Water Quality Standards and Classifications Fact Sheet

The Connecticut Water Quality Standards and Classifications and Accompanying Classification Maps are an important element in Connecticut's clean water program. The WQS set an overall policy for management of Connecticut's surface and ground waters in accordance with the directives provided by Section 22a-426 of the Connecticut General Statutes and Section 303 of the Federal Clean Water Act.

The WQS have several purposes
  • provide guidance and policy about water quality in the state and DEEP's goals for maintaining or improving that quality;
  • establish designated uses of surface and ground water;
  • indicate the general types of discharges allowed;
  • ensure the segregation of drinking water supplies from waters used for waste assimilation;
  • provide a framework for the establishment of priorities for pollution abatement, dispensation of State funding, remediation goals; and
  • provide guidance for location decisions for business and industry as well as other economic developments.

The WQS do not stand alone as a regulatory means of protecting public health and the environment. These standards are integrally related to, and applied by DEEP simultaneously with, other statutory and regulatory requirements governing water and waste management. As an example of how these pieces fit together, the following may be of assistance.

  • The WQS set forth the types of wastewater that can be discharged in various classifications in order to meet statutory goals. In addition, the WQS provide the guiding principles concerning waste assimilation, aquatic toxicity and the goals for receiving waters.

  • Section 22a-430 of the General Statutes allows and sets procedures for the permitting of discharges of treated wastewaters to the waters of the State.

  • If the type of discharge is allowed, then the details of application procedures and requirements for treatment, monitoring and reporting of the specific discharge are provided by Sections 22a-430-1 through 4 of the Regulations of Connecticut State Agencies.
Three Fundamental Elements

Element One. First, the water quality standards describe DEEP's general policies and goals for maintaining or restoring specified levels of quality for each use classification. The Standards describe discharges to ground and surface water consistent with DEEP's goals for each classification. The Standards also define the concept of a zone of influence for such discharges. Other key provisions of the standards include policies for protecting ground and surface water whose actual quality exceeds that quality associated with its classification. These policies are known as the anti-degradation principles. There are also policies and procedures that define the methods by which DEEP may alter an assigned classification. The Standards also include definitions, lake trophic classifications, bathing water standards and numerical criteria for aquatic toxicity.

Element Two. The second element is the water quality criteria which: (i) describe the uses DEEP has designated as appropriate for each water quality classification; and (ii) establish narrative and numerical factors used by DEEP to determine whether goals established in the standards are being met.

Element Three. The water quality classification maps are the third element of the Connecticut's Water Quality Standards and show the class assigned to each surface water and ground water resource throughout the state. The Water Quality Classification Maps have been adopted and are amended from time to time pursuant to the statutory process described in section 22a-426 of the Connecticut General Statutes. The maps are used to relate designated uses and the applicable Standards and Criteria for each class of surface and ground water resource to a specific location.

Water Quality Classifications

The water quality classifications established by Connecticut's Water Quality Standards are summarized below with a brief listing of the designated uses and allowable discharges for each classification.

Inland Surface Water Classifications

Class AA

Designated uses: existing or proposed drinking water supply, fish and wildlife habitat, recreational use (may be restricted,) agricultural and industrial supply.

Discharges restricted to: discharges from public or private drinking water treatment systems, dredging and dewatering, emergency and clean water discharges.

Class A

Designated uses: potential drinking water supply; fish and wildlife habitat; recreational use; agricultural and industrial supply and other legitimate uses including navigation.

Discharges restricted to: same as allowed in AA.

Class B

Designated uses: recreational use: fish and wildlife habitat; agricultural and industrial supply and other legitimate uses including navigation.

Discharges restricted to: same as allowed in A and cooling waters, discharges from industrial and municipal wastewater treatment facilities (providing Best Available Treatment and Best Management Practices are applied), and other discharges subject to the provisions of section 22a-430 CGS.

Coastal and Marine Surface Waters

Class SA

Designated uses: marine fish, shellfish and wildlife habitat, shell fish harvesting for direct human consumption, recreation and all other legitimate uses including navigation.

Discharges restricted to: same as for AA or A surface waters.

Class SB

Designated uses: marine fish, shellfish and wildlife habitat, shellfish harvesting for transfer to approved areas for purification prior to human consumption, recreation, industrial and other legitimate uses including navigation.

Discharges restricted to: same as for B surface waters.

Groundwater Classifications

Class GAA

Designated uses: existing or potential public supply of water suitable for drinking without treatment; baseflow for hydraulically connected surface water bodies.

Discharges limited to: treated domestic sewage, certain agricultural wastes, certain water treatment wastewaters.

Class GA

Designated uses: existing private and potential public or private supplies of water suitable for drinking without treatment; baseflow for hydraulically connected surface water bodies.

Discharges restricted to: as for GAA and discharge from septage treatment facilities subject to stringent treatment and discharge requirements, and other wastes of natural origin that easily biodegrade and present no threat to groundwater.

Class GB

Designated uses: industrial process water and cooling waters; baseflow for hydraulically connected surface water bodies; presumed not suitable for human consumption without treatment.

Discharges restricted to: same as for A (Note; same treatment standards apply), certain other biodegradable wastewaters subject to soil attenuation.

Class GC

Designated uses: assimilation of discharge authorized by the Commissioner pursuant to Section 22a-430 of the General Statutes. As an example a lined landfill for disposal of ash residue from a resource recovery facility. The GC hydrogeology and hydrologic setting provides the best safeguard to adjacent resources.

Discharges restricted to: potential discharges from certain waste facilities subject to specific permitting requirements.

Standards Adoption and Public Participation

Section 22a-426 of the General Statutes provides specific procedures for the adoption of all portions of the WQS. The Statute provides that any revision of the standards or classification map be subject to public notice requirements and a public hearing. Notice is printed in the Connecticut Law Journal and in newspapers of general circulation in the affected areas.

Classification maps are reproduced through the DEEP's Geographic Information System (GIS) and are available to the public in the DEEP store.

GIS Shapefiles of the Water Quality Classifications (Ground Water Quality Classifications Polygon, Surface Water Quality Classification Line or Surface Water Quality Classification Polygon) are available for download on GIS Data web page.

Additional Information:

Federal EPA Water Quality Standards

For further information, contact staff at the DEEP Bureau of Water Protection and Land Reuse: (860) 424-3020.

Content last updated on May 17,2021