Monday, May 16, 2005 Copyright © Las Vegas Review-Journal
$585 MILLION PLAN: Lake passes wastewater test
Clean Water Coalition wants to pump treated effluent to bottom of Lake Mead
Results from a recent dye study at Lake Mead could provide key support as the Clean Water Coalition moves ahead with a $585 million plan to pipe the valley's treated wastewater to the bottom of Lake Mead and release it.
Last year, researchers used a moving houseboat to pour magenta-colored liquid into the lake at several locations. They also used a special apparatus to release another type of dye into colder water 75 feet below the surface.
The harmless dye plumes were then tracked as they dispersed to measure how lake water mixes and flows.
The Clean Water Coalition received a final report on the study late last month.
"The reason we did the study was mainly to confirm what our modeling was saying," said Douglas Karafa, program administrator for the coalition. "Basically, that's what it did."
For almost three years, the coalition has been using computer models to predict the movement of water in Lake Mead as officials seek a new release point for the valley's ever-growing amount of wastewater.
The project, which is designed to protect local water quality through 2050 and beyond, would pipe effluent from the valley's sewage treatment plants to a spot at the bottom of Lake Mead about 250 feet down and more than three miles from shore.
The wastewater would then be released into the water through a series of smaller pipes spread across a lake-bottom mixing field up to 1,000 feet across.
The coalition plans to release a draft environmental assessment of the project in August. A final version of the assessment should come out in July 2006, along with a decision about how to proceed.
The soonest the project might be completed is 2011, but "it's more likely to be in 2012 or 2013," Karafa said.
The Clean Water Coalition is made up of the Clark County Water Reclamation District and the cities of Las Vegas and Henderson, which combine to release 150 million to 180 million gallons of treated wastewater into Lake Mead every day.
At present, that wastewater flows into the lake via the Las Vegas Wash, which drains most of the valley and empties into Las Vegas Bay.
The effluent is being concentrated there as a result of the region's ongoing drought, which has emptied a significant portion of Las Vegas Bay and caused the lake's overall water level to drop more than 70 feet from near-capacity levels in 1998.
That is one reason the coalition is looking for a new release point for effluent. The other is the health of the Las Vegas Wash and the wetlands it supports.
As Las Vegas and its output of wastewater have grown, the wash has suffered significant erosion damage, Karafa said.
The proposed pipeline project is expected to reduce the flow of effluent in Las Vegas Wash to about 30 million gallons a day, a level last seen in the late 1960s, "when the wetlands were at their peak," Karafa said.
More importantly, he said, the project would allow wastewater to be released over a larger area and in a more controlled way, vastly improving the rate of diffusion. And injecting the effluent into the colder water found at the bottom of the lake will help prevent algae blooms that can form in the warm, sun-infused water near the surface.
The coalition's preferred location for the underwater mixing field is at the bottom of the Boulder Basin, near the Boulder Islands, a site considered less vulnerable to the lake's rise and fall.
Karafa said dye released into the water there several times last year behaved as expected.
"The dye moved north and east along the west side of Sentinel Island. You would think it would move down toward the dam, but our modeling predicted just this sort of thing," he said.
"What we don't want is for the effluent to be put in the lake and get sucked down through Hoover Dam before it has a chance to dilute."
The way water mixes and flows in North America's largest man-made reservoir is influenced by wind, temperature and the operation of the dam to generate power and fill water orders from cities and farms in Arizona and California.
Just like water that flows into the lake from Las Vegas Wash, effluent from the proposed Las Vegas Bay release point would "generally head right down toward Saddle Island," Karafa said.
Saddle Island is home to the two intake pipes that supply the Las Vegas Valley with about 90 percent of it drinking water.
"The reality is we've never had a water quality issue, but it's a perception problem," Karafa said.
He said wastewater released into the lake is treated to near-drinking water standards, and the water pulled from the lake by the Southern Nevada Water Authority is treated even more before it arrives at the tap.
As for the project's $585 million price tag, Karafa said about $200 million comes from the need to drill a 12-foot-diameter, 7 1/2-mile tunnel through the River Mountains. The pipeline across the bottom of the lake accounts for another $200 million.
An increase in sewer rates and connection charges likely will be needed to help pay for the project, Karafa said. "These things always come down to rates."
How large the gradual rate increase might be depends on how much other funding the coalition is able to get from federal programs and other sources.
Once it is up and and running, the project will generate some revenue of its own -- enough to cover the cost of maintenance and operations, plus about $3 million a year -- by using the wastewater to generate hydroelectric power during its 400-foot drop from the River Mountains to the lake.
Karafa said some of the power will be used to operate the system, and the rest will be sold, most likely to the Southern Nevada Water Authority, which must pump the valley's drinking water back up the same slope.
Effluent from the Las Vegas Valley is released into Lake Mead in order to earn return-flow credits that enable Nevada to almost double its annual share of the Colorado River. Without the credits, the state's river allotment would not be enough to meet water demand in Southern Nevada.
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