Presentation Abstracts: FISC Meeting
3: Freshwater Quality and Availability
Aquifer Studies in the Southeastern United States with Emphasis on Contaminant Occurrence in the Upper Floridan and Biscayne Aquifers
Marian P. Berndt and Christy A. Crandall,
U.S. Geological Survey, Florida Integrated Science Center, Tallahassee, Florida
A major focus of the National Water-Quality Assessment (NAWQA) in its second decade (2002-2013) is on regional- and national-scale assessments of ground-water status and trends in principal aquifers. Goals of these regional studies are to better understand how natural features and human activities affect water quality and why some aquifers are more vulnerable to contamination than others. The information will help local, State, and regional decision makers in source-water protection of important drinking-water resources. The Floridan, Biscayne, and surficial aquifers in Florida systems were among the principal aquifers selected for study. Studies in these aquifers are based on samples collected from nearly 400 wells, including those used for monitoring, domestic purposes, and public-supply. Samples were collected from 1994 through 2005 and analyzed for nutrients, major ions, radon, and selected pesticides and volatile organic compounds. An additional 45 wells are being sampled in the surficial aquifer system in 2008.
The Floridan aquifer system is a highly productive carbonate aquifer that provides drinking water to approximately 10 million people in Florida Georgia, and South Carolina in 2000. Water samples were collected from 148 household, or domestic, wells in the Upper Floridan aquifer in these three States from 1998 through 2005. Results showed that no drinking-water standards were exceeded. The median nitrate concentration was 0.12 mg/L, but nitrate concentrations greater than 1.0 mg/L were common in unconfined parts of the aquifer where agricultural land use was common and dissolved oxygen concentrations were greater than 1.0 mg/L. Low level concentrations (less than 1 micrograms per liter) of pesticides were detected in about 20 percent of wells. Detection frequencies were highest (69 percent) in unconfined areas where nitrate concentrations were mostly greater than 1.0 mg/L. Atrazine, deethylatrazine, and metolachlor were the most frequently detected pesticides. Low-level concentrations (less than 0.5 micrograms per liter) of volatile organic compounds were detected in about 60 percent of samples.
About 4 million people in southeastern Florida rely on public-water supplies from the Biscayne aquifer, a highly permeable sand and limestone aquifer which is vulnerable to contamination by human activities. A total of 30 public-supply wells were sampled in Broward, Miami-Dade, and Palm Beach Counties (prior to treatment) and 32 shallow monitoring wells were sampled in urban areas in Broward County. Results from sample analyses had few relatively high (greater than 2 milligrams per liter) concentrations of nitrate in water from public-supply wells near agricultural lands and a few relatively high concentrations of arsenic (greater than 10 micrograms per liter) in water from some shallow urban wells near golf courses. Low level concentrations of pesticides were detected in 100 percent of public-supply wells and in 78 percent of the shallow, urban monitoring wells; however, no pesticide concentration exceeded any drinking-water standard. The most frequently detected pesticides were atrazine and tebuthiuron. Volatile organic compounds (VOCs) were detected in 77 percent of the public-supply wells and in 91 percent of the shallow, urban wells. The most frequently detected VOCs were in the public-supply wells, followed by cis-1,2-dichloroethene, methyl tert-butyl ether (MTBE), 1,4-dichlorobenzene, toluene, and p-isopropyltoluene. Concentrations of all VOCs were less than the maximum contaminant level (MCL) for public drinking water, except in two samples from public-supply wells near industrialized areas that had vinyl chloride concentrations (3 and 5 micrograms per liter).
The surficial aquifer system is also used for public supply and for domestic supplies, but to a lesser extent than the Biscayne aquifer. Studies in public supply and domestic wells began in 2008 in this aquifer and results will be used to determine the distribution of contaminants in the surficial aquifer in Martin, Palm Beach, Indian River, and St. Lucie Counties.
