SITE INFORMATION AND CORRESPONDENCE FILE 2

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West Clay Properties Page 2 639 West Clay Street May 19, 2009 Stockton, California 95206 2004, ranged between less than 50 and 200 pg/L from May 2004 to July 2006, ranged from 240 to 300 gg/L from October 2006 and September 2008 — with the exception of April 2007 (less than 50gg/L), and ranged from 820 to 700 pg/L between December 2008 and March 2009. The EHD believes additional monitoring wells are needed to delineate the lateral extent of groundwater contamination down-gradient of MW-14B. AGE has recommended installation of additional ozone sparge points east of the northern "cluster UST" area. The EHD has reviewed the analytical data for groundwater samples collected from MW-9, MW-10, and EW-1 since the ozone system went online in November 2006 and can not easily discern that ozone remediation has had a significant impact in reducing concentrations for chemicals of concern; therefore,the EHD will not support expanding the ozone system at this time. The EHD concurs with AGE that a monitoring well is needed east of MW-1. Furthermore, the EHD believes additional monitoring wells are needed northeast of B 15 and north of MW-8B, each screened within the same hydrological units as MW-1 and MW-2 (approximately forty to sixty feet bsg) to delineate the lateral extent of groundwater contamination down gradient of the source area. To address groundwater contamination within hydrogeologic unit HU2 near the "UST No. 3" area, a feasibility study is needed to identify a remedial technology, or combination of technologies, capable of mitigating petroleum hydrocarbon contamination in groundwater. Please submit estimates of the residual TPH-g, TPH-d, and benzene masses currently in soil and groundwater within the southern "UST No. 3" area, and TPH-g, MTBE, and benzene currently remaining in soil and groundwater within the "cluster UST" area. Also submit laboratory reports for soil samples collected during the removal of USTs: TK1, TK2, TK4, and the dispenser in December 1998; and provide boring logs for reinstalled extraction well EW-1, extraction well EW-2, and air sparge well AS-1 since the EHD does not have this information on file. Submit a work plan for well installations, feasibility study for the "UST No. 3" area, mass estimates, laboratory reports, and boring logs to the EHD by August 20, 2009. Please contact Vicki McCartney at(209)468-9852, or by email at vmccartney(csjcehd.com if you have any questions. Sincerely, Victoria L. McCartney,=REHS Nuel C. Henderson,Jr., PG Senior Registered Envirental Health Spe ialist Engineering Geologist c: Mr. William R. Little, PG, Advanced GeoEnvironmental, Inc., 837 Shaw Road, Stockton, California 95215 Mr. James L.L. Barton, PG, California Regional Water Quality Control Board Central Valley Region, 11020 Sun Center Drive, Suite 200, Rancho Cordova. California 95670