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WASTE DISCHARGE REQUIREMENTS ORDER NO. R5-2009-0049 -9- SAN JOAQUIN COUNTY DEPARTMENT OF PUBLIC WORKS HARNEY LANE LANDFILL SAN JOAQUIN COUNTY detention basin is equipped with a float-controlled automatic pump that regulates the water level in the basin by pumping to South Paddy Creek immediately south of the site. The detention basin also includes a weir that allows overflows from South Paddy Creek to enter the basin during severe storm events. The basin's pump does not operate during such periods. 42. All landfill drainage facilities, including cover swales, overside drains, perimeter ditches, culverts, and the storm water detention basin were designed to have sufficient capacity to accommodate a 24-hour, 100-year storm event. Landfill Gas Controls 43. To control LFG migration and mitigate LFG as a likely source of VOCs in groundwater (see Finding 30), the Discharger installed a landfill gas extraction system at the site in 1996. The system has been improved over time and presently includes 82 vertical extraction wells at Landfill 1 and 14 vertical extraction wells at Landfill 2, as follows: Depth Range, Screen Landfill Wells Coverage ft bqs Length, ft LF-1 Al - A10 NE 50 - 65 25 - 33 LF-1 131 - B8 Central eastern 65 - 85 33 - 40 LF-1 C1 - C13 SE 60 - 85 30 - 40 LF-1 D1 — D9 NW 60 - 65 30 - 33 LF-1 E1 — E13 Central western 60 - 80 30 - 40 LF-1 F1 - F11 SW 65 - 85 33 - 40 LF-1 G1 - G4 SW 65 - 70 33 - 35 LF-2 H1 - H14 Entire 42 17 1. Dual extraction well installed in 2005 to improve gas extraction Each LFG extraction well was installed with a 9P sam lin ort and a valve to control the P LFG collection rate. The LFG extraction system facilities also include associated piping, condensate sumps, blowers, controls, and a flare station. Once extracted, the LFG is piped to the flare station where it is flared along with any condensate pumped from the condensate sumps. See Attachment C. POSTCLOSURE 44. Quarterly monitoring of LFG probes conducted per LEA requirements indicates that since 1995, the maximum concentration of methane detected along the site perimeter has been reduced to less than five percent by volume and is less than one percent by volume in most probes. Carbon dioxide, another component of LFG (and possible contributor to elevated bicarbonate in groundwater, as noted in Finding 34), --has-beets-deteeted-up-to-l-6-per-eent-in--sever-al of-the-probes.