ABSTRACT: Approximately 25 billion gallons of industrial wastewater was injected into the Lower Floridan aquifer at a nylon-manufacturing plant north of Pensacola, Florida, from July 1963 to April 1991 and approximately 4.4 billion gallons of industrial wastewater was injected at an acrylic fiber-manufacturing plant southwest of Milton, Florida, from 1975 to January 1991. Water from four monitoring wells completed in the Floridan aquifer system at each of these plants has been sampled by the U.S. Geological Survey since December 1969 north of Pensacola, and since May 1975 southwest of Milton. The purpose of the sampling was to monitor the effects of this injection on ground-water quality and to assess the occurrence of seepage of injected wastewater to the overyling Upper Floridan aquifer. Large differences in hydraulic heads between the Upper and Lower Floridan aquifers, the lack of a potentiometric surface mound in the Upper Floridan aquifer corresponding to the mound in the Lower Floridan aquifer, the great thickness of the Bucatunna Formation separating these aquifers, and the water-quality data indicate that there is no hydraulic connection between these two aquifers at these plants, and thus no upward leakage of injected wastewater.
None of the selected water-quality characteristics (pH, specific conductance, and concentrations of total ammonia plus organic nitrogen, calcium, sodium, and chloride) had significant trends (from 1975 to 1991) in water from the north well, completed in the Lower Floridan aquifer 1.9 miles northwest of the injection wells at the plant north of Pensacola, indicating that water in this aquifer has probably not been affected by injected wastewater at this well. Significant trends in specific conductance and the concentrations of total ammonia plus organic nitrogen, calcium, and magnesium in water from the south monitor well, located 1.5 miles south of the injection wells at this plant, indicate mixing with wastewater in the Lower Floridan aquifer at this well. In water from shallow wells 1 and 2, completed in the Upper Floridan aquifer at this plant, pH was the only water-quality characteristic with a significant positive trend. Negative trends of concentrations of magnesium in water from shallow well 1 and of chloride in water from shallow well 2 in seasonal samples from April to October are of small magnitude and are probably not related to upwelling of wastewater from the Lower Floridan aquifer.
At the plant southwest of Milton, trend testing indicated a positive trend for calcium in water from the north well, located 1.5 miles north of the injection well. The low magnitude of this trend (less than 1 percent of the median value per year) and the lack of significant trends in the other indicator characteristics in water from this well indicate that the quality of water in the Lower Floridan aquifer at this well has probably not been affected by injected wastewater. Water from the standby injection well, located 1,600 feet from the injection well at this plant, and from the deep test well, located 1,025 feet from the injection well, had a significant positive trend in the concentration of total thiocyanate (analyzed at site 2 only) and significant negative trends in specific conductance and concentrations of magnesium, sodium, potassium, and chloride. These trends indicate that wastewater has affected the quality of water in the Lower Floridan aquifer at this well. Analyses of water from the shallow well, completed in the Upper Floridan aquifer at the plant southwest of Milton, showed significant positive trends in pH and the concentration of calcium, and a significant negative trend in the concentration of total ammonia plus organic nitrogen. The low magnitudes of the these trends and the fact that injected wastewater at this plant has lower pH values and a higher concentration of total ammonia plus organic nitrogen than water in this aquifer indicate that these trends are probably unrelated to upward seepage of wastewater from the Lower Floridan aquifer.