Wastewater Treatment in Sandpoint

What happens after you flush?

A brief history of the Sandpoint Wastewater Plant

The City of Sandpoint's current wastewater treatment plant was originally built with components purchased from the Farragut Naval Station in 1955. The primary clarifiers from the original plant are still in use today over 60 years later. The typical planned life of a wastewater facility is 20 years. Sandpoint's plant is now at the end of its useful life span and in May of 2017, the City began working with its consulting engineers to develop a new 20-year facility plan. As required by the State of Idaho, this plan must address hydraulic capacity, treatment capacity, project financing and operation and maintenance considerations to determine the effects of a project on the overall wastewater infrastructure.

Wastewater Regulation

Wastewater treatment reduces the amount of pollutants that are discharged into the environment. The wastewater that is produced in Sandpoint takes a journey through our wastewater distribution system to our treatment plant and ultimately it is discharged into the Pend Oreille River.

The Idaho Department of Environmental Quality and formerly the Environmental Protection Agency issues permits which regulate the amount of pollutants which may be discharged by each treatment plant. Reducing the amount of pollutants discharged into the Pend Oreille River is critical to the health of the river and anyone who uses the water downstream.

Up until the middle of the 20th century, dilution was the "solution to pollution." As populations grew, it became apparent that the amount of pollution that was being discharged was more than the receiving waters could naturally treat. The National Pollution Discharge Elimination Program was implemented by the Environmental Protection Agency and facility permits were issued beginning in the 1970's. These permits are valid for a set number of years and then must be renewed and comply with current standards. Sandpoint was issued it's most recent discharge permit on December 1, 2017. Under this new permit, Sandpoint is required to significantly upgrade its existing facility to meet new discharge requirements within five years or build a new treatment facility within ten years.

Inflow and Infiltration (I&I)

Sandpoint is located on soil that drains poorly. As a result, any large amount of precipitation raised the ground water level quickly. This ground water flows into the Sandpoint wastewater collection system through:

  • Cracks and holes in the system mains

  • Cracked or broken lateral lines that connect homes and businesses to the mains

  • Sump pumps and roof drains that are connected to the sewer system rather than the stormwater system

  • Uncapped cleanouts

  • Storm drain cross-connections

When we are experiencing high levels of I&I into our system, we exceed the peak flows of the City of Coeur d'Alene's plant which is serving a population of over 50,000. Even our typical wet weather flows are the same as the peak flows experienced by the cities of Post Falls and Rathdrum combined.

Without I&I, a 5.0 MGD plant would be sufficient for Sandpoint for decades. The added I&I flow on peak days makes the current required design capacity for a future plant 10.7 MGD. Building a plant that is twice the size of what is needed most days is very costly.

Infrastructure Improvements - CIPP

Sandpoint uses trenchless pipe rehabilitation to save millions in construction costs and reduce treatment costs.

Over the past 12 years, the City of Sandpoint has successfully invested in rehabilitating its wastewater pipeline infrastructure, while reducing I&I and treatment costs, by implementing cured-in-place pipe (CIPP) technology.

The CIPP process includes installing a seamless, jointless, resin-impregnated felt liner into the existing pipe (aka: a pipe-in-a-pipe). This process is considered trenchless because it does not require excavation or full pipe exposure. This approach saves Sandpoint ratepayers about 25% of the cost of open trench methods. To date, over 62,000 feet (11.7 miles) of pipe has been rehabilitated. This amounts to 23% of the total system.

The life estimates for CIPP are greater than 50 years. This is comparable to full replacement.

Should it stay or should it go?

In 2009, the City of Sandpoint purchased 32.2 acres at 100076 Baldy Mountain Road for $905,000. The property was purchased with the intent of building a regional wastewater treatment plant on the site at a future date. Possible users of a regional wastewater plant include the Cities of Sandpoint, and Dover, Kootenai/Ponderay Sewer District, Schweitzer Mountain Utilities, and Southside Sewer District.

