Wastewater

The Cheney Wastewater Division is responsible for operating and maintaining the collection and treatment processes to ensure the City is in compliance with all applicable state and federal clean water standards.

Collection System


The wastewater collection system consists of more than 40 miles of mains as well as 850 manholes and two lift stations. Wastewater is conveyed through the collection system to the treatment plant. The City's treatment plant has the capacity to treat 1.5 million gallons per day on an annual basis, but the plant can treat up to 2.7 million gallons a day during the month when the maximum flows are occurring.

Cheney Wastewater Treatment and Reclamation Facility
Overview

The City of Cheney’s Wastewater Treatment and Reclamation Facility (WTRF) is designed as an advanced secondary treatment plant utilizing biological removal of nutrients. The plant utilizes Eimco carrousel oxidation ditches to accomplish solids/organic removal and secondary clarification prior to final effluent discharging to 100 acres of wetlands owned by the city. The plant design MGD capacity is 1.90 annual average, 3.05 max month, 4.7 max day and 6.0 peak flow. Plant efficiency is regularly in the 90-98% range for removal of all constituents. Biosolids are removed from the plant and composted to class A standards for resale to the public. 

The Cheney WTRF has a fully equipped and staffed laboratory for testing of all regulator and process control parameters. Over eighteen thousand individual tests are conducted annually. The resulting data is entered into the Operator 10 data base for utilization of trending for process control and generation of the NPDES monthly report.

Currently Eastern Washington University is the only regulated industrial discharger under permit discharging to the Cheney WTRF. There are over twenty additional categorical dischargers in the city but they do not meet requirements for permitting. The city has developed a new industrial and technology park in 2009 and actively is looking for tenants for that site.

The collection system and lift stations are maintained by the Wastewater Collection Division. Storm water is a separated collection system that does not flow to the facility.

Process Description

Wastewater influent enters the treatment plant through the pre-treatment facility. Non-organics are removed via the pista grit chamber. Influent then is screened through a 0.100 inch opening rotary fine screen to remove any large debris. Discharge from the pre-treatment building is pumped to the conditioning tanks (CT”s). The CT’s mix the influent flow with return activated sludge (RAS). Low speed mixers homogenize the influent/RAS mix, maintaining an anoxic/anaerobic environment. Cellular phosphorus release from the microbes is achieved in the CT’s. Discharge from the CT’s flows into the aeration basins (AB’s). Dissolved oxygen is increased and continually monitored to maintain 2.0 mg/L. Organics removal, phosphorus uptake and ammonia nitrogen conversion by oxidation to nitrate nitrogen are accomplished in the AB’s. Discharge from the AB’s is to the secondary clarifiers (SC’s). Concentrated settled solids are pumped from the SC’s to the CT’s as RAS. Waste activated sludge (WAS) is proportionally removed and pumped to the sludge storage tank (SST). WAS is held in the SST for no longer than 72 hours prior to dewatering. While in the SST the WAS is aerated to prevent decay or cellular release of phosphorus. WAS is dewatered via a belt filter press (BFP). Inlet to the BFP contains 0.6% to 1.5% solids, depending on yearly process conditions. Final boisolids from the BFP contain 13% to 15% solids, again depending on yearly process conditions. Dewatered biosolids are then sent to the biosolids composting building on pan conveyors where it is blended with ground yard waste material and wood chips to create EcoGreen compost. Final effluent is chlorinated for pathogen reduction and then de-chlorinated and discharged into the City’s 100 acre tertiary wetlands for final polishing.

Cheney Tertiary Wetlands 


The Cheney Wastewater Treatment and Reclamation Facility (WTRF) wetlands were constructed in 1995 as a tertiary (final) enhancement for the WTRF effluent. Water that discharges from the WTRP is a highly treated “Class B” effluent. The effluent meets all Washing State Department of Ecology and Environmental Protection Agency water quality standards for discharge to constructed wetlands for final nutrient uptake. The WTRF removes virtually all organics and nutrients (phosphorus and ammonia) as it passes thru the facility. However, some nutrients remain in the final effluent and the constructed wetlands are designed to uptake these nutrients (phosphorus and nitrogen) as the water flows thru the wetlands. Cattails and canary reed grasses growing along the peripheral riparian zone of the wetlands utilize the nutrients as they develop in their yearly growth cycle. These nutrients are converted to energy for the growth of the plant. This nutrient uptake completes the treatment process and provides rich vegetative cover for the utilization of the wetland inhabitants. 

Removal of the nutrients is critical for protection of the receiving waters and downstream tributaries that flow into the Spokane River basin. Reduction of phosphorus and nitrogen ammonia entering the receiving streams is essential in preventing summer algae blooms and dense aquatic plant growth that reduce dissolved oxygen levels and inhibit or kill aquatic inhabitants.  

The Cheney WTRF wetlands are made up of five individual cells that total over 100 acres. The wetlands are encompassed within nearly 400 acres of upland and pine forested land owned by the City of Cheney. The wetlands and upland areas are habitat for most waterfowl, upland birds, marsh birds, raptors, reptiles, and small and large mammals that are found in the region. The dense cattails and grasses provide excellent nesting habitat and protection for the waterfowl and marsh birds. The heavy grasses and brush in the upland areas attract upland birds that forage and nest in the dense forest under growth. Small mammals utilize the wetlands, and uplands areas for cover and foraging. Larger mammals also enjoy the vast grazing opportunities offered by the wetlands and surrounding upland forests. Many predatory mammals and birds enjoy a diverse habitat as well. The open water bodies provide excellent resting and flyway access for the migratory birds that pass though the inland northwest, enhancing the nesting and foraging opportunities in conjunction with Turnbull National Wildlife Refuges mission. Otters, herons and ducks enjoy feeding on small causations, reptiles and fish that also inhabit the wetlands.

Helpful Resources


Cheney Wastewater Treatment and Reclamation Facility

WTRF

Cheney Tertiary Wetlands

Cheney Tertiary Wetlands