Charles City, IA

Treatment Plant Improvements

  • Client City of Charles City
  • Type Wastewater
  • Services Facility Plan, Treatment, Flow EQ
  • Construction Cost $2.5 Million
  • Project Manager Dale A. Watson, Ph.D., P.E., BCEE
  • Project Engineer Steve Troyer, P.E.,BCEE

CHALLENGE

FOX Engineering Associates was retained by the city to assist in solving wastewater permit compliance problems. Wastewater discharges were violating metals, ammonia, and flow limits and the city was under administrative orders to bring its wastewater discharges into compliance with its NPDES permit. Complicating matters, raw wastewater pumps were worn out, controls were outdated, and flow measurement was unreliable. Industrial dischargers were unable to obtain the level of wastewater utility service that they needed. The city was receiving pressure from IDNR to address its capacity issues.

2. Charles City

SOLUTION

Evaluation of the existing trickling filter wastewater plant, the contributing flows, and the waste load allocation model resulted in FOX’s recommendation to upgrade the plant through addition of an effluent diffuser in the river to obtain full advantage of the river’s mixing zone in accord with the environmental regulation. The diffuser eliminated the need to require stricter industrial pretreatment for metals and avoided the need to upgrade for nitrification. A second final clarifier and electrical modifications were also recommended.

Under phase one of the project, the diffuser and the final clarifier were designed and constructed. The diffuser is a 16-inch diameter by 100-ft long, ductile iron, river-joint pipe extending across one half of the Cedar River. Because the river channel has a rock bottom in the vicinity of the treatment plant, FOX engineers devised a unique and low-cost installation incorporating the diffuser piping into a new submerged rock dam. The final clarifier is a 60-ft diameter concrete structure designed to match the existing unit.

Phase two of the project involved pump and valve replacement in the raw lift station and upgrading of electrical controls and instrumentation. Three 2500 gpm wastewater pumps, equipped with variable drives were installed, along with controls using the latest in ultrasonic technology.

Phase three came about when the plant became overloaded and unable to handle the hydraulic and organic loads it was receiving. Industrial dischargers were unable to obtain the level of wastewater utility service that they needed. The city was receiving pressure from IDNR to address its capacity issues; FOX completed an evaluation of the existing plant and updated the Facility Plan. After obtaining IDNR approval of the facility plan, FOX assisted the city in applying for and obtaining a State Revolving Fund (SRF) loan to finance the plant improvement project.

FOX designed improvements to the facilities to address the capacity needs, including a new bio-tower to supplement the existing trickling filter, a third final clarifier, a 700,000 gallon sludge storage tank, conversion/expansion of the existing aerobic digesters, new intermediate pumping, additional raw pumping, and associated control and instrumentation improvements.

FOX provided engineering services throughout the construction-phase and start-up phase of the project to assist the city in obtaining proper control of the project.

OUTCOME

IDNR fines and penalties were avoided, a less restrictive discharge permit was obtained for the city avoiding the need to upgrade the plant for nitrification, and pumping costs were reduced. Operation of the plant was improved and made easier with the variable flow pumping capacity and the life of the raw wastewater pumping facilities was extended by 20 years. Better process control and monitoring have been achieved. The city wastewater plant has been able to remain in full compliance with IDNR requirements.

The plant improvements were completed at a cost of approximately $2,500,000, or about $400,000 less than anticipated.  Operation and control flexibility of the plant was greatly improved. The water pollution control plant and the city have regained extra capacity needed for economic development and have been able to remain in full compliance with IDNR requirements.