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📅 Fri December 11, 2015 - West Edition
Irwin Rapoport - CEG CORRESPONDENT
As a companion to Intake No. 3 on Lake Mead, the Southern Nevada Water Authority (SNWA) is building the low lake level pumping station, a project whose cost is estimated at $650 million, in the Lake Mead National Recreation Area, just 500 ft. (152.4 m) from the new intake.
“To ensure access to southern Nevada’s primary water supply is maintained and water demands are met,” stated a press release, “the SNWA Board of Directors approved an initial construction agreement in May 2015, to begin the development of a low lake level pumping station. The new pumping station, which was recommended for construction by a citizen’s advisory committee, will work alongside the SNWA’s third intake.
“The contract to build the station was awarded to Barnard of Nevada Inc., and its delivery is scheduled for 2020.
The station is needed to continue supplying water demands at low lake levels.
“Ongoing drought conditions in the Colorado River Basin have caused Lake Mead’s elevation to fall by more than 130 ft. (39.6 m) since 2000,” stated the project’s fact sheet. “In response, Colorado River users throughout the basin are working together to increase water conservation and minimize drought impacts. In southern Nevada, conservation has reduced water use by 30 percent since the drought began, despite a population increase of more than a half-million people during that same time period.
“While southern Nevada continues to do its part, the drought isn’t over,” it added. “Drought forecasts published by the Bureau of Reclamation show that Lake Mead’s water level is at risk of falling below 1,000 ft. (304.8 m) within the next decade. If that happens, the community’s intake pumps, which draw water from Lake Mead, will become inoperable.”
The SNWA currently operates two pump stations, both of which are currently 1,221 ft. (372.16 m) above sea level — full lake capacity. The lake’s current level is 1,078 ft. (328.6 m) above sea level, and Intake Pumping Station No. 1 completed in the 1970s, has an operating range down to 1,050 ft. (320 m) above sea level. Intake Pumping Station No. 2, built in the early 2000s, has an operating range down to 1,000 ft. (304.8 m) above sea level.
“L3 will ensure southern Nevada maintains access to its primary water supplies in Lake Mead,” states the fact sheet, “even if the lake dips below elevation 895 — the point at which [the] Hoover Dam can no longer release water downstream to California, Arizona, and Mexico. Low-level elevations also may require additional water treatment.”
Bronson Mack, of SNWA public outreach and media relations, goes further.
“These projects reinforce the importance of ensuring that we as a water agency can continue to provide water to our customers under any operating conditions in the Colorado River,” he said. “In the event that Lake Mead continues to decline, this is the type of infrastructure we need. We’re really pushing and stretching those limits.”
The operating range of L3PS will be down to elevation 875 ft. (266.7 m) above sea level.
Erika Moonin, the SNWA’s project manager, explained some of the design features.
“We have a 525 feet-plus deep shaft, about 26 feet in diameter to drill and blast,” she said, “and a large underground floor bank — almost 400 feet long that needs to be created, along with nearly 34 — approximately eight-feet in diameter — well shafts to be drilled. Those shafts are going to be 500 feet deep. The equipping of it will include large submersible pumps and the mechanical and electrical systems that go with them. The pumping capacity is going to be 900 million gallons per-day (MGD).”
A key design challenge is the siting of the station due to its proximity to a major, inactive fault line.
“The plan was to put it on the Intake No. 3 site and it has to be on that location,” said Moonin, “and we are going to shoe-fly it in between the faults to not encounter any fault issues. On the construction side, we’re looking to minimize the risk of drilling the well shafts, which we know are going to present some major challenges.”
On the mechanical side, the pumps are another challenging aspect,
“This is very sophisticated equipment: large deep-set submersible vertical pumps and double-section vertical turbines,” said Moonin. “We already purchased some large submersible pumps between 2004 and 2006 and they have been installed in Intake Pumping Station No. 2. We’re contacting three different manufacturers to provide one pump each and we are going to test them. The station is a unique design at these capacities — 30 million gallons per-day and about 525 feet of lift.”
Barnard will be installing the pumps upon the successful completion of the second work package negotiations.
The planning for the station began in 2005, the same time as Intake No. 3. Both infrastructure projects were paired.
