Geophysical Measurments and the Public Environmental Process

Howard C. Clark

Environmental uncertainty often centers about geologic unknowns. And limits to these unknowns by objective measurement have always been the purview of geophysics. From new disposal site selection to decades old hazardous waste dump remediation, decisions are made in a public forum quite different from the exploration arena. Geophysical measurements are critical in decision making in a process involving those unfamiliar with geology.

There are a number of geophysical measurements written into government regulations. Texas calls for geophysical surveys in the permitting and subsequent assessment and remediation opertaions in a variety of situations ranging from optional resistivity profiling at a landfill site to a required 3-D seismic survey of a salt dome as a disposal cavern candidate.

There is also a history of geophysical application in the administrative process. Resistivity has been used in Texas landfill evaluations since the late seventies. Regulations specify that resistivity may be used to refine stratigraphy and an annual survey has been part of the detection plan at a number of sites. Although presented in Barnes layer and Moore cumulative form, the underlying measurements provide a valuable dataset. Electromagnetic surveys have been used in reconnaissance because they offer a qualitative interpretation without the questions of processing. Refraction has seldom been used, in part because simple computation is difficult to communicate. Reflection applications have been slow to develop, partly because of the inherent velocity inversion offered by the typical objective. Microgravity has been applied innovatively where geometric definition of the host is required. Consequently, there is background drawn from a variety of geologic provinces.

There is a continuing need for experiments and benchmark sites which offer separation of objective data and interpretive opinion particularly because new regulations and siting guidelines require greater attention to geologic definition and therefore to geophysical measurements.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995