5.1        Introduction

Highly treated wastewater effluent is an important water resource in the Spokane Region.  Potential uses include streamflow augmentation, irrigation, wetlands creation, industrial water supply and groundwater recharge.  In this chapter, alternative effluent management strategies are reviewed by considering their applicability to Spokane County, defining effluent quality requirements, outlining implementation steps, identifying facility needs and associated costs, and listing key advantages and disadvantages.  Finally, the alternatives are compared against an array of evaluation criteria.

5.1.1        Existing Effluent Disposal

Currently, nearly all of the County’s wastewater is treated at the Spokane Advanced Wastewater Treatment Plant (SAWTP) and discharged year-round to the Spokane River near Riverside State Park.  To comply with the current NPDES permit for the SAWTP, the treatment plant must achieve “secondary treatment” standards for BOD and suspended solids, provide year-round ammonia-nitrogen removal and seasonal phosphorus reduction.

Effluent from five small County treatment facilities (package wastewater treatment plants or community septic tanks) is discharged to either community drainfields or infiltration ponds.  These facilities are being phased out as the County extends its sewer system to remote service areas.

5.1.2        Projected Effluent Quantity

Chapter 3 of the Basis of Planning Report gives a detailed evaluation of existing and future development to be served by the County’s wastewater treatment facility. Flow is collected in three major interceptors – two in the Spokane Valley area (North Valley Interceptor north of Interstate 90 and Spokane Valley Interceptor south of Interstate 90) and one in the North Spokane area (North Spokane Interceptor). Average wastewater flow projections for each of these interceptors are shown in Table 5‑1. There is little seasonal variation in these flows. Potential effluent demand under the various effluent end-use management options will be compared to these values.

5.1.3        Projected Effluent Quality

Effluent quality requirements will vary depending on the specific effluent end-use application.  To facilitate comparison of treatment costs for the alternatives, a “baseline treatment level” was established based on the anticipated requirements for year-round discharge to the Spokane River.  These standards were described in detail in Chapter 4 of the Basis of Planning Report and are summarized later in this chapter (see Table 5‑2).  Figure 5‑1 presents a representative treatment train capable of meeting the projected effluent quality requirements for discharge to the Spokane River.

Table 5‑1. Projected Effluent Flow

Figure 5‑1.  Process Schematic for Baseline Effluent Quality 

5.2        Alternatives Descriptions

5.2.1        Listing of Alternatives Surviving Initial Screening

Many effluent management alternatives were identified during the brainstorming workshop and in public meetings (see Chapter 3).  Those ideas selected for detailed review are listed below:

·        Discharge to surface waters

·        Spokane River

·        Little Spokane River

·        Tributaries

·        Irrigation of agricultural land

·        Irrigation of poplar farms

·        Irrigation of urban green spaces

·        Industrial reuse

·        Wetlands creation or enhancement

·        Groundwater recharge

5.2.2        Basis of Economic Comparison

In developing the relative capital costs for each alterative, four components were considered:

·        Treatment cost:  This represents the incremental treatment cost (or savings) compared to the baseline treatment train presented in Figure 5‑1.

·        Conveyance and storage cost:  This includes the cost of pipelines, pumping stations, reservoirs and outfalls needed to implement the alternative.

·        Site development cost:  This includes any on-site development costs associated with the effluent use alternative such as wetlands development, infiltration basins, etc.

·        Land cost:  This includes the cost of land for alternatives that require County-owned property.

A key challenge in developing the economic comparison is that the different alternatives result in differing levels of demand for the effluent.  Some alternatives can use all of the effluent on a year-round basis, whereas others can use only a portion of the effluent and/or operate on a seasonal basis.  For this reason, costs are presented based on a unit cost per million gallons/year of effluent utilized.

It must also be pointed out that specific infrastructure required for some alternatives cannot be accurately defined until additional study is completed. Consequently, the actual costs of implementing some of the alternatives may vary considerably from the values presented here.

5.3        Discharge to Surface Waters

5.3.1        Concept

Surface water discharge is the conventional effluent management practice for municipal wastewater plants.  During dry summer periods, highly treated effluent may provide an important water supply to augment streamflows and support beneficial uses.

During the alternatives development process, three opportunities for surface discharge were identified:

·        Discharge to the Spokane River

·        Discharge to the Little Spokane River

·        Discharge to smaller tributaries

The Spokane River runs through the northern portion of the Spokane Valley area and into the City of Spokane, while the Little Spokane River skirts the northeastern boundary of the North Spokane area. Major tributaries near the study area, shown in Figure 5‑2, include Latah Creek south of the City of Spokane, and Deadman Creek near the North Valley area. All of these water bodies have Class A (exceptional) designations, and are protected for beneficial uses such as fish and shellfish rearing, spawning, and harvesting; water supply; recreational use; wildlife habitat; and commerce and navigation.

5.3.2        Discharge to the Spokane River

In this alternative, treated effluent would be discharged to the Spokane River year-round. If all Spokane County flow were discharged to the Spokane River, the average effluent flow rate in 2025 and 2050 would be 34 and 42 cfs, respectively.  By comparison, average monthly streamflows in the river (as measured at the Spokane Gage) range from 1,400 cfs in August to 17,000 cfs in May.   During the critical 7Q20 streamflow condition (about 600 cfs), the Year 2025 effluent flow rate would represent approximately 6 percent of the total streamflow.

