Outstanding Environmental & Engineering Geologic Project Technical Program Schedule

AEG Outstanding Environmental & Engineering Geologic Project Award Lake Mead Intake No. 3 and Low Lake Level Pumping Station, Nevada

Barbara Luke, PhD, PE; Steven Hunt, PE; and Jason Bailey

SNWA Lake Mead Intake No. 3 tunnel during construction.

CREDIT: SOUTHERN NEVADA WATER AUTHORITY

Project Teams

Lake Mead Intake No. 3

MW/ Hill Joint Venture (now Stantec/ Jacobs), Parsons, Vegas Tunnel Constructors (JV of Impregilo and SA Healy) – Contract 1, Renda-Pacific – Contract 2, Barnard of Nevada – Contract 5, Arup, Brierley Associates, Contri, Associated Underwater Services, Herrenknecht, and Precast Management

Low Lake Level Pumping Station

MW/ Hill Joint Venture (now Stantec/ Jacobs), Parsons, Barnard of Nevada, North American Drillers, and Indar

Agencies Heavily Involved for Both Projects

Southern Nevada Water Authority, National Park Service, Colorado River Commission of Nevada, and Bureau of Reclamation

Key Outside Personnel

Eugene Smith, University of Nevada, Las Vegas; Greg Korbin, Independent Consultant; and Toby Wightman, Independent Consultant

National and International Significance of the Project

The project directly benefits the ~ 2.3 million residents of Nevada’s Las Vegas Valley and ~ 40 million more people who visit the area each year. Nearly 90 percent of Las Vegas’ water supply comes from Lake Mead. Until recently, access to the water was provided by two intakes. To address unprecedented drought conditions and provide longterm protection of Southern Nevada’s primary water storage reservoir, the Southern Nevada Water Authority

(SNWA) constructed a third drinking water intake capable of drawing upon Colorado River water at lake-surface elevations below 1,000 feet above sea level. Las Vegas has been and continues to be an innovator in water conservation initiatives, leading the way for its partners whose collective goal is to optimize use of the essential yet limited resource that is the Colorado River while also protecting ecology.

History of Project Need

The history associated with the need for this project dates back to 1922 with the Colorado River Compact, when river allocations were apportioned among Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming, leaving Nevada with the smallest share. The need for the project became evident in the early 2000s with the onset of an unprecedented drought which coincided with phenomenal growth across the dry southwestern United States and particularly in the Las Vegas Valley.

Lake Mead is the principal reservoir of the Colorado River’s lower basin, which provides sustenance to approximately 20 million people plus farmland and natural ecosystems in Nevada, California, Arizona, and northern Mexico. Its full-pool elevation is 1,229 feet above mean sea level and its maximum depth is 532 feet. Until recently Las Vegas had been taking its allocation via two intakes that could operate normally at water elevations above 1,075 and 1,050 feet. The reservoir was full in 2000, but unprecedented drought has caused water levels to fall since then (Figure 1). By June 2022, lake levels had dropped to 1,043 feet, a retreat from full pool of 186 feet, at which point the reservoir was holding only about 28 percent of its capacity. At this elevation, the highest of the water intake structures is exposed above the water surface.

The declining lake levels posed a water resources threat to Las Vegas. In July 2004, a team of engineers from the SNWA and a joint venture of then-named Montgomery Watson and CH2M HILL (MW-HILL) that included co-author Hunt began studying a third, deeper intake. This intake would ensure the Las Vegas Valley’s access to its primary water supply while also mitigating water quality issues associated with declining lake levels. The team considered two locations in Boulder Bay of Lake Mead and one in Black Canyon, about a half-mile upstream from Hoover Dam. SNWA water quality engineers sampled sites in the lake and chose one north of the now-flooded Las Vegas Wash. The site was favored because it had better water quality and it avoided the risk of intercepting contaminated sediments from the Wash and new contaminants flowing into the reservoir from the Wash. Figure 2 shows locations of the new construction: Lake Mead Intake No. 3, Intake No. 3 tunnel, Low Lake Level Pumping Station, and Intake No. 2 Connection Tunnel. The figure also shows the preexisting Intakes No. 1 and 2 and their associated infrastructure.

