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Ms. Sangeeta Lewis <br />September 2, 1999 <br />Page 2 <br />did not exceed 50 Mg per year for the next five years, the subject site qualifies for at least <br />5 -year deferral from NSPS requirements for submittal of a GCCS design plan and installation. <br />Therefore, the installation of a GCCS is not required at the time of closure for WMU-B under <br />HSPS. The need for a GCCS for the entire landfill, including WMU-B, must be re-evaluated <br />in year 2004. <br />LFG PERIMETER MONITORING NETWORK <br />According to the California Code of Regulations (CCR) Title 27, all municipal solid waste <br />landfills must implement a routine methane monitoring program to insure that (1) the <br />concentration of methane gas generated by the facility does not exceed 25 percent of the <br />lower explosive limit (LEL) for methane in facility structures (excluding gas control or <br />recovery system components); and (2) the concentration of methane has does not exceed <br />the LEL for methane (5% by volume) at the facility property boundary. If methane levels <br />exceed limits specified, then corrective action shall be administered, which may include the <br />installation of a GCCS. <br />C <br />A network of ten (10) LFG monitoring probes has been installed in native soils near the <br />property boundary and outside the landfill footprint. The probes extend to a depth of <br />approximately 3 feet below grade. Testing for combustible gas is performed on a quarterly <br />basis by Kleinfelder, Inc. on behalf of Forward Landfill Inc. 0 <br />Results of the quarterly LFG monitoring events were provided to SCS for the period from <br />1995 to 1998 by Kleinfelder, Inc. Based on the LFG monitoring results, no methane levels <br />have been detected in perimeter probes or on-site structures to warrant the installation of a <br />GCCS or other gas migration control measures. Assuming that the current perimeter <br />monitoring program for the Forward Landfill has been approved by the local enforcement <br />agency and/or CIWMB and combustible gas levels in soil remain below regulatory thresholds, <br />we see no need for the installation of a GCCS in WMU-B at closure. <br />Our evaluation was specific to gas migration and emissions control only. Evaluation of <br />potential LFG-related impacts to groundwater and related compliance measures is being <br />performed by others. <br />If you have any questions or need additional information, please contact either of the <br />undersigned at (925) 829-0661. <br />Very truly yours, <br />Step anie J. ou Jose h J. Miller, P.E. <br />$/ <br />Staff Engineer Vic President <br />SCS ENGINEERS ENGINEERS <br />G:\sw\projects\1999\109901700\corres\LFGReview.doc <br />