NBC » Caltrans is investigating whether microscopic organisms are attacking critical welds on the submerged foundation of the new Bay Bridge tower, potentially endangering the projected 150-year lifespan of the troubled $6.4 billion structure. While Caltrans engineers say there’s no immediate concern about the bridge failing, a recent underwater survey spotted pits — pockets of accelerated corrosion — on welds that bind massive piles that hold up the foundation.