The purposes of this report are to: (1) document the resolution of regional differences in hydrogeologic nomenclature and framework interpretation of the Floridan aquifer system between central and southern Florida and between west and east coastal areas; (2) establish a consistent hydrogeologic framework interpretation thoroughout central and southern Florida; and (3) develop hydrogeologic surface and thickness maps of units within the upper part of the Floridan aquifer system, thereby allowing for better comparisons of existing ASR sites and their performance and improved selection of future ASR sites.
Steven J Memberg
accessed as of 10/4/2010
accessed as of 10/4/2010
Alvarez-Zarikian, C. A.
Prepared in cooperation with the South Florida Water Management District
accessed as of 10/4/2010
Evans, W. L., III; Taylor, K. L.
Accessed as of 10/4/2010
The 706 wells inventoried and used in this study were drilled and constructed for various purposes and are irregularly distributed in the study area.
The review of previous studies in the study area, both regional and subregional in scope, found significant differences in the naming and definition of hydrogeologic units within the Floridan aquifer system. To make use of the data from these studies, it was necessary to identify these conflicts; and to guide this effort and develop a unified conceptual hydrogeologic framework, it was necessary to: (1) construct eight regional hydrogeologic sections through key wells, delineating major aquifers, subaquifers, and confining units across the study area north to south and west to east; and (2) develop an approximately correlative or approximate time-stratigraphic framework including construction of four stratigraphic sections. The differences in hydrogeologic nomenclature and interpretation across the study area from previous studies were identified and resolved within the unified conceptual hydrogeologic framework. Based on that conceptualization, data from previous studies of the Floridan aquifer system were extracted, archived, and utilized in conjunction with boundary depth determinations made for this study to map the boundaries and thicknesses of hydrogeologic units.
Development of an approximately correlative stratigraphic framework included delineation of a marker unit and marker horizons. The horizons are correlative points in the stratigraphic section rather than a unit with upper and lower boundaries. This approximate time-stratigraphic framework differed from the formation-based stratigraphy and provides a basis for better understanding the vertical and lateral extent of formations.
Two correlative stratigraphic marker horizons within the Floridan aquifer system and a marker unit near the top of the aquifer system were delineated or mapped to provide stratigraphic guidance in the identification and determination of aquifers and confining units and in the delineation of their lateral continuity. The two marker horizons originated from two previous studies of east coast Lower Floridan aquifer injection wells, where they are based on lithology and correlation of geophysical log (natural gamma-ray and sonic) signatures observed in boreholes. The depths of these same two marker horizons were extended throughout the study area by correlation of natural gamma-ray logs between wells.
Development of an approzimate time-stratigraphic framework An approximate time-stratigraphic framework was developed in this study primarily using geophysical log correlation between wells, beginning with stratigraphic marker units or lithologic changes established in certain wells or areas. A stratigraphic marker unit near the top of the Floridan aquifer system and two stratigraphic marker horizons within the middle and lower parts of the Floridan aquifer system were delineated and mapped to provide stratigraphic guidance in the identification and delineation of aquifers, subaquifers, and confining units. The two marker horizons originated from work by Duncan and others (1994a, b) in studies of east coast Lower Floridan aquifer injection wells located in Brevard, St. Lucie, Martin, and Palm Beach Counties. The marker unit has a finite thickness, whereas the marker horizons are points of correlation on natural gamma-ray logs. The two marker horizons originated from work by Duncan and others (1994a, b) in studies of east coast Lower Floridan aquifer injection wells located in Brevard, St. Lucie, Martin, and Palm Beach Counties; they were mapped by Duncan and others (1994a,b) using changes in lithology and natural gamma-ray logs for the purpose of establishing correlative relations. Starting with wells where they were determined by Duncan and others (1994a,b), the depths of these same two marker horizons were extended throughout the study area primarily using correlation of natural gamma-ray curves between wells.
Correlation of gamma-ray logs of wells in this investigation was carried out at a vertical scale of 1 in. = 125 ft using working copies plotted through Viewlog (tm) software. The entire section from surface to total depth was correlated between wells in order to best establish the depths of stratigraphic marker horizons. Correlation within the carbonate rocks of the Floridan aquifer system, which tend to have low natural radioactivity, was aided by plotting curves using an expanded scale, such as 0 to 100 API (American Petroleum Institute) standard units, instead of a more standard scale of 0 to 200 API units, to enhance gamma-ray curve variations.
The reliability of correlation of the marker horizons by gamma-ray logs in this study was improved by correlating all the deep wells with gamma-ray logs, not just wells on cross sections. Additionally, wells were correlated in loops, first regionally then locally, to check for correlation error of closure in returning to the original well. If an error greater than 20 to 30 ft was found, the correlations for the wells in a loop were reviewed and corrections were made. Once a regional loop was satisfactorily correlated, thereby establishing the correlations in a new region, then smaller loops were conducted in the new region.
Determination of hydrogeologic unit boundaries Hydrogeologic unit boundaries were determined in this study primarily using geophysical logs and lithologic descriptions. Where available, the results of hydraulic tests such as aquifer and packer tests were also reviewed. Additionally, in one area a formation boundary was used for the top of a confining unit because of the nature of the formation in the area and the unavailability of adequate other data. Assistance in the identification of units and determination of their boundaries between the major divisions of the study area was provided by the construction of hydrogeologic sections and the approximate time-stratigraphic framework, including the marker horizons and the marker unit previously described. Hydrogeologic unit boundaries determined in previous studies were reviewed for consistency in their methods of determination with those used in this study, and utilized wherever possible.
