Big Cottonwood Plant Knows the Trick to Quality Water

Big Cottonwood water plant marks 16 years of delivering high-quality water and earning the Directors Award from the Partnership for Safe Water.
Big Cottonwood Plant Knows the Trick to Quality Water
The team at Big Cottonwood plant includes, from left, Mike Gill, lead operator; and Russ Ranck, Ed Powell, Mike Tabish and Jacob Maughan, senior operators.

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Big Cottonwood Creek flows through the BIG Cottonwood Canyon watershed that supplies Salt Lake City with drinking water.

The canyon offers fishing, hunting, camping, hiking, rock climbing, skiing and other activities. Its national forest is intermixed with homes. In the midst of all this is the 42 mgd Big Cottonwood Water Treatment Plant. Its operators are fortunate to have very high-quality source water, kept that way with a vigorous watershed protection program.

Built in 1957, the plant is one of three conventional water treatment facilities owned and operated by the Salt Lake City Department of Public Utilities. The others are the 40 mgd Parleys facility with 10 operators and the 20 mgd City Creek facility with eight operators.

The Big Cottonwood plant treats 40 percent of the drinking water for the city’s 380,000 people. In the early 1980s, it received a capacity upgrade from 28 mgd to 42 mgd. A new clarifier and receiving basin modification in the early 1990s allowed more wash water to be recycled to the head of the plant.

In 1998, a $4.5 million reconstruction project brought seismic, chemical, mechanical and electrical upgrades. More recently, the utility upgraded the creek-side intake structure. Designed by CH2M Hill, the intake uses a Coanda screen (Cook Legacy) that removes debris larger than 1 millimeter, while allowing full plant flows to enter.

“Our biggest challenge is raw water turbidity, especially during spring runoff,” says Mike Gill, lead operator. “It can fluctuate from 1 to 1,000 NTU. We meet our finished water turbidity goal of less than 0.10 NTU by making chemical adjustments and diligently paying attention to what’s going on.” The plant received the Partnership for Safe Water Phase III Directors Award in 1998 and has kept that status for 16 years.

Reconstructing the plant

The Big Cottonwood facility lies on the Wasatch fault line. During the 1998 seismic upgrade, the contractor replaced external walls with reinforced ones without removing the roof. Other improvements included a new chemical building and storage tanks, and new chemical feed equipment (replaced again in 2006). The filter building valves (Val-Matic) and actuators (Rotork) are also new within the last three years.

The upgrades have made the operators’ lives easier. Turbidimeters (Hach Filter Trak 660) ensure that the finished water meets or exceeds EPA standards. The PolyBlend polymer activation system (UGSI Solutions Inc.) adds polymer when turbidity reaches about .07 NTU. Flow controls keep the filter bed flow at a constant rate during backwash, preventing turbidity breakthrough.

The new intake structure is gravity-fed with no mechanical parts except for the intake gate valve. Water flows over a weir and through the Coanda screen. “This is really neat technology,” says Gill. “It is set at an angle that causes the debris that builds up to just fall off. It’s almost like a self-cleaning screen, with very low maintenance.”

Sodium hypochlorite generated on site (Process Solutions, Inc.) is added first to achieve EPA chlorine contact time requirements, since the first connection to the water system is a few miles away. “Before 2003, we used chlorine gas, which required a lot of documentation and safety procedures,” says Gill. “Then we started ordering concentrated hypochlorite, which was expensive but much safer. We began on-site generation in 2010. It’s much easier to generate our own.”

After chlorination, operators add ferric chloride, cationic polymer and lime. The water is sent to two treatment trains, with four-stage flocculation and sludge collection equipment (all Ovivo). From there it can enter any of the eight dual-media filters. The water is fluoridated before distribution.

Seasonal challenges

Plant operation changes with the seasons. In late spring and early summer, snowmelt runoff creates higher flows and much higher turbidity. “Our average operating flow is 15 mgd, with a high of 38,” says Gill. “We don’t exceed 38 mgd because the filter performance suffers. We only run the filters at the higher end during the May-July runoff months. By August, the level in the creek starts to drop.” During high demand in summer, the plant can draw from up to 65 wells.

