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AOC 44 Delisting Report
Section 2 - Delisting Activities
An electromagnetic (EM) geophysical survey was conducted at AOC‑44 on January 6, 2005 to verify the initial geophysical results collected in 1996. All surface metal debris was picked up and thrown away prior to survey activities. The metal debris consisted of approximately 5 pounds of old tin cans and wire.
Prior to collecting geophysical data, a 75 by 100 foot grid oriented northeast‑southwest was established over the site area, as shown on Figure 44‑5 and Figure 44‑6. The easternmost corner of the grid (25 by 40 foot area) was omitted from data collection due to the presence of large trees in that portion of the grid area.
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 penetrating depth 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 anomalies at the site. Both the in‑phase (Figure 44‑5) and quadrature‑phase data (Figure 44‑6) were consistent across the survey area, with no variations that would indicate subsurface waste.