Wastewater Treatment and Infiltration/Inflow

The current status of Sandpoint's sanitary sewer system.

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. Portions of 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 August of 2018, the City Council adopted a facility plan to replace and reconstruct the facility at its current location by 2026. The replacement project will ensure the City remains in compliance with permit conditions and state and federal laws.

Recent Progress at the Wastewater Plant

  • New NPDES Permit and Conditions Issued 12/1/17
  • Refinanced existing bond for 2008 repairs (paid off in 2022)
  • Facility Plan approved by City Council and Idaho DEQ, (click here to learn more about the facility plan)
  • Interim Plant Upgrades designed and approved by DEQ in 2019 (chemical feed system to adjust pH and enhance phosphorous removal - install to be completed 2019)
  • Interim Equipment Upgrades, replace boiler 2019

Timeline to Replace Existing Wastewater Treatment Plant

Permit Violations and Water Quality

Since the implementation of the Clean Water Act and subsequent creation of the United States Environmental Protection Agency (USEPA) in the early 1970s, industrial, institutional and commercial entities have been required to continually improve the quality of their process wastewater effluent discharges.


  • Influent is sewer that enters the facility (untreated).
  • Effluent is treated sewer that leaves the facility and discharges into the river.

The determination of wastewater quality set forth in environmental permits has been established since the 1970s in a series of laboratory tests focused on four major categories:


  • Organics. A determination of the concentration of carbon-based (i.e., organic) compounds aimed at establishing the relative “strength” of wastewater (e.g., Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Organic Carbon (TOC), and Oil and Grease (O&G)).
  • Solids. A measurement of the concentration of particulate solids that can dissolve or suspend in wastewater (e.g., Total Solids (TS), Total Suspended Solids (TSS), Total Dissolved Solids (TDS), Total Volatile Solids (TVS), and Total Fixed Solids (TFS)).
  • Nutrients. A measurement of the concentration of targeted nutrients (e.g., nitrogen and phosphorus) that can contribute to the acceleration of eutrophication (i.e., the natural aging of water bodies), and
  • Physical Properties and Other Impact Parameters. Analytical tests designed to measure a varied group of constituents directly impact wastewater treatability (e.g., temperature, color, pH, turbidity, odor, metals).

Is the City dumping raw sewage into the river?

No. We have not and do not discharge untreated sanitary sewer into the river.

Have we had permit violations? Yes.

What is a violation? Why do they happen at our facility? And, what are we doing about it?

Our facility operates under the conditions of the above mentioned NPDES permit. Click here to view the permit. This permit became in effect on December 1, 2017 and is valid for five years. The permit requires that we conduct specific and regular lab tests to measure the characteristics of the sewer throughout the treatment process and ultimately the quality of effluent that leaves the plant. All testing relates to one of the four categories noted above - some of which have thresholds (or allowable) limits, specific to our plant, as noted in the permit. Additionally, the permit contains specific administrative and operational requirements.


Violations occur and are reported by the City anytime anything occurs that does not strictly meet the permit requirements. Recently, the Idaho Conservation League (ICL) reported on discharge violations at facilities throughout the state, noting 20 violations at the Sandpoint Wastewater Treatment Plant between 2016 - 2018. The majority (12) of these violations related to organics. The remaining seven violations related to solids, nutrients, and physical properties. Below is a more detailed summary regarding these violations.

Clear flows: what's the big deal?

Clear flows are stormwater and groundwater that enters the sanitary sewer system and makes its way to our treatment plant - otherwise known as Inflow and Infiltration (I/I). This is a major problem in Sandpoint. Here's why:


1. At peak flows, the future plant has to treat a volume equivalent to 50,000 residents.


2. Excessively high infiltration and inflow is a struggle to treat efficiently and makes meeting permit conditions a challenge.

Why should you care about I&I?

Fundamentally, Inflow and Infiltration directly impacts rates.


If we can reduce Inflow and Infiltration, it may be possible to construct a smaller treatment plant. And, if you'll recall from the above violations summary, high flows caused by inflow and infiltration were the cause for numerous permit violations. Reducing high flows directly impacts our ability to remain compliant with permit conditions and protect the environment.

Common sources of the problem:

Clear water flows into 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, yard drains, and roof drains that are connected to the sewer system rather than the stormwater system
  • Uncapped cleanouts
  • Storm drain cross-connections

Are these common sources of clear water the cause of our high flows in Sandpoint? Crews have been working to find out!

What action has been taken to date?

The problem is not new. In fact, the City first began collecting data to define the source of the problem in 1995! 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 Sewer Lateral Inspection Program (SLIP) has proactively helped address a portion of the issue. Approximately 42% of the private system has been inspected and 13% of the private laterals have been replaced.

Private sources.

Despite all of the effort to date, we are still seeing excessively high flows at the plant. This video is footage from inside a sanitary sewer mainline pipe. The clear water flowing into the mainline pipe is from a private sewer lateral, more than likely a sump pump in the basement is draining into the system, this is called inflow. The last part of the video zooms in on the lateral and mainline connection where groundwater is leaking into the system - this is infiltration.

What did we learn from smoke testing?

21% of the smoke test results related to public infrastructure (mains, manholes, cross-connections) and the remaining 79% related to private system (yard drains and clean outs)

Questions that still need to be answered before decision-making:

  • What areas of town contribute the most to the flows at the plant? Quantifying flows in the mainlines during peak flows at the plant will tell us if a portion(s) of town is contributing more than others so that possible improvements can be focused in areas that will have the greatest impact of reducing flows. Flow monitoring must be conducted in the spring when rain on snow events provide the most volume of flow. The spring of 2019 did not provide conditions conducive to flow monitoring and the effort is now scheduled for 2020.

  • What if all the private sources were repaired? Since the majority of the leaking mainlines in town have been repaired and we still high flows, the current conclusion is that a significant amount of flow is on the private side. To determine the effectiveness of focusing on fixing private sources, a demonstration project is being reviewed by staff. The project would include repairing 100% of issues in a small portion of town and evaluating what (if any) effect doing so has on flows. This effort requires collecting a variety of flow data before and after repairs, as well immediately adjacent to the demonstration area.

  • How many sump pumps may be contributing to flows? Collecting this information requires input from residents and can help us determine if focusing on removing these sources would reduce flows.

  • How many private laterals in town are failing? The SLIP program has helped; however, nearly 60% of the laterals have not been inspected. The City could inspect the laterals but costly equipment is required; or, the code relating to SLIP could be advanced in a manner that required all lines be inspected by the property owner within two years. The above mentioned demonstration program will help determine if continuing to repair laterals reduces flows at the plant.

Next steps...

  • Public Education Campaign
  • Collect data to dive deeper into where and why
  • CIPP mainlines (Summer 2020)
  • Manhole repairs and other low hanging fruits
  • Survey residents to learn about inflow sources
  • Use data to develop options and cost benefit analysis for future decision-making by City Council

All data collection is leading up to future decisions:

  1. What can be repaired and how effective will the repairs be at reducing plant flows?
  2. What are the results of a cost-benefit analysis and how much should we invest in repairs?
  3. What amount of responsibility should fall on the private property owner? How is that responsibility enforced?

The work continues...

  • Rate payers continue to pay off our current bond.
  • System repairs in treatment and collections are ongoing.
  • Data collection throughout 2020.
  • Rate study in 2020 will assess options to pay for reconstructing the wastewater treatment plant.
  • Public Education efforts will launch first of the year, 2020.
  • City staff will continue to meet with potential funding agencies and work with legal to craft shovel-ready, design-build documents for replacing the wastewater treatment plant.