Chlorinated ethene source remediation: Lessons learned

The past decade has seen rapid progress in source zone remediation, and an increasing understanding of the capabilities and limitations of potential technologies. Research has produced a large database from well-monitored demonstrations, more effective models to improve decision-making, and a better understanding of the physical, chemical, and biological constraints to achieving complete restoration. This experience has led to technology selection guidance to help managers develop reasonable expectations for treatment.133 It also has led to several publications from researchers funded through SERDP and ESTCP on source zone treatment (including technology-specific cost and performance reports), available at http://www.serdp-estcp.org/Featured-Initiatives/Cleanup- Initiatives/DNAPL-Source-Zones. Experience also has shown that different technologies are needed for different times and locations, and that deliberately combining technologies may improve overall remedy performance. Guidance on adaptive management and integrated strategies for DNAPL sites has been developed to help practitioners select the best combinations and develop realistic objectives. 52,134 Such guidance should improve source treatment and save money, through more cost-efficient characterization and monitoring, more efficient and appropriate uses of remedial technologies, and greater consensus on source treatment decisions. Challenges remain, however, particularly at complex sites that are difficult to characterize and where prolonged treatment and/or multiple technologies have failed to achieve remedial goals. Many DNAPL sites still cannot be restored to regulatory criteria within a few years or within a "reasonable time frame" (often considered roughly 30 years), and therefore will require long-term management.