of flooding: Occasional None Frequency of ponding: None Calcium carbonate, maximum content:5 percent Gypsum, maximum content:1 percent Maximum salinity: Very slightly saline to moderately saline (2.0 to 8.0 mmhos/cm) Sodium adsorption ratio, maximum:2.0 Available water capacity: Moderate (about 7.6 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 7w Hydrologic Soil Group: C Hydric soil rating: No Minor Components Wann Percent of map unit:10 percent Landform: Terraces Hydric soil rating: Yes Fluvaquents Percent of map unit:5 percent Landform: Marshes Hydric soil rating: Yes North Hangs Mine February 2023 31 5. Geology and Hazard A geologic hazards study by Kumar & Associates was conducted on the property. It can be found in Appendix 3. 6. Groundwater and Aquifer Recharge Areas Mining activity at the North Hangs Mine will be conducted below the groundwater table. This is facilitated through the dewatering process during mining; dewatering pumps drain the active pit of groundwater to allow for mining activity to take place below natural grade. The dewatering of the pits will take place under an approve CDPHE discharge permit and CDWR gravel well permit. Groundwater is located approximately four feet below the surface of the ground onsite. No wells are located within 600 feet of the proposed pit 2. Mining activity will expose groundwater from the very beginning of operations. Dewatering of the pit will take place to bring the groundwater table below the operating floor. This allows equipment to safely and effectively mine the alluvial deposit. The pit pump will be active continuously during the mining season, which typically is mid-April to early-November, depending on weather. The pit pump will not run during flood events or when temperatures drop below freezing. The only known aquifer in the area is the shallow alluvial aquifer of the Colorado River. Depth to water table in the permit area varies depending on location and time of year but averages roughly four feet below ground surface. According to the U.S. Geological Survey’s Ground Water Atlas of the United States, the only groundwater aquifer system below the alluvial one in this area is the Unita-Animas Aquifer System. This is located beneath the Mancos Shale that underlays the site alluvium and will not be reach by mining or affected by mining Wastewater and sewage will be stored in a portable vault toilet that will be service by a contractor. This will prevent sewage or effluent from wastewater from entering the Colorado River alluvial aquifer. The 100-YR floodplain of the Colorado River encompasses the entire site. See the Floodplain Analysis for details. 2 https://gis.colorado.gov/dnrviewer/Index.html?viewer=dwrwellpermit North Hangs Mine February 2023 32 7. Environmental Impacts An environmental impact analysis has been conducted by Environmental Solutions, Inc. and can be found in Appendix 2. 8. Nuisance A detailed discussions of all potential impacts to adjacent land from generation of vapor, dust, smoke, noise, glare or vibration, or other emanations can be found under the Additional Standards for Gravel Operations section further on in this SUP application. 9. Hours of Operation Hours of operation at the North Hangs Mine will be limited to Monday thru Saturday, 7am to 7 pm. As specified in Article 7-1001.H.