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WASTE DISCHARGE REQUIREMENTS ORDER NO.R5-2009-0049 SAN JOAQUIN COUNTY DEPARTMENT OF PUBLIC WORKS HARNEY LANE LANDFILL SAN JOAQUIN COUNTY Other VOCs have also been sporadically detected in groundwater at trace concentrations, including carbon tetrachloride; chlorobenzene; 1,2-dichlorobenzene; 1,4-dichlorobenzene; dichloromethane; trichloroethane; and trichlorofluoromethane (Freon 11). No VOCs have generally been detected in the other three wells at the site, except for a few sporadically detected in upgradient well MW-1 and reported as probable false positive results. 31. Historical monitoring data for the site generally indicates declining concentrations of VOCs coincident with improvements to the LFG extraction system. Since 2007, the primary VOCs historically detected in groundwater at the site (e.g., PCE, Freon 12, and 1,2-Dichloropropane) have been detected at trace or non-detect levels. 32. Elevated concentrations of general minerals have also been historically detected in groundwater at the site, primarily in downgradient well MW-4, as follows: Constituent Concentration (mg/L, except where noted) Upgradient Downgradient/ NW-1) 2 Average' 19952 20083 Chloride 11 123 120 Bicarbonate Alkalinity 160 310 97 Total Dissolved Solids 237 573 510 (TDS) Specific Conductance, 315 870 619 pmhos/cm 1. Historical average since 1995. 2. Annual average of quarterly results. 3. Second Quarter 2008 monitoring data. Lower concentrations of chloride, but possible elevated concentrations of bicarbonate alkalinity, have been detected in the other downgradient wells at the site, and in upgradient well MW-1. Time series plots of the monitoring data from MW-4 show declining trends for bicarbonate alkalinity, TDS, and specific conductance since 1995, but no significant change for chloride. 33. The Discharger has attributed elevated concentrations of chloride detected in the UWBZ at MW-4 to an upgradient source (claimed percolation from the nearby migrant labor camp's sewage treatment ponds), but has not provided any upgradient monitoring data to substantiate this claim. Chloride is a common constituent of landfill leachate that can migrate to groundwater from an unlined landfill. To resolve this issue and establish background concentrations for chloride, Provision G.5 of these WDRs requires that the Discharger establish a background monitoring well immediately upgradient of Landfill 2, but downgradient of the labor camp's ponds (i.e., either by installation of a new well or by utilization of an existing.monitoring well of suitable construction).