Laserfiche WebLink
WASTE DISCHARGE REQUIREMENTS ORDER NO. R5-2010-0016 -9- <br />SAN JOAQUIN COUNTY DEPARTMENT OF PUBLIC WORKS <br />NORTH COUNTY LANDFILL <br />SAN JOAQUIN COUNTY <br /> <br /> <br />years compared to historical averages, a possible impact from carbon dioxide in <br />LFG. <br /> <br />37. A release to groundwater consisting of low to trace concentrations of VOCs, <br />primarily BTEX (benzene, ethylbenzene, toluene, and xylenes) compounds, was <br />confirmed in down gradient well G-4 in July 2002. Subsequent evaluation <br />monitoring found that the VOC impacts to groundwater did not extend down <br />gradient to well G-6. By January 2003, maximum VOC impacts at G-4 had <br />attenuated to trace concentrations. The EMP concluded that the VOC impacts <br />were sporadic and likely associated with LFG. No VOCs have been detected in <br />any of the wells since 2006 <br /> <br />Corrective Action <br />38. In 2006, the Discharger installed an LFG extraction system in accordance with a <br />May 2005 Corrective Action Plan (Corrective Action Plan For the Prevention of <br />Future Groundwater Impact by Landfill Gas at the North County Recycling Center <br />and Sanitary Landfill). The system (which became operable in June 2007) was <br />intended to control off-site migration of landfill gas and to address concerns <br />regarding LFG as a suspected source of VOCs sporadically detected in <br />groundwater. The system included installation of 7 vertical extraction wells in <br />existing modules M1 and M3; 2 LCRS risers between M1 and M3; horizontal wells <br />installed in collection trenches in expansion module M4; and associated collection <br />system piping, condensate handling facilities, blowers and a flare station. The plan <br />anticipated that future modules would be constructed with LFG extraction facilities <br />similar to Module 4 and tied into the system. <br /> <br />39. Based on the two semiannual monitoring events since startup of the LFG collection <br />system in 2007, lower LFG constituent concentrations have been detected in <br />interior well SG-6 compared to prior to system startup, including methane (<30% <br />by volume), and carbon dioxide (<30% by volume) and VOCs (generally <100 <br />ppbv). See Finding 29. <br />LANDFILL OPERATIONS <br />40. Refuse is spread and compacted in approximately two-foot lifts until 14 feet above <br />surrounding refuse, as determined by laser. The top slope of the working face is <br />usually graded (also by laser) to a 4% minimum slope for drainage. <br />41. The discharger uses onsite borrow for daily and intermediate cover soil. Tarps are <br />also employed as alternative daily cover (ADC). Cover soil is obtained from <br />excavation of the next module and/or from existing onsite stockpiles. A refuse to <br />soil ratio of approximately 5:1 is maintained for daily cover, which is applied at the <br />working face in 6-inch minimum lifts. Intermediate cover of 12-inches minimum <br />thickness is placed in areas that will be inactive for at least 180 days per Title 27, <br />CCR Section 20705.