Stormwater System Helps Keeps Tahoe Blue

Straddling the state line between Nevada and California, Lake Tahoe rests at a surface elevation of 6,225′ in the Sierra Nevada Mountain Range. Considered one of the most pristine large lakes in the world, the lake’s water is 99.994% pure, according to the Tahoe Fund, an environmental group that supports projects around the Lake Tahoe Basin.

The Nevada Tahoe Conservation District and the Nevada Department of Transportation want to keep Tahoe pristine. When the district needed a stormwater solution to combat serious sediment runoff from Highway 431 that could potentially threaten the iconic lake, it reached out to Jensen Precast to make it happen.

“We got a cold call from the Nevada Tahoe Conservation District,” says Ramsay Salter, Jensen Water Resources Project Manager, who was the lead engineer on the Highway 431 project. “I worked with a professional engineer at the district, and we put together a plan of attack to complete it. I provided her with direct engineering services, including various hydraulic calculations. I kept a very open line of communication with her. We worked well together on this project.”

Sediment runoff from natural hillside erosion, combined with NDOT’s safety practice of spreading traction sand on Highway 431, was rapidly overwhelming the previously installed fine filtration systems that protect Lake Tahoe. Fine filtration systems have been installed around Lake Tahoe Basin by NDOT and are monitored by the North Tahoe Conservation District as part of its ongoing water quality best management practices program. The district sought a pretreatment system for runoff that would remove the coarse sediment and reduce the maintenance requirements.

“We always want to have two levels of treatment for the stormwater if possible,” says Meghan Kelly, PE, District Manager/Senior Project Engineer for the Nevada Tahoe Conservation District, who worked with Salter on the project. “We want to both treat it to the highest quality possible and reduce the intense maintenance needs on the secondary process.”

Jensen Precast provided detailed engineering services to the North Tahoe Conservation District and manufactured a Jensen Deflective Separator as a pretreatment solution for the existing fine filtration systems. Installed along the Highway 431 upslope of Incline Village in North Lake Tahoe, the JDS60-2430 is a hydrodynamic separator that adds 1.2 ft3/sec of treatment capacity to remove coarse sediment runoff before it reaches the fine sediment filters.

“With the installation of this JDS unit, the Nevada Tahoe Conservation District has established a very logical treatment train,” says Walter Stein, PE, Jensen Stormwater Systems Manager. “It’s a nonblocking screening system with swirl concentration to remove particles 50 microns and larger, leaving an influent stream better suited for the fine membrane and filter cartridge systems and increasing their filter run times.”

The hydrodynamic separator screens trash and debris from stormwater runoff without blocking the screen. It is built with inert noncorrosive HDPE and corrosion-resistant 316L stainless steel internals inside durable precast concrete.

If your project calls for a stormwater solution to reduce sediment and system maintenance requirements, contact us for a quote.