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Wm. J. Hunter & Associates 2220 Loma Vista Dr <br /> Registered Geologists ,° Jif Sacramento, CA 95825 <br /> Petroleum & Mineral Appraisers ? „ , _ (916) 972-7941 <br /> . 17 p, ; J FAX (916) 972-1683 <br /> February 10, 1997 <br /> Michael. Infurna, Sr. REHS <br /> San Joaquin County PHS <br /> Environmental Health Division <br /> P O 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 /> We 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, ethylbenzene, toluene, <br /> xylene & TPHg based on the most recent data <br /> • The water table was measured at an average depth of 16 . 171 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 . 81 . The <br /> water table is slightly above the screened intervals in the <br /> monitoring wells . <br /> Based upon the latest work, the hydraulic gradient indicates that <br /> a depression exists 3n 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 /> 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 /> • <br /> 1 <br />