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' Project Quarterly Update Report--Revision i December 30, 1991 9110 Thornton Road, Stockton, Cal ifornla. Page 4 • Sampled groundwater from domestic wells 9036, 1927, 1912, 8968, 9140, 9156, and 9172 on August 9, August 26 and September 26, 1991. Domestic wells 9147 and 9149 ' were also sampled on August 9; and domestic well 9172 was sampled on September 12 In addition to the three other sampling dates. ' GROUNDWATER MONITORING Monitoring of the depth-to-water in the monitoring wells was conducted three times during this reporting period on July 29, August 26 and September 26 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 1.91 feet in the monitoring wells during the period from June 24, 1991, to September 26, 1991. The calculated average groundwater-table elevation across the site as of September 26, 1991, was approximately 36.94-feet below mean sea level (msi). The average depth-to- groundwater epthto-groundwater across the site as of September 26, 1991, was approximately 48.89-feet below ground surface. Since the groundwater levels were first monitored In May 1986, the local groundwater-table elevation has ' fluctuated seasonally, but has declined steadily overall. The seasonal and overall 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, because of 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 ' TECHNOLOGY, INC.