“But in 2008, when the economy took a downturn,” said Moonin, “we deferred the pumping station and it was a good thing because of the continued concern of climate change and Lake Mead’s level going down. That gave us the opportunity to revisit the criteria for the pumping station and now it is deeper than what we originally planned. It’s bigger and is essentially going to replace all of our pumping capacity for the future. The station will only operate at the low lake level, between elevations 1060 feet to 875 feet. At 1050 feet and up we can operate station #1 and at 1000, we can operate pumping station No. 2. The new station gives us the flexibility if there is no more water going through the dam.”
The ongoing decline of Lake Mead is serious and heightens the need for the new infrastructures. The SNWA cannot delve any deeper into the lake to supply water for the area.
“This is the lowest point that we can pump,” said Moonin, “because the new intake is at elevation 860 feet and these pumps will be able to operate at 875 feet, which is only 15 feet above. That’s when we would start getting some vortexing over the intake.”
The drilling operations will encounter highly fractured and faulted metamorphic rock.
A staff of 20 engineers and inspectors, plus various consultants, is assisting Moonin. Parsons Corporation is taking on the role of the program manager.
The pumping station will be 525 ft. (160.02 m) deep, reaching to an operating pumping elevation of 875 ft. (266.7 m) above sea level. That is approximately 52 stories underground. It has two basic levels: the forebay at the bottom, and the supporting equipment at the top. The pumps will sit just below the 875 ft. elevation mark. There also is an electrical building that is about 11,000-sq. ft.
The station can be operated and monitored by personnel on site and remotely. It will be connected to the SNWA’s SCADA system.
To link the pumping station to the existing water network, 4,000 ft. (1,219.2 m) of pipe — two lines, along with two discharge aqueducts, will be installed in the next few years.
“The pipes will be fabricated at a diameter and have welded joint,” said Moonin, “so we don’t expect any leaks. We’re just now discussing the pipe specifications with the manufacturers and looking at the different pipe materials.”
Barnard construction crews have been on site since May.
“We’ve been performing pre-construction services for the SNWA,” said Jordan Hoover, Barnard’s project manager, “which involves working directly with their design engineer to help finalize and develop a constructible product and we have been able to analyze the construction risk and select optimized means and methods. We try to prepare in every way possible.”
Hoover’s team will drill and blast to excavate the access shaft that will be lined with concrete and then create the 400 ft. forbay cavern via a drill and shoot method. The drilling of the 34 well shafts will be done from the surface by blind bore drilling. The construction of the above-ground pump station will be negotiated in a future contract.
The shaft excavation, which should take three years to complete, has to be as precise as possible.
“We’ll be drilling 10-foot production rounds — loading and shooting — and then we do a mucking cycle to excavate out the shot material that is hoisted to the surface and dumped,” Hoover said. “We then provide temporary ground support in the rock and repeat the process. In strategic increments we’ll suspend the excavation and install the concrete liner.”
Encountering the large fault and smaller ones will be an ongoing challenge.
“Especially the large one and those that are bearing of water,” said Hoover. “To be able to predict and intercept them during the excavation process, we’ll be doing a pre-excavation water control probing and grouting program at 100-foot intervals. The probe holes will intercept the water and the grouting system will help seal off the flowing water and consolidate any features that are groutable.
“The 34 well shafts will be drilled concurrent with the access shaft excavation,” he added. “They will be drilled from the surface using a blind bore drilling method. The shafts will be lined with a steel liner once they are completed. Once those are complete, we will excavate out the rock directly beneath the well shafts in the forbay chamber.”
The material from the shaft excavation, cavern and tunnel work — more than 150,000 tons (136,077 t) of rock, will be used on site to help provide fill areas, develop more yard and site for the pump station, and create a view-shed berm around the completed pump station. The berm, because the station is in a national park, will shield it from view and give the area a more natural appearance.
The paved road that Vegas Tunnel Contractors built for the intake project will be used by Barnard to provide clean access to the job site for personnel, construction materials, and vehicles. The work will be 24 hour days, via three shifts.
“At peak we anticipate more than 120 craft employees working on the project, as well as 80 subcontractor personnel,” said Hoover.
