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Project Quarterly Update Report July 30, 1991 9110 Thornton Road, Stockton, California Page 4 ' • Sampled groundwater from domestic wells 9036, 1927, 1912, 8968, 9140,'9156, and 9172 on April 29, May 27 and June 24, 1991 ' GROUNDWATER MONITORING ' Monitoring of the depth-to-water in the monitoring wells was conducted three times during this reporting period on April 24, May 27 and June 24, 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) Analysis of the groundwater monitoring data indicates that groundwater elevations have decreased ' across the site by about 0 2-0 3 feet in the monitoring wells during the period from March 28, 1991, to June 24, 1991 The average depth-to-groundwater across the site as of June 24, 1991, was approximately 47 4-feet below ground surface The calculated average groundwater-table elevation across the site as of June 24, 1991, was approximately 35 4-feet below mean sea level (msl) Since the groundwater monitoring wells were first monitored in May 1986, the local groundwater- table 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 I GROUNDWATER �f�n TECHNOLOGY, INC