Frequently asked questions
Boise Creek restoration projects
Ownership of Boise Creek
Restoring stream habitat
Please refer to King County’s information for septic system owners.
Septic systems: Septic systems or “on-site sewage systems” are comprised of septic tanks connected to septic drainfields. The tanks allow the solid wastes to settle out from the wastewater before flowing to the drainfield. Once in the drainfield, water filters through the soil. This filtering action lets harmful bacteria be safely removed by natural bacterial processes. Water that has filtered from a septic drainfield completely through the soil column ultimately rejoins the local waterway as a clean groundwater. In this way, properly functioning septic systems help local natural waterways—creeks, streams, rivers and lakes-- be replenished with clean water, free of harmful bacteria and disease pathogens in human waste, as well as the fats, oils, greases and detergents associated with wash water.
Septic systems in Boise Creek: Septic systems are the only way residential sewage waste and wash water are treated in the Boise Creek portion of unincorporated King County. In Boise Creek septic systems often don’t work in the ideal way described in the paragraph above. Many Boise Creek septic systems are old (installed beginning in the early 1920’s) and many likely haven’t been well maintained. Often these systems weren’t designed or installed professionally and with an approved permit from the Health Department. Another major factor compromising healthy septic system functioning is that the groundwater is close to the surface, as the basin sits on hard compacted soil deposited during the Osceola Mudflow from Mt. Rainier thousands of years ago. The high groundwater table means Boise’s soils are often completely saturated. This prevents septic wastewater from being treated by the beneficial drainfield actions of filtering through the soil column and treatment by normal bacterial processes.
King County’s Involvement in Boise Creek Septic Systems: Under the current Municipal Phase I NPDES Stormwater Permit, which is administered by Washington State as required by the federal Clean Water Act, King County is required to seek failing septic systems (and any other land uses) that are causing high levels of bacteria to enter the County’s stormwater conveyance system that drains to Boise Creek. For the last few years County staff have been investigating the area to comply with this Permit requirement. Investigations have included performing desktop GIS analysis of air photos to look for any kinds of land use that could lead to high levels of bacteria entering the stormwater system. Staff have driven all the roads in the basin and have walked much of the basin, observing the stormwater system and potential illicit discharges to it, including soil erosion, potential manure runoff and other concerns. Staff have obtained water quality samples from 44 established locations in the stormwater system. Directly related to this work, County staff found two septic systems so far in 2014 with wastewater and wash water flowing directly into the stormwater system, and from there directly into Boise Creek. These illicit septic discharges are violations of the King County water quality code and Washington State water quality regulations. Code and regulatory violations aside, most people would agree that having human wastewater flow into Boise Creek—including fecal waste, detergents and kitchen fats, oils and greases—is a bad idea and should be prevented by proper septic system installation and maintenance.
For more information about Boise Creek habitat restoration projects, please contact Mason Bowles, Senior Ecologist, WLR Ecological Restoration and Engineering Services Unit.