What is Low Threat Tetrachloroethylene (PCE) Solvent Closure in California?

Understanding Low-Threat Solvent Case Closure for PCE Contamination in California

What is Low-Threat Closure & PCE Solvent Closure in California

For many of those managing investigation and cleanup of property contaminated with tetrachloroethylene (PCE) and other solvents in California, low-threat solvent case closure is the best but least understood option. This lack of clarity leads to frustration and mistrust. Let’s get familiar with low-threat solvent case closure and develop some general criteria beginning with the cleanup goal.

PCE Case Closure and Cleanup Goals: Reasonable Timeframe and Criteria

California State Water Resources Control Board (SWRCB) policy does not require that contamination is completely gone at the time of case closure; it specifies compliance with cleanup goals and objectives within a reasonable timeframe. This means that case closure can occur with contamination left in place as long as cleanup goals, such as relevant environmental screening levels (ESLs) or maximum contaminant levels (MCLs), are met in a reasonable timeframe. What defines a reasonable timeframe is ultimately decided by the regulatory oversight agency, but the decision considers the pace of natural cleanup mechanisms such as biodegradation. SWRCB closure orders for low-threat petroleum hydrocarbon sites state a reasonable time frame for plumes of a limited extent is multiple decades or longer, but expect more restrictions because PCE is less susceptible to natural cleanup mechanisms and has much lower ESLs. The general criteria for achieving cleanup goals are:

Criteria: Establish that natural mechanisms can reduce levels to cleanup goals and that contamination levels are at a point where natural mechanisms can reduce levels within a reasonable time frame.

Decreasing Groundwater Contaminant Plume

During the reasonable timeframe when residual contamination is naturally reduced to cleanup goals, the groundwater contamination plume must be decreased. Future plume stability is established at the time of closure by showing that the residual contaminant plume in groundwater is decreasing. As a result of a decreasing contaminant plume, risk management measures are not necessary and the site does not require future SWRCB oversight, another requirement for low-threat PCE case closure.

Criteria: Establish that the residual contaminant plume in groundwater is decreasing.

Contamination Restrictions

It must also be established that during the reasonable timeframe, the remaining contamination:

  • Cannot pose a risk to human health due to vapor intrusion or direct contact,
  • Cannot pose a risk to the environment or deeper water-bearing zones, and
  • Cannot pose any nuisance conditions.

These conditions must be established in such a manner that any risk management measures necessary are shown to work, implementation of risk measures are documented, and future SWRCB oversight is not required.

Criteria: Establish that either in post-cleanup or with post-cleanup risk management not requiring SWRCB oversight:
1) vapor intrusion or direct contact with residual contamination will not occur;
2) residual contamination will not risk the environment or travel to lower water-bearing zones, and
3) residual contamination will not cause a nuisance condition.

Consult with Our Experts for Low Threat PCE/Solvent Case Closure

We reviewed low-threat PCE solvent case closure as outlined in California’s Assessment Tool for Closure of Low-Threat Chlorinated Solvent Sites and developed three general criteria for case closure. If you are interested in low-threat PCE/solvent case closure for your site, we have over 40 years of experience. Call (831) 475-8141 or click on the button below for a free consultation.