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ioCalifornia Regional Water Quality Control Board Central Valley Region i Stgven T. Butler, Char aston H. Hickoz Gray Davis Secretaryfor Sacramento Main Office Governor Environments! IntemetAddress! httpV/www.swreb.ca.gov/--rwgcb5 Proiettion 3443 Routier Road, Suite A, Sacramento, California 95827-3003 Phone (916) 2$5-3000 • FAX (916) 255-3015 TO: Gordon L. Boggs FROM: Marty Hartzell UST Program Manager Associate Engineering Geologist DATE: 22 September 2000 SIGNATURE: ,�4 u SUBJECT: REVIEW PROBLEM ASSESSMENT REPORT AND FINAL REMEDIATION PLAN, FORMER CHEVRON STATION #9-5775,301 WEST KETTLEMAN LANE, LODI, CLEANUP AND ABATEMENT (C&A) ORDER NO. 5-00-704 I reviewed the 24 July 2000 Problem Assessment Report (PAR) and the 25 August 2000 Final Remediation Plan (FRP) submitted by Secor Intemational Incorporated (Secor) for the subject site. The PAR and FRP provide a summary of site soil and groundwater investigation activities and results, and a proposed strategy to remediate soil and groundwater contamination. However, these reports do not present a complete assessment of site contamination, and do not show that the groundwater plume is being stabilized as required by the C&A Order. Specific discrepancies with the PAR and FRP are Discussed as follows: Soil contamination is shown to extend below the former underground storage tanks (USTs) to 72 feet at soil boring SB -1. Low concentrations of benzene and MtBE were identified at this maximum depth; therefore, the vertical extent of soil contamination has not been defined on-site. Groundwater contamination is shown in the shallow and deep monitoring wells on-site and extends from the former UST area south across Kettleman Lane into the shopping center parking lot (see enclosed Figures 1 and 2 from the FRP). As shown on Figures 1 and 2, the extent of groundwater contamination has not been defined north of the former UST area, and south of MW -10. Secor installed multiple monitoring wells both on-site and off-site in June 2000 to delineate the extent of groundwater contamination, and to provide a sentinel well between the on-site contamination and the City of Lodi Municipal Well 12 (Well 12) approximately 500 feet southwest of the site. The sentinel well, MW -813, was screened in silty clay from 85 to 90 feet, which is inappropriate. As shown in the PAR and FRP; MW -8B is downgradient from the site, approximately 200 feet from the former USTs, and has been non -detect for all constituents sampled on 12 July and 24 July. Water levels from this well measured on 12 July and 24 July were shallower than surrounding deep zone wells and could not be used for contouring. In comparison, MW -1013 was completed in clayey silt from 85 to 90 feet, with silty sand above. MW -1013 is cross gradient approximately 300 feet from the former USTs, and has shown low MtBE contamination in the 12 July and 24 July sampling events. Therefore, MW -8B is not. screened appropriately to serve as a sentinel well for Well 12, and must be replaced. Prior to installing -another well in this area, Chevron must complete continuous core data collection (e.g. cone penetrometer testing) ,with discrete groundwater sampling to identify permeable aquifer units. As directed in C&A Order #3, Chevron is to "Install and continuously operate a soil vapor extraction system, and an interim pump and treat system in the area of the highest soil and groundwater MtBE California Environmental Protection Agency p Recycled Paper !