Applicability to Spokane County

Year-round discharge to the Spokane River is currently practiced for most wastewater generated in the Spokane Region.  When considering ways to modify or expand this practice, it is important to consider factors that influence the ability of the river to assimilate the pollutant loading.  These factors include: 

·        Proximity to existing dischargers. Currently, there are four major dischargers to the Spokane River in Washington: Liberty Lake Water and Sewer District, Kaiser Aluminum, Inland Empire Paper and the City of Spokane (SAWTP).  The first three discharges are located along the Spokane River between the Idaho border and the Upriver Dam, whereas the SAWTP’s discharge is downstream of the confluence with Latah Creek. Spreading out point discharges along the river minimizes local toxicity issues associated with ammonia, metals, and selected organics, and it increases the river’s ability to assimilate impacts from nutrients and dissolved-oxygen-consuming pollutants.

·        Interaction with Spokane Aquifer. It would be preferable to discharge treated effluent to a reach of the river that is recharged with groundwater from the aquifer (“gaining reach”). This has multiple benefits.  First, the aquifer recharge adds hardness to the river, which reduces the toxicity of heavy metals of concern.  Second, discharge to gaining stretches of the river reduces potential regulatory and public concerns regarding migration of the wastewater discharge into the aquifer. 

Figure 5‑3 shows the major municipal and industrial discharges on the Spokane River in Washington (green circles), as well as gaining and losing reaches of the river. Red circles indicate discharges to the Little Spokane River.  Based on the factors identified above, and discussions with Ecology, Reach 4 appears to be the most attractive location for a new wastewater discharge to the Spokane River.  It is in a gaining stretch of the river, has free-flowing characteristics to promote re-aeration, and provides a good separation from the SAWTP discharge.  Locating a discharge at this location would require consideration of the interrelation with upstream discharges such as that from Inland Empire Paper.

Effluent Quality Requirements

Chapter 4 of the Basis of Planning Report provided a detailed review of anticipated effluent quality requirements for a new discharge to the Spokane River. Since receiving waters are most sensitive to effluent discharge during the late summer (when streamflows are lowest), it is likely that Ecology would establish a seasonal permit for a new wastewater discharge.

Based on preliminary discussions with Ecology and review of NPDES permits for other discharges to the Spokane River, anticipated effluent quality requirements have been identified for surface water discharge (see Table 5‑2).  Refinements to these requirements will be driven by the exact location of the discharge, results of mixing zone studies, effluent concentrations of metals, results of the dissolved oxygen TMDL study, and negotiations with the Phosphorus Technical Advisory Committee (TAC).

Figure 5‑3.  Existing Dischargers and River/Aquifer Interaction

Table 5‑2. Projected Effluent Quality for Surface Water Discharge

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.

6.        This effluent quality would be achieved using a treatment train similar to that shown in Figure 5‑1.

Implementation

Implementing a new surface water discharge for the County’s treated effluent would require:

·        Negotiating a new NDPES discharge permit with the Department of Ecology. This effort would include:

·        Conducting dilution studies and a mixing zone study to determine local impacts of the proposed discharge on toxicity and temperature.

·        Conducting modeling to assess the near-field impact of the discharge on dissolved oxygen levels.

·        Using Ecology’s new water quality model to assess the far-field impacts of the discharge on algal growth and dissolved oxygen levels.

·        Negotiating with the Phosphorus TAC to allow a new point source discharge of phosphorus. Although the Long Lake Phosphorus Management Agreement does not allow new point source discharges of phosphorus, initial discussions with Ecology and the TAC indicate that these groups would consider Spokane County as an existing discharger to the river, not as a new discharger.

·        Conducting public information/public involvement efforts to assure the public that the new discharge would not adversely impact beneficial uses of the receiving water.

·        Gaining necessary permits for construction of the outfall, including a Corps of Engineers 404 permit and a Shoreline Management permit.

Facility Requirements and Cost

Assuming water quality criteria can be met, this alternative can handle all Spokane County flow on a year-round basis.  Facility requirements primarily consist of an outfall pipeline and a multi-port diffuser.  Depending on the location and elevation of the treatment plant, effluent pumping may be required.   The estimated capital cost for this alternative is presented in Table 5‑3.

Table 5‑3.
Capital Cost of Surface Discharge to Spokane River ($/MGY)

1.             Alternative can handle 8,000 MG/year (21.9 mgd for 365 days)

Key Advantages and Disadvantages

Advantages

·        Highly treated effluent can augment low streamflow during the late summer, supporting fisheries and providing an environmental benefit.

·        Surface water discharge facilities are simple to construct, operate and maintain.

·        Anticipated water quality requirements for stream discharge can be met with conventional treatment technologies.

·        The capital cost for an outfall is low.

Disadvantages

·        Surface water discharge does not maximize use of the effluent as a water resource.

·        Depending on the results of the dissolved oxygen TMDL, effluent quality requirements may be more restrictive than anticipated, requiring higher treatment costs.  Although unlikely, it is possible that the allowable quantity of effluent discharged may be limited during critical periods of receiving water quality.  