Contact Information: Marian P. Berndt, U.S. Geological Survey, Florida Integrated Science Center, 2010 Levy Avenue, Tallahassee, FL 32310; phone: 850-942-9500; email: mberndt@usgs.gov
Monitoring of Surface-Water and Ground-Water Resources in Florida
James L. Pearman, U.S. Geological Survey, Florida Integrated Science Center, Orlando, Florida
The Florida Integrated Science Center (FISC) has four ‘water’ offices located in Tallahassee, Tampa, Orlando, and Fort Lauderdale. An important component of each of these offices is the collection of continuous basic data throughout the State of Florida in regard to streamflow, stream level, lake level, ground-water level, water-quality parameters, and evaporation. Periodic data are collected on many stream sites, ground-water stations, spring stations, and water-quality sampling locations. Operation and maintenance of the data program in Florida is approximately an $18 million annual effort with about $4 million supplied by USGS and $14 million by the cooperators. Approximately 65 percent of the budget is related to surface water, 20 percent is ground-water activities, and 15 percent is water-quality data collection.
During the 2008 fiscal year, the Florida water offices operated 428 continuous discharge sites (discharge and water level), 229 stream level or miscellaneous measurement locations, 407 continuous ground-water level stations, approximately 1,100 periodic ground-water level monitoring sites, 145 continuous water-quality monitoring gages, 125 periodic water-quality sampling locations on streams, springs, and ground-water sites, and 12 evaporation stations. This statewide network consists of over 2,400 individual locations visited at least once on an annual basis.
Basic data are necessary for any type of long-term analysis of water conditions in the State of Florida. Several continuous streamflow stations have record beginning in the late 1920’s and early 1930’s. The oldest station, Suwannee River at White Springs, has data back to 1906. Ground-water level data collection primarily began in the late 1940’s with the oldest site, Orange County Well 47, having record back to 1930. These extensive datasets are necessary in the analysis of long-term climate change, ground-water usage, and changes in water use and the impact upon Florida’s water resources. Low-flow statistics, flood-frequency analyses, and flow duration characteristics from streamflow stations are used in the design of highway bridges, wastewater treatment plants, reservoirs, and water intake structures. Incremental values of streamflow, water level, water-quality parameters, and evaporation act as data inputs and calibration targets for hydrologic models used as predictive tools in quantifying how water levels, flows, and water quality are impacted by possible future changes in water use, climatic change and meteorological variability. Additionally, the vast historical and ongoing hydrologic data collection record in Florida can serve as a platform for biological, coastal processes, and climatologic investigations.
Contact Information: James L. Pearman, U.S. Geological Survey, Florida Integrated Science Center, 12703 Research Parkway, Orlando, FL 32826; phone: 407-803-5577; email: jpearman@usgs.gov
Can Lake Istokpoga be a Model for the Future of Lake Okeechobee?
Michael J. Byrne, U.S. Geological Survey, Florida Integrated Science Center, Orlando, Florida
Lake Istokpoga , a large lake northwest of Lake Okeechobee and west of the Kissimmee River, shares the same type of land use as Lake Okeechobee, mainly improved pasture and orange groves. The water quality in both lakes is determined by the concentration of total Kjeldahl nitrogen (TKN), total phosphorous (TP), and dissolved phosphate (PO4). Nitrogen and phosphorous are the basic building blocks for life and the Redfield ratio for N:P is 16:1. A lower ratio may be indicative of a phosphorous limited system, and higher ratio nitrogen limiting. Growth of aquatic life is often limited by availability of an essential nutrient. The ratio of TP:PO4 is also an important measure since the dissolved phosphate is the form of phosphorous that is easiest to assimilate by organisms. Data collected at Lake Istokpoga shows that Arbuckle Creek, the inflow point to the lake, has a TKN:TP ratio higher (14:1) than that of C41A Canal (20:1), the outflow point, or that of the lake itself. These data also show the ratio of TP to dissolved phosphate (PO4) in the water entering Lake Istokpoga is higher (7:10) than the water leaving the lake (1:10). Analysis of these data suggests that Lake Istokpoga is a phosphorous limiting system, with most bio-available phosphorous eliminated before the water leaves the lake.
The tributaries on the eastern side of the Kissimmee River exhibit much higher ratios of TKN:TP (5:1), and TP:PO4 (8:10). These tributaries are ineffective in reducing phosphorous, mainly due to the abundance of phosphorous. The concentrations of TKN are similar on both sides of the Kissimmee River. Managers must determine the source of the excess phosphorous on the eastern side of the Kissimmee River and reduce the importation.
