Significant Environmental Hazards

Section 22a-6u of the Connecticut General Statutes (CGS) requires the owner of property which 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, including a licensed environmental professional, 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 significant environmental hazard (SEH) conditions that must be reported to DEEP when identified (because pollution is above threshold concentrations defined in the law) 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.
Consult CGS Section 22a-6u and the notification Guidance and Instructions for further details regarding how the threshold concentrations triggering notification are determined.

Significant Environmental Hazard Notification 

Frequently Asked Questions About the Reporting of Significant Environmental Hazards

Fact Sheet on Reporting of Significant Environmental Hazards

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

Electronic Document Transmittal Form - must be the cover page for SEH Notifications

Reference Tables for Significant Environmental Hazard Condition Notification Threshold Concentrations (Please note: These are general guidelines.  See CGS 22a-6u and the form instructions for further guidance.):

A listing of Significant Environmental Hazards with their respective time frames for notification and self-implementing initial response requirements can be found in the Significant Environmental Hazards Quick Summary Table.  [Please note: This table is for informational “at-a-glance” purposes, and the statute [CGS 22a-6u] should be consulted for specific wording and requirements of the law.]
Water Supply Well Receptor Guidance Document – Use of this guidance is strongly recommended to conduct water supply well receptor surveys when determining the presence of nearby drinking water receptors that may be impacted by an identified SEH condition.

Follow-up Reporting

For follow-up reporting, easy-to-use forms have been developed for soil, drinking water, and groundwater hazard conditions. The forms are the preferred method of reporting follow-up actions on SEH conditions because they are designed to assist the environmental professional in providing a complete description of any continuing actions being taken to monitor, mitigate, or abate these types of SEH conditions.

Electronic Document Transmittal Form - must be the cover page for SEH Status Updates

List of SEHs and SEH Map

List of Significant Environmental Hazards Reported to DEEP provides details on the status of open and controlled hazard conditions.

DEEP maintains a Map of Significant Environmental Hazard Locations

  • “Open” hazards are displayed in RED, signifying that further evaluation of the hazard condition and mitigation or abatement of the hazard is necessary.
  • “Controlled” hazards are displayed in YELLOW, signifying that there are controls on the hazard through measures that may require periodic actions to ensure the reported condition remains mitigated and continues to pose minimal short term risk.
  • “Resolved” hazards are displayed in GREEN, signifying that a hazard condition has been abated to permanently eliminate exposure to contamination that exceeds the significant environmental hazard notification threshold or that such contamination no longer exists.
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. The complete SEH file can be found by visiting the file room at DEEP Headquarters at 79 Elm Street, Hartford. Please call ahead if you intend to visit the file room: (860) 424-4180.  If you believe any information is erroneous, please contact

Relationship of Significant Environmental Hazard Condition Notification Response Activities to Site Remediation Activities


The Significant Environmental Hazard Statute is intended to identify and abate short-term risks associated with specific environmental conditions identified in the law.  This statute, CGS 22a-6u, does not require that a release be fully remediated in order for a significant environmental hazard 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.  Long-term risks can result from changes in site activities and uses which could change exposures, migration of contaminants over time, long-term exposure to contaminants at concentrations lower than the significant hazard thresholds, and other factors.  Many sites that have submitted notifications of significant environmental hazards may have not completed further remediation activity to achieve compliance with the State Remediation Standard Regulations.

If you are investigating a residential heating oil tank leak, reporting under the SEH statute is required if

  • drinking water wells are located within 500 feet and groundwater contains any petroleum component over the Groundwater Protection Criteria (for ETPH 250 parts per billion [ppb or µg/l]) or 
  • any petroleum component is detected in a drinking water well at any level.

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 (860) 424-3705.

Content Last Updated June 3, 2024