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Y � THOMAS R. FLINN DIRECTOR r. w 4G/Fp R� THOMAS M. GAU CHIEF DEPUTY DIRECTOR MANUEL SOLORIO DEPUTY DIRECTOR STEVEN WINKLER DEPUTY DIRECTOR ROGER JANES BUSINESS ADMINISTRATOR April 9, 2009 Mr. Todd Del Frate California Regional Water Quality Control Board Central Valley Region 11020 Sun Center Drive, #200 Rancho Cordova, California 95670-6114 P. OOX 1810 - 1810 E. HAZELTON AVENUE STOCKTON, CALIFORNIA 95201 (209) 468-3000 FAX (209) 468-2999 www.sjgov.org/pubworks SUBJECT: DISPOSITION OF LANDFILL GAS CONDENSATE, FOOTHILL LANDFILL Dear Mr. Del Frate: fj� On March 4, 2009, San Joaquin County staff noticed that the landfill gas (LFG) condensate pump discharge at Foothill Landfill was connected to the secondary leachate sump of Module 1. This connection was made by the contractor during the Foothill Site Improvement Project. The intent of the design of that contract was that LFG condensate would be delivered to the primary leachate sump through a 4 -inch leachate riser. However, the detail in the design drawings (Figure 1) was not to scale and seems to show connection to a 12 -inch pipe, which is the diameter of the pipe to the secondary sump. This mistake was overlooked by inspection and County staff until now. County staff immediately interrupted this connection, diverting LFG condensate to the leachate tank near the LFG flare station. The volume of the sump was less than the condensate delivered to it, so it was clear that the pressure of the pump discharge had caused a portion of a weld between HDPE liners to separate. However, liquid had not been detected in the lysimeter beneath the sump, indicating that the welds between the primary and secondary sump membranes at the base of the liner were intact. The level of condensate within the pipe was found to be constant, a few feet below the surrounding ground surface at the elevation of the boot that allows the secondary sump pipe to emerge through the primary membrane to the surface (Figure 2). We had not observed saturated soil in that area. Under the observation of the Local Enforcement Agency (San Joaquin Count Environmental Health Department) staff, we exposed the pipe and boot, and found that a weld between two geomembranes had separated immediately above the pipe, at the same elevation as the condensate within the pipe. Flow of condensate at this point was indicated by the saturation of soil above this location only; similar wetting was not observed at other locations along the seam between boot and primary membrane. The separation itself could not be observed directly, as it was covered by geocomposite. The boot and geocomposite remains exposed at this time. It is clear that the separation of a portion of the boot weld relieved the pressure within the space between primary and secondary membranes. The condensate flowed through the separation once this separation occurred, traveling above and along the primary liner and into the primary sump. Condensate had not been released into the environment.