Municipalities have been hearing about Total Maximum Daily Loads (TMDLs) now for several years.  As a review, a TMDL is a long-term plan to improve the water quality in a specific geographic area. A water body is considered healthy when its designated use(s) are met.

A TMDL affects municipalities in two main ways; through its wastewater treatment facility (WWTF) permit or through its Municipal Separate Storm Sewer System (MS4) permit.

The focus of this issue of Infrastructure Insights is to identify several innovative approaches municipalities can take in working towards TMDL compliance. These approaches and a brief description are outlined below.

  1. Use Water Quality Trading. There are opportunities to work on the agricultural landscape to reduce runoff. These practices also promote healthy soil and nutrient and topsoil conservation on a farm. On a per pound basis, these practices are often less costly than constructing infrastructure such as detention ponds within a municipality. Examples of best practices that could result in credits for phosphorus or suspended solids include reduced tillage, filter strips, riparian buffers, and cover crops.

  2. Trading WWTF Credits to the MS4 Program. In most cases, the WWTF limits in place for suspended solids are more restrictive than the “add-on limits” for a TMDL. The WWTF could potentially trade those credits to the municipalities MS4 program. Typically, these credits could only be used for a MS4 after the baseline 20 percent total suspended solids reduction is achieved. If a WWTF will be using a filter to reach more stringent phosphorus requirements and the treatment level will be lower than required at the WWTF, those credits could potentially be traded to the MS4 as well.

  3. Piggy Backing on an Adaptive Management Program. If a MS4 is a partner to an Adaptive Management Program, the MS4 can achieve compliance for a particular reachshed when the water quality criteria at the Point of Compliance is reached. This is a way for an MS4 to take advantage of an existing Adaptive Management Program that strives to reduce water pollution through a variety of methods. The City of Oconomowoc, WI is using this strategy for the main reachshed in the City where the phosphorus reductions required in its MS4 permit will be difficult to achieve.

Contact an expert today for more information on innovative TMDL approaches.

About the Author

David W. Arnott

David W. Arnott, P.E.
Team Leader/Senior Project Manager

Dave has extensive experience in the planning, design, and construction project management of wastewater treatment facility renovation and upgrade projects. Areas of expertise include treatment processes, hydraulics, mechanical equipment, and wastewater disinfection. He also has experience in sanitary and water pumping station design and sanitary sewer wet weather facilities.

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