Geology topics

Research about Tallahassee, Florida

Source-linked reports with geographic coverage including Tallahassee, Florida.

5 recordsLinked to original sources

USGS2007

Hydrogeologic investigation, water chemistry analysis, and model delineation of contributing areas for City of Tallahassee public-supply wells, Tallahassee, Florida

Ground water from the Upper Floridan aquifer is the sole source of water supply for Tallahassee, Florida, and the surrounding area. The City of Tallahassee (the City) currently operates 28 water-supply wells; 26 wells are distributed throughout the City and 2 are located in Woodville, Florida. Most of these wells yield an ample supply of potable water; however, water from several wells has low levels of tetrachloroethylene (PCE). The City removes the PCE from the water by passing it through granular-activated carbon units before distribution. To ensure that water-supply wells presently free of contamination remain clean, it is necessary to understand the ground-water flow system in sufficient detail to protect the contributing areas. Ground-water samples collected from four public-supply wells were analyzed for tritium ( 3 H), chlorofluorocarbons (CFCs), and sulfur hexafluoride (SF 6 ). Using data for the CFC compounds, apparent ground-water ages ranged from 7 to 31 years. For SF 6 , the apparent ages tended to be about 5 to 10 years younger than those from CFCs. Apparent ages based on the tritium/tritiogenic helium-3 ( 3 H/ 3 He trit ) method ranged from 26 to 33 years. The three dating methods indicate that the apparent age of ground water generally decreases from northern to southern Leon County. This southward trend of decreasing ages is consistent with increasing amounts of recharge that occur as ground water moves from north to south. The ground-water age data derived by geochemical and tracer analyses were used in combination with the flow model and particle tracking to determine an effective porosity for the Hawthorn clays and Upper Floridan aquifer. The effective porosities for the Upper Floridan aquifer that resulted in best model matches were averaged to produce an effective porosity of 7 percent, and the effective porosities for the Hawthorn clays that resulted in a match were averaged to produce an effective porosity of 22 percent. Probabilistic contributing areas were determined for 26 City wells using MODFLOW and MODPATH. For each probabilistic contributing area delineated, the model was run 100 times and the results were analyzed statistically. For each of the 100 runs, a different hydraulic conductivity for each of the zones was assigned to the Upper Floridan aquifer. The hydraulic conductivities were generated randomly assuming a lognormal probability distribution; the mean of the distribution was equal to the hydraulic conductivity from the calibrated model. The 5-year time-dependent capture zones (TDCZs), assuming effective porosities of 0.1, 1, and 7 percent for four representative wells, were delineated. The higher probabilities of capture (greater than 40, 60, and 80 percent) were similar for all effective porosities, and the TDCZ delineated using a 7-percent porosity was slightly smaller; the lower probabilities of capture (greater than 10 and 20 percent) showed a large range of variability.

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USGS1993

Ground-water quality near an inactive landfill and sludge-spreading area, Tallahassee, Florida

Ground-water quality of a 120-acre area encompassing an inactive landfill southwest of Tallahassee, Florida, was assessed by installing and sampling 21 monitoring wells. Sludge from a municipal sewage-treatment plant was also applied to the land surface near the landfill site. Water samples were collected from the 21 monitoring wells from June 1987 through September 1990 and analyzed for concentrations of major ions, nitrogen species, trace metals, field measurements, and more than 140 organic constituents. Water quality in the Upper Floridan aquifer at the study site was compared to background water quality in other areas of Leon County. Ground-water quality of the study site was evaluated by the location of wells sampled in relation to the landfill and the sludge-spreading areas. Results of nonparametric statistical analysis indicated that potassium and nitrite plus nitrate as nitrogen concentrations in water samples from wells completed in the Upper Floridan aquifer at the study site were significantly different at the 5 percent probability level from those in samples from background wells completed in this aquifer in Leon County. Median potassium concentrations were 0.4 mg/L (milligrams per liter) in water from wells at the study site and 0.7 mg/L in water from background wells in Leon County. Median nitrite plus nitrate concentrations were 6.48 mg/L in water samples from wells at the study site and 0.51 mg/L in water samples from background wells. Graphical comparison of the water quality characteristics in water from six categories of wells; upgradient, landfill, adjacent to the landfill, downgradient onsite, downgradient offsite, and background Leon County, indicated that sodium, bicarbonate, sulfate, iron, manganese, and dissolved solids concentrations and specific conductance values were highest within the landfill. Upgradient and downgradient well categories include wells in areas affected by sludge spreading. Localized reducing conditions were indicated in a downgradient area by median iron concentrations of 930 and 30 ug/L (micrograms per liter) in samples from wells only 5 feet apart. Nitrite plus nitrate concentrations were lowest in water from wells in the landfill compared to water from the other categories. Concentrations of most trace elements and organic compounds were mostly below detection limits, although State maximum contaminant levels of 1 ug/L for benzene and vinyl chloride and 3 ug/L for tetrachloroethene were exceeded in 14 samples. Concentrations of sodium, potassium, chloride, sulfate, nitrite plus nitrate, total organic and ammonia nitrogen, and ammonia nitrogen in ground water were statistically analyzed in areas affected by sludge-spreading and other areas. Only nitrite plus nitrate and chloride concentrations were significantly different between the two areas. Median nitrite plus nitrate and chloride concentrations in sludge-spreading areas were 6.9 mg/L and 2.9 mg/L, respectively, compared to 1.1 mg/L and 1.8 mg/L in other areas.

