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J. D. Fretwell

Publications and source records attributed to J. D. Fretwell.

8 recordsLinked to original sources
USGS1988

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

Ninety-nine percent of the 79.72 million gal/d of water used in Pasco County, Florida is groundwater from the Upper Floridan aquifer. In addition, 53.5 million gal/d is exported for use in Pinellas County. Chemical quality of the water generally falls within recommended limits for drinking water except near the coast. A groundwater flow model was used to predict drawdowns in water levels under five different development plans for west Pasco County. One of these plans was incorporated in an estimated groundwater development plan for 2035 for Pasco, Pinellas, and part of Hillsborough County. Reduction in evapotranspiration accounts for nearly all the water required for each development plan. Two plans showed less effect in drawdown and potential of saltwater intrusion than the other three. For the overall groundwater development plan for Pasco, Pinellas, and parts of Hillsborough Counties, the average potentiometric surface in 2035 would be from 8 ft higher to 20 ft lower than the average 1976-77 potentiometric surface. Reductions in head would increase the potential for infiltration of contaminants in areas where surficial materials are thin, sinkhole development in sinkhole prone areas, and upconing and lateral intrusion of saltwater. The potential for dewatering the surficial aquifer is great in the Cross Bar Ranch and Cypress Creek well-field areas. Evapotranspiration of groundwater would be reduced by 19% between 1976-77 and 2035. Exchange of water between the rivers and the aquifers will be reduced by 13%. Springflow will be reduced by 6%, and three springs will cease to flow. Model boundary inflow and outflow also will be reduced.

Florida↗
USGS1985

Water resources and effects of development in Hernando County, Florida

In spite of the hill and valley terrain in the Brooksville Ridge area of Hernando County, Florida, little surface drainage occurs within the county. Recharge to the Floridan aquifer system occurs as infiltration of precipitation within the county or as ground-water flow from Sumter County to the east and Pasco County to the south. Discharge is principally to the Gulf of Mexico, but some ground water flows north into Citrus County before it reaches the Gulf. The Floridan aquifer system is generally unconfined. Water quality is generally good except near the coast where high chloride occurs. Water from the Floridan aquifer system accounted for 87 percent of the water used for irrigation, industry, and rural and public supply in 1982. Sixty-seven percent of this water was used by industry. Rock mining, the major industry, used 99 percent of the industrial water. The anticipated increase in population in the county between 1982 and 2000 will increase demand for water primarily from public water-supply systems. This higher demand will cause about a 1 percent reduction in flow from Weeki Wachee Springs, but little change in lake levels or saltwater intrusion will occur if the projected additional supplies are developed far enough inland from the coast. (USGS)

Water-Resources Investigations Report↗
USGS1983

Chloride concentrations in the coastal margin of the Floridan Aquifer, southwest Florida

The Floridan aquifer is the principal source of freshwater supply in southwest Florida. The freshwater part of the aquifer is underlain by saltwater in lower formations and is bounded on the west by saltwater in the coastal parts of the aquifer. A zone of mixing lies between the saltwater and freshwater. The saltwater and freshwater boundaries are defined by chloride concentrations of 19,000 milligrams per liter on the coastward side and 250 milligrams per liter on the landward side. Lateral intrusion of saltwater can occur along the coast in areas where the hydraulic gradient declines and upconing can occur in inland areas of heavy ground-water withdrawals. Safeguards against saltwater intrusion in these areas are necessary because flushing of the aquifer is a very slow process. A network of chloride monitor wells is proposed for the zone of mixing in the upper producing zone of the floridan aquifer. Seventy wells were selected at 54 sites to monitor chloride concentrations along the 250-milligram-per-liter line of equal chloride concentration. One-fourth of the wells are located in areas of increasing chloride concentrations or heavy ground-water withdrawals and the remaining wells are intended to improve delineation of the interface and to monitor long-term changes in chloride concentrations. (USGS)

Water-Resources Investigations Report↗
USGS1983

Ground-water resources of coastal Citrus, Hernando, and southwestern Levy counties, Florida

Ground water in the coastal parts of Citrus, Hernando, and Levy Counties is obtained almost entirely from the Floridan aquifer. The aquifer is unconfined near the coast and semiconfined in the ridge area. Transmissivity ranges from 20,000 feet squared per day in the ridge area to greater than 2,000,000 feet squared per day near major springs. Changes in the potentiometric surface of the aquifer are small between the wet and dry seasons. Water quality within the study area is generally very good except immediately adjacent to the coast where saltwater from the Gulf of Mexico poses a threat to freshwater supply. This threat can be compensated for by placing well fields a sufficient distance away from the zone of transition from saltwater to freshwater so as not to reduce or reverse the hydraulic gradient in that zone. Computer models are presently available to help predict the extent of influence of ground-water withdrawals in an area. These may be used as management tools in planning ground-water development of the area. (USGS)

Water-Resources Investigations Report↗
USGS1982

Position of the saltwater-freshwater interface in the upper part of the Floridan Aquifer, southwest Florida, 1979

Ground-water withdrawals in southwest Florida are increasing because of urban growth, industrial expansion and increased agricultural irrigation. As a result, the potentiometric surface of the Floridian aquifer has been lowered in some areas, allowing seawater to encroach into the aquifer and threaten the freshwater resources of the area. Effective management of groundwater is needed to control the encroachment and protect the freshwater aquifer.

Florida↗