Clark County previews 2026 stormwater code and manual; hearing set for June 16

Clark County public works staff on a work session gave the council a final preview of the proposed 2026 stormwater code and manual and said they will ask the council at a June 16 public hearing to adopt an ordinance that would make the manual effective July 1, 2026.

The presentation, led by Devin Rostopher, clean water division manager in public works, and Trista Koblowski, senior stormwater planner at OTEC, outlined mandatory changes required by the county's municipal stormwater Phase I permit under the federal Clean Water Act and other proposed updates to improve environmental outcomes and ease implementation. "We are here to provide a final work session on the 2026 Clark County stormwater code and manual, prior to a public hearing that we have scheduled on June 16," Rostopher said.

Why it matters: the manual functions as an environmental regulation, development regulation, engineering standards guide and operations/maintenance reference. Staff said updates are needed for permit compliance and to reflect best available science, and they emphasized measures intended to protect drinking water, reduce pollutant loads and improve long‑term infrastructure performance.

Key changes and policy choices

- Deep stormwater dry wells: Staff said the proposed 2026 manual will not recognize deep stormwater dry wells (facilities that can reach roughly 100 feet) as approvable flow control facilities because the risks to the aquifer are not well studied; shallow dry wells (up to about 25 feet) remain commonly used. Rostopher noted most municipalities in Clark County plan to similarly restrict deep wells.

- Phosphorus treatment expansion: The manual would add a phosphorus treatment requirement for watersheds draining to Vancouver Lake (including portions of Salmon Creek, Burntridge Creek, West Slope watersheds and Whipple Creek), expanding protections already in place for the Lacamas watershed to reduce nutrient loading and algal‑bloom risk.

- Wetland and flow protections: Staff described modest revisions to wetland protections to preserve hydro‑periods and removal of an alternative flow control standard in Mill Creek to better align with best available science on erosion and stream flashiness.

- High‑performance bioretention mix and pollutant controls: The draft adds a high‑performance bioretention soil mix that staff said can be used to manage phosphorus where the default mix exported phosphorus; Rostopher cited King County findings that the high‑performance mix reduces 6PPD more effectively than the default mix. The manual also includes more emphasis on metals and PCB source control for existing commercial/industrial sites.

Public input and revisions

Staff described an extensive outreach timeline beginning in October 2024 with the development and engineering advisory board (DEIB) and the county action team on stormwater (CAT on stormwater). Early drafts were submitted to the Department of Ecology in June 2025. Staff reported an early comment period that generated about 200 technical comments (mostly from the Clean Water Commission) and a spring general public comment period that produced 13 comments, of which staff incorporated eight into the draft.

Because of public feedback, staff reversed proposed prohibitions that would have disallowed certain treatment facilities on individual urban residential lots (restoring flexibility used in the 2021 manual) and reversed a proposed ban on using compost‑amended vegetated filter strips on driveways, instead prioritizing training and inspector guidance. Staff also clarified modeling requirements for temporary construction sediment ponds and certain small UIC (underground infiltration control) downspout units.

Costs, retrofits and implementation

Staff said the manual preserves multiple compliance pathways (above‑ground and underground BMPs) to accommodate different site constraints and to balance upfront construction costs with lifecycle maintenance obligations. Retrofit work on older facilities is primarily conducted through the county's capital plan as required by the stormwater permit, and staff reiterated applicability thresholds in the manual: 5,000 square feet of new or replaced hard surface triggers the full suite of stormwater management controls, and a 2,000‑square‑foot threshold triggers a smaller set of controls.

Regulatory milestones and next steps

Rostopher told the council that Ecology issued a preliminary approval and an equivalency determination confirming the county's proposed 2026 manual is equivalent to the state's manual. The manual has a SEPA determination of nonsignificance pending (one tribal comment acknowledged and thanked staff). The planning commission reviewed the manual and is holding a public hearing the following evening; council consideration of the ordinance is scheduled for June 16. If adopted, staff said the manual would become effective on July 1, 2026.

Council reaction and follow‑up

Council members praised the outreach and documentation. One committee member said, "You addressed all of our concerns, and you did it on paper, and the public is able to see and digest that." Staff answered follow‑up questions on the reversed restrictions, retrofit authority, and the permit's compliance point system.

The council did not take a formal vote in the work session; staff will present the ordinance and revised manual at the June 16 public hearing for formal consideration.