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USGS1988

Effects of treated municipal effluent irrigation on ground water beneath sprayfields, Tallahassee, Florida

Groundwater quality data collection began in November 1979 at a spray-irrigation site near Tallahassee, Florida, before the initial application of secondary-treated municipal wastewater in November 1980. Effects of effluent irrigation on groundwater quality were evident about 1 year after spraying began and have continued to increase during the study period of 1983-85. Chloride and nitrate concentrations in groundwater have continued to increase since about 1 year after spraying began. Nitrate-nitrogen concentrations have increased from 0.03 mg/L to as much as 11 mg/L in water from one well in the surficial aquifer and from 0.07 to 15 mg/L in one well in the Floridan aquifer system. The greatest increases in concentrations have occurred in water from wells that top the surficial and Floridan aquifers. Increase in concentration occurred in water from some wells in the Floridan outside and downgradient of pivots, indicating lateral movement within the Floridan. The increase in sodium concentrations has been similar to the in chloride concentrations. Increases increases in the concentrations of other inorganic constituents have been minor compared to increases in chloride, sodium and nitrate concentrations. Nine volatile organic halocarbon compounds were detected in 18 effluent samples. Low concentrations of two of these halocarbons--chloroform and trichloroethene (TCE)--were detected intermittently in water sampled from six wells. None of the organic compounds detected in effluent or groundwater exceeded Florida drinking water standards.

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USGS1985

Wastewater application by spray irrigation on a field southeast of Tallahassee, Florida: Effects on ground-water quality and quantity, 1980-82

A field southeast of Tallahassee, Florida, used for land application of wastewater by spray irrigation was the site of a ground-water monitoring study to determine effects of spray irrigation on water-table elevations and ground-water quality. The study was conducted during 1980-82 in cooperation with the City of Tallahassee. The wastewater has relatively high concentrations of chloride, nitrogen, phosphorus, organic carbon , coliform bacteria, sodium, and potassium. These substances are usually attenuated before they can impact the ground water. However, increases in chloride and nitrate-nitrogen were evident in ground water in some of the monitoring wells during the study. Chloride concentrations increased five-fold or more in some wells directly affected by spray irrigation, and nitrate-nitrogen concentrations increased eight-fold or more. Ground-water levels in the area of the spray field fluctuated over a range of several feet. These fluctuations were affected somewhat by spray irrigation, but the primary control on water levels was rainfall. As of December 1982, constituents introduced to the system by spray irrigation of effluent had not exceeded drinking water standard in the ground water. However, the system had not yet stabilized and more changes in ground-water quality could be expected.

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USGS1978

Water-quality assessment of runoff from a rural highway bridge near Tallahassee, Florida

Runoff from a rural highway bridge on U.S. 27 near Tallahassee, Florida, was found to have an insignificant water-quality loading impact on the Ochlockonee River. Potential annual-runoff loads on the bridge surface for virtually all constituents studied were less than one percent of those transported by the river at the study site. The loading rates for some parameters were significantly related to traffic counts, but the regression equations were limited to traffic ranges between 3,800 to 4,200 vehicles per day in 1977-78. Precipitation samples indicated that a significant percentage of the constituent loading to the bridge surface is from atmospheric deposition. (Woodard-USGS)

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