Progress Indicators
On-site sewage system failures
Map
Description

This indicator measures the number of small on-site sewage systems (OSS) with an identified and unresolved failure (“failures”). Failures range in severity and potential for environmental and public health harm, though typically more severe failures are reported. This indicator helps us track and manage failing OSS, which are a leading pressure impacting water quality and shellfish bed health in Puget Sound.   

Progress Indicator Chart

Figure 1. The number of on-site sewage systems with known and unresolved failures across Puget Sound local health jurisdictions and within marine recovery and sensitive areas across 2024. Note: unresolved failures vary in their degree of severity. Some failures may mean a system is non-compliant with its permit (administrative issues), or it may indicate a significant equipment issue. We do not have information on the severity of failures, though typically more severe failures tend to be reported.

In Puget Sound, fecal pollution impacts water quality, harvestability and food safety of shellfish, and can cause public health concerns in swimming areas. Small on-site sewage systems (OSS) treat wastewater close to where it is generated and many properties across Puget Sound are supported by this essential wastewater infrastructure[1]. However, improper management of OSS can result in fecal pollution and environmental and public health concerns.  

Failing OSS are a leading pressure impacting water quality and shellfish bed health in Puget Sound[2].  An OSS failure can be caused by bad system design, improper maintenance, changes to site conditions, weather events, or simply because the system has reached the end of its life expectancy. Though most failures do not result in surfacing sewage or sewage entering Puget Sound, failures have the potential to worsen or significantly impair environmental and public health.  

Malfunctioning OSS release pathogenic bacteria, viruses, and chemicals that may eventually enter streams, rivers, lakes, Puget Sound, and the ocean. These pollutants can harm local ecosystems by killing native plants, fish, and shellfish. Harmful bacteria from malfunctioning OSS may contaminate nearby surface waters, pose health risks to swimmers, and can also accumulate in shellfish to the point where they are no longer safe to eat.  

Proper OSS maintenance is the first step to preventing failures. Regular inspections by certified individuals can identify problems in OSS before they cause significant (and often costly) issues. Though often perceived as simple and static, OSS are truly complex, small-scale wastewater facilities. With roughly 550,400 OSS in the Puget Sound (as of December 2024), routine maintenance is critical to keeping these systems in good function and preventing public and environmental health impacts. 

The responsibility to manage these systems appropriately is split between homeowners and local health jurisdictions (LHJs). While homeowners must ensure proper use and care of their OSS, LHJs must support homeowners by establishing operation & maintenance programs that offer education, training, rebates, and technical assistance to ensure proper OSS management[1]. It is the responsibility of the homeowner to notify LHJs and address failures of their OSS as soon as possible[3]. Should a failure be identified, LHJs can support homeowners in identifying the least costly course of action to reinstate the function of the OSS. LHJs are often limited by funding and staff capacity, impacting their ability to provide these essential services to homeowners. 

Failures can and still occur despite routine maintenance, LHJ assistance, and homeowner vigilance. This indicator measures the number of small OSS with an identified and unresolved failure. The indicator helps us track and manage OSS failures to understand progress towards minimizing the number of unresolved failures present in Puget Sound.  

 

[1] Schneider, L., Glasoe, S., Story, C., Hofstad, L., Thomas, J., Washington State Department of Health, Skagit County Health, BH Consulting, & Washington On-Site Sewage Association. (2016). Puget Sound Septic System Management Programs Best Management Practices Reference Manual. https://doh.wa.gov/sites/default/files/legacy/Documents/Pubs/332-166.pdf. 

[2] Shellfish Beds Interdisciplinary Team, Puget Sound Partnership, Washington State Department of Health. (2023). Shellfish Beds Implementation Strategy: Protect and Restore Shellfish Beds in Puget Sound. https://pspwa.box.com/s/d3u2rf092imo9pt4foqgrw3m6p6rj9yv. 

[3] Chapter 246-272A WAC.

Key Progress Indicator Results

At the end of the baseline period (2024), 3,098 OSS had an unresolved failure. This number represents less than 1 percent of all known systems.  

  • In June of 2024, 3,208 OSS across local health jurisdictions (LHJs) had an unresolved failure. By December of 2024, this number decreased to 3,098.  

  • Failures were less frequent in marine recovery and sensitive areas. At the end of 2024, 371 of 86,425 systems had an unresolved failure in marine recovery and sensitive areas. The percentage of all systems with unresolved failures at the end of 2024 was 0.43 percent compared to 0.56 percent across full LHJs.  

  • A very small percentage of systems across the region has unresolved failures. However, these failures do still have the potential to cause impacts to environmental or public health.

Methods
Monitoring Program

Puget Sound local health jurisdictions with on-site sewage system management areas. 

