TMDL Effectiveness Monitoring and Assessment

How Cadmus developed guidance documents to assist states in their efforts

Section 303(d) of the federal Clean Water Act requires states to develop Total Maximum Daily Loads (TMDLs) for pollutants causing violation of applicable water quality standards for each impaired water body. A TMDL determines the maximum amount of pollutant that a water body is capable of assimilating while continuing to meet the existing water quality standards. After management recommendations for improving water quality have been implemented, TMDL effectiveness monitoring and assessment are conducted to determine if the TMDL targets and water quality standards have been met. This information serves as an important source of feedback for refining and optimizing management approaches.

Technical Guidance and Tools for TMDL Effectiveness

EPA Region 10 retained Cadmus to develop two TMDL effectiveness monitoring guidance documents to assist states in their efforts to measure the environmental results of TMDL implementation actions: Technical Guidance for Exploring TMDL Effectiveness Monitoring Data and Recommendations for Developing TMDL Effectiveness Monitoring Plans. These documents provide watershed managers with a concise, easy-to-follow approach for making better use of their data and making more informed resource allocation decisions.

TMDL Effectiveness Assessments for Union River and Dungeness River Watersheds, Washington

When both the Union River and Dungeness River watersheds were listed as impaired for fecal coliform bacteria, TMDLs were developed and implemented to address these listings. Cadmus was retained by U.S. Environmental Protection Agency (EPA) Region 10 to provide the State of Washington Department of Ecology to evaluate the effectiveness of implementation efforts in meeting TMDL targets for the Union River Watershed and the Dungeness River Watershed and Bay.

Cadmus employed advanced statistical techniques to evaluate trends in water quality variables over time:

  • Mixed effects models.
  • Seasonal and regional Kendall trend tests.
  • Multiple regression.

Additionally, Cadmus provided the state with recommendations for ways to better address their requirements for delisting water bodies from the impaired waters list, as well as recommendations for future monitoring efforts that, if implemented, will provide additional information about pollutant sources, as well as provide additional data to further assess the effectiveness of the TMDL and best management practices (BMPs) on improving water quality.

TMDL Effectiveness Monitoring Program for Bear Creek Watershed, Oregon

The Oregon Department of Environmental Quality established TMDLs for ammonia, biological oxygen demand, phosphorus, sediment, bacteria, and temperature in the Bear Creek Watershed. The parties responsible for implementing these TMDLs have been making a concerted effort to address the water quality impairments through implementation of agricultural and stormwater BMPs, land-use planning, structural and operational improvements to infrastructure, and public education. Given the significant investment of resources in implementation efforts, there is significant interest in demonstrating the effectiveness of these management practices on improving water quality. Cadmus was retained by EPA Region 10 to design a water quality monitoring plan to evaluate the effectiveness of management practices on improving water quality and in meeting pollutant load reduction goals set by the TMDLs.

As part of the plan development, Cadmus conducted a power analysis to determine the number of samples that need to be collected for each water quality parameter to identify statistically significant trends. The power analysis uses information from multiple linear regression analyses to determine the optimal number of samples to be collected to identify different amounts of change with statistical significance.

The results of these analyses ensure that enough data are available to identify future trends (where they exist) without sampling more than necessary. The monitoring plan Cadmus developed is currently being implemented by the state.

The final reports for each of the assessments are available for download from the Department of Ecology’s website:

Union River:
Dungeness River: