SITE INFORMATION AND CORRESPONDENCE

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Revised Soil and Groundwater Investigation Work Plan Mountain House Development Site#6 July 2007 • SB-N to investigate the extent of affected media cross gradient of GP 160 and GP161. • SB-O to investigate the extent of affected media cross gradient of GP161. • SB-P to investigate the extent of affected media up gradient of GP161. • SB-Q to investigate the source, magnitude, and extent of affected media at GP161. • SB-R and SB-S to investigate the extent of affected media down gradient of GP 152. • SB-T to investigate the extent of affected media down gradient of GP 156. • SB-U to investigate the extent of affected media down gradient of GP 156 and GP 157. • SB-V to investigate the extent of affected media down gradient of GP 157 and GP158. • SB-W to investigate the extent of affected media down gradient of GP158. • SB-X to investigate the extent of affected media down gradient of GP 160. • SB-Y and SB-Z to investigate the extent of affected media down gradient of GP161. • SB-AA to investigate the extent of affected media up gradient of GP 160. Some or all of primary boring locations SB-R, SB-S, SB-T, SB-U, SB-V, SB-W, and/or SB-X may not be advanced if affected soil and groundwater are not found first in up-gradient borings SB-C, SB-K, SB-L, and/or SB-M(in the Byron Road ROW). Details regarding the proposed boring program are provided in Table 1. Collection of Soil Samples Prior to direct-push advancement, each boring will be hand cleared to 8 feet bgs. Below 8 feet bgs, soil borings will be continuously cored with the GeoProbe Dual Tube sampling system. The sampler will contain a plastic acetate liner that retains a relatively undisturbed soil core. The soil samples selected for analysis will be cut from the plastic liners, sealed with Teflon tape and plastic end caps, labeled with identifying information, and stored in a pre-chilled ice-chest for transportation to the laboratory. Each borehole will be logged for lithological content using the Unified Soil Classification System as a guide including color,relative moisture content, and other observable distinguishing characteristics (i.e., color changes, debris,rootlets,or odor). SAIC will utilize a photo-ionization detector(PID)to screen soil for the presence of volatile organic compounds. Lithologic observations,PID screening results, and other observations will be recorded on field logs. If affected soil is observed, soil samples will be collected from within and from beneath the affected zone to determine the magnitude of the vertical extent of the COCs in soil. If affected soil is not present in a boring,then soil samples will be collected at a depth where affected soil was observed in adjacent borings. If no affected soil has been observed in adjacent borings,then soil samples will be collected from just above groundwater. At each boring location,risk assessment samples will be collected from either the most-affected soil within the 0 to 10 feet bgs interval or from a depth of 5 feet bgs if no hydrocarbon impact is observed. If the most-affected soil is encountered below 10 feet bgs,then three intervals will be sampled: (1)the top 10 feet bgs for risk assessment, (2)below 10 feet bgs from the most-affected interval to assess the magnitude of COCs, and(3)beneath the affected soil to determine the vertical extent. However, if the most-affected soil occurs in the upper 10 feet bgs,then samples from the top 10 feet bgs may represent the most-affected interval and the risk-assessment interval. 4 :::: Mei`® From Schee to Solutions