“In the winter, the demand is lower, since people don’t have to water their lawns,” Gill says. “The creek level as measured by the 20-foot Parshall flume drops to about 15 to 20 cfs, a dramatic change from spring runoff season, when it can be 400 to 1,000 cfs.”

In winter, the operators drain one side of the plant and clean out the flocculation basins with a 180 psi fire hose to prevent buildup, then do the same thing on the other side. They also inspect the flocculators and drives. “We had a flocculator break once during a winter clean-out, and one side of the plant was down for two to three weeks for repair,” Gill says. They also walk the sludge collection bays and inspect the sludge collectors for loose bolts or a cracked flight.

Different strengths

The operators work as a team to solve problems. “We had struggled for years to get our chlorine feed to split equally to the two trains,” says Gill. “We feed the chemical right before it splits and, depending on the inlet flows, the water will distribute differently to the two sides.” The team recently built a new manifold in the inlet channel to enable small adjustments to the feed as plant flows change: “That was a team effort; we used several different operator ideas in the final design.”

Operators have a say on new equipment choices. “I attend meetings with management, and I pass along any equipment preferences,” Gill says. “The project goes out to bid, so we might not get the particular brand we had in mind, but we get equipment with the features we need.”

Gill started as an operator at the plant 18 years ago. After a few months, he earned his Grade 4 (highest) water certification and was promoted to lead operator in 2008. He reports to Bill Meyer, water treatment manager. Reporting to Gill are Jeff Brinck (nine years), Andrew Killpack (13 years), Dom Martin (three years), Jacob Maughan (two years), Ed Powell (21 years), Russ Ranck (21 years) and Mike Tabish (six years).

All operators perform lab tests for alkalinity, hardness, pH and chlorine residuals. They also calibrate equipment and do small repairs. Heavier maintenance is handled by the utility’s pump repair and electrical staff.

Team members bring different strengths to the job. Says Gill, “Jeff Brinck has a laboratory background and was able to suggest how we could improve our water testing methods. He was also helpful in explaining why certain methods were necessary and how the tests actually worked.” Other operators are skilled with computers or are mechanically inclined. All are Grade 4 certified and have worked their way up to senior operator. “They are go-getters,” Gill says.

Future plans

The plant is “running great,” according to Gill, yet several areas need improvement. “Sedimentation is a weak link, since we just don’t get enough sedimentation time at higher flows,” says Gill. “CH2M HILL did a study a few years ago and recommended plate settlers to improve the efficiency of the basin. We have requested money to be budgeted for this project, but it probably won’t happen for five to 10 years.”

Operators are awaiting a SCADA upgrade in 2016. “The old one is not reliable and requires diligence,” says Gill. “We’ve worked with it enough to learn that we have to watch more closely.

It’s mainly a communication problem between the computers, the PLC and the equipment.” The operators have been meeting with the Carollo Engineers firm to discuss SCADA design and offer opinions on options.

In the meantime, the team will continue to make great-quality water. “We’ve been told we have great-tasting water, probably because we keep the chlorine residual at 1.0 mg/L in the water leaving the plant,” says Gill. They will also continue with the Partnership program.

“We’re always looking to improve a process, and I enjoy going to other plants to see how they do things,” says Gill. “Turbidity will always be the thing to watch, although we have a pretty good handle on it. For the most part, our job is uneventful, because the longer you operate the plant, the fewer surprises it presents. And no operator likes surprises.”

Something Fishy

Operators at the Big Cottonwood Water Treatment Plant have some interesting companions: 20 Bonneville cutthroat trout. The fish live in a 55-gallon tank inside the plant, 5 feet from a control room, staffed around the clock 24/7.

A portion of the raw water entering the plant flows into the tank, and it’s very clean, since it comes from a creek fed by mountain springwater.

“The idea for the trout happened after Sept. 11,” says Mike Gill, lead operator. “In 2002, Salt Lake City was planning to host the Winter Olympics, so security was a big concern. All three
of our water plants have fish as a first line of defense, or bio-monitor, against any water safety issues.”

The Utah Fish and Game Department provides the trout, which are native to the area. “We have a large bag of fish feed that we buy at a local store, and the operators feed the trout twice a day,” says Gill. He is quick to point out that the fish are just an added safety tool: “Operator diligence and our raw water turbidimeter and pH meter are what we really rely on.”


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