This is the sixth in a series of blog posts discussing key features of Connecticut’s new release-based cleanup regulations (the “RBCRs”), R.C.S.A. § 22a-134tt-1 et seq.
The RBCRs require that, following discovery of a release, the “nature and extent of the release must be determined” so an appropriate remediation strategy can be designed and the release can be closed. This process, called “characterization,” is explained in this blog post and the companion Release Report video.
Characterization is required for both new and existing releases. The last few posts in this series have discussed old and new releases separately: the second and third posts in this series discussed discovery and reporting of old or existing releases, and the fourth and fifth posts in the series discussed reporting of new releases and immediate actions in response to new releases and especially serious existing releases. This post, and those posts that follow in the series, will apply to both new and existing releases.
Characterization Process
Characterization requires the development of a conceptual site model, defined by the RBCRs as a three-dimensional representation “of environmental conditions at a release area that is developed through a multi-phased investigative approach” validated by facts and observations. Information relevant to the development of a conceptual site model includes historical information, physical setting (e.g., site topography and geology), chemical properties of the substance(s) discovered, receptor pathways and potential receptors (e.g., water supply wells and occupied buildings), and sampling results. Development of a conceptual site model is a technical and fact-specific endeavor that requires the expertise of a licensed environmental professional (LEP).
The RBCRs specify that characterization must be accomplished in accordance with “prevailing standards and guidelines.” Connecticut’s Department of Energy and Environmental Protection (DEEP) has released a draft “Release Characterization Guidance” which might be updated before the effective date of the RBCRs (and will be updated at DEEP’s discretion thereafter). The Release Characterization Guidance Document has many similarities with the familiar Site Characterization Guidance Document that outlines the prevailing standards and guidelines for characterizing Transfer Act sites.
The titles of the documents highlight an important difference in approach: the Site Characterization Guidance Document applies to the characterization of sites as a whole under the Transfer Act, while the Release Characterization Guidance reflects the release-by-release approach of the RBCRs. In contrast to the Transfer Act, the RBCRs do not require site-wide investigation. Note that sites already in the Transfer Act as of March 1, 2026, must still complete site-wide investigation.
Characterization Milestones
Characterization is by nature an iterative process. A Phase I site assessment or other set of visual observations can identify an area where a release may have occurred. A Phase II or other limited subsurface investigation can answer the question of whether a release has in fact occurred, and further sampling (e.g., in a Phase III) can delineate the vertical and areal extent of the contamination. Characterization begins when a release is first suspected, discovered or witnessed and it may not end until multiple rounds of sampling are complete.
That said, the RBCRs set forth two important characterization milestones:
Tier Characterization: A release that takes one year or more to remediate is assigned to a risk-based tier that determines the level of oversight applicable to the remediation process. These oversight tiers will be discussed in the next post. To assign a release to the appropriate oversight tier, “tier characterization” must be completed within the first year after the discovery or occurrence of the release.
Tier characterization requires that contamination be delineated to identify the extent of each substance present at more than 50 percent of the applicable cleanup standard (or to the laboratory reporting limit if that is higher). Pesticides must be characterized only to the extent necessary to determine if they are present due to the application of pesticides for their intended purpose (rather than an accidental spill). A streamlined characterization approach is also available for polluted fill, as will be discussed in a future post.
Closure Characterization: A release cannot be closed under the RBCRs until closure characterization is complete. Closure characterization requires that the horizontal and vertical extent of a release be delineated to the point that such release is no longer detected, or that the extent of the release has otherwise been determined in a manner consistent with prevailing standards and guidelines.
Once a release has been characterized, the remediation program can be planned and carried out. Remediation and closure under the RBCRs will be discussed in forthcoming posts. In our next post, we will discuss the oversight tiers assigned after the tier characterization process.