CORRESPONDENCE_2003-2004 - Laserfiche WebLink

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r r trench is seen to settle faster than the refuse at the edge of the trench. The LFG headers are installed across on landfill slopes where this effect is observed. Off-site migration was previously controlled,with the last detection above regulatory limits occurring in June 2002. Adjustments to the LFG collection system restored control at that time. The LFG system therefore appears to be adequate in controlling LFG migration if fully functional; however, operational data from the LFG system in January and March 2004,prior to the detection of off-site migration, indicated that the collection of LFG from the northwest corner of the Primary Site was becoming compromised by accumulation of condensate within the main LFG pipe (the LFG"header") due to settlement of the landfill where the pipe was supported. The County therefore began investigating the problem and replacing or adjusting the LFG piping beginning in May 2003. Combustible gas was detected at above regulatory limits (5%methane) in soil gas well GW-1 on June 17, 2004. Since that time, combustible gas concentrations above regulatory limits have been measured at one or more probes of wells GW-1, -2, and 3. Mitigation actions taken since that time have significantly reduced the concentration of LFG at these wells (letter of October 1, 2004). To date, combustible gas has not been detected in the foundation vents of the adjacent migrant labor housing, indicating that human health and safety is not threatened at this time. The following Plan describes the steps taken beginning in May 2003, which will continue until regulatory limits are reached. Mitigation Steps The steps to re-establish control of LFG migration are as follows. 1. Determine the problem Combustible gas above regulatory limits at monitoring wells GW-1, -2, and -3 (June 2004 data) indicates inadequate collection of LFG from the wells in that vicinity. For example, reduced and inconsistent vacuum along the LFG header indicates differential settlement along the header is causing the accumulation of LFG condensate within the header and reducing the function of the wells in that portion of the LFG system. 2. Locate the areas along the LFG header where condensate is accumulating. a. Expose the header at select locations and install temporary pressure taps to measure vacuum. A significant decrease in vacuum from one location to another along the header indicates a low spot with accumulated condensate between those two locations. b. Remove vegetation along the alignment of the header in question, expose the header approximately every 25 feet, and survey to locate the low spot. Remediation Plan for LFG Migration 2 San Joaquin County Public Works/Solid Waste Harney Lane Sanitary Landfill October 4,2004