For the purpose of determining hydrogeologic boundaries in each well, geophysical logs and, when available, lithologic data were plotted together at a uniform scale (1 in. = 125 ft) using Viewlog (tm) software. Borehole geophysical logs were grouped by type into four columns that include: (1) natural formation gamma ray, spontaneous potential (SP), and caliper curves, (2) formation resistivity curves, (3) formation porosity curves, and (4) borehole flow and fluid properties logs including fluid resistivity, temperature, and flowmeter. Lithologic data were plotted in a fifth column using graphic symbols.
The vertical distribution of hydraulic head in a test well was used to assist in determining boundaries in some water-management district well construction reports, and after review, these boundaries were usually accepted in this study. Generally, however, determination of the hydrogeologic boundaries through hydraulic head and hydrogeochemical data could not be done in this study, because these data were not available in most wells.
Most of the hydrogeologic data used to determine hydrogeologic unit boundaries in this study were archived in the South Florida Water Management District (SFWMD) DBHYDRO database; the data include geophysical logs, packer and aquifer performance tests, lithologic descriptions, and formation contact depths. The most complete coverage of these data is in the SFWMD area, but data on many of the wells used in the other water-management district areas were also archived in this database. Most of the lithologic descriptions in DBHYDRO were done by the Florida Geological Survey (FGS) and came from their database. Other data and lithologic descriptions used that are not in DBHYDRO were available from well construction reports done by consulting firms and government agencies other than FGS, including the USGS and the State water-management districts. Hydrogeologic unit boundary depths determined during this study or obtained from other investigations were also archived in DBHYDRO.
Hydrogoelogic sections The regional synthesis and development of a new hydrogeologic conceptualization of the Floridan aquifer system in the study area was in large part based on eight hydrogeologic sections created for this study. The primary purpose of these sections was to assist in delineating aquifers, subaquifers, and confining units between the major divisions of the study area. Working copies of the sections were constructed at a vertical scale of 1 in. = 125 ft with geophysical logs and lithologic columns plotted for each well using Viewlog (tm) software. Geophysical logs were grouped by function as previously described. Aquifer and formation boundaries and marker horizons were delineated.
Key wells were used to constrain interpretations across each section. Selected wells on each section were sufficiently deep to intersect the primary zones of interest and have high quality geophysical logs and ancillary data (such as water-quality or water-level data). The ancillary data could be used to help identify an aquifer or determine whether a permeable zone was a unique aquifer or a flow zone within a larger aquifer. Priority was given to State water-management district test wells, but wastewater injection and oil test wells were also used. Five sections were extended west to east across the peninsula as tie lines, and three sections were extended north to south, one along each coast and one along the center of the peninsula.
Stratigraphic and hydrogeologic maps Maps of the two stratigraphic marker horizon surfaces and the top surface and thickness of hydrogeologic units, including aquifers, subaquifers, and one confining unit, were constructed in this study. The mapping was completed in three steps: (1) determination of the stratigraphic marker horizon and hydrogeologic unit boundary depths in wells used in the study, (2) generation of surface maps by fitting the well data to a statistical model, and (3) review and revision of these surfaces and generation of thickness maps.
Generation of surfaces by fitting data to a statistical model Stratigraphic marker horizon and hydrogeologic unit surface maps were produced using ordinary kriging techniques available with Viewlog (tm) software.
A semivariogram model and associated parameters, which are range, sill, and nugget, were selected based on the best visual and statistical fit for each surface data set. Due to the regional southerly dip of strata and units comprising the Floridan aquifer system into the southern Florida basin, a linear trend had to be removed from all data prior to selecting the semivariogram model.
Review and revision of surfaces and generation of thickness maps Generating the stratigraphic marker horizon and hydrogeologic unit surfaces was an iterative process. After the first round of kriging, the surfaces and control point values were plotted. Data points that were anomalous because of a value inconsistent with those in nearby wells were reviewed, and any that were determined or evaluated in this study were reevaluated to establish their reliability. One of the following steps then was taken:
Anomalous points were reviewed for how well they met the criteria used in this project for boundary depth determination. Upon this additional review, points found not to meet project criteria or based on a weak data set (for example, a control point based solely on poor quality geophysical logs without supporting borehole fluid logs, lithologic descriptions, or hydraulic tests) were removed from the interpolation or retained with the uncertainty indicated manually by dashing contour lines.
Anomalous points with strong supporting data were assumed to be reliable and were retained.
In rare cases, data points met project criteria with relatively strong supporting data at the local well scale, but were removed from the interpolation because of the undue influence they exerted at a larger scale.
After modifications were made to the input data set based on this review, the integrity of the kriging model was checked and the surface was regenerated. Once satisfactory upper and lower surfaces for a hydrogeologic unit were completed, they were used to generate the unit thickness map by subtraction.
The final step in the generation of surface and unit thickness maps was manual modification, In addition to reviewing individual anomalous data points, the surfaces as a whole were reviewed for consistency. Contours lines on maps were moved to account for all data points, and the positions of zone pinchouts, if present, were interpreted and drawn in manually. Finally, contour lines were smoothed and, where necessary, dashed to indicate less confidence in their position because of large areal data gaps or values that were less certain.
For a more complete discussion of the steps above, see SIR 2007-5207.
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