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Wm. J. Hunter & Associates 2220 Loma Vista Dr <br /> Registered Geologists Sacramento, CA 95825 <br /> Petroleum & Mineral Appraisers (916)972-7941 <br /> Dig a FAX (916)972-1683 <br /> February 10, 1997 <br /> FEB 13 1997 <br /> Michael Infurna, Sr. REHS <br /> San Joaquin County PHS ENVIRONMENTAL�Z➢vIHES� <br /> Environmental Health Division <br /> P.0 Box 388 <br /> Stockton, CA 95201-0388 <br /> Ref . FOURTH QUARTER, 1996, GROUNDWATER MONITORING REPORT; 1876 <br /> ' Country Club Drive, Stockton; Site Code 1844 <br /> Dear Mr. Infurna, <br /> tWe are enclosing the results of the twelfth groundwater measure- <br /> ments, sampling & laboratory results done on December 18, 1996, <br /> covering the above property Included are copies of the field <br /> ' logs made by Del-Tech, a table summarizing sampling results, <br /> laboratory reports, a site map showing the pieziometric surface <br /> based on the 12/18/96 data, including directions of all of the <br /> hydraulic gradients measured to date We have also maps showing <br /> lines of equal concentrations of benzene, ethyibenzene, toluene, <br /> xylene & TPHg based on the most recent data <br /> The water table was measured at an average depth of 16 . 17 ' bgl , <br /> (-12 03 ' msl, ) a drop of . 77 ' since the July sampling The <br /> lowest average depth was recorded at 22 . 20 ' bgl in January, 1994 , <br /> ' the highest was the July, 1996 event, a difference of 6 . 8 ' The <br /> water table is slightly above the screened intervals in the <br /> monitoring wells . <br /> I <br /> Based upon the latest work, the hydraulic gradient indicates that <br /> a depression exists in the area between monitoring wells #1, #2 , <br /> & #3 as shown on PLATE I . This pattern has not been seen before, <br /> ' and the reason is not known. There are no withdrawal wells <br /> within the radius of influence, and the change in groundwater <br /> levels should not have been a factor <br /> ' A summary of all laboratory results of water samples taken since <br /> monitoring began is shown on TABLE I . Laboratory reports & QA/QC <br /> ' results are included in the back of the report . MW-1 continues <br /> to show the highest levels of contamination Between the July & <br /> December samplings, benzene increased from 5475 ug/L to 9240 <br /> ug/L, toluene increased from 265 ug/L to 1110 ug/L, ethylbenzene <br /> i <br /> ' went from 645 ug/L to 983 ug/L, xylene from 1665 ug/L to 5180 <br /> ug/L, and TPHg from 32 mg/L to 43 . 1 mg/L. MTBE increased from <br /> 265 ug/L to 844 ug/L <br /> All tested substances were below detection limits in MW-2; the <br /> July event measured low levels of BTEX & TPHg. <br /> 1 <br />