Regional Wastewater Conveyance System & Treatment Plant

Regional Wastewater Conveyance System & Treatment Plant

Location: Washington and Benton counties, Ark.

Client: Northwest Arkansas Conservation Authority

Completion Date: 2010

Burns & McDonnell, in association with USI Consulting Engineers, provided engineering services for the planning and design of a new regional wastewater conveyance system and treatment plant for the Northwest Arkansas Conservation Authority (NACA), serving 10 cities in the northwest Arkansas region, including Bentonville, Rogers and Springdale. The planning area for this new regional wastewater utility encompasses nearly 200 square miles.

A facilities plan projected the service requirements for the regional facilities and recommended a plan to extend wastewater conveyance facilities to NACA's member cities, a method of metering wastewater flows from each of the member cities, a plan for the construction of the new regional wastewater treatment plant serving an ultimate flow capacity of 80 million gallons per day (MGD), and an implementation plan for constructing facilities in phases in accordance with the needs of NACA's member cities. The total estimated project cost of the initial phase of the project was $64 million.

The initial phase of conveyance facilities includes 58,000 feet of gravity interceptors to serve Bentonville and Centerton, 16,000 feet of force main to serve Highfill, and 28,000 feet of force main to serve Tontitown. Flow meter structures measure flows from each of the cities.

The initial phase of treatment plant construction provided 4 MGD treatment capacity readily expandable to 6 MGD. Treatment processes include influent pumping, fine screens, vortex grit removal, an activated sludge process designed for ammonia reduction and nitrogen and phosphorus removal, polishing filters, ultraviolet disinfection and post aeration. Sludge will be dewatered by belt filter processes.

The wastewater treatment plant was designed to achieve advanced treatment discharge standards of 10 mg/l BOD5, 15 mg/l TSS, 2 mg/l NH3 and 1 mg/l P to achieve regional nutrient removal requirements satisfying interstate water quality agreements. Construction bids for the project were taken in early 2009. Immediately following the bidding of the project, the U.S E.P.A. issued revisions to the NPDES permit limiting phosphorus discharges to less than 0.1 mg/l P. Wastewater treatment plant modifications are under design to achieve this more-stringent effluent criteria.

The project planning also included development of service agreements between NACA and its initial customer cities, development of regulations for use of NACA's system, and estimating initial and future service charges to the cities for financing project capital costs and operation and maintenance expenses. Further steps have been taken for the planning and design of the regional wastewater treatment plant. Environmental permitting studies were performed at the regional wastewater treatment plant site.

  • Wastewater planning and design for regional wastewater utility
  • New gravity interceptor sewers
  • New pumping stations and force mains
  • Metering of customer wastewater flows
  • Environmental studies and permitting
  • 80-MGD ultimate capacity treatment plant
  • Biological nutrient removal
  • Polishing filters
  • Sludge dewatering
  • Administration/laboratory building
  • Customer city service agreements
  • Customer city service charges