Connecticut Department of Energy & Environmental Protection

Significant Environmental Hazards

Beginning on March 1, 2026, Public Act 25-6 Section 3 changes the Significant Environmental Hazard (SEH) Program to apply only to newly discovered existing releases at sites that have been accepted into a Brownfields program and releases being remediated under the Property Transfer Program.

Newly discovered existing releases that will no longer be regulated as SEHs will be regulated as Significant Existing Releases (SERs) as described in RCSA 134tt-1(e) in the Release-Based Cleanup Regulations (RBCRs) beginning March 1, 2026.

In accordance with Section 22a-134tt-2(a)(4) of the RBCRs, this transition affects existing SEH conditions as of February 28, 2026, in this way:

SEH conditions that have not been resolved but are in compliance with the requirements of the SEH law may be subject to RCBRs on or after March 1, 2028. This enables a two (2) year period to fully abate and obtain a certification of the SEH condition ahead of adhering to the RBCRs

OR

SEH conditions that have not been resolved and are not in compliance with the SEH law may be subject to RBCRs process and timeline requirements starting on March 1, 2026.
Section 22a-6u of the Connecticut General Statutes (CGS) requires the owner of property that is in a brownfields program or the Property Transfer Program and is the source or location of pollution causing a significant environmental hazard to notify the Department of Energy & Environmental Protection (DEEP) after they become aware of such conditions. A technical environmental professional (TEP) must notify clients and the owner of a property if, while investigating pollution, a determination is made that an environmental hazard is present. A TEP is anyone who collects soil, water, vapor, or air samples to investigate and remediate soil or water pollution as an employee or consultant of a public or private employer.  In some circumstances, if an owner does not notify DEEP, the TEP's client must report the hazard to DEEP.

Types of Significant Environmental Hazard Conditions

The SEH conditions that must be reported to DEEP when pollution is identified above threshold concentrations are:

  • Public or private drinking water supply wells with detected pollution (above or below the groundwater protection criteria),
  • Polluted groundwater 500 feet upgradient of or within 200 feet in any direction of a drinking water supply well with pollution detected above the groundwater protection criteria,
  • Polluted groundwater within 15 feet of an occupied building with the potential to pose a short-term risk to indoor air quality,
  • Polluted groundwater discharging to a surface water body with the potential to pose a short-term risk to aquatic life,
  • Polluted soil present within two feet of the surface with the potential to pose a short-term direct contact risk to humans, and
  • The presence of vapors from polluted soil, groundwater or residual free product at levels posing a potential explosion hazard and imminent threat to human health, public safety and the environment.

Reference Tables for Significant Environmental Hazard Condition Notification Threshold Concentrations:

Significant Environmental Hazards Quick Summary Table - lists Significant Environmental Hazards with their respective time frames for notification and self-implementing initial response requirements 
 

Documents should now be directly uploaded into the REACT portal for the Remediation Division.  Please see instructions at Transmittal of Documents.

Significant Environmental Hazard Notification 

Notification Form for Reporting Significant Environmental Hazards
(Guidance and Instructions)

Follow-up Reporting

These forms are the preferred method of reporting follow-up actions on SEH conditions as they are designed to provide a complete description of any continuing actions being taken to monitor, mitigate, or abate these types of SEH conditions.

List of SEHs

List of Significant Environmental Hazards Reported to DEEP contains information on hazard notices for open and controlled hazard conditions.

Disclaimer: DEEP does not guarantee that this information is complete and/or free from erroneous entries.  This information is updated periodically and may not represent data currently available.  If you believe any information is erroneous, please contact DEEP.SEH@ct.gov.

Relationship of SEH Condition Notification Response Activities to Site Remediation Activities

The SEH statute is intended to identify and abate short-term risks associated with specific environmental conditions identified in the law.  It does not require that a release be fully remediated in order for the SEH to be considered abated.  In some such cases a monitoring program to ensure continued protection of the environment may be required by DEEP.  Long-term risks may exist at a release area after short-term risks (significant current exposures) have been abated.  Many sites that have submitted SEH notifications may have not completed further remediation activity to achieve compliance with Release-Based Cleanup Regulations.

Advisory for Short-Term Risks Associated with TCE in Indoor Air

As a result of the increased understanding of the developmental risks posed by volatilization of trichloroethylene (TCE) into indoor air the Connecticut Department of Public Health (DPH) and DEEP developed joint guidance in February 2015.  DEEP recommends including specific evaluation of these risks using the DPH/DEEP guidance when assessing groundwater and soil vapor for potential short-term risks if TCE is present in site groundwater or soil vapor.

For further information, please contact the Remediation Division at DEEP.SEH@ct.gov or (860) 424-3705.

Content Last Updated March 16, 2026