·        Future regulatory changes may increase treatment requirements and associated costs.

·        Siting a new outfall may encounter opposition from current dischargers or other interest groups.

5.3.3        Discharge to the Little Spokane River

This alternative involves discharging treated effluent from the North Spokane Service Area to the Little Spokane River below Dartford. Because of the conveyance distance involved, the alternative does not include sending flows from the Spokane Valley to a discharge point on the Little Spokane River.

As shown in Figure 5-3, the stretch of river below Dartford is a gaining reach, where the aquifer contributes to river flow. During critical summer months, the estimated streamflow at Dartford is approximately 250 cfs (personal conversation, Stan Miller).  By comparison, the projected effluent flow rate from the North Spokane Service Area in 2025 and 2050 is 8 and 9 cfs, respectively; or less than 4 percent of the summer streamflow. 

Applicability to Spokane County

The key considerations for locating a new outfall on the Little Spokane River are the same as those for the Spokane River. As Figure 5-3 shows, there are two existing discharges to the Little Spokane River, so proximity to these discharges would be a consideration. In the stretch of river below Dartford, potential impacts of a new outfall on the aquifer would be minimal because the aquifer discharges to the river.

While there are portions of the Little Spokane River where declining flows have been a concern in the past, these areas are upstream of Dartford and therefore would not be positively impacted by the addition of treated effluent (see later discussion of discharge to tributaries).

Effluent Quality Requirements

It is anticipated that effluent quality requirements for this alternative would be similar to those for discharge to the Spokane River.

Implementation

Most key implementation considerations are the same as for discharge to the Spokane River. The lower part of the Little Spokane River (from its confluence with the Spokane River to River Mile 5) is a state-designated wild and scenic river. While this designation does not carry the same regulatory significance as a federal designation, there likely would be some public opposition to any activities impacting the river in this area.  This may require additional mitigation.

Facility Requirements and Cost

This alternative can handle flows from only the North Spokane Service Area.  Wastewater from the Spokane Valley must be handled by other means such as discharge to the Spokane River.

Given the topography of the Little Spokane watershed, it has been assumed that effluent from a new plant could be discharged by gravity.  The estimated unit cost is presented in Table 5‑4.

Table 5‑4.
Capital Cost of Surface Discharge to Little Spokane River

1.             Alternative can handle 1,790 MG/year (4.9 mgd for 365 days)

Key Advantages and Disadvantages

Advantages

·        Key advantages listed for the Spokane River discharge option apply to this alternative.

·        This concept returns the flows generated within the Little Spokane watershed to the river rather than exporting them out of the watershed.

·        Sending a portion of Spokane County’s effluent to the Little Spokane River further spreads out the loading to the region’s receiving waters, making greater use of assimilative capacity and reducing localized impacts.

Disadvantages

·        Key disadvantages listed for the Spokane River discharge option apply to this alternative.

·        This alternative handles only the flow generated in North Spokane.

·        This alternative does not address the declining stream flows experienced in the upper reaches of the Little Spokane River watershed. 

·        Discharge to the Little Spokane River would likely encounter opposition from local residents and environmental groups.

5.3.4        Discharge to Tributaries

The concept of this alternative is to augment minimum streamflows in smaller tributaries to augment beneficial uses such as fisheries, or to offset declining streamflows due to overuse of surface withdrawals and groundwater pumping.

Applicability to Spokane County

Three tributaries were identified as potential locations for augmenting streamflow.

Latah Creek. As shown in Figure 5‑2, Latah Creek is one of the closest tributaries to the planning area. There is little stream gauging information for this tributary, however the estimated summer flow in the stream is approximately 20-30 cfs (personal conversation, Stan Miller). Because of insufficient data, further study would be required to determine where an outfall should be located to augment streamflow and how much effluent would be needed.  During the alternatives workshop, discharge to Latah Creek was discussed with staff from Ecology, the County and the City.  There was little support for the concept because no significant environmental benefits were identified. 

Crab Creek (Lincoln and Grant Counties). This concept was examined as a streamflow augmentation option in the City of Spokane’s Facilities Plan^[i], based on interest from Lincoln County, the State of Washington, and other parties. Crab Creek is located approximately 15 miles west of Medical Lake.

Upper Tributaries of the Little Spokane River. As mentioned earlier, declining flows in the upper Little Spokane River basin have been a concern. In 1975, water availability was of such concern that the major tributaries of the Little Spokane River were closed to further water appropriation, and water rights issued were conditioned to specific “base” flows measured at Dartford.  Continuing development of exempt wells contributes to water shortages in the basin.

Effluent Quality Requirements

The majority of tributaries in the region are designated Class A streams, and thus would be subject to the type of treatment illustrated in Figure 5‑1.  In discussions with the City regarding the potential Crab Creek discharge, Ecology indicated that water quality requirements may be relaxed somewhat if the streamflow augmentation project significantly benefits water quality in a stream. However, this would need to be evaluated on a case-by-case basis.  For purposes of analysis, it is assumed that the treatment train shown in Figure 5‑1 would be required for discharge to any tributary.

