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WESTERN 1386 EAST BEAMER STREET 003 GEO-ENGINEERS WOODLAND CA 68-5 00, {530)668-5300, FAX(530)662-0273 REGISTERED GEOLOGISTS wege@cal.net Michael J. Infurna Jr. June 25, 2009 San Joaquin County Public Health-Services, Environmental Health Division 600 E. Main Street Stockton,CA. 95202 (209)468-3454 minfuma@sjg,ehd.com RE: Revision of sampling frequency for Sanchez Property, case number 1844, located at 1876 Country Club Blvd., Stockton, CA. Dear Mr. Infarna: Currently the above mentioned site is being remediated using groundwater pump and treatment from excavation well MW 10 with discharge of treated groundwater to the sanitary sewer. The current quarterly monitoring samples all wells (13) associated with this site for the analytes TPHg, BTEX, 5 Oxygenates along with 1,2 Dichloroethate(1,2 DCA) and 1,2 Dibromoethane (1,2 EDB). This sampling frequency with the above mentioned analysis is no longer necessary for the evaluation of the progress of the sites remediation and/or groundwater plume stability. The analytes TPHg and BTEX are currently detected in groundwater samples obtained from monitoring wells MW6A,MW8A and MW 10 (the-pumping well) and need further evaluation for reduction in concentration and the effects of the groundwater pumping system. The analyte MtBE is currently detected in groundwater samples obtained from monitoring wells MW2,MW4, MW6A, MW6B, MW8A,MW9A and MW 10 (the pumping well) and need further evaluation for reduction in concentration and the effects of the groundwater pumping system. Monitor wells MW3, MW5,MW7A, MW7B and MW9B have been below laboratory lower detection limits for all analytes tested for over 2 years. Western Geo-Engineers proposes the following sampling frequency with a reduction in wells sampled and analytes evaluated. Proposed sample frequency for the analysis of TPHg and BTEX should be reduced to semiannual for wells MW6A,MW8A and MW9A and annually for wells MW6B,MW8B and MW9B. 3