CORRESPONDENCE_2007 (1/07 - 6/07)

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4 THOMAS M. GAU CHIEF DEPUTY DIRECTOR MANUEL SOLORIO DEPUTY DIRECTOR STEVEN WINKLER DEPUTY DIRECTOR ROGERJANES BUSINESS ADMINISTRATOR THOMAS R. FLINN DIRECTOR January 23, 2007 Mr. Todd Del Frate California Regional Water Quality Control Board Central Valley Region 11020 Sun Center Drive, #200 Rancho Cordova, California 95670-6114 P. O. BOX 1810 -1810 E. HAZELTON AVENUE STOCKTON, CALIFORNIA 95201 (209) 488-3000 FAX (209) 488-2999 www.sjgovorg/pubworks SUBJECT: INCREASE OF CORRECTIVE ACTION, CORRAL HOLLOW SANITARY LANDFILL Dear Mr. Del Frate: This letter is in response to your letter of December 7, 2006, regarding the continued detections at our impacted shallow aquifer monitoring well MW -5 of volatile organic compounds (VOCs), apparently from landfill gas. It seems clear that increased corrective action is needed, and we discussed over the phone the approach that we contemplate: increasing LFG collection along the edge of the landfill near the impacted well, coordinated with the planned extension of the closure cap in that area. As you noted, Section 20430 0) of Title 27 CCR is the correct section for a site where corrective action is not as effective as hoped. I think it important that this site is in corrective action, rather than in detection monitoring where discovering a new release requires assessing the "extent of release". Rather than that time-consuming activity, which may bear little fruit, I propose that we go directly to additional corrective action. VOCs in the groundwater have gradually decreased after the start of operation of the LFG system. Ten VOCs were seen with a maximum concentration of 9.2 ppb were reported in the quarterly groundwater monitoring at MW -5 immediately before the operation of the LFG system (October 2001). In contrast, only five VOCs were reported in the most recent quarterly monitoring (October 2006) with a maximum concentration of 7.4 ppb. The dramatic decrease in combustible gas seen in the perimeter migration monitoring wells (see Results of Corrective Action, Corral Hollow Sanitary Landfill Landfill Gas Collection System, September 27, 2002). Let me know if you need a copy of this report. Unfortunately, certain VOCs remain consistently and repeatedly detected, so it is appropriate to enhance the corrective action effort to increase the effectiveness of corrective action. I believe the difficulty in collecting LFG from the aquifer near MW -5 area is due to the thinness of refuse at the landfill's edge and distance from the landfill's edge to the LFG wells. It seems likely that some LFG is not being collected from that outlying area, in spite of the significant collection effort applied, and that this gas continues to impact groundwater of the shallow aquifer. The LFG system is now being operated at near -maximum withdrawal, with many wells showing methane content below 10%, so it would be unwise for us to further increase collection from this system. The solution is to increase the level of LFG collection in that area by other means.