The U.S. Geological Survey is conducting a water quality study as part of the nationally implemented Rural Clean Water Program in the headwaters of the Conestoga River, Pennsylvania. The study, which began in 1982, was designed to determine the effect of agricultural best management practices on surface--and groundwater quality. The study was concentrated in four areas within the intensively farmed, carbonate rock terrane located predominately in Lancaster County, Pennsylvania. These areas were divided into three monitoring components: (1) a Regional study area (188 sq mi): (2) a Small Watershed study area (5.82 sq mi); and (3) two field site study areas, Field-Site 1 (22.1 acres) and Field 2 (47.5 acres). The type of water quality data and the methods of data collection and analysis are presented. The monitoring strategy and description of the study areas are discussed. The locations and descriptions for all data collection locations at the four study areas are provided. (USGS)