A nonprofit overseeing the Norwalk River Valley Trail is starting path clearing in Tarrywile Park, marking the first portion of Fairfield County’s longest trail in Danbury. Plans call for a 10-foot-wide stone dust path between Tarrywile Lake and Parks Pond, stretching the length of four-and-a-half football fields. The project is part of a larger 30-mile trail system connecting Danbury to Norwalk and is funded in part by $8.3 million in state construction grants.