Consensus Report

Alternatives for Managing the Nation's Complex Contaminated Groundwater Sites (2012)


Each report is produced by a committee of experts selected by the Academy to address a particular statement of task and is subject to a rigorous, independent peer review; while the reports represent views of the committee, they also are endorsed by the Academy. Learn more on our expert consensus reports.

Across the United States, thousands of hazardous waste sites are contaminated with chemicals that prevent the underlying groundwater from meeting drinking water standards. These include Superfund sites and other facilities that handle and dispose of hazardous waste, active and inactive dry cleaners, and leaking underground storage tanks; many are at federal facilities such as military installations. While many sites have been closed over the past 30 years through cleanup programs run by the U.S. Department of Defense, the U.S. EPA, and other state and federal agencies, the remaining caseload is much more difficult to address because the nature of the contamination and subsurface conditions make it difficult to achieve drinking water standards in the affected groundwater. This report estimates that at least 126,000 sites across the U.S. still have contaminated groundwater, and their closure is expected to cost at least $110 billion to $127 billion. About 10 percent of these sites are considered "complex," meaning restoration is unlikely to be achieved in the next 50 to 100 years due to technological limitations. At sites where contaminant concentrations have plateaued at levels above cleanup goals despite active efforts, the report recommends evaluating whether the sites should transition to long-term management, where risks would be monitored and harmful exposures prevented, but at reduced costs.

At a webinar held in December 2012, Michael Kavanaugh, chair of the report-authoring committee, presented the report’s findings and, along with other committee members, answered questions from the public. Click here to access a recording of the webinar. A PDF of the presentation given at the webinar is available to download here.

Key Messages

  • At least 126,000 sites across the country have residual contamination at levels preventing site closure, and this number is likely an underestimate. About 10 percent of the 126,000 sites are estimated to be complex from a hydrogeological and contaminant perspective. No information is available on the total number of sites with contamination in place above levels allowing for unlimited use and unrestricted exposure, although the total is certainly greater than 126,000.
  • Approximately ten percent of Superfund facilities affect or significantly threaten public water supply systems, but similar information from other programs is largely unavailable.
  • The estimated "cost to complete" for sites that have not reached closure is $110-127 billion. This number is highly uncertain and likely to be an underestimate of future liabilities.
  • For the suite of currently available remedial technologies, significant limitations persist that make widespread achievement of drinking water standards unlikely at most complex groundwater sites in 50–100 years.
  • There are limited data with which to compare remedial technology performance. Additional independent reviews of remedial technologies are needed to summarize their performance under a wide range of site characteristics.
  • As our understanding of chemical toxicity and dose-response relationships evolves, there could be changes in drinking water and indoor air standards for important contaminants, such as the solvent TCE. Such changes could potentially lead to determinations that existing remedies at some hazardous waste sites are no longer protective of human health and the environment.
  • Consideration of the vapor intrusion pathway is needed at all sites where volatile organic chemicals (VOCs) are present in the soil or groundwater aquifer. As a precaution, vapor mitigation could be built into all new construction on or near known VOC groundwater plumes.
  • At many complex sites where the effectiveness of site remediation has reached a point of diminishing returns prior to reaching cleanup goals, the transition to passive management (like monitored natural attenuation or MNA) should be considered using a formal evaluation called a Transition Assessment.
  • Cost savings are anticipated from implementation of the Transition Assessment but funding will still be needed to maintain long-term management at these complex sites.
  • New research is needed in many areas to support the shift to long-term management of complex sites, including remediation technology development, tools to better assess vapor intrusion and MNA, and modeling that can incorporate back-diffusion and desorption. Overall research and development have been unable to keep pace with the needs of practitioners trying to conduct remediation on complex sites.