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FLORIDA PROJECTS

Feasibility of aquifer storage and recovery (ASR) and water supply development in the Upper Floridan aquifer, Broward County, Florida with the application of sequence stratigraphy to delineate the distribution of porosity and permeability

Project Chief: Ronald S. Reese
Cooperator: Broward County
Period of Project: October 2008 - September 2011

Problem Statement

Click to enlarge - Figure 1. Physiographic units and subdivisions of the study area, location of hydrogeologic cross sections and wells used on the sections, and location of Hillsboro canal marine seismic profile tract. Physiographic units are from Parker and others (1955, pl.12).

Figure 1. Physiographic units and subdivisions of the study area, location of hydrogeologic cross sections and wells used on the sections, and location of Hillsboro canal marine seismic profile tract. Physiographic units are from Parker and others (1955, pl.12).

Water supply in eastern Broward County, Florida has largely been provided by the shallow Biscayne aquifer. Water-level declines and saltwater intrusion into this shallow aquifer, however, have limited further development and constrained water-management practices including curtailment of new water-supply well-field permits. Therefore, the county is examining the potential of the Floridan aquifer system (FAS) as an alternative water supply, either directly by pumping from supply wells or indirectly by aquifer storage and recovery (ASR). ASR would increase available supply by diverting fresh water to displace native, brackish groundwater in the Upper Floridan aquifer of the FAS for subsequent recovery. As fresh groundwater supplies are becoming more limited, extraction of brackish FAS groundwater for public supply by municipal providers is increasing. This brackish water, however, must be treated by reverse-osmosis desalination or diluted by mixing with freshwater from the surficial aquifer. A key to understanding the spatial distribution and hydraulic connectivity of permeable zones in the FAS beneath Broward County is the development of a sequence-stratigraphic framework that produces a consistent method of county-wide correlation. Unconformable surfaces or their relative conformities are present at the top and bottom of rock units and have uniform or similar age and are predictable. The recognition of the vertical arrangement of stratal patterns bounded by these surfaces helps connect flow or permeable zones and confining layers or units, and also helps to estimate their thickness, porosity, and permeability. Definition and understanding of the extent, thickness, structure, and distribution of hydraulic conductivity and salinity within layers or zones in the FAS should improve the predictability of finding alternative water supply with sufficiently low salinity and high yield and contribute to successful water-supply development.

Objectives

1) Use existing data and data collected in this study to delineate the litho- and sequence-stratigraphic framework of the Upper Floridan aquifer in Broward County;

2) Describe and map the structure, thickness, and physical extent of permeable zones and semi-confining units within the Floridan aquifer system.

3) Define the distribution of hydraulic properties and salinity within these units, and relate these to stratigraphic frameworks.

Click to enlarge - Figure 2. Aerial view of test corehole G-2984 on the Hillsboro canal during drilling.

Figure 2. Aerial view of test corehole G-2984 on the Hillsboro canal during drilling.

Approach

  • Compile and synthesize existing lithologic descriptions, geophysical log data, borehole videos, water-quality, and hydraulic test data.
  • Obtain and describe lithologic samples from previously drilled wells.
  • Collect borehole geophysical data in existing wells, importantly including digital optical images of borehole walls.
  • Drill a test corehole into the Upper Floridan aquifer with the collection of continuous core, and geophysical logs.
  • Describe and analyze core collected from the test corehole and develop a sequence-stratigraphic framework.
  • Analyze and synthesize all data and interpretations and develop a hydrogeologic framework based on litho- and sequence-stratigraphic frameworks.
  • Define the distribution of hydraulic properties and salinity within the hydrogeologic framework.

Results

The test corehole has been completed, and cores have been described and analyzed (well G-2984, figs.1, 2). Water-based seismic-reflection data were acquired along the Hillsboro canal where the test corehole was located and interpreted and integrated into the study (fig. 1). A lithostratigraphic framework was delineated, and a provisional sequence-stratigraphic framework was established based on core and borehole geophysical data and expanded from the test corehole to the study area. The litho- and sequence-stratigraphic frameworks were used in defining the hydrogeologic framework and in better understanding the distributions of transmissivity and salinity in the permeable zones. Three hydrogeologic cross-sections were constructed to illustrate the frameworks (fig. 1). A SIR report has been written and is in review.

Information Product

U.S. Geological Survey Scientific Investigations Report “Stratigraphic and hydraulic characterization and salinity distribution of the Floridan aquifer system of Broward County, Florida” (in review)

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