ARCHIVED REPORTS_2014 - Laserfiche WebLink

Home Browse Search

enhanced vacuum within waste mass in close proximity to impacted groundwater. The third well will be used to provide an enhanced vacuum within the waste mass below the over lying impermeable liner. The construction details of typical LFG well is shown in Appendix A. The existing LFG extraction system has wells installed on approximately a 250-ft spacing within the centroid of the waste mass of Area"I". This pattern follows the State-of-Engineering Practice in LFG design. Engineering practice has shown that such a spacing provides sufficient vacuum within the waste mass to limit the buildup of LFG, but not exert such a vacuum that will cause the intrusion of oxygen into the waste mass. The proposed wells maintain the approximate 250-ft spacing between wells, yet keep the wells approximately 250-ft from the edge of the waste mass to limit the potential for oxygen intrusion. ' It is proposed that the three additional extraction wells and up-sizing of the LFG piping network be installed by December 31, 2014. This installation will also require approval from San Joaquin County Environmental Health Department and perhaps other agencies. However, the County believes the required permitting by these agencies can be obtained to meet this schedule. Although the present detection of VOCs in well MW-3 is not consistent between monitoring events, it appears that low levels of VOCs are present in the groundwater at MW-3, due to the entrapment of LFG under the HDPE liner placed over a portion of Area"I". The commencement of enhanced LFG extraction from Area"I" in the vicinity of MW-3 and from below the HDPE liner commencing in 2015 will have a high probability of eliminating the detection of VOCs at MW-3 by 2020. Soil Gas Well Work Plan Well SG-I is a single probe station that was installed as part of the EMP in 2003. Wells SG-2 through SG-I I were not originally intended to function as a system for the detection of groundwater impacts nor for the detection of off-site migration. These single-probe monitoring wells originally intended to function as shallow LFG monitoring stations and approved by RWQCB staff for that purpose. They were selected for the collection of vadose gas samples, because the County could use them to fulfill the monitoring requirements for CalRecycle and the CVRWQCB in force at that time (2004). However, the County has since installed a more extensive 3-probe vadose zone monitoring network consisting of 25 wells (SG-12 and SG-102 through SG-125) for perimeter migration monitoring (Figure 2). SG-12 was installed in 2004 and SG-102 through SG-125 were installed in 2009. These vadose monitoring stations are located along the landfill's property boundary at approximately 1,000-ft centers. Their construction details are contained in Appendix B. Because the newer vadose zone monitoring network consists of 3-probe wells,the County proposes to discontinue TO-15 monitoring of most of the existing single-probe well locations. ' Several of the 3-probe wells that are closest to existing waste disposal areas are proposed for vadose zone TO-15 monitoring. They include: • SG-117, located to the east of Area 2 and in the general vicinity of SG-7. ® SG-118, located to the east of Area 2 and in the general vicinity of LFG flare station. • SG-119, deep well located along the southern limit of Area 2 and a replacement for SG-8. Foothill Sanitary Landfill 5 Department of Public Works/Solid Waste Engineering Feasibility Study County of San Joaquin—August 2014