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Ground Zero Analysis 40 PHONE NO. : 209 8.38 9883 Or <br /> y. OS 1998 04:32PM P2 <br /> GROUND ZERO ANALYSIS, INC. <br /> ENVIRONMENTAL HEALTH DIVISION <br /> 1714 Main Street 304 E. Weber Ave. I hirdoor <br /> Escalou, California 95310 P. O. Box 388, Stoc n CA 95201-0388 <br /> Telephone: (209) 838.9888 Approved <br /> Faes:m,7e: (209)838.9883 Denied ❑ <br /> Conditions 5( <br /> May 5, 1998 Date by <br /> A/�FkSO¢l1"j Pr R1GRj-W t,.7t <br /> Mr. Ron Rowe ^1 �1 by 2.�/,IA j v3m� <br /> San Joaquin County-Public Health Services Z• Y r!C)G SJbA.tc( WJwcrw) Ta <br /> Environmental Health Division InJbTALt. 1_.�—pC ZZ tGYLC ,,,fak�3\1 <br /> 445 North San Joaquin Street el- <br /> P.O. Box 388 3 CCK TO mom!�Y 5 A�?1 t71 Wut <br /> Stockton. CA 95201-0388 i:rOz nhl 40d ;rt_z avtq, � <br /> lZ�r s ffQ&Y, -W1 cZL)AaTr:?-u-( <br /> Subject: Knowles/Roek Property, 102 South Wilson Way, Stockton, California tNo 'T i,,Jj�,t 6 C <br /> Recommendations for 8260 Analyses - Second Quarter 1998 u3tb ib D1 , i <br /> -omp?_� J26Smr1(_. <br /> 4. Ahe Aoljl 'it) bowel 5 <br /> Dear Mr. Rowe: <br /> men a Cu V t sampling <br /> g snit) T YLrh <br /> Following up on our phone conversation I am writing to present recommen auv or sampling <br /> groundwater for oxygenate additives by EPA method 8260. <br /> As we discussed, high concentrations of MTBE, in conjunction with a dramatic increase in hydrocarbon —Wryt,E <br /> concentrations, appeared in 1vfW4 in November, 1997. The presence of MTBE in this well was AIM 6tr4'jtAJ <br /> confirmed in December, 1997 and again in February, 1998. MTBE was not detected in this well when TD Nt ttwP t8 <br /> first sampled in July, 1997. This is interpreted as the encroachment of a plume of contamination W11-r( i?.156 <br /> originating offsite. Low levels of MTBE have also been twice detected in MW9, north of and generally to &10a tib <br /> crossgradient from the site. lL <br /> On the other hand, it is unclear whether or not diisopropyl ether (RIPE) or tertiary butyl alcohol (TBA) <br /> are consistently present in groundwater in the site area. It is uaknown whether the source(s) may be <br /> onsite or offsite UST leaks or other sources (leaking sewers, industry, etc.) The initial round of 8260 <br /> analyses (11/97) reported relatively low concentrations of DIPE and/or TBA in most wells north, east <br /> and west of the former USTs. These constituents were not reported as present in most wells south of the <br /> former USTs nor in the vapor wells installed within the onsite gasoline source area. The second round <br /> of 8260 analyses (02/98)detected DIPE and TBA only in wells MW 1l and MW 12 although the detection <br /> limits were somewhat higher than during the initial sampling. <br /> To meet the objectives listed below while conserving financial resources, the following is suggested: <br /> 1) Monitor the MTBE plume in the vicinity of MW4: <br /> (Sample wells MW3 and MW4) <br /> Sample MW4 for oxygenate additives to gauge changes in concentration. Also sample MW3 in <br /> order to detect plume migration. Both MW3 and MW7 are generally dowagradient of MW4 <br />