Excavation Area. Soil excavation areas will be clearly marked, taped off, or temporarily fenced following completion of each day’s field activities. The specific security measure applied will be based on the depth of the soil excavation. In addition, excavation sidewalls will be sloped to prevent generation of confined spaces and limits potential falls if someone does enter. If necessary, dust generation will be minimized through water application to excavated soils and/or the excavation area.
Excavation Area. Soils excavation in the vicinity of the Red Wing Secondary Production Area (as shown on Figure 5) began on October 24, 2008 to address exceedances of nickel identified at SB-28 during the June 2008 SRI. An initial area of approximately 18’ by 23’ was removed to a depth of 4.5’ and one base sample (PE01) and four sidewall samples (PE02 through PE05) were collected for PPMs+Ba analysis. As proposed in the IRM Work Plan, two intervals were sampled per sidewall (from 0.5-1.0’ and 2.0-2.5’), with the exception of the north (PE03) sidewall due to the presence of a subsurface concrete footer extending to a depth of approximately 3 feet. As such, only one sample at the 3.0’ – 3.5’ interval was collected at that location. Analytical results for samples collected in the SB-28 excavation are summarized in Appendix B and on Figure 5. Reported metals concentrations in the base sample and the northern and eastern sidewall samples (PE03 and PE04), respectively, were all below the corresponding SCO. However, the upper and lower intervals from both the western (PE02) and southern (PE05) sidewall samples exceeded the SCO for nickel. As such, additional soil removal and a second round of post-excavation sampling took place on November 12, 2008. Due to a concrete footer extending approximately 1.5 feet below grade, no additional shallow-interval sidewall samples could be collected along the western “PE02” sidewall. Reported nickel concentrations from one sample, the “PE05A” upper interval sample at 26.4 mg/kg, were well below the commercial-use SCO of 310 mg/kg. However, all other samples exceeded that SCO. Additional soil excavation and delineation sampling was therefore undertaken on two occasions (January 6 and 8, 2009). As shown on Figure 5, nickel concentrations at these sidewalls remained above that SCO. As such, Sun Chemical concluded that delineation sampling was warranted prior to proceeding with any additional remediation in this area. In addition, further soil removal was not needed at this location to facilitate completion of the facility demolition and site regrading. ENVIRON marked this area with survey stakes. The staked locations were surveyed by Control Point Associates on March 11, 2009. Additional sampling in this area is proposed below in Section 6.
