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AOC 56 RFI Closure Report
Section 2 - Closure Activities
Although contaminants were not detected above closure standards in the three RFI surface soil samples, geophysical results indicated that it was likely that a disposal trench was located at the site. To achieve site closure, all waste and waste residue was excavated and removed. This section describes closure activities at the site.
Excavation of the geophysical anomaly confirmed the presence of a waste trench. The waste and waste residue was excavated and removed from January through April, 2004. During this period, 3,858 cubic yards of soil and debris were excavated and removed from the site. All excavation activities were performed by Eagle Construction and Environmental Services of San Antonio, Texas.
The dimensions of the excavation pit extended approximately 157 feet by 87 feet, for a total of 10,247 square feet. Anti-tank mine fuses, various sizes of ordnance scrap, crumpled empty drums, and empty paint cans are among the items found buried at AOC‑56. All ordnance scrap found was inspected by unexploded ordnance (UXO) specialists. No unexploded ordnance or explosive residue was found. A total of 411 items found were cut by the UXO specialists prior to disposal so that the items would not be mistaken for UXO in the future. Geophysical anomalies were excavated until it could be confirmed that they were not associated with waste management activities. Photos of the excavation and items found during excavation activities can be found in Figure AOC56‑13.
Excavated material was stockpiled onsite for characterization prior to disposal. Two waste characterization samples were collected and analyzed for total petroleum hydrocarbons (TPH) and toxicity characteristic leaching procedure (TCLP) metals. Disposal of the waste was conducted from February 2004 to April 2004, under waste profile CG-25591 (C-8) at Covel Gardens Landfill, San Antonio, Texas. Manifests are provided in Appendix D.
Confirmation sampling was performed on February 19, 2004, after the soil was excavated. Two samples were taken from the bottom of the excavation pit, and six were taken from the sidewalls of the pit. Each sample was analyzed for barium, chromium, copper, nickel and zinc (SW6010B); arsenic (SW7060A); cadmium (SW7131A); lead (SW7421); mercury (SW7471A); VOCs (SW8260B); SVOCs (SW8270C); and explosives (SW8330), by APPL Laboratory in Fresno, California.
Samples AOC56‑SW01 through AOC56‑SW06 and AOC56‑BOT01 through AOC56‑BOT02 were collected on February 19, 2004 after the initial excavation of all waste from the AOC 56 disposal trench. All samples had results below the CSSA background levels for each metal, except AOC56‑SW01, which had results exceeding background for zinc. All VOCs, SVOCs, and explosives results were below RLs and therefore met RRS1 criteria. The AOC56‑SW01 area was overexcavated and re-sampled on March 23, 2004. The new sample, AOC56‑SW07, showed 4.5 mg/L below the CSSA background level for zinc, deeming the site ready for closure under RRS1. All samples from both confirmation sampling events are shown on Figure AOC56‑13. Confirmation sample results can be found in Table AOC56‑2. A complete list of results is provided in Appendix A.
After confirmation samples confirmed site cleanup was complete, the excavation was backfilled and brought to grade with approximately 3,800 cubic yards of native clean fill material.
Figure AOC-56 14 - Photos from Excavation of AOC‑56
Site Photo A – Excavation area at site AOC‑56, January 2004
Site Photo B – Items found and removed from the site during excavation, including casings and projectiles, January 20, 2004
Site Photo C – Old crumpled drums found buried at AOC‑56, January 12, 2004
Site Photo D – Mine fuses uncovered at AOC‑56, January 8, 2004