• Arizona Contractor & Community

SRP Contractors Demolish Navajo Generating Station's Three Iconic Stacks

Navajo Generating Station's (NGS) three iconic 775-foot smokestacks – a Page, AZ landmark for 45 years – were demolished in a single explosive blast on Friday, falling northward like trees being felled. The NGS reinforced concrete stacks were the third-highest man-made structures in Arizona and were equivalent in size to a 77 ½ story high-rise building 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, was simultaneously demolished.

The long-anticipated demolition, a milestone in the NGS decommissioning process, was a coordinated effort of former plant operator Salt River Project (SRP), decommissioning program manager Tetra Tech, decommissioning general contractor Independence Excavating, Inc., and explosives sub-contractor Dykon, Inc., among others. Operation of NGS officially ended in November 2019 when SRP permanently shut down all three units at the plant, located on the Navajo Nation just east of Page. "In my many years as a civil engineer, I have never witnessed such a powerful, historic and epic event," said Gary Barras, SRP director of Project Management & Construction. "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."

URL : https://media.srpnet.com/srp-contractors-demolish-ngs-three-iconic-stacks/ Dust from the blast was minimized by water being sprayed from "dust bosses," also known as water cannons. Shielding material was installed to protect nearby structures that will remain after the plant is decommissioned. Over the past several weeks, contractors prepared the stacks for blasting by drilling holes for explosives into the base of each stack. Steel I-beams 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, said Barras. "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, the demolition and blasting plans were overseen by a licensed structural engineer and a licensed blaster. The three reinforced concrete stacks were built in the mid-1990s to replace the three original NGS stacks as part of the NGS Scrubber Project to remove sulfur dioxide from NGS emissions. Since decommissioning began nearly a year ago and before any demolition work was done, all regulated materials such as fluids, oils, chemicals, or asbestos were safely removed. Items like light bulbs, batteries, and mercury switches were also removed. Barras said 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. "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," he said. "I send a heartfelt thanks to the past NGS workers and also say thank you to the many others who worked hard daily to generate reliable power at our plants." Working with SRP, a number of U.S.-based contractors will continue demolition and reclamation responsibilities at the plant site including disassembling the power block and addressing cleanup and restoration. SRP anticipates that decommissioning will take approximately three years to complete at a cost to the NGS owners of around $150 million. Based on the initial study, SRP estimates that more than 90 percent of the decommissioned plant will be salvageable. The Navajo Nation has elected to retain a number of facilities at the plant including the warehouse and maintenance buildings, lake pump system, and railroad that are valued at around $175 million. The owners also paid nearly $19 million to the Nation for cost savings associated with not decommissioning those facilities and paid $3.6 million to fund a solid waste disposal program for the Nation. In addition to extending operations at NGS for nearly three years to ensure a transition period for the Nation and plant employees, the NGS owners agreed to a 35-year extension lease that will provide lease payments totaling about $110 million to the Navajo Nation and will allow continued access to the site for decommissioning, long-term monitoring and ongoing operation of the transmission system. The federal government has also pledged to provide 500 megawatts of transmission capacity from the NGS transmission station that is valued at more than $80 million. The NGS owners will pay the Nation's share of operations and maintenance costs at the station for 10 years, at a project value of $5 million. Prior to closure, SRP 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 has also instructed contractors conducting decommissioning operations to extend hiring preference for contract work to qualified members of the Navajo Nation. The owners of NGS include the U.S. Bureau of Reclamation, SRP, Arizona Public Service Co., NV Energy, the Los Angeles Department of Water & Power, and Tucson Electric Power Co.


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