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Mr.Mark Clardy <br /> Page 5 <br /> April 3, 2006 <br /> • REMEDIAL APPROACH <br /> As discussed above, the human health protection issues revolve around direct contact with <br /> impacted soil. To address these potential human health issues, SAIC proposes to excavate <br /> ' impacted soil to eliminate the direct contact pathway. <br /> Soil Excavation <br /> ' In the residential portion of Neighborhood B, single family residences are proposed. Typically,a <br /> homeowner would face direct contact with impacted soil to an approximate depth of 3 or 4 feet <br /> ' when planting trees or shrubs, etc. In most instances, direct contact is limited to 1 to 2 feet deep. <br /> However, exposure to impacted soil deeper than that is possible during installation of other <br /> features in a yard, such as a swimming pool. This activity could lead to homeowners and/or a <br /> ' contractor being exposed to impacted soil as deep as 12 to 15 feet. Therefore, Shell and SAIC <br /> propose to excavate soil to a depth of approximately 15 feet within the impacted areas defined <br /> during the site investigation. Figure 3 shows the impacted areas, and shows the vertical extent of <br /> ' impacted soil. As the soil borings advanced outside of the areas defined on Figure 3 did not <br /> exhibit impact, excavation is not proposed in these areas. Note that soil impact extends deeper <br /> than 15 feet in three areas: B-3,B-4, and B-9. These areas will be excavated to a maximum <br /> depth of 15 feet. In the other nine areas, impact is observed to attenuate at a depth less than 15 <br /> ' feet, and these areas will be excavated to the vertical extent of impact. Table 1 presents the <br /> anticipated number of cubic yards of soil that will be excavated and disposed of based on a <br /> maximum anticipated excavation depth of 15 feet. The following sections provide specifics on <br /> the excavation. <br /> Excavation Procedures <br /> ' Excavation sidewalls will be sloped at a minimum of 1:1 (horizontal to vertical) to minimize the <br /> likelihood of sloughing of the sidewalls. Depending on the equipment, a ramp and a platform <br /> ' may be constructed within the excavation to aid in the work. To aid in segregation of clean and <br /> impacted soil,the following excavation strategy will be used: first marking the impacted area, <br /> and focusing excavation on that area to the limits of the equipment; then cutting the sidewall <br /> ' slope that will consist mainly of clean material. This procedure will generate mainly impacted or <br /> clean soil depending on whether the impacted area or sidewall is being addressed. This <br /> procedure is described in more detail below. <br /> ' As excavation progresses, SAIC personnel will periodically monitor the excavation sidewalls,to <br /> evaluate progress toward removal of the impacted soil. SAIC will assist the excavation <br /> contractor in segregating impacted soil from non-impacted soil. The impacted area will be <br /> ' targeted first, and impacted soil will be loaded directly into trucks for hauling to the landfill. <br /> This initial excavation will be advanced to as great a depth as is practical and safe, and the <br /> excavation will have vertical or nearly vertical sidewalls. Once the vertical limit has been <br /> ' reached, excavation will be sloped to develop the sidewalls. As this soil will generally be non- <br /> impacted, the soil will be stockpiled adjacent to the excavation. If some impacted soil is noted <br /> during this operation, it will be stockpiled separately on plastic sheeting. Once the excavation <br /> ' has been expanded,the next central core portion will be targeted, and the soil again loaded <br /> directly into trucks for hauling to the landfill. This procedure will be followed until the target <br /> depth is achieved. <br />