Tools and Guidance for Creating Site-Specific Numeric Water Quality Criteria for Nutrients Available

Web Tool

As numeric nutrient criteria are developed by various states, the United States Environmental Protection Agency (U.S. EPA) has defined three categories of approaches: 1) Reference Condition Approach, 2) Stressor-response Analysis, and 3) Process-based (Mechanistic) Modeling, and has provided specific guidance for the first two approaches. One of our current research efforts is focused on the third “modeling” approach. The project team is developing case studies, decision support tools, and a Nutrient Modeling Toolbox for deriving site-specific water quality criteria for nutrients (LINK1T11). This model-based approach can be used alone or in combination with the other methods and may be particularly useful when the permit writers and permitees are faced with understanding the relative contributions from multiple sources. It is our goal that this research will be used as a starting point of specific guidance for process-based modeling.

Strong science is the hallmark of the Clean Water Act. Under Section 304(a) (1) of the Act, the U.S. EPA is directed to develop water quality criteria that is effects based; reliant on all aspects of water quality – chemical, biological and physical, process for assessing concentration and dispersal of pollutants; and on the effects of pollutants on response variables such as biological community diversity, productivity, and stability, including eutrophication and rates of organic and inorganic sedimentation for various water bodies.

The focus of our Nutrient Modeling Toolbox is centered on the examination of existing models to meet Congressional direction in Section 304(a)(1). It also focuses on scientifically defensible methods for using all forms of scientific water quality data and information reflecting chemical, biological, and physical effects.

The Nutrient Impact Modeling Toolbox provides a mechanism that can quantitatively link nutrient loads to water quality and ecological response indicators on a site-specific basis. This Toolbox is designed to help local governments, utilities, states, and other stakeholders select modeling approaches based on a variety of factors. These factors include:

  • Types of water bodies.
  • Biological, physical, and chemical response indicators relevant to water body types.
  • Data availability.
  • Modeling options and limitations.
  • Regulatory applications associated with the various modeling options for derivation of water quality standard criteria.
  • Total maximum daily load allocations and effluent limits for point sources.

The models also consider targets for nonpoint source best management practices, and data and information for nutrient trading.

The Nutrient Modeling Toolbox contains information and access to approximately 30 models including process-based load-response models, empirical-based load-response models, and stressor-response submodels used to create hybrid models. There is an information sheet on each model, and all models presented in this Toolbox are publicly available. The models vary in simplicity and data requirements, and relatively modest resources can be brought to bear at an initial screening level to obtain preliminary results. This will help some users determine if a more rigorous data collection effort is warranted.

Within the Nutrient Modeling Toolbox, a Model Selection Decision Tool will guide users to find the most appropriate model(s) for their situation. The Selection Tool begins with a model classification matrix that considers waterbody type and response endpoint(s). It further refines model selection with questions on model application, dimensionality, temporality, and other secondary factors.

Ultimately, the goal for these modeling applications is regulatory decision making. Over half of the states currently have no formal review process. Fourteen states have some type of protocol such as guidance, review panel, or modeling quality assurance planning (QAPP) requirements. Six states have a list of approved models and some states are not yet using models.

Interaction with regulators at every step of the Nutrient Modeling Toolbox process is recommended. By involving regulators at project initiation, prior to model development and prior to model application, it’s possible to ascertain existing protocols for regulatory review of models, problems, QAPP requirements, and to reconcile differences between model results and regulatory frameworks.

To ensure communities are familiar with ourNutrient Modeling Toolbox, we have collaborated with the Water Environment Federation, National Association of Clean Water Agencies, and Association of Clean Water Administrators to inform U.S. EPA, state regulators, and end-users on the appropriate application of the Nutrient Modeling Framework and Toolbox. Look to the various websites for information about web seminars and other educational opportunities. The partner associations’ websites also contain additional information on web seminars, educational opportunities, and a link to download the Nutrient Modeling Toolbox at no charge.

To help ensure the usefulness of the Toolbox, the research team’s approach included review by a Stakeholder Advisory Panel from various agencies that could ultimately benefit from its implementation.


Stakeholder Advisory Panel:

  • Arthur Butt, Virginia Department of Environmental Quality
  • John Buzzone, Washoe County, NV
  • Tom Fikslin, Ph.D., Delaware River Basin Commission
  • David Senn, San Francisco Estuary Institute
  • Mike Suplee, Montana Department of Environmental Quality
  • Susan T. Fitch, Arizona Department of Environmental Quality
  • Mindy Scott, Sanitation District No. 1 of Northern Kentucky
  • Terri Svetich, Reno, NV
  • Martha Sutula, Southern California Coastal Water Research Project


We also engaged our own technical advisory committee:

  • Steven Peene, Applied Technology and Management, Inc.
  • Jim Pletl, Ph.D., Hampton Roads Sanitation District
  • Thomas Stiles, Bureau of Water, Kansas Department of Health and Environment
  • David Taylor, Massachusetts Water Resources Authority
  • Elke Ursin, Florida Department of Health
  • Jennifer Wasik, Metro Water Reclamation District of Greater Chicago
  • Steve Whitlock, United States Environmental Protection Agency
  • Harry Zhang, Ph.D., P.E., CH2M Hill
  • Elgin Perry, Ph.D., Statistics Consultant
  • Paul Stacey, New Hampshire Fish and Game Department


Research Team

Principal Investigator: 
  • Joseph V. DePinto, Ph.D., LimnoTech

Co-Principal Investigators: 

  • Clifton F. Bell, P.E., PG, Brown and Caldwell
  • Steven C. Chapra, Ph.D., F. ASCE, Tufts University
Research Project Manager:
  • Penelope E. Moskus, LimnoTech
Research Team: 
  • Victor J. Bierman, Jr., Ph.D., BCEEM
  • David W. Dilks, Ph.D.
  • Scott C. Hinz
  • Theodore A.D. Slawecki
  • Hua Tao, Ph.D., LimnoTech
  • Kyle F. Flynn, P.H., Tufts University
  • Kent W. Thornton, Ph.D., FTN Associates
  • Patricia McGovern, P.E., Patricia McGovern Engineers (PME)
  • Lorien J. Fono, Ph.D., P.E., Patricia McGovern Engineers (PME)
  • Nicole Clements, Nicole Clements Consulting, LLC

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