 |
| Resource Library > Technology Transfer > Programs and Initiatives > Source Zone Treatment > Site Characterization |
|
Site Characterization
In order to develop rational and cost-effective remediation strategies at sites contaminated with petroleum fuels or chlorinated solvents, it first is necessary to assess whether a NAPL phase is likely to be present in the subsurface, and if so, to evaluate the location, nature and extent of NAPL contamination. The presence and potential for potential of NAPL at contaminated sites needs to be characterized because: 1) the properties and principles that govern the behavior of NAPL and dissolved-phase constituents are quite different; 2) NAPL can persist for decades or centuries as a significant source of groundwater or soil-vapor contamination; and 3) without adequate precautions or understanding of NAPL presence and behavior, site characterization activities may result in expansion of the NAPL contamination to previously unaffected regions, with resulting increases in remediation costs. Therefore, because knowledge of the occurrence and location of NAPLs is essential for design of a remediation system, and accurate knowledge of the site-specific nature of the subsurface is vital for evaluating the potential for, and physical limits on remediation, a thorough site characterization is required for NAPL sites.
A primary goal in the assessment of a site contaminated with petroleum fuels or chlorinated solvents is to establish whether significant quantities of a NAPL phase are present in the subsurface. If NAPL is present, the site characterization should assess the long-term contribution of NAPL to site risks and what potential remedies could be used to reduce NAPL impacts. Specific objectives of NAPL site evaluation may include:
- Estimation of the quantities and types of NAPLs released and present in the subsurface;
- Delineation of NAPL release areas;
- Determination of the zone(s) in the subsurface where NAPL is present;
- Delineation of site stratigraphy;
- Determination of fluid-media properties; and
- Determination of the nature, extent, migration rate, and fate of contaminants.
Many lines of evidence can contribute to the evaluation of a NAPL site. These are described in detail by Cohen and Mercer (1993) and Pankow and Cherry (1996).A structured approach to the process of evaluating a NAPL site and identifying potential remediation strategies is presented by the US Environmental Protection Agency (USEPA, 1994) and is further developed in the document entitled Remediation of Chlorinated Solvent Contamination on Air Force and Industrial Properties.
The process of site characterization, and of developing an accurate conceptual site model (CSM) can benefit greatly from application of available computer-based visualization tools, to organize, present, and evaluate available site data. Information presented in a visual format also can be utilized in site screening, to enable the site manager to qualitatively assess site-specific factors that may affect the decision-making process.
|
|
|
|
|
