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F <br /> w- <br /> '- ENVIRONwIENTAL HEALTH EPARTME <br /> oA....',N, NT <br /> ' SAN JOAQUIN COUNTY <br /> y { Donna K. Heran, R.E.H.S. Program Coordinators <br /> Director 304 East Weber Avenue,Third Floor <br /> Laurie A. Cotulla,R.E.H.S. Stockton,California 95202-2708 Carl HugginBorgrs, <br /> n, .H.S., S. <br /> Mike Huggins,R,E.H.S.,R.D.I. <br /> o44:i i� i;`p Assistant Director Telephone: (209)468-3420 Margaret Lagorio, R.E.H.S. <br /> Fax: {209) 464-0138 Robert McClellon, R.E.H.S. <br /> Teff Carruesco, RT.H.S. <br /> Website:wwwsjgov.org/ehd/ Kasey Foley, R.E.H.S. <br /> DON PRATT AU G 2 8 2006 <br /> ARCO PRODUCTS COMPAMy M HAMZEH Y HAJIAN PPT <br /> PO BOX 1257 111 QUINTAS LANE <br /> SAN RAMON CA 94583 MORAGA CA 94556 <br /> RE: Former ARCO Station #548 SITE CODE: 1127 <br /> 1612 Hammer Lane <br /> Stockton CA 95209 <br /> San Joaquin County Environmental Health Department (SJC/EHD) has reviewed Work <br /> Plan for Soil Vapor Extraction and Air Sparge Feasibility Testing(Work Plan) dated <br /> August 4, 2006 submitted on your behalf by SECOR International Incorporated (SECOR) <br /> and has the following comments. <br /> Interim remediation by soil vapor extraction and air sparging (SVE/AS) was conducted at <br /> this site from September 2000 to June 2004. SJC/EHD previously considered that air <br /> sparging had not been initiated during that interim remedial period, but review of quarterly <br /> reports submitted during that time indicate that air sparging was performed, for different <br /> periods of time, at least through the second quarter of 2002. <br /> The interim SVE system was shut down in June 2004 based on low influent vapor <br /> concentrations. At the time of shut down three vapor wells were being utilized, VW-4, <br /> VW-5S and VW-5D. VW-4 is located near the current dispenser island; VW-5S and <br /> VW-5D are located in the former tank pit area. Documented soil contamination at this site <br /> is located mostly near the former tank pit area, from 15 feet below surface grade (bsg) <br /> (sample T-2-N) to 98 feet bsg (MW-8). The highest concentrations of contamination in <br /> soil were reported at depths of approximately 15-36 feet bsg (various samples). Depth to <br /> groundwater across the site is approximately 26 feet bsg, indicating a significant portion of <br /> the contaminated soil is currently submerged. The soil interval between 15-26 feet bsg is <br /> only partially addressed by the screen intervals of the existing SVE wells. <br /> This site currently has only one groundwater monitoring well, MW-7, that is screened <br /> appropriately for monitoring the shallow groundwater contamination. In lieu of installing <br /> additional shallow groundwater monitoring wells ARCO elected to use existing vapor <br /> extraction wells that currently intercept first groundwater as monitoring wells. SJC/EHD <br /> agreed to this usage of the SVE wells on the condition that the wells are purged prior to <br /> sampling, and that they are not used for remediation. This condition on the use of these <br /> wells still exists. <br /> The Site Conceptual Model (SCM) states that the radius of influence of the SVE wells is <br /> 30 feet, which would encompass most of the impacted soil around vapor extraction wells <br /> VW-5S and VW-5D, which are the wells SECOR is proposing to use for a test. SJC/EHD <br /> does not see the necessity to redetermine the ROi for the SVE wells. SJC/EHD also does <br />