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AOC 46 Closure Report
Section 2 - Closure Activities
Excavation activities commenced at AOC‑46 on 16 February 2005. Prior to excavation, surface soil samples were collected to verify the extent of contamination at the site. Eight surface soil samples were collected on 2 February 2005 and analyzed for the following metals: barium, chromium, copper, nickel, zinc, arsenic, cadmium, lead, and mercury.
Six of the eight surface soil samples exceeded RRS1 (background) for one or more metals. Metals that exceeded RRS1 include zinc, copper, and lead. Sample locations are presented on Figure AOC46‑5. Sample results are presented in Appendix B. Surface soil samples are denoted SS.
Since several surface soil samples exceeded RRS1, the entire site was excavated to bedrock, approximately 18 inches below ground surface (bgs). Initial excavation activities were conducted on 16 February 2005. Subsequently, overexcavation was required at one sample location (AOC46‑BOT01) due to an RRS1 exceedance. The overexcavation was conducted 3 March 2005.
Approximately 56 CY of Class 2 non-hazardous waste was generated at AOC‑46 during excavation activities. Disposal of AOC‑46 waste was conducted under waste profile CG‑25591 C‑20. All waste was disposed at Covel Gardens Landfill. Waste manifests are provided in Appendix A.
2.2 - Confirmation Sampling
Following excavation on 16 February 2005, six confirmation, or closure, samples were collected to verify complete removal of contamination (Figure AOC46‑5). Two samples were collected from the bottom of the excavation (denoted BOT) and three samples were collected from the excavation sidewall (denoted SW). Each sample was analyzed for barium, chromium, copper, nickel, zinc, arsenic, cadmium, lead, and mercury.
One of the six samples, AOC46‑BOT01, exceeded RRS1 for lead with a concentration of 107.22 milligrams per kilogram (mg/kg). The RRS1 value for lead is 84.5 mg/kg.
Overexcavation at AOC46‑BOT01 was conducted on 3 March 2005 to remove remaining lead contamination. After overexcavation was complete, an additional sample (AOC46‑BOT03) was collected to confirm the lead contamination was removed. The lead analysis result for AOC46-BOT03 was 19.27 mg/kg. This result is well below RRS1, indicating that the lead contamination was removed during overexcavation.
Table AOC46‑1 shows all results of the confirmation sampling events. A complete listing of all analytical results is included in Appendix B.