Introduction

Spokane County Utilities provides wastewater management for residential, commercial and industrial customers in the Spokane Valley and North Spokane service areas.  In recent years, the County has rapidly expanded its wastewater collection system to reduce the number of septic tanks located over the Spokane Aquifer.  This sewer expansion program is projected to continue through the year 2015 to provide wastewater service to all existing development within the County’s sewer service area.  Along with the sewer system extensions, the County’s sewer service area is projected to experience significant growth over the next twenty years.  Both factors will sharply increase the quantity of wastewater that must be responsibly managed.

Currently, wastewater generated in the County is sent, via a sewer network, to the Spokane Advanced Treatment Plant (SAWTP) which is owned and operated by the City of Spokane.  A 1980 interlocal agreement established the basis for the City to treat up to 10 million gallons per day of County generated wastewater.  The County expects to exceed that capacity by the end of 2007.  Due to physical, environmental and implementation constraints, additional capacity at the SAWTP may not be available for use by the County, or may be insufficient for the County’s long-term needs.

Given this situation, the County has begun a planning process to develop long-term wastewater management strategies that will provide reliable service, protect the environment, and be economical to local ratepayers.  In so doing, the County will integrate its planning with other regional service providers to identify opportunities for increased efficiency or enhanced benefit to the watershed.  Balanced with these considerations is the County’s need for solutions that can be reliably implemented should regional or intergovernmental approaches prove too difficult, expensive or slow.

This Basis of Planning Report provides the foundation for subsequent identification, evaluation and selection of appropriate wastewater management strategies.  It identifies the goals and objectives of the planning process, describes the current characteristics of the planning area, projects future wastewater flows and loadings, defines key water quality and water resource issues, reviews the capabilities of existing wastewater systems, and presents insight into the values and concerns of interested stakeholders.

Goals and Objectives

Chapter BPR-1 describes the goal, objectives, and planning elements for the development of the Facilities Plan and EIS. At the outset of the planning process, the following goals were established to guide development of a successful wastewater management program for Spokane County:

§         Provide reliable wastewater service – both near-term (20-years) and long-term (50-years)

§         Protect public health

§         Protect and improve the region’s water resources – surface water and groundwater

§         Provide cost-effective solutions for County ratepayers

§         Provide for growth in concurrence with the Growth Management Act

§         Ensure the County has adequate authority and control to meet future wastewater needs

§         Gain approval by the public, elected officials and regulatory agencies

§         Provide for growth consistent with goals and policies of the Spokane County Comprehensive Plan

To support these goals, the project team also identified a range of project objectives.  The objectives describe specific measures of success used to guide the project and gauge its outcome.

The Basis of Planning report is just one element of the County’s current wastewater planning efforts.  A Comprehensive Wastewater Master Plan (CWMP) Update is being prepared under a separate contract by Engineering and Economic Services. The demographic and flow projections developed in the CWMP Update serve as the basis for the flow and loading projections presented in the Basis of Planning Report. The County is also working to develop a new interlocal agreement with the City.  Key areas of focus will be the future allocation of capacity at the SAWTP and within the City’s conveyance system, methodologies for equitable cost sharing, and the responsibilities and rights of the City and County.  Finally, this report will serve as a springboard for development of the Wastewater Facilities Plan and Programmatic Environmental Impact Statement (EIS). These documents will provide the County with a recommended wastewater management strategy that meets both near-term (20 year) and long-term (50 year) needs, and is environmentally responsible.

Planning Area Characteristics

The planning area comprises many varying features which impact wastewater management and treatment. These characteristics are described in Chapter BPR-2.

Planning Area Definition

The planning area for this facilities plan consists of two land masses: one located in North Spokane and one located in the Spokane Valley (see Drawing ES-1.  Planning Area). The 20-year boundaries for these planning areas are defined by the Draft Urban Growth Area (Draft UGA) and the service boundaries between the County and the nearby City of Spokane and Liberty Lake Sewer and Water District No. 1. The Draft UGA was established as part of the County’s on-going long-range planning, and has yet to be approved by the Spokane County Board of County Commissioners.

While the Facilities Plan will examine infrastructure requirements for a 50-year planning horizon, this is a longer horizon than the Growth Management Act (GMA) requires public agencies to consider. However, it is assumed that only areas contiguous with the Draft UGA will be served in the future by the County’s wastewater program.

