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PUBLIC HEALTH SERVICES <br /> OP�urN c <br /> SAN JOAQUIN COUNTY r ` ? <br /> ENVIRONMENTAL HEALTH DIVISION <br /> Karen Furst, M.D., M.P.H., Health Officer <br /> 304 East Weber Avenue, Third::Floor Stockton, CA 95202 4`'Fib <br /> 2091468-3420 <br /> PAUL SUPPLE coo <br /> ARCO STATION #4493 <br /> P O BOX 6549 FEB 01 2000 <br /> MORAGA CA 94570 <br /> RE: ARCO Station #4493 SITE CODE: 1042 <br /> 205 N. Center Street <br /> Stockton CA 95202 <br /> i <br /> San Joaquin County Public Health Services, Environme ital Health Division (PHSIEHD) has <br /> reviewed the"Revised Work Plan for Additional Assessment and Interim Remediation of <br /> Hydrocarbons in Groundwater" dated January 11, 2000 1hat was prepared by Secor International <br /> Incorporated (Secor) on behalf of the above referenced site and has the following comments. <br /> The revised work plan proposes to drill one continuous core soil boring near on-site well MW-4, the <br /> installation of three off-site shallow groundwater monitoring wells and the installation of an interim <br /> remediation biosparge system with two wells. <br /> The soil boring and shallow groundwater monitoring well are proposed to further investigate the <br /> vertical and lateral extent of the petroleum hydrocarbon ontamination at this site. The continuous 1 <br /> core soil boring will be drilled by a method that will allow for the collection of discrete soil and <br /> groundwater samples. Proposed depths for collection o water samples are approximately 30, 45, <br /> and 60-feet below surface grade (bsg). Soil samples wil be collected every five feet. Total depth j <br /> of the boring will be at least 60-feet bsg, or until three consecutively "clean'soil samples are f <br /> collected. The three off-site monitoring wells will look at the lateral extent of the shallow <br /> groundwater contamination. <br /> PHSIEHD approves the proposal for the continuous core soil boring and the shallow monitoring <br /> wells. PHSIEHD feels that in addition to the proposed s iallow monitoring wells there is a need for <br /> deeper, discretely screened monitoring wells off-site. As was discussed in PHSIEHD <br /> correspondence dated December 14,1999, shallow wat r samples may not be providing reliable <br /> information as to the lateral extent of the subject sites contaminant plume. Review of the lithology <br /> from the continuous core boring will give an indicationOT the appropriate target screen interval for <br /> deep off-site wells. <br /> PHSIEHD does not approve the installation of a biosparge system and biosparge wells at this time. <br /> PHSIEHD is not aware of any soil parameter analysis that has been done at this site to determine <br /> what the concentrations of available biological media ar , or what the soil porosity and permeability <br /> rates may be. In a meeting on January 26, 2000 PHSIEHD discussed this site with a i <br /> representative from the Regional Water Quality Control Board, Central Valley Region <br /> (CVRWQCB). It was understood frons this discussion that the Regional Board would not <br /> recommend any type of remediation system to be implemented at a site before feasibility testing <br /> has been done. PHSIEHD has no data which indicates that biosparging has been shown to be an <br /> effective remediation method for methyl tertiary butyl ether(MtBE). If ARCO has used this <br /> .j <br /> A Division of San Joaquin County Health Care Services <br />