In 1939, a special program for the systematic collection of chloride data in southeastern Nassau County was inaugurated in which three agencies participated. The Nassau County Department of Public Works constructed the sampling wells, the Ground Water Branch of the U.S. Geological Survey began to collect at period intervals water samples which were analysed at the Mount Prospect Laboratory of the New York Department of Water Supply, Gas and Electricity, The Nassau County Department of Public Works and the U.S. Geological Survey have continued financial cooperation for the maintenance of this program up to the present time.