End of an era

Dec. 18, 2021, the three iconic 775-foot smokestacks of the Navajo Generating Station (NGS)—which served as a symbol of the coal-dominated western U.S. for nearly 50 years—were demolished in a single explosive blast.

One right after the other, the reinforced concrete stacks fell, signifying the end for the Page, Arizona-based station that was once the largest coal-fired power plant west of the Mississippi. In addition to the stacks, the 199-foot-high steel-frame Unit 3 electro-static precipitator, which captured fly ash so it would not be emitted into the atmosphere, also was demolished.

“In my many years as a civil engineer, I have never witnessed such a powerful, historic and epic event,” says Gary Barras, director of project management and construction for Salt River Project (SRP), Tempe, Arizona, which operated NGS. “In just 54 seconds, three monumental giants toppled, the earth trembled and the skylines visible from spectacular Lake Powell, Antelope and Glen canyons changed forever.”

Constructed in the early 1970s, NGS was developed to meet a growing need for electric generation in the Southwest. Located on a 300-acre site leased from the Navajo Nation, the 2,250-megawatt plant provided power to Southern California, Nevada and Arizona for more than four decades.

The three reinforced stacks that eventually would become a landmark for Page residents were built in the mid-1990s to replace the three original stacks as part of the NGS Scrubber Project. The $420 million project, prompted by Clean Air Act amendments between 1977 and 1990 to assess and protect visibility in national parks and wilderness areas, included installing the new generating units to remove sulfur dioxide from NGS’ emissions.

These stacks were among the tallest structures in Arizona, earning the title as the third-highest man-made structures in the state. They were equivalent in height to a 77 ½ story high-rise building.

Until 2019, NGS consumed roughly 8 million tons of low-sulfur bituminous coal each ear, supplied by the Kayenta Mine near Kayenta, Arizona. The coal was hauled 81 miles from mine silos to the power plant via the Black Mesa and Lake Powell Railroad.

The plant was also a major provider of jobs to the region. In 2012, NGS and Kayenta Mine payments accounted for about a quarter of the Navajo Nation’s revenues, with Navajo tribal members making up 83 percent of plant employees. A majority of mine employees were members of the Navajo and Hopi Nations.

However, the plant ultimately was forced to close under the pressure of increased operating costs and a shift toward renewable energy within the U.S. The Kayenta Mine closed in August 2019 after sending its final shipment of coal to the plant, and NGS sent its last electrons to Phoenix, Tucson and Las Vegas Nov. 18, 2019, after burning its remaining coal.

Analytical approach

Decommissioning of the plant was a coordinated effort among SRP; decommissioning program manager, Pasadena, California-based Tetra Tech; decommissioning general contractor, Independence Excavating Inc., an Independence, Ohio-based subsidiary of DiGeronimo Cos., also of Independence; and explosives subcontractor, Bixby, Oklahoma-based Dykon Inc., among others.

The contractors began mobilizing on-site in February 2020, starting with environmental remediation of the site. This remediation work included removing fluids, de-energizing and preparing the site for abatement and demolition.

“We worked actually pretty solid through the month of March on some of the initial unit demolitions … and then, COVID hit,” says Doug Thomas, senior project manager for Independence Excavating. “We got together with Tetra Tech and SRP in late March and decided the infection rates were [too] high in the Navajo Nation and the area, so we shut the job down for four months.”

For those four months, Thomas says they demobilized crews and idled equipment. “Through those four months, we kept the equipment on-site, but sent the guys home,” he says. “We [then] got policies, procedures [and] COVID protocols in place to where we could restart the job.”

The decommissioning process restarted in August 2020 under new COVID-19 protocols, including temperature monitoring, masks and social distancing.

“We started significant structural demolition in October, starting with explosive felling of three of the old stacks that were 220 feet high. Then, we got into explosive felling of the big stacks, which were 775 feet high,” Thomas says.

The long-anticipated demolition of the larger stacks was a milestone in the NGS decommissioning process. For several weeks leading up to the blast, contractors prepared the stacks by drilling holes for explosives into the base of each stack. Steel I-beams also were wedged into the stack windows and vent openings to prevent each stack from twisting in an unintended manner and to help them fall in the planned location.

“More than 300 holes were drilled near ground level on the northern 18-inch-thick inside walls on each of these stacks,” Barras says. “The vertical reinforcing steel within the concrete was saw cut along the southern quadrants at the bases of these 70-foot-diameter structures.”

Once explosives were loaded into the holes, a licensed structural engineer and a licensed blaster oversaw the demolition and blasting plans.

