Coggon Gets Updated Wastewater System

The City of Coggon, Iowa, was under an administrative consent order from the Iowa Department of Natural Resources to make its trickling filter wastewater treatment plant compliant with the City’s National Pollutant Discharge Elimination System permit. The City’s treatment system exceeded biochemical oxygen demand, E. coli, and ammonia limits. It also contained mercury contamination believed to be from a leak in a 1930s-era mercury-filled bearing in the trickling filter, which had been replaced but the contamination was not properly mitigated.

The City hired Fehr Graham to complete an anti-degradation alternatives analysis and facility plan to determine the best treatment option. After reviewing multiple treatment options and technologies, we found a sequencing batch reactor plant was the best solution for Coggon to keep costs low and prevent the City from having to purchase more land. Our experience with similar projects helped us make progress even though portions had been started by the City’s previous engineer. Our knowledge of Iowa’s design standards, permitting process, and funding requirements helped get the project back on schedule. 

The former plant was converted to an equalization basin to buffer high flows while a new lift station pumps wastewater to the new mechanical treatment plant a half-mile north. Mechanical wastewater treatment plants operate most efficiently when the wastewater rate is consistent. The new equalization basin provides consistency by collecting excess wastewater during heavy rainfall events and then gradually releasing the wastewater to the treatment plant. This allows for better treatment and a smaller treatment facility. 

The City used the Community Development Block Grant Program and the United States Department of Agriculture Construction Loan Program to fund the project. Construction was completed this year.