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Project Quarterly Update Report May 1, 1991 i 9110 Thornton Road, Stockton, California Page 6 1 According to National Weather Service local climatological data for the Stockton area, below-normal ' annual precipitation has been recorded for the past five years However, in 1982 and 1983, just prior to this 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 monitoring period ' During this reporting period, twelve groundwater-monitoring wells could not be monitored or sampled A ' prolonged decline In water level has caused monitoring wells MW-2, MW-3, MW-4, MW-5, MW-8, MW-10, and pumping wells PW2 and PW3 to go dry Monitoring wells MW-6 and MW-12 are also no longer In service 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 1 ' Ther n G ou dwater Gradient Maps for February and March 1991 (Figures 4 and 5) represent the Interpreted groundwater-table elevations beneath the site for each of the last two months of this reporting period The regional groundwater-gradient direction remains to the east as previously ' reported The gradient magnitude was found to be approximately 0 002 foot-per-foot (ft/ft) for both months ' During this reporting period, no petroleum product odors or separate-phase hydrocarbons were found in any of the monitoring wells or pumping wells GROUNDWATER SAMPLING AND ANALYSES Sampling of the operational groundwater monitoring wells (I e , wells which contained enough water to g sample) was performed once during this reporting period on February 21, 1991 Samples were collected in accordance with Groundwater Technology's SOPS 9, 10, 11, and 12 (Appendix B) Groundwater I sampling was conducted by first purging water from each well using a clean polyvinyl chloride (PVC) baler. Each well was purged of a minimum of four well volumes of water by hand bailing, unless the wells could be purged dry The groundwater was then allowed to recover to at least 80 percent of the original static water level prior to sampling The groundwater samples were obtained using a U S Environmental Protection Agency (EPA)-approved Teflon R sampler B E C�f -i GROLRIDHATE[tI TECHKOLOGl INC