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;Qr <br /> ,r^fir' -r`•°:T ��; ';ice- � - . <br /> Mr. Mike Hansen -2- 4 April 1988 <br /> been presented to explain the presence of the TPH plume and <br /> the absence of the benzene plume. Benzene usually migrates , <br /> faster in ground water than most other components of <br /> gasoline so having a TPH plume larger than benzene plume is <br /> unusual and needs to be explained. Please provide <br /> chromatograms (including interpretations) from the most <br /> recent analysis of those wells with non-detectable benzene <br /> and detectable TPH. <br /> We have no- objections to water samples being collected from <br /> the fringe wells and analyzed for TPH by EPA method 8270; <br /> however, the results may still be ambiguous. <br /> - Y-our a _ . - <br /> qua.fer 't°este have shown"that�aii-fer response toy <br /> pumping is- rapid; however, the tests also showed that the <br /> aquifers can not be pumped atthe rates suggested. Proper <br /> data analysis and interpretation needs to be done to <br /> determine how many recovery wells will be sufficient to <br /> remediate each site' in a reasonable period of time. Results <br /> to date suggest to us that one recovery well is insufficient- <br /> to control the plumes of contamination and remediate the <br /> site in a timely manner. Also, statements in each report <br /> that ground water flow rates are low, at a maximum of 20 <br /> inches per day, suggest the contrary to us; as 20 inches per <br /> day is over 600 feet per year! <br /> Please submit the missing data, and the requested chromatograms, <br /> as an addendum to each PAR by 8 April 1988. The other points can' <br /> be addressed, with adequate solutions, in the Final Remedial Plan,, <br /> for each site which is due 4 June <br /> If you have any questions, please call me at (916) 361-5731. '. <br /> GARY S. JOHNSON N� <br /> Engineering Geologist <br /> GSJ:gj <br /> cc: v4s. Laurie Cotulla, San Joaquin Local Health DistrictId, <br /> Stockton <br /> Mr. Dave Ellis, Groundwater Bire-mediationServices, <br /> Wilmington, Delaware <br /> Mr. Kent Parrish, Exceltech, Fremont <br /> �1 <br /> J � <br />