Implementation

Implementation considerations would include those described for discharge to the Spokane River.  In addition, easements and right-of-ways would be required for long conveyance pipelines.  Studies would be required to determine how much effluent could be sent to the tributaries during various times of the year.

Facility Requirements and Cost

Depending on the carrying capacity of the tributary, this alternative may not be able to handle all effluent generated by Spokane County.  For the purposes of this analysis, it has been assumed that one-half of the wastewater generated by the County in 2025 could be discharged to tributaries.  The remaining flow must be discharged either to a major stream or reused in some other manner.

Since the baseline treatment train would be used, the primary cost would be associated with conveyance.  With the exception of Latah Creek, discharge to a tributary would require pumping treated effluent from 20-40 miles.  Estimated costs are based on sending Spokane County’s flow through a 20-mile pipeline.  The estimated cost of this option is presented in Table 5‑5.

Table 5‑5.
Capital Cost of Surface Discharge to Tributaries

1.  Alternative can handle 4,000 MG/year (11 mgd for 365 days)

Key Advantages and Disadvantages

Advantages

·        Key disadvantages listed for the Spokane River discharge option apply to this alternative.

·        This concept could potentially enhance water resources in the region by augmenting low streamflow or providing an alternative water supply to groundwater.

·        This alternative spreads out loadings to receiving waters, reducing localized water quality impacts.

Disadvantages

·        Key disadvantages listed for the Spokane River discharge option apply to this alternative.

·        Requires significant infrastructure for conveyance.

·        Streamflow augmentation in tributaries may not be adequate for all of the County’s flows, requiring an additional surface water discharge to a major river.

·        Additional study would be necessary to determine whether there is a true water quality or beneficial use benefit to augmenting streamflow in the tributaries.

·        Discharging treated wastewater to tributaries may be opposed by local property owners.

5.4        Irrigation of Agricultural Land

5.4.1        Concept

This alternative investigates the use of treated effluent for irrigation of agricultural properties in Spokane County. Reclaimed water would be used for irrigation on a seasonal basis to match crop demand.   For the remainder of the year, effluent would be discharged to surface water.  The concept is illustrated in Figure 5‑4.

5.4.2        Applicability to Spokane County

Potential Reuse Locations

While development in the Spokane Valley has reduced the number of farms in the County, many agricultural areas were protected through the growth management practices outlined in the 1980 County Comprehensive Plan and continued in the 2000 Draft Comprehensive Plan (Draft Comp Plan, 2000). The Draft County Comprehensive Plan includes agricultural land in its designation of Natural Resource lands, offering protection to “ensure their viability for future generations” (Draft Comp Plan, Page NR-15). According to the County’s Planning Department, protection of these natural resource lands is anticipated to extend far into the future, well beyond the horizon of either the current Comprehensive Plan or this Facilities Plan. 

Protected agricultural lands (based on zoning information from the Draft Recommended Comprehensive Plan) are shown in Figure 1‑5. The five primary areas have been numbered for later use in reuse demand analyses. This figure also shows the total acreage for each area, and the boundaries of the Draft Urban Growth Area (in black) and the Aquifer Sensitive Area (in red). 

When evaluating agricultural reuse in these areas, there are several issues that need to be considered:

·        Within the agricultural land designation, the County identifies “large tract” (one residential unit per 40 acres) and “small tract” (one residential unit per 10 acres) agricultural properties that have long-term commercial significance.  The large tract properties are more attractive for an effluent reuse program because they result in fewer contracts with farmers, require fewer metering points and are more likely to remain in agricultural use on a long-term basis.

·        Much of the southern portion of Area 5 is being converted to small ranchettes, and the recent construction of a new high school will promote further development. Based on this development pattern, any agricultural demand in Area 5 is likely to be associated with small-scale farming operations.

·        Although not in a protected agricultural area, there are existing farms in the Chattaroy area along the Little Spokane River east of Area 4 (see Table 5‑6). Providing reuse water for irrigation in this area would offset the surface water or groundwater impacts of existing irrigation withdrawals. Local topography favors sending reuse water from the planning area to the Chattaroy area.

·        Many of the potential reuse locations in all areas would require pumping to higher elevations. For example, there are potential reuse sites in the Green Bluff area (northern portion of Area 5); however, reaching these locations would require pumping to an elevation of approximately 2,400 feet.

Estimates of Demand Potential

David Bezdicek of Washington State University provided guidelines regarding evaporative demand for representative crops grown in the designated agricultural areas. These irrigation requirements (shown in Figure 5-5) take into account monthly precipitation, as well as the impacts of agricultural management practices (harvesting, planting, etc.) that reduce the full evaporative demand.

For purposes of evaluation, the estimated demand for water has been based on a blend of grain, wheat, alfalfa and pasture production. This provides a representative mix of cropping patterns that may occur in the region.  To maximize water use, particularly in September and October, it would be best to maximize use of pasture crops.  However, this may not be economically attractive to farmers.

Figure 5‑6.  Net Irrigation Requirement for Crops in Spokane County

To determine the volume of water demand for each of the designated agricultural areas, the following assumptions were applied to the data shown in Figure 5-6:

·        60% of the total land in the protected agricultural areas would be available for crop production.

