Improving Water Quality in the Spokane River and Spokane Valley-Rathdrum Prairie Aquifer 

In early 2000, Spokane County began a planning process, with HDR as their principal consultant and advisor, to develop long-term wastewater management strategies that would provide reliable service, protect the environment and be economical to local ratepayers. 

Initially, we developed a programmatic approach to providing wastewater service, including total maximum daily load negotiations with the Washington State Department of Ecology. Our staff prepared a facility plan for the County that recommended a new treatment plant be constructed with a discharge to the Spokane River. The County selected a membrane bioreactor facility with an initial capacity of 8 million gallons per day, expandable to 24 MGD. 

In addition to preparing the facility plan, we developed a preliminary design for a new facility, which included a detailed process analysis and model to evaluate water quality impacts to the Spokane River and the underlying aquifer. We provided preliminary design for a new state-of-the-art reclamation facility to produce the highest quality reclaimed water, designed to meet the lowest effluent phosphorus limits in the nation at 0.010 mg/l. 

We also developed an innovative Water Quality Offset (trade) under the existing Washington Administrative Code for a nonpoint source load reduction of phosphorus from sewering 15,000 on-site septic systems over the Spokane Valley/Rathdrum Prairie Aquifer to compensate for the new wastewater effluent point source discharge to the Spokane River.

During project development, we served as the consulting engineer in the planning phase and as the owner’s representative during procurement and design/build delivery of this 143-million-dollar project. Additionally, we also provided construction management of four separate concurrent design-bid-build projects that provided the two wastewater pump stations, forcemains and outfall to serve the new reclamation facility. The experience gained from being intimately involved in all phases of the program, from initial concept development to ongoing, continuous monitoring of performance, equipped us well to provide alternative delivery projects and programs that deliver maximum value.

On December 1, 2011, and ahead of schedule, the facility began treating wastewater from the incorporated and unincorporated areas of Spokane Valley. We have continued to serve as the Owner’s Engineering Representative supporting the County’s regional water reclamation facility, collection system improvements, biosolids management planning and plans for effluent reuse.