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FLORIDA PROJECTS

Borehole geophysical logging for the Florida Power & Light Turkey Point Plant groundwater, surface water, and ecological monitoring plan

Project Chiefs: Kevin J. Cunningham, Robert A. Renken
Co-Investigators: Michael A. Wacker, Jeffrey F. Robinson
Cooperator: Florida Power & Light Company
Period of Project: October 2009 - September 2010

Problem Statement

Click to enlarge - Figure 1. Groundwater monitoring well-cluster locations within the project study area.

Figure 1. Groundwater monitoring well-cluster locations within the project study area.

The effect of salinity and temperature differences and aquifer heterogeneity on density-driven convection, and the combined impact on surface water, groundwater, and ecologic conditions is being evaluated at the Florida Power & Light Company (FPL) Turkey Point Nuclear Plant in southeastern Florida (Figures 1 and 2). The power plant contains a large unlined cooling canal system with warm water; which has salinities elevated above typical, natural surface water in southeastern Florida, circulating within the canals in the uppermost part the highly permeable karst carbonate Biscayne aquifer. The salinity of the cooling water is greater than natural groundwater salinities in the area, and thus, the presence of unstable density-driven convection is possible. The potential for unstable density-driven convection is somewhat diminished, however, by cooling water temperatures that are greater than local groundwater temperatures.

Objectives

(1) Evaluate potential detrimental effects of hypersaline water originating from a thermoelectric cooling canal system water on ambient water quality in a karst carbonate aquifer underlying Florida Power and Light’s Turkey Point facility;

(2) Design and construct an improved network of monitoring wells using high-frequency carbonate cyclostratigraphy, digital borehole imaging, ichnology, advanced borehole geophysical logging, and borehole flow meters to assist in the identification and selection of vuggy-porosity flow zone monitoring zones.

Click to enlarge - Figure 2. Aerial view of part of Florida Power & Light (FPL) Turkey Point Nuclear Power Plant in southeastern Florida.

Figure 2. Aerial view of part of Florida Power & Light (FPL) Turkey Point Nuclear Power Plant in southeastern Florida.

Approach

A monitoring plan mandated by the State of Florida as a condition for certification of two nuclear-power unit upgrades required the construction of 14 groundwater monitoring well sites. For each of the 14 groundwater monitoring wells, USGS staff acquired numerous borehole geophysical logs, which are listed in the Results section. Combined use of high-frequency carbonate cyclostratigraphy, digital borehole imaging, ichnology, advanced geophysical logging, and borehole flow meters assisted in delineation of principal groundwater flow zones of the Biscayne aquifer. These data can be used to provide aquifer characterization and numerical modeling parameters for the Biscayne aquifer, and will be a benefit to FPL in developing a conceptual hydrogeologic model of the Biscayne aquifer.

Results

Geophysical logs were acquired by the USGS at 14 exploratory coreholes in an area around and in the FPL Turkey Point Plant (Figure 1). The geophysical logs and cursory observations of rock core were used to identify the base of the Biscayne aquifer and zones of higher permeability within the Biscayne aquifer and used for planning of the construction of three discreet monitoring wells (shallow, middle, and deep) at each of the 14 monitoring-well cluster locations. The following geophysical borehole logging tools were run in the 14 exploratory coreholes: digital optical image tool, digital acoustic image tool, three-arm caliper tool, borehole fluid resistivity and temperature tool, water-quality tool (measures borehole fluid resistivity, temperature, pH, dissolved oxygen and oxidation-reduction potential), natural gamma-ray tool, electromagnetic induction tool, spontaneous potential tool, single-point resistivity tool, full-waveform sonic tool (measures compressional, shear, and stoneley-wave velocities, and various flow meter tools are various wells (heat-pulse flow meter, electromagnetic flow meter, and spinner flow meter).

Information Product

A final summary technical letter for technical transfer agreement between the USGS and FPL.

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