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A common criticism of the remedial investigation/feasibility study process at Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) sites is that too much time and money are spent studying the problem before remediation can be started. A factor leading to this perception may be that the timing, type, and spacing of soil and groundwater sampling at these sites are inappropriate. The purpose of this paper is to propose a 3-step sampling strategy for quickly obtaining sufficient information to make remediation decisions and thus reducing overall characterization costs. The significant element in the strategy is that most of the expensive, time-consuming sampling and analyses using permanent monitoring devices are reserved for the end of the 3-step process as confirmation of the conceptual site model developed as a result of the investigation.
Step 1 is to identify the presence and source of contamination. Sample collection methods for this step should be nonintrusive or minimally intrusive; few permanent monitoring devices should be installed; and field screening analytical methods should be emphasized. The resulting data are used to assess the potential for risk to human health and the environment and identify potential pathways and barriers to migration that are the focus of subsequent investigation.
Step 2 is to delineate the contaminant source and determine contaminant fate and transport. Many samples may be collected at discrete intervals (both lateral and vertical), using temporary devices. The resulting geochemical and geotechnical data are used to determine feasibility of remediation and identify presumptive remedies.
Step 3 is to quantify risk and determine cleanup goals. Permanent monitoring devices should be installed if long-term monitoring will be necessary. The resulting data are used to document the presence of contaminants above background or regulatory criteria.
field screening, sampling, site characterization
Principal Scientist, The MITRE Corporation, San Antonio, Texas