Proposed project would block lake pollutants from tap water

Friday, July 18, 2003 | 11:26 a.m.

The Southern Nevada Water Authority is considering a huge engineering project to keep contaminated Lake Mead water out of the system's intakes.

The proposal brought to the authority board as a concept Thursday would wrap the intakes with a cylinder of heavy plastic from the surface to about 40 feet from the bottom of the lake. The idea would be to draw cleaner, colder and deeper water into the intakes that feed the region's water customers, blocking the warmer -- and more contaminated -- water from the top.

Lake Mead provides drinking water to about 90 percent of Clark County's population. Water authority officials are concerned that the water levels in the lake, dropping relatively swiftly after four years of drought in the Colorado River basin, will bring contaminated water near the surface into the water intakes. Thermoclines, or layers within the lake water, hold much of the contamination that comes from the Las Vegas Wash and other surface sources.

With the lake levels falling, and the possibility of a liquid vortex similar to what happens when water is let out of a bathtub, the prospect for the contaminated water getting into the intakes is growing on a daily basis.

The lake is now at about 1,142 feet above sea level, down from about 1,200 three years ago. The falling levels have prompted conservation efforts locally, and officials are concerned that the water supply could be threatened if the drought lasts another several years.

In the meantime, water quality is directly threatened, officials say.

"As the water has declined, that brings the warmer water near the surface closer and closer to our intakes," Marc Jensen, water authority engineering director, said.

"It is extremely critical to put this curtain in," Pat Mulroy, water authority general manager, told the board.

Kay Brothers, water authority deputy general manager, said a "very preliminary" estimate of the cost for the project is about $5 million. She said the barrier would probably be a heavy plastic liner similar to those used to line farm ponds and landfills.

The water authority uses two main intakes, commonly dubbed the first and second straws, to supply the region's water agencies, including those for North Las Vegas and Henderson and the Las Vegas Valley Water District, which supplies Las Vegas and unincorporated Clark County. Those intakes are near Saddle Island in the lake.

A third, smaller intake provides water to the system to customers in Henderson and might also need to have a barrier in place, Jensen said.

Jensen told the authority board that a number of federal agencies with various oversight duties on the lake, including the Army Corps of Engineers, the Bureau of Reclamation, the National Park Service and the U.S. Fish and Wildlife Service, would probably have to sign off on the barriers.

But with those approvals, the cylinders could be closed by next summer, Jensen said.

"There is quite a bit of urgency in moving forward with this proposal," he said.

Colleen Dwyer, spokeswoman for the Bureau of Reclamation, said her agency understands that urgency.

"We'll work closely with the park service and any other affected federal agencies and the water authority to examine the potential impacts, and evaluate the proposal," Dwyer said. "It sounds like an interesting idea."