Hybrid solution works for new Coggon Wastewater Treatment Plant


November 2015 to July 2018



» Completed Topographic Survey.
» Helped secure funding.
» Designed and planned facility.
» Prepared preliminary and final plans and specifications.
» Completed construction staking, observation and administration.

The City of Coggon, Iowa, was under an administrative consent order from the Iowa Department of Natural Resources to bring its trickling filter Wastewater Treatment Plant into compliance with the City's National Pollutant Discharge Elimination System permit. The City's treatment system exceeded biochemical oxygen demand, ammonia limits and contained sources of mercury. Disinfection requirements also had to be met. Another complication was the plant's proximity to the floodplain. The City hired Fehr Graham to complete these much-needed upgrades.

We completed an antidegradation alternatives analysis to figure out ways to rid the system of pollutants. We used a hybrid activated sludge treatment system that combines continuous flow and sequencing batch reactor (CF/SBR) technologies for a small footprint, which Coggon needed to keep costs low and not have to purchase land. After reviewing multiple treatment options and technologies, we found the hybrid CF/SBR was the best solution for Coggon.

This was the first time Fehr Graham had worked with the City, but our experience with similar projects helped us to 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. Our team used mercury estimates from the Environmental Protection Agency to determine how much remediation would be needed for the mercury already in the system.

The City used the Community Development Block Grant Program and the United States Department of Agriculture (USDA) Construction Loan Program to fund the project. Construction was completed in 2018.