Customized pump system solves compliance challenges for Montana water district
The small community of Carter, Mont., sits 100 miles south of the Canadian border. Some 200 residents within the north central plains are served by the Carter-Chouteau County Water and Sewer District, which also owns the county’s public water system.
The town’s water system was built in 1976 and comprises 48 miles of distribution piping, four boosting stations and a clean water transfer station. Despite upgrades in 2006 and 2007, the district came under a U.S. Environmental Protection Agency (EPA) order to install filtration or risk disconnection from the nearby Missouri River. The rural area relies entirely on the waterway to supply its domestic and irrigation needs. So, in 2012, the Carter-Chouteau Sewer and Water District launched the Carter Water Treatment Systems Improvement Project with a total budgeted cost of $504,000. The approved design was completed in June 2012. Construction began in December 2012 and the project brought the system into EPA compliance under budget and ahead of the mandated March 31, 2013, deadline.
“We had to reengineer our pumping operation in order to comply with the EPA’s Long Term 2 [LT2] Enhanced Surface Water regulations,” said Darin Arganbright, director of the Carter-Chouteau County Water and Sewer District. “We didn’t really have a problem, but compliance allowed us to create a better filtration process and modernize other elements of our system to make it safer for our residents.”
Improved Water Quality
The chosen solution was a custom-designed pumping system from Grundfos that met EPA requirements for improved water quality while eliminating the need and the sizable cost to construct a water treatment facility.
The Denmark-based global pump and pumping systems provider tapped its Grundfos Engineered Systems (GES) group to help the small community operation realize “big system” efficiencies, by integrating project engineering, intelligent controls, and vertical turbine and booster pumps as a comprehensive service offering.
“The project focused on the EPA-required water filtration treatment system, but the preferred solution would not have been possible without the Grundfos integrated pumping and controls system,” said Matthew Mudd, P.E., project engineer with Great West Eng. Inc. The Montana-based firm, which designed and oversaw the project, has provided similar engineering services for more than 25 years. “In the end, the project ensured a consistent supply of safe water with virtually no increase in energy costs—which is significant, considering the new system has more equipment, added filtration and two additional pumps.”
As with most water delivery systems, there were a lot of logistics to oversee, explained Joe Veches, distributor/pump specialist with Northwest Pipe Fittings, a Montana-based independent wholesale distributor serving three Midwestern states. Veches assisted during the design process by developing pumping specifications for the project. “The system draws water from the Missouri, filters it to make it potable, and then pumps it two miles upstream to the community’s distribution pumps,” he said. “The challenge the district faced with this upgrade was both pumping distance and elevation change.”
There were other hurdles during the yearlong project as well, according to the project engineer.
Maintaining Pressure Across Pump Stations
“In order to meet the EPA compliance deadline and maximize the district’s limited budget, we faced an accelerated and harsh winter construction period, where we couldn’t afford any delays,” Mudd said. “From an operational perspective, we have pressure limitations with the filter housings and variable head conditions associated with filter fouling. Therefore, we needed a system that could provide sufficient and reliable discharge pressures to achieve the required total design head from the first pump station to the next while managing the variable pressures across the filters.”
Mudd noted that the design team preselected three different cartridge filter manufacturers and models, which complied with Montana’s filtration requirements. The approved project bid included a HUR 3x170 up-flow cartridge filter system from Harmsco that separates dense solids with 1-μ pre-filters before they reach the parallel LT2 final treatment filters, which helps extend filter life.
“The district saved more than $1 million in total project costs by using the cartridges instead of a conventional mechanical water treatment process, and integration of the GES vertical turbines and booster pumps and their custom control system eliminated the need for a costly intermediate wet well,” Mudd said.
While the system saved money and was easy to operate, the selection of cartridge filters also presented some design challenges.
“Because of the river’s high sediment load, filters often clog, which can lead to a loss of pressure that can damage the filter equipment, and the piping if [the filters] get plugged up,” Veches said. “Moreover, the river’s particle distribution, temperature and manganese concentration fluctuate with the seasons, so the system had to accommodate flexibility in both filter treatment levels and chlorination amounts.”
Because the first pump house moves water several miles to the second pump house, the design team was concerned that, by the time the water was filtered, the system would not have enough pressure to reach the next pump house using a single pump setup.
“So, we designed a custom panel that would operate two vertical turbine pumps, which draw the water from the river and provide enough pressure for it to be filtered while not exceeding the pressure limitations of the filter units. They also control two vertical multi-stage centrifugal booster pumps that direct water to the very remote distribution pump house,” Veches said.
Integrated Pressure Boosting System
The system pressure is boosted via a BoosterpaQ Hydro MPC, an integrated pressure boosting system that offers up to six vertical multistage CR pumps in parallel operation, designed to optimize pumping efficiency over a range of flow rates. Ideal for water supply systems as well as industrial and irrigation applications, these integrated pumping systems utilize an advanced controller that, along with variable frequency drive (VFD) controlled motors, adjust pump speed and the number of pumps in operation to meet the frequently changing system demand.
Instead of using constant speed pumps regulated by maintenance-prone pressure reducing valves, the new system would deliver the minimal pump output necessary to achieve optimal performance—all without direct human intervention, an important consideration for the water district’s part-time operation staff.
“Rather than running flat out at top horsepower and bleeding off excess pressure to reach the desired output, the more energy-efficient option is to design a system that starts from zero and ramps up to meet the specific demand,” Veches said. “Demand is not a constant, [so] why not vary output?”
Mudd, Veches and others on the design team selected Peerless M8LB vertical turbine pumps to pump the water through chemical (chlorination and polyphosphate) and filter treatment stages while the boosting stations transported the treated water to the distribution system and a series of holding tanks. Grundfos acquired the Peerless Pump Co. in 2007.
“Over time, the filters foul and the GES system senses the differential pressures on each side of the filter train and notifies the water district’s operators when the filters need to be cleaned or replaced,” Mudd said. “On the downstream side, the vertical multistage booster pumps raise pressures from 60 to 100 psi, up to 176 psi.”
Removing the Guesswork
The control panel offers a standard remote monitoring feature so that operators can readily see pump status (on- or off-line), as well as the power consumption for each pump, which serves as one indicator of fouling.
“We could have built the system using older equipment, but the GES digital system, with a combination of flow sensors and pressure sensors, made it easier to engineer a smarter, more sophisticated system,” Arganbright said. “The VFDs take the guesswork out, automatically making adjustments based on pressure and flow. We’re now able to review actual system data and know our real-time performance.”
Another enhancement was the replacement of outdated and manually controlled chemical injection equipment with flow-paced pumps that give the water district the ability to fine-tune the injection of chemicals into the system. This upgrade alone increased monitoring accuracy, improved mixing efficiency and reduced the district’s chemical costs.
“Previously, we didn’t have a flowmeter, so it was kind of a guess on a daily basis as to where to set the chlorine level,” Arganbright said. “The new system has a flowmeter that tells the chlorine pump exactly how much to allocate based on a particular flow volume. Now we’re not wasting any electricity or chemicals having the pumps run full speed all the time, as it was before.”
According to project engineer Mudd, the project demonstrates that other small, rural systems with limited technical expertise can also easily operate cartridge filtration equipment and enjoy efficiencies common of larger operations. He noted that the project was recently awarded the Montana American Council of Engineering Companies’ “Honor Award” in the Water Resources Category.
“It’s a cost-effective system compared [with] a full-fledged water treatment plant. The most important thing is that we have safer water for our residents,” Arganbright said.