Physical Environment

Spokane County is located in northeastern Washington adjacent to the Idaho border. While the County has an array of landscapes ranging from the mountainous area in the northeast to the semiarid basalt plains in the southwest, the planning area is nearly all urban landscapes with flat to moderately-rolling hills. The climate in the planning area is relatively temperate, with average monthly temperatures ranging from approximately 30 degrees F in January to just over 70 degrees F in July. Precipitation is relatively low, averaging 17 to 21 inches per year and ranging from approximately ½-inch to 2.5 inches per month. Soils in the planning area are porous with low water-holding capacity, although soils in the southeastern and northern parts of the County are fine- to medium-textured with moderate to slow permeability. These areas support much of the County’s farming.

Water Resources

Many significant water resources are located in and around the planning area (Drawing ES-2.  Surface and Ground Water Sources). By far, the most significant groundwater resource is the Spokane Valley-Rathdrum Prairie Aquifer, which serves as a source of drinking water for over 400,000 people. In the planning area, the aquifer is recharged along its margin on all sides from percolation through porous soils overlying the aquifer and through seepage from the Spokane River. Because of its importance as a primary drinking water source, the United States Environmental Protection Agency has declared the aquifer a “sole source” aquifer. Many other aquifers, most of them also drinking water sources, are located within the County. Because of the high permeability of soils overlying much of the aquifer, contamination by surface and subsurface activities is always a primary concern.

In addition to its rich groundwater resources, Spokane County has many surface water bodies that provide a variety of economic, recreational and aesthetic benefits and uses. The Spokane River is the principal surface water body in the planning area. It begins in Idaho at Lake Coeur d’Alene and flows west through Washington and finally into Long Lake. Various reaches of the river gain water from or lose water to the Spokane Rathdrum Aquifer.  This interaction is also observed in lower segments of the Little Spokane River, which originates north of Spokane County and flows south to Long Lake. The other primary surface water feature in the planning area is Latah Creek, which originates in Benewah County, Idaho and flows north to a confluence with the Spokane River at the west side of the City of Spokane.

Human Environment

Growth in Spokane County has increased since 1890, with a steady increase of approximately 2 percent per year since 1940. The current (1999) population in the County is 414,000, of which 121,000 are located within the planning area and over 58,000 are currently served by the County’s sewer system.

Land use within the planning area is primarily suburban residential, with the City of Spokane and surrounding areas providing the economic and cultural center for much of eastern Washington and northern Idaho. This change has largely occurred over the last 60 years as orchards and vegetable farming were replaced by urban uses. This conversion of land use resulted from accessibility to roads, a dependable supply of water, and level land characteristics with few physical constraints to development. Prime farmland still exists directly north of the planning area, and on the western and southeastern boundaries of the County.

A wide range of governmental agencies has interest in wastewater management issues in Spokane County. These agencies span many jurisdictional levels: local, regional, state and federal. Local wastewater service providers include the County, the City of Spokane, the Town of Millwood, and the Liberty Lake Sewer and Water District. Many other agencies have an interest in the facility plan because of their regulatory functions, responsibility for facilities located within the watershed, interest in the surface and groundwater resources, or ability to impact development or implementation of the plan.

Planning Projections

Chapter BPR-3 develops planning projections for three planning horizons: 2020, which coincides with the planning horizon used in Spokane County’s Growth Management Plan; 2025, which provides the County with a 20-year management strategy after the recommended plan has been implemented; and 2050 for long-range planning. Planning projections include the following three primary elements:

§         Population and land use forecasts

§         Wastewater flow projections

§         Wastewater loading projections

Population and Land Use Forecasts

Planning projections given in the Basis of Planning Report rely on projections of population growth and development of industrial and commercial properties developed through the CWMP Update. These projections account for current users of the system, existing residents and commercial/industrial facilities within the current Urban Growth Area that have not yet been connected to the County’s system (i.e., are served by septic tanks), and new development within the planning area.  These projections are shown in Figure ES‑1. Because the CWMP Update only provided estimates of development through 2020, several assumptions were made to estimate the increase in development between 2020 and 2050.

Figure ES‑1.  Population and Commercial/Industrial
Development Projections

Wastewater Flow Projections

Wastewater flow projections include both base sanitary flow from residences, businesses, institutions, and industrial establishments, and extraneous flow (groundwater or stormwater) that enters the separated sewer system. Average flow projections were calculated by starting with the 1999 base flow determined through meter readings at three City/County connections, and adding:

§         Future residential, commercial, and industrial sanitary flow based on the population and land use estimates reflected in Figure ES‑1, and

§         Inflow and infiltration (I/I) estimated at 2 gallons per capita per day (gpcd) in 2000, increasing to 10 gpcd in 2020, and remaining steady at 10 gpcd through 2050.