·        Irrigation with treated effluent would begin the last week of April and continue through the end of September (October demand is minimal).

·        Monthly irrigation demand is spread evenly over all days of the month.

Based on these assumptions, Table 5‑6 shows the total irrigation demand for each of the five designated agricultural areas.  By comparison, the average effluent production rate in 2025 and 2050 is projected to be 22 and 27 mgd, respectively.

Table 5‑6.
Irrigation Demand for Designated Agricultural Areas

   1.          See Figure 5-5 for location of designated agricultural areas.

Based on the estimates of reuse demand shown in Table 5‑6, there is sufficient potential demand in Areas 1, 2, 4 and 5 to handle all effluent production from April through September for the year 2025.  Area 3 could handle all of the effluent in May through August, and most of the effluent during April and September.  Reuse demand in October would be minimal in all areas. 

Interest Level of Potential End Users

A targeted survey of farmers in the region was not conducted as part of this project. The City of Spokane’s 1999 Facilities Plan also investigated agricultural reuse as an effluent management option; however, no investigations were made into the potential interest of regional farmers. Issues that have been raised by farmers during other feasibility studies of agricultural reuse in Northwest communities include:

·        Cost.  For farmers with existing water supply, there must be an economic incentive to switch to reuse. 

·        Adequacy/availability of current water supply.  Interest is typically higher among farmers that lack adequate irrigation water.

·        Water quality.  Farmers value the nutrient content of the reclaimed water but are concerned about other parameters that could impact their crops such as salinity, chlorine or metals.

·        Food Processors.  Farmers are concerned about the reaction of the food processing industry to irrigation with treated effluent.

·        Water Pressure.  Various irrigation systems have differing pressure requirements for operation.  For example, “big gun” irrigation systems require significantly higher pressure than most irrigation methods. Farmers would prefer the reuse delivery pressure to be adequate to operate their preferred irrigation equipment.

·        Reluctance to dedicate land for long-term agricultural uses. Although the areas investigated for this study are protected for long-term agricultural use, current owners may perceive a reduction in value if they feel long-term agreements or use of reclaimed water could complicate their ability to convert their property to other uses in the future.

·        Regulation.  Use of reuse water brings with it an added set of regulatory requirements that farmers must comply with. 

Based on the results of other feasibility studies for agricultural reuse, it is clear that farmers would not be willing to pay the true cost to deliver the reuse water to their sites.  At best, they would be willing to a price equivalent to that for other irrigation water supplies in the region.  Since this represents only a fraction of the true costs to supply the water, an agricultural reuse program would need to be heavily subsidized by the wastewater utility.

Water Resource Implications

The optimal locations for agricultural reuse are in areas where treated effluent could replace existing surface water or groundwater withdrawals.

Effluent also could serve as a new source of water in areas that have no water supply.  This is attractive from the perspective of increasing the value of the land; however, it does not free up other water supplies for alternative use.

A large-scale agricultural reuse program could reduce or eliminate the need for surface water discharge during much of the summer; however, irrigation demand in September and October may be insufficient to use all of the effluent.  Figure 5‑7 compares the month-by-month trends for streamflow in the Spokane River and irrigation demand, and shows that river flows remain low after the irrigation demand sharply decreases.  Consequently, during the late summer and early fall, effluent would need to be discharged to receiving waters, necessitating high levels of nutrient removal. 

5.4.3        Effluent Quality Requirements

Effluent quality requirements for agricultural reuse are set forth in Washington’s Water Reclamation and Reuse Standards ^[ii], and were summarized in Chapter 4 of the Final Basis of Planning Report. The reuse rules allow various qualities of reclaimed water to be used for agricultural irrigation, depending on the crop to be grown, the irrigation method, setback provisions and other considerations.  Since the specific types and uses of potential crops are not known at this time, it has been assumed that effluent must be treated to Class A reuse standards, allowing it to be used for the greatest variety of crops and with the least restrictions on the end-user. This quality of water would have the greatest appeal to farmers.

Class A water has more stringent disinfection requirements than the effluent parameters listed in Table 5‑2 for surface water discharge.  However, the treatment process shown in Figure 5‑1 would be capable of meeting these tougher standards.  Because some nutrient loading is beneficial to crops, it may be possible to reduce the amount of ammonia-nitrogen and phosphorus removal that must be provided at the County’s treatment facility during the summer.

While there are no specific guidelines for reuse over the aquifer in Washington, the Idaho Division of Environmental Quality developed the Special Supplemental Guidelines for Spokane Valley-Rathdrum Prairie Aquifer Wastewater Land Application (1995) ^[iii] to provide direction for a land application project for the Hayden Area Regional Sewer Board (HARSB) in Idaho. These guidelines recommend that both hydraulic application and nitrate-nitrogen loading be limited to amounts required for crop uptake. As a general guideline, it has been assumed that nitrate concentrations would need to be reduced to less than 10 mg/L for large-scale agricultural irrigation over the aquifer.

5.4.4        Implementation

Reclaimed water programs are administered jointly by the Departments of Ecology and Health, with irrigation programs permitted through Ecology.  As part of the regulatory review process, the wastewater utility must complete an Engineering Report that describes the design and operation of the proposed program and indicates the means of compliance with all applicable standards and regulations.

