If you’re building a brand-new surface water treatment plant, facing new requirements for Cryptosporidium and disinfection byproducts, and importing technology that’s never been used in the United States before, you’d better have your operators on board.

At Butte-Silver Bow, Montana, operators were not only on board — they shared the driver’s seat as their water utility planned and commissioned the new 7 mgd Basin Creek water treatment facility last year. It was the first in the country to use ceramic membranes.

“Our operations staff was essential,” says Jim Keenan, chief operator. “They were involved with the pilot testing. Our maintenance man and electrician along with our operators built a pilot plant with an upflow clarifier followed by mixed media and ran it next to the membrane pilot. They were involved in the startup. They took part in training from the engineering firm (HDR), the membrane manufacturer (METAWATER USA), and the automation programmer.”

Operator Mark Reilly agrees: “It was quite a learning curve.” A veteran of eight years in the water treatment field, Reilly was familiar with the plate settler and clarifier technology in the district’s other two plants, but had no experience with membranes. 

“It was completely new, but participating in the startup and the commissioning was a good way to learn. It was mostly reviewing documents, then going out every day and figuring out how things worked.” Recalling an earlier career starting up plants in the polysilicon industry, he adds “It’s important to go slow. METAWATER thoroughly simplified it for us. They were here for about three months going over the computer screens.”

Water and Butte

The relationship between water and Butte goes back to the Wild West days. The mining boom of the late 1800s created a huge demand for water for gold, silver, and copper operations, while often leading to contamination of groundwater and surface water supplies. As early as 1891, Butte, recognizing the need for reliable sources and systems to provide for the growing community, formed the Butte City Water Co.

An early dam on Basin Creek provided some water, but not enough. In 1902, the Big Hole River/South Fork Reservoir was built, pumping water 27 miles across the Continental Divide to Butte residents and industries. A third supply from the Moulton Reservoir was added in 1907.

Surface water treatment plants followed at Big Hole (16 mgd) and Moulton (2.5 mgd) in the mid-1990s. Planning for the Basin Creek plant began in 2010 when the Montana Department of Environmental Quality ruled that filtration would be required to guard against Cryptosporidium and DBPs in water from the Basin Creek Reservoir, the utility’s third source. Historically, the utility had simply disinfected the water with chlorine gas and applied an algaecide as necessary on the reservoir.

Choosing membranes

“We positioned the new plant on land close to power and existing pipelines and at an elevation (5,710 feet) to maximize the potential for gravity flow through the plant and into the distribution system,” Keenan says. Pilot testing proved the effectiveness of ceramic membranes and indicated that they were durable enough to withstand the pressures of gravity feed to the plant. The manufacturer offered a 20-year full-replacement warranty on the membrane modules.

In the new plant, started up in the first half of 2017, up to 7 mgd of raw water enters from the Basin Creek Reservoir at up to 75 psi. Self-cleaning 300-micron basket strainers (Amiad USA) remove debris ahead of the membranes. A rapid-mix pump disperses chemical flocculants into the raw water while pressure is maintained through a hydraulic detention pipeline.

The ceramic membranes follow. Four 100-module units each contain 10 racks of 10 modules, for a total of 400 modules. Each module contains 269 square feet of membrane surface and produces 69 gallons per square foot of membrane per day. With a pore size of 0.1 micron, the membranes provide an effective barrier against turbidity, bacteria, and viruses. Periodic backwashing with air and water removes retained solids and deposits them in a backwash waste recovery tank.  

The filtered water (permeate) is collected in a pressurized pipe that moves the finished water from the plant to a standpipe, which maintains enough hydraulic head to transport the water to the distribution system by gravity.

Water recovery

Backwash water flows to the recovery system, featuring a plate settler provided by WesTech Engineering and a recovery ceramic membrane consisting of two METAWATER units with six modules in each (total of 120). Water recovered by the plate settler and the membranes meets the same quality standards as filtrate from the full membrane system and is discharged with the finished water. Backwash solids, along with solids retained by the membranes, are pumped to the utility’s wastewater treatment plant.

The membranes are cleaned weekly with a chemically enhanced 5 ppm solution, which is pumped into the backwash tank and then soaks the membranes for about 30 minutes. A full clean-in-place operation was originally scheduled for six-month intervals, but cleaning wasn’t required for at least the first nine months after startup. In a clean-in-place, a solution of chlorine (3,000 ppm) and citric acid (1 percent) is heated and allowed to circulate and fully clean the membrane surfaces.

The choice of the METAWATER units followed a competitive bidding process that included life-cycle costing. The recommended clean-in-place interval and the 20-year full-replacement warranty were other deciding factors, as was the manufacturer’s success with ceramic membranes across Asia. “The durability of the membranes and their ability to withstand upstream pressure of 75 psi was another important factor,” Keenan says.

Excellent product

Jim Dennehy, Butte-Silver Bow supervisor of water treatment, reports that the project cost about $30 million, paid for through the state’s Natural Resource Damage Program underwritten by settlements with the mining industry. Day-to-day operating costs are paid for through the utility’s rate structure.

