TAMPA BAY TRIBUTARIES BASIN. Hydrogeological Setting

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1 TAMPA BAY TRIBUTARIES BASIN Hydrogeological Setting Aquifers within the Tampa Bay Tributaries Basins ground water flow system include the Floridan aquifer system, the intermediate aquifer system, and the surficial system. The Floridan aquifer system is composed of limestone sequences from the Paleocene to the Miocene epochs. These formations (starting with the deepest) include the Cedar Keys Formation (Paleocene), Oldsmar limestone, Lake City limestone, Avon Park Formation, the Ocala Group (Eocene), the Suwannee Limestone (Oligocene), and the Tampa member of the Arcadia Formation (Miocene). The system is divided into the Lower and Upper Floridan aquifers, which are separated by the middle, semi-confining unit (Miller, 1986). The upper aquifer is the main source of potable water for the Tampa Bay Tributaries Basins area and provides more than 10 times the water supplied by either the intermediate or surficial aquifers (Fernald and Purdum, 1998). Within the Tampa Bay Tributaries Basins the potable water zone of the Floridan aquifer system ranges from approximately 250 feet in the Manatee River Basin to more than 1,500 feet in the Hillsborough River Basin (Causey and Leve, 1976). The intermediate aquifer system is comprised of a sequence of carbonates and clastic sediments (clay, quartz sand and sandstones, and phosphates) of the Hawthorn Group (Miocene to Pliocene). Within the area the Hawthorn Group is divided into the lower, predominantly carbonate section, the Arcadia Formation, and the upper, clayey, silty section, the Peace River Formation (Scott, 1988). The finer-grained sediments of the Hawthorn provide a confining layer for the underlying Floridan aquifer system. The intermediate aquifer is absent in the northern part of the Hillsborough River Basin and becomes more persistent as the Hawthorn Group sequence thickens to more than 400 feet in a southern direction. Thin beds of shell, sand, and limestone, which are generally separated by thick beds of clay, produce a water source sufficient for domestic and small irrigation supplies (Peek, 1958), and possibly in the eastern part of the area, public supply (SWFWMD, 2000). The surficial aquifer system occurs throughout most of the area, being absent only in the northern part of the Hillsborough River Basin. It is made up of thin layers of sand, with minor amounts of shell and shell beds, clay and silt. The surficial aquifer yields enough water for potable use in the highland areas (Fernald and Purdum, 1998), but overall has limited use. Physiographic Features Two physiographic features, the highlands in the north and east areas and the lowlands in the central and west areas, dominate the Tampa Bay Tributaries Basins region (White, 1970). The highlands include the Brooksville Ridge and the Polk Upland, which are separated by a lowland feature, the Zephyrhills Gap. The Zephyrhills Gap is part of the Western Valley lowland, which lies in the central part of the Hillsborough River Basin. The gap trends westward and connects to broad, relatively flat plains of the Gulf Coastal Lowlands, the predominant feature of the Tampa Bay Basin and the western parts of the Little Manatee River and the Manatee River basins.

2 Ground Water - Surface Water Interactions To a great extent the geology and the relationship of these physiographic features influence the ground water and surface water interactions within the region. In the Brooksville Ridge surface water drainage is generally contained within the ridge. Ground water with the ridge is unconfined so that rainfall and surface water percolate through the surficial sands and recharge directly to the Floridan aquifer. A mantle of sand, as well as layers of clay, silt, and thin beds of limestones overlying the thick sequence of limestone characterizes the Polk Upland. Internal surface water drainage exists to some extent and as a result the Polk Upland provides recharge to the intermediate and Floridan aquifers. Surface water in the Polk Upland also serves as a source to several of the region's rivers and streams. Once water has entered the ground water system regional flow in intermediate and Floridan aquifers is toward Tampa Bay. Ground water flow within the surficial aquifer is likely follow the local topographic slope. Ground water flow within the three aquifers and to surface water may be complex. Flow is dependent on the potentiometric surface of each system. Each aquifer system has its own potentiometry that varies over space and time. The surficial aquifer is recharged primarily by rainfall and to a lesser extent by surface water bodies. The surficial aquifer may contribute water to the intermediate aquifer, but more importantly will contribute to nearby surface water bodies. Water within the intermediate aquifer may continue downward eventually reaching the Floridan or move more laterally and contribute to streams and rivers. The Floridan aquifer system contributes to surface water directly through spring discharge and indirectly to the intermediate aquifer and to surface water through diffuse upward leakage. Springs and karstic sinks exist throughout the area. The greatest concentration of karstic features lies north of the City of Tampa and is expressed as a distribution of small, generally circular and coalescing lakes and ponds. Elevations within these surface water bodies often reflect groundwater levels, indicating the strong connection between surface water and ground water. Several springs occur along the rivers of the region, including Crystal, Eureka, Sulpher, Lithia, and Buckhorn Springs. All the springs are second order magnitude (6.46 to 64.6 million gallons per day) or less. When the elevation of the potentiometric surface of the Floridan aquifer system is higher than the water table of the surficial aquifer system, water from the Floridan leaks upward to the intermediate aquifer, surficial aquifer, and to land surface. If the Floridan aquifer potentiometric surface is high enough, wells drilled into, unless capped or valved, will flow freely at land surface. This upward flow, known as artesian flow, is known to exist throughout much of the Tampa Bay Tributaries Basins where the Floridan aquifer is confined. Water Use The Tampa Bay Tributaries Basins are within the South West Florida Water Management District (SWFMD). SWFWMD periodically summaries and analyzes freshwater use for the 16 counties in its jurisdiction. The Tampa Bay Tributaries Basins are situated within Pasco, Hillsborough, Polk, Manatee, and Sarasota counties. Table 1 indicates the total fresh water use for these counties in For the five counties in which the basins occur the total withdrawal was approximately million gallons per day (MGD). This figure represents approximately 67 percent of the total withdrawals within the district for that year. Of the total withdrawals more than 80 percent came from