Contact Information: Michael Byrne, U.S. Geological Survey, Florida Integrated Science Center, 12703 Research Parkway, Orlando, FL 32826; email: mbyrne@usgs.gov
Dynamic Simulation of Canal Stages and Surface-Water Structure Operations in SEAWAT to Evaluate Conjunctive Water Use in Miami-Dade County
Joseph D. Hughes1, Eric D. Swain2, Linzy Brakefield-Goswami2, Christian D. Langevin2, and Richard G. Niswonger3
1 U.S. Geological Survey, Florida Integrated Science Center, Tampa, Florida
2 U.S. Geological Survey, Florida Integrated Science Center, Ft. Lauderdale, Florida
2 U.S. Geological Survey, Florida Integrated Science Center, Carson City, Nevada
The Biscayne aquifer is currently the sole source of potable water in Miami-Dade County, Florida. Overlying the Biscayne aquifer is an extensive man-made network of canals that are in close hydraulic-connection to the ground-water system and managed using a system of operable control structures. During the wet season, the canals mitigate urban flooding and route excess water into Biscayne Bay. Conversely, the canals are used during the dry season to meet water-supply needs and to control saltwater intrusion in coastal areas by maintaining relatively high aquifer levels. With an increasing population and the proposed hydrologic changes as part of Everglades Restoration, Miami-Dade County is facing numerous hydrologic challenges that require a numerical modeling tool capable of simulating conjunctive use of surface-water and ground-water.
Although numerical models have been developed for the Biscayne aquifer in Miami-Dade County, these models either lack the ability to dynamically represent surface water flow through the canal network, do not consider density-dependent surface-water and ground-water flow, or do not contain the resolution necessary to address water resource issues at the county scale. As a result, an integrated surface-water/ground-water model that considers density-dependent surface-water and ground-water flow is being developed from an existing SEAWAT model. This model was originally developed to quantify rates of submarine freshwater discharge to Biscayne Bay but did not consider flow through the canal network. The numerical model will be used to determine 1) the impact of municipal well fields on surface- and ground-water levels and environmental conditions, 2) the location of well-field recharge areas, 3) the effect of well-field withdrawals on Everglades National Park and Biscayne Bay, 4) the effect of the Lake Belt Region on ground-water flow, and 5) the degree to which sea-level rise will cause saltwater intrusion into coastal well fields.
A modified version of the MODFLOW stream-flow-routing (SFR) package is being developed to dynamically represent canal routing and structure operations in Miami-Dade County. The modified SFR Package will permit simulation of seasonally-varying structure operations designed to control ground-water seepage from Everglades National Park and freshwater flow to Biscayne Bay. Approaches being considered to simulate stream flow range from a simple “level-pool” approach to numerical approximation of the St. Venant equations. Structures are being implemented in a general fashion so that structure flows based on canal stages, other operating rules, observed flows, or combinations of operational approaches can be simulated. Structures being considered in the modified SFR package include a simple, design discharge constrained excess volume based structure, gated spillways, gated culverts, and pumps. The modified package will use a simple mixing approach to simulate solute transport in the canals and account for the dependence of fluid density on canal concentrations when used with SEAWAT.
Contact Information: Joseph D. Hughes, U.S. Geological Survey, Florida Integrated Science Center, The University Center for Business, 10500 University Center Drive, Suite 215, Tampa, FL 35512; phone: 813-975-8620; email: jdhughes@usgs.gov
Streamflow Losses through Karst Features in the Upper Peace River Basin, Polk County, Florida
Patricia Metz and Bill Lewelling
U.S. Geological Survey, Florida Integrated Science Center, Tampa, Florida
In October 2001, the U.S. Geological Survey, in cooperation with the Southwest Florida Water Management District, began a study to evaluate the distribution, timing, and volume of surface-water/ground-water exchange in the Upper Peace River Hydrologic Area in Polk County, Florida. Historically, ground-water levels in this area were above the river levels, signifying a gaining stream. Wells and second-order magnitude springs flowed at the surface and tributaries drained the surrounding scarps. Today, because of ground-water development in this area, the Upper Peace River is a losing stream and streamflow losses are predominately through karst features found in the river channel and the flood plain.
