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Nutrient-impaired waters exist in every corner of the state. Nutrients enter surface waters from many sources including run-off from agricultural lands and urban stormwater. Discharges from wastewater treatment facilities also contain nutrients. Through the water quality permitting process, the MPCA makes sure that new or expanding wastewater treatment facilities do not make worse an existing impairment while a TMDL is in development.

For example, Lake Pepin is impaired for excess nutrients, including phosphorus, and a TMDL is currently in development. Proposals for a new or expanded wastewater discharge containing phosphorus in Lake Pepin's watershed must consider the existing impairment and the resulting legal restrictions.

Pre-TMDL phosphorus trading

To be protective of the environment, fulfill the requirements of the Clean Water Act and meet the needs of communities, the MPCA developed Pre-TMDL Phosphorus Trading (PTPT). PTPT allows new and expanding wastewater treatment facilities to receive a discharge permit prior to completion of an applicable phosphorus-related TMDL. Through PTPT, a new or expanding facility may increase its phosphorus discharge by purchasing a phosphorus reduction from another source. The MPCA documents the transfer of nutrient load, or trade, through the NPDES permitting process.

Facilities that have the potential for their effluent phosphorus concentration to be below the phosphorus lakes and reservoir standards, such as noncontact cooling water with no chemical additives and facilities where source water is primarily ground water (i.e., ground-water pumpouts and mine dewatering), will not be required to participate in Pre-TMDL Phosphorus Trading. New and expanding facilities that are not able to reduce phosphorus in the discharge to below the phosphorus lakes and reservoirs standard will be allowed to participate in PTPT and trade phosphorus loading to assure no net increase in the allowable mass of phosphorus discharged upstream of the nutrient impaired water. This includes WWTFs that have been determined to be de minimus (discharge less than 1800 pounds per year).


The MPCA's initial attempts at Pre-TMDL Trading met mixed reactions and reached the docket of the Minnesota Supreme Court in 2006. In a ruling released in May 2007, the court agreed with the MPCA's interpretation of the Clean Water Act and upheld a wastewater treatment facility permit issued to the cities of Annandale and Maple Lake. The court acknowledged that the MPCA made a “reasonable interpretation” of the law by allowing a reduction in phosphorus discharge at one facility to make up for an increase at the proposed Annandale-Maple Lake facility. The ruling provided significant guidance to the MPCA in developing Pre-TMDL Trading.

View the Minnesota Supreme Court Opinion

In September 2007, Pre-TMDL Phosphorus Trading was brought forward to the MPCA Citizens' Board as an informational item. Comments received were taken into account during the development of PTPT. The Board approved Pre-TMDL Phosphorus Trading on June 24, 2008.

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