Brackish-water desalination plant modulates ground deformation in the city of Cape Coral, Florida

The groundwater abstraction and injection cycle in coastal aquifer systems can locally change the piezometric head in aquifer system, leading to differential settlement on the ground that may compromise infrastructure safety. Furthermore, long-term, extensive groundwater extraction may cause significant damage to water resources. Ironically, Florida, a state known for its abundant water resources, has been experiencing major water supply issues in some areas that began to intensify with rapid population growth over the last five decades. As the demand for drinking water in Florida continues to rise, local authorities have turned to using brackish and saline water sources. As of 2022, more than 80% of the desalination plants in the United States are concentrated in the coastal areas of central and south Florida. Using satellite radar interferometry, we have investigated the spatiotemporal evolution of surface subsidence driven by groundwater pumping for brackish-water reverse osmosis (BWRO) desalination facilities in the City of Cape Coral, Florida. We employed Persistent Scatterer Interferometry (PSI) to process all available Sentinel 1A and 1B scenes over the region along two ascending orbits. The deformation time-series obtained from independent SAR data sets are compared spatiotemporally with the groundwater level that provides feed water to the BWRO facilities. The deformation pattern shows one main lobe of subsidence with rates of up to 25 mm/year centred around the operating wells in the north BWRO wellfield that we interpret as human-induced compaction. The spatial correlation between the subsiding area and the active production wells argues in favour of surface deformation induced by the BWRO operations. Based on the InSAR-derived displacement field and well data, we propose a model to explain the spatial heterogeneity of the subsidence process. The ground deformation is reproduced by an elastic model mimicking the reservoir compaction using planar negative closing dislocations. Modelling of the subsidence shows ∼ 0.67 Mm³ yr⁻¹ vol loss due to compaction of the aquifer. The subsidence deformation was also used to compute the cumulative drainage area of the producing wells.