Soil Remediation and Post-Excavation Sampling. The June 2008 soil sampling defined eight primary sub-slab locations with contamination above commercial-use SCOs and/or pigment staining, shown on Plate 3. These estimated excavation boundaries were determined based on the analytical results and the observations of pigment staining, as well as by the locations of building structural components and former operational activities. For example, the northern, southern and western boundaries of the impacted area in the Blue Wing (at borings SB-10 through SB-14A) were defined based on the absence of soil contamination and significant pigment staining at neighboring borings SB-7, SB-8, SB-9, SB-14 and SB-15. The eastern boundary of this remediation area was defined by the position of a retaining wall that forms the western side of the Grind & Mix Department, located one floor level below the Blue Wing (as noted above, the main building was constructed in several levels on a hill). The actual extent of IRM activities is provided on Plate 5. Post-excavation soil sampling was completed to document the effectiveness of the IRM in meeting the remedial goals. As proposed, this sampling was conducted in accordance with the post-excavation sampling frequencies specified in DER-10. DER-10 specifies those sampling frequencies based on the perimeter of an excavation. As all excavations at the Site were between 20 to 300 feet in perimeter, per DER-10, one post-excavation sidewall sample was obtained per 30 linear feet of sidewall and one basal sample was obtained per 900 square feet of excavation floor. These post-excavation sampling locations are shown on Figures 2 through 8 (to locate for specific excavation-area details, refer to the enlargement key provided on Plate 5). The sidewall samples for a given excavation were obtained from the interval(s) at which soil contamination requiring remediation was identified. For example, post-excavation sampling proximate to locations SB-16 and SB-17 was conducted at 0.5-1.0’, the only depth interval at which soil contamination was detected. Post-excavation sampling near locations SB-10 through SB-13, where soil contamination was detected at multiple depth intervals, targeted the uppermost and deepest intervals (i.e., 0.5-1.0’ and 4.0-4.5’) in which metals were detected above commercial-use SCOs. The actual post-excavation sampling depths for each IRM area are provided in the tables in Appendix B and in the databoxes included on the detail figures. As proposed, all post-excavation so...
