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BEENMs, Kay Huffman 28 March 1988 7 1WISSA5SoclA7Es PM, ;'✓ transport to the laboratory. Drilling equipment was steam cleaned prior to use and sampling equipment- was washed with trisodium phosphate between samplos to prevent possible crass-contamination, The OVA was used to qualitatively determine the presence or absence of volatiles in the samples. The subsurface lithoiogy and hydrogeologic characteristics, OVA survey results, and well construction are summarized below and d:.tailed on the boring logs in Attachment A. Moderate- to high-permeability sands interbedded with clay and silt worn encountered in all 4 borings, Boring B-4 was drilled to 0 ft below grade and borings 8-5, B-6, and B-7 were drilled to 39 ft below grade. Ground water was encountered at approximately 26 ft below grade and monitoring wells were constructed in all 4 borings. To accommodate seasonal changes in ground water elevations in accordance with San Joaquin County Local Health District r guidelines, monitoring well MW-4 is screened from 23 to 38 feet below grade, MW-5 from 22 to 37 feet below grade, MW-6 from 23 to 33 feet below eY-J�, and MW-7 from 24 to 34 ft below grade. The ground water monitoring wells were constructed with 4-inch-diameter, .020-inch slot, PVC well screen and blank casing. Number 3 Monterey sand was tremied into the annular space around the well screen to approximately 2 ft above the well screen. Two feet of bentonite pellets, hydVated with potable water, were used to separate the sand from the sanitary surface seal. To prevent unauthorized access, locking stovepipes and traffic-rated vaults were set over the monitoring wells. WELL DEVELOPMENT, SAMPLING AND SURVEYING The monitoring wells were developed on 3 and 4 February 1988, using a surge block and bailer. In addition, three wellbore volumes were removed from each of the monitoring wells prior to sampling with steam-cleaned teflon bailers. Development water was contained in trash cans and stored onsite pending the results of the chemical analyses. The monitoring well top-of-casing elevations were surveyed by R.W. Siegfried and Associates SSA) of Stockton. A benchmark relative to mean sea level (msI) was established by SA on the corner of Robinhood Drive and Pershing Avenue. Water levels were measured on 20 January 1988 and the data are shown in Figure 4 and Table 2, The ground water. gradient across the site is northeasterly. i CHEMICAL ANALYSES Soil samples were collected it approximatr.ly 5-ft intervals from each boring for possible chemical anal) -is and ground ,rater samples were collected from each monitoring well for znalysis, All samples were transported to Brown and Caldwell Analytical Laboratories of Emeryville, California (B&C) under chain of custody. The soil samples were analyzed for TFHC at a detection limit of 10 ppm and the ground water samples were analyzed for TFHC and BTX at detection limits of 1 ppm and 0.05 ppb, respectively. The chain-o'-custody �' forms, analytic reports, and quality assurance/quality control procedures for