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geology and hydrogeology of the florida keys >
In general, water resources in the Florida Keys are insufficient for the human population of the area. Studies by Parker et al. (1955) and Klein (1970) indicate that most Keys have only ephemeral freshwater lenses and cannot be relied on for perennial supplies of potable water. Only the largest of the Lower Keys, Big Pine and Key West for example, have permanent freshwater lenses. Even the large Upper Keys, Elliott Key for example (Klein, 1970), do not have permanent lenses, even though rainfall increases northward. The Lower Keys are more likely to have lenses because of their geometry and geology. These Keys, In plan view (Fig. 5-4), retain the broad flat of an ooid shoal in contrast to the Upper Keys which are narrow and elongate parallel to the shelf. In addition, the surficial lithologic unit of the Lower Keys (oolite) is less transmissive than that of the Upper Keys (reef).
Although some groundwater is used for irrigation (on Big Pine Key), and some potable water is provided by cisterns and reverse-osmosis facilities, more than 95% of water for domestic use is now provided by the Florida Keys Aqueduct Authority via pipeline from a wellfield on the mainland. Currently about 57,000 m3 day-1 (15 Mgal day-1, U.S.) are pumped to the Florida Keys (NOAA, 1995). The volume of this flow for two days is comparable to the volume of the freshwater lens beneath Key West during the wet season, as estimated by Mackenzie (1990).
The majority of water pumped to the Keys is for domestic use. Key West and Key Colony Beach (Marathon) have sewage-treatment facilities and ocean outfalls. Much of the remaining freshwater is disposed of as sewage through septic tanks and shallow wells (10-30 m) beneath the islands. The sewage is rich in nutrients, providing a potential environmental problem in this region of oligotropic waters. The ultimate fate of the sewage beneath the islands is a topic of continuing study (Shinn et al., 1994). Based on water usage and disposal methods, it is clear that freshwater piped to the Florida Keys can be a significant contribution to small and ephemeral lenses of these islands.
U.S. Department of the Interior, U.S. Geological Survey
This page is: http://sofia.usgs.gov/publications/papers/keys_geohydro/resources.html
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Last updated: 04 September, 2013 @ 02:04 PM (KP)
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