CORRESPONDENCE_2003-2004 - Laserfiche WebLink

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Off-site migration has been previously controlled, with the last detection above regulatory limits occurring in June 2002. LFG collection system adjustments restored control at that time. The LFG system therefore appears to be adequate in controlling LFG migration if fully functional; however,monitoring 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 comer 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 surface and LFG pipe. The County therefore began investigating the problem by replacing or adjusting the LFG piping beginning in May 2003. Combustible gas was detected 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). 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. The following Plan describes the steps taken,beginning in May 2003,which will continue until compliance to the regulatory limits is reached. MITIGATION STEPS The steps to re-establish control of LFG migration are as follows. 1. Determine therop blem 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. Further investigation revealed reduced and inconsistent vacuum along the LFG header,which indicates differential settlement along the header, 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. 3. Remove condensate - s e blockage by re-establishing proper drainage across the low spots by one of two methods: a. Replace the header using PVC pipe installed above ground. Remediation Plan for LFG Migration 2 San Joaquin County Public Works/Solid Waste Harney Lane Sanitary Landfill Revised December 14,2004