Total Maximum Daily Load

Connecticut Water Quality Action Plans

Total Maximum Daily Load Program

Download a CT Water Quality Action Plan by Waterbody ID TMDL

The updated CT Draft Statewide Bacteria Core Document and 23 watershed appendices are now available for public comment from 10/16/2024 through 12/13/2024. See the Bacteria TMDL webpage for details.

What is a Total Maximum Daily Load (TMDL)?

Description of a pollution budget. The amount of a pollutant that a waterbody can handle without negative impacts. A Total Maximum Daily Load Plan or a TMDL is a type of Water Quality Action Plan (WQAP) that determines the amount of a pollutant that can be present in a waterbody without causing negative impacts to fish, wildlife, recreation, or other uses (like a budget). Waterbodies that are above the pollution line have too much pollution and are exceeding their budget. They need a plan in place to restore the waterbody so that it stays within its budget to meet Water Quality Standards (WQS). TMDLs are also used to protect waters by staying below the pollution budget line. A TMDL is the sum of all point sources of a pollutant, nonpoint sources and the natural background amounts in a watershed. A margin of safety is also included to account for any unknown sources. Connecticut has developed many TMDLs since 1999 for different types of pollutants such as bacteria, nutrients and toxicity.

TMDL = Point Sources(WLA) + Nonpoint Sources (LA) + Background + Margin of Safety

Sources of Water Pollution

Describes point sources and nonpoint sources of pollution. Point Sources (WLA) in a watershed come from the end of a pipe from permitted activities such as discharges. These sources of pollution are typically identifiable and can be traced back to a single point.

Nonpoint Discharges (LA) are more difficult to identify because there can be many sources in a watershed that do not trace back to a single point. Nonpoint sources of pollution are not regulated and can include, surface water run-off from agriculture, fertilizers, animal waste, erosion and urban run-off.

Implementation of TMDLs

Water Quality Action Plans including TMDLs can be implemented in several ways depending on the source that the pollution is coming from.

Point sources such as discharges to surface waters are implemented through the The Surface Water Discharge Permit Program at CT DEEP also known as the National Pollutant Discharge Elimination System or NPDES (under federal law). This program regulates discharges into surface waters (either directly or through municipal storm sewer drainage systems, or through other drainage systems such as wetlands or swales). TMDL requirements are added into the applicable permits. Permit limits are designed to achieve water quality standards. Point sources are assigned a waste load allocation for each permit in the watershed.

Nonpoint source implementation is more difficult since there is no single pipe to assign a waste load allocation to. These sources are assigned a load allocation The Watershed Management Program https://portal.ct.gov/deep/water/watershed-management/watershed-management at CT DEEP assists in the development of comprehensive watershed management plans, to protect and restore water quality. Development and implementation of these plans focus on addressing a specific nonpoint source that could affect water quality. The US EPA has described Nine Elements that must be addressed in an approved Nonpoint Source Watershed Based Plan.

Recently, CT DEEP has made updates to TMDL development. One of those updates is to include additional information in TMDLs to help with the development of Nonpoint Source Watershed Based Plans. Some of the 9 elements can be addressed in the TMDL. Others will need to be addressed in an NPS plan, which only needs to include those elements that couldn’t be addressed in the TMDL. The 9-element requirements for 319 funding of Watershed Based Plans are also identified below. This process allows for a comprehensive Water Quality Action Plan that not only identifies the sources of pollution, but also identifies ways and actions that can be taken to fix it.

Image describes the hierarchy of TMDL development. Core document, Appendices, Addendum.

Connecticut Department of Energy & Environmental Protection

Connecticut Water Quality Action Plans