The NPDES Permit issued to the City of Sandpoint, and which took effect on December 1, 2017, gives the City until November 30, 2019 to determine if the current site or the Baldy Mountain Road site will be used to meet the new phosphorous discharge limit. On August 1, 2018 City Council made the decision to stay at the existing location. Unfortunately, none of the other potential partners for a regional plant are currently in a position to commit to assisting in funding the construction of a plant at the Baldy Mountain Road site. The costs to go to the Baldy Mountain Road site substantially exceeded the costs of staying at the existing location.

Lakeview Park - Existing Site

Preferred Alternative: Significant upgrades and additions, or a new plant altogether will be built at the existing site. Several technologies have been identified that could be used at the site to meet current and expected future permit limits. Although it would be ideal to open up more waterfront area and remove much of the treatment plant infrastructure with a move to another site, the major advantage of using the current site is the expense of conveying the wastewater to and from the new site is not incurred. Major disadvantages of staying at the current site include the proximity to residential housing and the limited space available for new treatment structures. It is intended that all planned improvements at the existing plant would need to be inside the current fence line.

Baldy Mountain Road

Relocating the plant to this location was evaluated in great detail but ultimately, not selected. It would have provided a new plant at the Baldy site and required that the majority of the wastewater flowing to the current site be pumped to the new site and then pumped back to the current discharge point after being treated. The headworks, disinfection, outfall, and a pump station would likely have remained at the current site permanently. Solids handling could have been moved to the new site at considerable expense. The image to the left highlights the areas of the current site that would have remained in service if this option had been selected. The blue area is the solids handling structures and the red areas are the headworks and discharge structure. A pump station would also have built and most likely located near the headworks building.

What options were considered?

  1. Do Nothing

  2. Alternative 1 - New Technology at Existing Site

  3. Alternative 2 - "Bridge Improvements" Plus New Technology at Existing Site

  4. Alternative 3 - "Bridge Improvements" Plus New Technology at Baldy Site

  5. Nothing at Existing Site Plus "Bridge Improvements and New Technology at Baldy Site

Evaluation Criteria

  • Regionalization is important; focus on Sandpoint first

  • Biological treatment of Maximum Daily Flow (10.65 MGD)

  • Ability to meet current permit

  • Flexibility to adapt to tighter future permits

  • Ability to expand

  • 20-year life (Industry Standard)

  • Impact on ratepayers

Other Important Factors: Reliability, Odor, Ease of Implementation

Alternative Summary

Sandpoint City Council Selection

At the recommendation of the Citizen's Advisory Committee and City Administration, the Sandpoint City Council selected Alternative 2 at it's August 1, 2018 Council Meeting.

In addition to the advantages identified, there was significant discussion on the impact to ratepayers. Moving the plant to the Baldy site would cost $28 - 50 million more in order to transport the wastewater to and from the site. Staying at the current site means that the Baldy Mountain Road site could be sold and proceeds used to help fund construction at the existing site.

Next Steps

With the initial stay/go decision made, consultants and staff moved forward with drafting the Wastewater Facility Plan. The full draft document may be downloaded here. This draft will be presented to Sandpoint City Council on October 17th, 2018 for approval to submit to the Idaho Department of Environmental Quality (IDEQ) for review. After incorporating comments from IDEQ, the draft Wastewater Facility Plan will become final. A rate study will be completed in 2020 to fully assess potential impacts to rate payers and staff will continue to coordinate with funding sources. Engineering and construction of the new plant is tentatively scheduled to be completed by 2024. The timeline below is included in the draft facility plan and intended to represent an the implementation schedule.

Balancing Needs/ Opportunities

Any plant improvements made at the current site will be designed with being a good neighbor to the surrounding community as a priority. Improvements to the unofficial trail along the river are being planned with the ultimate goal being to make it an official, maintained city trail extension. Conversations will continue regarding the options. The possibility of incorporating a water education center at the current site will also be explored.