A sulfate injection pilot test was planned for a site in the northeastern United States for in-situ treatment of elevated arsenic concentrations and dissolved hydrocarbons in glacial deposits within a small coastal stream valley. A numerical groundwater model was developed and used to evaluate sulfate distribution under different scenarios and to constrain the hydraulic parameters, and support the design of an optimized reactant injection plan.
Groundwater flow and sulfate fate and transport models were developed, calibrated, and sensitivity-tested. The modeling analysis included:
Results of the flow model improved the hydrogeological characterization, including the effects from silt formations that were important to the pilot test injection design. Based on the modeling, an optimized system of eight injection wells operating at one gallon per minute (GPM), with a sulfate injectate concentration of 500 milligrams per liter (mg/L), resulted in sulfate delivery to the majority (80 percent) of the target treatment area and significantly improved the performance of the pilot study.