Part I. Role of Geophysics in Environmental Assessments
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(Environmental Geophysics: Stewardship of the subsurface environment through non-invasive investigations.)
• Ground penetrating radar (GPR)
• Two loop electromagnetic induction (EM)
• Magnetic surveys
• Seismic refraction/reflection
• DC resistivity
• Non-conventional EM techniques:
- Transient electromagnetic methods
- Very low frequency (VLF),
- Controlled source magnetotellurics.
WHY USE GEOPHYSICS ??
For engineering, groundwater & other hydrogeologic studies, geophysics offers a cost-effective means for obtaining a quantitative, spatially representative overview of subsurface conditions.
In environmental site assessments, "blind" test borings are to be discouraged for obvious reasons:
Puncturing even one drum of certain common, but extremely toxic, products could enormously complicate the site remediation and restoration, threaten the natural environment and astronomically escalate the cost of cleanup.
In addition, test borings and drilling can lead to "channels" from one geologic level to another — contaminants that were originally emplaced at shallow depth, and, for example, were relatively immobile in the unsaturated zone, might readily migrate downward to the water table along a new borehole; or there might be significant cross-contamination between aquifers at different levels cut by an exploratory drillhole.
Part II. An Overview of Geophysical Applications
Applications to Engineering and Groundwater Investigations
Surface geophysics is often used in engineering and groundwater studies:
Environmental Site Assessment
(For current or potential chemical releases)
Surface geophysics can remotely & non-invasively detect
Such information allows plans to be optimized for investigatory test coring, test pits and trench excavations, or allows work underway to be accordingly modified.
If site remediation is called for, surface geophysical studies can then serve as a prelude to developing a comprehensive restoration strategy.
Geophysical investigations can continue as the site is restored in order to
• Optimize the on-going remediation procedures,
• Recalibrate previous geophysical or direct sampled (from borings, test pits, etc.) interpretations as new information becomes available,
• Detect new areas for concentrated investigation,
• Assess effectiveness of remediation/restoration activity.
Cautionary note: Base-line
information needs to be established at the earliest stage of the site assessment/investigation.