A contract for preliminary engineering was awarded in June 2005 and the team began studying alignments from the site of the proposed new shaft and pumping station, about a half mile north of the existing pumping stations, to the location of the proposed new intake. Borings were completed along a straight alignment, a west curved alignment and a far-west curved alignment. The straight and slightly curved alignments placed most of the proposed tunnel in high permeability, low-rock-quality volcanic rock under very high groundwater head ranging from 10 to 17 bar. These risks were considered unacceptable. In 2006, after considering geologic and tunneling risks and costs, the longer, far-west curved alignment was selected. The intake structure would be placed at the 860-foot elevation which is approximately 374 feet below the maximum lake level and was about 220 to 275 feet below lake levels during construction. It would draw from the reservoir even at “dead pool” conditions (895 feet), which is the water-surface elevation at which Hoover Dam would no longer be able to release water downstream or operate turbines to generate electricity.

As water levels continued to fall during the worst drought in the history of the Colorado River Basin, the SNWA’s Lake Mead Intake No. 3 with its dedicated Low Lake Level Pumping Station

Figure 1. The surface of Lake Mead is currently at its lowest level since the 1930s when it was first filled.

CREDIT: SOUTHERN NEVADA WATER AUTHORITY Figure 2. Locations of the new construction with respect to topography and existing infrastructure. View is to the North. Intake Tunnel No. 3 is approximately 3 miles long.

CREDIT: SOUTHERN NEVADA WATER AUTHORITY

would ensure that Southern Nevada maintained access to its primary, allotted water supplies in Lake Mead.

Problem Solved

Considering costs and risks, SNWA decided to use design-build (DB) contracting for the intake tunnel contract. (Subsequent connecting tunnel work was contracted as design-bid-build.) DB tenders were submitted in 2007 and a contract was awarded in early 2008. Construction work started in May 2008 and the intake was completed in 2015.

Applying cutting-edge technology, a 23.7-foot-diameter, dual-mode tunnel boring machine (TBM) was employed to excavate the three-mile-long tunnel under Lake Mead (Figure 3). A TBM is a mobile, linear manufacturing facility that creates useable space underground. TBMs vary greatly in form and complexity according to the ground and groundwater conditions encountered. The TBM for the new intake tunnel was a purposebuilt, state-of-the-art—and ultimately record-setting—machine designed to handle the extremely difficult ground and water conditions. At a cost over $25 million, it was manufactured in Germany by Herrenknecht AG, a leading firm in the industry, and was the first to be designed to accommodate extensive pressurized face tunneling at groundwater heads up to 17 bar. The dual-mode feature allowed both pressurized face operation and open mode operation, which is favored when working in less permeable ground. Manufacturing took over a year and resulted in a machine with trailing gantries over 600 feet long, weighing over 1,400 tons, and requiring a team of highly skilled crafts to operate. The machine was shipped from Germany to the Port of Long Beach and required 75 trucks to deliver it to the site. The completion of the tunneling work on this project has been considered an engineering marvel.

As discussed below, the tunnel would have to pass through complex and variable geologic features including hard, faulted Precambrian gneiss, faulted volcanic rocks, weak Tertiary cemented alluvium, and volcanic basalt flows at depths ranging from 380 to 600 feet and under groundwater heads ranging from 9 to 15 bar.

Approximately 2,400 precast concrete segment rings, each weighing more than 32 tons, were needed to line and reinforce the tunnel. The segments were designed to resist over 600 feet of rock and 17 bar of groundwater pressure when dewatered.

The tunnel terminated at an intake structure. This massive concrete and steel unit was constructed at the shoreline and barged across the lake (Figure 4). Once in position, it was lowered onto a steel frame placed in a 70-foot-deep depression that had been dug into the bottom of the lake at a water depth of over 300 feet. After precise positioning, the lower third of the riser was encapsulated in more than 11,000 cubic yards of concrete which was placed by doppler pipe tremie method in an unprecedented 12-day continuous underwater pour (Figure 5).

Figure 3. The face of the tunnel boring machine (TBM). Figure 4. Raw water intake structure enroute to placement at the bottom of Lake Mead.

CREDIT: SOUTHERN NEVADA WATER AUTHORITY

Figure 5. Fleets of trucks loaded on barges to deliver concrete almost three miles from shore to secure the raw water intake structure.

The new intake began conveying water in September 2015. By 2017 it became the sole supplier of water being distributed to the SNWA’s water treatment facilities.

The new pumping station was originally to be one of five contracts for the new intake, but the design work on it was stopped in 2009 due to economic downturn. SNWA and MWHILL resumed pump station planning in 2014. SNWA awarded a fast-track design contract in December 2014 and a progressive construction-manager-at-risk (CMAR) contract in early 2015. The fast-track approach allowed construction to begin by June 2015 and be completed in 2020.

