The Biscayne Aquifer
By: Harry Jenkins
Emporia State University
Hydrogeology, Spring 2009
The aquifer is a composed up of mostly limestone and sandstone with some sands. The Biscayne Aquifer is a wedge shape of highly permeable limestone and less permeable sandstone in southeast Florida. The Biscayne aquifer is a costal unconfined aquifer. The aquifer is 35 to 40ft. near the everglades and thickens northeastward. The Biscayne aquifer is on the boundary of Biscayne Bay and the Atlantic Ocean. The Biscayne Aquifer is a major source of water of Key West, Dade, Broward, and the southeastern part of Palm Beach County. Water is drawn from the aquifer then pumped through a pipeline to Key West. Major metropolitan city including Miami, Homestead, Hialeah, Hollywood, Fort Lauderdale along with a few others depend on the aquifer as a main source of water.
The FKAA (Florida Keys Aqueduct Authority) provides water for the residents and visitors alike in Key West.
The FKAA pumps groundwater from the Biscayne Aquifer for its some residents more than 100 miles away. The south Florida area suffered harsh droughts from 1999-2005 caused ground water level to drop which cause saline water to move inland.
Figure 1, The extent of the Biscayne Aquifer
Susceptible to Contamination
The Biscayne Aquifer is high susceptibility to contamination due to its exposure at the land surface and high permeable rates. The most common contaminate in the aquifer is saline water and chemicals carried by runoff into canals. During the wet season pesticides and fertilizers are use heavily and become susceptible to runoff. Other contaminates include landfills, septic tanks, sewage water treatment ponds and storm water disposal wells.
The Aquifer has been contaminated from landfills, saltwater, and septic tanks from the surrounding area in the past. Saltwater intrusion has been a problem for the Biscayne Aquifer for more than ten years. The construction of the C- 111 canal in southeastern Miami- Dade County in the earl 1960’s allowed saltwater to move inland. Parker et al. (1955) identified saltwater intrusion in the Miami area resulting from groundwater pumping and from the construction of the uncontrolled canals which lowed the water table in the Biscayne Aquifer and allowed saltwater encroachment.
Water pumped from the Biscayne aquifer is potable. The water is hard and contains iron deposited. The water contains low concentrations of chloride and dissolved solids. Water from Dade and Broward County is brown due to contact with organic materials. They are a few sites in that have contaminated the aquifer in the pass and remedial work is underway on a few landfills that are known to contaminate the aquifer.
Figure 2, Shows the geology of Florida this data was obtain at the Geocommunity website.
The Biscayne Aquifer is composed up of limestone, sandstone and sand. The geologic formations that make up the aquifer are Pleistocene with some Pliocene age formation. Formation in the aquifer are lens like and inconsistent not expanding across the whole formation. Geologic formation are intertwined with one another.
Figure 3, The extent of the Biscayne Aquifer
In Dade County oolitic limestone and quartz sands forms the upper layers of theaquifer(Parker and other, Plate4). Oolitic limestones are thickest near the coast and thin westward. Fine to medium fill solution cavities (Parker and other, 1955, Plate4) in Oolitic limestones which gives it high permeability rates and allows rapid response to rain fall.
Figure 4, The extent of the Biscayne Aquifer
The fort Thompson formation expands over most of the aquifer. The southern half of the Aquifer consists of limestone and grades northward into sandy deposits. The base of the aquifer acts as a retard layer made up of low permeable silty clay. To the north the aquifer base is made up of a mixture of low permeable calcareous sand, shell, silt along with some low permeable silty clay. The base of the Biscayne Aquifer slopes south westward.
Figure 5, The extent of the Biscayne Aquifer
Where the aquifer is exposed at the surface or thin layers of soil allow the aquifer to response to rain rapidly. Rain, wetlands, canals are major part of recharge to the aquifer. During the wet season sheets of water move south towards the Everglades to recharge the aquifer. In places where the aquifer is exposure, as the sheets move across the aquifer recharge almost immediately. Canals, levees, dams, and other control structures help the South Florida Water Management District manage water resources in south Florida. Canals in southern Florida pervert floods during the wet season and provide water to the aquifer maintaining water table levels. During the wet season Florida can receive multiple torrential downpours. The SFWMD utilizes pumping station to pump large amounts of water from canal into conservation area to control flooding.
