Purpose and scope: The objectives of this investigation were to describe the hydrology and geology of six landfill sites and to determine, when possible, changes in water levels due to landfill operations, the direction and extent of leachate movement, and changes in water quality in the surficial aquifer and the Floridian aquifer. The scope of this report is to evaluate pertinent data and results from six landfill site studies that have been conducted in Hillsborough County since 1969.