Other key implementation steps would include:

·        Conducting a needs survey/feasibility study to define potential demand and end-user requirements.

·        Developing long-term agreements with private farmers or purchasing sufficient land to meet the program requirements.

·        Developing an organizational structure to manage the reuse program.

·        Siting and permitting critical infrastructure components such as reservoirs and pipelines.

·        Preparing predesign and detailed design for all facilities.

·        Conducting environmental assessments necessary to meet regulatory requirements.

·        Developing operational plans, including reliability and emergency response measures.

·        Developing and implementing monitoring plans.

·        Implementing a comprehensive public education program.

The choice between purchasing land for irrigation or developing long-term agreements with private farmers is a key consideration.  The first option would give the County more control over the long-term use of water and crop selection for agricultural areas.  On the other hand, it would require greater capital expense, add the administrative task to develop and maintain the lease relationship, and may encounter opposition from individuals opposed to the County’s purchase of large tracts of farmland. Developing long-term agreements would require that the farmer be committed to long-term agriculture.  It also may require two separate negotiations (with the owner and the leaser) if the property is privately owned and leased to a private farmer.

Another key decision is whether the County would operate the reuse system or partner with a local water purveyor for this service. 

5.4.5        Facility Requirements and Cost

The requirements described below are based on a system configuration that includes pumping of treated effluent to one or more reservoirs located near the various reuse areas, and subsequent pumping through a distribution system to serve agricultural customers. There are four major components to this system:  treatment, transmission, storage and distribution.

Treatment

To produce Class A reclaimed water, the required treatment train would be equivalent to that presented in Figure 5‑1; however, the reuse standards specify additional reliability and redundancy components that must be incorporated into the treatment plant.

Transmission

Transmission distances to the designated agricultural areas vary widely. Serving Area 5 would require pipeline lengths of 6 to 8 miles from a North Spokane Plant and 8 to 12 miles from a plant located in the Spokane Valley.  Pumping from the North Spokane area to Area 4 would require approximately 15 miles of transmission line. Transmission distances to Areas 3, 1, and 2 increase to 25 miles, 30 miles, and over 40 miles, respectively.

To the extent possible, transmission lines would be located in public right of way. For purposes of this analysis, it is assumed that the County would not need to pay to acquire any property or easements for reuse transmission.

Storage

There are two options for storage: provide storage to meet all seasonal irrigation demands, or provide irrigation water “on demand” with limited local storage to meet peak demands.

To maximize reuse of treated effluent, it would be necessary to provide storage during the early spring in order to meet the peak demand of June and July. Storage volume requirements were calculated based on annual average 2025 flows and 5,000 total acres of land application area. With this demand, the excess flow produced in April and May at 2025 flow rates would be sufficient to make up the deficit in wastewater flows through June, July and August, resulting in no excess storage during the non-irrigating period (late August through mid-April).  This allows the County to avoid adverse impacts due to long-term storage.  Experience shows that issues such as algal growth and odor generation can lead to serious water quality degradation if reclaimed water is stored for long periods without major reservoir maintenance efforts.  The total storage volume required at 2025 flows would be 400 million gallons. Initial requirements, based on 2005 flow rates, would be 2,400 acres of land under irrigation and a reservoir capacity of 200 million gallons. 

For “on demand” application, detailed discussions with farmers would be required to determine the daily peaking factor appropriate for sizing storage. Initial estimates of facility requirements are based on two days of storage.

Any storage reservoirs located over a potable water aquifer would need to be lined.

Distribution

Most irrigation systems can be categorized as medium pressure (50-60 psi) or high pressure (100-125 psi). Medium pressure systems include center pivot, lateral move, and solid set irrigation, whereas high pressure systems are needed for “big gun” irrigation. If the County were to implement agricultural reuse, it would make sense to provide a medium pressure system, with individual farmers providing booster stations as needed for “big gun” equipment. 

Cost

The estimated cost of this alternative is presented in Table 5‑7. This cost is based on conveyance of all flow from April through September to a storage reservoir located 14 miles from the treatment plant, and distribution to multiple farms with an average size of 450 acres.

Table 5‑7.
Capital Cost of Agricultural Reuse

1.         Alternative can handle 4,000 MG/year (21.9 mgd for six months)

5.4.6        Key Advantages and Disadvantages

Advantages

·        Effluent reuse can have significant water resource benefits where irrigation water is currently obtained from surface water or groundwater resources. It would conserve and stretch potable water supplies

·        For agricultural property without a water supply, a reuse program would increase crop yields and property value.

·        Implementing a reuse program could reduce or eliminate discharge to surface waters during the spring and mid-summer months.

Disadvantages

·        During October and possibly September, irrigation demand would not be sufficient to use all of the County’s effluent.  Consequently, treated effluent would need to be discharged to the river during low streamflow conditions unless other effluent management strategies were implemented for this period. 

·        Effluent storage reservoirs may prove difficult to site and permit.

·        Infrastructure development costs are high.

·        Operational costs for pumping would be high.

·        This concept requires long-term agreements with farmers or purchase of large tracts of agricultural property.  Both options may be difficult to implement.