The new Low Lake Level Pumping Station has the world’s largest combined flow capacity and deepest submersible pumps alongside the nation’s largest man-made reservoir. The pumping station is a hybrid. There are twenty-two low-lift pumps that feed the Alfred Merritt Smith Water Treatment Facility and twelve high-lift pumps that feed the River Mountains Water Treatment Facility. Both the pumping and discharge systems are dual, feeding water into two separate 144-inch conveyance pipelines. Some of the pump piping is located unhoused and above ground, as is the gantry crane (Figure 6).

Through the progressive CMAR approach, SNWA, MW-HILL, Parsons, and Barnard (the contractor brought in at the 50 percent design stage) worked collaboratively to improve the design through insights on constructability, value engineering, cost estimating, and schedule. The fast-track schedule was a significant accomplishment. Earthwork construction was started about six months after awarding design, and pumping station construction (well shafts, access shaft, forebay, and riser shaft) was started about nine months after awarding design and six months after awarding the progressive CMAR contract. Despite challenges, the pumping station was completed below budget and on time. The pumping station can deliver up to 900 million gallons per day to SNWA’s treatment facilities. It started operating in April 2022 when the falling lake water levels rendered another SNWA primary intake pumping station inoperable.

The final cost of the Lake Mead Intake No. 3 project was approximately $817 million. The estimated cost to design and build the Low Lake Level Pumping Station was $650 million but the project came in at $522 million.

Figure 6. Low Lake Level Pumping Station.

CREDIT: PARSONS

Environmental and Engineering Geologic Principles Applied

Site Investigation

The geologic setting for the project was extremely complicated due to an extensive detachment fault system that accommodated about 12 miles of translation of volcanic rocks in the River Mountains across the state line from Arizona to Nevada. Following Tertiary volcanic eruptions, a large horst of Precambrian rock was uplifted, forming Saddle Ridge. Saddle Ridge became Saddle Island after Lake Mead was formed. The starting point of the new intake tunnel and pumping station is on Saddle Island about a half-mile north of the pre-existing intakes and treatment facilities (Figure 2). Much of the intake tunnel alignment geology was hidden below Lake Mead, which began filling in 1934. Extensive geologic desk studies and pre-reservoir aerial photo review were combined with a phased subsurface investigation program of over twenty 600-foot-deep lake borings, bathymetry, and seismic refraction surveys. Borings were completed along all three potential tunnel alignments. Geologic and tunneling risks were considered, along with costs. Of the three alternatives, the far-west curved alignment was selected to minimize geologic risks associated with fault zones, high permeability rock under extremely high water pressure, and geothermal impacts. A thorough, detailed geotechnical baseline report was prepared for the selected alignment.

Geology

Bedrock is a combination of variably mylonitized Precambrian amphibolite and quartz-feldspar gneiss basement rocks, Tertiary volcanics, and Tertiary cemented alluvial fan deposits. The latter rock includes the Muddy Creek and Red Sandstone Formations, which are highly heterogeneous mixtures of sand, silt, clay, and conglomerate. These formations were the preferred geology for mining because of their low hydraulic conductivity. The Saddle Island Precambrian rocks are highly faulted from Basin and Range tectonic activity. The faulting contributed to uncertainties in stability and seepage into the tunnel during construction.

The Saddle Island detachment fault is the most prominent structural feature of Saddle Island. The detachment fault divides the rock into the Upper Plate and the Lower Plate, two distinct geologic domains which would both have to be penetrated for the projects. The detachment fault was formed during crustal extension in the area and is reported to be a single-stage deformation along an evolving, normal-sense displacement fault with thickness ranging from 60 to 100 feet (Duebendorfer et al., 1990). On Saddle Island, the fault strikes northeast and dips to the northwest at approximately 30 degrees. Movement of the fault is dated as Miocene and younger than 13.5 Ma but it predates the deposition of the 5 to 9 Ma Muddy Creek Formation.

The high-angle normal faults that bound the Saddle Island horst displace the detachment fault.

The tunnel encountered seven geologic units, of which two are Precambrian and the rest are of Tertiary age (Table 1; Figure 7; Figure 8).

Table 1. Geologic units encountered with percentages traversed by the tunnel alignment as proposed in the Geotechnical Baseline Report (GBR) compared to as-built (Actual). The pumping station was constructed within the Lower Plate unit (Pcl).

