National Park Service
U.S. Department of the Interior
Water Resources Division
Natural Resource Program Center
Technical Report NPS/NRWRD/NRTR-2006/356

The National Park Service Water Resource Division is responsible for providing water resources management policy and guidelines, planning, technical assistance, training, and operational support to units of the national park system. Program areas include water rights, water resources planning, regulatory guidance and review, hydrology, water quality, watershed management, watershed studies and aquatic ecology.

Cover Photo: Grey Angelfish on Biscayne National Park coral patch reef; photographer unknown

Technical Reports

The National Park service disseminates the results of biological, physical and social research through the Natural Resource Technical Report Series. Natural resources inventories and monitoring activities, scientific literature reviews, bibliographies, and proceedings of technical workshops and conferences are also disseminated through this series.

Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the National Park Service

Copies of this report are available from the following:

National Park Service
Water Resource Division     (970) 225-3500
1201 Oak Ridge Drive, Suite 250
Fort Collins, CO 80525

National Park Service
Technical Information Center     (303) 969-2130
Denver Service Center
P.O. Box 25287
Denver, CO 80225-0287

This report constitutes the completion report for PMIS project #289 funded by the NPS Natural Resources Preservation Program component of the Natural Resource Challenge and fulfills the reporting requirement of Task Order 03-21, of Interagency Agreement #IA238099002 between the National Park Service and the U.S. Geological Survey

EXECUTIVE SUMMARY

Biscayne National Park (BNP) is adjacent to the Miami-Dade County South Dade Landfill Facility and the Miami-Dade Water and Sewer South District Plant. The base of the landfill is lined with a geotextile membrane to separate it from the underlying Miami Limestone, the host rock for the Biscayne Aquifer. The sewer plant injects treated sewage into the lower Floridan Aquifer that is overlain by an aquitard termed the Middle Confining Unit. The Biscayne Aquifer borders the western margin of BNP and the Floridan Aquifer underlies the entire park. There is concern about leakage of contaminated aquifer water into BNP and its potential effects on water quality.

Water samples from shallow nearshore and offshore wells in BNP have been analyzed to characterize the groundwater beneath the park and to assess the potential for contaminants entering the park from subsurface flow. Samples from seven well sites were collected approximately quarterly from August 2002 until March 2004. The well sites form a transect from the western shore of Biscayne Bay at Black Point southeastward across the shelf to Pacific Reef. Samples were analyzed for conductivity (salinity), dissolved oxygen, temperature, redox potential, nutrients, metals, strontium isotopes, radon, sulfate, and wastewater compounds.

Low-salinity water was present in nearshore wells and indicates either some leakage from the Biscayne Aquifer or surface-water intrusion. Elevated nutrients indicate surface-water exchange is more likely than groundwater flow. Lack of seasonal variation in groundwater salinity indicates minimal exchange either with the surface water or with fresh groundwater flow, both of which exhibit seasonal variation. The groundwater beneath the Florida shelf can be characterized as reduced (anoxic) seawater, modified by microbial respiration to remove oxygen and interaction with sediments and minerals in the host limestone. Analyses of 109 water samples collected from wells across the Florida shelf beneath BNP between August 2002 and March 2004 show no consistent evidence of wastewater contaminants occurring in groundwater beneath BNP. In addition, no significant upward leakage from the Floridan Aquifer was detected in the shallow groundwater beneath BNP. The western edge of Biscayne Bay is influenced by surface water and perhaps Biscayne Aquifer water, whereas the rest of the Florida shelf is underlain by uncontaminated marine groundwater.

ACKNOWLEDGMENTS

The authors thank the USGS Coastal and Marine Geology Program and the National Park Service (NPS) for funding this study. Richard Curry (NPS) assisted with permitting, field logistics, and conceptual design. Kate Ciembronowicz, Brian Blake- Collins, Russ Peterson, B.J. Reynolds, and Nate Smiley assisted with fieldwork. We also thank Charles Holmes, Mario Fernandez, and Barbara Lidz for their diligent reviews, which have greatly improved this report.

Related Information:

SOFIA Project: Ground Water Characterization in Marine Areas of Biscayne National Park