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FLORIDA PROJECTS

Hydrogeologic and Seismic-Reflection Analysis of Cretaceous Formations, Sub-Floridan Confining Unit, and Floridan Aquifer System in Miami-Dade County

Project Chiefs: Kevin J. Cunningham
Cooperator: Miami-Dade County
Project Period: June, 2014 to June, 2019


Problem Statement

A refined hydrogeologic framework is needed in Miami-Dade County and surrounding areas (fig. 1) to improve conceptualization of the hydrogeology and, therefore, the groundwater flow system, within the Floridan aquifer system (FAS), and deeper Paleocene and Cretaceous Formations. Peninsular and marine seismic-reflection and geologic data on the southeastern Florida Platform indicate greater geologic complexity than previously acknowledged (Cunningham and Walker, 2009; Cunningham and others, 2012; Cunningham, 2015; Cunningham and others, 2015). Tectonic and karst structures identified in offshore areas indicate that faults and collapse features may serve as pathways for groundwater flow across otherwise low-permeability carbonate strata separating regionally extensive high-permeability rock zones in the FAS.


Background

Widespread and competitive use of the FAS in southeastern Florida for numerous and conflicting needs requires application of innovative technologies to manage water resources in an effort to mitigate unforeseen impacts of injected wastewater management activities. Deep-well injection of effluent in the Boulder zone of the Lower Floridan aquifer (LFA) currently represents the primary water-management option for the disposal of municipal wastewater in Miami-Dade County. Mandated elimination of ocean outfalls to mitigate degradation of marine ecosystems and coastal environments, and revised Underground Injection Control regulations, have necessitated reform of wastewater injection. The zone of brackish water contained within the Upper Floridan aquifer (UFA) is an Underground Source of Drinking Water reserved as an alternative source of water for municipal supply through the use of aquifer storage and recovery, blending, and reverse osmosis. Demand for the limited brackish-water resources of the UFA has increased concern that injection of relatively low density effluent into the high-density saline waters of the Boulder Zone may promote buoyant upward LFA leakage of the injected effluent, which has already occurred at several southeastern Florida wastewater-injection sites (Maliva and others, 2007).


Goals and Objectives

An overarching goal of this project is to develop a 3-D geologic model (geomodel) that improves the current understanding of the geologic and hydrogeologic architecture of a faulted and karstic FAS and underlying Paleocene and Cretaceous Formations. A 3-D geomodel can reduce risk associated with upward buoyant wastewater movement by developing an accurate representation of seismic-sequence stratigraphic relations, and imaged tectonic and karst structural features.

Geomodels capture physical variations that impact groundwater flow within the faulted and karstic carbonate rocks of the southeastern Florida Platform. Two- and 3-dimensional seismic-reflection data (fig. 2) integrated with existing and new geologic and hydrogeologic data are being used as critical input to identify potential high-permeability tectonic and karst elements. Non-unique geomodel solutions have been applied to aquifer sustainability, waste disposal, and other carbonate platforms around the globe.

The principal objectives of the Miami-Dade Floridan and Cretaceous aquifers study are:

  • Construct a refined geologic and hydrogeologic framework of the FAS, underlying Paleocene confining units and the upper part of Cretaceous formations in the eastern part of Miami-Dade County. Calculate the probability of injected fresh wastewater transport along fluid-flow pathways from the Boulder Zone into Underground Sources of Drinking Water and provide the framework for informing the estimation of injection volumes and containment efficacy within deeper Cretaceous aquifers.

  • Construct an FAS and Cretaceous Formation geologic database and geomodeling tools to assist Miami-Dade County water resource management decisions and activities.

Major tasks

  • Compile, acquire, and interpret new and existing geologic, hydrologic, and geophysical well data from new FAS well field wells and a new wastewater treatment plant Cretaceous well.

  • Acquire, process, and interpret seismic-reflection data.

    Figure 1. Study area including reflection-seismic program

    Figure 1. Study area including reflection-seismic program.

    Figure 2. 3D seismic volume and horizons in eastern Miami-Dade County.

    Figure 2. 3D seismic volume and horizons in eastern Miami-Dade County.


  • Confirm seismic-attribute models of vertical fluid-flow probabilities using multi-beam bathymetric mapping, and high-resolution backscatter water-column gas detection with a remotely operated vehicle.

  • Correlate well stratigraphy with seismic-sequences for 2-D and 3-D sequence stratigraphic interpretation.

  • Analyze the continuously-cored geologic and hydrologic rock properties in newly drilled FAS and Cretaceous Formations wells.

  • Employ advanced geologic modeling techniques to create a 3-D geomodel that offers visualization products clarifying key stratigraphic units, seismic sequences, structural features, major high-permeability zones, and confining units.

Results: New stratigraphic conceptual models of the Cenozoic and Mesozoic aquifer and confining units of the southeastern Florida Platform are evolving using seismic imaging integrated with new borehole data.


Information Products

USGS Reports or journal articles or both.


References

Cunningham, K.J., 2015, Seismic-sequence stratigraphy and geologic structure of the Floridan aquifer system near “Boulder Zone” deep wells in Miami-Dade County, Florida: U. S. Geological Survey Scientific Investigations Report 2015–5013, 28 p., accessed March 14, 2016, at https://pubs.usgs.gov/sir/2015/5013/.

Cunningham, K.J., Kluesner, J.W., Westcott, R.L., and Edwards, J.H., 2015, Potential fluid-migration pathways indicated by multichannel-seismic data from the southeastern Florida Platform: American Association of Petroleum Geologists Annual Convention & Exhibition, May 31-June3, Denver, CO, accessed March 14, 2016, at http://www.searchanddiscovery.com/abstracts/html/2015/90216ace/abstracts/2089125.html.

Cunningham, K.J., and Walker, C., 2009, Seismic-sag struc¬tures in Tertiary carbonate rocks beneath southeastern Florida, USA—Evidence for hypogenic speleogenesis?, in Klimchouk, A.B., and Ford, D.C., eds., Hypogene Spe¬leogenesis and Karst Hydrogeology of Artesian Basins: Simferopol, Ukraine, Ukrainian Institute of Speleology and Karstology, Special Paper no. 1, p. 151–158, accessed March 14, 2016, at https://institute.speleoukraine.net/libpdf/Cunningham%20Walker_SEISMIC-SAG%20STRUCTURAL%20SYSTEMS%20IN%20FLORIDA_HypoConf_2009.pdf.

Cunningham, K.J., Walker, C., and Westcott, R.L., 2012, Near-surface, marine seismic-reflection data define poten¬tial hydrogeologic confinement bypass in the carbonate Floridan aquifer system, southeastern Florida: Society of Exploration Geophysicists Annual Meeting, Las Vegas, NV, 6 p., accessed March 14, 2016 at https://library.seg.org/doi/abs/10.1190/segam2012-0638.1.

Maliva, R.G., Guo, W., and Missimer, T., 2007, Vertical migration of municipal wastewater in deep injection well systems, South Florida, USA: Hydrogeology Journal, v. 15, p. 1387-1396.

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