Consensus Report

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For more than 100 years, the Coeur d'Alene River Basin has been known as "The Silver Valley" for being one of the most productive silver, lead, and zinc mining areas in the United States. Over time, high levels of metals (including lead, arsenic, cadmium, and zinc) were discovered in the local environment and elevated blood lead levels were found in children in communities near the metal-refining and smelter complex. In 1983, the U.S. Environmental Protection Agency (EPA) listed a 21-square mile mining area in northern Idaho as a Superfund site. EPA extended those boundaries in 1998 to include areas throughout the 1500-square mile area Coeur d'Alene River Basin project area. Under Superfund, EPA has developed a plan to clean up the contaminated area that will cost an estimated $359 million over 3 decades--and this effort is only the first step in the cleanup process. Superfund and Mining Megasites: Lessons from Coeur d'Alene River Basin evaluates the issues and concerns that have been raised regarding EPA's decisions about cleaning up the area. The scientific and technical practices used by EPA to make decisions about human health risks at the Coeur d'Alene River Basin Superfund site are generally sound; however, there are substantial concerns regarding environmental protection decisions, particularly dealing with the effectiveness of long-term plans.

Key Messages

  • A major controversy at the Coeur d'Alene River basin site arose because EPA did not base its risk assessment and remediation decisions on the blood lead levels that had been measured but on the IEUBK model to estimate potential levels and related health risks
  • Children of ages 1 to 4 are the group at highest risk from lead exposure. The committee found it inappropriate that the HHRA presented aggregate data on childhood lead screening for children 0-9 years old, as that information is misleading and tends to underestimate the risk among the principal target group.
  • EPA adequately characterized the feasibility of alternative remedial actions for addressing risks to human health; however, the long-term effectiveness of the selected remedy in the Coeur d'Alene River basin is questionable because of the possibility, even likelihood, of recontamination from floods and damage to protective barriers used in residential remediations.
  • EPA has not adequately characterized the substantial hydrologic and climatic variations that can occur in the basin. Contaminant transport models are based on average flows and conditions, and the RI only minimally characterizes the extreme events (for example, flood events that transport large amounts of contaminated sediments) that substantially affect the fate and transport of metals throughout the basin.
  • EPA is proposing to use adaptive management to implement interim ecologic protection remedies; however, the committee is concerned about the rigor of EPA's adaptive management approach at this site, particularly regarding performance indicators needed to evaluate progress.
  • EPA's ERA describes the likelihood, nature, and severity of adverse effects on plants and animals resulting from exposure to metals associated with mining operations throughout the study area. The committee found the assessment to be generally consistent with best scientific practices.
  • EPA's HHRA is correct in concluding that environmental lead exposure poses elevated risk to the health of some Coeur d'Alene River basin residents.
  • EPA's evaluations provide a useful depiction of the location of contaminated soils, sediments, and surface waters over the large spatial scale of the basin.
  • EPA's segmentation of geographic areas within the basin for assessment and remedial actions does not facilitate a basinwide analysis of sources, transport, and fate of contaminants.
  • EPA's site characterization also did not adequately address groundwater the primary source of dissolved metals in surface water.
  • Evaluations of chemical speciation and mineralogy were extremely limited in the RI.
  • For EPA's decision making regarding environmental protection, the committee has substantial concerns, particularly regarding the effectiveness and long-term protection of the selected remedy.
  • For arsenic, EPA collected no information about actual human uptake and based its risk assessment on arsenic concentrations in environmental samples.
  • IEUBK model are consistent with current scientific knowledge; however, the committee concluded that there were some technical issues, particularly the uncertainties associated with the default assumptions for bioavailability of soil lead, soil and dust ingestion rates, and the parameter used to extrapolate from a single blood lead estimate to the distribution of concentrations throughout a population.
  • In considering effects on organisms, the high variability in exposures related to extreme events, including low-flow conditions and flood events, was not considered.
  • The IEUBK model results should not be the sole criterion for establishing health-protective soil concentrations because model uncertainty and site complexity may interact in unexpected or unknown ways.
  • The committee concludes that an effective program for mining megasites should emphasize long-term adaptive management. The desirable program components are a stable management structure, long-term monitoring components, active state and local involvement in the remediation process, a broad perspective regarding what actions should be undertaken in addition to cleanup, and long-term funding.
  • The committee found that scientific and technical practices used by EPA for decision making regarding human health risks at the Coeur d'Alene River basin Superfund site are generally sound. The exceptions are minor.
  • The effects of psychological stress on mental health are not considered in the HHRA. However, there is strong scientific evidence that living in or near an area designated as a Superfund site is associated with increased psychological stress and may also cause adverse health effects.
  • The threat to aquatic life in the basin results primarily from the influx of high levels of dissolved zinc from groundwater to surface waters.