When working on a massive structure such as NGS, Thomas says planning plays the most crucial step in the overall demolition process. He notes that demolition teams needed to be especially cognizant of following engineering analysis when coordinating charger placements and timing while also deciding what material needed to be gutted and removed from the structure to make that process work.

“Our safety department is, I will say, very good at working with … crews to really discuss, analyze and look at the task that needs to be done and look at the hazards that are associated with it—whether that’s heat, cutting [materials] in accordance with an engineering plan or working around fluids,” Thomas says.

Independence’s demolition crews worked a total of 220,000 man-hours for the NGS project, with no lost time or recordable incidents. The project had only two minor recordable accidents, which SRP says were lacerations on subcontractor workers. Prioritizing field-based performance, Thomas says crews depended on open dialogue and daily meetings to ensure safety and efficiency.

“[This demolition] was done with day-to-day coordination between the safety and the field crews to really identify the hazards for each task and mitigate the best way to handle those,” he says.

Other safety precautions included eliminating electrical hazards from a nearby switchyard by isolating the plant from the electrical grid.

Following the stack demolition, crews shifted their attention to the other main units of NGS, consisting of three boilers, two remaining electrostatic precipitators and a turbine bay.

The electrostatic precipitators were felled through dynamite detonations. To prepare for the blast, hundreds of V-shaped torch cuts had to be made at the base of the steel support beams and high up to separate the 203-foot-tall precipitator infrastructure at all points it connected to the adjoining 21-story boiler infrastructure.

According to SRP, there could be no place where the falling precipitators might have a “sticker” (something as small as a bolt head) that could catch and pull the boilers down with the precips or cause the precips to not fall as they were supposed to.

Instead, SRP says the separation allowed the huge structure to rotate, collapse and fall into the area where the three huge stacks once stood.

“We shot the electrostatic precipitators in January 2021, we shot the main boilers in March, we shot the turbine bay in June, and all of this while continuing the demolition, clearing material and shipping it off site,” Thomas says. “The demolition was completed in September 2021, and now we’re still completing some of the underground decommissioning work, some civil work, and we’re still shipping off [material].”

As of early January, Independence Excavating has shipped 120,000 tons of metals and 600,000 gallons of fluids, including 430,000 gallons of high sulfur fuel, for processing. The company also is tracking 31 recyclables for shared incentives with SRP, with more than 92 percent of all commodities being recycled.

The logistics for this recycling effort proved to be a challenge because of the remote location of NGS. “A lot the steel mills were approximately a 10-hour drive [away],” Thomas says. “So, whether it’s Colorado, Utah or California, those were the only main destinations. [We also had] the absence of rail. The closest rail was approximately two and a half, three hours away. So, you’d have to truck [materials] to that location and then get it on the rail.”

Thomas estimates that crews sent 30 to 40 trucks of sorted materials per day to steel mills, recycling facilities or repurposing facilities.

Community focus

While the demolition of NGS marks a new era for SRP and the Navajo Nation, Barras says he hopes the memory of the power plant and its employees lives on.

In a news release announcing the demolition, Barras says, “While the momentary demolition of these three stacks will soon be forgotten, we should always remember and be thankful for how our lives were made better because NGS provided reliable power to the Southwest for decades.

“The time, effort and energy that went into the demolition by the decommissioning team was extensive and important but paled in comparison to what was required by the people who designed, built, operated and maintained NGS,” he adds.

Prior to the plant’s closure, SRP says it offered new positions within the company to all 433 regular NGS employees. With operations concluded at the plant, nearly 300 accepted offers for redeployment to other SRP positions. SRP also instructed contractors conducting decommissioning operations to optimize job opportunities to qualified members of the Navajo Nation.

“The closure of the plant put an awful lot of people out of work, unfortunately. Between the plant, the mine and the railroad that went between [the two], it really made an impact on the local community,” Thomas says.

For the NGS contract, Independence Excavating hired 47 Navajo Nation members, some of whom have chosen to stay with Independence.

The Navajo Nation has elected to keep some facilities at the plant, including the warehouse and maintenance buildings, lake pump system and railroad that are valued at $175 million, SRP says. The plant owners—SRP, Arizona Public Service Co., NV Energy, the Los Angeles Department of Water & Power and Tucson Electric Power Co.—paid $18.3 million to the Navajo Nation for cost savings associated with not decommissioning those facilities and $3.6 million to fund a solid waste disposal program.

“Our work is on the Navajo Nation … and we want to do whatever we can to help the Navajo people in that region. So, [these initiatives] are really the right thing to do,” Barras says.

The author is assistant editor of Construction & Demolition Recycling. Email her at hrischar@gie.net.