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.` California Regional Water Quality Control Board <br /> vCentral Valley Region <br /> Winston H.Hickox Robert Schneider,Chair Gray Davis <br /> Secretaryfor Sacramento Main Office Governor <br /> Environmental Internet Address: http://www.swrcb.ca.gov/—mgcb5 <br /> Protection 3443 Routier Road,Suite A,Sacramento,California 95827-3003 <br /> Phone(916)255-3000•FAX(916)255-3164 <br /> 19 December 2002 DEC 2 0 2002 <br /> ENVIR., `'1``_iIT HEALTH <br /> Mr. Mike Lescisin PERi:o i/SERVICES <br /> Diamond Walnut Growers Inc. <br /> 1050 South Diamond Street -- <br /> Stockton, California 95201 <br /> REVIEW OF SUBSURFACE INVESTIGATION,DIAMOND WALNUT GROWERS, <br /> STOCKTON PLANT, SAN JOAQUIN COUNTY <br /> We have reviewed the 1 November 2002 Summary Report ofAdditional Subsurface <br /> Investigation (Report) submitted by ATC Associates Inc. (ATC) on behalf of Diamond Walnut <br /> Growers Inc. (DWG) for its Stockton Plant. In September 2002, DWG installed five additional <br /> monitoring wells near MW-3, which during this investigation contained 4,000 µg/1 of hexavalent <br /> chromium and 6,200 µg/1 of total chromium. We have the following comments on the report. <br /> 1. The Report contains analytical results for the five new monitoring wells. MW-6,which is <br /> about 120 feet downgradient of MW-3, contained the highest hexavalent chromium <br /> concentration at 71 µg/1. The results correlate with earlier soil investigation results. This is <br /> good news, as it appears that the groundwater pollution has not significantly migrated <br /> laterally. <br /> 2. The Report contains recommendations to install a monitoring well to define the vertical <br /> extent of the groundwater pollution and to video log the construction details of the facility <br /> well. DWG proposes to complete and submit a work plan to accomplish this work. We <br /> concur that this work is necessary and DWG should proceed with the work plan and <br /> schedule. <br /> 3. Although not mentioned in the Report,we requested that DWG install a monitoring well <br /> downgradient of MW-3 beyond the facility boundary. Based on the concentrations in MW-6, <br /> DWG should delay the installation of this well until the deeper water zone beneath the source <br /> area is defined and a few quarters of monitoring in MW-6 have occurred. <br /> California Environmental Protection Agency <br /> C', 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 <br /> simple ways you can reduce demand and cut your energy costs,see our Web-site at http://w .swrcb.ca.gov/rwgcb5 <br />