Sunnymede Wet Weather Flow Management

Project Description

Sanitary sewer overflows (SSOs), caused by infiltration and inflow (I&I) are common problems encountered by nearly all wastewater utilities. The City of Fort Smith faced these same challenges in their Sunnymede Sewer Basin and began addressing the problem by focusing on reducing I&I and mitigating localized SSOs caused by bottlenecks in the collection system. Although these improvements were necessary and corrected many of the SSOs, I&I cannot feasibly or completely be eliminated from any collection system. In addition to the collection system rehabilitation and capacity improvements, the City of Fort Smith needed to ensure that all SSOs are mitigated.

The Sunnymede Wet Weather Flow Management Project focused on maximizing the capacity of the downstream sewerage system and diverting wet weather flow to a new high-rate clarifier and earthen equalization storage basin. A new pump station comprised of three (3) dry weather pumps and three (3) wet weather pumps was constructed. The dry weather pumps convey normal wastewater flow, between 1.0 and 8.0 million gallons per day (MGD) to the Massard Basin and Waste Water Treatment Plant while the wet weather pumps convey peak wet weather flow to a high rate clarifier and 22-million gallon equalization basin.

The project was confronted with several challenges, the first of which was siting 22 million gallons of equalization storage located near areas identified in the 100-year floodplain and floodway. The second challenge was constructing such a facility adjacent to residential areas and the University of Arkansas Fort Smith. Startup and operation of the new remote treatment facility was also a design challenge. The new facility is only operational during wet weather events, a time when the Utility’s manpower is least available. Through PLC programming and SCADA, we were able to automate the facility startup sequence and limit the manpower required to operate the new facility to a single operator.