Decorah has provided municipal wastewater treatment service since 1916 when a septic tank and slow-sand filter were constructed for treatment of Decorah’s wastewaters. Details of that system are available from a set of plans still preserved by the City.

In 1935, the septic tank-sand filter facility was replaced by a trickling filter treatment plant which was subsequently renovated in 1962. This trickling filter plant was located on a site near the Upper Iowa River at the east edge of the City.

The trickling filter plant was vulnerable to flooding. In fact, when the flood levee was constructed in the late 1940’s, it was located such that the plant continued to lie on the river side of the levee.

By 1976, the facility was subject to both hydraulic and organic overloads. Industrial growth within Decorah, along with a substantial population increase, had created loads on the plant which were simply more than it could treat and still meet reasonable effluent standards for discharge to the Upper Iowa River. At that time, the Decorah City Council decided to replace the plant with a larger and more effective treatment facility.

Decorah’s new activated sludge treatment facility was placed on-line November of 1985. The plant treats wastewater from the City of Decorah and, from the unincorporated community of Freeport. Discharge from the plant is to the Upper Iowa River in a reach of the river that is classified by the Iowa Department of Natural Resources as a Class A BWW. This class of water is to be protected for wildlife, fish, aquatic and semi-aquatic life, and primary and secondary human contact water uses.

The construction cost of the plant was approximately $4,500,000 with about $3,500,000 of that amount coming as a grant from the U.S. Environmental Protection Agency and $225,000 as a State of Iowa grant.

In 2004, the plant underwent several improvements that included, Ultraviolet Disinfection, New main pumping station equipment including controls, new ventilation equipment, and a new one million gallon Biosolids storage tank. The cost of the improvements was approximately $1,400,000 and financed through a State Revolving Fund Loan.