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r ENVIRONMENTAL HEALTH DEPARTMENT SAN JOAQUIN COUNTY { )•"'`" �'•,per , Unit Supervisors � •Z Donna K.Herap,I2.E.H.S. � 304 East Weber Avenue,Third Floor Carl Borgman,R.E.H.s. Director Mike Huggins,RE_H.S.,R.D.I. Al Olsen,] .EJLS. :Stockton, California 95202-2708 nougl w.W;lson,R_E.H.S. Program Il�gnager Tele hone:; 209 468-3420 Margaret La orio,A E.H.S. cry' u p ): g Laurie A.Cotulla,R.E.II S. Program ManagerFax: (209).464-0138 Robeit M0_ellon,R,E_H_S, Mark Baroellos,R.E.H,S. ' PAUL SUPPLEJUN 2.1_. 2004 .---------___..-- ARCO PRODUCTS COMPANY PO BOX 6549 MORAGA CA 95470 RE: - Former ARCO#548 SITE CODE: 1127 - 1612 Hammer Lane Stockton CA 95209 r San JoaquinCounty 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 white 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. SVEIAS 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. SJCIEHD verbally informed Pinnacle in this conversation that a feasibility study comparing at least two dean 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 3 been routinely sampled since December 2001, However,due to the construction details of thesewells,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 SJCIEHD 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 110, 1998 work plan submitted by Pinnacle did not include proposals to address these two specific issues.