In October 1992, the U.S. Geological Survey (USGS), in cooperation with the Idaho Division of Environmental Quality, Boise Regional Office (IDEQ-BRO), began a comprehensive study of ground-water quality in the lower Boise River Basin. The study in northern Ada County has been completed, and this report presents selected results of investigations in that area. Results and discussion presented herein are based on information in publications listed under “References Cited” on the last page of this Fact Sheet.