2012-09-06_REVISION - M2008070 (25)

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Design and Operations Plan Western Gravel E & P Waste Disposal Facility 2.3.3 Hydrogeologic Conditions October 24, 2011 Page 11 of 51 As discussed above, the site is located at the northern portion of the Pice ance Basin in the Colorado Plateau physiographic province. The terrain is characterized by high plateaus and deep valleys. The White River flows in a general east to west direction and along the north and east sides of the proposed facility. The White River drainage basin drains part of the Colorado Plateau, Wyoming Basin, and Southern Rocky Mountains and is a tributary of the Green River. Hydrogeologic data is provided in Appendix C. 2.3.3.1 Regional Groundwater Occurrence Regional groundwater in the Piceance Basin occurs both in alluvium and bedrock. Alluvium aquifers composed of narrow and thin deposits of sand and gravel, located along streams and rivers, are the most productive aquifers in the Piceance Basin. The major alluvial aquifer is the White River Alluvium. Regionally from the Towns of Meeker to Rangely, alluvium saturated thickness can range from zero along valley walls to more than 140 feet; however, data is limited and the aquifer extent is unknown in certain areas. White River alluvial aquifer transmissivities rang e from approximately 860 square feet per day (ft /d) to 93,000 ft /d and hydraulic conductivities range from approximately 5.4 x 10 cm/sec to 2.5 x 10 -2 cm/sec. The major bedrock aquifers are known as the lower Tertiary Eocene age Upper and Lower Piceance Basin aquifer systems. The upper aquifer system exhibits several permeable zones within the Uinta Formation and upper Parachute Creek Member of the Green River Formation and is approximately 700 feet thick. T he lower aquifer system is part of the lower Parachute Creek Member and semi - confined below the Mahogany Member and above the Garden Gulch Member of the Green River Formation. The lower aquifer is approximately 900 feet thick. The upper and lower bedrock aquifer systems are separated by the Mahogany Zone of the Parachute Creek Member. The oil shale Mahogany Zone exhibits poor permeability; however only inhibits but does not stop groundwater movement. Bedrock of the upper aquifer consists of silty sandstone, siltstone, and marlstone of the Uinta Formation underlain by fractured dolomitic marlstone of the upper Parachute Creek Member. Bedrock of the lower aquifer is part of the lower Parachute Creek Member consisting of fractured dolomitic marls tone. Although some primary porosity exists, much of the observed permeability can be attributed to solution enlargement along fractures produced during deformation. Bedrock hydraulic conductivities of the aquifers range from 1x10 cm/sec to 1x10 -5 cm/sec. Snowmelt at higher elevations provides groundwater recharge. Snowmelt migrates down through the upper aquifer system through the Mahogany Member and into the lower aquifer system. Groundwater continues to move laterally and/or upward then discharges into streams and/or rivers from both upper and lower aquifer systems. The general direction of groundwater flow in the north Piceance Basin is towards the White River. 2.3.3.2 Regional Groundwater Quality Bedrock groundwater quality in the Piceance Basin is considered poor because of nahcolite (sodium bicarbonate — NAHCO deposits, dawsonite (NaAl(OH) and salt beds (halite — NaC1) located within the basin. Groundwater within the lower aquifer reportedly contains several hundred milligrams pe r liter (mg /1) of chloride. In the northern Piceance Basin Tertiary aquifer system, dissolved solids are gained in the water as groundwater migrates along the basin from upland recharge areas to discharge areas. As groundwater migrates along the flow path, the upper aquifer exhibits dissolved solids concentration increases from 500 mg /1 to 1,000 mg /1 and the lower aquifer exhibits increases of approximately 1,000 mg /1 to 10,000 mg/1. NWCC, Inc.