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c Q WIN THOMAS R.FLINN P.O.BOX 1810-1810 L HAZELTON AVE=NUE DIRECTOR STOCKTON,CALIFORNIA 98201 is M .1 (209)468-3000 FAX(209)468-2999 —Agov.org THOMAS M.GAU DEPUTY DIRECTOR MANUEL SOLORIO Weddrig tOrYOU DEPUTY DIRECTOR STEVEN WINKLER DEPUTY DIRECTOR ROGER JANES BUSINESS ADMINISTRATOR January 30, 2007 Mr. Todd Del Frate California Regional Water Quality Control Board Central Valley Region 11020 Sun Center Drive, #200 Rancho Cordova, California 95670-6114 SUBJECT: SECOND SEMESTER AND ANNUAL 2006 GROUNDWATER AND SURFACE WATER MONITORING REPORT; FOOTHILL SANITARY LANDFILL Dear Mr. Del Frate: i Enclosed is the Second Semester and Annual 2006 Monitoring Report for the Foothill Sanitary Landfill. Field and monitoring parameters are below established concentration limits for all wells except MW-3 (the impacted well) where the concentration of Chloride (10 mg/L) slightly exceeded the concentration limit calculated by Sanitas (9.9 mg/L). We believe that this exceedence is within the limit of accuracy of that calculation. This concentration is well below drinking water standards (California DHS), and therefore not a detriment to the use of the groundwater. However, we will examine the next analysis with interest. Groundwater monitoring continues on a semi-annual basis in accordance with our WDRs. VOCs were not detected in groundwater samples except at MW-3, where one VOC (Trichloroethene) was reported at trace concentration (less than 0.2 ppb). The detection is inconsistent and non-repeating, and this compound has not been reported at this well for over five years. We do not expect to see it next semester. If the landfill was in Detection Monitoring, then this reported trace concentration would not trigger a retest or Evaluation Monitoring. Impact by VOCs (consistent, repeated detections) is not indicated in any well since cessation of i impact in October 2002. Groundwater data from this site, the other three County-owned sites, and other non-County sites, shows that such non-repeating, inconsistent reports often occur, and do not indicate a release from the Unit. I suspect you also see this phenomenon at other sites. As you know, this impact was caused by temporary ponding at the edge of the refuse fill adjacent to MW-3 in the late 1990's. Corrective action (grading to prevent future ponding) is apparently successful. VOCs were detected in all soil gas samples, mostly in low concentrations. I believe that this shows that the corrective action taken to eliminate ponding at the edge of the landfill adjacent to MW-3 was effective. The data also shows that soil VOCs at these concentrations beneath our property does not threaten groundwater. Soil gas VOC monitoring continues on a semi-annual basis, in accordance with the WDRs.