The new A$95 million civil contract will run for three years, with an option of a two year extension, subject to performance.
The scope of work includes maintenance services, such as minor civil works, bauxite residue management, and bulk materials handling services at the Kwinana bauxite residue storage, refinery and port facilities.
There is also potential for other civil works across Alcoa's mining, port, and refining sites elsewhere in WA.
SRG managing director David Macgeorge said the contract extension was significant for the company, and demonstrated the value of the WBHO Infrastructure acquisition in March.
WBHO was picked up from voluntary administration for $15.2 million, paid in existing cash and equipment finance facilities, saving some 275 jobs at a time when skilled workers are challenging to access.
The deal came after WBHO's South African parent company pulled out of Australia citing a "hardline" COVID-19 policy.
WA's COVID policies were rescinded on March 3, leading to a massive spike in cases that continues today, and is posing its own staffing challenges.
WBHO has historically generated around $150 million or revenue per annum and has a track record of positive earnings and growth.
Macgeorge said the Alcoa contract would support over 100 local jobs.
"This term contract win provides further evidence of SRG Global's strategic transformation to a high value annuity/recurring services business with specialist capability employing 2700 people globally," he said.
SRG has now secured some $600 million in work over the past six months.
Its shares were last traded up 6% at 62.5c, valuing it at $265 million.
The stock has traded between 43c and 69c over the past year, peaking in early April.