Geologic Geologic unit description unit GBR, % Actual, %

Pcl Lower Plate: amphibolite gneiss and schist 5.3 7.7 with quartz and pegmatite dikes DF Detachment Fault: strongly foliated phyllonite 0.7 1.0 with zones of crushed and brecciated rock from the Upper and Lower Plates. The phyllonite is predominantly composed of soft. platy minerals such as chlorite and micas. Pcu Upper Plate: quartz feldspar gneiss, biotite 9.1 13.3 schist, amphibolite, and quartz monzonite, with Tertiary intrusive sills and dikes of dacite, andesite, granite. Tvsi Saddle Island Volcanics: andesite, dacite, 0.0 3.4 rhyolite, and tuffaceous breccia with intrusive dikes of dacite and andesite

Tmc1, Tcm1 – Muddy Creek: gypsiferous mudstone 75.6 60.2 Tcm2, (old alluvium) Tcm3, Tmc2 – Muddy Creek: interbedded siltstone, Tcm4 sandstone and conglomerate (old alluvium) Tmc3 – Muddy Creek: tan conglomerate (old alluvium) Tmc4 – Muddy Creek: conglomeratic breccia (old alluvium) Trs Red Sandstone: conglomeratic breccia with 8.2 13.2 gravel and occasional cobbles (older alluvium) Tcm Callville Mesa Unit: basalt and debris flows 1.0 1.3

Design

As noted previously, three alignments for the tunnel were studied during predesign. After assessing cost and geologic tunneling risks, the westernmost alignment was selected. It was the longest option, but it minimized tunneling in the faulted Precambrian metamorphic rocks and volcanic rocks and maximized tunneling in the more favorable Tertiary Muddy Creek and Red Sandstone formations. While these rocks were relatively weak, they had much lower permeability, resulting in better ground for tunneling and completion of cutter change and other TBM maintenance interventions.

Formal risk management programs with frequently updated risk registers were employed during the design and construction phases for both the intake and pumping station projects to allow risks to be understood by all the parties and effective mitigation measures to be selected. For Lake Mead Intake No. 3, several risk workshops were held during design and more than ten risk workshops were held during construction. During design and construction of the Low Lake Level Pumping Station, six risk workshops were held with participants from SNWA, the design team and the progressive CMAR contractor team.

Construction

The intake tunnel contract involved conventional drill-blast construction of an access shaft nearly 600 feet deep and 30 feet in diameter, a large TBM launch chamber, and a starter tunnel (Figure 9). The main body of the tunnel, over 15,000 feet long at 20 feet inside diameter, was excavated by TBM. This circular tunnel was lined with 14-inch-thick precast concrete segments. The segments were lowered underground, transported to the TBM, assembled into rings, and installed by pushing out of the shield as the TBM advanced. The lining was back-pressure grouted during extrusion from the shield, with fluid grout pressures often exceeding 20 bar.

The underground work was inherently dangerous, particularly due to complex geology, site-characterization uncertainties, and groundwater conditions beneath the reservoir. Faulting creates flow paths for the groundwater, which was under extremely high pressure due to hydraulic head of the lake above, as well as zones of highly permeable

Figure 7. Historic airphoto showing the Las Vegas Wash before filling of Lake Mead, overlain by geologic units interpreted at tunnel depth. A portion of the intake tunnel alignment, labeled as “Revised”, is overprinted along with boring locations. The alignment was shifted from its proposed location based on information gained from five subsequent borings (in blue).

Figure 8. Geologic profile along tunnel alignment, with TBM operation mode and excavation chamber pressure. Major faults shown in red. Refer to Table 1 for geologic unit descriptions.

CREDIT: STEVEN HUNT

Figure 9. TBM starter tunnel, excavated by drill-blast method, for Lake Mead Intake No. 3.

CREDIT: SOUTHERN NEVADA WATER AUTHORITY

altered rock and fault gouge. In 2010, the tunneling project suffered a major setback—resulting in a nearly two-year delay and approximately $44 million cost—when the TBM’s starter tunnel that was being advanced by the drill-blast method intercepted an unexpectedly extensive zone of saturated and highly permeable faulted rock under about 14 bar of groundwater pressure, causing it to be inundated by water and an inrush of fault debris

Figure 10. Fault debris and heavy inflows from a high-angle normal fault in the starter tunnel. Photo taken about 24 hours before the inrush accelerated. This experience demonstrated the tremendous power of groundwater and risks to construction that can be posed by a large fault zone.

