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Wm. <br /> J Hunter & Associates 2220 Loma Vista Dr <br /> Registered Geologists Sacramento, CA 95825 <br /> l�Petroleum &Mineral Appraisers (916) 972-7941 <br /> FAX (916) 972-1683 <br /> June 23, 1998 <br /> Carol Oz, REHS <br /> San Joaquin County PHS <br /> Environmental Health Division <br /> Site Mitigation Unit <br /> P O Box 388 <br /> Stockton, CA 95201-0388 <br /> REF: FIRST QUARTER 1998 GROUNDWATER MONITORING REPORT FOR <br /> 2315 NO. ELDORADO STREET, STOCKTON; SITE CODE 2080 <br /> We have enclosed copies of the field report, water analyses results, a gradient map, and <br /> maps showing inferred lines of equal concentrations of benzene, ethylbenzene, toluene, <br /> xylene, and TPHg based upon the latest sampling event The field work was done on <br /> April 2, t998 by DelTech Geotechnical Support Services as directed by your office <br /> t <br /> PLATE I shows the approximate potentiometric surface based upon the latest sampling <br /> event T4T gradient is to the east, the slope varies from 005'/ft to 0251!ft Groundwater <br /> was mea$ured at an average depth of 30 81' bgl, (-20 34' ms] datum,) a rise of 6 67' since <br /> December This rise in the water table is seen in other wells in the area, and is due to the <br /> heavy rains that have occurred this past year <br /> PLATES II thru VI show the inferred iso-concentration lines for benzene, ethylbenzene, <br /> toluene, xylene, and TPHg based upon the April 1998 data Levels of BTEX have gone <br /> down in 1V -1, MW-5, & MW-6. Benzene has increased in MW-2, MW-3, & MW-4. <br /> Ethylbenze e& toluene levels went down in MW-2,but have increased in MW-3 & <br /> MW-4. centrations of xylene increased in MW-2, 3, & 4. Levels of TPHg decreased <br /> in MVV-6,CoUt increased in the other wells MTBE, TBA, ETBE, & TAME were below <br /> detection limits in all wells using EPA 8260 procedure DIPS was detected in MW-3 at <br /> 240 ug/L, an4 in MW-4 at 83 ug/L Refer to TABLES B & C for a summary of <br /> laborabory results to date <br /> The top ofthd well screen in N1W-I is at 55' bgl, in MW-2 & 3 it is at 43', and in MW-4, <br /> 5, & 6 it is at 65' below grade Because the water table has risen to about 31' bgl, it is <br /> above the perforations in all of the wells This prevents an accurate analysis of changes in <br /> levels of contaminants However, a comparison of the maps of equal concentrations <br /> from the last three samplings reveals that the configuration of the plume has remained <br /> quite uniform This indicates that there is little if any lateral movement <br /> RECOMMENDATION: <br /> n <br /> 1 <br />