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Mr Harlin Knoll <br /> October 16, 1998 <br /> Page 2 of 2 <br /> concentrations of 11,000 ppb, 5,800 ppb, 1,300 ppb, 10,000 ppb, and 72,000 ppb, respectively No <br /> petroleum hydrocarbon constituents were detected in wells MW2, MW3, MW4, and MW8 Figure 3 <br /> shows the estimated extent of dissolved benzene in groundwater Analytical results are summarized In <br /> Table 2 Laboratory data sheets and chain of custody documentation are included in Attachment B <br /> OTHER SITE ACTIVITIES <br /> In addition to quarterly groundwater morutoring activities, Ground Zero advanced three borings in the <br /> vicinity of the former USTs and fuel dispensers to investigate current subsurface conditions The results of <br /> the investigation were submitted to PHS/EHD in a technical report dated August 25, 1998 <br /> Ground Zero is also conducting a survey of potential receptors to impacted groundwater through evaluation <br /> of nearby domestic wells Information was obtained from PHS/EHD and the Department of Water <br /> Resources The receptor survey may be included in a Risk Based Corrective Action (RBCA) evaluation The <br /> RBCA evaluation would include all the elements per ASTM designation E-1739-95 and would compare the <br /> magnitude of contamination with Risk Based Screening Levels (RBSLs) developed using the computer program <br /> "Tier 2 RBCA" Based on the results of the RBCA evaluation, Ground Zero would pursue closure as a low-risk <br /> case,identify any data deficiencies,or recommend an appropriate corrective action <br /> The next quarterly monitoring and sampling is scheduled for November 1998 and will include monitoring <br /> depth to water in all site wells, purging and sampling wells MW I, MW4, MWS, and MW8, and analyzing <br /> samples for TPHg and BTEX <br /> Please contact John Lane or Greg Stahl at your convenience if you have any questions or comments <br /> regarding the site <br /> C CEG�O <br /> Sincerely, <br /> Ground Zero Analysis, Inc C� <br /> Q JOHN P <br /> LAVE <br /> N No 6795 <br /> Q <br /> John P Lane 9j� Q= <br /> CA Re erect Geologist 795 0 _ <br /> OF CR GEED <br /> ,0 <br /> Gregory P Stahl, RG 5023 4` GREGORY P. � <br /> CA Certified Hydrogeologist 264 NoT5023 <br /> JPL <br /> �F OF D <br /> Attachments <br /> cc Mr Carl Knowles <br /> Mr Patrick D Riddle, Esq <br /> Ms Patricia Anderson, CRWQCB Sacramento <br /> • <br /> groundze/knowles ham/rgxx1s/3gm1998 doc <br />