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1400, .111W Mr. Michael Infurna, SJCEHD September 14,2006 Well Installation Work Plan Addendum Palisades Station No. 835, Stockton,CA Page 2 within the steel casing will be evacuated from the borehole. Details associated with completing the deeply screened monitoring wells are presented in the following sections of the Addendum. SCOPE OF WORK Soil Borings and Well Construction Six of the eleven borings proposed in the April 7, 2006 Work Plan (MW-12 through MW-14, MW-18, MW-19, and MW-21) were proposed to be completed using a truck mounted drill rig equipped with 8-inch and 15-inch diameter hollow stem augers. Locations of each well boring are shown on Figures 2 and 3. Stratus is proposing in this ndum to complete these soil borings using a sonic coring drill rig equipped with 7-inc or 9-inch diameter threaded steel casing. Borings MW-12 through MW-14, -18, MW-19, and MW-21 will subsequently be constructed as groundwater monitoring wells, as described below. The initial 5 feet of each boring will be advanced with hand tools or air-knife/vacuum extraction equipment to reduce the possibility of damaging underground utilities. Soil cores will be continuously recovered from the boreholes. Soil samples will be collected from the soil core, at selected intervals, by hand driving pre-cleaned brass tubes into the center of the core. The ends of the bottom-most, intact tube from each sample interval will be lined with Teflon TM sheets, capped, and sealed. Each sample will then be labeled, placed in a resealable plastic bag, and stored in an ice-chilled cooler. Strict chain- of-custody procedures will be followed from the time the samples are collected until the time the samples are relinquished to the laboratory. Additional samples from the soil core will be screened for volatile organic compounds using a photoionization detector (PID). Stratus will record PID readings, soil types, and other pertinent geologic data on a borehole log. A minimum of two soil samples from each boring will be submitted for chemical analysis. Additional samples may be selected for chemical analysis based on soil type and field observations. Diagrams illustrating the proposed construction details for wells MW-12 through MW-14, MW-18, MW-19, and MW-21 are presented in Appendix A. The screening intervals of these wells remain unchanged from the screening intervals proposed in the April 7, 2006 Work Plan. Each deeply screened monitoring well will be constructed using 2-inch diameter PVC well casing and 10 feet of 0.02-inch diameter factory slotted well screen. Centralizers will be utilized to situate the well casing within the center of the borehole. A filter pack of#3 LonestarTM sand will be placed in the annular space around the well casing from the bottom of the well screen to approximately 3 feet above the top of the well screen. Approximately 5 feet of coated bentonite pellets will be placed on top of the filter pack to provide a transition seal for the wells. Neat cement will be used to backfill the remaining K:AUSA GasolineA0835\Work Plans\USA835 workplan addendum 2006.doe STRATUS