Equitable Wastewater Futures Program

The interactive map to the right shows the age of OSS in King County. Click on a parcel to learn more and use the zoom buttons to adjust the scale.

With routine maintenance, a septic system will last for about 30 years on average. Of the urban septic systems in King County, around 70% are past their expected lifespan. 

These aging systems are more likely to fail, which can expose people to untreated sewage and contaminate nearby bodies of water.

Failing septic systems affect the community in a number of ways and pose a serious threat to public health.

When septic systems fail raw sewage can back up into homes, leak onto neighboring properties, contaminate water supplies, and cause illness. 

Sewage backups are one of the most easily recognized signs of a failing septic system. They cause odors, damage to homes, and the spread of disease-causing organisms.

Failing septic systems that leak untreated wastewater into the environment contaminate groundwater sources, rivers, and streams.

This can lead to the spread of waterborne diseases and also pose a threat to aquatic ecosystems.

Contamination limits swimming, kayaking, and other recreational activities.

Fecal contamination doesn't just pose a threat to humans enjoying water recreation. Shellfish, like oysters and clams, filter feed and accumulate harmful bacteria from polluted waters.

In addition to being a health risk to consumers, it can also lead to closures of shellfish beds, causing economic hardship and jeopardizing cultural practices for communities that depend on shellfish harvesting for their livelihood and sustenance.

Fecal pollution disrupts the intricate web of life within aquatic ecosystems. The influx of nutrients from untreated wastewater fuels the growth of harmful algal blooms, depleting oxygen levels, suffocating marine life, and leading to cascading effects throughout the food chain.

Learn more about fecal pollution in our waterways in the following story map.

Septic systems are vulnerable to flooding, which is predicted to occur more frequently in King County due to climate change.

The home you see here is an example of a small urban lot with an OSS. It sits directly on the Duwamish River, which is where untreated wastewater would end up in the event of OSS failure.

Check out this  article from Yale Climate Connections  to find out more about how climate change and rising water tables interfere with OSS wastewater treatment.

Lot size and soil quality matter

When a septic system fails, a new system cannot be installed in exactly the same place. Also, OSS require proper soils for adequate wastewater treatment. Because of this, smaller urban lots can typically only replace their OSS once or twice.

Sewer connections can be more sustainable long-term. However, many urban areas have high density of OSS and still remain unsewered. Several of these areas are featured in the map tour you will see later on.

Many urban neighborhoods throughout King County are still unsewered due to the expense of extending sewer to developed neighborhoods.

Did you know that replacing an OSS costs an average of $40,000? And sewer connections can be even more expensive!

These costs are usually wholly covered by the homeowner, which is why  maintaining existing septic systems  is so important.

You can find out more about financial assistance options for OSS repair or replacement  here on our website .

These include flexible payment plans and reduced interest rate loans for income-qualified homeowners through the  King County Housing Repair Program  and  Craft3 .

And if you live in Seattle, you can check out the  City of Seattle's Home Repair Loan Program  that provides assistance to homeowners who live within the jurisdiction.

Through our work permitting and inspecting OSS, we have seen growing numbers of OSS failures in urban areas. This pushed us to look beyond the individual cases to the broader systemic issues, and how past policies and distribution of resources have resulted in this outcome.

We operate under a legally mandated fee-for-service model, which means our programs and staff are funded by the fees we charge for services. So, the services we offer are associated with the permits we sell.

Working on systemic issues – such as investigating how best to connect urban communities on septic systems to municipal sewer systems – is traditionally not within our scope or staff capacity.

Now, thanks to Foundational Public Health Services funding from the state Legislature, we have the staff capacity to secure funds for future sewer connections.

Learn more about FPHS on the  Washington State Department of Health’s website .

The goal of Public Health Seattle & King County's Equitable Wastewater Futures Program is to find wastewater solutions for lots in urban areas.

We have funded two pilot projects using $2 million from the King County Climate Equity Capital Pool to extend sewer connections to up to 24 homes in 2024. This work will also make sewer connection opportunities available to new neighborhoods.

Both projects are expected to be completed by December 2024.

An important focus of this project was identifying pilot neighborhoods to help us solve wastewater issues based on public health concerns and social vulnerability.

When most sewers were built, the focus was on expanding urban services around Lake Washington. Other neighborhoods in Seattle, Tukwila, Burien, Federal Way, Kent and Auburn did not get funding for sewer connections. Today, around 40% of urban OSS are in areas highly vulnerable to public health emergencies.

We are working to secure funding sources for more sewer connections in the future and will prioritize funding applications using the CDC's social vulnerability index.

 The CDC/ASTDR Social Vulnerability Index  shows which communities are especially at risk during public health emergencies because of factors like socioeconomic status, household composition, minority status, housing type, and transportation.

The  Determinants of Equity data tool  helps us identify disparities and focus our efforts in areas with the greatest need.

We use these tools in our work with the goal of "making King County a welcoming community where every person can thrive." Learn more about our  True North and Values  on our website.

According to King County codes, properties in the Urban Growth Area must be connected to sewer if an OSS fails and sewer is available within 200 feet of the property boundary.

OSS failures and associated costs disproportionately affect low-income communities of color located in urban areas who were previously left out of government- and developer-funded sewer infrastructure development.

There is an imminent need for neighborhood or community-level planning and broad-scale capital funding to support conversions to sewer in low-income, urban areas.