$10 million FEMA grant to improve Marlette dam, Carson water

On Oct. 22, U.S. Sens. Catherine Cortez Masto and Jacky Rosen, both Democrats representing Nevada, announced the Silver State would receive a $10 million grant from the Federal Emergency Management Agency “to enhance the safety and functionality of the Marlette Lake Dam, reducing the risk of a dam breach during an earthquake,” according to a news release.

The Nevada State Public Works Division, the grant sub-applicant, has undertaken a yearslong project to fortify the historic dam of the mountain lake, which sits around 7,800 feet in the Carson Range and supplements Carson City’s drinking water.

“I am proud to see these federal funds come into our state to make essential improvements to the Marlette Lake Dam and better resist an earthquake,” said Cortez Masto. “These funds will help protect our water supply in Storey County and Carson City while keeping Nevadans safe and healthy.”

According to the State Public Works Division (SPWD), total construction costs are around $20 million, and the state of Nevada has allocated $13.4 million for planning and construction of the project, plus the FEMA grant.

“SPWD is proposing to stabilize Marlette Lake Dam to reduce hazards from seismic events by enlarging the downstream embankment with fill, replacing the existing corroded and leaking outlet works, and raising the crest of the dam to address freeboard deficiencies,” reads a 2024 environmental assessment from FEMA. “SPWD is also proposing to replace the aging spillway, which is currently undersized and open to snow and debris that could restrict emergency flows, with a covered concrete box culvert.”

What are the “hazards from seismic events?” According to the FEMA assessment, “The Marlette Lake Dam is in an area of high seismic hazard. Annual inspections indicate a high probability of a dam breach should there be an earthquake of magnitude 6.5 or larger because of the age and condition of the dam.”

The assessment says the Marlette Lake Dam is classified as a “High Hazard Dam” in the National Inventory of Dams kept by the U.S. Army Corps of Engineers.

“A dam breach of the Marlette Lake Dam would cause substantial damage to the dam and the existing structures, roadways, and infrastructure downstream, including State Route (SR) 28 and a sewage effluent pipeline that runs beneath the road,” reads the assessment. “A dam breach could jeopardize the health and safety of people downstream, while also impacting the ecology and water quality of Lake Tahoe and the delivery of water to Carson City and areas of Storey County and Lyon County.”

The lake must be lowered or “dewatered” for construction purposes, the assessment says.

“SPWD assumes that the lake drawdown process would begin in October 2024 and end in March 2025, at the latest,” reads the assessment. “Major project construction would extend from May 2025 through October 2025, after which the cofferdam would be removed to allow the lake to begin to refill, and the site would be stabilized and remain inactive during the following winter.

“In May 2026, final construction of the mechanical control building and minor appurtenances, in addition to capping, would be completed and the site would be restored by summer 2026. The lake is expected to take approximately 6 years to naturally refill, depending on annual precipitation.”

Although Marlette Lake contributes to Carson City’s water supply, the city is prepared for the long wait as the Quill Water Treatment Plant in west Carson undergoes a major revamp for more capacity.

In September, the Carson City Board of Supervisors approved a $22.8 million contract with Farr Construction Corp. for a new filtration system and structural improvements at the plant. The project will increase the plant’s capacity to treat surface water from nearby creeks and the Marlette system from 1 million gallons a day to 4 million gallons a day. Expected to be completed in 2026, the Quill project will include space for an additional filter vessel that, if installed, would increase the plant’s capacity to 6 million GPD.

Carson City Public Works officials have maintained more potable water from surface-water sources well help conserve groundwater sources from municipal wells. Carson City Utility Manager Andy Hummel previously explained how the Quill project will comport with the state’s ongoing work on the Marlette system. The city could add another filter train when the state’s project is complete.

“Carson City’s use of the Marlette water system has historically been up to 2,000 acre-feet of water per year,” Hummel told the Appeal on Oct. 23. “Due to raw water quality and the ability of Quill Treatment Plant to treat that water, we’ve been able to treat and use typically half or less than that in recent years — this has highlighted the importance of the upgrades to Quill to maximize our use of the available water.”

Hummel said the Marlette system includes Marlette Lake, Hobart Reservoir “and what we call the east slope springs.”

“We will still get some of that water with Marlette down for rehabilitation, but it will take a number of years to get the full amount back as Marlette fills back up,” he said.

On the FEMA grant, Hummel added: “We are in full support of the state’s efforts to improve the reliability and resilience of Marlette. This grant will help in meeting those goals.”

The Marlette system dates to the 1800s and the Comstock boom.

“Marlette Lake was constructed in 1873 when a small earthen dam was erected at the outlet of a broad glaciated-basin that naturally drained into Lake Tahoe,” according to the Nevada Department of Wildlife. “In 1959, the dam was raised reaching its present height of 45 feet. The lake has several uses; water is conveyed via a series of open flumes and pipes (inverted siphon) to Virginia City for domestic water use, along with supplying Carson City with drinking water.

“The state of Nevada purchased Marlette Lake and the surrounding land in 1963, allowing for backcountry recreation. Fishing was then allowed in 2006. Finally, the lake is used as a brood lake for rainbow and cutthroat trout where spawning operations occur annually and offspring are used to stock waterbodies around the state.”

Protecting fish from the lake drawdown — NDOW confirmed hundreds of trout have already been relocated into nearby Hobart and Spooner Lake — and a cultural resources survey are part of the dam project, according to the FEMA assessment.

Nevada State Parks points to the rich history surrounding the water system.

“Initially developed in 1873, an ingenious water system furnished the water required by extensive steam engine operations of the mines and the nearly 30,000 people of the boom towns,” according to state parks. “The system was comprised of Marlette Lake, Hobart Reservoir and an intricate system of wooden box flumes and pipelines. The Marlette Flume and another flume from the north entered a 3,994 foot tunnel that emptied onto the east side of the Carson Range and joined the Inverted Siphon, the key pipeline through Washoe Valley.

“This 813 psi pipeline was the highest pressure pipeline in the world at the time and represented an engineering feat that most thought could not be done. At its peak, the water system delivered up to 10 million gallons a day to the Comstock.”