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THOMAS R.FUNN P.O.BOX 1810-1810 E.HAZELTON AVENUE DIRECTOR STOCKTON,CALIFORNIA 95201 Yt �r• e (209)468-3000 FAX(209)468-2999 a www.sj9ov.org/pubworks THOMAS M.GAU ' CHIEF DEPUTY DIRECTOR MANUEL SOLORIO Wodftg fat YOU DEPUTY DIRECTOR STEVEN WINKLER DEPUTY DIRECTOR ROGER JAMS BUSINESS ADMINISTRATOR July 21, 2008 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 2008 GROUNDWATER AND SURFACE WATER MONITORING REPORT; FOOTHILL SANITARY LANDFILL Dear Mr. Del Frate: Enclosed is the First Semester 2008 Monitoring Report for the Foothill Sanitary Landfill. Groundwater monitoring continues on a semi-annual basis in accordance with our WDRs. Wells MW-4 and MW-5 have been sampled twice since installation. The data from these wells show concentration limit exceedence for sulfate, but with so little data, we hesitate to draw a conclusion. It may be appropriate to use intra-well statistical evaluation for these wells due to their distance from the landfill and from the other three wells. Four of the five wells, including the upgradient well W-4, show modest concentration limit exceedences for bicarbonate. Because the upgradient well MW-4 shows this feature, we do not believe that the results of the analysis are due to landfill activity. Bicarbonate concentration has historically been greater in this quarter. We will inspect the next quarter's data carefully to assess any trend. A trace concentration of one organophosphate (Guthion)was reported at well MW-5. This compound was not detected in the previous monitoring event or in any other well. A trace concentration of a different organophosphate (Fensulfothion) was reported at this well last quarter, but not this quarter. Inconsistent, non-repeating reports of trace concentrations usually are the result of the very low detection limits (below 0.2 ppb in this case) available in a laboratory that also processes samples from other sources with concentrations much higher than the detection limit. The great distance of this well from the landfill also makes it unlikely that these results are caused by the landfill. However, the County will continue to analyze all wells for organophosphates, and we will be interested to see the results of the third quarter's analysis from this well. Other results are unremarkable. All groundwater wells are free of VOCs; laboratory contamination with Acetone was not apparent this quarter. Surface water was not available for sampling this semester.