Innovative, Elaborate Project Helps Guarantee Supply to Nevada’s Largest City
By Thomas Renner
Snowstorms raced through the Western region of the United States with alarming frequency in early 2019. Snow fell even into June, when the opening day of summer saw up to 20 inches bury the high terrain of the Colorado Rockies. Colorado’s snowpack was at 132 percent on average in May, according to the Denver Post. Skiers and winter sports enthusiasts enjoyed a banner winter, and so did reservoirs. The state’s water storage levels were at or above average for only the fifth time since 2000.
Colorado was not the only state to savor the bounty from winter’s steady snowfall. The Las Vegas Valley draws 90 percent of its water supply from Lake Mead. Snowmelt in the mountains that feed the Colorado River filter to Lake Mead, a man-made lake about 24 miles from the Las Vegas strip. It is the largest reservoir in the United States in terms of water capacity, and serves water to Arizona, California, Nevada and some parts of Mexico. The lake is 112 miles long and has 247 square miles of surface area. Hoover Dam, the national landmark that delivers water and produces electric power to southwestern American states, sits just seven miles away from Lake Mead on the border between Nevada and Arizona.
A drought that has extended for nearly two decades, however, has gripped the region. The water level at Lake Mead, the primary source of the community’s drinking water, dropped more than 130 feet since January 2000. The federal government is projecting a high probability that Lake Mead water levels may fall below 1,075 feet in 2021, triggering the first-ever shortage of Colorado River water and possibly reducing the amount of water available to Nevada. The record snowfall in the first few months added three feet to Lake Mead, but did little to alleviate water shortage concerns.
The Southern Nevada Water Authority is already taking steps to avert any disruption of water service to Las Vegas. Next year, it will start operation of a $650 million project that provides a water safety net for city residents. The Low Lake Level Pumping Station will have the capacity to deliver up to 900 million gallons a day to two water treatment facilities. The project is one of the most sophisticated, expensive and largest pumping stations in the world, and is a critical step toward ensuring the region’s water supply over the long term.
“It is a backup, redundant pumping station to use in the event our other two pumping stations are unable to pump due to lowering lake levels,’’ says Erika Moonin, SNWA project manager. “The Bureau of Reclamation is the governing body that forecasts watershed along the Colorado River. It will take many years of incredible snowpack for Lake Mead, Lake Powell and other reservoirs to recover from this long-standing drought and the consequences of climate change.”
A Look at the System
The complex pumping station includes a 525-foot deep access shaft, with a 26-foot finished diameter. There are 34 deep well shafts equipped with submersible pumps that feed the pumping station. Barnard of Nevada, Inc. serves as the general contractor for the project. Its team worked closely with the SNWA and the construction manager, Parsons.
Among the first steps in the project was to create a forebay, a 12,500SF cavern that is 500 feet beneath the pumping station. Pumps draw water from the forebay, and the water then enters the header pipe and flows through two large-diameter aqueduct systems to deliver water to two treatment plants.
Twenty-two low lift pumps will deliver raw water to the Alfred Merritt Smith Water Treatment Facility, and 12 high lift pumps will deliver raw water to the River Mountains Water Treatment facility. The water is treated with ozone and then goes through a filtration system before entering the transmission system and eventually, the homes in the Las Vegas valley. There are more than 2.25 million residents in the region, the most densely populated area in Nevada. Las Vegas also welcomed more than 42 million tourists in 2018.
“A scale model was developed at Utah State and tests were performed to assess the many factors of how water entered the forebay from the intake tunnel, how it traveled to each of the 34 well shafts, its velocity, and more,’’ Moonin said. “Engineers used the data from this model testing, among many other things, to determine the appropriate size of the forebay.”
The pumps at the Low Lake Pumping Station provide the power. The 22 low lift pumps, which weigh approximately 68 tons, are 23 feet long and can produce up to 30 million gallons of water per day, according to Moonin. The high lift pumps weigh 79 tons and are 28 feet long and can also produce 30 million gallons of water per day.
Installing them was one of the most pressing challenges in the project. The team first created the forebay, access shaft and riser shaft by drilling and blasting and removed more than 58,000 cubic yards of blasted rock. According to SNWA, it used 271 controlled blast rounds and more than 98,000 pounds of package blasting explosive materials. The forebay was completed in the summer of 2018.
Concurrently, workers used the blind bore drill method to excavate 34 pump shafts. The shafts reached 500 feet down to a precise location in the forebay. Pumps were dropped into the cavern with a gantry crane with a capacity of 220 tons.
“The rock is hard but fractured, and water flows through the fractures with direct connectivity to Lake Mead,’’ Moonin said. “In order to proceed with excavating the underground caverns and well shafts in these challenging work conditions, a significant grouting program was used to prepare the ground for drilling of the well shafts and drill-and-blast excavation of the forebay.”
Core sampling and extensive geotechnical studies helped identify as many ground condition challenges as possible, Moonin said, and the grouting campaign and careful excavation led to successful completion of the underground work.
Heavy Duty Doors
Valves at the pumping station are protected by 12 floor doors manufactured by The BILCO Company of Connecticut. The doors are strategically placed on the project’s vaults, which house and provide access to large diameter valves. The doors are reinforced for AASHTO H-20 wheel loading.
Single- and double-leaf doors were used in the project, and will allow workers to access valves that require adjustment and perform maintenance on the pumps. Although the doors are quite large and heavy, they are supplied with BILCO’s engineered lift assistance to ensure safe and easy one-hand operation.
“There are conduits and drain lines that required access,’’ said Tyler Askin, Barnard’s project engineer at Lake Mead. “The doors were a product that one of our suppliers had used in the past and had the most experience with, and the specifier thought they would be a good choice, especially for this application.”
‘We Must Remain Vigilant’
The above-average snowpack from the winter of 2019 will help in the short term. But conservation remains a priority in the community, and community officials warn the region could still face a water crisis.
“While we appreciate this year’s above-average snowpack, one good year doesn’t mean the drought is over,’’ Brenda Burman, U.S. Bureau of Reclamation Commissioner, said after the release of a report in August. “We must remain vigilant.”
The Lake Mead Low Level Pumping Station will take a big step toward providing corrective action. Lake Mead is situated about 32 miles from Las Vegas, far away from the public eye and the glitz that is associated with the city. Shows, entertainers and casinos may drive Las Vegas’ tourism industry, but the pumping station plays a more important role: guaranteeing the city’s water supply.
“It’s really an unsung project, but it’s important for the Las Vegas community to guarantee their water supply,’’ Askin said. “It’s one of those projects a lot of people are unaware of. It’s not alongside a highway where you can see progress every day. Water’s not something people think about it until they don’t have it. This will help make sure that doesn’t happen.”
Thomas Renner writes on building, construction, manufacturing and other trade topics for trade publications throughout the United States and Canada.