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GROUND ZERO ANALYSIS, INC. 1714 Main Street Escalon,California 95320-1927 Telephone (209)838-9888 Facsimile (209)838-9883 April 27, 2006 Mr Harlin Knoll San Joaquin County Environmental Health Department 304 East Weber Avenue, Third Floor Stockton, CA 95202 Subject First Quarter 2006 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 first quarter 2006 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 sample 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 MW1, MW2, MW3, MW4, MW5, and MW9 on February 21, 2006 The depth to groundwater beneath the site ranged from 34 30 feet below the top of the well casing (btoc) in well MW3 to 35 96 feet btoc in well MW2 Groundwater elevations in site wells rose an average of 2 88 feet between November 22, 2005 and February 21, 2006 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 February 21, 2006 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 February 21, 2006 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 the pre-purged levels The samples were decanted into 40-m1 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 #2359) 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 logs and water level measurements are included in Attachment A 6 1GROUNDZE1KNOWLEs 11AM1REP0RMQMR1200611QM2006 doc