The purpose of this paper is to delineate the lithofacies, depositional environments, cyclostratigraphy, porosity, and permeability of the karst limestone of the Pleistocene Biscayne aquifer in north-central Miami-Dade County, Florida (Fig. 1 and Fig. 2). This paper demonstrates how carbonate cyclostratigraphy is crucial to the definition of spatial distribution of porosity and permeability within a triple-porosity (matrix, touching-vug, and conduit porosity) karst aquifer. This study is part of a more comprehensive investigation to assess the efficacy of karst limestone underlying the Miami-Dade County's Northwest Well Field (Fig. 1) to attenuate movement of pathogenic organisms (Renken et al., 2005). County officials are concerned that proposed expansion of extractive limestone rock mines near the well field will increasingly influence the ambient quality of groundwater. The U.S. Environmental Protection Agency requires public water supplies derived from "ground water under direct influence of surface water" use enhanced disinfection and filtration treatment processes to remove pathogenic organisms (Federal Register Notice, 2000).

Figure 1. Locality of study area. (A) Southeastern USA and location of Miami-Dade and Broward Counties, Florida. (B) Location of the Lake Belt area in SE Florida. (C) Location of the study area within the Northwest Well Field and much of the Lake Belt area. (D) Details of part of the study area, including location of injection, observation, and some of the municipal supply wells within the Northwest Well Field. For additional information about this figure, please contact Kevin Cunningham at kcunning@usgs.gov. [larger image]

The application of cyclostratigraphy has proven critical to the development of a new conceptual hydrogeologic framework within the Biscayne aquifer (Cunningham et al., 2004b, 2004c, 2006). In this paper, a high-resolution cyclostratigraphic model throughout the entire thickness of the karstic Biscayne aquifer is used to select consistent, correlative flow zones between an injection well and the point of tracer recovery, a Northwest Well Field production well. This framework serves as the physical basis for scoping, designing, and executing a series of conservative and colloidal tracer tests (Renken et al., 2005).

Figure 2. Correlation of ages, formations, stratigraphy, and hydrogeologic units of the Tamiami Formation, Fort Thompson Formation, and Miami Limestone from various authors and this study. For additional information about this figure, please contact Kevin Cunningham at kcunning@usgs.gov. [larger image]