SITE INFORMATION AND CORRESPONDENCE_FILE 1

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ENVIRONMENTAL HEALTH DEPARTMENT SAN JOAQUIN COUNTY Unit Supervisors Donna K. Heron, R.E.H.S. Carl Bor man, R.E.H.S. N: Direcla 304 East Weber Avenue, Third Floor Borg man, Huggins, R.E H S , R.D.I. Al Olsen, R.E.H.S. Stockton , California 95202-2708 Douglas W. Wilson, R.E.H.S . Rogram Manager Tejephone: (209) 468-3420 Margaret Lagono, R. E. H.S . 9 <iF 66. Laurie A. Cotulla, R.E.H.S. Robert McClelton, R.E.H.S. - Program Manager Fax: (209) 464-0138 Mark Barcellos, R.E.H.S. PAUL SUPPLE JUS! 2 12004 ARCO PRODUCTS COMPANY PO BOX 6549 MORAGA CA 95470 RE : Former ARCO #548 SITE CODE : 1127 1612 Hammer Lane Stockton CA 95209 San Joaquin County Environmental Health Department (SJC/EHD) has reviewed the proposal "Modification of Remediation Activities" dated May 13, 2004 submitted on your behalf by URS Corporation (URS) and has the following comments . URS proposes to modify the remedial activities at your site by discontinuing operation of the soil vapor extraction/air sparge (SVE/AS) system for an unspecified period of time while evaluating trends in the concentrations of groundwater contamination reported at quarterly groundwater monitoring and sampling events . URS supports this proposal by noting decreased system air influent concentrations between November 2003 and February 2004, and by decreasing trends in reported contaminant concentrations in the groundwater. SVE/AS was initiated at this site in September 2000 . At that time , a final corrective action plan (CAP) had not been submitted . In conversation with your consultant, then Pinnacle, it was discussed that the system was considered to be an interim remediation strategy. SJC/EHD verbally informed Pinnacle in this conversation that a feasibility study comparing at least two clean up alternatives must be completed for this site, followed by a CAP. All of the monitoring wells at this site have screen intervals that are completely submerged , and have been so since approximately 1993. To obtain data on the quality of the shallow groundwater, the vapor extraction wells that have water in them have been routinely sampled since December 2001 . However, due to the construction details of these wells, the groundwater samples collected from them have been grab samples , and therefore may not be representative of true groundwater conditions, especially considering that some of these wells are currently being used for remediation. In SJC/EHD correspondence dated June 18, 1998, you were directed to submit a work plan that included the installation of additional monitoring wells to monitor and sample shallowest groundwater, and a proposal to investigate the vertical extent of contamination in both the soil and groundwater, among other directives . The August 10, 1998 work plan submitted by Pinnacle did not include proposals to address these two specific issues .