Study Site

Our study site, an aquifer targeted by the Orange County ASR operations, is located in east-central Florida as part of the St. Johns River Water Management District (SJRWMD). It includes one ASR well for injection and two monitoring wells at a distance of 30.5 and 152.4 m from the injection well.³⁶ The storage zone extends between a depth of 318.5 and 362.7 m, therefore coinciding with the Eocene Avon Park Formation of the Lower Floridan Aquifer in the Floridan Aquifer System.³⁶⁻³⁸ This formation was deposited under cyclic shallow open marine to tidal-flat conditions with sometimes restricted seawater circulation and arid climate.³⁹⁻⁴¹ In Orange County, the formation is dominated by dolomite and dolomitic wackestones that consist of dolomite, calcite, trace amounts of clay, natural OM, and pyrite in the form of framboids and euhedral crystals.^36,42 The dolomitization took place during the middle Eocene by normal to hypersaline seawater.^43,44 Gilboy⁴⁵ described the occurrence of salt marsh and swamp deposits of peat and carbonaceous material in the Avon Park Formation. Sediment samples were collected from core W-18722 at the Core and Cuttings Repository of the Florida Geological Survey in Tallahassee (Florida). This core was obtained during the drilling of the monitoring well at a distance of 152.4 m from the injection well. Three samples (43 OC, 55 OC, 63 OC) were selected for this study. The selection targeted samples showed concentrations of Mo above 150 mg/kg. While samples 43 OC (depth: 338.3 m) and 55 OC (depth: 354.6 m) were collected directly from the storage zone, sample 63 OC (depth: 365.9 m) was located below the storage zone.