Mapped Fractures and Sinkholes in the Coastal Plain of Florida and Georgia to Infer Environmental Impacts from Aquifer Storage and Recovery (ASR) and Supply Wells in the Regional Karst Floridan Aquifer System

Abstract

The regional Floridan aquifer system (FAS) extends from the submerged carbonate platform of the Atlantic Ocean, Gulf of Mexico, and Straits of Florida in the southeastern United States (US), throughout Florida and the coastal plain of Alabama, Georgia, and South Carolina. This carbonate aquifer system is characterized by bedding planes, fractures, dissolution cavities, and other karst features that result in preferential flow of ground water, particularly in response to anthropogenic perturbations such as groundwater withdrawals and aquifer injections. The FAS was divided into six sub-regions for groundwater-modeling purposes in 1989, with results concluding that breaches of those groundwater divides had occurred and those breaches were attributed to large withdrawals of ground water in the US southeastern coastal plain. Those results suggest the model did not elucidate preferential flow conditions through fractures and other karst conduits. We hypothesized that incorporating fractures and sinkholes into groundwater models could improve results and predict adverse impacts to environmentally sensitive areas. We analyzed extensive fracture networks and sinkholes previously mapped throughout Florida and in Dougherty County, Georgia. Some of those fractures extend from one sub-region into an adjacent sub-region of the FAS and may be facilitating the breaching of groundwater divides described in the 1989 groundwater model for this regional aquifer system. The greater total fractures and fracture density in Dougherty County (1,225 and 141.3/100 km 2 , respectively) compared to 21 north-Florida counties (10-91fractures per county and 0.6-3.8/100 km 2 , respectively) presumably is due to the scale of fracture mapping and shorter mean lengths of mapped fractures in Dougherty County (1.2 km), compared to north Florida counties (26-118 km), rather than to orders of magnitude increases in fracture densities in that part of the FAS. The number of sinkholes identified in Dougherty County in a recent, unrelated project using 2011 Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images, was approximately an order of magnitude greater than the number of sinkholes mapped in analog form in that county and published in 1986.

Implications of Declining Ground Water and Water Quality in the US Southeastern Coastal Plain Ecoregion and Areawide Environmental Impact Statement Required for Mining in the Greater Okefenokee Swamp Basin—Part 1

“…The extent of those three sets of fractures, previously mapped in Florida, are shown in Figure 3. Figure 2a of Xu et al (2016) illustrated the mapped fractures in Florida, overlain by modern-day sinkholes, which are so numerous in some areas that they obscure the fractures.…”

“…An example of the density of fractures mapped within the Georgia portion of the Floridan aquifer system is provided by the fractures mapped by Brook & Allison (1986) in Dougherty County, Georgia. Those mapped fractures are shown in Figure 4b of Bacchus, Bernardes, Xu, & Madden (2015b) and Figure 3a of Xu et al (2016). We are not aware of similar efforts to map the locations, extent and density of fractures in the Georgia portion of the Greater Okefenokee Swamp Basin, including areas in southeast Georgia where mining is occurring and proposed.…”

Analysis and Extent of Santa Fe River Flooding in North Florida Attributed to Rainfall and Wind Damage Associated with Hurricane Irma

“…The shapefiles for the SFR Basin used in this study were obtained from the USGS WBD. The sub-regions of the Floridan aquifer system included in Figure 1 were created using widely-accepted map vectorization procedures, including the control-point based georeferencing of the sub-regions map included in Krause & Randolph (1989) and the heads up digitizing of the resulting georeferenced map image (Xu et al, 2016). Shapefiles for USGS active and inactive gage locations for surfacewater monitoring were obtained from the USGS National Water Information System (NWIS) (USGS NWIS, 2018) for south and north Alligator Creeks in Bradford County; the New River in north central Florida; Olustee Creek; the Sampson River; and the SFR.…”

Management Implications of Aquifer Fractures on Ecosystem and Habitat Suitability for Panthers in Southern Florida

“…That groundwater mining results in threats to water resources by increasing saltwater intrusion into the aquifer system and resulting in other forms of water quality degradation, sinkholes, and induced recharge to the aquifer from the overlying [54], Sonenshein and Hofstetter [55], and Wilcox et al [56] to coastal wetlands and/or nearshore benthic marine habitats [57]. Bacchus [26] provided photographs of irreversible damage to depressional wetlands after catastrophic wildfires caused by unsustainable groundwater withdrawals.…”