The existing Arkansas City Water Treatment Plant (WTP) has been in operation since the early 1900s and has exceeded its service life. A combination of rising water demands and increasingly frequent and sever maintenance issues have led to the determination that a new 5.4 MGD (expandable to 6.3 MGD) water treatment facility using greensand and reverse osmosis is the most prudent path forward.
The city currently uses 10 wells within the Arkansas River alluvium to supply water to the existing WTP. Through evaluation of potential water sources, we concluded that continued use of the Arkansas River alluvial well field as the primary water source is the most reliable and economic alternative. Upgrades and improvements will be made to the existing wells to improve performance and production. The Arkansas River Alluvial Well Field will be the only raw water source used at the new WTP.
The wellfield was identified by state regulators as being groundwater under the direct influence of surface water. However, our team questioned this determination. After an initial desktop evaluation, it was decided to proceed with Microscopic Particulate Analysis (MPA) testing. MPA testing has been completed for all water supply wells and results show that all wells may be reclassified to groundwater. Significant cost savings associated with treatment requirements and monitoring will be realized by the city.
The key water treatment process objectives are the removal of manganese, chlorides, total hardness and total dissolved solids (TDS). Due to prolonged drought, groundwater quality has worsened over time. The city desired a water treatment process that could accommodate both changing water quality as well as future regulations related to emerging contaminants of concern. A treatment process consisting of GreensandPlus followed by reverse osmosis (RO) was proposed. GreensandPlus removes a large portion of iron and manganese. RO removes chloride, total hardness and TDS.
Due to the quality of raw water entering the facility, approximately 55 percent of the finished water will be RO permeate with the remaining 45% bypassing the RO. This treatment scheme achieves the desired finished water goals while significantly reducing chemical costs associated with stabilizing the finished water. The WTP design will incorporate a below-grade raw water charge tank, vertical turbine raw water booster pumps, GreensandPlus filtration, cartridge filters, RO high-pressure pumps, RO treatment, RO permeate and bypass blending, 1.5 million-gallon finished water clearwell, high service pumping, and chemical feed systems (sodium hypochlorite for preoxidation, sodium bisulfite for oxidant quenching, antiscalant, sodium hydroxide for finished water stability, sodium hypochlorite for finished water disinfection, and liquid ammonium sulfate for chloramination).
The project execution strategy consists of multiple stages all aimed at reducing overall project cost and compressing the schedule. The project stages are as follows: 1.5 million gallon finished water clearwell design and construction, GreensandPlus and RO equipment proposals, GreensandPlus and RO equipment piloting, balance of plant design, and balance of plant construction.
