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(s] u Second Quarter 1993 Monitoring and Sampling Report July 15, 1993 �f Southland Site No. 20304, 455 Grant Une Rd., Tracy, CA 3 • The groundwater samples were analyzed for BTEX and TPH-G using EPA Methods 8024/8015. The analytical results reported that dissolved BTEX and TPH-G concentrations were detected in the groundwater samples collected from monitoring wells MW-1, MW-8, MW-9, and MW-10. The highest concentrations of benzene (16,000 parts per billion [ppb]) and TPH-G (48,000 ppb) were detected in the groundwater samples collected from well MW-10. Figure 3 Illustrates the distribution of benzene and TPH-G concentrations. Review of the historical data shows that the BTEX and TPH-G concentrations aerial distribution and magnitude detected in the samples collected during the June 17, 1993, sampling event are within the same order of magnitude as previous results. Table 1 summarizes the analytical results of this sampling event and the historical analytical data. The laboratory analytical reports and the chain-of-custody records for the June 17, 1993, samples are included in Attachment 5. EXTRACTION WELL. INSTALLATION On May 11, 1993, Groundwater Technology installed an 8-Inch-diameter extraction well. The details and results of the Installation were presented In our Extraction Well Installation Report dated June 7, - 1993. The scope of work (outlined in our Work Plan for Groundwater Extraction Well Installation, dated March 15, 1993) consisted of Installing one 8-inch-diameter extraction well (GWE-1) to a depth • of 30 feet. This well will be used to gain hydraulic control (containment) of the identified dissolved petroleum hydrocarbon plume through proposed groundwater extraction and treatment (see Groundwater Technology's Remedial Action Plan, Addendum No. 2, dated April 30, 1993, for details of proposed remedial activities). During the June 17, 1993, monitoring and sampling event, limited access to the extraction well prevented data acquisition from the well. CONCLUSIONS AND RECOMMENDATIONS The anomalous groundwater elevations In wells MW-9 and MW-10 may be caused by the shallower screening interval used in these two wells. The anomalous groundwater elevation measured In well MWA I may be because of changes in subsurface lithologies and/or manufactured conduits affecting groundwater elevations. The groundwater monitoring wells and extraction well will be surveyed during the next quarter. The potentiometric surface elevation as measured in the ground- water monitoring wells decreased an average of 1.0 foot since the previous quarter monitoring event. The overall trend of the groundwater gradient is toward the northeast at 0.003 ft/ft. Based on the groundwater monitoring and analytical data collected to date, Groundwater Technology recommends that quarterly monitoring continue during 1993. Permitting and design for a soil and groundwater remediation system is currently being conducted. Groundwater Technology expects to submit the design package to the City of Tracy Community Development Department, Planning Division for review and approval In late August 1993. 37678043,020 GROUNDWATER TECHNOLOGY,INC.