The Northeast Sammamish Sewer and Water District needed a minimum of 500,000 gallons of additional storage, and a booster pump station and transmission main to redirect water to supply the new reservoir. As a result of a public outreach effort, the district decided to design the reservoir as a partially buried, reinforced concrete tank and dual-zone booster pump station on a site with a 0.29-acre buildable area. In addition, water quality sampling discovered arsenic at both supply wells and hydrogen sulfide at one supply well.
RH2 completed an analysis of several treatment alternatives for removal of arsenic and hydrogen sulfide based upon treatment effectiveness, cost and compliance with the district’s policy of providing a chemical-free water supply. The preferred arsenic removal alternative was iron-media sorption and the preferred hydrogen sulfide removal alternative was catalytic granulated activated carbon filtration. These alternatives were tested through a pilot study.
The reservoir was designed with a custom shape contoured to match site constraints and maximize the storage capacity. The booster pump station, treatment building and parking area were placed on top of the reservoir.
RH2 provided construction administration services and performed local and master SCADA and HMI systems design and programming. RH2 assisted the district in obtaining a Public Works Trust Fund loan, which provided funding for approximately 83 percent of the $5.87 million construction.