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PURL HU 0 IV, <br /> EALTH SEeICES � oG <br /> SAN JOAQUIN COUNTY <br /> 3 JOGI KHANNA N,1D,Nl.,P.H <br /> Health Officer c' P <br /> R t' <br /> P.O. Box 2009 (1601 East Hazelton Avenue).G Stockton, California 95201 L f F o R <br /> ;i (209) 468-3400 s- <br /> ROD NELSON <br /> LAIDLAW CORPORATION f.t <br /> 1444 TILLIE LEWIS19 <br /> STOCKTON CA 95206 GSC <br /> i <br /> RE: 1444 Tillie Lewis,,, Stockton SITE CODE: 2454 <br /> i� <br /> San Joaquin County PubAc Health Services, Environmental Health <br /> Division (PHS/EHD) has reviewed the Problem Assessment Report. <br /> dated May, 20, 1992, submitted by RESNA and has the following <br /> comments. <br /> We concur that the bulk: of the contaminated soil was removed <br /> during the March 1991 over-excavation and that contamination <br /> remains in the saturated zone beneath the former tank location ' <br /> and in areas beneath the building. <br /> 1 Once contaminants reach' the water table, they generally float- on. , <br /> top of the water and migrate with the water as it moves in its <br /> flow path or gradient direction. The contaminants may also move <br /> vertically, up and down, with corresponding fluctuations in the <br /> water table. The depth' to water data collected to date for this <br /> site shows vertical drops in the water table of up to 5.84 feet, <br /> indicating a vertical zone of contamination within the saturated <br /> soils. This "smearing" of contamination within the saturated <br /> zone can contribute to ;the general contaminant plume for many, <br /> years, possibly decades, and may hinder the natural biological <br /> degradation process as ;well. <br /> The groundwater contaminant plume for this site has been <br /> adequately defined with the installation of the six monitoring <br /> wells. The two downgradient monitoring wells, MW5 and MW6, to <br /> date have not indicated contamination and will detect any further <br /> movement of the plume in that direction. Therefore, becausethe <br /> extent of the contamination has been- determined and any migration <br /> of the plume can be detected, the conditions at this site.. can be , <br /> monitored for a year, as recommended, by RESNA. <br /> As the extent of the contamination is known, several alternatives <br /> for further activity at the site should be considered. The cost <br /> effectiveness and efficiencies of appropriate active remediation <br /> systems should be evaluated. If a passive, long term groundwater : <br /> monitoring program is being considered for this site, it should <br /> i <br /> A Division of Sul Joaquin County Health Care Semces J <br /> i <br />