Water Treatment Plant GAC Project for Town of Friday Harbor, WA: 2010 - The Town of Friday Harbor is a full service city which includes a water utility. The water department owns a watershed and reservoir on the west side of San Juan Island and uses surface water from the reservoir as its primary source. This surface water is treated at the Town's mixed media rapid sand filtration facility, also on the west side of the island, and piped 4.5 miles to the Town's water department facility via a 12" transmission main.

The system has worked well in the past, but with enforcement of progressively lower limits on trihalomethanes, the Town began having trouble consistently meeting MCL's. This was primarily due to seasonally high organics passing through the filtration process, then having ample time in contact with post filtration chlorination while traveling to and through the Town's distribution system, for THM's to form in the system.

After consideration of a range of alternatives, the Town decided to add granular carbon adsorption to the process chain. It was felt that doing so would not only be a solution to the THM problem, but would also help with taste and odor complaints that accompanied the seasonal conditions that led to it. The nearby Roche Harbor water utility had had similar problems, and had met with great success by installing GAC adsorption.

The project consisted of installation of a new Calgon Model 10 granular activated carbon adsorption system within a pre-engineered metal building having a concrete foundation capable of supporting the new tanks fully loaded with granular carbon and water. Other work included piping (exposed and buried) and valves to connect the activated carbon system into the existing water treatment system, civil work around the building, and site restoration.

The process unit is manually controlled and consists of two steel tanks approximately 20 feet tall and 10 feet in diameter, a valve tree allowing selection of lead-lag configuration and choice of parallel or series flow, connection piping to the existing system allowing total or partial by-pass of the new system if desired.The project was bid and awarded to Faber Construction of Lynden, WA for an after tax cost of $571,447.80.

Wayne Haefele & Associates provided construction inspection, on-site construction management and start-up support for the Town of Friday Harbor on this project. Wayne prescribed the disinfection dosage, flushing, and dechlorination method before the units went on line, performed verification sampling and testing during flushing of disinfection water and performed bacteriological sampling before and after the media was loaded. During start up Wayne provided support to the plant operators, working with them to develop protocols for backwashing, bringing the units on line and managing flows and pressures in conjunction with the existing rapid sand filters. This project was completed below the bid cost at $568,170.75 in July of 2011. It was a roaring success, completed on time, below budget and exceeding all water quality goals.