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Project Quarterly Update Report May 11, 1992 Southland, 9110 Thornton Road, Stockton, California 2 ■ Sampled groundwater from domestic welts 9036, 8968, 9140, 9156, 1927, and 9172 (Ivy Motel) on January 30, 1992 ' a Sampled groundwater from domestic wells 1912, 8968, 9140, 9036, 9156, and 9172 on February 24 and March 30, 1992 2.1 Groundwater Monitoring IThe depth to water In the monitoring wells was monitored three times during this reporting period, on January 30, February 24, and March 30, 1992 The monitoring data are presented in Table 1 Groundwater monitoring was performed according to Groundwater Technology standard operating procedures (Appendix A) Analysis of the groundwater monitoring data indicates that groundwater elevations have increased across the site by about 1 02 feet in the monitoring wells from January 30, 1992, to March 30, 1992 fThe calculated average groundwater elevation across the site as of March 30, 1992, was 33 81 feet below mean sea level (msl) The average depth to groundwater_across the site as of March 30, ) `1992, was 45 74 feet below-ground surface I 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 I 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 at the rear of the 7-Eleven Store This leaking water pipe was repaired and the mounding condition was corrected I According to the National Weather Service local climate data for the Stockton area, below-normal annual precipitation has been recorded for the past five 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-elevated groundwater level at the beginning of the Imonitoring period GROUNDWATER .---TECHNOLOGY, INC I