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