Issaquah adopts updated sanitary sewer system plan, sets phased extension and capacity policies

The Issaquah City Council on May 19 unanimously adopted a revised sanitary sewer system plan that lays out capital projects, phased sewer‑extension timelines for unsewered neighborhoods near environmentally sensitive areas, and code changes to address septic systems, grinder pumps and fats, oils and grease (FOG) from commercial establishments.

The plan, presented by Matt Ellis, the city’s utility engineering manager, sets three tiers for sewer extension priorities — Tier 1 (100‑year floodplain, shoreline buffer, and commercial/industrial) with a 20‑year goal; Tier 2 (stream buffers, wetland boundaries, documented high groundwater) with a 30‑year goal; and Tier 3 (critical aquifer recharge areas and wellhead protection zones) with a 40‑year goal. The council adopted Resolution No. 2025‑11 to approve the plan.

Why it matters: the plan updates Issaquah’s infrastructure strategy, prioritizing sewer installation where failing septic systems would most likely harm streams, wetlands and groundwater; it also creates clearer rules for when developers must fund upgrades and how the city will phase technical and inspection requirements.

Ellis told the council the plan updates the 2002 system plan and includes a capital improvement program with near‑term and long‑range projects. A major CIP on the list is the SW 18 South, Newport and Wildwood sewer remediation, currently estimated at about $1,200,000, with design in 2026 and construction in 2027. Ellis said the design will proceed while staff continue to search for upstream causes (for example, illicit storm connections) that might reduce the need to upsize pipes.

The plan also addresses operational matters: the city will require inspections and an inventory of private grinder pumps, maintain standardized lift‑station equipment and spare parts to assist homeowners, and adopt a 3‑year compliance window for commercial establishments to install appropriately sized grease interceptors or other best management practices for FOG control. Developers whose projects add flows that contribute to surcharging will be required to pay for system upgrades tied to that impact, Ellis said.

Interagency reviewers — including Washington State Department of Ecology, King County Board of Health and Sammamish Plateau Water and Sewer District — provided comments during the plan’s review. Ellis said Ecology asked the city to account for recent state legislative changes affecting housing growth forecasts and to clarify overflow reporting; the plan references reporting overflows to Ecology through the state’s reporting system within 24 hours. Sammamish Plateau staff asked whether the city’s sewer‑extension policy would apply beyond Issaquah’s current sewer service area; Ellis said the city’s extensions are limited to its service area and that extensions outside city limits would require annexation.

Council discussion noted the plan’s long public review and commended staff. The council emphasized three points adopted in the plan and implementation approach: (1) coordinating septic‑inspection and connection timing in code amendments (to be returned later this year as updates to Issaquah Municipal Code Titles 13 and 16); (2) a phased, practical compliance window for FOG controls to reduce burden on existing businesses; and (3) continued coordination with other sewer purveyors and state agencies.

No changes to service‑area responsibilities were made: Issaquah will plan extensions only where it is the sewer provider; areas served by Sammamish Plateau remain under that district’s purview unless annexed. The council approved the plan by roll call without dissent.

Looking ahead: staff will submit the final plan to Ecology and King County for formal acknowledgement, complete the attorney concurrence and bring the detailed code revisions on on‑site septic inspection and grease trap requirements back to council later this year for adoption.