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1117 Lone Palm, Suite 8 <br /> (YA <br /> Modesto, Californiatc-e95351 <br /> www.atc-enviro.com <br /> 209.579.2221 <br /> Fax 209.579.2225 <br /> September 28, 2001 <br /> 54.62583.0001 <br /> Ms. Mary Serra <br /> Regional Water Quality <br /> Control Board <br /> 3443 Routier Road, Suite A <br /> Sacramento, CA 95827-3003 <br /> Subject: Addendum to Workplan for Additional Subsurface Investigation at Diamond <br /> Walnut Growers, 1050 South Diamond Street, Stockton, California <br /> Dear Ms. Serra: <br /> ATC Associates Inc., on behalf of Diamond Walnut Growers (DWG), has prepared this <br /> addendum to the July 27, 2001 workplan for the performance of additional subsurface <br /> investigation activities at the above referenced site (Figure 1). This addendum addresses <br /> comments on the workplan as discussed in correspondence dated August 31, 2001 from the <br /> Regional Water Quality Control Board (RWQCB). <br /> Soil Boring Locations <br /> One additional soil boring will be advanced along East Worth Street, east-northeast of existing <br /> monitoring well MW3. Proper access agreements will be obtained by ATC prior to the advancement <br /> of this boring. ATC has also slightly modified the locations of the proposed soil borings downgradient <br /> of monitoring well MW3 and upgradient of wells MWl and MW2 based on observations during the <br /> August 28, 2001 site visit. Proposed boring locations are shown on Figure 2. <br /> Soil Sampling and Selection <br /> Soil samples will be collected at five-foot intervals or estimated changes in lithology. An <br /> estimated two soil samples from each of the borings, collected from depths of 20 feet and 40 feet, <br /> will be submitted for laboratory analysis of hexavalent chromium by EPA Method 7199. These <br /> selected sample depths are based on results of previous investigations at the site. All other <br /> collected soil samples will be held and stored at the appropriate temperature. Pending initial <br /> analytical results, additional samples may be submitted for analysis of hexavalent chromium. <br /> w:\62583\repotts\WKPIan-borings.dm 1 <br />