Flood runoff no threat to drinking water

Federal, state and local water officials spent more than a week in July chasing floodwaters into Lake Mead to find out whether runoff laced with bacteria poses a threat to drinking water and recreation.

The results of testing, monitoring and tracking the plume of floodwaters from a July 20 storm that shot as far as five miles into Las Vegas Bay indicate that swimmers, boaters and fishermen have nothing to fear at the surface.

The plume of muddy water reached out into the bay 30 feet beneath the surface, said James LaBounty, a limnologist with the Bureau of Reclamation, during a meeting of the Lake Mead Water Quality Forum last week.

LaBounty has been studying a river of runoff from the Las Vegas Valley that has been tracked to Hoover Dam for more than nine years. The storm's flood added tons of sediment, bacteria and urban contaminants to the Las Vegas Wash, which leads to the valley's drinking-water intake system six miles downstream.

The floodwater plume mixed with the lake's waters but did not reach drinking-water pipes about 130 feet beneath the surface at Saddle Island.

However, LaBounty warned that if heavy rains occurred from January to May, the contaminated runoff could float on the surface, posing a potential hazard to swimmers and boaters.

No one has tracked winter rainstorms or tested the water during that time of year, noted Kevin Eubanks of the Clark County Regional Flood Control District, who headed the study.

LaBounty and biologist Larry Paulson began sampling the water at four points in the wash and the bay about 12 hours after the storm struck, dipping test tubes into the water twice a day for the first three days.

The staff of the city of Las Vegas water-treatment plant worked around the clock testing the samples for bacteria and its indicators, Supervisor Debra Bolding said.

The lab analysis detected a spike of 240,000 coliform cells per 100 milliliters, which surprised the scientists, Bolding said.

The sampling and testing continued over eight days, giving water officials a snapshot of what happens in the waters.

But the study did not look at flooding and its impact on swimming beaches, where most people would be affected, Bolding said.

The Southern Nevada Water Authority laboratory, which tested the lake for bacteria and other contaminants, did not find anything resulting from the floodwaters, microbiologist Peggy Roefer said.

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