A fine-tuned process and effective operator training help a North Carolina water plant win a series of honors for maintaining low turbidity.
The Robert A. Harris Water Filtration Plant keeps adding to its history of low finished-water turbidity. The latest milestone is the 2015 Area Wide Optimization Program award from the North Carolina Water Operators Association.
It was the sixth such award and fourth in a row for the plant in Eden, North Carolina. The drinking water source is the Dan River, a mountain river flowing through agricultural land. That could be a challenge, but the plant design coupled with attentive operation means turbidity readings remain well below the limit of 0.3 NTU. “I can’t think of a time when we’ve ever made it to 0.2 NTU,” says Dena Reid, plant superintendent.
The Dan River begins in the Appalachian Mountains in southwestern Virginia, then wanders through the hilly farm country of northern North Carolina before passing through Eden, about 95 miles northwest of Raleigh, the state capital. A pumping station sends raw water through 7,000 feet of 30-inch pipe to an 80-million-gallon pond where particulates can settle out.
At current usage that pond holds a seven-day supply of water. So, if turbidity in the river begins spiking because of heavy rains or heavy fertilizer use upstream, the utility can shut down the pumps and draw from the pond while turbidity returns to normal. Raw water typically measures 30 to 40 NTU. When it hits 200 NTU, the pumps are shut down. The flowing river keeps other potential problems under control. When the river slows, TOC can increase, and in a drought TTHMs can increase, Reid says.
From the pond, water flows into the rapid mixer where chemicals are added, and then into a flocculation basin. Next come seven sedimentation basins followed by seven filters that are the first point of chlorination. Fluoride, corrosion inhibitor, and more chlorine are added in the final step before distribution.
Next to the water plant are two 4-million-gallon storage tanks. There are five more tanks around the city, totaling 2.25 million gallons. The distribution system comprises 7,000 feet of 30-inch pipe and 11,000 feet of 24-inch pipe.
During summer the plant team adds alum, a polymer, and a pre-caustic to the raw water. In winter, the flocculation agent of choice is polyaluminium chloride because of its better performance in colder temperatures.
Although the 80-million-gallon pond settles particulates, it is not accumulating sediment quickly. A couple of years ago the city asked engineers to check how much had accumulated. In 37 years the pond had lost about 8 million gallons of capacity, so it will be a long time before the pond bottom needs cleaning, Reid says.
In addition to serving city residents and businesses, Eden supplies Dan River Water, which distributes water in the surrounding county up to 10 miles from the city limits.
Eden earned AWOP awards in 2010, 2012, 2013, 2014 and 2015. That missing year, 2011, in a way made the subsequent string of awards possible. Reid took over as superintendent in 2010. “We had a huge turnover in staff,” says Reid. “There were retirements and resignations as people went to other jobs. We have only eight people here.”
With all the new operators on staff, Reid needed a way not just to train them in the basics but to train them in a way of thinking. “To achieve the AWOP award, you need to be able to optimize your basin turbidity,” she says. “As long as you’re not over 10 NTU in the raw water, you should be under 1 NTU in the sediment basins at least 95 percent of the time. We set a higher goal: less than 1 NTU in the basins when the raw water was not over 20 NTU.”
To help her staff, Reid developed an excursion report that is filed when turbidity readings begin spiking in either a sedimentation basin or a filter. These are not simple reports that record the time and date of a problem. They are guides to help operators look at the system and troubleshoot it. It starts with turbidity in the sedimentation basins because optimization here is the key to achieving overall low turbidity readings, Reid says.
At the top of the report are the standard date, time, and other basics, but then the report becomes a checklist of points operators need to consider. “We’re trying to get everyone, especially new operators, to understand that if there is a bad reading, you don’t simply write it down and walk away,” Reid says. “You have to identify the problem that caused the reading.”
The first item on the sedimentation basin report asks whether there was incorrect calibration.
“They have to gain an understanding that equipment fails,” Reid says. “If someone is downstairs and bumps one of the turbidimeters, that can affect its performance.”