§         Total County average wastewater flow is projected to increase to 20.6 mgd by 2020, 21.9 mgd by 2025, and 27.3 mgd by 2050.

These values were summed to generate the total flow projection shown in Figure ES‑2. Flow peaking factors were evaluated to determine the maximum month, week, day, and peak instantaneous flow.

Figure ES‑2.  Wastewater Flow Projections

Wastewater Loading Projections

Wastewater loading projections reflect a combination of the baseline flows described above, unit loading rates, and peaking factors that reflect maximum month, week, and day conditions. To develop a reasonable projection of future wastewater loadings, an assessment of County and City data was supplemented by a review of other local wastewater utilities with generally similar service area characteristics. Average concentrations for utilities in the area are generally lower than literature values. Because the County’s data are limited (quarterly sampling has been conducted over three years), the Facilities Plan will be developed using literature unit loading values. However, it is recommended that the County’s recently implemented sampling program be continued to generate more reliable local data. Wastewater peaking factors were developed based on the average peaking factors for other communities in the area. The final projected wastewater loadings are shown in Table ES‑1.

Table ES‑1.  Projected Wastewater Loadings

Water Quality and Water Resources Issues

Chapter BPR-4 reviews the characteristics of key water resources that may be impacted by the County’s wastewater management program – the Spokane Valley-Rathdrum Prairie Aquifer, and the Spokane and Little Spokane Rivers. These water bodies comprise the major components of a large, hydraulically interconnected water system in the Spokane region. As such, actions affecting one of the resources may have direct or indirect impacts on the other resources as well. The chapter also reviews regulations. Water quality issues and other factors that will shape quality requirements for discharge of effluent to receiving waters, beneficial reuse of effluent and beneficial reuse of biosolids.

Spokane Valley-Rathdrum Prairie Aquifer System

The prolific exchange of surface water and groundwater through the hydraulic connection between the rivers and the aquifer can have significant implications with regard to the quality and quantity of the surface and groundwater resources in the County. Permits for water purveyors using the Spokane aquifer total 1,009 cfs, which is approaching the natural supply of the aquifer and may actually exceed the aquifer’s ability to meet demand. If more groundwater is pumped than is available, the water table will be lowered and flow in the Spokane and Little Spokane rivers may decrease. With minimum streamflows in these rivers established by state regulation and by recommendations of the Washington Department of Fish and Wildlife, and with ongoing watershed planning in the state, the future may see a situation where little or no “new” water will be available for consumptive use.

Water quality in the aquifer has been monitored routinely for the past 20 years. This data shows that while the quality of water in the aquifer is generally good to excellent, the aquifer is clearly impacted by development. In unsewered areas with residential and commercial development, clear trends exist toward increasing contaminant concentration in some wells. Stormwater injection through drywells also leads to degradation of water quality. On a positive note, in areas where sewering has occurred and/or development has slowed or stopped, contamination levels have fallen.

Surface Waters

The surface water features of interest in the planning area – the Middle Spokane River (from Nine Mile Bridge to the state line), the Little Spokane River, and Long Lake – are designated for “characteristic uses” such as water supply; stock watering; fish and shellfish rearing, spawning, and harvesting; wildlife habitat; primary contact recreation; and commerce and navigation. To preserve the designated characteristic uses, instream water quality must comply with the numerical and narrative guidelines given in the Washington State Surface Water Quality Standards. Water quality standards for the Spokane and Little Spokane River system are established for fecal coliform, dissolved oxygen, total dissolved gas, temperature, pH, turbidity, toxic materials, radioactive materials, aesthetics, and nutrients. There are currently seven permitted point source discharges to the Spokane River between Coeur d’Alene Lake and Long Lake, and two point source discharges to the Little Spokane River.

Potential effluent quality requirements for new surface water discharges in the study area are impacted by the water quality standards described above, and by Total Maximum Daily Loads (TMDLs) which have been established or are being established to address identified water quality limitations. Table ES‑2 below shows likely effluent quality requirements for discharge of wastewater to the Spokane or Little Spokane Rivers. Actual values will be determined by Ecology through the NPDES program, and the County must be able to demonstrate that the effluent discharge will allow the receiving water to meet water quality standards. Consequently, the values shown in Table ES‑2 must be regarded as speculative at this time.