During the dry season, the locations of prominent karst features, surface orientations, and dimensions were measured in selected reaches of the river and flood plain. These karst features were characterized as a coalescing group of vertical pipes, collapsed sinkholes, and numerous interconnected horizontal and vertical fractures that show evidence of scouring by moving water. Some of the openings are large enough for a person to enter. To quantify the streamflow losses to these karst features, measurements were made during the dry seasons (late spring) of 2002, 2003, and 2006.
In May 2002, streamflow ceased along an approximate three-mile segment of the river, with losses to karst features ranging from about 2 to 30 cubic feet per second (ft3/s). In May 2003, streamflow losses did not exceed 16 ft3/s. During 2004 and 2005, because of three hurricanes that affected this area, the river flowed up into the flood channel most of the time. During 2006, streamflow again ceased in the river along an approximate three-mile section, and streamflow to the karst features did not exceed 12 ft3/s.
Contact Information: Patricia A. Metz, U.S. Geological Survey, Florida Integrated Science Center, The University Center for Business, 10500 University Center Drive, Suite 215, Tampa, FL 33612; phone: 813-975-8620; email: pmetz@usgs.gov
Documenting the Hydraulic Connection between Inland Sinkholes and Springs along Florida’s Northwest Coast
Richard Jay Verdi, U.S. Geological Survey, Florida Integrated Science Center, Tallahassee, Florida
South of Tallahassee, along the coastline of the panhandle of Florida, a series of 13 springs discharge ground water from the Upper Floridan aquifer into Spring Creek, a small tidal creek that flows into the Gulf of Mexico. The freshwater to brackish flow discharging from these springs varies seasonally, altering both the net outflow and salinity of Spring Creek. The discharge from this group of coastal springs is controlled in part by streamflow occurring at two inland streams: Lost Creek and Fisher Creek, two streams in the karstic Woodville Plain of Wakulla County that flow into sinkholes. Ground-water discharge rates at another nearby spring, Wakulla Spring, have been correlated to streamflows into sinkholes in the adjacent area.
The U.S. Geological Survey, in cooperation with the Florida Department of Environmental Protection, began collecting long-term data in 2007 to better understand the relation between the Spring Creek Springs Group, Wakulla Spring, and Lost and Fisher Creeks. Stream discharge and salinity data were collected at the downstream end of Spring Creek, and discharge data were collected at Lost and Fisher Creeks to supplement ongoing data collection efforts at Wakulla Spring. Discharge measurements on tidally affected Spring Creek required Acoustic Doppler Current Profiler techniques. Data from all sites are available in real time at http://waterdata.usgs.gov/fl/nwis/nwis.
The timing and magnitude of streamflows following an exceptionally large rainfall event in late February 2008 provided potential evidence of a hydraulic connection between the two creeks and the coastal springs. Following rainfall of about 6.8 inches on February 21-22, streamflow at Lost Creek peaked at 1,900 ft3/s on February 23, and streamflow at Fisher Creek peaked at 224 ft3/s on February 26. The following day, on February 27, net daily discharge at the Spring Creek Springs Group peaked at 1,730 ft3/s, a significant increase over the net daily discharge range from - 442 to 282 ft3/s during the 3 weeks prior to the event. Dye injected into Fisher Creek emerged at Wakulla Spring, 10 days later, directly linking the two.
The flow increase at the Spring Creek Springs Group was accompanied by a salinity drop from a daily average of approximately 27 ppt before the event to about 2 ppt immediately afterwards. During the entire month of March, salinity at Spring Creek showed daily values of less than 10 ppt and daily discharge of up to 1,330 ft3/s. This increase in flow and decrease in salinity are attributed largely to increased recharge to the Upper Floridan aquifer at the sinkholes downstream of Lost Creek and Fisher Creek. Additional recharge to the Upper Floridan aquifer is occurring at smaller sinkholes in the region, and conduit flow from these karst features may also contribute to ground-water discharge from the Spring Creek Springs Group.
Contact Information: Richard Jay Verdi, U.S. Geological Survey, Florida Integrated Science Center, 2010 Levy Avenue, Tallahassee, FL 32310; phone: 850-942-9500; email: rverdi@usgs.gov
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