A major new reservoir in Northern Colorado that is intended to help secure water for nearly 1 million people has hit an alarming snag before it has even gotten underway. Chimney Hollow Reservoir began filling this spring, but the process was abruptly halted after officials discovered uranium in some of the rock used to build the dam, NPR's KUNC News reported. What happened? The reservoir is designed to hold Colorado River water for 12 growing Fr…