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I I 1 GROUND ZERO ANALYSIS, INC. 1714 Main Street Escalon,California 95320-1927 Telephone (209)838-9888 i Facsimile (209)838-9883 October 4, 2004 � PVV Mr Harlin Knoll San Joaquin County Environmental Health Department \\A11304 East Weber Avenue, Third Floor Stockton, CA 95202 Subject Third 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 third quarter 2004 The site location is presented on Figure I 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 MW1, MW2, MW3, MW4, MW5, and MW9 on September 17, 2004 The depth to groundwater beneath the site ranged from 40 34 feet below the top of the well casing (btoc) in well MW3 to 41 85 feet btoc in well MW2 Groundwater elevations in site wells fell an average of 4 24 feet between May 12, 2003 and September 17, 2004 The water table beneath the site lies above the screened intervals in wells MW4 and MW5, although the purging of well MW5 caused the water level in that well to fall to within the screened interval at the time the sample was collected from the well Groundwater flow was generally toward the northeast with an average gradient of 0 0027 (approximately 14 feet per mile) A potentiometric surface map for September 17, 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 MWS on September 17, 2004 Physical parameters (temperature, specific conductance, pH and turbidity) were measured and recorded during the purging process All downhole equipment was decontaminated prior to and between each use by washing with a solution of laboratory-grade detergent and then double- rinsing with water Groundwater samples were collected using dedicated disposable bailers after physical parameters stabilized, and water levels recovered to at least 95% of 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 802113, respectively Purged G 1GROUNDZEIKNOWLES HAMIREPORTSIQMR1200413QM2004 doc