3 ground water (SWFWMD, 2000) and the majority of the ground water came from the Floridan aquifer. Table 1. Summary of Total Water Withdrawal/Use In Million Gallons Per Day by County and Category, 1997 County Agric. Indust/ Comm Mine/ Dewater Domest Self-S Recreation/ PWS Withdrw PWS Use Total Withdrw Total Use Hillsborough Manatee Pasco Polk Sarasota Total l (modified from SWFWMD, 1997) Abbreviations: Agric. = Indust/Comm = Mine/Dewater = Domest Self-S = Recreation/ = PWS Withdrw = PWS Use = Total Withdrw = Agricultural Industrial/Commercial Mining and Dewatering Domestic Self-Supply Recreation/Aesthetic Public Supply Withdrawal Public Supply Use Total Withdrawal Table 1 indicates water use by county into the following categories: Agricultural, Industrial/Commercial, Mining/Dewatering, Public Supply Withdrawal, Public Supply Use, Domestic Self-Supply, Recreation/Aesthetic, Total Withdrawal, and Total Use. As indicated in the table, major water withdrawals are predominantly for public water supply and agricultural uses. Water Use Caution Areas The SWFWMD defines Water Use Caution Areas as those areas within the District where existing and reasonably anticipated sources of water and conservation efforts may not be adequate to: A) supply water for all existing legal uses and reasonably anticipate future needs and B) sustain the water resources and related natural systems. There are five constraints in establishing Caution Areas: (1) Impacts to native vegetation, primarily wetlands, (2) Impacts to minimum flows and levels, primarily spring flows, (3) Impacts to ground water quality in terms of increased salt water intrusion, (4) Impacts to existing legal users, and (5) Failure to identify a source of supply for future development. Figure 1 indicates that there are four Water Use Caution Areas in the Tampa Bay Tributaries Basins area. These are the Northern Tampa Bay WUCA, Southern WUCA, Eastern Tampa Bay WUCA, and the Highlands Ridge WUCA, with the Southern WUCA being the most impacted (SWFWMD, 2000). The Hillsborough, Eastern Tampa Bay, and Southern WUCAs exist within the Tampa Bay Tributaries Basins. It should be noted that saline water in probably the most significant threat to ground water quality within the

Tampa Bay Tributaries Basin. Over-pumping of groundwater in the basin can potentially have an adverse affect on the local ground water supplies.

4 Tampa Bay Tributaries Basin. Over-pumping of groundwater in the basin can potentially have an adverse affect on the local ground water supplies. Figure 1. Water Use Caution Areas (WUCAs) for Southwest Florida Water Use Caution Areas

5 REFERENCES CITED Causey, L.V. and G.W. Leve, 1976, Thickness of the Potable-Water Zone in the Florida Aquifer, Bureau of Geology, Florida Department of Natural Resources, Map Series No. 74, Tallahassee, Florida. Fernald, Edward A. and Elizabeth D. Purdum, eds., 1998, Water Resources Atlas of Florida, Florida State University, Tallahassee, Florida. Peek, Harry M., 1958, Ground-Water Resources of Manatee County, Florida, Florida Geological Survey, Report of Investigations No. 18, Tallahassee, Florida. Scott, Thomas S., 1988, The Lithostratigraphy of the Hawthorn Group (Miocene) of Florida, Florida Geological Survey, Bulletin No. 59, Tallahassee, Florida. South West Florida Water Management District, 2000, District Water Management Plan June, South West Florida Water Management District, 1997, Estimated Water Use. White, William A., 1970, The Geomorphology of the Florida Peninsula, Bureau of Geology, Florida Department of Natural Resources, Geological Bulletin No. 51, Tallahassee, Florida.

Geology and Soils. Technical Memorandum

Geology and Soils. Technical Memorandum Geology and Soils Technical Memorandum TO: FDOT FROM: HDR, Inc. DATE: February 2013 PROJECT: St Johns River Crossing FPID No: 208225-3-21-01 Clay, Duval, and St. Johns Counties; Florida Geology and soils