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Interim Investigation Report June 21, 1996 Chapin Brothers Automotive Stockton, California A-3.0 FIELD METHODS FOR WELL DEVELOPMENT AND SAMPLING The following sections summarize field methods used in association with the development of the wells and collection of groundwater samples at the site Development Monitoring well MW5 was developed by surging with a vented surge block and pumping The ' well were purged of over 40 gallons Subjective Inspection Prior to purging or sampling, the wellheads were inspected and found to be in good condition A tdisposable plastic bailer was lowered to the groundwater surface, retrieved, and inspected for floating product or other subjective evidence of contamination No floating product was present An electronic ' water level indicator was used to measure the depth to groundwater and the total depth of each well relative to a surveyed mark on the wellhead The thickness of the water column was then used to calculate the volume of water in the well and thus to arrive at a calculated minimum purge volume M Well Purging collection each well was purged using a 1 5-inch-diameter, decontaminated, Prior to samplep g g e submersible electric pump The volumes purged correspond to a minimum of three well volumes (casing and gravel pack volume) Table 3 lists the date of sampling, well casing elevation, depth to water, groundwater elevation, and product thickness for each well for this monitoring cycle and all known previous sampling events Field parameters of pH, temperature and electric conductivity were measured using a field instrument during purging of each well and are presented on Table 1 Groundwater Sampling ' Following purging, each monitoring well was allowed to recover to greater than 90% of the original well volume Each monitoring well was sampled using a 1 5-in-diameter, disposable polyethylene bailer lowered approximately a third of the way through the groundwater surface in the well Groundwater samples were then transferred into two sterilized 40-m1 glass vials equipped with Teflon ' septa Each vial was checked to ensure that no air bubbles were entrapped, and then each sample container was immediately labeled, placed into an ice chest kept at 4°C using ice, and logged on a chain- of-custody form The samples were transferred the following day into the custody of a courier employed by Sparger Technology Analytical Laboratories LUSH GEosciENCEs