Hudson River sludge being dredged in advance of the new Tappan Zee bridge is presenting serious environmental challengers for developers

The crews preparing to build the new $3.9 billion Tappan Zee Bridge are still determining the best methods to keep the waters of the Hudson River clear and clean as they dredge more than 950,000 cubic yards of tainted sludge from the river bottom in the late summer and early fall.