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• / \ California Regional Water Quality C"i ntrol Board Central Valley Region Robert Schneider,Chair Gray Davis Winston H.Hickox Secretaryfor Sacramento Main Office Governor Environmental Internet Address: http://www.sv b.ca.gov/—mgcb5 Protection 3443 Routier Road,Suite A,Sacramento,Califmnia 95827-3003 Phone(916)255-3000•FAX(916)255-3164 RE (MW ED 6 August 2002 AUG 0 8 2002 ENVIRONMENT HEALTH EI /SRVICES Mr. Mike Lescisin Diamond Walnut Growers Inc. dba Diamond of California 1050 South Diamond Street Stockton, California 95201 REVIEW OF RESPONSE TO COMMENTS AND WORKPLAN,DIAMOND WALNUT GROWERS, STOCKTON PLANT, SAN JOAQUIN COUNTY We have reviewed the 1 August 2002 Second Quarter 2002 Monitoring Report (QMR) and the 29 May 2002 Workplan for Additional Well Installation (Work Plan) submitted by ATC Associates Inc. (ATC), on behalf of Diamond Walnut Growers Inc. (DWG) for its Stockton Plant. Monitoring well MW-3 contained 7,000 µg/1 of hexavalent chromium during the second quarter sampling event on 10 April 2002. We concur with the proposed work so long as DWG incorporates the following comments into the work. 1. The Work Plan proposes to install six groundwater monitoring wells. All the proposed wells are planned to be screened between about 45 to 65 feet below ground surface. A 20 foot screened interval is too long and could cause dilution of pollutant concentrations. The well screen should not extend beyond boundaries of known pollution nor pierce a confining layer, which may cause the spread of the pollution into other groundwater zones. The screened interval should be no longer than 15 feet and be determined in the field by a responsible licensed professional. 2. The QMR says, "Hexavalent chromium was detected in monitoring well MW-2 at a concentration of 0.026 mg/1 and in monitoring well MW-1 at a concentration of 0.0006 mg/l." Despite these relatively low concentrations, ATC proposes to install two additional monitoring wells near MW-1 and MW-2. The resources required to install these two wells should be used to define the known pollution present in the groundwater in MW-3. Therefore, the monitoring wells shown on Figure 2 of the Work Plan near SB-3 and S13-4 should be moved. Monitoring wells are necessary between MW-3 and the facility well FS and downgradient of MW-3 beyond the facility boundary. Since it may California Environmental Protection Agency Qd Recycled Paper The energy challenge facing California is real. Every Californian needs to take immediate action to reduce energy consumption. For a list of simple ways you can reduce demand and cut your energy costs,see our Web-site at http://www.swrcb.ca.gov/mgcb5