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Peer review backs reinstating a reduced 510 pressure zone for Highlands, flags sprinkler risks
Summary
A peer review of Highlands water-pressure alternatives found the consultant analysis sound and recommended a reduced reinstatement of the 510 pressure zone as the best long-term fix, while advising additional investigation into how lower-than-original pressures might affect about 70 residential fire-sprinkler systems.
A consultant peer review presented to the Kirkland City Council on April 7 supported the technical analysis behind alternatives to address pressure changes in the Upper Highlands and recommended moving forward — with one important caveat.
Consor engineers told the council that work performed by RH2 used industry-standard hydraulic modeling and that the set of alternatives considered were appropriate for planning and budget decisions. The strongest-performing long-term fix agreed by the peer reviewer was a reduced-size reinstatement of the prior "510" pressure zone that restores service to customers who saw the largest pressure drops after a 2024 system modification.
A key caveat: residential fire-sprinkler performance. Consor and city staff emphasized the need to assess approximately 70 properties where sprinkler systems were designed for the higher historic pressures in the original zone. Staff has mailed notifications and opened sign-up for a “bucket test” (a field flow test) and contracted a specialist firm to collect data. "If the potential residential fire sprinkler system performance issues can be addressed, then alternative one as recommended really is the right option," the peer reviewer said.
Short-term step: temporary boost. Staff are also moving forward with a short-term, temporary regional booster pump station (an alternative Consor described as a reasonable short-term fix that can be implemented quickly and address summer pressure needs), noting that one of the pump contracts required additional council action because bids exceeded the preauthorization threshold; staff have purchased the pump itself to avoid schedule delay.
Next steps: staff will collect bucket-test results, quantify sprinkler risk, and return to council with findings and a recommendation for which alternative to construct and when. The council did not adopt a final engineering decision April 7; staff emphasized they expect to preserve schedule by advancing short-term measures while completing the technical follow-up.