Data Source

Compilation of Puget Sound local health jurisdiction data which are submitted to Washington DOH biannually.

This Progress Indicator tracks the number of on-site sewage systems (OSS) with a known and unresolved failure. This indicator relies on the identification of failures by homeowners or local health jurisdictions (LHJs) and additional reporting when failures are resolved. LHJs collect data on OSS to protect public health and Puget Sound water quality [1]. Failures range in severity, from administrative issues to more severe equipment issues. We do not have information on the severity of failures, though more severe failures are typically reported by LHJs.  

The Washington Administrative Code (WAC) identifies a failure as “a condition of an OSS or component that threatens the public health by inadequately treating sewage or by creating a potential for direct or indirect contact between sewage and the public”[2]. Examples of failures include:  

  • Sewage on the surface of the ground,  

  • Sewage backing up into a structure caused by slow soil absorption of septic tank effluent,  

  • Sewage leaking from a sewage tank or collection system,  

  • Cesspools or seepage pits where evidence of groundwater or surface water quality degradation exists, 

  • Inadequately treated effluent contaminating groundwater or surface water, or 

  • Noncompliance with standards stipulated in the permit.   

All LHJs must, at a minimum, adopt this definition of failure into their local health codes. They may add to this definition but may not subtract from it[3]. 

The methods to identify failures vary. In some cases, homeowners or neighbors may report surfacing sewage, backing up of sewage into the home, or other equipment issues directly to their LHJ. In other cases, failures may be identified through routine inspections. Some LHJs with water quality issues also have Pollution Identification and Correction (PIC) programs that help identify OSS failures.   

Data are collected by LHJ practitioners and submitted via survey reporting form to the Washington State Department of Health (DOH) on-site sewage management program twice a year. This form asks each LHJ to document their numbers of systems with unresolved failures. Data are then transferred from DOH to the Puget Sound Partnership (Partnership), where Partnership staff manually review LHJ entries for anomalies and confirm values with DOH and LHJ staff as warranted. Data are collected at the county scale, though OSS failures within marine recovery and sensitive areas (sub-areas within counties with enhanced management requirements) are also provided in this report.  

LHJ biannual reports illustrate a snapshot of OSS data at the time of reporting. This means that unresolved failures may be double counted if multiple reports are summed together. We avoid this by reporting on failures per specific report submittal dates and by reporting net change over time.  

Current reporting period: 2024 

Baseline period: 2024 

Each reporting period for this indicator is one calendar year; each calendar year includes two biannual reports submitted by LHJs covering January through June and July through December, respectively. We will evaluate trends over time by comparing the regional indicator value of the most recent reporting period (one year) to the regional value of the baseline period (2024). 2024 is selected as the baseline period because it is the first year for which LHJs reviewed local methods and implemented widespread updates to their data systems.  

Limitations:  

  • Data comprehensiveness and quality varies by LHJ, depending on available resources. LHJs are often understaffed and under-resourced, which can impact their ability to comprehensively assess the inspection status of OSS, both within marine recovery and sensitive areas and across their full county. Beginning in 2022, LHJs completed a significant effort to update databases and data systems to provide the data reported here. Most database updates are still in progress as of July 2025, and staff continue to work with technology staff to develop workflows that allow them to query this data accurately. Dedicated and sustained funding to LHJs can help improve the quality and comprehensiveness of local data.   

  • Failures tend to be underreported. Failures may go unnoticed or underreported to LHJs, which may impact our overall understanding of the status and trends of failures in OSS across Puget Sound.  

  • Data are currently non-spatial. This impacts our ability to understand the relationship between water quality and OSS management. We can note which OSS are in marine recovery or sensitive areas, but not specific locations therein. Improving the spatial data capabilities of LHJs is a regional priority.   

  • The exact conditions of systems identified as “failures” may vary across LHJs. All LHJs must adopt, at a minimum, the Washington Administrative Code definition of a failure, but may include additional clauses that could make failure data inconsistent across jurisdictions. We rely on the best judgment of LHJs to identify systems that fit within the state’s definition of a failure.  

  • Not all OSS are inventoried or regularly inspected, therefore there may be unknown failures. Efforts to find and address failures may vary by locality. For example, county Pollution Identification and Correction (PIC) Programs support identification of failures by assessing water quality, but the capacity of these programs to perform water quality assessments may vary. Marine Recovery and Sensitive Areas also represent areas of enhanced management requirements; thus, failures may be more likely to be identified in these sub-county areas of Puget Sound than across the wider counties. 

  • The number of failures identified is directly related to the ability of LHJs to review systems. As Operation and Maintenance programs are developed, enhanced, or implement higher standards of OSS functionality, failures are likely to increase because of this increased surveillance. Failures should still decrease over time if programs are maintained through stable staffing, funding, and enforcement. 

