A leaky reservoir that holds treated wastewater could mean a $6 million repair bill for Carson City.
Brunswick Canyon Reservoir, in a remote area at the eastern edge of Carson City, holds 3,000 acre feet of water, but has been leaking half of its contents each year for several years.
That's about one-half billion gallons annually. Seven million gallons of treated effluent go into the reservoir each day.
Water from the reservoir is used to irrigate city parks, golf courses and the state prison farm during all but the winter months.
The Nevada Division of Environmental Protection cited concerns over nitrates seeping into the groundwater and told the city the reservoir needs to be lined with an impermeable synthetic liner.
"There is no immediate health or environmental concern, but there is the potential," said Joe Maez, an engineer with the division's Bureau of Water Pollution Control.
"The seepage rates that are showing up are well beyond our standards," he added.
The reservoir was built in the early 1980s, when sealing wasn't required, according to City Engineer Larry Werner.
"Effluent quality wasn't a big thing then, but environmental folks have gotten more concerned since then," he said.
"The concerns are nitrates. They're highly mobile, they follow water," he said.
It will cost more than $2 million to line the reservoir, but the city will need to build a temporary reservoir to store the water while repairs are made. The total impact could be anywhere between $5 million and $6 million, he said.
"Finding another site and building a dam is going to be costly. It may be more cost effective to just walk away and build a new one," he said.
Werner said he will take options to the board of supervisors in March or April.