ARCHIVED REPORTS_2014_1 - Laserfiche WebLink

Home Browse Search

By February 2007, five years after the groundwater was found to be impact-free, construction of the Site Improvement Project was substantially complete; however,the vegetation in the evapotranspirative (ET) cover was not well established. Further work was needed to establish the vegetation. This project also included a barrier between existing Area"I"refuse and new refuse. CVRWQCB staff ordered the County to install a gas-tight barrier equivalent to a base landfill liner such as is required to place refuse on native soil. This barrier was installed in spite of County objections, based on concern that covering unlined refuse with an impermeable barrier could cause more groundwater impacts. In November 2007,the ET area was again reseeded,but growth remained insufficient for adequate ET cover. In November 2008,the closure cap soil was amended and fertilized, and again seeded. In the spring of 2009, vegetation was growing healthily on the ET cap area. On June 10,2009, CVRWQCB staff issued a notice of violation for discharge of wastes outside of containment due to the presence of VOCs in the soil within County property. Refuse was not discharged at those locations. On March 4,2009, San Joaquin County staff noticed that the LFG condensate pump discharge was connected to the secondary leachate sump of Area 1 rather than to the leachate collection and removal system (LCRS). In April 2009,the LFG condensate was removed from the secondary sump, and the soil gas trench(installed beneath the liner of Area 1)was activated to enhance the protection of groundwater. An investigation in October 2009 indicated that the condensate had been forced between the primary and secondary liner up the side of the landfill, and had been discharged a few feet below ground surface into the anchor trench along the side of the landfill where the primary and secondary liners terminate. In March 2011,the continuing removal of liquid from the secondary sump, including increased removal during a high-water level event in the primary sump, indicated hydraulic communication between the primary and secondary sump. In October 2011, as agreed by District staff,the County installed automatic pump in the secondary sump to maintain the liquid head above the liner below 12", in accordance with CC Title 27. This pump continues to operate. VOCs were again confirmed in MW-3 in the first quarter 2011, approximately five years after covering portions of Area"I" with HDPE liner material. This was the first VOC detection in this well since fourth quarter 2001. No other well indicates impact. In considering the timeline of detections and corrective actions, a four or five year lag between action at the surface and result in the groundwater may be apparent: • The four to five year time lag between a surface action and groundwater response is due to the approximate 270 foot thickness of the vadose zone at the MW-3 location • Winter of 1995/96 and continuing through three winters: water ponded over refuse near MW-3 (Ponding of surface water over refuse increases moisture content of the refuse, resulting in increased landfill gas production and the eventual impact to groundwater years later). Foothill Sanitary Landfill 4 Department of Public Works/Solid Waste Vt Semester 2014 Groundwater Monitoring County of San Joaquin—July 31,2014