The new reservoir and treatment plant for the City of Port Townsend’s water system are taking shape. City Manager David Timmons anticipates the new treatment facility would begin testing and commission in October, and be fully online delivering water early in 2017.

Two projects are being built side by side: a water treatment facility and a 5 million-gallon reservoir. The reservoir project is replacing the existing city reservoir, built on an adjacent site in 1979. Plans for removal of the 1979 reservoir – not seismically reinforced and nearing the end of its service life – are still under discussion.

The new treatment plant, mandated by the state Department of Health because of more stringent regulations on surface-source drinking water, uses a membrane filtration system. The treatment regimen is needed to meet state and federal mandates for adequate treatment for the cryptosporidium parasite, which is resistant to the city's current chlorine treatment.

Once operational, the new plant is to replace the existing city treatment plant. The city gets its water from a 37,361-acre watershed in the Olympic National Forest that drains into the Big and Little Quilcene rivers.

Funding for the two projects, originally budgeted to cost $26 million, comes from a combination of state grants and low-interest loans from the Drinking Water State Revolving Fund and Public Works Trust Fund. The state recently forgave $2 million of the loan amount, and the overall project is expected to come in under budget at $23 million. Local match funding comes from capital surcharge fees added to every bill of city water system customers; Timmons notes that once the loans are paid off, customers no longer pay this surcharge.

SEISMIC FEATURES

The reservoir is being built to withstand a major earthquake, using a special design and wrapping process. DN Tanks, a California-based company that specializes in design and construction of large stressed-concrete, earthquake-resistant reservoir tanks, is the subcontractor handling the stressing process. The company builds about 30 tanks a year. The 160-foot-diameter tank – poured in place, with 264 sets of diagonally wrapped reinforcing cables in the 10-inch-thick walls, in place of traditional rebar – is isolated from the tank bottom using compressed neoprene padding. Vertical tension is provided by 132 threaded tension posts, tightened down as the concrete cures.

Once the tank concrete has cured sufficiently, the entire tank exterior is wrapped with about 185,142 feet – nearly 35 miles – of 3/8-inch galvanized steel cable, tensioned to 14,950 pounds. The seven-strand wire, wrapped around and around the tank like a giant spool of thread, acts to counteract the pressure of the water from inside the tank.

“Concrete is not great in tension” said Nick Belmont, regional manager for DN Tanks. “Eliminate the tension, and this design has a 100-year seismic life.”

A purpose-built machine circles the tank, slowly rolling out wire from a spool at 200 feet per minute, tensioning it as it goes. Spool ends are locked off at an “anchor tree” of steel anchor points cast into the tank side, and a new spool is attached to the previous wire using special “finger trap”–type wedge fittings. If any manufacturing flaw is discovered in the wire, the entire spool is rolled back and a new one started. A monitoring system records the wire as it is wrapped, making a permanent record of every inch of the wrapping process.

Once the wrapping process is completed, a layer of spray-on “shotcrete” concrete is applied over the wire wrap, encapsulating and protecting it. Then, a second layer of tensioned wire is wrapped over the first, which is also covered with shotcrete concrete spray and waterproofed. The finished tank is then topped off with a 10-inch slab roof, made in panels. Interior baffling ensures that water stored in the reservoir is circulated "first in, first out."

The tank design has proven itself in significant earthquakes. According to DN Tanks, 27 of its water tanks – all built using a similar process to the one being used in Port Townsend – were located within 30 miles of the epicenter of the 1994 magnitude 6.7 Northridge Quake. Not one of the tanks had a structural failure, in an area where many older steel and unreinforced concrete tanks failed.

MEMBRANE FILTRATION

The new water treatment plant features three banks of membrane filters that filter out particles larger than 0.04 microns, small enough to remove almost all organic contaminants. Each filter bank can handle 1.5 million gallons of water per day. Only two filter banks are used at a time, allowing flexibility in taking a bank offline for maintenance; the assemblies can be expanded if the city's water needs grow. City water is still disinfected ("chlorinated") using sodium hypochlorite; retention time is provided by the baffling system inside the new reservoir. According to Ian Jablonski, city water quality specialist, if the measurable residual chlorine levels stay as anticipated, less chlorine may need to be used than in the present water treatment system, reducing operating costs. The City of Aberdeen uses the same filter system and has seen this result.

The filters are backwashed daily, flushed with sodium hypochlorite once a week, and have a full, heated cleaning every six weeks. Backwash water would be removed via the sanitary sewer lines, adding 35,000 gallons of water to the sewer load. Jablonski explained that poor permeability of the glacial till soils at the site prohibited creating an infiltration system to handle backwash water.

The new reservoir and treatment plant are located on city property near 20th and Rainier streets, between Discovery Road and the back of the Hamilton Heights neighborhood off Hastings Avenue. City Manager David Timmons noted that while building the construction access to the site, the city had brought all utilities into the area, making nearby parcels easier to develop for future housing.

A new bike path now connects the Hamilton Heights neighborhood to Discovery Road, near where the new Howard Street roundabout is to be built next year.