Subcontractors on the project include North American Drillers for blind bore drilling.
Barnard is still exploring its concrete ready mix options of either batching onsite or utilizing local ready mix plants.
Air will be provided to the crews working in the cavern by a site ventilation system.
“Additional precautions include back-up power for life safety systems underground” said Hoover. “Mine rescuers and re-breathers also are on site as an additional safety precaution. The underground monitor detects CO2 levels and air flow to ensure a safe work environment. Barnard onsite safety team and superintendents lead these efforts every day onsite.”
Crews also are being trained to protect wildlife, including the endangered desert tortoise.
“We are in a pretty remote environment and we’re constantly aware and monitoring for endangered species,” said Hoover. “This also will bring us into contact with everything from scorpions and other insects (some poisonous) to coyotes and roadrunners. We’re making sure to provide protection to the crew and that we’re minimally disrupting nature.”
Barnard has a corporate safety program and a site-specific one also is being developed that will be assisted by a safety team and educators, which Hoover said, will “make sure that we proving a safe work environment on a daily basis.”
He added that a work site plan has been developed for all the facilities that are needed.
Hoover and Barnard have a lot of experience on such projects, including a 2010 SNWA project that was part of the third intake system, which had Barnard construct the Intake #2 connection and modification — a 375 ft. (114.3 m) deep shaft and installation of an isolation gate and hoist.
At this point, Barnard is planning out the complicated and varied operation, and that includes close cooperation with the SNWA in terms of sharing information and developing contract terms.
Hoover is the first to recognize that the success of the project depends upon a team effort.
“We have a full staff of field engineers, department managers, a general superintendent and shift superintendents, crew foremen and craft personnel,” he said. “They are the ones who are constructing this project every day. It’s a complicated and challenging project and everything through conception to design, engineering, and construction, and ultimately its commissioning and future operations, requires extensive consideration to succeeded. As a contractor we’ll have more than 20 staff members helping to manage and oversee the construction process.”
The explosives to be used are pre-packed and overseen, supervised and detonated on each shift by an assigned blaster-in-charge who is certified with a blasting license by the state of Nevada.
The amount of explosives and where each blast is placed will be determined by rock and soil conditions and the effect that is desired.
“We look at that very carefully and the availability of different product,” said Hoover. “Ultimately we’ll develop a detailed blasting plan that includes the number of hole depths and products loaded in both production and trim holes. The results will be continuously monitored and may be adjusted to develop optional shots each round of production. This is what we have been looking at for the last three months and we’ll be doing that every day for the next three years of construction.
“The engineers and geologists have produced a geotechnical baseline report and that has allowed us to develop anticipated approaches to the ground,” he added, “which allows us to develop our construction techniques and durations and a realistic construction approach schedule and costs.”
The equipment to be brought in by Barnard includes a Liebherr 150 ton (136 t) crane to provide most of the mucking and hoisting for the shaft and cavern excavation work, two Atlas Copco hydraulic drills for drilling the blast rounds, a small Caterpillar excavator for the excavations of the mucked material, a Normet shotcrete robot for the shotcrete installation and application, and in the forebay cavern, a drill jumbo and a LHD for mucking.
Barnard’s closest equipment yard and shop is 250 mi. (402.3 km) from the site.
“We will have a support crew of mechanics that will provide equipment maintenance and fabrication abilities on site,” said Hoover. “It will be a mix of experience with traditional heavy civil equipment and with drilling equipment.”
Barnard has been planning for the project for several months.
“Because the project site is somewhat remote, our equipment department has to prepare for equipment breakdowns and backup equipment” Hoover said. “We maintain an inventory of spare parts and always maintain contact with our equipment vendors about the availability of parts in the event of a breakdown.
“The equipment used underground — Cat mini-excavator, Atlas Copco drills, and LHD — will experience the most daily wear and tear when used underground up to three shifts per-day,” he added. “These are the pieces of equipment that we really focus on having back-ups and are prepared to fix in the event of a breakdown. In addition to repairs, our on site mechanics perform all of the equipment routine maintenance and services. We consider our underground equipment to be a key to success on this project.”