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Groundwater Seepage in the Florida Keys

Project Proposal for 1998

Project Title: Groundwater Seepage in the Florida Keys
Location of Study Area: Florida Bay and Reef Tract
Project Start Date: FY 1996
Project End Date: FY 1999
Project Number: 7242-37657
Project Chief: E. A. Shinn
Region/Division/Team/Section: Eastern/Geologic/Marine and Coastal/St. Petersburg
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 will provide data needed by those who make hydraulic and nutrient models of South Florida.
South Florida Water Management, Florida Marine Research Institute and University of South Florida, Florida State University and University of Miami
Department of Environmental Protection
National Park Service

Park service biologists are interested in the delivery of nutrients from below, especially from the so-called "river of sand" that underlies the area.
Other Environmental Organizations and Businesses
The results of this study could impact management of the Florida Keys marine sanctuary and thus, future development and tourism in the Florida Keys


Project Summary: The purpose of this study is to determine the volume and composition of groundwaters seeping upward from the sea floor into Florida Bay and the coral reef tract. The method involves the use of seepage meters installed on the porous rock bottom of Florida Bay. The volume (expressed as l/day/M2) is used to calculate monthly and yearly additions to the overlying marine environment. Analysis of nutrients in the collected waters are needed to model nutrient loading.

Project Justification: The Florida Keys contain 25,000 septic tank systems, approximately 5,000 cesspools, and 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 to be caused by sewage nutrients leaking from groundwater on both sides of the Florida Keys. Determining the volume and composition of groundwaters seeping into the marine environment from the sea floor is vital to management decisions in the area. The data can be used for I)planning future disposal systems, 2) modeling the hydrology of Florida Bay, and 3) understanding the distribution of benthic flora and faunna.
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 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 objective of this study is to determine the volume and composition of groundwaters seeping upward through the rock water interface into Florida Bay and the coral reef tract. These studies are necessary to determine 1) if the level of nutrients and other contaminants is rising (i.e. baseline data) 2) to provide data for modeling efforts and 3) explain the mortality of certain benthic organisms such as corals and seagrass.

Overall Strategy, Study Design, and Planned Major Products: The strategy of this study is to install seepage meters and measure (quarterly) the volume of groundwater seepage into the overlying marine environment. The waters will be analyzed for major nutrient levels. The primary product will be a set of volume values which can be used by hydraulic modelers to determine the source and movement of Florida Bay waters. Submarine groundwater input into Florida Bay has been ignored by modelers and results are current models are likely to be erroneous. An additional major product will be an improved seepage meter design. Our experiments indicate that those presently in use, including those designed previously (by us) for this project produce bogus results.


Overall: This project consists of reinstalling newly designed seepage meters at sites where more than 50 have been already installed. The new meters consist of a circular (1 m2 surface area) flexible heavy gauge clear vinyl sheet cemented to the rock bottom with hydraulic cement. Each meter has a central port to which a plastic volume collection bag is attached. The volume of water collected in the bag is measured on-site. Because of irregularities in the surface and variable internal porosity and permeability of the limestone, 2 to 4 meters are installed at each site. These new meters produce reliable seepage estimates not possible with the inflexible fiberglass meters already installed. The "hard" meters were found, in the presence of waves, to actually pump water from the limestone.



1. Begin installing 50 new seepage meters.
2. Determine the volume of seepage from meter sites quarterly
3. Sample waters from existing and new meters for nutrient analysis


1. Continue installing the new design meters and make modifications as needed.
2. Sample meters biannually for nutrient and other chemical analyses.
3. Calculate annual seepage volume of ground water into Florida Bay and the Reef tract.
5. Begin synthesis of results (Shinn, Reich Hickey and Tihanaky)


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

Planned Deliverables/Products: Papers will be given orally at national annual meetings 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 waste water planning department.

Planned Outreach Activities: Ongoing outreach activities have already made this one of the more highly visible projects in south Florida. These outreach efforts will continue through video, Television, meetings with concerned groups, National Meetings, and the various committees attended by the investigators.

Prior Accomplishments in Proposed Area of Work: Fifty five fiberglass seepage meter were installed on rock surfaces in Florida Bay and the reef tract and measurements of seepage were made for 6 months. Data collection ceased when tests indicated results were bogus. After much redesign and testing we developed a new meter which will be installed in the latter part of 1997 and early 1998.

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


Accomplishments and Outcomes, Including Outreach: Our studies show that conventional seepage meters made from the ends of 55 gallon oil drums, produce bogus results in areas subject to wave pulsing. Oil drum based seepage meters have been used to obtain results reported in dozens of peer reviewed publications. Our tests indicate that in the presence of waves, any "hard" meter design acts as a one-way pump and tends to over estimate the actual volume of seepage. This effect was tested in-situ by attaching various meter designs to plywood sheets isolated from the bottom. Under field conditions, the "hard" meters filled the volume collection bags at a rapid rate, even when it was impossible for groundwater to enter.

As a result of these tests we developed and tested two new seepage meter designs. One meter is a modification of the conventional oil drum type. To make these the end is removed and a clear flexible vinyl end is installed. The unit resembles a large snare drum. A port is positioned in the center for attaching the removable volume collection bag. These kinds of units are designed for insertion into sediment which is the application in all previously published seepage studies. The second design, for installation on hard rock surfaces, consists of a sheet of clear vinyl plastic cemented directly to the rock with hydraulic cement. A port for the volume collection bag is attached to the center. The unit flexes with each passing wave such that the rock beneath the meter "feels" the same wave-induced positive and negative pulses as the surrounding bottom. Net outflow is channeled into the volume collection bag. The recently completed sediment facies map of Florida Bay (see proposal by Ellen Prager) shows that more than 70 percent of the bottom in eastern Florida bay consists of Pleistocene rock. Preliminary results indicate that seeping groundwater may replace all of the water in eastern Florida Bay in less than 1 year. This information has not been incorporated in any hydraulic modeling attempts.

In our outreach efforts, a USGS video, titled "The Edge of the Continent" highlights this work as does a video on the Geology of Florida, produced by the State Geological Survey. The study has also been featured on PBS television.

Deliverables, Products Completed:
Shinn E. A., Reich C. D., Hickey, D. T., Bohlke, J. K., Plummer, L. N., Coplen, T. B., Busenbeberg, E., Chanton 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, strong backs and portland cement mixing capability.
1998 - Same as above but including modeling with visual modflow.
1999 - Ability to synthese 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: Boat, vinyl sheet supplies, cement, scuba etc.
1998: Same as above, computer upgrades, lab facilities.
1999: Same as above.

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Last updated: 24 April, 2014 @ 01:01 PM (KP)