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Research about Hillsborough County, Florida

Source-linked reports with geographic coverage including Hillsborough County, Florida.

9 recordsLinked to original sources
USGS2004

Simulated effects of ground-water augmentation on the hydrology of Round and Halfmoon Lakes in northwestern Hillsborough County, Florida

Pumpage from the Upper Floridan aquifer in northwest Hillsborough County near Tampa, Florida, has induced downward leakage from the overlying surficial aquifer and lowered the water table in many areas. Leakage is highest where the confining layer separating the aquifers is breached, which is common beneath many of the lakes in the study area. Leakage of water to the Upper Floridan aquifer has lowered the water level in many lakes and drained many wetlands. Ground water from the Upper Floridan aquifer has been added (augmented) to some lakes in an effort to maintain lake levels, but the resulting lake-water chemistry and lake leakage patterns are substantially different from those of natural lakes. Changes in lake-water chemistry can cause changes in lake flora, fauna, and lake sediment composition, and large volumes of lake leakage are suspected to enhance the formation of sinkholes near the shoreline of augmented lakes. The leakage rate of lake water through the surficial aquifer to the Upper Floridan aquifer was estimated in this study using ground-water-flow models developed for an augmented lake (Round Lake) and non-augmented lake (Halfmoon Lake). Flow models developed with MODFLOW were calibrated through nonlinear regression with UCODE to measured water levels and monthly net ground-water-flow rates from the lakes estimated from lake-water budgets. Monthly estimates of ground-water recharge were computed using an unsaturated flow model (LEACHM) that simulated daily changes in storage of water in the soil profile, thus estimating recharge as drainage to the water table. Aquifer properties in the Round Lake model were estimated through transient-state simulations using two sets of monthly recharge rates computed during July 1996 to February 1999, which spanned both average conditions (July 1996 through October 1997), and an El Niño event (November 1997 through September 1998) when the recharge rate doubled. Aquifer properties in the Halfmoon Lake model were estimated through steady-state simulations of average conditions in July 1996. Simulated hydrographs computed by the Round and Halfmoon Lake models closely matched measured water-level fluctuations, except during El Niño, when the Halfmoon Lake model was unable to accurately reproduce water levels. Possibly, potential recharge during El Niño was diverted through ground-water-flow outlets that were not represented in the Halfmoon Lake model, or a large part of the rainfall was diverted into runoff before it could become recharge. Solute transport simulations with MT3D indicate that leakage of lake water extended 250 to 400 feet into the surficial aquifer around Round Lake, and from 75 to 150 feet around Halfmoon Lake before flowing to the underlying Upper Floridan aquifer. These results are in agreement with concentrations of stable isotopes of oxygen-18 (d18O) and deuterium (dD) in the surficial aquifer. Schedules of monthly augmentation rates to maintain constant stages in Round and Halfmoon Lakes were computed using an equation that accounted for changes in the Upper Floridan aquifer head and the deviation from the mean recharge rate. Resulting lake stages were nearly constant during the first half of the study, but increased above target lake stages during El Niño; modifying the computation of augmentation rates to account for the higher recharge rate during El Niño resulted in lake stages that were closer to the target lake stage. Substantially more lake leakage flows to the Upper Floridan aquifer from Round Lake than from Halfmoon Lake, because the estimated vertical hydraulic conductivities of lake and confining layer sediments and breaches in the confining layer beneath Round Lake are much greater. Augmentation rates required to maintain the low guidance stages in Round Lake (53 feet) and Halfmoon Lake (42 feet) under average Upper Floridan aquifer heads are estimated as 33,850 cubic feet per day and 1,330 to 10,000 cubic feet per day, respectively. These rates equate to 26 inches per month of water applied to the entire surface of Round Lake and 0.34 to 2.5 inches per month of water applied to Halfmoon Lake.

