WASTEWATER TREATMENT PLANT FACILITY PLAN + NUTRIENT REDUCTION – EVANSDALE, IA

Project Overview

Changing regulatory standards and the environment can put communities in a difficult situation. The City of Evansdale’s activated sludge wastewater treatment plant was constructed near the Cedar River in the mid-1970s. Subsequent major flooding in the Cedar River watershed in the years since resulted in the construction of a flood protection dike along the outskirts of the entire community, protecting most homes from catastrophic flooding events, except the wastewater treatment plant, which ended up on the wet side of the levee. During the historic floods of 2008 and 2016, treatment process functionality was threatened, and some components were damaged. Separate from the risk of flooding, the City received a new NPDES permit which required the construction of disinfection technology at the wastewater treatment plant.

Due to the plant’s location in the regulatory floodway and the new requirement to construct disinfection technology, and the future requirements, to reduce nutrient discharges in the Cedar River watershed, the City partnered with McClure to develop a long-term facility plan for improvements. After a six-month planning study, McClure developed three viable recommendations that would comply with new Iowa DNR and Iowa Administrative Code requirements for floodplain construction, implement disinfection technology as required, and address nutrient reduction in a meaningful manner consistent with the Iowa Nutrient Reduction Strategy. Ultimately, the City has elected to move forward with the construction of a new wastewater treatment plant located on the dry side of the flood protection levee. The plant will utilize cutting-edge biological treatment technology called aerobic granular sludge, in which nitrogen and phosphorous are removed to targeted levels in a single reactor without the need for downstream clarification, thereby reducing the capital cost of the project.

Project Highlights:

• 1 MG hydropillar tower.
• Coordination with FAA.
• Tank mixing system.
• Tank designed to serve two pressure zones in conjunction with a booster station.