King County Quirks Worth Knowing
Marine Recovery Area: annual inspections, and a possible expansion
King County's Marine Recovery Area currently covers parts of
Vashon-Maury Island: the Quartermaster Harbor shoreline (Governor's
Lane, Shawnee-Magnolia Beach, Harbor Heights, and Tahlequah) and the
East Passage shoreline (Dolphin Point, Glen Acres, Hawthorne,
Klahanie, and Summerhurst). Systems inside it need a mandatory
annual inspection by a licensed maintainer under BOH 13.60.010.F,
regardless of system type.
A possible county-wide expansion is pending, unconfirmed.
A proposal under review would expand the Marine Recovery Area to
all King County shoreline properties, with either continued annual
inspections or a risk-based schedule: every 3 years for permitted
gravity systems, annually for other types, and extra review every 9
years for higher-risk systems near water. Reporting points to a
vote around November 2026, with enforcement phased in over 3 years
after approval if adopted. This came from a secondary county
webpage summary, not the Board of Health Code text itself, so treat
the status and timeline as unconfirmed until the county's own code
reflects it.
Critical Aquifer Recharge Areas
Development in a Critical Aquifer Recharge Area has to show
compliance with King County Code 21A.24.316 (BOH 13.24.010.C,
13.28.020.A.2.h). One specific restriction: disinfection can't be
used to meet required treatment levels for a system sitting in a
critical aquifer recharge area (BOH 13.28.030.S.4).
Mandatory sewer connection inside the Urban Growth Area
If a property sits inside the Urban Growth Area and within 200 feet
of a public sewer line, the OSS has to be abandoned and the
property connected to sewer once the septic system needs repair,
replacement, or has failed (BOH 13.04.050). A failing system on a
UGA lot near sewer can trigger a mandatory sewer connection instead
of a repair.
Minimum lot size depends on soil type, not just zoning
For new lots served by an OSS, King County Code 13.24, Table
13.24-1 sets minimum lot sizes tied to soil type: as small as
13,000 square feet for soil type 1 on public water, up to 5 acres
for a private well on any soil type. Two lots the same zoned size
can carry very different septic-eligible minimums depending on the
soil report.
Owner-occupants can self-install and self-monitor gravity systems
BOH 13.20.040 lets an owner-occupant personally design and install
a gravity system for their own single-family home, under the
conditions the section sets out. That same owner can also
personally monitor a gravity OSS, or the septic-tank component of
an alternative system, instead of hiring a licensed maintainer for
that piece — consistent with the "owner" column in the
inspection table above.
Named county programs
King County names two OSS initiatives on its program page but
publishes no detail on either: the Equitable Wastewater Futures
Program, aimed at aging urban septic systems, and the Vashon-Maury
Pollution Identification and Correction (PIC) Project. Both point
toward the same underlying issue: an aging septic inventory
concentrated in older urban areas and on Vashon-Maury Island.
Possible permitting delays, undated. King County's
own OSS landing page mentions current permitting-review delays tied
to a system transition, staffing changes, and high application
volume. The note gives no timeline and no date, so it may no
longer be current. Ask the department directly about current
turnaround times before you plan a project around a specific date.
No county page describes an outright OSS moratorium.