Carson looks to west side creeks to strengthen city's water supply

Surface water is the key to maintaining a good water supply in Carson City.

Carson City balances tapping surface and groundwater to keep the water flowing out of the tap. Preferably, the Utilities Department looks to surface water which made up 59 percent of water consumed last year.

During the winter months, in fact, the city can serve all its customers with only surface water, allowing winter snows and rains to recharge the aquifers.

As the name indicates, surface water refers to water drawn from streams, rivers and lakes - in Carson City's case, primarily the creeks in Kings and Ash canyons with additional supplies from the Marlette and Hobart reservoirs in the Carson Range and the Carson River.

Groundwater comes from the city's 24 wells, which tap into the underground aquifers.

"Groundwater is a natural storage reservoir," said Tom Hoffert, the city's utilities operations manager. "Once you tap into it and use it, you lower the amount of water, which takes several years for nature to replenish."

Surface water, on the other hand, is a source that flows by regardless of whether Utilities use it or not.

"What we're doing is not letting as much of the water flow by," Hoffert said. "If you don't use surface water when you have it, it's lost and gone forever."

Typically, Utilities has to start pumping the wells in March. Groundwater remains a prime water source through the summer months until October. Lawns and agriculture increase water usage four-fold in summer, from about 4.5 million gallons a day in winter to a peak summer demand of 20 million gallons a day.

Hoffert has three projects in the works this year on the west side to shorten the city's need for groundwater by at least a month and at the same time help Mother Nature in boosting the underground water table.

Water flowing in the west side creeks is the key to accomplishing this.

-- The city earlier this year signed the Marlette-Hobart Agreement with the state that guarantees the city a minimum of 525 million additional gallons of water a year from the state-owned Marlette and Hobart reservoirs.

These reservoirs could supply Carson City with upward of 900 million gallons of water to which Utilities did not previously have access. The Marlette-Hobart Agreement gives the city enough water rights to have a comfortable water supply for 75,000 residents, the projected population when all the land available for development is used up.

-- The city's Quill Ranch Water Treatment Plant's operation permit, however, doesn't allow for the treatment of enough water to handle the new Marlette-Hobart supply. Hoffert in August plans to apply for permission to double the plant's treatment capacity from 3,200 gallons per minute to 6,400 gallons per minute.

-- Extra treated water requires extra storage. Instead of building more steel storage tanks, Hoffert proposes injecting the excess treated water into the city's aquifer to strengthen the groundwater supply.

"We want to maximize the use of Marlette-Hobart," Hoffert said. "The full benefit of that water has not been realized by Carson City. That's the key."

Hoffert said all this new water will come with no rate increases needed and no capital expenditure funds will have to be spent to double the capacity of the water treatment plant.

Quill Ranch already has the equipment to double treatment capacity. All Hoffert needs is a permit from the state Bureau of Health Protection Services to rerate the treatment capacity from 3,200 gallons per minute to 6,400 gallons per minute.

Quill Ranch was built in 1992 with a new water treatment technology. Because the diatomaceous earth technology didn't have much of a track record then, the state only permitted Quill Ranch to operate at half speed.

"We've always known that we're going to rerate this plant," Hoffert said. "Until we had the additional water from Marlette-Hobart, there was no need to rerate."

Hoffert has to prove that the process can effectively treat water at the proposed new volume. He said an American Waterworks Association study shows an increased filtering ability for the powder and other cities, such as Fontana, Calif., have proved that the process produces good water at the increased output Hoffert seeks.

The goal is to supply customers with water containing less than .5 nephelometric turbidity units. Recently, Quill Ranch produced water with only .148 units.

The creeks in Ash and Kings canyons already produce rather clean water. The raw water turbidity level now is about 1 and at its worst doesn't exceed 6 units. Hoffert said some treatment plants in big cities start with water carrying 200 turbidity units.

Diatomaceous earth is a white powder mined near Lovelock that consists of fossilized plant life. Moistened D.E. is caked onto a round, 5-foot-diameter stainless steel mesh and this combination serves as the water filter.

Raw water forces its way through the D.E., which removes turbidity, bacteria, giardia and viruses to make the water safely drinkable.

Quill Ranch has four enclosed cylinders about 10 feet long that each hold 35 such discs coated with the white powder to the thickness of one-eighth to one-quarter of an inch.

The plant now can treat 4.6 million gallons a day - the same amount of water the city's population uses in winter. Groundwater supplies the additional water needed in summer and the water drawn from wells does not need to be treated, Hoffert said.

Once the plant is rerated, Quill Ranch will be able to treat 9.2 million gallons a day.

"When the water's there (in the creeks), we'll be able to treat the water that's there," Hoffert said. "We saw during the last four years, when we have heavy runoff, we have upwards of 5,000 to 6,000 gallons a minute coming down but we could treat only 3,200 gallons."

Since the creeks only produce water at such a rate during winter and spring, Quill Ranch will produce extra water during those seasons.

Hoffert intends to store that water for when its needed: summer.

But he doesn't plan to add to the city's 11 storage tanks to hold the new Marlette-Hobart water. Instead, Hoffert wants to inject the treated water into the underground aquifer.

A storage tank costs about the same amount as drilling the well: $300,000. The tank, however, can hold only 4 million gallons while Carson City's underground aquifer has an indefinite capacity far beyond that.

The Utilities Department now is equipping a 405-foot deep aquifer storage and recovery well drilled recently in Kings Canyon. This well will be able to inject and remove water at the rate of 450 gallons per minute - the rate of a medium production well in Carson City.

The water level at this well will definitely rise but Hoffert believes the underground aquifers are linked and that water injected in Kings Canyon could increase water level at other wells.

Injecting water in the aquifer will allow the Utilities Department to have more control of the underground water table. During the last seven-year drought, nature only recharged the aquifer at one-fourth the rate water was pumped from the ground.

"We can sustain a higher ground water level for summer," Hoffert said. "During wet years, we have an ample supply of surface water. During arid years, the underground reservoir has not recharged to the levels we saw the previous year."

On the other hand, two years ago the groundwater basin was so full that some basements flooded. Extra water, obviously, would not be treated in those years.

"We have to prove the water quality, prove the impact on the aquifer, prove the ability of the aquifer to receive the water, and we have to prove when we can put water in and when we have to stop," Hoffert said.

The Nevada Division of Environmental Protection and the state Bureau of Health Protection Services both need to sign off on this concept. Hoffert hopes to start injecting treated water into the aquifer in September 2001.

"With this in place, it makes Carson City more drought resistant by giving Carson City more avenues for meeting the city's production needs," Hoffert said.


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