CORRESPONDENCE_2007-2009 - Laserfiche WebLink

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effectiveness of the LFG collection system in controlling combustible gas at SG -4 because none of the wells of that system targeted the sand lens. To control landfill gas in accordance with environmental regulations, the County proposes the following two-step remediation process. Step 1: increase the collection of LFG from the existing system. The flow rate was increased May 18, 2007, including the collection of LFG from well GX-8, which is most likely to influence the sand lens. The LFG collected at this well has decreased from approximately 60% to 51 % since operation began, indicating that approximately 15% of the gas collected is air being drawn into the landfill. While this reduction in gas quality is not extreme, it shows that the well is "stressed" and is likely collecting LFG from its full radius of influence. Since the collection rate was increased, combustible gas has been measured at SG -4. It therefore appears that this step was not successful. Step 2: Install a new LFG well to collect from the sand lens This well will be installed at a location accessible by drill rig on the northeast corner of the landfill (Figure 2). It would be designed to collect LFG from the sand lens with the collection section exclusively in the sand (Figure 3). The presence of refuse above the sand lens may create a situation where the sand lens itself becomes part of the LFG collector. Although the landfill is not lined, and therefore not provided with a constructed protection against leachate movement, the well is designed to maximize separation between refuse and soil through the placement of compacted soil, bentonite, and neat cement plug. Unless otherwise directed, the wells will be completed in the presence of Environmental Health Unit 6 staff and in accordance with a drilling permit obtained by the Solid Waste Division of the Public Works Department. Refuse cuttings will be removed to the active landfill face at the end of each working day. If the well is not completed at the end of the working day, any open excavations deeper than three feet will be covered with a one -inch thick piece of plywood, the edges sealed around with soil and plastic sheet to prevent landfill gas from escaping into the atmosphere. Remediation Plan - LFG Well Installation Solid Waste/Public Works Foothill Sanitary Landfill Page 2 of 3 San Joaquin County — May 24, 2007