Table ES‑2.  Potential Effluent Quality Requirements

1.        Required value will be defined by dissolved oxygen TMDL process.

2.        Required value will be defined by mixing zone study for toxicity.

3.        Required value will be defined through negotiation with Phosphorus TAC.

4.        Instantaneous value.

5.        Required value will be defined based on monitoring of actual effluent metals concentration.

Effluent Reuse

With appropriate levels of treatment and system management, reclaimed water has been used successfully for many applications. Reuse programs in the study area must consider the state’s guidance provided in the Water Reclamation and Reuse Standards, which outlines four classes of reclaimed water that can be used for different applications. These range from Class A water, which has the most stringent treatment requirements but minimal restrictions on use, to Class D water which has limited uses which must be accompanied by strict controls to minimize human contact. Reuse must also be protective of groundwater quality. Potential reuse opportunities and some of their considerations are listed below.

Irrigation: Water quality requirements are typically impacted by the opportunity for human contact, the opportunity for contact with food for human consumption, and the level of sterilization the food crop will receive before reaching the consumer. The classification of the reclaimed water (A through D) as well as management practices impact acceptable reuse for irrigation.

Impoundments: Restrictions on the use of reclaimed water in impoundments varies depending on the level of treatment the water has received.

Industrial and Commercial Applications: Class D reclaimed water can only be used for sanitary sewer flushing, whereas Class A reclaimed water has a variety of potential industrial and commercial applications. Additional treatment requirements may be imposed by the specific needs of the end user.

Wetlands: The Washington reuse standards establish conditions under which reclaimed water may be used to create or enhance wetlands. Natural or constructed wetlands that receive reclaimed water are considered waters of the State, and are differentiated from treatment wetlands, which are considered part of the wastewater treatment process and not waters of the State. In addition to the designated reclaimed water classes, Washington uses restrictions on total suspended solids (TSS), nutrients, and metals to assure that water quality in the constructed wetlands and any downstream waters of the State are protected.

Streamflow Augmentation: This application is defined as use of reclaimed water for a beneficial purpose such as in-stream flow enhancement, irrigation supply, water right replenishment, and fisheries propagation, and must meet the requirements of the federal water pollution control act.

Groundwater Recharge: Both surface percolation and direct injection of reclaimed water require a minimum of Class A reclaimed water quality. Additional nitrogen reduction must be provided for surface percolation, and direct injection to a potable aquifer requires significant additional treatment beyond that needed for the Class A designation.

Biosolids Management

Land application, composting and landfilling are the biosolids management techniques typically used in Eastern Washington and Northern Idaho. These uses are regulated by Ecology using rules which closely follow those promulgated by the U.S. EPA under 40 CFR 503 (“Part 503 regulations”). These regulations use three measures to determine the level of restriction placed on the application practice: 1) concentration of trace elements, 2) quantity of pathogens, and 3) vector attraction. Several degrees of pathogen reduction are recognized, with associated differences in the level of restriction placed on reuse of the treated biosolids.

Existing Wastewater Facilities and Programs

The County’s wastewater management facilities are integrated into a regional network of conveyance and treatment facilities serving the greater Spokane area. A simplified schematic of the regional network is shown in Figure ES‑3.

Figure ES‑3 reflects that the County’s interceptor system receives flow from the City of Millwood, and has agreed to accept “excess” flow from the Liberty Lake Sewer and Water District No. 1. All flow from these dischargers and from most sewered areas of the County are treated at the City of Spokane Advanced Wastewater Treatment Plant (SAWTP) and discharged to the Spokane River.

Conveyance Facilities

Through the end of 1999, the County’s collection system included 270 miles of sewer. These sewers serve two distinct systems, one serving Spokane Valley and one serving North Spokane. The Spokane Valley system includes two main interceptors that discharge to the City’s collection system: the Spokane Valley Interceptor (SVI) which serves the area south of Interstate 90, and the North Valley Interceptor (NVI) which serves the area north of Interstate 90. Because of the topography of the North Spokane area, five major pumping stations are used to lift wastewater to the City’s collection system. Flow from these pumping stations is combined in a single interceptor that discharges to the City.

Through a 1980 interlocal agreement, Spokane County purchased capacity in the City’s collection system to convey 10 mgd of County wastewater to the SAWTP. If the County needs to send wastewater flows in excess of its current capacity allowance, improvements to the City’s collection system will be needed. However, the nature, cost, and implementation time frame for these improvements will be determined in part by the City’s on-going combined sewer overflow (CSO) planning effort.

