The Weston Observatory, at 381 Concord Road, will host a colloquium entitled “Tracking Salt in Drinking Water” at 7 p.m. Nov. 13. The talk will be given by James R. Besancon, an associate professor of geosciences at Wellesley College, as part of a series of presentations organized by Boston College’s department of earth and environmental sciences. The event is free, but reservations are required; call 617-552-8300. For more information, visit www.bc.edu/westonobservatory. Full story for BostonGlobe.com subscribers.