1. (a) Requirement to Characterize Nature and Extent of a Release (1) Upon discovery, the nature and extent of a release shall be determined, pursuant to the requirements of this section. This characterization is necessary prior to determining the appropriate remedial action for an existing release. Remediation of any release shall not be determined to have satisfied the requirements of the RBCRs unless and until the nature and extent of such release has been determined, as required in this section.

   1. (2) Required Information (A) Characterization of a release shall require the development of a conceptual site model, which may include, but shall not be limited to, evaluation of:

      1. (i) The physical setting of the release, such as topography, soil type, geology, and hydrogeology;
      2. (ii) Chemical properties of each substance discovered;
      3. (iii) The historical, current, and anticipated land uses of the release area and surrounding real property;
      4. (iv) Receptor pathways and potential receptors, such as existing uses of groundwater and proximity to water supply wells, nearby occupied buildings and nearby surface water;
      5. (v) Historical information and records;
      6. (vi) Observations of the release area and surrounding real property; and(vii) The results of soil, groundwater, or other environmental media testing, including the results of any field screening and all laboratory analytical data concerning such release.
      7. (B) (i) When specifying prevailing standards and guidelines pursuant to subsection (b) of this section, the commissioner shall identify the information necessary to develop a conceptual site model of a release and to complete closure characterization of such release; and(ii) Prevailing standards and guidelines specified by the commissioner shall indicate that a determination that the release remediation closure report for a release prepared pursuant to section 22a-134tt-8(a) of the RBCRs shall be considered closure characterization and shall satisfy the requirements of this section.
      8. (C) Closure characterization of an existing release shall include the preparation of a conceptual site model narrative by an LEP in accordance with prevailing standards and guidelines.
   2. (3) Tier characterization of a release shall be completed as soon as is prudent, but not later than one year after discovery of such release.
   3. (4) No release remediation closure report shall be verified by an LEP or certified by a PEP until closure characterization of a release is complete. Notwithstanding the requirements of this section, a release remediation closure report prepared pursuant to section 22a-134tt-8 of the RBCRs shall be considered to complete closure characterization of a release provided it contains such characterization information necessary to demonstrate compliance with the applicable provisions of such section.
   4. (5) If an immediate action is required by section 22a-134tt-5 of the RBCRs, then any characterization necessary to perform such actions, or verify the effects of such actions, shall be completed as required by such section.

2. (b) Identification of Prevailing Standards and Guidelines (1) The commissioner may specify, by posting on the department’s internet website, methods or protocols for the characterization of a release through the development of a conceptual site model which shall include, but shall not be limited to, methods or protocols for identifying and evaluating the information specified by subsection (a)(2) of this section. Methods or protocols posted on the department’s internet website pursuant to this subdivision shall be considered prevailing standards and guidelines.

   1. (2) If characterization is conducted pursuant to the prevailing standards and guidelines specified by the commissioner pursuant to subdivision (1) of this subsection, such characterization shall be sufficient for all purposes required by the RBCRs.

   2. (3) (A) If characterization is performed using standards and guidelines other than those prevailing standards and guidelines specified by the commissioner pursuant to subdivision (1) of this subsection, such standards and guidelines, and any methods or protocols used pursuant thereto, shall be documented and submitted for the commissioner’s review;

      1. (B) The documentation required by subparagraph (A) of this subdivision shall be submitted to the commissioner one time, at the earliest of the following:

3. (i) upon completion of an immediate action completed pursuant to section 22a-134tt-5 of the RBCRs, if an immediate action is required for such release;

   1. (ii) upon submission of a release remediation closure report, if remediation is completed not more than one year after discovery of such release; or(iii) upon assignment of the release to a cleanup tier, if such release is required to be assigned to a cleanup tier.
   2. (C) If the commissioner determines that such standard or guideline, or any method or protocol used pursuant thereto, is not scientifically valid and defensible, or not of a level of precision, accuracy, and sensitivity to sufficiently determine the nature and extent of a release, the commissioner shall identify in writing the reasons for such conclusions and such characterization shall not be relied upon to demonstrate compliance with the RBCRs. Along with such written statement, the commissioner shall specify a deadline for the completion of characterization pursuant to the requirements of this section.

(Effective March 1, 2026)