CONDUIT FLOW: PATHWAYS TO POOR ASR RECOVERY AND SURFACEWATER CONTAMINATION IN FLORIDA
Recovery efficiency (at 250 mg/L chloride concentration) reported by USGS was 3.1%, 2.7%, and 7.2% (storage periods: 0, 8, and 5 days, respectively) for Lake Okeechobee ASR wells proposed for use in the northern vicinity of the ERP. Actual recovery efficiency was lower, since chloride concentrations of injected recovery fluids were 150, 100, and 70 mg/L, respectively, for those tests. Dye tracer tests conducted this year by USGS in the Biscayne (surficial) aquifer, south of Lake Okeechobee, revealed groundwater travel times of several hours over distances predicted to require days. Evidence that injected fluids resurface in nearshore waters (induced discharge) is seen in stable nitrogen isotope data from macroalgae smothering reefs in southeast Florida.
Those results reflect conduit flow of injected fluids that can cause large-scale subsurface discharge of nutrients and other contaminants into Floridas sensitive surface waters, including the surf zone. Poor recovery, rapid travel times, and discharge points for the karst aquifer system are not addressed by groundwater models used for decision-making. Similar flow responses have been addressed in other areas of the regional Floridan aquifer system using a finite-element groundwater model. This approach can identify probable discrete flow paths and discharge points.