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: (1) calibration to steady-state and pumping
conditions, (2) sensitivity testing of hydraulic parameters, (3) simulation of groundwater
flow patterns for pilot test design support, and (4) expansion of the model to simulate fourdimensional sulfate distribution (spatially and temporally).
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.