ARCHIVED REPORTS_2012_3 - Laserfiche WebLink

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*qu�h • THOMAS M.GAU P.O.BOX 1810.1810 E.HAZELTON AVENUE DIRECTOR STOCKTON,CALIFORNIA 95201 (209)468-3000 FAX(209)468-2999 ;�j F••at+� www.sjgov.org/pubworks FRITZ BUCHMAN DEP UTY.DIRECTOR Worlding f(W YOU MICHAEL SELLING DEPUTY DIRECTOR STEVEN WINKLER DEPUTY DIRECTOR ROGERJANES BUSINESS ADMINISTRATOR July 23, 2013 Mr. Todd Del Frate California Regional Water Quality Control Board Central Valley Region 11020 Sun Center Drive, #200 Rancho Cordova, California 95670-6114 SUBJECT: FIRST SEMESTER 2013 GROUNDWATER AND SURFACE WATER MONITORING REPORT; FOOTHILL SANITARY LANDFILL Dear Mr. Del Frate: Enclosed is the First Semester 2013 Groundwater and Surface Water Monitoring Report for the Foothill Sanitary Landfill. Groundwater monitoring continues on a semi-annual basis in accordance with our WDRs. General parameters, minerals and inorganic results are unremarkable. One VOC, less than 1 ppb, was reported in well MW-3. This well was free of VOCs from early 2002 until approximately five years after the placement of an impermeable barrier over Module "I" refuse. The reappearance of this compound after years of non-detection is troubling, especially when many of those years of non-detection were without a LFG collection system; however, this is consistent with a five-year lag time between "cause" on the surface and "effect" seen in the groundwater. In this case, the cause of the groundwater impact was the placement of an impermeable barrier over refuse of this unlined landfill. The County continues to be concerned that placing an impermeable liner over refuse of an unlined landfill promotes movement of LFG towards the groundwater, and that this effect cannot entirely be countered by a LFG collection system. The enclosed report includes a review of these events. The County increased corrective action by replacing LFG collection well GX-2A and increasing LFG pipe size to better serve GX-7 and -9. We are presently at the maximum collection rate for our LFG system but anticipate that the LFG-to-Energy plant will increase LFG collection by at least 10%. The water level in MW-1 was sufficient to measure elevation, but not to collect a sample. This well is cross-gradient from the landfill, so data from this well is not needed at this time in evaluating the data from the up-gradient or down-gradient wells. However, this well is useful in estimating groundwater elevations under the site. MW-1 will be replaced with MWAA prior to the next monitoring event.