King County committee examines three I&I policy paths as staff warns private property drives most of the problem

Chair Balducci opened the March 4 meeting of the Regional Wastewater Quality Committee to receive briefings on the Regional Wastewater Services Plan update and related 2027 rate work.

"I and I is extraneous water that enters the sanitary sewage system from groundwater or stormwater," said Johnson Nguyen, a planner with WTD's separate‑conveyance program, introducing the technical case for immediate policy attention. Nguyen told the committee that excessive I&I drives conveyance‑capacity and peak‑flow needs and that, based on prior studies, "it's estimated that approximately $1,700,000,000 in conveyance capacity projects are due to I and I" (2016 dollars). He added that studies estimate up to about 75% of I&I originates on private property.

Why it matters: that volume and cost implication help explain why the county and its partner agencies are re‑examining how costs are assigned and what tools the region should use to reduce excessive flows into the sewer system. WTD has included $7,400,000 in the adopted 2026–27 King County budget to support the RWSP update.

Staff framed three high‑level policy options for committee feedback. Option 1 would largely maintain current practice: accept flows and expand conveyance and treatment when economically justified, using an updated cost‑benefit ratio that staff says is being revised. Option 2 would incentivize I&I reduction in areas with high contributions (for example, through side‑sewer inspection rebate programs or targeted rehabilitation grants), paired with expanded permanent monitoring to verify benefits. Option 3 would establish systemwide flow limits and penalties for component agencies that exceed them; WTD said that option would require far more permanent flow monitoring and probably changes to contracts or county code to implement.

Committee reaction and follow‑up: several members welcomed the options but asked staff to broaden the forthcoming economic analysis. "When you're comparing the cost of dealing with I&I, are you comparing it simply against additional conveyance, or are you also taking into account the costs imposed on the treatment facilities?" asked John McClellan (MUPAC chair) and Commissioner Warren pressed the staff to include treatment‑plant capital and O&M impacts and lifecycle costs in the cost‑benefit assessment. WTD staff said that inclusion is planned for phase 2 of the technical update.

Commissioner Warren also criticized the briefing for being overly constrained by past practice and raised concerns about how the Robinswood agreement is being interpreted in the conversation about uniform rates. Staff and other members agreed historical context and archived reports should be surfaced to help decision‑makers see who has contributed most to I&I and how past investments were allocated.

Equity considerations were central to the discussion. WTD staff noted that areas with the highest measured I&I tend to have higher Social Vulnerability Index scores; members warned that a penalty‑based approach could pose affordability risks unless exemptions, subsidies or targeted assistance accompany any penalty or surcharge program.

Next steps: staff said the division will update the technical cost‑benefit approach in phase 2 (to include treatment and O&M), search archival records to answer historical questions about contributions and past investments, and accept committee feedback on the first three policy memos through the end of March. WTD also plans to select an independent third‑party consultant to review the capital program by roughly June.

The committee did not take formal action on policy options at this meeting; the briefing was explicitly described as an informational and feedback step in the RWSP update process.

Ending: Chair Balducci asked members to review the memos and provide written comments by the end of March; staff committed to follow up individually with members who requested deeper dives.