Utilizing Numerical Simulation to Understand the Implications of Injection-Induced Seismicity for Managed Aquifer Recharge in Coastal Virginia

Abstract

As demand for freshwater increases in coastal Virginia, overpumping of the Potomac Aquifer has led to accelerating land subsidence, declining groundwater levels, and saltwater intrusion. To slow these deleterious effects, the Hampton Roads Sanitation District is developing the Sustainable Water Initiative for Tomorrow (SWIFT) project to replenish the Potomac Aquifer through a network of up to five managed aquifer recharge facilities in southeast Virginia. Large-scale fluid injections into deep geologic formations have a well-documented history of causing earthquakes, particularly in the energy sector; however, there has yet to be a demonstrable connection between managed aquifer recharge and injection-induced seismicity. Nevertheless, the SWIFT project is unique because target aquifer lies unconformably above the crystalline basement rock, where pre-existing basement faults may occur. Although the Virginia Coastal Plain does not generally experience natural earthquakes, fluid injections from large scale aquifer recharge may produce sufficient fluid pressure to induce seismicity, if critically-stressed and optimally oriented faults exist within the deep basement rock below the Virginia Coastal Plain. While the presence of such faults remains unknown, this study is designed to estimate the extent and depth to which injection-induced pressure transients may travel during MAR injections at the James River Wastewater Treatment Plant, which is scheduled to come online in 2026. Results from numerical simulation show that (i) injection-induced pressure transients in excess of 40 kPa may reach depths of $\sim 3 {\mathrm km}$ and (ii) basement rock permeability largely imposes first-order control on the depth and extent of injection-induced fluid pressure propagation.