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ri1 . GROUND ZERO ANALYSIS, INC. 1714 Main Street Escalon,California 95320-1927 Telephone (209)838-9888 Facsimile (209)838-9883 April 27, 2004 Mr Harlin Knoll San Joaquin County Environmental Health Department 304 East Weber Avenue, Third Floor Stockton, CA 95202 Subject First Quarter 2004 Groundwater Monitoring Report Knowles Property, 1140 W Hammer Lane, Stockton, CA Dear Mr Knoll This report summarizes activities at the subject site during the first 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 wells MW1, MW3, MW4, MW5, and MW9, 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 February 19, 2004 The depth to groundwater beneath the site ranged from 35 55 feet below the top of the well casing (btoc) in well MW3 to 37 20 feet btoc in well MW2 Groundwater elevations in site wells rose an average of 3 22 feet between November 12, 2003 and February 19, 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 0017 (approximately 9 feet per mile) A potentiometric surface map for February 19, 2004 is presented on Figure 2 Monitoring well construction details are summarized in Table 1 Groundwater monitoring data are summarized in Table 2 A Ground Zero technician purged at least three well casing volumes of groundwater from monitoring wells MWI, MW3, MW4, MW5, and MW9 on February 19, 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 80% of pre-purged levels The samples were decanted into 40-m1 glass vials preserved with 1 1 • hydrochloric acid solution The samples were subsequently placed in an ice chest refrigerated to a temperature of approximately 4°C G IGROUNDZHIKN0WLES HAMIREP0RTSIQMR1200411 QM2004 doc