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  Bureau of Environmental Analysis, Restoration and Standards

Total Maximum Daily Loads (TMDLs)

Waters of the state are regularly assessed to determine if surface water quality standards are met and designated uses are supported. Waters that do not meet the applicable standard(s) or support the applicable designated use(s) are placed on the 303(d) List of Water Quality Limited Waters (303(d) List), as part of New Jersey’s biennial Integrated Water Quality Assessment Report. Section 303(d) of the federal Clean Water Act requires development of a TMDL for the pollutant(s) causing the impairment. Impaired waters are ranked and prioritized for TMDL development as part of the development of the 303(d) List every two years.

The factors considered in TMDL ranking and prioritization are described in the Integrated Water Quality Monitoring and Assessment Methods. Federal regulations concerning TMDLs are contained in USEPA's Water Quality Planning and Management Regulations (40 CFR 130,7(c)). New Jersey’s rules regarding TMDLs are set forth in the Water Quality Management Planning rules at N.J.A.C. 7:15-5.

Many of the waters placed on New Jersey's 303(d) List are impaired primarily by nonpoint sources of pollution or regulated stormwater sources rather than traditional point sources. For these impairments, development of a watershed restoration plan or watershed based plan can be an effective alternative to a formal TMDL. These plans characterize pollutant sources, the reductions needed to attain standards and the means to achieve the reductions. Implementation of these plans can often be achieved through receipt of Water Quality Restoration Grants for Nonpoint Source Pollution.

A load reduction target must be established for each pollutant listed as a cause of water quality impairment on the 303(d) List. A TMDL can include multiple load reductions but a separate TMDL equation must be derived for each pollutant causing water quality impairment. TMDLs must be calculated so that surface water quality standards for each pollutant will be attained. The critical condition and seasonal variation need to be considered, plus a margin of safety (MOS) to account for uncertainty, are all part of the TMDL development. The TMDL is allocated among all of the sources of the pollutant, including point sources, nonpoint sources and natural background.

Point sources are any discernible, confined, and/or discrete conveyance from which pollutants are or may be discharged, such as wastewater treatment facilities, combined sewer overflows and/or stormwater. All point sources receive wasteload allocations (WLAs) as part of the TMDL.

Nonpoint sources (NPS) of pollution are diffuse sources, such as overland runoff and air deposition, other than a point source from which pollutants are or may be discharged or harbor other activity that contributes or may contribute to water pollution. NPS receive Load Allocations (LAs) as part of the TMDL.

A Margin of Safety (MOS) is also required as part of the TMDL but it can be expressed as either an explicit part of the TMDL equation or may be accounted for through conservative assumptions made in calculating the TMDL. Reserve Capacity is an optional TMDL component included as a pollutant load for later allocation.

TMDL Equation:

Total Maximum Daily Load = LAs + WLAs+ MOS + RC*

LA = Load allocations from nonpoint sources
WLA = Waste load allocations from point sources
MOS = Margin of saftey to account for scientific uncertainty
*RC = Reserve capacity set aside for future development (optional TMDL component)

Mathematical models are used to simulate water quality conditions throughout the impaired waterbody and its watershed, including the sources of pollutants, the relationship between pollutant loading and the water chemistry and other environmental responses resulting in water quality impairment. The model is also used to evaluate pollutant reduction scenarios and waterbody response to these scenarios. The selection and application of an appropriate model leads to scientifically-defensible, TMDL-assigned pollutant reductions. There are different types of mathematical models that vary in the level of complexity:

Simple models calculate the percent reduction of pollutants neccessary to meet Surface Water Quality Standards without a need to mimic pollutant changes in the environment and are sometimes adequate for a TMDL.

Complex models can simulate changes in pollutant concentrations and flow in the contributing drainage area. Pollutant transformation and relationships to other pollutants in the area are often mimicked in complex water quality modeling.

The figure below shows an example of a (complex) model calibration figure for in-stream dissoved oxygen from the Raritan River TMDL technical report (Kleinfelder/Omni 2013, Vol. 3, pg. K-20 )

tmdl charts

  • Verify the water quality impairment

  • Analyze water quality data in the watershed

  • Collect additional data if needed (e.g. stream water quality data, stream characteristic measurements, weather data, etc.)

  • Present information on water quality impairment and seek input from stakeholders

  • Construct and test the TMDL model

  • When there is a good model fit, run the TMDL model for different pollutant reduction scenarios

  • Select appropriate reductions to meet the water quality standard under modeled critical waterbody conditions

  • Convene a Model Evaluation Group appropriate to review complex models to vet that constructed/validated models are ready for TMDL proposal

  • Propose TMDL to the Water Quality Management Plan

  • Public review of proposed TMDL report

  • Submit final TMDLs to USEPA for approval

  • Adopt TMDL as a Water Quality Management Plan amendment

  • Implement TMDLs through New Jersey Pollutant Discharge Elimination System permit revisions and grant restoration projects

  • A TMDL is "proposed" when DEP publishes the TMDL Report as a proposed Water Quality Management Plan amendment in the New Jersey Register for public review and comment in accordance with N.J.A.C. 7:15-3.4

  • Following the public comment period, DEP prepares a response to comments and minor revisions to the TMDL

  • The revised document with response to comments is “established” upon submittal to EPA for review

  • Following EPA’s review and approval process, the TMDL is deemed “approved.” DEP can then implement the TMDL and it can proceed to be “adopted” as an amendment to the Water Quality Management Plan, in accordance with N.J.A.C. 7:15-3.4

  • The Notice of Adoption is published in the New Jersey Register

There are various informed opportunities during the development of a TMDL for public participation. Public meetings may be held to present information and solicit feedback. Additionally, formal public comments are sought when a TMDL is proposed - either in person at a hearing, in writing or both.

Illustration by Jodie Battaglia

For more information, please contact Kimberly Cenno, Bureau Chief,
Bureau of Environmental Analysis, Restoration and Standards at (609) 633-1441.

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Last Updated: February 2, 2021