Hydrogeology of deep-well disposal of liquid wastes in southwestern Florida, USA

Abstract

Deep-well injection has been used to dispose of municipal liquid wastes in southwestern Florida since 1988. The liquid wastes are injected into an extremely high-transmissivity zone of fractured dolomite in the Early Eocene Oldsmar Formation of the Floridan aquifer system; this zone is commonly referred to as the Boulder Zone. Data collected during the drilling and operational testing of southwestern Florida injection wells provide insights into the nature of the injection zone and overlying confining beds. The location of high-transmissivity zones that are capable of accepting large quantities of waste water is vertically and horizontally variable and cannot be predicted with certainty. A 40.9-m thick high-permeability interval in one injection well, for example, was absent in a well drilled only 85.4 m away. Some upward migration of low-density injected fluids has occurred, but at no site were the injected liquids detected in deep monitor wells, such as occurred at injection-well sites along the coasts of southeastern, west-central, and east-central Florida. The primary confinement of the injected liquids (i.e., deepest effective confining beds) consists of unfractured beds of low-permeability dolomite within the Oldsmar Formation, whose locations are also laterally and vertically variable. The origin and controls of the distribution of fractures in the Oldsmar Formation are poorly understood.