Water resources and effects of ground-water development in Pasco County, Florida

Abstract

Pasco County, on the west-central coast of Florida, has a hill and valley terrain that ranges in altitude from sea level along the Gulf of Mexico to 300 feet above sea level in the ridge area near Hernando County. The principal perennial streams are the Withlacoochee and Hillsborough Rivers in the eastern part of the county and the Pithlachascotee and Anclote Rivers near the coast. The county is rural except for some intensive residential and commercial development along the coast; only 13 percent of the population is located in incorporated areas. The Floridan aquifer system, the principal source of water in westcentral Florida, is comprised of carbonate rock of Tertiary age.Only the upper part of the system (the Upper Floridan aquifer) is tapped for water supplies in Pasco County. Formations of the Upper Floridan aquifer in Pasco County consist of, in ascending order, the Avon Park Formation, the Ocala Limestone, the Suwannee Limestone, and the Tampa Limestone. These formations represent the freshwater part of the Floridan aquifer system in Pasco County. The aquifer is overlain by surficial deposits of sand and clay that range from zero to about 100 feet in thickness. In some parts of the county, the sand constitutes an unconfined surficial aquifer.Water from the Upper Floridan aquifer accounted for 99 percent of the about 80 million gallons per day of water used for irrigation, industry, and rural and public supply in Pasco County in 1984. Thirty-one percent of this water was used for agricultural irrigation. Thirty-seven percent was used by the two major industries, rock mining (limestone) and food processing. Approximately 55.0 million gallons per day of water withdrawn from the aquifer was exported via pipeline to Pinellas County to the south and west. Of this, 1.5 million gallons per day were bought back by Pasco County.run with maximum projected pumpage and reduced rainfall for the'year 2035. Projected pumpage was based on expected demands on Pasco County's water resources. In addition, five different development plans to accommodate projected increases in withdrawal from west Pasco County from 1985 to the year 2035 were used to show the different potential drawdowns resulting from each plan. The drawdowns resulting from the projected pumpage simulations were used to evaluate the potential effect of projected withdrawals on heads in the aquifer, reduction in spring flow, and on saltwater encroachment. Data-Collection SitesData from 539 wells were used in this study (appendix A). Water samples collected from 64 wells during the study were analyzed for common inorganic constituents including calcium, magnesium, potassium, sodium, chloride, fluoride , silica, sulfate, iron, nitrite, and nitrate (appendices B and C) . Also determined at the time of sampling at most wells were temperature, specific conductance, and pH. Potentiometric surfaces for September 1984 (Barr andSchiner, 1984;Barr, 1984) were mapped based on measurements in 123 wells in the Upper Floridan aquifer. Lithologic or water-table data were co...