The ice plant where Will works as a night watchman can be seen as a symbol of hope, a symbol of labor, and a symbol of the lack of productive imagination and untapped resources. It also helps make Will a sympathetic character, and, when taken with the ice in Minnie's final bedroom scene, links him symbolically with the woman.
What is Will doing on Saturday night? Working. His job is to guard the building which houses one of Jefferson's most precious resources – ice. The ice plant can be seen as symbol of hope – it contains both cold and water. When combined, these two things make ice and might to a lot toward cooling the passions of the townspeople. When McLendon and the gang drive away from the ice factory, all hope (symbolically) is lost. There doesn't seem much hope of the vigilante gang cooling off.
The extreme dry and heat of Jefferson in September didn't create the irrational prejudices and value systems that perpetuate the tragedies of the story, but they certainly exacerbate them. What Jefferson needs is rain, water, a cool breeze. The ice locked away in the ice plant is a symbol of how the town's real needs, including rain, are frozen, hidden, inaccessible, obscured by dust. The imaginations of the characters can't break free from the cultural and geographical surroundings to see clear to a better way than private violence and public pressure.
Around the same time Will is abducted from his work at the ice plant, Minnie is being iced down by her rather "friends." Sadly, at this point, the ice is too late – the damage to Will and too Minnie is done. No amount of ice can bring either of them back from the breaking point.