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Disco Property, 110 Filbert Street, Stockton - 2 -. 2 January 2001 { f construction at this site, including monitoring wells MW-8S and—8D,were installed by CH2M Hill using auger-drilling methods to 95 feet and 145 feet, respectively. Monitoring wells installed using. auger-drilling methods provide sample results much quicker than mud-rotary wells, and are more cost effective. Therefore, monitoring well installation using auger-drilling methods must be attempted prior to using mud-rotary at the proposed drilling locations. Mud-rotary drilling methods are appropriate for the proposed deep monitoring well due to setting an eight-inch conductor casing through the intermediate zone to protect the deep zone from cross contamination. A minimum two-inch annular seal is required around the eight-inch conductor casing, and centralizers must be used to properly center the conductor in the borehole. A six-inch diameter extraction well will be installed on-site and screened across the intermediate sand zone. As presented in the Workplan, the extraction well boring will be completed using mud-rotary drilling methods with continuous core recovery from 50 to 120 feet to determine the exact screen interval. Once the extraction well is installed and developed, an aquifer test will be performed as part of a feasibility study to determine if groundwater extraction will effectively capture contamination in the source zone. The Workplan is approved with the following additions and/or comments: • The proposed deep monitoring well must be moved 230 feet southeast of its original position, as i shown on attached Figure 2. • Auger-drilling methods must be used, as appropriate, to install the intennediate monitoring wells. • A minimum two-inch annular seal is required around the proposed eight-inch diameter conductor casing, and centralizers must be used to center the conductor casing in the borehole. 0 The extraction well screen interval must be designed based on continuous core data, and not arbitrarily set at 100 to 120 feet. • Bentonite pellets coated with ethyl compounds should not be used in monitoring well constniction at this site. Please contact Ms. Dottie Lofstrom at (209) 468-3436 at the County and me at least two business days prior to any site work. If you have any questions or comments, please call me at (916)255-3115. Marty Hartzell Associate Engineering Geologist Attachment cc: Ms. Dottie Lofstrom, San Joaquin County EHD, Stockton Ms. Wennilyn Fua, UST Cleanup Fund, SWRCB, Sacramento Mr. Steven Ronzone, Del Monte Foods, San Francisco ( Mr. Steven Erickson, Del Monte Foods, Walnut Creek Mr. Keith Sheets, CH2M Hill, Oakland