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USGS2002

Comparison of the hydrogeology and water quality of a ground-water augmented lake with two non-augmented lakes in northwest Hillsborough County, Florida

The hydrologic effects associated with augmenting a lake with ground water from the Upper Floridan aquifer were examined in northwest Hillsborough County, Florida, from June 1996 through May 1999. The hydrogeology, ground-water flow patterns, water budgets, and water-quality characteristics were compared between a lake that has been augmented for more than 30 years (Round Lake) and two nearby nonaugmented lakes (Dosson Lake and Halfmoon Lake). Compared to the other study lakes, Round Lake is in a more leakage-dominated hydrogeologic setting. The intermediate confining unit is thin or highly breached, which increases the potential for vertical ground-water flow. Round Lake has the least amount of soft, organic lake-bottom sediments and the lake bottom has been dredged deeper and more extensively than the other study lakes, which could allow more leakage from the lake bottom. The area around Round Lake has experienced more sinkhole activity than the other study lakes. During this study, three sinkholes developed around the perimeter of the lake, which may have further disrupted the intermediate confining unit. Ground-water flow patterns around Round Lake were considerably different than the nonaugmented lakes. For most of the study, groundwater augmentation artificially raised the level of Round Lake to about 2 to 3 feet higher than the adjacent water table. As a result, lake water recharged the surficial aquifer around the entire lake perimeter, except during very wet periods when ground-water inflow occurred around part of the lake perimeter. The non-augmented lakes typically had areas of ground-water inflow and areas of lake leakage around their perimeter, and during wet periods, ground-water inflow occurred around the entire lake perimeter. Therefore, the area potentially contributing ground water to the non-augmented lakes is much larger than for augmented Round Lake. Vertical head loss within the surficial aquifer was greater at Round Lake than the other study lakes, which is additional evidence of the limited confinement at Round Lake. A comparison of the water quality and lake-bottom sediments at the three lakes indicate that Round Lake is strongly influenced by the addition of large quantities of calcium-bicarbonate enriched augmentation water. Round Lake had higher alkalinity, pH, calcium and dissolved oxygen concentrations, specific conductance, and water clarity than the two non-augmented lakes. Round Lake was generally saturated to supersaturated with respect to calcite, but was undersaturated when augmentation was low and after high rainfall periods. Calcium carbonate has accumulated in the lake sediments from calcite precipitation, from macrophytes such as Nitella sp., and from the deposition of carbonate-rich mollusk shells, such as Planerbella sp., both of which thrive in the high alkalinity lake water. Lake-bottom sediments and aquatic biota at Round Lake had some of the highest radium-226 activity levels measured in a Florida lake. The high radium-226 levels (27 disintegrations per minute per dry mass) can be atrributed to augmenting the lake with ground water from the Upper Floridan aquifer. Although the ground water has relatively low levels of radium-226 (5.8 disintegrations per minute per liter), the large volumes of ground water added to the lake for more than 30 years have caused radium-226 to accumulate in the sediments and lake biota. The Round Lake basin had higher calcium and bicarbonate concentrations in the surficial aquifer than at the non-augmented lakes, which indicates the lateral leakage of calcium-bicarbonate enriched lake water into the surficial aquifer. Deuterium and oxygen-18 data indicated that water in well nests near the lake consists of as much as 100 percent lake leakage, and water from the augmentation well had a high percentage of recirculated lake water (between 59 and 73 percent lake leakage). The ground water surrounding Round Lake was undersaturated with respect to calcite, indicating that the water is capable of dissolving calcite in the underlying limestone aquifer. Annual and monthly ground-water outflow (lake leakage) was significantly higher at Round Lake than at the non-augmented lakes for the 3-year study period. Minimum estimates of the total annual ground-water inflow and outflow were made from monthly net ground-water flow values. Based on these estimates, total annual groundwater outflow from Round Lake was more than 10 times higher than for the non-augmented lakes. Local ground-water pumping, augmentation, and hydrogeologic factors are responsible for the high net ground-water outflow at Round Lake. Localized ground-water pumping causes the head difference between the lake and the Upper Floridan aquifer to increase, which increases lake leakage and results in lower lake levels. Augmenting the lake further increases the head difference between the lake, the water table, and the Upper Floridan aquifer, which results in an increase in lateral and vertical lake leakage. The lack of confinement or breaches in the intermediate confining unit facilitates the downward movement of this augmented lake water back into the Upper Floridan aquifer. The increase in ground-water circulation in the leakage-dominated hydrogeologic setting at Round Lake has made the basin more susceptible to karst activity (limestone dissolution, subsidence, and sinkhole formation)

