Integrated, High Resolution Geophysical
Investigation Over
a Former Waste Lagoon
Christopher Papadakis, John L. Petruccione, Vaughn E. Berkheiser
As part of an environmental study, three geophysical
methods (EM-31,
magnetics and GPR) were utilized to map near-surface conditions at a former
latex waste lagoon in southern Georgia. The goals of the
geophysical
survey
were: (1) to identify the former lagoon boundary; and (2) determine the lateral
extent and location of buried steel drums and other ferromagnetic debris
reportedly used as fill material. The general location of the lagoon within the
2.7 acre site was visible on aerial photographs but subsequent backfilling and
grading had eliminated any surface expression of the lagoon boundary.
Electromagnetic and magnetic gradient data were required on a 10 × 10 foot grid pattern. Quadrature and in-phase EM-31 data collection were employed in the vertical dipole mode to measure near-surface conductivity (<15 feet) and the magnetic component response to the induced EM field. Magnetic gradient data permitted interpretation of near-surface ferromagnetic bodies without the need for base station reoccupation or diurnal corrections. All EM and magnetic data were in-field downloaded and preliminary computer contour maps were generated to locate strong anomalies. To further define detected targets, high resolution GPR (500 Mhz) data were collected over interpreted EM and magnetic anomalies and in areas of cultural interference (building, fences, etc.).
The EM-31 and magnetic maps reveal a series of strong anomalies (bullseye
contours) interpreted as ferromagnetic objects within the waste lagoon fill.
Continuous GPR profiles over these areas recorded strong parabolic reflections
(<6 feet) interpreted as solitary metallic objects. In conjunction, the
geophysical
data results correlated well in defining the lagoon boundary and
areas of concentrated ferromagnetic infill. Subsequent drilling and excavation
guided by these
geophysical
interpretations confirmed the presence of crushed
metallic drums and ferromagnetic debris. The integrated
geophysical
survey
provided a high-resolution, near-surface site characterization which enabled the
project to be performed in a timely and cost effective manner.
AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995