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.410 Califon Regional Water Quality C "rol Board <br />Central Valley Region <br />Karl E. Longley, ScD, P.E., Chair <br />' ;nda S. Adams <br />?cre tory for <br />_nvrronmental <br />Protection <br />Arnold <br />Schwarzenegger <br />Governor <br />Sacramento Main Office <br />11020 Sun Center Drive #200, Rancho Cordova, California 95670-6114 --,=-11-1 <br />Phone (916) 464-3291 • FAX (916) 464-4645 <br />http://www.waterboards.ca.govicentralvalley JUL <br />0 2007 <br />24 July 2007 <br />Ms. Donna Sartini-Gardner <br />1206W. Struck Ave. <br />Orange, CA 92867 <br />EN VI f-3 HEWN " <br />Mr. Ronald Jr. and Ms. Bonnie Barber <br />10411 Small Rd. <br />Manteca, CA 95336 <br />DOCUMENT REVIEW, DONNA GARDNER PROPERTY, 26056 N. THORNTON ROAD, <br />THORNTON, SAN JOAQUIN COUNTY (REGIONAL BOARD CASE # 390412) <br />i reviewed the Quarterly Report — Second Quarter 2007 (Report) submitted on 20 July 2007 by <br />your consultant Advanced GeoEnvironmental Inc. (AGE). The Report contains the results of <br />April 2007 groundwater monitoring event and AGE's recommendation to reduce the frequency <br />of groundwater monitoring for monitoring wells MW-1, -2, -5, and —6 from quarterly to annual <br />sampling and analyses with quarterly water level measurements. <br />Depth to water varied from 9 to 14 feet below ground surface. Groundwater flow direction has <br />varied over the last three quarters from northwest to northeast. Historically, wells MW-2, <br />MW-3 and MW-4 (enclosed Figure 2) have been impacted by petroleum hydrocarbons. <br />MW-2 analyses have been non-detect for all constituents since December 1995, while MW-3 <br />analyses have been non-detect since October 2005. MW-1, -5, and —6 have not reported <br />impacts from petroleum hydrocarbons since installation in 1990-91. <br />After three consecutive rounds of quarterly monitoring (consistent with historical data from <br />1991 through 2002), monitoring well MW-4 groundwater analyses continue to report petroleum <br />hydrocarbons: Total Petroleum Hydrocarbons as gasoline, 300 micrograms per Liter (ug/L); <br />Toluene, 5.6 ug/L; Ethylbenzene, 2.4 ug/L; and Xylenes, 2.7 ug/L. MW-4 is located in close <br />proximity to Thornton Municipal Supply Well #2 (Well #2 is less than 50 feet north and <br />downgradient of MW-4). Well #2 was also sampled during the second quarter of 2007; <br />analytical results were non-detect for all constituents (consistent with historical data from 1991 <br />to 2002). <br />A report of an additional investigation to determine whether shallow groundwater near MW-4 is <br />influenced by Well #2 during pumping (in lieu of drilling deeper for vertical definition next to the <br />MW-4 and Well #2), was originally requested by 1 April 2007 and delayed to collect additional <br />data. It is my understanding from conversations with AGE that the additional investigation <br />report is nearly complete, and is now due 24 August 2007. <br />California Environmental Protection Agency <br />Zc2j' Recycled Paper