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WASTE DISCHARGE REQUIREMENTS ORDER NO.135-2009-0049 _5_ SAN JOAQUIN COUNTY DEPARTMENT OF PUBLIC WORKS HARNEY LANE LANDFILL SAN JOAQUIN COUNTY GROUNDWATER 26. The beneficial uses of the ground water at the site are municipal and domestic supply, agricultural supply, industrial process supply, and industrial process supply. 27. The upper water-bearing zone (UWBZ) at the site is unconfined. The UWBZ occurs in alluvial deposits of the Turlock Lake and Laguna formations, which consist of laterally discontinuous layers of gravel, sand, silt and clay. The overall permeability of these deposits is estimated to be about 1 x 10-2 cm/sec based on onsite boring log information and slug testing of a well screened in similar deposits at the North County Landfill (approximately 1.5 miles east of the site). 28. The depth to groundwater ranges from about 131 feet bgs (-30 feet MSL) on the upgradient perimeter of the landfill to about 124 feet bgs (-35.5 feet MSL) on the downgradient perimeter. Up to eight (+/-4) feet of seasonal variation in the water table has been observed along the downgradient perimeter, possibly due to the influence of the nearby detention basin. Historical groundwater elevation monitoring data indicate that the groundwater table has been declining over time due to regional and local pumping. The monitoring data indicate that the average ground water gradient at the site is about 0.003 foot/foot to the south-southwest. 29. Four groundwater monitoring wells, including one upgradient (MW-1), two cross gradient (MWs-2 and 4), and one downgradient (MW-3), were installed at the site in 1987. No other groundwater monitoring wells have since been installed at the site. 30. A 1987 groundwater investigation (see 20 June 1991 Solid Waste Water Quality Assessment Test for Harney Lane Sanitary Landfill, prepared by Kleinfelder, Inc.) found low to trace concentrations of volatile organic compounds (VOCs) in the UWBZ, primarily in cross-gradient well MW-2. The Discharger subsequently confirmed a landfill release and in 1994 implemented an Evaluation Monitoring Program (EMP) to investigate the nature and extent of impacts. Ground water monitoring results for VOCs detected at the site may be summarized as follows: VOC Average Concentration, Ng/L 1995' 2005' 2008 Benzene /n a <0 2 0.6 Dichlorodifluoromethane <0.42 2.0 <0.72 (Freon 12) 1,2-Dichloropropane <0.42 0.6 <0.42 Tetrachloroethene (PCE) 0.5 1.1 0.5 Toluene n/a3 <0.22 0.9 Total Xylenes n/a3 <0.42 <1.12 1. Four-quarter average using non-detects at detection limit. 2. Constituent not detected. 3. Constituent not analyzed.