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WM. J. Hunter & Associates - 2220 Loma Vista Dr Registered Geologists Sacramento, CA 95825 .Petroleum &Mineral Appraisers (916) 972-7941 FAX (916) 972-1683 r , r April 28, 1998 Margaret Largorio, Supervising RENS Site Mitigation Unit San Joaquin County PHS Environmental Health Division 304 East Weber Ave , Third Floor Stockton, CA 95202 RE: FIRST QUARTER 1998 GROUNDWATER MONITORING REPORT FOR 2969 LOOMIS ROAD, STOCKTON, CA. SITE CODE 2015 This report covers the results of the work done on March 30, 1998 by DelTech Geo- Technical Support Services as directed by our office and witnessed by a representative of the San Joaquin County EHS The report includes a map showing the potentiometric surface based upon the latest work, gradient directions since work began, a summary of all water analyses since initiation of the project, DelTech field notes, custody chains, and copies of the laboratory analyses The depth to water was measured in all four wells, but as instructed by the San Joaquin Co EHD, only MW-1 & MW-4 were sampled . The approximate potentiometric surface is shown on PLATE 1. The hydraulic gradient is very low, about 0005'/ft (2 64' per mile,) and the direction is indeterminate The water table has risen an average of 4 73' since the December, 1997 sampling event, the highest level since monitoring began There appears to be a slight depression in the area of MW-1 &MW-4, which might explain the relatively high levels of TPHd encountered A review of PLATE H shows that the gradient has been highly divergent at this location, with no predominant direction of flow This supports our previous conclusions that there is little or no horizontal communication between this site and other aquifers in the area TABLE A summarizes the results of all water analyses since initiation of the project BTEX& TPHg were below detection levels in MW-1, TEPH as diesel measured 0.435 mg/L This is about 3 times higher than recorded in December, 1997 - 0.151 mg/L However, the levels of TPHd in MW-4 dropped from 22 mg/L in December to 11.5 mgfL in March BTEX& TPHg were not detected in MW-4, however, the detection limits had be raised due the high concentration of TEPH, and those results may not be 1 valid I' CONCLUSION: The data continues to show a very limited aquifer at this location The contamination is restricted to a very small area beneath the removed tanks, and there is no evidence of . extensive lateral movement The amount of gasoline components measured at this site have been extremely low to non-detect Although TEPH as diesel is present at detectable 1