2014-05-05_HYDROLOGY - M1977348 - Laserfiche WebLink

Home Browse Search

April 2014 5 10381640A 2.5.2 Hydrogeology The Site is located in the Colorado Piedmont subprovince. The Dakota - Cheyenne aquifer is the principal aquifer of the Colorado Piedmont subprovince, and is comprised of the Early Cretaceous Dakota Sandstone and the Cheyenne Sandstone Member of the Purgatoire Formation (Topper and others 2003), and is overlain by the Carlile Formation and Niobrara Formation. The Niobrara Formation and Carlile Formation are not considered to be part of a principal aquifer system, but portions of these units can yield some water to a few stock wells in parts of the Colorado Piedmont (Topper and others 2003). Previous mining activities and the existing monitoring wells at the Site are limited to the Niobrara Formation and the top of the Carlile Formation (the Codell sandstone), and do not penetrate into the Dakota - Cheyenne aquifer. The groundwater flow direction has been observed to generally flow easterly to southeasterly using data from monitoring wells MW -1 through MW -4 (Golder 2011). Previous hydraulic testing of monitoring wells MW -1 through MW -3, have yielded hydraulic conductivities in the range of 10 -7 to 10 -10 centimeters per second (cm /sec) (Secor 1998). Hydraulic conductivity testing of well MW -4 conducted by rising head and falling head slug tests (Golder 2011) resulted in values in this same range. Wells MW -1 through MW -3 are inferred to be installed within or at the interface of the Codell sandstone and Niobrara A (Laporte Member) limestone band (Secor 1998). Based on the borehole logs, the A band contains thin shale layers in the screened interval of wells MW -2 and MW -3. The lithology at well MW -4 is not known due to the lack of a borehole log. Groundwater at the Site has been thought to occur along the contact of the Codell sandstone and the Niobrara Formation. Five core samples of the Codell sandstone at the Boettcher Quarry were tested for grain density, porosity, and permeability to gas (Reservoirs Inc. 1998). Grain densities ranged from 2.69 to 2.73 grams per cubic centimeter (g /cc), porosities from 5.0 to 13.0 percent by volume (% BV), and permeability to gas from 0.01 to 0.05 millidarcy (md). 2.5.3 Background Geochemical Conditions The Wyoming State Geological Survey published the Green River Basin Water Plan II, Groundwater Study in 2010 (Surdam 2010). The study looked at the current assessment of available groundwater resources in the Greater Green River Basin (GGRB) of southwestern Wyoming and small adjacent areas of Colorado and Utah. This study breaks down the GGRB basin into sub - basins and characterizes the aquifers groundwater chemistry characteristics for water quality purposes. Two of the sub- basins identified are the Washakie and Sand Wash basins. These basins straddle the Wyoming /Colorado border and are approximately 80 miles west and northwest of the Site. The Niobrara Formation occurs as part of the Cody shale unit of the Washakie and Sand Wash basins. Five groundwater chemistry samples of produced water were collected from production well heads from the Niobrara Formation. The samples had concentrations of barium between 0.19 mg /L and 42 mg /L, with an average concentration of Golder Associates �10t81640a104001gwcharw lIinstallfieldrep fnl- 30apr14110381640a gwcharrpt _holcim- boettcher_fnl- 28apr14- with holcim edits. docx f.