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Hunter & Associates t ' `�� ' �'�L 711 2220 Loma Vista Dr
<br /> Wm. J. � ,,-, ;
<br /> Registered Geologists r, - Sacramento, CA 95825
<br /> etroleum &Mineral Appraisers } ;r" 1
<br /> 00 (916) 972-7941
<br /> FAX (916) 972-1683
<br /> February 13, 1995
<br /> Steven Sasson, Sr 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: FOURTH QUARTER 1997 GROUNDWATER MONITORING REPORT
<br /> FOR 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 /> December 2, 1997 by DelTech Geotechnical Support Services as directed by your office
<br /> PLATE I shows the approximate potentiometric surface based upon the 12/2/1997 data
<br /> The gradient is to the east, the slope varies from 0057ft to 0257ft Groundwater was
<br /> • measured at an average depth of 37 48' bgl, (-27 01' msl datum,) a drop of 3 20' since
<br /> June
<br /> PLATES H thru VI show the inferred iso-concentration lines for benzene, ethylbenzene,
<br /> toluene, xylene, and TPHg based upon the December data The shape of the plume has
<br /> not changed significantly since the June sampling, but the levels of contaminants in the
<br /> wells has changed somewhat Levels of BTEX have decreased in MW-1, 2, 3, & 5, but
<br /> they have gone up in MW-4 & 6 Refer to TABLES B & C for details TPHg does not
<br /> show any obvious trend MTBE, ETBE, & TAME were below detection limits in all
<br /> wells using EPA 8260 procedure TBA was detected in MW-3 at 78 ug/L, and in MW-4
<br /> at 38 ug/L DIPE was measured in MW-i at 9 4 ug/L, in MW-2 at 5 6 ug/L, in MW-3 at
<br /> 78 ug/L, in MW-4 at 38 ug/L, and m MW-6 at 11 ug/L The December sampling was the
<br /> first time samples were analyzed for oxygenates using method EPA 8260 Addditional
<br /> sampling will be required to more fully evaluate those compounds The July, 1996 work
<br /> indicated significant levels of MTBE in MW-2, MW-4, MW-4, MW-5, & MW-6
<br /> However, those analyses are suspect since MTBE has not been detected in the four (4)
<br /> samplings since then
<br /> In September & October, 1997, five (5) strataprobe holes were located offsite for the
<br /> purpose of delineating the limits of soil and groundwater contamination The locations of
<br /> those holes and the inferred limits of contanunation are shown on PLATE IA Details of
<br /> that work are given in the WJH report titled "Interim Report Covering Results of
<br /> Strataprohe Work Performed 9129, 9130, & 10/8-1997 23-15 North Eldorado St,
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