With limited land availability, expansion of facultative pond storage capacity was not a feasible alternative. Therefore, in early 2014, the design of a mechanical Water Resource Recovery Facility (WRRF) was initiated. Key project components of the first phase of the mechanical WRRF include master lift station pump capacity increase, new preliminary treatment with fine screening and grit removal, biological phosphorus removal, total nitrogen removal, extended air biological treatment, two final clarifiers, return and waste activated sludge pumping, chlorination/dechlorination disinfection facilities, effluent aeration, and effluent pumping and flow metering. The first phase of the mechanical WRRF was designed to serve a population of 7,500, with future phasing laid out to serve an ultimate population of approximately 30,000.
Due to the high cost of land acquisition, construction of a continuous discharge mechanical WRRF was evaluated for economic and environmental viability. Considering the land acquisition, capital, and long-term operation and maintenance costs, construction of a mechanical WRRF had a lower net present worth cost than the other alternatives that were considered and represented the recommended solution to meet the City’s wastewater treatment needs. However, the facility’s receiving water, Cherry Creek, is an intermittent stream that does not always experience instream flow. This put Watford City in the unique situation of proposing to be the first continuous discharge WRRF in the State of North Dakota to discharge to an intermittent creek. AE2S developed a wasteload allocation model that incorporated the stream morphology and effluent flow and load characteristics to predict the impacts of the discharge on the receiving water.
The Watford City WRRF is also the first publicly funded municipal infrastructure project in North Dakota to utilize the Construction Manager At Risk (CMAR) process for project delivery. AE2S was involved with the critically important selection of the CMAR. The CMAR entity worked closely with AE2S during the design phase to provide constructability reviews, as well as develop a guaranteed maximum price (GMP) for construction of the WRRF. The construction project is complete, on time, and on budget.
A key focus during the design of the WRRF was to minimize cost while maximizing reuse of existing infrastructure. Several existing wastewater treatment facility components were repurposed for inclusion into the mechanical WRRF project. First and foremost, the mechanical facility was constructed within the footprint of one of the City’s existing lagoon cells. Larger influent pumps were installed in the master lift station, allowing the existing wetwell to be kept in service. The existing aerated ponds have been repurposed into biosolids treatment and storage ponds, and the existing control structures will be retrofitted to serve as inlet and decant control structures.