Pressure management strategies for large-scale aquifer recharge: Mitigating the potential for injection-induced earthquakes

• Aquifer recharge by injections drive pressure transients into basement rock. • Pressure transients from injections may be sufficient to induce seismicity. • Gradually increasing injection rates reduces initial pressurization magnitude. Long-term groundwater withdrawals in coastal Virginia have led to declining groundwater levels, saltwater intrusion, and land subsidence, threatening regional water security and infrastructure. Managed aquifer recharge (MAR) through underground injection offers a promising solution to mitigate these effects. A large-scale MAR project is under construction in southeast Virginia to replenish the Potomac Aquifer, with a combined injection rate of up to ∼ 189,000 m 3 /day at two sites. The first site, scheduled for 2026, will begin operations with an initial injection rate of ∼ 61,000 m 3 /day. Given that the Potomac Aquifer lies unconformably above crystalline basement rock, injection-induced pressure transients may propagate into the basement, increasing the risk of injection-induced seismicity. To assess this risk, a regional-scale numerical model was employed, incorporating ensemble simulations with 50 models using spatially random and equally probable permeability distributions within the basement. The simulations of a 61,000 m 3 /day injection scenario indicate significant pressure propagation into the basement, with fluid pressures reaching up to 40 kPa in some areas, which could be sufficient to induce seismicity. However, a ramp-up strategy for the injection rate, extending over a 12-month period, was found to effectively reduce the pressurization rate in the basement and mitigate the seismic risk. These results provide a probabilistic understanding of pressure changes in the basement rock and inform strategies for minimizing pressure transients that may induce seismicity while achieving effective aquifer recharge.