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Determination of Groundwater-Flow Direction and Rate Beneath Florida Bay, the Florida Keys and Reef Tract

Project Proposal for 1998

Project Title: Determination of Groundwater-Flow Direction and Rate Beneath Florida Bay, the Florida Keys and Reef Tract
Location of Study Area: Florida Bay and Reef Tract
Project Start Date: FY 1996
Project End Date: FY 1999
Project Number: 7242-37654
Project Chief: E. A. Shinn
Region/Division/Team/Section: Eastern/Geologic/Marine and Coastal/St. Petersburg
E-mail: eshinn@usgs.gov
Phone: (813) 893-3100 ext. 3030
Fax: (813) 893-3333
Mailing Address: 600 4th St. S, St. Petersburg, FL 33701
Program Element(s)/Task(s) Element 1. Task 1.6
Collaborators, Clients:
Army Core of Engineers
Our results and ongoing monitoring activities should provide additional means of determining, the effectiveness of "replumbing" the everglades.
South Florida Water Management, Florida Marine Research Institute and University of South Florida, Florida State University and University of Miami
Department of Environmental Protection
Data provided by this study has been used by this department and is expected to be used in the future.
National Park Service
The park service is interested in the delivery of nutrients from below, especially from the so-called "river of sand."
Other Environmental Organizations and Businesses
The results of this study will have a profound impact on future development and tourism in the Florida Keys


Project Summary: Treated sewage is injected into the limestone under the Florida Keys via on-site disposal systems (OSDs). There are 25,000 septic tank systems, approximately 5,000 cesspools, and approximately 1,000 class 5 injection wells. Depth of injection wells ranges from 10 to 30 m. Excessive algal growth, coral diseases and both marine grass and sponge mortality is perceived by the local population, NOAA, and EPA, to be caused by sewage nutrients leaking from groundwater on both sides of the Florida Keys. Determining the rate and direction of saline groundwater movement beneath the Keys and Florida bay is considered critical to understanding the fate and effects of subsurface waste water disposal in the Florida Keys.

Project Justification: Management issues: As a result of this and related work, the state of Florida (in 1996) modified rules for installation of class 5 disposal wells. In addition, the EPA, citing our earlier work, has issued a warning statement to the State of Florida Department of Environmental Protection stating that "the geology of the Florida Keys is unsuitable for class 5 disposal wells." Reliable data on the flow direction and rate of groundwater movement in the Florida Keys as well as contamination levels is vitally needed.
Clients include State of Florida DEP, EPA, NOAA (this is a NOAA Sanctuary) ENP, and Monroe County. Monroe County is planning a multi-billion dollar sewage disposal system and is has been following our work very closely. The PI meets regularly with Monroe county and NOAA Sanctuary management and serves on the Technical Advisory Panel (TAP) for the Florida Keys Marine Sanctuary Water Quality Advisory Committee.

Project Objectives: The objectives of this research are to determine the rate, direction of flow and contamination levels of saline groundwater in the Florida Keys and Florida Bay. Contamination studies are necessary to determine if nutrient and other contaminant levels are rising, and to provide a baseline of data for future decision making.

Overall Strategy, Study Design, and Planned Major Products: The strategy of this study is to use artificial tracers to determine rate and direction of flow. Tracers are injected into well clusters, existing sewage treatment facilities, and sewage disposal wells. In addition to tracer studies groundwaters will be collected for contamination analysis so as to provide a base-line against which the effects of population increase and success of future wastewater treatment facilities can be evaluated in the future.


Overall: Seventy eight submarine monitoring wells have been installed in the Florida Keys reef tract, Florida Bay and Shark river slough and an additional 14 were installed in Biscayne bay in conjunction with a Miami WRD modeling, study. Six additional multi- depth wells were installed onshore at the Keys Marine Laboratory bringing the total number of wells to 84. All wells were continuously cored and cores reside at the St. Petersburg Coastal Center. Twenty of the 84 wells were installed to form two (200 ft diameter) circular clusters, each with an injection well in the center. The clusters, located on opposite sides of Key Largo, were designed to determine groundwater flow direction and rate. Each is screened at two depths, (-20 and -45 ft). The following tests have been conducted using the well clusters: 1) three separate dye tracer tests using fluorescein and Rhodamine, 2) one test using a colaphage (done in conjunction with University of South Florida) and 3) a single test with Sulfur Hexafluoride (SF6) as the tracer. The first two sets of tests determined flow direction and provided sufficient information to "zero-in" on the actual flow rate. An additional well (100 ft from cluster) was added to each cluster once the direction of movement was determined. The third test (using a combination of dyes and SF6) provided accurate flow-rate estimates. This data facilitates the design of future rate and direction experiments.