“It’s worked out really well,” Dennehy notes, remembering boil orders from the distant past. “We’re all filtration now. Turbidity in water from Basin Creek is 0.009 NTU.” Operator Reilly says the whole system is operator-friendly. He and 10 others on the operational staff take care of all three of the utility’s water treatment plants, rotating every two to three weeks.

Besides Dennehy, Keenan, and Reilly, the team includes operators Randy Eldred, Don Hancock, Tom Stajcar, Joe Holland, John Kuchtyn, Zach Gleason, Dean Stringer, Tom Starcevich, Mike Waldman and Doug Wedlake; Ed Houchin, maintenance; and Chuck Lee, electrician.

At first the utility thought the Basin Creek plant would need 24/7 staffing, but that’s not the case. Operators are on duty eight to 10 hours a day including weekends. With the latest automation in place, the plant can be operated remotely. “I can see it on my phone,” Keenan says.

Lessons learned

In water treatment, it seems every silver lining has a few black clouds. Basin Creek has experienced a kink or two, but Keenan says, “We’re pretty good at solving problems here. During the startup period, we discovered a whole lot of entrained air in the filtrate.

“With gravity flow, we have no finished water tank, and we noticed that the water we were discharging looked really milky, not a good thing for our customers to notice from a brand-new plant.” At first the staff and engineers couldn’t figure out where the entrained air was coming from, but eventually they traced it to the backwash process.

“The units are designed to backwash every four to six hours with pressurized backwash water,” Keenan says. “We discovered they were backwashing too long.” When the cycle was completed, a large volume of pressurized air that had built up was released into the filtrate. An adjustment to the programming solved the problem, and the superaerated water was never discharged to the distribution system.

Another change in programming helped address an issue with the pair of membrane racks in the recovery system. Each of the racks undergoes a number of different sequences (backwash, chemical cleaning and others) at regular intervals, and when one rack is down during a sequence, the other accepts the full flow. 

Keenan says the transmembrane pressure data point was frequently getting too high and shutting down the recovery unit. When one of the two racks was going through a sequence, the operating rack would accept so much flow that it could never fully recover to its normal transmembrane pressure. “We worked with the programmer to smooth out the process,” Keenan says.

A third issue arose with the chemical feed system. “Originally, we were feeding a calcium hypochlorite solution,” Keenan says. “We were having trouble pumping the solution because the calcium hypo was mixed as a solid through a tablet feeder. It was forming a pasty material that plugged up the associated plumbing.” After trying to dilute the material and run the pumps at a faster pace, the team simply switched to straight sodium hypochlorite solution.

Stepping up

Basin Creek is enjoying its time as an embracer of innovative technology. Visitors from all over the world have come to witness the operation. The plant hosts dozens of engineering students from nearby Montana Tech, and the plant has received several awards including the 2018 American Council of Engineering Companies Grand Project Award, and the 2018 ENR Best Water Project Mountain States award.

Credit for this mile-high success story can be traced directly back to the beginnings of plant design and construction and, most important, operator involvement. “We have operators on our staff who’ve been here for 30-plus years, and some who are much younger,” says Dennehy, who has 34 years with the utility. “They all adapt to new technology differently, but everyone has accepted their new roles.”

Keenan observes, “Our guys really stepped up. They had an idea what was coming, and they saw what was coming. I remember our first meetings with the design engineer; I think they were really surprised because our operators, as well as our maintenance man and electrician, were so involved and peppered them with many questions and ideas. They’ve done an awesome job.”

Relying on gravity

Butte-Silver Bow (Montana) has put Newton’s first law of gravity to productive use, saving costs in transporting water around one of the most complex water systems in the United States.

The utility maintains seven pressure zones and moves water across the Continental Divide near Feely for the Big Hole source, and across Fish Creek for the Basin Creek source. At Basin Creek, the reservoir lies at 5,887 feet elevation when full, and the Basin Creek treatment plant is at 5,710 feet. Just as Newton’s apple fell, water flows downhill from reservoir to plant and enters at up to 75 psi.

Water flows through the plant by gravity, and produced water is discharged to a standpipe that in turn supplies water to customers by gravity. As the standpoint empties, the membrane filters automatically increase output, operating essentially on an on-demand basis. “We don’t have a finished water storage tank,” says Jim Keenan, chief operator. “We operate most of the year on gravity bypass.”

Two additional structures built along with the treatment plant have improved the distribution system. A new pressure relief valve at the point of entry to the distribution system has replaced an older one that was wearing out. The new 4 mgd Southside Pump Station allows the utility to move Basin Creek water into any of the city’s other pressure zones as needed.

“The Basin Creek Reservoir supply often exceeds Basin Creek pressure zone demand,” Keenan says. “The new pump station also allows us to displace water from the Big Hole Water Treatment Plant in the spring when the Big Hole source water is most difficult to treat.” In the other seasons, as long as reservoir water remains plentiful, Basin Creek production is maximized because it is more economical than the water from the Big Hole source.