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| Resource Library > Technology Transfer > Programs and Initiatives > Source Zone Treatment |
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 As a consequence of the widespread production, transportation, use, and disposal of petroleum fuels and solvents, accompanied by inadvertent releases of these substances in the form of non-aqueous-phase liquids (NAPLs), fuel and solvent contamination is present at numerous sites throughout North America and Europe. Typically, following a release the NAPL invades the subsurface environment where it dissolves very slowly, thereby adversely affecting groundwater.
In the late 1980s and early 1990s, it was realized that NAPLs can be extremely persistent in the subsurface environment, and are capable of functioning as long-term sources of contaminants in the subsurface. By the late 1990s, almost all chlorinated solvent sites and many fuel-spill sites were assumed to contain a continuing NAPL source, even those sites where NAPL was not directly observed. Better technologies that are capable of removing or destroying residual NAPL were developed in response. However, the benefits of these methods are difficult to assess and justify as most are not commonly used and NAPL sites prove to be very challenging to characterize. Essentially to date, there are two general competing remediation options for NAPL sites:
- Application of aggressive but emerging source treatment technologies to remove NAPL from source zones, or
- Application of long-term, low-intensity treatment or containment alternatives that leave most of the NAPL mass in place and focus on long-term management of the NAPL dissolution products.
If NAPL removal does not achieve a meaningful reduction in the extent of contaminants in the environment, or in the projected lifetime of the source zone, or full and accurate characterization data does not exist at the site to confirm the extend of NAPL removal, then resources applied to source-zone treatment or removal could be better used for other risk-control measures.
At the nearly 17,000 sites on Department of Defense (DoD) installations potentially requiring environmental cleanup, there is a need for innovative source-zone treatment technologies that offer cost-effective risk reduction. Unfortunately, the number of currently available commercial technologies capable of providing effective treatment of source zones at NAPL-affected sites is limited. Characterization tools, techniques, and methods are limited in their capabilities to properly characterize NAPL sites, especially in more difficult heterogeneous, challenging subsurface environments. Furthermore, there currently is no consensus in the academic, technical and regulatory communities on the ecological or environmental impacts or benefits resulting from treating or removing light non-aqueous-phase liquids (LNAPLs) such as petroleum fuels, or dense non-aqueous-phase liquids (DNAPLs) such as chlorinated solvents, from NAPL source zones. The cost of source-zone treatment is high, and the anticipated benefits need to be understood before significant resources are committed to source-zone removal. Since it is not economically practical to remove all NAPL mass from most source zones, it is necessary to weigh the likely benefits and costs associated with partial NAPL mass removal using some aggressive in-situ technology (e.g., alcohol or surfactant flushing; steam flooding; air sparging; chemical oxidation) against the benefits and costs associated with some NAPL source-zone control or containment measure (e.g., substrate enhancement, engineered barrier, natural attenuation).
This technology roadmap is intended to assist Air Force environmental managers in identifying and applying more effective methods for remediating and managing sites contaminated with NAPLs. The majority of sites on Air Force property already have entered the remedial design or remedial action stage of remedy development, although very few sites have attained cleanup goals. While some remediation systems are necessary to contain contaminants and prevent potential exposure to susceptible receptors, most Air Force sites are located in industrial or airfield areas where there is little risk of human or ecological exposure. This technology roadmap combines the "lessons learned" from two decades of remediation experience within AFCEE, with recent emphasis on risk-based and site-specific cleanup objectives. The Source Zone technology roadmap contains modules on individual Web pages that will:
- Introduce Air Force environmental managers to the general nature of the NAPL contamination problem,
- Describe the basic elements of many of the currently available approaches for dealing with NAPL source zones, and provide a comparison of the relative performance and costs associated with these approaches,
- Acquaint Air Force environmental managers with some of the regulatory and policy issues associated with NAPL source-zone remedial approaches,
- Provide a conceptual framework and tools for screening NAPL source-zone sites, enabling Air Force environmental managers to evaluate the relative costs and benefits associated with various remedial approaches, and to identify appropriate response actions,
- Provide case-history examples of application of several different remedial approaches at NAPL source-zone sites, and
- Identify additional resources that are available for Air Force environmental managers dealing with NAPL source-zone sites.
The intended result is a more realistic and cost-effective approach to NAPL source-zone remediation at Air Force sites.
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