CREDIT: SOUTHERN NEVADA WATER AUTHORITY

(Figure 10). The key to overcoming this tremendous obstacle was successful partnering among SNWA, the design-build team, SNWA’s engineering team, and consultants who were experts in the local geology. The geologists and geotechnical engineers on SNWA’s team collaborated with the design-build team while making effective use of the geologic observation method.

After launch from the starter tunnel, the TBM had to bore through the over 100-foot wide detachment fault at a depth of about 600 feet under nearly 15 bar of groundwater pressure (Figure 8). Despite tremendous risk of blocky rock face collapse, squeezing ground entrapment and inrush like that on the Starter Tunnel, the custom-built TBM bored through the massive detachment fault zone and more than six additional large faults (Figure 8) with no impacts to mining—a feat that had not previously been accomplished under such challenging ground and groundwater conditions.

As noted previously, the TBM was designed to allow both open- and closed-mode boring. In closed mode, the machine’s excavation chamber was pressurized to counterbalance water and earth pressure as was needed in higher permeability zones of rock. Open-mode boring was possible in the lower permeability Tertiary Muddy Creek unit which allowed muck to be removed via a conveyor belt system. Open-mode tunneling was anticipated to allow higher advance rates than closed mode; however, small inflows of water in the range of 50 to 100 gallons per minute (gpm) mixed with the tunnel muck and quickly degraded it to a soupy consistency that was not suitable for removal with the belt conveyor. In the end, approximately 60 percent of the tunnel was bored with slurry system mucking and 40 percent with open-mode belt conveyor mucking.

Approximately 7,600 feet or 52 percent of the tunnel was bored at face pressures of 8 to 14 bar and 4,300 feet or 30 percent was bored at face pressures of 12 to 14 bar, both of which were new world records. The project also set a record for the highest-pressure operation of a TBM at 15 bar, which was maintained for a short distance.

At its terminus the bored excavation holed through the preplaced intake structure (Figure 11). Equipment and systems were disassembled and transported back through the tunnel, to be hauled out via the access shaft. When a temporary bulkhead on the intake riser was removed in September 2015, the connection was complete.

The most valuable lesson learned from the use of the dualmode TBM was that pressurized face tunneling at and slightly above ambient groundwater pressure was effective at preventing detrimental blocky rock face collapse, face instability, lost ground voids, and squeezing ground within the highly faulted, highly permeable ground having groundwater heads in the range of 8 to 14 bar. Despite high permeability, high-head ground conditions, and the extremely tricky and highly technical process of joining the bored tunnel to the riser structure, the final inflow from the intake tunnel before it was flooded for operation was less than 30 gpm (Figure 12).

Development of the pumping station involved constructing a 26-foot-diameter access shaft more than 530 feet deep, then excavating a 526-foot deep, 377-foot long, 34-foot wide by 36foot-high forebay (cavern) at its bottom (Figure 13). The forebay connects with 34 vertical well shafts, each 500 feet deep and 6 feet in finished diameter, each accommodating a submersible

Figure 11. Hole-through: the bored tunnel has intercepted the “soft eye” of the intake structure. Shown are TBM cutter-head face below intake riser which is blocked by a temporary bulkhead.

CREDIT: STEVEN HUNT

Figure 12. Completed tunnel before flooding. Total inflow less than 30 gpm.

CREDIT: SOUTHERN NEVADA WATER AUTHORITY

Figure 13. Low Lake Level Pumping Station forebay. Two rows of 6-ft diameter well shafts penetrate the ceiling.

CREDIT: SOUTHERN NEVADA WATER AUTHORITY

pumping unit (Figure 14). All the rock mass for the access shaft, forebay chamber and well shafts was grouted from the ground surface to over 550 feet deep to reduce permeability and stabilize poor rock quality at numerous high angle normal fault zones.

The most notable accomplishment in excavating for the pumping station was the well shafts. These were drilled and steel casings placed with unprecedented verticality using laserguided directionally-drilled pilot holes followed by two rounds of steered, down-bored slurry drilling. The well shafts, access shaft, forebay chamber, and riser shaft were completed within the highly faulted Precambrian gneiss of the Lower Plate unit under a high groundwater head, up to 10 bar. The groundwater head and recharge during pump station construction was very high because the new, adjacent connecting tunnels for the Lake Mead Intake No. 3 supplied close-proximity recharge water to the rock mass. When tying the new system into the existing water conveyance infrastructure, construction had to adhere to a 72-hour limit on outages to not disrupt the municipal supply.

