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WASTE DISCHARGE REQUIREMENTS ORDER NO. R5-2010-0016 -8- SAN JOAQUIN COUNTY DEPARTMENT OF PUBLIC WORKS NORTH COUNTY LANDFILL SAN JOAQUIN COUNTY GROUNDWATER 32. The beneficial uses of the ground water at the site are municipal and domestic supply, agricultural supply, industrial service supply, and industrial process supply. 33. The upper water-bearing zone (UWBZ) at the site is unconfined or semi-confined and occurs in the alluvial deposits of the Turlock Lake and/or Laguna formations (see Finding 24). The overall permeability of these deposits is estimated to be about 9 x 10–3 cm/sec based on slug testing data from the boring for well G-1 (see Table 3, Geologic and Hydrogeologic Report, Appendix C, JTD). 34. The average depth to groundwater at the site is about 154 feet bgs (-36.5 feet MSL) with about six (+/-3) feet of seasonal variation. The groundwater gradient is typically about 0.004 ft/ft toward the southwest (or west-southwest), corresponding to a groundwater flow velocity of about 13.5 ft/yr. At times the measured flow direction has shown substantial historical variation, however, and/or has not been consistent site-wide, indicating possible onsite or offsite influences (e.g., onsite sedimentation basin, localized pumping). 35. There are currently seven groundwater monitoring wells at the site (see Attachment B), including one upgradient (G-1 on eastern site perimeter), one side gradient (G-2 on the western site perimeter), and four down gradient (Gs-3D, 4, 5 and 6, all along the western site perimeter). Monitoring of side gradient well G-2 was discontinued in 1997 and the status of the well is not known. Provision G.8.c requires that the Discharger investigate well G-2 and submit a status report as to its condition, including plans for repair or replacement, as necessary. 36. Historical monitoring data for the landfill shows generally good water quality in the UWBZ, as follows: Constituent Concentration (mg/L, except where noted) Upgradient Downgradient Historical1 20082 Historical 1 20082 Chloride 17 29 8 7 Bicarbonate Alkalinity 91 150 94 120 TDS 201 220 172 160 Specific Conductance, µmhos/cm 267 364 230 199 _____________________________ 1. Based on annual average. 2. Based on First Half 2008 monitoring results. Time series plots of the data do not indicate any clear exceedances over upgradient concentrations, but show moderately higher concentrations of bicarbonate alkalinity in both the upgradient and downgradient wells in recent