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,a s SECOR www secorcorn INTERNATIONAL S E 1 NCORPORATED 3017 Kilgore Road Suite 100 ilmRwi PEQI-I} Rancho Cordova CA 95670 r� 916-861-0400 TEL n r'I!T (� r 916 861-0430 FAx i October 14, 2003 031J OCT l 7 PPS 1: 19 Ms Lori Duncan San Joaquin County Environmental Health Department 304 East Weber Avenue, Third Floor Stockton, California 95202-2708 RE Results of Water Level Monitoring ARCO Service Station No 595 6100 North Highway 99 Stockton, California SECOR Project No 77BP 50595 04 0336 Dear Ms Duncan On behalf of BP, SECOR International Inc (SECOR) submits this report to document the results of continuous monitoring of water levels in selected groundwater monitoring wells over a 7-day period at the site referenced above The purpose of this work was (1) to determine if the intermittent pumping of the on-site domestic well influences depth to water and hydraulic gradient within the shallow and deeper water bearing zones beneath the site, and (2) to investigate the validity of the July 2002 water level measurement in deep well DMW-2, which reported a water level that was • approximately 10 feet lower than water levels recorded in the other wells screened in the deeper water-bearing zone This work was conducted in accordance with SECOR's Work Plan For Monitonng Influence of On-Site Domestic Well dated February 19, 2003, which was approved by the San Joaquin County Department of Environmental Health Services (SJCEHD) in a letter dated February 28, 2003 (Attachment 1) DATA LOGGER INSTALLATION AND WATER LEVEL DATA EVALUATION On May 6, 2003, pressure transducers with built in data-loggers were installed in three groundwater monitoring wells screened in the shallow water-bearing zone (MW-1, MW-3, and MW-7) and in three groundwater monitoring wells screened in the deeper water-bearing zone (DMW-1 through DMW-3) The pressure transducers/data loggers were set in wells MW-1, MW-3, and MW-7 between approximately 3 feet to 4 5 feet below the measured depth to groundwater, and in deeper zone wells DMW-1 through DMW-3 between approximately 10 feet and 16 5 feet below the measured depth to water Each pressure transducer/data logger was programmed with the correct date and time, and to record water levels at 1-minute intervals over the 7-day monitoring period On May 12, 2003, the pressure transducers/data loggers were removed from the wells Following extraction, each pressure transducer/data logger was properly decontaminated with an alconox solution, and rinsed with water Field data sheets are included as Attachment 2 Water level data from each pressure transducer/data logger was uploaded onto the computer for evaluation Results of monitoring indicated that depth to groundwater in deep wells DMW-1 and DMW-3 fluctuated approximately 02 feet during the monitoring period Depth to groundwater in shallow wells MW-1 and MW-7 fluctuated over a 0 5-foot and 0 3-foot range, respectively Due to the volume of water level data acquired during the study (approximately 700 printed pages), water level data from each of the pressure transducers/data loggers is presented on a compact disc, which is included as Attachment 3 Between May 6, 2003 and May 11, 2003, depth to groundwater in shallow well MW-3 fluctuated ' within 0 3 feet Water levels within the well exhibited a notable 0 4-foot increase on May 8, 2003 € a� W,RC0105951Misc Letters\Aesults of Water Level Monitoring doe Yi