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USGS1980

Hydrogeologic data for Eureka Springs landfill and adjacent area, north-central Hillsborough County, Florida, 1969-73

Well location and construction data are summarized for 218 wells in the Eureka Springs landfill and adjacent areas in north-central Hillsborough County, FL. Most of the data are for 88 wells within the immediate vicinity of the landfill. Water-quality data are presented for 93 of the wells and 13 surface-water sites. Also presented are water-level data for the surficial and Floridan aquifers for 162 of the wells and lithologic logs for 43 of the wells. (USGS)

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USGS1979

Hydrologic data for the Morris Bridge well-field area, Hillsborough County, Florida, 1971-78

Well data are summarized for 102 wells constructed in the Morris Bridge well-field area in north-central Hillsborough County. Of the wells reported, 20 are public-supply wells that have yields averaging 1,800 gallons per minute and specific capacities that range from 36 to 346 gallons per minute per foot of drawdown. Also presented are 28 drillers' logs, 7 lithologic logs, and an index of 64 geophysical logs of 18 wells in the well-field area. The report also includes hydrographs of water levels of 10 observation wells, hydrographs of stream stage and streamflow of the Hillsborough River, and hydrographs of rainfall for two stations.

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USGS1978

Water-quality data for landfills, Hillsborough County, Florida, January 1974-October 1977

Periodic water-quality data were collected at four landfills in Hillsborough County from January 1974 through October 1977. Water samples were analyzed for nitrogen and phosphorous species, cations, trace metals, chloride, specific conductance, chemical oxygen demand, biological oxygen demand, and coliforms. Select ground-water samples were analyzed for herbicide and pesticide. Results of chemical and bacteriological analysis form four landfills are presented as basic data. Geologic logs and well descriptions are presented for wells drilled at the landfills after January 1974.

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USGS1978

Hydrogeologic factors affecting the availability and quality of ground water in the Temple Terrace area, Hillsborough County, Florida

Ground water occurs in two aquifers in the Temple Terrace area of Hillsborough County, Fla. The lower one is the artesian Floridan aquifer; the upper is the water-table aquifer. The Floridan aquifer is a thick sequence of limestone and dolomite layers which include several permeable zones that generally are treated as a single hydrologic unit. The top of the Tampa Limestone is considered to be the top of the Floridan in the Temple Terrace area. The public supply wells of the city tap the Tampa Limestone and the underlying Suwannee Limestone, in the upper part of the Floridan. The general direction of ground-water movement in the Floridan aquifer is from north to south, but within the city the direction of movement is from northeast to southwest. The quantity of water moving southwest through a 1.8 mile section of the aquifer is about 2.7 million gallons per day. Ample supplies of water in a cavernous limestone, considered to be the most productive water-yielding zone in the aquifer, are available for additional development from the Floridan aquifer. Water-quality data are included also. (Woodard-USGS)

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USGS1975

The potentiometric surface and water quality of the Floridan aquifer; in southwest Hillsborough County, Florida, 1952-74

Large ground-water withdrawals and a 10-year period of below- normal rainfall have caused the potentiometric surface of the Floridan aquifer to decline more than 10 feet (3 metres) in most of a 200- square-mile (520-square-kilometre) area of southwest Hillsborough County (fig. 1). The lowered ground-water levels and the consequent threat of salt-water intrusion concern farmers and residents who depend on ground water for irrigation and domestic purposes. Exten sive crop irrigation is continuing; small towns such as Ruskin, River- view, Sun City Center, and Apollo Beach are rapidly expanding; and new communities are being planned. In addition, there are plans to mine the extensive phosphate deposits a few miles east of this heavily- f armed area. All these activities require large supplies of fresh ground water. The Hillsborough County Commission cooperated with the U. S. Geological Survey to study changes of water levels and water quality in southwest Hillsborough County. The purpose of this report is to compare the position of the potentiometric surface in 1953 with that in 1973 and to show chloride and sulfate concentrations in ground water in 1974.

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