Risks Increasing For Properties With Chlorinated Solvent Contamination

For properties where chlorinated solvents have been released, new regulatory challenges and related liability concerns are increasing as a result of controversial human health studies recently published by the federal Environmental Protection Agency (EPA). The following summarizes the new challenges and presents recommendations for addressing them.

Issues Presented by Chlorinated Solvents

Properties with chlorinated solvent contamination are already particularly difficult to clean up to meet regulatory standards. The two chlorinated solvents most typically of concern are tetrachloroethylene (PCE), a chemical long used in dry cleaning, and trichloroethylene (TCE), used in parts washing and degreasing activities. Both of these chemicals can migrate in groundwater, sink through water into bedrock where they are difficult to reach, contribute in certain conditions to indoor air contamination (known as "vapor intrusion"), and already are subject to very stringent cleanup standards.

New EPA Risk Assessments and the Regulators' Responses

Now, the rules for remediating these two solvents will be changing as a result of human health risk assessments conducted by the EPA. Human health assessments look at both the potential "excess" cancer and non-cancer (such as neurotoxic) risk related to a contaminant. EPA determined that the cancer and non-cancer risks related to TCE exposure were greater than previously believed. As a result, it is anticipated that EPA will lower the cleanup standard for drinking water to a more stringent level, and vapor intrusion screening standards for TCE are also expected to go down.

When the EPA sets a drinking water standard (known as the Maximum Contaminant Level, or MCL) of a particular contaminant, that requirement applies to public drinking water supplies in every state although any state can be more — but not less — stringent. Where groundwater is a potential drinking water source, states typically adopt the MCL as the groundwater cleanup standard. There is speculation that the results of the health assessment will produce a new standard that could be five times lower than the current MCL for TCE. As a "sinker," TCE is already difficult to remediate in groundwater to the current drinking water standard of 5 parts per billion. High levels of TCE in groundwater will generally decrease quickly with appropriate treatment, but once TCE levels are reduced, the final increment of the cleanup is the most difficult. If the...