Tri City Rock, which sells concrete, stone, and landscaping materials, maintains its business is not posing a health risk to children at the nearby Stratford School.

(Left/Top) Dozens of parents contacted the NBC Bay Area Investigative Unit with safety concerns regarding their children's school and its close proximity to the concrete plant. (Right/Bottom) Glenn Wong, 5, says he often tries to warn his classmates when he sees plumes of dust traveling from the concrete plant towards the school playground.