Treatment Facilities

Nearly all of the wastewater generated in the Spokane County service area is conveyed to the SAWTP for treatment and disposal. A small portion of the wastewater is treated at five satellite wastewater treatment facilities that are owned and operated by the County. These treatment facilities have capacities ranging from 22,500 to 86,000 gallons per day. One facility is scheduled to be removed from service within 5 years; three others will be removed from service within 20 years. The Hangman Valley Treatment Plant is the only small facility that is planned to remain in service for the foreseeable future.

The SAWTP is located in northwest Spokane along the north bank of the Spokane River. It was initially constructed as a primary treatment plant in 1958, and has since been upgraded and expanded to its current capacity and process configuration, which includes the following:

§         Screening, flow measurement, and aerated grit removal

§         Venturi meter to split divert excess flow (over 77 mgd) to CSO primary clarifiers, where flow is either stored and returned to the plant for full treatment, or clarified and combined with effluent from the secondary treatment process

§         Preaeration and primary clarification

§         Activated sludge treatment with alum addition and secondary clarification for removal of carbonaceous BOD, TSS, ammonia-nitrogen, and phosphorus (through process modifications, nutrient removal is only practiced during the summer permit season)

§         Chlorination/dechlorination

§         Gravity thickening of primary sludge

§         Dissolved air flotation thickening of secondary sludge (soon to be eliminated through solids handling improvements)

§         Anaerobic digestion

§         Belt filter press dewatering (currently being upgraded through solids handling improvements)

Effluent from the treatment process is discharged year-round to the Spokane River, while dewatered biosolids are beneficially used through land application to agricultural fields in Spokane and Lincoln counties.

The plant has generally been viewed as having an average dry weather capacity of 44 mgd and a maximum secondary treatment capacity of 77 mgd. The preliminary treatment facilities have a hydraulic design capacity of 146 mgd and the CSO treatment system has an estimated storage capacity of 70 mgd. This capacity is being re-evaluated in light of a new NPDES permit, which was issued to the City in March of 2000. This permit included changes in the ammonia-nitrogen and metals discharge criteria. Preliminary results of this current investigation indicate that near-term capacity bottlenecks will occur in the liquid stream, solids handling, and activated sludge processes. A phased solids handling improvements program has been approved by the City, and will be completed in 2004.

Stakeholder Values and Concerns

Stakeholders from various sectors of the community were interviewed during the Basis of Planning phase to gain an understanding of the various community priorities, issues and concerns regarding wastewater management. The objective was to understand the variety of community issues early in the planning process so they could be considered during the review and identification of wastewater management alternatives.

Twenty-two representatives from various agency, business association, development, industry, environmental, and neighborhood stakeholder groups were interviewed during the summer of 2000. A set of fourteen questions were asked, and the following summarizes the comments:

§         Most of those interviewed felt the County has been providing good sewer service, however, concerns were raised regarding the current City/County wastewater management arrangement.  There was strong support for both the County expanding its wastewater management services and for developing a comprehensive regional wastewater management approach.

§         Most (85%) felt that County rate payers or all in the region should help pay for City of Spokane Combined Sewer Overflow (CSO) reduction.  This was typically supported because it could provide additional capacity for County wastewater flows at the Spokane Area Wastewater Treatment Plant or because all in the region benefit from cleaner rivers and lakes.

§         The top wastewater priorities were public health, aquifer/drinking water protection, and Spokane River water quality protection.

§         Support was expressed for a new effluent discharge to the Spokane River; use of the Liberty Lake treatment plant; use of reclaimed wastewater for agricultural irrigation, urban irrigation, creation of wetlands, and underground storage for irrigation or stream flow augmentation. However, there were varied opinions and concerns regarding a new effluent discharge to Little Spokane River, and using highly treated wastewater for irrigation of school and park landscapes. The majority of those interviewed felt recharge of the Spokane Aquifer with treated effluent would not be a viable option due to public health concerns and public perceptions.

§         Most supported recycling of treated effluent and biosolids, with some concerns expressed, and most indicated they would pay more to achieve recycling benefits. Half of those interviewed supported including recreational enhancements at new wastewater treatment facilities, and many ideas were shared on how the County might increase public benefit from new facilities.

§         Various recommendations and suggestions were provided during the interviews.  The County was encouraged to consider industrial reuse in the Valley, use of mini treatment plants, and increased conservation, public education, and CSO reduction.

The planning team will consider all provided comments as the wastewater management alternatives and recommendations are developed.