·        This alternative has risk associated with changing land use.  However, applying effluent to agricultural areas that have been protected through the County’s comprehensive planning and zoning process would reduce the risk that land will not be available for long-term effluent reuse.

·        Local water purveyors may view this new water supply as competition that could reduce their revenue.

·        Revenue from sale of the water would pay for only a fraction of the development and operating costs.  Consequently, wastewater ratepayers would need to subsidize to program.

5.5        Irrigation of Poplar Farms

5.5.1        Concept

This alternative involves a variation of agricultural reuse in which hybrid poplars would be grown.  From an effluent management perspective, poplars are attractive because they have a high water demand.  Also, the harvested poplars may produce revenue for the wastewater utility. 

The use of poplars is an emerging management practice for municipal wastewater.  In the Northwest, several communities are in various stages of implementation. The most established program is in Woodburn, Oregon where poplars have been grown for the past seven years.

Applicability to Spokane County

In the Spokane climate, poplars would have an estimated water consumption rate of 5 feet per year.  If this water were applied over the six-month summer permit season, the required area of trees under irrigation would be 2,400 acres in 2025 and 3,000 acres in 2050.  Taking into consideration buffers, harvesting requirements and other property management functions, the total property requirements would increase about 50 percent to 3,600 and 4,500 acres in 2025 and 2050, respectively.  To maintain control of the irrigation and harvesting operations, the County would need to purchase the property and operate the facility.

With such a large land requirement, the cost of this alternative becomes highly dependent on the cost of land and the length of conveyance pipelines to deliver the water.   Two scenarios were considered:

·        A site in Peone Prairie located within 7 miles of the treatment plant.  Estimated property costs in this area would be $10,000 per acre.

·        A site in the Palouse, located 20 miles from the treatment plant.  Property costs in this area are based on $2,000 per acre.

Effluent Quality Requirements

Poplars may be irrigated with Class C reclaimed water, which requires secondary treatment and effective disinfection.  Since the poplar farm would only receive water during the six dry-season months, effluent would need to be discharged to a receiving water during the winter.  This would require the ability to provide nitrification during cold weather conditions to meet in-stream toxicity limits for ammonia.

Implementation

Implementation requirements would be similar to that for agricultural irrigation with the exception that market surveys and long-term agreements with farmers would not be needed.  Instead, the County would need to identify and acquire the large tracts of land needed for the poplar system.

Facility Requirements and Cost

Key facility requirements for a poplar system are outlined below:

·        Treatment plant – advanced secondary treatment with nitrification (for winter discharge condition.

·        Effluent pumping – a high head lift station would be needed to convey the effluent to the irrigation site.

·        Transmission main – depending on the site location, a 7 to 20 mile pipeline would be required.

·        Storage – a minimum of two days of operational storage should be provided to balance supply and demand variations and to accommodate emergency situations.

·        Site development – the property would need to be prepared for growth of poplar trees, including clearing and grading, construction of access roads, installation of surface runoff controls, and installation of groundwater monitoring wells.

·        Irrigation system – a mechanical irrigation system would need to be installed.

The estimated unit capital cost is shown in Table 5‑8 for both the Peone Prairie and Palouse sites.  Compared to the baseline treatment system, elimination of effluent filtration and phosphorus removal is projected to save approximately $1.50 per gallon of capacity.  This savings is offset by the other development costs for the system.

The potential revenue from a poplar operation is highly speculative.  Initially, poplars were thought to provide a quality source of pulp for paper mills; however, the acceptance of the poplar pulp has been mixed and the revenue generated small.  Lately, interest has grown in the use of poplars as a clear softwood for non-structural products, such as blinds.  The market value and demand potential for these products may be significant, but this has not been firmly established.  If such a market exists, it is likely that the commercial wood products industry would grow poplars in sufficient quantity to satisfy the demand.  In such a market place, a small to mid-size municipal utility would be a very small player with limited market access and pricing leverage.   For these reasons, no revenue stream has been included for harvested poplars.

Table 5‑8.
Capital Cost of Poplar Farms

1.     Alternative can handle 4,000 MG/year (21.9 mgd for six months)

Advantages and Disadvantages

Advantages

·        Eliminates discharge to receiving waters during the dry-season.

·        Harvested poplars may generate revenue, although this remains uncertain.

·        Growth of poplars may be positively viewed by the public and regulatory agencies as a “green solution” to wastewater management.

·        Allows use of a less complex, less expensive treatment system.

Disadvantages

·        Requires purchase of large tracts of agricultural land.  The agricultural community and other land use interests may view this unfavorably.

·        Operational costs for pumping would be high.

·        Results in a more complex system to operate than river discharge.

5.6        Irrigation of Urban Greenspaces

5.6.1        Concept

Urban reuse involves the use of treated effluent as an irrigation supply for golf courses, school grounds, parks, and cemeteries. Reuse would be during the summer months only, when irrigation demand is highest. The basic concept of the program is illustrated in Figure 5‑8.

Urban irrigation using treated effluent has been practiced for decades across the nation and in the Northwest. In Oregon, the Unified Sewerage Agency of Washington County has been irrigating school grounds and golf courses with treated effluent for over 20 years. In Washington, urban irrigation was included in several demonstration projects administered by the Departments of Ecology and Health ^[iv]. Treated wastewater effluent is used for landscape irrigation by the City of Sequim, and for irrigation at local churches, city parks, and a private residence in the City of Yelm.

