Fifteen and Counting

For the water utility servicing one of Minnesota’s Twin Cities, the Partnership provides a motivation and a method to improve every facet of operations.
Fifteen and Counting
Tom Blanchard, maintenance worker, works on pipes for the plant’s Vantage hydronic boiler (Fulton).

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For 15 consecutive years, St. Paul (Minn.) Regional Water Services (SPRWS) has been honored with a Director’s Award from the Partnership for Safe Water. But that doesn’t mean St. Paul is resting on its laurels.

Its remarkable record, matched by only a dozen other water utilities in the nation, serves only to motivate the team to keep improving the efficiency and performance of the McCarrons Water Treatment Plant and the distribution system. Having met high standards for turbidity control, and having sharply reduced taste and odor complaints, the agency now aims for even more pristine water, better treatment process control, greater source water protection, watershed improvement and more.

Jim Bode, supervisor of water quality, explains that, having met the Partnership’s Phase 3 requirements for a decade and a half, St. Paul is striving for Phase 4 recognition at the McCarrons plant and for Partnership Phase 1 classification for its distribution system.

A long journey

Standing at the large tabletop model of the SPRWS system in the tile-floored central room of the 1922 vintage filtration building, Bode and Che Fei Chen, water-quality specialist, point out how raw water moves more than 17 miles from the Mississippi River to the McCarrons plant.

Two 60-inch underground conduits transport river water to a chain of small lakes — Pleasant, Sucker and Vadnais — north of the plant. The water passes from lake to lake through a series of underground conduits and surface channels. Finally, from Lake Vadnais, it flows through a pair of 90-inch underground conduits to the plant on Rice Street in the northern part of the city.

Sucker and Vadnais lakes and their shorelines are owned and protected by SPRWS; swimming and boating are prohibited. Swimming is permitted in Pleasant Lake, although motorized boating is not. The public accepts the prohibitions, Bode says, especially in the post-9/11 era.

The surface water is supplemented by groundwater drawn from a series of 10 wells, drilled from 438 feet to 465 feet deep into the Prairie du Chien-Jordan aquifer. The well water cools the surface water and adds mineral content, which aids in softening and flocculation. On an annual basis, the ratio is about 90 percent surface and 10 percent well water.

Tough standards

At the plant, the incoming flow is coagulated with aluminum sulfate, then mixed with slaked pebble lime in a rapid-mix system to begin the softening step. After a three-stage flocculation process and sedimentation, the water is recarbonated with carbon dioxide.

Next come 24 biologically active granular activated carbon filters containing FILTRASORB 300 carbon from Calgon Carbon Corporation, removing particulate and enabling the plant to meet stringent turbidity standards. The filters, rebuilt and upgraded in 2006, also have dramatically reduced taste and odor complaints from the plant’s population base of 415,000.

Bode brings up a spreadsheet on his computer showing that before the filters were installed, taste and odor complaints could run as high as 250 per year — almost one customer phone call per business day. Now, the complaints number about one per month. “Our raw water tends to have a musty, beet taste to it,” Bode says. “It’s not a health risk, but the reduction in taste makes this a less stressful atmosphere to work in. Aesthetics are a big deal here.”

The filters still contain the original GAC media: “We haven’t had to replace any carbon yet. The bacteria are very diverse and still very active. As long as they’re happy, we’re happy.”

Finally, the product water is disinfected with chlorine, delivered as liquid by railcar and gasified via evaporation at the plant. It is ammoniated to form chloramines, which maintain the chlorine residual throughout St. Paul’s lengthy distribution system. “Chloramines are much more stable and persist throughout our system, preventing regrowth,” Bode says.

The chlorinators and ammoniators are from Severn Trent Services and Evoqua Water Technologies. The chemical feed pumps are Pulsafeeder.

For finished water storage, St. Paul maintains 111.5 million gallons of capacity in 14 elevated storage tanks and seven ground-level or underground reservoirs.

Always improving

Excellent turbidity performance and effective taste and odor control are just two examples of continuous process improvement at St. Paul. Just about all aspects of the treatment plant and distribution system are constantly analyzed for better performance. The plant’s automation system is a good example.

