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kn �� lir GROUND ZERO ANALYSIS, INC. Escal1714 Main Street Telephone e (209 8 8-98881927 o��nn Telephone {209)838-9888 Facsimile (209)838-9883 FEB 0 2 2005 January 31, 2005 ENVIRONMENT HEALTH PEPMIT/SERVICES Mr Harlin Knoll San Joaquin County Environmental Health Department 304 East Weber Avenue, Third Floor Stockton, CA 95202 ` Subject Fourth Quarter 2004 Groundwater Monitoring Report 7835 Thornton Road, Stockton, CA (APN#077-490-27) Dear Mr Knoll This report summarizes activities at the subject site during the fourth quarter 2004 The site location is presented on Figure 1 Activities conducted during the reporting period included monitoring depth to water in site wells, purging and sampling well MW5, and analyzing groundwater samples for benzene, toluene, ethylbenzene, total xylenes (BTEX), and total petroleum hydrocarbons as gasoline (TPHg) • GROUNDWATER MONITORING AND SAMPLING An experienced Ground Zero technician measured the depth to groundwater in wells MW 1, MW2, MW3, MW4, MW5, and MW9 on November 24, 2004 The depth to groundwater beneath the site ranged from 38 51 feet below the top of the well casing (btoc) in well MW3 to 40 15 feet btoc in well MW2 Groundwater elevations in site wells rose an average of 1 77 feet between September 17, 2004 and November 24, 2004 The water table beneath the site lies above the screened intervals in wells MW4 and MW5 Groundwater flow was generally toward the east-northeast with an average gradient of 0 0022 feet per foot (approximately 12 feet per mile) A potentiometric surface map for November 24, 2004 is presented on Figure 2 Monitoring well construction details are summarized in Table 1 Groundwater monitoring data is summarized in Table 2 A Ground Zero technician purged at least three well casing volumes of groundwater from monitoring well MW5 on November 24, 2004 Physical parameters (temperature, specific conductance, and pH) were measured and recorded during the purging process Groundwater samples were collected using a dedicated disposable bailer after physical parameters stabilized, and the water level recovered to at least 80% of the pre-purged level The samples were decanted into 40-ml glass vials preserved with a hydrochloric acid solution The samples were subsequently placed in an ice chest refrigerated to a temperature of approximately 4°C The samples were transported to Argon Laboratories (FLAP 42359) under chain of custody protocol and analyzed for TPHg and BTEX utilizing EPA methods 8015B and 8021B, respectively Purged groundwater was contained in a labeled 55-gallon drum pending disposal Copies of field purge Iogs and water level measurements are included in Attachment A G 1GROUNDZ81KNOWLES HAMIREP0RTSIQMR1200414QM2004 doc