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California Regional Water Quality Pontrol Board <br /> l\- Central Valley Region <br /> v Robert Schneider,Chair Gray Davis <br /> Winston H.Hickox � Governor <br /> Secretaryfor Sacramento Main office <br /> Environmental httemet Address: http*/Iwww.swreb.ca.gov/— gcb5 t� <br /> Protection 3443 Routier Road,Suite A,Sacramento,California 95827-30032. <br /> Phone(916)255-3000•FAX(916)255-3015 _y r,; <br /> ,7 <br /> 8 February 2002 n <br /> W m,� <br /> lk Jay Allen c <br /> Phil DC4 _ <br /> Nick Nickerson -:: <br /> Unocal DBG/AMG Deputy General Counsel Stone Brothers <br /> Montgomery Wards Management Company <br /> 8788 Elk Grove Blvd. g 1024 W. Robinhood Dr. <br /> Building 3, Suite 15 535 West Chicago Avenue Stockton, CA 95207 <br /> Elk Grove, CA 95624 Chicago,IL 60671 <br /> REVIEW QUARTERL Y MONITORING REPORTS, <br /> FORMER UNOCAL STATION#5098 AT 5606 PACIFIC AVENUE,AND FORMER MONTGOMERY <br /> 00 PEA)CI 5-00-707 <br /> ICENST O %TON,SAN JOAQUIN COUNTY, <br /> CLEANUP AND ABATEMENT <br /> Board staff reviewed the 9 November 2001 Third Quarter 2001 Groundwater Monitoring Report <br /> (Q3-2001 Report) submitted by Environmental Audit,Incorporated(EAI), and the 15 January 2002 <br /> 4th Quarter 2001 Groundwater M&S Report (Q4-2001 Report) submitted by Gettler-Ryan Inc. (GRI) <br /> on behalf of Unocal. Unocal is the primary responsible party for this commingled plume site. <br /> We have the following comments on the Q3-2001 and the Q4-2001 Reports: <br /> 1. After shut down of Delta College's Robinhood Irrigation Well (RIW) in August 2000, one year <br /> of groundwater monitoring shows the predominant groundwater flow has returned to an easterly <br /> direction, and monitoring wells completed in the"shallow" and"deep" intervals reflect this <br /> change. Now that the RIW pumping influence has been eliminated,hydrographs for shallow and <br /> deep monitoring wells (Figures 7 and 8 in the Q4-2001 Report)mirror one another in <br /> groundwater elevation. Therefore,we believe it is appropriate to view the"shallow" (screen <br /> interval from 30 to 50 feet) and"deep" (screen interval from 50 to 70 feet)monitoring wells as <br /> completed in one interconnected water-bearing zone, and not segregated as individual aquifers. <br /> Therefore, complete a site conceptual model (SCM)to show site characteristics and the <br /> distribution of chemicals in soil and groundwater. The SCM will serve to communicate factors <br /> considered when making decisions about the site investigation and cleanup and ultimately the <br /> closure of the site. At a minimum, the SCM must include two hydrostratigraphic cross-sections, <br /> one across the former Unocal site and one across the former Wards site constructed through the <br /> contaminant source areas and parallel to the current groundwater flow direction(see attached <br /> Figure 4 from EAI's Q3-2001 Report). On the cross-sections, define the hydrostratigraphic units <br /> as discussed in Item No. 2, and show the lateral and vertical extent of groundwater contamination <br /> for the Q1-2002 monitoring event. The SCM should be reviewed and updated in future quarterly <br /> monitoring and status reports. <br /> California Environmental Protection Agency <br /> 0 Recycled Paper <br /> The energy challenge facing California is real. Every Californian needs to take immediate action to reduce energy consumption. For a list of simple <br /> ways you can reduce demand and cut your energy costs,see our Web-site at http://www.swrcb.ca.gov/rwgcb5 <br />