Figure 14. Overview of the Low Lake Level Pumping Station well shaft pad under construction.

CREDIT: SOUTHERN NEVADA WATER AUTHORITY

Protection and Enhancement of the Environment

The intake and pumping station have met the standards of a 100-year solution for the southern Nevada region. The new system should sufficiently mitigate threats to regional water diminution, even as the metropolitan area continues to develop.

In addition to preserving supply capabilities via the new intake, managing water usage by an ever-growing customer base has been vital to meeting the challenges of the Colorado River and its reservoirs as a diminishing resource. According to the Colorado River Compact, Southern Nevada is allotted 300,000 acre-feet annually from the river, but conservation efforts have allowed the region to use less than this consistently. The region’s water conservation programs, which have been operating in earnest since 2002, emphasize mitigating consumptive water loss through limiting outdoor irrigation and enhanced treatment and recycling of wastewater.

Every gallon of water used in Southern Nevada and then treated and returned to the Colorado River earns a return-flow credit that allows SNWA to take another gallon out. It must return to the river enough water so that its consumptive use is less than its allotment. Approximately 40 percent of SNWA’s service area water is used indoors. Virtually all of that (about 99 percent) is recycled for direct or indirect reuse. If it goes down a drain, it can be reused. Therefore, consumptive uses like landscape irrigation are a primary focus area for conservation.

The intake tunnel and pumping station are located within the Lake Mead National Recreation Area, which was the first of its kind when it was created in 1936 and is operated by the National Park Service to benefit about 7 million visitors annually. Siting the project in a cherished public space meant challenges for environmental protection and visitor safety. One goal for the pumping station was minimizing distraction from the natural landscape and outdoor activities offered in the National Recreation Area. Extensive coordination with the Park Service was undertaken to make the project visually compatible with its surroundings. Some accommodations included constructing a viewshed riprap berm around the facility using excavated material from tunneling, limiting the use of above-grade structures, utilizing low-sheen finishes, and matching any painted and stained features to their natural surroundings.

The project’s risk assessments addressed environment and nature. Lake Mead ecology and potential environmental impacts were identified in detail and monitored for compliance during construction.

Many accommodations for environmental protection were made during construction. Construction water was pumped to SNWA’s raw water treatment plant to prevent water loss and eliminate the need for independent treatment. An onsite batch plant for the massive amount of concrete needed for the intake structure was implemented to limit truck traffic through the National Recreation Area. Commercial power was provided to eliminate the need for temporary diesel generators. All material

excavated underground was repurposed onsite for riprap, fill, berms, road-base materials, and the like.

Benefits to the Public

The new intake benefits the Las Vegas Valley by ensuring access to a most precious resource: water (Figure 15). A reliable water supply is critical to making the desert fit for human habitation. Without this historic project, in concert with dedicated conservation efforts, Southern Nevada’s water supply would be threatened and the vibrant life of metropolitan Las Vegas would be unsustainable. The new water-delivery system will permit access for the people and ecosystems of Southern Nevada to their primary water supply even if lake levels continue to decline.

Southern Nevada has become a leader in water conservation. Since the drought began in the early 2000s, use of Colorado River water by Southern Nevadans has decreased by 23 percent, despite a 52 percent increase in population during that same period. Ongoing community conservation efforts are expected to reduce water use even further, while preserving quality of life.

Hydrologic modeling indicates a high probability that Lake Mead’s water levels will continue to decline. This will have water-supply repercussions for Southern Nevada and the rest of the Lower Basin stakeholders. In August 2021, the federal government declared a lower-basin shortage on the Colorado River starting in January 2022. The shortage declaration requires Nevada to reduce its annual Colorado River allocation by about 13,000 acre-feet. In addition, Nevada had already contributed another ~ 8,000 acre-feet in reductions as part of a Drought Contingency Plan to help protect Lake Mead. Mandated reduction amounts will increase should Lake Mead water levels continue to decline.

An additional public benefit of the project is technological advancement. During the design and construction of the new water intake system, boundaries were crossed that yielded innovations that caught the attention of practitioners around the world and are thereby elevating industry standards. To date, we have cataloged more than eighty papers, presentations, and articles that have disseminated such information about the project.

