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3. Water 3.1 Groundwater Quality The main concern for the quality of groundwater at the Site is the potential for impairment of groundwater quality due to leaching of constituents from CKD that was disposed of in previously mined areas of the quarry. Disposal of CKD into previously mined areas of the quarry began in 1986 and has continued to date. The amount of CKD disposed in the quarry area from 1986 through 2001, during operation of the old wet kilns, was approximately 100,000 tpy (K-S & Company, 1999). Locations of historic CKD disposal areas in the Permit area aze shown in Figure 2. The bottoms of the CKD disposal areas coincide with an elevation approximately ten feet above the top of the underlying Codell Sandstone. Approximately eight to ten feet of argillaceous limestone was reportedly placed in the bottom of the CKD disposal areas prior to the placement of CKD to isolate the CKD from groundwater in the Codell sandstone. In 1991, the Fremont Sanitation District received permission from the Colorado Department of Health to use sewage sludge from the Fremont Sanitation District as a cover material for the CKD (Hegeman, 1991). Four groundwater monitoring wells (MW-1, MW-2, MW-3, and MW-4) were installed in the bottom of a mined area (former Cut 6) in 1991 (Figure 2) and were completed in the Codell sandstone (Table 2). These wells were installed by the Fremont Sanitation District to evaluate the potential impact of the disposal of sewage sludge on groundwater quality at the Site. Wells MW-1, MW-2, and MW-3 were installed in the western half of the mined area which was subsequently backfilled with mining waste/overburden (i.e, Smoky Hill Limestone). Well MW-4 was installed in the eastern half of the mined azea which was subsequently filled with CKD and sludge. As the mined area was filled, the monitoring well casings were continually extended above the ground surface. The backfilling of this mined area was completed in August 1998 and disposal continued into an adjacent mined area (former Cut 8). Wells MW-1 through MW-4 were abandoned by K-S & Company in 1999. Drilling and abandonment logs for MW-1 through MW-4 aze provided in Appendix A. Monitoring wells MW-5, MW-6, and MW-7 were installed in August 1998 as part of a Hydrogeologic Assessment performed to help characterize the hydrogeology of the quarry area (RGI, 1999). This assessment was performed in anticipation of proposed federal regulations for the disposal of CKD and was submitted to DMG as part of TR-06. The objective was to install three groundwater monitoring wells: two wells downgradient from the CKD/sludge disposal areas (i.e. Cut 6 and Cut 8) and one well upgradient from the CKD/sludge areas. MW-5 was completed in the Codell Sandstone and possibly part of the underlying Blue Hill Shale (Figure 2, Table 2). It was originally thought that MW-5 would be located downgradient of CKD in Cut 6; however, subsequent groundwater elevation data indicated that MW-5 likely was not truly downgradient (Figure 4). MW- 5 was abandoned in April 2000 when the area was mined through (K-S & Company, 2000). An initial attempt to install MW-6 in Cut 2 approximately 1000 feet north of the primary crusher was made. This location was in the central portion of Cut 2 which had already been mined and backfilled with shaley overburden. Due to the unstable nature of the fill material, the drillers were not able to keep the borehole open to install the well casing and packing materials in this location (RGI, 1999). MW-6 was then placed upgradient of the mined area on the north side of Cut 3 near the northern boundary of the mine, and was completed in the Fort Hays and Smoky Hills Limestone (Figure 2, Table 2). MW-7 was placed downgadient of the mine area on the first bench above the Arkansas River and was completed in the Codell Sandstone (Figure 2). Three boreholes were drilled before BLASLAND, BOUCK 8 LEE, INC. t2nyoa engineers & scientists 31 Gmundwnter Manirorin8 Plen R.dot