U.S. Water News Online
LAS VEGAS -- Ongoing drought has brought Lake Mead surface
impurities closer to intakes for Las Vegas-area drinking water,
prompting an expensive and ambitious proposal to draw cleaner water
into water intakes.
The Southern Nevada Water Authority is developing a $5 million
impermeable membrane -- an inverted L-shape plastic curtain -- to dip
at least 100 feet beneath the lake's surface and stretch about 300 to
400 yards lengthwise.
``This is a very difficult kind of project,'' said Marcus Jensen,
water authority engineering director. ``Very effective, but it's
going to be challenging.''
The curtain could be in place by next summer, although another
alternative could extend intakes downward toward the lake's bed.
Engineers believe the curtain would be more cost-effective.
Similar technology has been used to protect the fishery of
Northern California's Lewiston Lake, where warm water is shielded
from cool water to protect maturing fish eggs.
It's a touchy issue for bureaucrats attempting to operate a
multibillion-dollar water system during the region's worst recorded
They say Lake Mead water remains safe for swimming and, after
treatment, for drinking.
But surface pollutants have increased as the lake level has fallen
60 feet -- from 1,213 feet above sea level in January 2000 to 1,143.
The lake could drop another 14 feet by next summer, officials say.
The water authority's intake tunnels are at 1,050 feet and 1,000
The drought has produced algae blooms, mucking up filters that
cleanse water drawn through the towers, and reducing treatment plant
capacity as much as 20 percent when filters are rinsed. The water
authority must dip into limited groundwater supplies when the flow of
lake water is limited.
The surface also has a mix of chemicals and organic materials --
primarily perchlorate and total organic carbons, which form
trihalomethanes when mixed with chlorine.
Perchlorate, a jet fuel ingredient, was produced decades ago at a
Henderson industrial plant and continues to slowly leach into the
lake. Treatment facilities have been built to limit the perchlorate
The recent opening of a water authority ozone treatment facility
is expected to help reduce trihalomethane formation by limiting
chlorine's catalytic role.
Warm summer weather boosts surface temperatures by as much as 20
degrees, increasing the interaction of chlorine with algae, pine
needles and grass clippings swept into the lake.
On a recent morning, water authority lab technician John Corso and
three colleagues made a weekly 10-minute boat ride to take water
samples several hundred yards off of Saddle Island.
Around surrounding cliffs, they could see a six-story white ring
of mineral deposits from when water levels were higher.
Lab tech Steven Lujan dropped plastic tubes to depths ranging from
33 to 188 feet to collect samples for testing for bacteria,
perchlorate, trace metals and inorganic materials.
Lab boss Linda Blish said the falling lake levels have not sparked
immediate health problems, but have raised concerns about new
``You always have to watch what's going on in your water source,''
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