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POU�p Q Zi THOMAS R. FLINN DIRECTOR 4<IFO HtN THOMAS M. GAU CHIEF DEPUTY DIRECTOR MICHAEL SELLING DEPUTY DIRECTOR STEVEN WINKLER DEPUTY DIRECTOR ROGER JANES BUSINESS ADMINISTRATOR y August 19, 2010 Mr. Todd Del Frate California Regional Water Quality Control Board Central Valley Region 11020 Sun Center Drive, #200 Rancho Cordova, California 95670-6114 P. PDX 1810 - 1810 E. HAZELTON AVENUE STOCKTON, CALIFORNIA 95201 (209) 468-3000 FAX (209) 468-2999 www.sjgov.org/pubworks SUBJECT: GAS -IMPERMEABLE BARRIER OVER REFUSE AT FOOTHILL LANDFILL Dear Mr. Del Frate. � I The San Joaquin County Department of Public Works Solid Waste Division is in receipt of your letter of August 11, 2010, in which you reaffirm the requirement by Water Board staff that the County maintain the gas -impermeable barrier over unlined refuse at Module "I" at the Foothill Sanitary Landfill. We share the commitment to protecting the waters of the State, however, because of the potential for serious negative consequences of this requirement, we must state, for the record, our continuing objection on the grounds that placing an impermeable membrane over refuse may threaten groundwater, and again ask that Board staff reconsider this requirement. A liner of this type should only be placed under refuse. Placing an impermeable liner over refuse that does not also have a base liner inhibits the upward escape of landfill gas, but allows gas to move downward under positive pressure toward groundwater, possibly resulting in associated groundwater contamination. We may now be seeing the effect of gas entrapment at the Foothill Landfill: methane beneath the Module 1 liner has increased significantly after the placement of the impermeable liner on the side -slope of Module "I". Similar effects have been seen at other landfills as discussed in previous correspondence. Groundwater monitoring results indicate that the groundwater at the site is free of volatile organic compounds (VOCs) at this time. However, continuing to maintain a gas -impermeable barrier, and possibly extending this barrier over more refuse in the future, could significantly change these conditions with possibly disastrous results. It is worth noting that neither CCR Title 27 nor the Waste Discharge Requirements (WDRs) for the site require a landfill liner between old and new refuse. Finding 46 of the WDRs states that a composite liner is required under refuse at new municipal solid waste landfills and at expansion areas of existing landfills. Placement of additional waste over existing Module "I" refuse does not fall under either of these two categories.