Minnesota is a land blessed with water.  However, a recent lawsuit has placed the issue of the quality of Minnesota ’s surface waters squarely in the limelight.

The lawsuit, brought by the Minnesota Center for Environmental Advocacy (MCEA) against the Minnesota Pollution Control Agency (MPCA), was brought when the MPCA granted a new sewage discharge permit to the Cities of Annandale and Maple Lake .  According to the MCEA, the MPCA erred in granting a new permit for discharging phosphorus to a tributary of the Mississippi River, which flows into Lake Pepin —a water body listed as an impaired water body under the Federal Clean Water Act.

The lawsuit has resulted in the stoppage of at least 60 development projects across the state.  At issue is the application of the Clean Water Act to Lake Pepin, into which the Minnesota, St. Croix and upstream portions of the Mississippi Rivers all flow.  Lake Pepin has been listed as an impaired water body due to high phosphorus concentrations. The MPCA must complete a study of the contributing river basin that allocates the amount of phosphorus that each wastewater source can discharge, called a “total maximum daily load”, or TMDL.

However, an extensive TMDL study is not expected until 2009.  Until then, no new sources of phosphorus discharge are allowed in this watershed, which encompasses a significant portion of the state.  Although the Minnesota Supreme Court is due to deliver a ruling on a challenge to this lawsuit, the fact remains that fewer than 20 percent of Minnesota ’s lakes and river miles have been assessed by the MPCA for their impairment status under the Clean Water Act.  What solutions are available to allow for growth while minimizing increases in phosphorus loading to surface water bodies?  Sustainable technologies such as engineered wetland treatment systems and soil disposal systems are potential solutions for many communities and developments.

The design of wastewater treatment and disposal systems that use proven technologies to distribute treated water to the native soil, thereby eliminating the need to discharge to surface waters, is a practicable solution to this issue.  These technologies may include soil infiltration beds, infiltration trenches, and drip irrigation disposal fields, which are combined with engineered wetlands to treat wastewater.

Infiltration beds and trenches utilize pressure distribution to disperse treated wastewater to the native soil.  Drip irrigation disposal fields utilize proven drip irrigation technology to pressure distribute treated wastewater to native soil through buried tubing.  Numerous infiltration bed, trench, and drip irrigation disposal systems are in operation throughout Minnesota .  Soil disposal presents a viable option for avoiding the issue of TMDLs entirely—and for preserving the quality of surface water resources.

by Brian Davis
Ph.D. Senior Design Engineer
North American Wetland Engineering, LLC

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