Water table level in the aquifer are affected mostly by precipitation falling directly on the aquifer. Water table levels may vary from 2 to 8 feet per year due to recharge, discharge and pumping from local municipal wells. During prolonged drought periods land owner and framers increase pumping rate to maintain lawns and crops.
High permeable rate are beneficially to the SFWMD to maintain water levels near coastal regions. The SFWMD uses the massive canal systems to divert water to major control structures near the coast to maintain water level to pervert saltwater intrusion. During the wet season the control are open most of the time to release excessive amounts of water to the Atlantic Ocean. The structures are close during the dry seasons to maintain water level in canals.
Figure 6, The extent of the Biscayne Aquifer
The canals systems that control water in the south Florida area are connected to the aquifer. As water passes from the canal to the aquifer the canal is known as a “losing stream.” This aquifer canal relationship serves as a major source of recharge that maintains water table levels. The level of communication between the aquifer and canals may decease with time as fine sediment settles, lining the bottom of the canal.
Groundwater flow is in a Northeast direction to the ocean. During 1946 flood prevention was of a great importance, control structures were place in all major canals to control fresh water movement. The SFWMD control water movement in all of Southern Florida. Canals and levees contain water in Lake Okeechobee and three other water conservation areas. Canals provide freshwater to the aquifer of recharge. Water levels in the canals are maintain at certain levels urban areas and agriculture fields to prevent flooding.
Figure 7, The extent of the Biscayne Aquifer
Figure 8, The extent of the Biscayne Aquifer
The SFWMD operates and maintains about two-thousand miles of cannels and levees, sixty pumping station, and 2,200 water control structures. The SFWMD regulates the management and storage of storm water as well as the dredging or filling of wetlands. In addition, the District is actively working to improve water quality in America’s Everglades and to restore habitat and water resources throughout the region. Click Here to see the ground water usage in 1950-1980 Water Withdrawal.
Water management practices implemented by water resource agencies would include SWAPP, SDWA, The Drinking Water Toxic Program, and Dry-cleaning Solvent Surveillance Program along with a few others. SWAPP stands for Source Water Assessment and Protection Program. This program is meant to ensure that drinking water is safe, not just at the tap, but at its source. The Florida Department of Environmental Protection (DEP) is initiating the SWAPP as part of the federal Safe Drinking Water Act (SDWA). The Department of Environmental Protection protects conserves and manages Florida's natural resources and enforces the State's environmental laws and restores waterways. The Drinking Water Toxic Program is responsible for coordinating state-wide groundwater sampling for chemical contamination of private drinking water supplies. Dry-cleaning Solvent Surveillance Program is responsible for identifying areas in the state having drinking water contaminated as a result of discharges of solvents used in the dry-cleaning process. The main problems facing water resource agencies include increasing water demand of the gowning population; the prevention of further saltwater intrusion; maintain water quality in the Biscayne aquifer and the surrounding lake, bays, and canals.
Water levels are the highest around municipal well fields, water conservation areas. Large municipal well are commonly constructed with 40 to 60 ft in diameter casing and open hole below the casing 75 to 100 ft in Dade County. Specific capacities from test are from about 1,000gal/min/ft of drawdown. Wells use for irrigation a not cased and are drilled at spacing of 300ft. Trucks mounted with pumps on them are moved from well to well pumping in short interval at rates of 1,000 gpm.
The Biscayne Aquifer is consender to be a prizes resouces to residents in florida because of its high recharge rates. Saltwatee inrusion and canal containation are the main problems facing water resouce agenice in South Florida. The Biscayne Aquifer is the sole source of water for more than half of the population in southeast Florida. The SFWMD has develop a series of guidelines to help improve water quality in the Biscayne Aquifer.To insure the Biscayne Aquifer is available for future use in the future.
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