Lightbulbs on meters burn out, and meters can go out of calibration. The report form asks: Is there an air bubble in a turbidimeter? If the equipment checks out, the next report section asks about the chemical feeds of coagulant, coagulant aid and pre-caustic. At the bottom of the reporting form is a list of corrective actions to take: a jar test, a chemical feed adjustment, a turbidimeter flushing and cleaning, a calibration check, a sample flow adjustment.
“Operators have to see past the numbers,” Reid says. “Water treatment is not seeing a number and twisting a knob. You won’t see the same numbers every day because water changes. You have to think of water as an organism, a living thing. It will change, and an operator has to change with it and keep it happy.”
Teamwork is key
Reid is a Grade A operator, as is Melanie Clark, the chief operator. Also on the team are:
- Operators Keith Johnson, Grade B; Rodney Johnson, Grade C; Anthony Mock, Grade B; and Sammy Setliff, Grade A
- Relief operators Don Gelinas, Grade A; Will Clark, Grade B
Operators are strictly dedicated to operating the plant. Relief operators take over during vacations and other absences, and when they are not operating they perform cleaning, equipment maintenance and other vital functions.
When something goes wrong, everyone helps. In summer 2016, turbidity readings in the plant suddenly jumped above the 0.07 NTU alarm set in the plant. The operator went through the standard checks and found no reason for the high reading. He called chief operator Clark and they discussed possible problems. More team members came in, put their heads together and started walking through every inch of the plant.
The problem was under a grating, not clearly visible, where a 1-inch flocculent feed line joined a 36-inch pipe. The 30- or 40-year-old saddle holding the 1-inch line on had broken, and water was pouring out of the joint.
“This is a team,” Reid says. “No one individual runs the plant, and no one person is responsible for keeping turbidity under control. I don’t try to conquer any problem individually because I’m afraid my mind will close in, and I will see the problem only through my own perspective. That’s the way everybody’s mind works, and solving problems requires other people with different perspectives.”
Reid sees turbidity as the first sign that something may be wrong. It comes from her background. “When I started in water, I started at a plant that ran directly off the river,” she says. “When you work at a plant like that you get, I think, a better sense of turbidity challenges. There could be a downpour way upstream, and you never see it until suddenly you have muddy water coming in.
“I’ve gained a bit of a nickname around here. They call me the ‘turbidity Nazi,’ but that’s because I have high goals. If something is going wrong, you react. You don’t let the number increase just because the state allows it. And when a plant will naturally run with low turbidity, why not do that?”
Water for development
The Robert A. Harris Water Filtration Plant was built in 1978 as an 11 mgd facility. It was built partly to accommodate a MillerCoors brewery, a few years after Eden was created.
Previously, three cities occupied Eden’s location on the Dan River. Leaksville, Spray and Draper were independent cities, but in 1967 the residents voted to merge them and create Eden. A history of the county says the community’s economic progress is due to its position on the Dan, which is the city’s drinking water source, and the Smith River, which crosses the state border a few miles north of Eden, runs through the city and joins the Dan slightly upstream of the water plant intake.
In 1994, the filtration plant was enlarged to 21 mgd, but all that capacity is no longer needed. The departure of industry has reduced demand to 3 to 4 mgd. The MillerCoors brewery closed in fall 2016. The loss of customers brought new challenges: running a 21 mgd water plant at about one-quarter of capacity. It’s a balancing act, says Dena Reid, water plant superintendent.
Team members constantly turn the service pumps on and off. Filters running at less than 1.3 mgd aren’t compacted enough to lower turbidity, so operators run about 1.3 mgd through each of the plant’s seven filters in rotation. Once the two 4-million-gallon clearwells are full, the plant is shut down until demand requires more.
Meanwhile, development experts point to North Carolina’s population growth (5.3 percent from 2010 to 2015) and the potential for a strain on public water systems due to climate change. With excess capacity available, water is a talking point for Eden officials trying to attract new businesses. Says Reid, “I sure hope it works.”