It is a state project and therefore governed by the prevailing (very high, artificially high) wage law.
It was almost certainly not immigrant labor since the wages were mandated to be high.
That really doesn't mean what you think it does. My next door neighboor has an alarm business. When he put a system in the high school, they made him pay prevailing wage but they imposed no rules on who he could hire. In fact, according to him, he could have hired bums/illegals and on paper paid them the prevailing wage and pocketed the difference. He didn't but could have.