DNAPL REMEDIATION: IS IT WORTH THE COST?

It has been known for some time now that the presence of DNAPL in an aquifer constitutes a continuing source of groundwater contamination that presents obstacles to remediation and site closure. Several technologies are now becoming available in the marketplace to remediate DNAPL. These include air sparging, in-situ chemical oxidation, surfactant/cosolvent flushing, and in-situ thermal treatment. In this paper, each of these technologies is described, discussed and compared to containment remedies, both in general, and in a case history presented for one site. Uncertainties and limitations associated with the innovative technologies make an assessment of their effectiveness in achieving regulatory standards difficult. When considered with the high cost of implementation and the possible need for additional treatment to address residual contamination, it may be difficult to justify implementing a DNAPL removal or treatment technology. Containment remedies require ongoing operation and maintenance for very long periods of time, but they do limit costs and generally satisfy the regulatory needs of mitigating environmental impacts and reducing future risk. Other site factors such as property use and regulatory closure requirements can impact the remedy selection, but in general it appears that the current innovative technologies may not offer a lower cost way of reducing the liabilities and risks associated with a site.