Additional monitoring wells will be installed (approximately 20 wells at 10 sites) to evaluate the "river of sand" hypothesis. These wells will be drilled in central, northern and western Florida Bay in the vicinity of Flamingo. Waters will be collected for chemical analysis to determine if contaminated waters are entering the bay from below, (i.e. the deep Floridan aquifer or shallow Biscayne aquifer) If water levels permit, we will also install a series of wells in the Taylor slough area of the southern Everglades. These wells will support another related fragile environments projects.

The overall future direction of this project is shifting toward nutrient and contaminant monitoring and evaluation of the "river of sand" hypothesis. Water samples will be collected biannually for the remainder of the study.

1. Install 20 to 25 additional monitoring wells.
2. Conduct additional tracer studies using both well clusters and existing (working disposal wells).
3.Sample wells for chemical analyses.

1 . Continue tracer studies.
2. Sample wells biannually for nutrient and other chemical analyses.
3. Drill additional wells as needed.
4. Model cross keys ground water flow and tidal pumping using visual mod flow.
5. Begin synthesis of results (Shinn, Reich Hickey and Tihanaky)

1. Sample wells biannually
2. Complete synthesis of results
3. Produce several publications

Planned Deliverables/Products: Papers will be given orally at national annual meetings (One was given at GSA in 1995 and at AAPG in 1997. A methods paper by Reich has been published. Final products (report) will be delivered to various clients including State of Florida Department of Environmental Protection, Federal EPA , NOAA, (Florida Keys National Marine Sanctuary) Everglades National Park, and Monroe County planning department.

Planned Outreach Activities: Ongoing outreach activities have already made this one of the most highly visible projects in south Florida. These outreach efforts will continue. Highlights of the study appear in a video USGS outreach video, and in "The Geology of Florida" produced by the State Geological Survey. Highlights of the study have also appeared on PBS television special, "The Aquarius Habitat."

Prior Accomplishments in Proposed Area of Work:

New Directions, Expansion of Continuing Project (if applicable):


Accomplishments and Outcomes, Including Outreach: Tracer tests in the well clusters have shown: 1) tidal pumping and higher sea level in Florida bay is the major force driving groundwater movement, 2) groundwater movement is primarily perpendicular to the Florida Keys thus major flow is towards the east and the reef tract (there is also flow toward Florida Bay), 3) the maximum rate of flow (towards the east) is 3.5 m/day. (approximately 100 m/month or 1 km/year).

Collaborative studies with USGS Reston based VIRD research group using CFCs and Oxygen and Hydrogen isotopic data support limited movement of Florida Bay groundwater into the inner reef tract east of Key Largo.

This study has already led to modifications of State regulations for installation of sewage disposal wells. Because of our work the EPA has determined that "the geology of the Florida Keys is not suitable for the use of waste disposal wells."

Highlights of the study appear in a video USGS outreach video, and in "The Geology of Florida" produced by the State Geological Survey. Highlights of the study have also appeared on PBS television special, "The Aquarius Habitat." )

Deliverables, Products Completed:
Shinn E. A., Reich C. D., Hickey, D. T., Bohlke, J. K., Plummer, L. N., Coplen, T. B., Busenbeberg, E., Chariton J., Burnett, W., Dillon, K., Corbett, R., 1996, Assessing the Origin and Fate of Ground Water in the Florida Keys, Florida Bay Science Conference, Program and Abstracts.

Reich, C. D., 1996, Diver-operated manometer simple device for measuring hydraulic head in underwater wells, Journal of Sedimentary Research Vol. 66, No.5, p. 1032-1034.

Shinn, E. A., Reich, C. D., Hickey, T. D., Tihansky, A. B. 1997, Geology and tidal pumping in the Florida Keys, AAPG annual meeting Dallas TX. abstracts p 106-107

Shinn, E. A., Reich C. D., Halley, R. B., Reese, R. S. 1995, Hydrogeologic aspects of sewage disposal in the Florida Keys GSA annual meeting New Orleans, abstract


Required Expertise:
1997 - Expertise in carbonate sedimentology, survey and sampling techniques, coring, well installation, boat operations, diving, GPS, Nutrient analyses, Flurometer analysis.
1998 - Same as above but including modeling with visual modflow.
1999 - Ability to synthesis all of the results into a final report, articles and presentations.

Names of Key Project Staff:
1997 - Shinn, Reich, Hickey and Tihansky
1998 - Shinn, Reich, Hickey, and Tihansky
1999 - Shinn, Reich, Hickey, and Tihansky

Major Equipment/Facility Needs:
1997: Coring platform, boat, cement,, coring equipment and miscellaneous supplies for completing wells (bits, rod, casing, PVC pipe, screens, cement, sand etc.)
1998: Same a above, and computer upgrades, lab facilities.
1999: Same as above.

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