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Wm. J. Hunter & Associates 2220 Loma Vista Dr Registered Geologists Sacramento, CA 95825 Petroleum & Mineral Appraisers -- (916) 972-7941 ffl:�h San trim FAX (916) 972-1683 March 9 1996 REL;VRI) MAR 2 2 9996 Michael Infurna, Sr REHS ENVIRONMENTAL HEALTH San Joaquin County PHS PFRMfT/SERVICES Environmental Health Division 445 No San Joaquin Street Stockton, CA 95202 Ref FIRST QUARTER, 1996, GROUNDWATER MONITORING REPORT, 1876 Country Club Drive, Stockton; Site Code 1844 Dear Mr Infurna; We are enclosing the results of the tenth groundwater measure- ments, sampling & laboratory results done on February 1, 1996, covering the above property. Included are copies of the field logs made by Del-Tech, a table summarizing sampling results, laboratory reports, a site map showing the pieziometrzc surface based on the 2/1/96 data, including directions of all of the hydraulic gradients measured to date We have also maps showing lines of equal concentrations of benzene, ethylbenzene, toluene, xylene & TPHg based on the most recent data A review of this work is discussed below 1 The water table was measured at an average depth of 18 38 ' bgl, (-14 .22 ' msl, ) a drop of slightly over 1 ' since the December sampling. The average maximum change in groundwater elevation has been 3 . 821 since monitoring began. The lowest average depth was recorded at 22 201 bgl in January, 1994 , the highest was the latest event, February, 1996, at 18 38 ' bgl 2 The hydraulic gradient as calculated from the latest event , (shown on PLATE I, ) indicates a change in direction and slope near MW-2 & MW-3 . From MW-2 & MW--3 north, the slope is very flat, at about . 141 /1001 . From those two wells south, the slope increases to 3 .21 /1001 . This is the first time that such a complete reversal in the potentiometric surface has been observed. Although the gradients have varied widely as shown on PLATE 1, the direction generally was consistent from well to well We do not have an explanation for this event 3 A summary of all laboratory results of water samples taken since monitoring began is shown on TABLE I That data shows MW-1 continues to have the highest levels of BTEX & TPH--G, MW-3 has the second highest, and MW-2 the lowest This ratio has remained consistent since monitoring began MW-4 & MW-5 revealed minor amounts of BTEX from the December, 1995 sampling apparently caused by contamination from the baler blanks It is not known whether the contamination was a result of water used for cleaning 1