 

[1] Washington State Department of Health, (n.d.). On-site Sewage Systems (OSS). Wastewater Management, Department of Health, State of Washington. Accessed at https://doh.wa.gov/community-and-environment/wastewater-management/site-sewage-systems-oss#:~:text=Small%20on-site%20sewage%20systems%2C%20also%20known%20as%20septic,flows%20of%20less%20than%203%2C500%20gallons%20per%20day.

[2] WAC 246-272A-0010

[3] Schneider, L., Glasoe, S., Story, C., Hofstad, L., Thomas, J., Washington State Department of Health, Skagit County Health, BH Consulting, & Washington On-Site Sewage Association. (2016). Puget Sound Septic System Management Programs Best Management Practices Reference Manual. https://doh.wa.gov/sites/default/files/legacy/Documents/Pubs/332-166.pdf. 

 

Critical Definitions

  • On-site sewage system (OSS): Integrated system of components, located on or near the property it serves, that stores, treats, and manages the dispersal of sewage [1].  

  • Small OSS: OSS with daily flows less than 3,500 gallons per day[2].  

  • Failure: A failure is the condition of an on-site sewage system or system component that threatens environmental and public health by inadequately treating sewage or by creating a potential for direct or indirect contact between sewage and the public. Failures range in severity and potential for environmental and public health harm; most failures do not result in surfacing sewage or sewage entering Puget Sound. Any failure has the potential to worsen and/or significantly impair environmental and public health. See the revised Washington Administrative Code for more details on situations that constitute a failure.  

 

[1] Chapter 246-272A WAC: (n.d.). https://app.leg.wa.gov/wac/default.aspx?cite=246-272A&full=true. 

[2] Washington State Department of Health, (n.d.). On-site Sewage Systems (OSS). Wastewater Management, Department of Health, State of Washington. Accessed at https://doh.wa.gov/community-and-environment/wastewater-management/site-sewage-systems-oss#:~:text=Small%20on-site%20sewage%20systems%2C%20also%20known%20as%20septic,flows%20of%20less%20than%203%2C500%20gallons%20per%20day.

Interpretation of Results

This Progress Indicator report represents the first year for which we have improved data on OSS management. We thus apply the “Limited Data” designation to this indicator and will address indicator trends over time as we compile additional years of data.   

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Over the baseline period (2024), the number of systems with known and unresolved failures varied by local health jurisdiction (LHJ). Failures were primarily located outside of marine recovery and sensitive areas (Figure 2).  

  • At the end of 2024, Pierce County had the highest number and percentage of systems with unresolved failures (1,618 OSS, 1.5 percent of known OSS) across the full LHJ. Skagit county had the fewest number of systems with unresolved failures (12 OSS) across the full LHJ, though Kitsap had the smallest percentage of systems with unresolved failures (16 systems, 0.03 percent of known OSS).  

  • At the end of 2024, Mason County had the highest number of systems with unresolved failures in their marine recovery and sensitive areas (154 OSS or 1.2 percent of known OSS). King county had the highest percentage of systems with unresolved failures in these areas (1.9 percent) though this represents only 5 systems with unresolved failures. Skagit and Kitsap counties had the fewest number of systems with unresolved failures in their marine recovery and sensitive areas (2 OSS).  

  • On average at the end of 2024, LHJs each reported 282 systems with unresolved failures. In contrast, LHJs each reported 34 systems with unresolved failures in their marine recovery and sensitive areas.  

Bar chart of on-site sewage systems with unresolved failures broken out by county and system location (local health jurisdiction or marine recovery or sensitive area).

Figure 2. The number of on-site sewage systems with unresolved failures at the end of 2024, across full local health jurisdictions (blue, left column) and within marine recovery and sensitive areas (orange, right column).

Puget Sound LHJs dedicate significant time and resources to assisting homeowners with proper OSS management and rapidly addressing identified failures. However, the landscape of OSS management is complex, authority for enforcement varies, and homeowner awareness of best practices varies.  

Trends in this indicator are thus affected by:  

  • Dedicated and sustained funding for LHJs to educate homeowners, offer incentives and financial assistance, manage failures data, and resolve failures,  

  • The capacity of LHJ Operation & Maintenance programs to investigate and identify failing systems,  

  • Homeowner awareness, financial ability, and capacity to repair failures when they occur,  

  • Capacity of LHJs to support homeowners through the permitting and compliance process to resolve failures,   

  • Consistent enforcement of inspection requirements, and  

  • External factors like weather conditions or the availability of professionals to resolve failures.  

Datasets

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Reporting Guidance
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Subcategories

No Subcategories for this Puget Sound Indicator.