State of Colorado Takes Novel Approach to Conditional Site Closure
Many brownfields sites, such as properties with underground storage tanks or dry-cleaning buildings, take too long to meet EPA’s applicable groundwater standards. Low-concentration groundwater plumes may persist for decades despite efforts by the responsible party to complete remediation. However, the truth is that many of these sites pose little risk to public health and the environment. The State of Colorado’s Department of Public Health and Environment (CDPHE) has come up with an alternative way to help responsible parties “close” these kinds of sites.

While some states allow a risk-based closure using either alternate concentration limits or results from a human health risk assessment pursuant to 40 C.F.R. § 264.94, few states have formalized a process for risk-based closures. In October 2014, CDPHE initiated a mechanism for closing these low risk sites through an approach known as “Conditional Closure.” Conditional Closure is considered on a case-by-case basis using an overall site conceptual model and risk profile to make a determination regarding the need for ongoing monitoring.

How does it work?
Specific details of the CDPHE Policy for Conditional Closure of Low-Threat Sites with Residual Ground Water Contamination can be found here, but the main requirements that need to be met for consideration include:

  • The site usually can’t be regulated under certain programs like Superfund, or be a Resource Conservation and Recovery Act (RCRA) treatment, storage, and disposal (TSD) facility. However, the site can be a RCRA-regulated site, such as a dry cleaner. The program also does not apply to sites in the Colorado Voluntary Cleanup Program (VCUP).
  • Sources of the impacts have been remediated to the extent possible.
  • The plume size is either stable or decreasing in all dimensions.
  • The contaminant concentrations are within approximately 10-20 times the standard or less, are stable, and are decreasing over time. The concentrations must be predicted using fate and transport modeling to meet applicable screening levels within a reasonable time frame. Based on the sites that have been approved for Conditional Closure thus far, this timeframe is generally within 10 years.
  • Active remediation or containment systems are no longer necessary.
  • Vapor intrusion and other cross-media transfers have been addressed.
  • No potential threats to environmental or human health are found downgradient of the site. This includes surface water, drinking/irrigation wells, and adjacent aquifers.

The good news is that the CDPHE will allow for some discretion if not all of these requirements are met, and the policy applies to both industrial/commercial and residential properties. For example, the agency could potentially approve Conditional Closure of a site with an offsite plume that has migrated onto residential property assuming the site conditions are suitable, including the plume’s stability, control of exposure pathways, and groundwater concentration trends.

Currently, there is no set timeframe for how long the Conditional Closure review process may take, but according to the CDPHE, recent reviews have taken at least two months.

So, what are the pros of Conditional Closure?
  • Removes the requirement for routine monitoring and reporting.
  • Reduces the need for oversight by the regulatory agency.
  • Reduces waste generation associated with sampling.
  • Establishes safe land uses through completion of an institutional control if required.
And the cons to consider before you pursue…
  • Requires an institutional control to prevent future unsafe land use in certain circumstances.
  • Does not preclude legal damages being pursued by private parties.
  • Allows for regulatory reopeners by the CDPHE if new information warrants action.
Where to start?
Responsible parties submit a comprehensive report to the CDPHE to demonstrate compliance with the requirements. The first step is to gather all existing data. Next, hire a knowledgeable consultant to review all the existing data and to help identify and determine any data gaps. In some instances, all the data needed may have already been collected.

What does the outcome look like? 
If the CDPHE determines all conditions are met, it may set an alternative concentration limit, i.e., a new groundwater standard calculated to protect human health and the environment at that site. Or, the CDPHE will require an institutional control to prevent unsafe uses of the site (for example, a prohibiting groundwater extraction). Depending on the site, the CDPHE may also require public meetings to discuss the Conditional Closure decision.

In summary
CDPHE has established a relatively unique program that can help save owners money on long-term monitoring and reporting, and assists the agency in prioritizing higher risk sites above low-risk sites. This type of forward-thinking provides both the regulated community and the regulatory agencies with a new tool to promote redevelopment of impaired properties where generally applicable groundwater standards have not been met.

Conditional Closure goes beyond a mere “comfort letter” to define the site’s future status, so that borrowers, lenders, and developers can have greater future certainty and end long-term monitoring requirements. If your site is clean to the extent practicable and is undergoing routine monitoring, it is well worth evaluating whether your site is eligible for Conditional Closure.

If you’re interested in learning more, please contact:
Allison Riffel, P.E., Senior Project Manager
[email protected]


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Allison Riffel
Allison Riffel, PE
Engineering Specialist, Golden, CO

Allison is a professional engineer with over 20 years of experience in site assessment, remediation, regulatory compliance and permitting. She specializes in remediation of chlorinated solvents, petroleum, and PCBs under RCRA, TSCA, CERCLA, and state voluntary cleanup programs with regulatory expertise in 11 states.

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