“We installed a SCADA system in 1998,” says Bode. “We’re constantly trying to upgrade the alarms, operator interface and architecture. Two years ago, we brought in Larry Larsen as a staff SCADA administrator, and we are making a full network switch from a Data Highway Plus network to Ethernet. That will improve our data processing speed, particularly in our chemical feed pumps and low- and high-service pumps, as well as our pressure readings in the distribution system and effluent monitoring for water-quality control.”

In the past, SCADA services were contracted out, but Bode prefers someone on staff working on improvements eight hours a day: “We have better control. It’s a very positive development.” The utility is also moving toward faster cellular connections for remote pump stations, tanks and towers: “We have been operating on privately licensed radio.”

Another initiative is source water improvement. In 2011, aiming to combat eutrophication, the agency installed an oxygenation system (Mobley Engineering) containing 3,000 linear feet of porous-hose oxygen diffusers in Lake Vadnais. It has worked, and a similar system is being installed in three of the deepest sections of Pleasant Lake. The diffusers can deliver 100 percent oxygen, keeping the water and sediment zones of the lakes in an oxidized state and tying up phosphorus in the bottom sediment.

“Our raw water has low turbidity with moderate natural organic material concentration,” says Bode. “After we installed the oxygenation system at Vadnais Lake, our raw water DO and redox potential both increased, improving coagulation and flocculation at the plant. The floc particles settle better.”

Better distribution

St. Paul is taking steps toward more efficient and effective operations in a number of other areas, including the distribution system, a 1,200-mile network of mostly older 6-inch cast-iron pipes.

Rich Hibbard, civil engineer, says the utility is also taking part in the Partnership’s Water Distribution System Optimization Program at the Phase 1 stage. At present, the emphasis is on main breaks, pressure levels and chlorine residual.

Hibbard says the team has done “a pretty good job” over the last 30 years documenting main breaks, which have run as high as 149 per year and occur mostly during the city’s frigid winters. The data goes back to 1980. The utility is now using the data to make correlations among a number of factors to estimate the likelihood that a given line will break.

Through a statistical model, SPRWS aims to predict potential breaks based on the size and age of pipe, the location in specific pressure zones, the operating pressure, soils and land use. “The idea is to predict the probability that a main will break, and that will help us make huge strides in our capital improvement plan,” Hibbard says.

Meanwhile, St. Paul is focusing a similar microscope on pressure issues. The distribution system contains 16 pressure zones, relatively isolated from each other. At present, pressure readings are taken at booster stations, but the Partnership standards include continuous monitoring of pressure zones. “We plan eventually to monitor pressures at the lowest and highest points in each of the zones,” says Hibbard. “We’re setting up a pilot project to do that, using Telog HPR 32 pressure recorders that can read pressure up to 20 times per second and can pick up daily fluctuations. If that runs smoothly, we’ll probably expand the program.”

Hibbard plans to use public park facilities to test the program, tapping into their plumbing systems and recording data via wireless signals: “It’s possible that pressure issues have been causing some of our main breaks.”

Looking ahead

Despite the progress and the honors, SPRWS looks ahead to new challenges and requirements. Bode mentions continued efforts to eliminate nitrification in the distribution system and to remove phosphorus from the source water supply, along with continued improvements in turbidity reduction, controls strategy, disinfection, solids thickening and dewatering, and filter backwash water profiling. The utility also keeps an eye on potential regulations, especially those limiting lead and copper. “Changes in those rules could be a challenge for us,” Bode says.

In late 2013, SPRWS issued a request for proposals for an asset management master plan for the plant and distribution system. “We expect a report back in May detailing what things need to be fixed first,” Bode says. “We want to look at the condition of the plant and whether we would have room for ozone for disinfection if needed. Our clarifiers are old and don’t have flowmeters on them. Our softening and settling processes are outdated, and they limit our capacity.”

Bode, Hibbard and staff expect the next round of improvements to help drive SPRWS toward President’s or Excellence Award recognition associated with Phase 4 in the Partnership for Safe Water program. “It will be tough, but we’d like to get there,” says Bode. The beat goes on.


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