City staff propose limiting construction dewatering in Redmond's aquifer area to protect supply wells; ordinance eyed for June

City environmental and utilities staff recommended tightening Redmond Municipal Code 13.25 to restrict temporary construction dewatering within the city's Critical Aquifer Recharge Area (CARA) to elevator pits, footings and utilities only, citing groundwater protection and predictability for water supply, water quality and monitoring.

Deputy Public Works Director Chris Stenger introduced the item and said Jessica Atlakson, senior environmental scientist, would summarize the background, rationale and proposed code language. The staff presentation traced a multi-year process of technical analysis, stakeholder outreach and interim limits that began with a triple-bottom-line study in 2021 and continued through policy analysis in late 2021 and interim restrictions in 2022. "We're here this evening to provide a bit of a deeper dive into the rationale and history of Redmond Numismal code 13 decimal 25, temporary construction dewatering," Stenger said at the start of the presentation.

Staff emphasized the city's dual-source water system: roughly 60% of drinking water is purchased from Cascade Water Alliance and about 40% is produced from Redmond's groundwater wells. Jessica Atlakson summarized the hydrogeology and risks: the aquifer is very shallow (often 5 to 10 feet below ground surface in winter), transmissive, and overlaps the downtown and Marymoor Village areas where substantial underground construction is planned. "Because our aquifer is so transmissive, basically, water moves through it very, very quickly. Any pumping will create a depression or lowering of the groundwater level outside of that area," Atlakson said, and noted some large projects have lowered groundwater up to 1,500 feet from a site.

Temporary construction dewatering involves pumping groundwater from drilled dewatering wells to lower the local water table so below-grade construction (for example, underground parking) can proceed; the pumped water is typically discharged to the stormwater system and eventually to the Sammamish River. Staff said limiting dewatering in CARA primarily to elevator pits, footings and utilities would reduce drawdown effects on supply wells, preserve predictable groundwater quality and simplify monitoring and drought-response actions.

Atlakson said the proposed ordinance would replace an interim rule that had prohibited dewatering for parking garages where additional building height was awarded; under the new code language, the CARA restriction (footings, elevator pits, utilities) would be the single standard. Staff argued the change gives both the water utility and the development community predictability: the utility avoids unexpected drops in supply and changes in water quality; developers can adjust designs (moving parking above grade and using added building height incentives) and reduce dewatering costs; and the city can manage drought response more easily. Staff asked that the dewatering ordinance be put on the June 17 consent agenda so it can be adopted concurrently with the Redmond 2050 code updates.

Council members expressed support and asked operational questions about vested projects and possible incentives to encourage projects already vested under the current code to follow the new standards. Staff said three projects remain vested under the current code (one active dewatering project had finished as of the meeting) and multiple other projects already meet the proposed limits. Staff also said the code changes would be easier to implement if adopted concurrent with the zoning updates; they pledged continued stakeholder outreach. "We're only allowing dewatering for footings, elevator pits, and utilities," Atlakson summarized of the proposed CARA language.

No final vote was taken at the study session; staff asked to place the ordinance on the consent agenda for the June 17 council meeting and to continue outreach to affected stakeholders.