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' Project Quarterly Update Report July 28, 1992 Southland, 9110 Thornton Road, Stockton, California 2 Analysis of the groundwater monitoring data Indicates that groundwater elevations have decreased across the site by about 152 feet in the monitoring wells from March 30, 1992 to June 29, 1992 The calculated average groundwater elevation across the site as of June 29, 1992, was 35 33 feet below mean sea level (msl) The average depth to groundwater across the site as of June 29, 1992, was 47 26 feet below ground surface Since the groundwater levels were first monitored In May 1986, the local groundwater elevation has fluctuated seasonally, but has declined steadily 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 well MW-9, which ' reflected a mounding of the groundwater surface from November 1988 to April 1989 because of a leaking water pipe behind the 7-Eleven Store This leaking water pipe was repaired and the mounding condition was corrected According to the National Weather Service local climate data for the Stockton area, below-normal annual precipitation has been recorded for the past fire years However, In 1982 and 1983, before the current drought period, annual precipitation was almost twice normal Therefore, the magnitude ' of the decline in the groundwater-table elevation may be in response to the prolonged drought conditions occurring after an abnormally-levated groundwater level at the beginning of the monitoring period During this reporting period, the following groundwater monitoring wells could not be monitored on ' the specked dates because they were dry ' ■ Wells MW-2, MW-3, MWA MW-5, MW-10 and PW-2 on June 29, 1992 Additionally, monitoring wells MW-6 and MW-12 are no longer in service and monitoring wells MW-11 ' and MW-14 were not monitored or sampled at Southland's direction The well completion data and ` current status of the monitoring wells at the site are summarized on Table 2 A potentiometric surface map (Figure 4) was prepared using monitoring data collected on June 29, ' 1992 Figure 4 shows a groundwater flow direction to the east with a gradient of approximately 0 003 foot per foot GROUNDWATER JECHNOLOGY, INC I