5.6.2        Applicability to Spokane County

Location of Potential Reuse Sites

Using the County’s land use information system, an investigation was conducted to identify green space that could potentially be included in an urban irrigation program.  In the Spokane area, the most significant green space are those associated with golf courses, parks, cemeteries and schoolyards.  Figure 5‑9 presents the location of these facilities in the greater Spokane region.  Appendix C, consists of tables showing all of the parks, cemeteries, and schools included for evaluation.

Figure 5‑9.  Potential Urban Irrigation Sites

Golf courses are typically the most attractive reuse customers because of their large water demand.  Areas with multiple golf courses include Liberty Lake, along the Little Spokane River in North Spokane, near Latah Creek at the south end of the City, and along the Spokane River near the western boundary of the City.

In some communities, green space at industrial parks offer important reuse opportunities.  Based on discussions with County personnel, industrial campuses with significant green space are limited to the Liberty Lake area.

To initially screen candidate reuse sites, two criteria were used: 

·        Proximity to the planning area

·        Complexity vs. benefit of administering reuse program

The first criterion was used to rule out sites such as the Sundance and Fairways Golf Courses (located 15-20 miles from the planning area).  The second criterion was used to eliminate sites with small demand potential such as individual schools with a single private owner.

Potential Reuse Demand

Demand for urban irrigation water was assessed similar to that for agricultural irrigation, except that demand was based on turf requirements rather than a mixture of crops. Urban irrigation demand in gallons per day per acre is shown in Figure 5‑10.

To put the potential demand in perspective, a typical 150-acre golf course would have a maximum demand in August of 900,000 gpd, which represents 4 percent of the County’s projected effluent flow rate in 2025. During other summer months, a smaller portion of the effluent would be used.  Extending this concept, Table 5‑9 illustrates the relationship between the size of a reuse site and the percentage of the total County flow that can be used on the site.  As this table illustrates, many large sites or clusters of smaller sites would be needed to use a substantial portion of the County’s projected flow in 2025.  As shown in Figure 5-9, potential reuse sites are highly dispersed with few clusters of sizeable acreage.  Consequently, achieving a large volume of demand would require an extensive distribution network. 

Table 5‑9.
Urban Irrigation Reuse Potential

Golf Courses

Fourteen golf courses were evaluated as potential urban reuse sites. These are shown in Table 5‑10. Ninety-eight percent of the total golf course area is assumed to be irrigable.

Table 5‑10.
Urban Golf Course Sites

To evaluate the geographical distribution of reuse demand from golf courses, the courses listed in Table 5‑10 were separated into six regions:

·        North Spokane: Wandermere

·        East County: Valley View, Liberty Lake, MeadowWood

·        South Spokane: Manito, The Creek at Qualchan

·        Central Spokane: Indian Canyon, Downriver

·        Esmeralda

·        Painted Hills

The projected reuse demand for the golf courses within each region is presented in Table 5‑11.

The Spokane Country Club was excluded from the demand projections based upon discussions with a representative from the club, who indicated that they irrigate using water from a private well, have very low irrigation costs, and are not likely to consider replacing this source with treated effluent.

The County Parks department would be willing to use reclaimed effluent for irrigation of County-owned golf courses; however, two of their courses (Liberty Lake and MeadowWood) are located in an area that is being annexed by Liberty Lake and is within the Liberty Lake Water and Sewer District. The County could implement reuse for irrigation of these courses if it maintains ownership of them; however, the Liberty Lake Water and Sewer District may also be interested in irrigating these courses if it has trouble expanding its discharge to the Spokane River.

Table 5‑11.
Monthly Irrigation Demand for Golf Courses

Comparing the water demands in Table 5‑11 with the projected effluent production rate in 2025 (22 mgd) demonstrates that if all golf courses in the region were served by reclaimed water, the peak demand would represent 40 percent of the available effluent.  The average reuse demand over the course of the summer would be about 25 percent of the available effluent.  If only one of the golf course “regions” were served, less than 10 percent of the County’s summer effluent production would be used.

Urban Parks, Schools, and Cemeteries

In Spokane, the identified parks, schools, and cemeteries are relatively small compared to golf courses.  Table 5‑12 summarizes information on these facilities with respect to size range, number of sites, total area, and irrigable area.  The estimates of irrigable area are based on research conducted for the Unified Sewerage Agency of Washington County, Oregon’s Recycled Wastewater Master Plan (1991).  In this study, the following values were developed to estimate irrigable area based on total area for each land use category:

·        Schools:                       57%

·        Parks:                           55%

·        Cemeteries:                  94%

The County is currently developing Plante’s Ferry Park near Trent, which will have 90 acres of irrigated land that will be served by a local irrigation district rather than a private well. The Parks Department is open to using reclaimed effluent for irrigating Plante’s Ferry Park if it can help offset part or all of the anticipated $10,000 - $15,000/year cost of purchasing water through the irrigation district.

Table 5‑12.
 Urban Parks, Schools and Cemeteries