NewsdayTV's The Grumman Plume investigates how a decades-old cover-up by aerospace giant Grumman spiraled into Long Island's most urgent environmental crisis. As early as the mid-1970s, toxic chemicals from Grumman's Bethpage plant were seeping into the groundwater. Now, the resulting toxic plume?one of the most complex and persistent contamination sites on Long Island?continues to threaten the region's drinking water.