Advancement of Public’s Understanding of Geology and Engineering Geology

Before launching a large capital improvement project like the new intake, the SNWA engaged in significant stakeholder meetings to gather important feedback, data, and direction. Stakeholders included the business community, member agencies, a

Figure 15. Lake Mead at dusk.

diverse community outreach, and a citizens advisory group. Collateral materials, presentations, media assets, and other outreach efforts worked in tandem with overall organizational messaging to open up dialog and advance the public’s understanding of this critical water infrastructure project.

Constituents have ample opportunity to learn more about their water supply and water conservation in Southern Nevada. The SNWA’s website provides information and video regarding the construction of both the Lake Mead Intake No. 3 and the Low Lake Level Pumping Station. Visitors to the Las Vegas Springs Preserve can visit the WaterWorks exhibit (Figure 16) to learn more about the history of water in the Las Vegas Valley and get hands-on experiences that engage them on the inner workings of water-resource treatment and delivery in Southern Nevada.

Figure 16. WaterWorks exhibit at the Las Vegas Springs Preserve educates visitors about water treatment and delivery in Southern Nevada. Visitors enter through a ring representing the lining for the new intake tunnel.

CREDIT: SOUTHERN NEVADA WATER AUTHORITY

Enhancement of Local Cultural and Historical Understanding

Water is life, and twenty-plus years of extraordinary drought conditions have shown that to sustain life in the desert one must use water responsibly. Hard data documents the success of SNWA’s comprehensive conservation program for the benefit of Southern Nevada’s people and ecosystems.

Summary

To address unprecedented drought conditions and provide longterm protection of Southern Nevada’s primary water storage reservoir, Lake Mead, the Southern Nevada Water Authority (SNWA) constructed a third drinking water intake capable of drawing upon Colorado River water at lake elevations below 1,000 feet. Intake No. 3 ensures the Las Vegas Valley’s access to its primary water supply if lake levels continue to decline due to drought conditions. It also protects municipal water customers from water quality issues associated with declining lake levels. The construction of the intake began in 2008. A 24-foot-diameter tunnel boring machine was used to excavate a 3-mile-long tunnel under Lake Mead to connect with a new intake structure secured to the bottom of the lake. Intake No. 3 began conveying water to SNWA’s water treatment facilities in September 2015.

The intake works with SNWA’s Low Lake Level Pumping Station which allows the community to access water supplies below Lake Mead’s “dead pool” elevation of 895 feet, the point at which no water can pass through Hoover Dam to generate power or meet downstream water demands in California, Arizona and Mexico. Development involved constructing a 26-foot-diameter access shaft more than 500 feet deep, then excavating a 12,500-square-foot forebay at its bottom. The forebay connects with 34 vertical shafts, each 500 feet deep and 6 feet in diameter, which accommodate the station’s submersible pumping units. Completed in 2020, the new pumping station started operating in April 2022 when the dramatic drop in the elevation of Lake Mead rendered one of the community’s primary intake pumping stations inoperable. The low lake level pumping station has the capacity to deliver up to 900 million gallons of water per day to SNWA’s treatment facilities.

About the Authors

Barbara Luke, PhD, PE, is Professor Emerita at the University of Nevada, Las Vegas; Steven Hunt, PE, is the SW Tunnel Practice Lead with Black and Veatch, Las Vegas, Nevada; and Jason Bailey is a Management Analyst with the Southern Nevada Water Authority.

Reference

Duebendorfer, E. M., Sewall, A. J., and Smith, E. I., 1990, The Saddle Island detachment; An evolving shear zone in the Lake Mead area, Nevada, in Wernicke, B. P., Basin and Range extensional tectonics near the latitude of Las Vegas, Nevada: Boulder, Colorado, Geological Society of America Memoir 176.

Presentation of the Project during the Opening Session

Peter Jauch, SNWA’s Director of Engineering, will be presenting the project during the Opening Session on Wednesday, September 14, 2022. He will also be accepting the award on behalf of the Southern Nevada Water Authority. Jauch currently serves as the Director of Engineering for the Southern Nevada Water Authority and Las Vegas Valley Water District in Las Vegas, Nevada. During his 25 years with the Authority and District, Peter has been involved in the planning, design and construction of over $1.7 billion in water infrastructure. Peter is a graduate of the University of Arizona and a licensed professional engineer in Arizona and Nevada. Peter is passionately curious about people and processes, and also enjoys making new memories with family and friends.

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