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Staying thirsty: Denton’s water origins

Staying thirsty: Denton’s water origins

Staying thirsty: Denton’s water origins
July 10
11:33 2015

Erica Wieting | Senior Staff Writer

@ericawieting

What does water taste like? Some argue that it doesn’t taste like anything. Others claim hints of fruit and vegetables. But in Denton, the consensus is that it just tastes good, and the taste of the water has everything to do with where it came from.

“One of the biggest factors that plays into water quality is keeping contaminants out of our lake,” said Kathy Gault, City of Denton Water Production regulatory coordinator. “It is easier to keep them out than to remove them once they get in.”

Contaminants include litter, chemicals, oils and other substances harmful for people to ingest. Denton utilizes two separate water treatment plants to remedy this: the Lake Lewisville Water Production Plant and the Lake Ray Roberts Plant.

Step 1: Filtration

Before it can be consumed or used to wash our dishes and clothes, lake water goes through a series of filtration and disinfection procedures. Randy Markham, water production superintendent at the Lake Lewisville plant in Denton, said the first step in water clarification is to sift out unwanted particles in the water, which is done through the use of a filtration system.

“It can also take care of organics in the water,” he said. “So it could possibly take care of something like pesticides or herbicides that get into this part of the filter to the plant.”

Most of the particles are caught within the first few inches of the filters, which have about 4 feet of water on top of them. It’s the microscopic particles in the water like clay, Markham said, that want to stay in suspension all the time, easily slipping through the filters. So they need to plan accordingly.

“The City of Denton water production plants treat their respective source waters with ferric sulfate to coagulate and remove the suspended particles in the water,” Gault said.

Suspended particles in the water carry a negative charge, Markham said, so they perpetually bounce off of each other like opposite ends of a magnet. When the iron-based chemical ferric sulfate is added to the water, it loosens these particles and creates coagulation.

The suspended particles then go through a process called flocculation, Markham said. This involves the addition of a man-made chemical or polymer, which has a high positive charge. Because there are now positive and negative charges in the water, they are able to form larger units making them bigger targets for the filters. At the plant, Markham said, this material is called “floc.”

“We add [the chemicals] at the very beginning of the process,” Markham said. “We have to put them in the water and rapidly mix it together so all the chemicals are able to mix with all the dirt that’s in the water.”

Step 2: Settling

Basins outside of the plant allow water to move toward its next destination. Three mixers in each of six basins stir the water at slow speeds as it moves. The basins, Markham said, are about 15 feet deep. Each basin has an individual capacity of about 500,000 gallons of water.

“One of the things we’re concerned about is making sure that all the water has the same time to mix, and then all the same time to settle,” Markham said.

A major factor in the mixing of the water, he said, is making sure the water flows out of the basins at the same rate as well. This is done through the installation of v-notches, called weirs, on the edges of the basins.

Markham said without weirs the water could short circuit. The weirs also prevent water from sloshing over the sides in windy conditions.

“You can have this stuff kind of come back up,” Markham said, “And then that would make your filters get dirty quicker.”

Step 3: Disinfecting

The chief disinfectant currently used at the plant is called ozone, a substance about 1,000 times stronger than chlorine, which the plant used to use.

“Ozone is being used because of cryptosporidium and giardia, which are little particles in the water that come from cattle or sheep,” Markham said. “If you don’t do a good job of getting those particles out of the water, [they] can get all the way through a filter.”

Chlorine is not strong enough to kill particles because they have hard shells.

“Some people are using ultraviolet light, [which] will basically make it sterile to where it can’t reproduce,” Markham said. “We’re using ozone to destroy it.”

The plant maintains water quality by leveling pH. A level of seven is considered neutral. The plant raises the pH of the water to prevent it from becoming corrosive, which could erode pipes.

“It’s not a very efficient process,” Markham said. “That’s just the way it goes.”

When ozone is obtained, it is sent to a vaporizer, which raises the compound from about -320 degrees Fahrenheit to a gaseous state at 60 degrees Fahrenheit.

“We’re dissolving ozone into the water and disinfecting the water,” Markham said. “Ozone does its job and there’s no residue. It’s gone real quick. We bubble that into the water just like in a fish aquarium, where you’ve got the little rock and the water [and] the air’s bubbling through the rock.”

In any building at the plant where ozone is being used, sensors detect the amount of ozone in the air. If more than two sensors detect a high level of ozone, the machine is automatically turned off.

“It’s saying, ‘You’ve got a leak, it’s dangerous, shut it down,’” Markham said.

Step 4: Distribution

The Upper Trinity Regional Water District is located in Lewisville and supplies water to the area of Denton County—but not to the actual city of Denton.

“The city of Denton has their own drinking water plant,” said Brian Kelm, Superintendent of the Lakeview Regional Water. “They provide to the city itself.”

The Lakeview Reclamation Plant, Kelm said, supplies to the surrounding area in cities like Corinth and Flower Mound.

Markham said Denton supplies about 500,000 gallons of water to Sanger every day and 400,000 to Krum.

“We own the pipeline that goes to Krum, but the water is city of Denton water that goes through the pipe,” Kelm said. “That one’s an unusual one.”

Markham said before 1997, Denton sold water to Lake Dallas and Corinth.

During the summer, the plant sends 33 million gallons of water per day to surrounding areas. In the winter it dispatches about 17 million.

A 54-inch pipeline runs from the Lake Ray Roberts Production Plant to Denton. Operators at the Ray Roberts and Lewisville plants are in constant communication with each other and processes at each plant are extremely similar. Between the two plants, Denton consistently wins awards for the tastiness of its water.

“We’ve won best in state a couple times,” Markham said. “A more recent one we like to do is the Texas American Water Works Association that has a taste test.”

This year the city came in third.

“Our goal,” Gault said, “is not only to meet, but to exceed, water quality standards at the state and federal levels.”

Featured Image: Toward the end of the process, water is almost completely clear. Erica Wieting | Senior Staff Writer

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