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AOC 49 Delisting Report
Section 2 - Field Activities
Since AOC‑49 was identified as a potential trench area, a geophysical survey was conducted to determine if subsurface waste is present at the site. An electromagnetic (EM) geophysical survey was conducted at AOC‑49 on January 6, 2005. Prior to collecting EM data, a 100 by 100 foot grid was established over the area of the suspected trench. The survey area covered the entire site area and a large amount of area surrounding the site, as seen in Figure AOC49‑5 and Figure AOC49‑6.
EM measurements were taken using a Geonics EM‑31 ground conductivity meter and recorded with a Polycorder data logger. The conductivity meter consists of transmitter and receiver coils that are separated by 12 feet. The instrument has a nominal depth of penetrating of approximately 16 feet when operated in the vertical‑dipole mode. The instrument measures both quadrature‑phase and in‑phase components of an induced magnetic field. The quadrature‑phase component is a measure of apparent ground conductivity while the in‑phase component is more sensitive to the presences of ferromagnetic metal. A lateral variation in apparent ground conductivity indicates a lateral change in subsurface physical properties (i.e., related to degree of disturbance).
The EM geophysical survey did not reveal any evidence of subsurface waste at AOC‑49 or the surrounding area. Both the in‑phase (Figure AOC49‑5) and quadrature‑phase data (Figure AOC49‑6) were consistent across the survey area, with no variations that would indicate subsurface waste.