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baa J Second Quarter 1993 Monitoring and Sampling Report July 15, 1993 Southland Site No. 20304, 455 Grant Line Rd., Tracy, CA 2 GROUNDWATER MONITORING DATA Groundwater monitoring was performed on June 17, 1993. Before monitoring, the wellcaps were opened to allow the water In each well to stabilize to atmospheric pressure. The DTW and the depth to separate-phase hydrocarbons were measured to the nearest 0.01 foot from the top of the well casing using an ORS Environmental Equipment INTERFACE PROBE Well Monitoring System. Attachment 2 Includes Groundwater Technology's Standard Operating Procedures for groundwater monitoring. Separate-phase hydrocarbons were not detected In any of the monitoring wells. The water-table i elevations calculated from the June 17, 1993, monitoring data were used to prepare a potentiometric surface map (Figure 2). Wells MW-9 and MW-10 are screened into a shallow or perched water- bearing zone. Because wells MW-9 and MW-10 have repeatedly shown groundwater elevations different from those in the surrounding wells, they were not used to calculate the potentiometric groundwater surface. Data from monitoring well MW-11 Indicated an anomalous groundwater elevation and therefore was not used to calculate the potentiometric groundwater surface. The -- potentiometric surface elevation, as measured In the groundwater monftoring wells, decreased an average of 1.0 foot since the previous quarter monitoring event. The groundwater flow direction Is • toward the north-northeast with a hydraulic gradient of approximately 0.004 to 0.008 foot per foot (ft/ft). The historical and current water-level measurements are presented in Attachment 3, Table 1. MONITORING WELL SAMPLING AND ANALYTICAL RESULTS On June 17, 1993, groundwater samples were collected from 12 monitoring wells (MW-1 through MW-6, MW-8 through MW-12, and MW-15). Monitoring well MW-13 and MW-14 are sampled on an annual (December) basis because historically the analytical results have reported petroleum hydrocarbon concentrations below the method detection limits. Before sampling, at least 4 well- casing volumes of groundwater were removed from each of the monitoring wells unless the wells were purged dry. Field measurements of temperature, conductivity, and pH were recorded during well purging (Attachment 4). The groundwater samples were collected using a Teflon® sampler and placed In analyses-specific sample containers with analyses-specific preservatives. The samples were then sealed and labeled with the Job Identification number, the sample number, date, time, and type of laboratory analysis required. The samples were stored on ice and transported under chain- of custody protocol to GTEL Environmental Laboratories, Inc. In Concord, California. 37678043.020 GROUNDWATER TECHNOLOGY, INC.