Purpose and scope: The Meadowbrook artificial-recharge project, a cooperative effort between the U.S. Geological Survey and the Nassau County Department of Public Works (NCDPW) since 1975, is intended to demonstrate the feasibility of using reclaimed wastewater to replenish and improve the quality of Long Island's ground water. This report presents the results of geologic, hydrologic, and hydrochemical studies that were done at the Meadowbrook artificial-recharge site to define conditions prevailing before the start of recharge operations.