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Project Quarterly Update Report May 1, 1991 9110 Thornton Road, Stockton, California Page 4 • Sampled groundwater from domestic wells TMG, 1912, 1927, 8968, 9140, 9156, and 9172 on February 21, and March 28, 1991 • Due to contract negotiations between Groundwater Technology and the Southland Corporation, monitoring and sampling activities were not conducted during the month of January 1991 GROUNDWATER MONITORING Monitoring of the depth-to-water to the monitoring wells was conducted twice during this reporting period, on February 21 and March 28, 1991 The monitoring data are presented In Appendix A Groundwater monitoring was performed in accordance with Groundwater Technology Standard Operating Procedure (SOP) 8 (Appendix B) lie Analysis of the groundwater monitoring data indicates that groundwater elevations have increased by about 1 7-feet in the monitoring wells during the period from December 28, 1990, to March 28, 1991 This increase in water level elevations is most likely due to recharge associated with the precipitation received during this reporting period The depth-to-groundwater at the site as of March 28, 1991, was approximately 471-feet below ground surface The calculated groundwater-table elevation as of March 28, 1991, was approximately 35 2-feet below mean sea level (msl) Since the groundwater monitoring wells were first monitored in May 1986, the local groundwater-table I elevation has fluctuated seasonally, but has declined steadily overall The decline in the groundwater levels is depicted in the hydrographs for monitoring wells MW-7, MW-8, and MW-9 (Figure 3) Monitoring wells MW-7 and MW-8 are representative of the majority of the wells at the site The one exception to the general water-level decline was the data from MW-9 which reflected a mounding of the groundwater surface between November 1988 and April 1988, due to a leaking water pipe at the rear of the 7-Eleven Store This leaking water pipe was repaired and the mounding condition was corrected GROLNDWATER 'n;CHNOLOGI INC