Maryland Department of Environment, 1309 pp, 2018

Trenches installed in 2016 provided new interim measures for remediating groundwater at the RWM by reducing dissolved Cd and Zn concentrations mainly in the groundwater intermediate zone, thus eliminating the potential for future unacceptable groundwater discharges from there to surface water. Groundwater in the shallow zone was noted to have a higher pH due to placement of slag fill, and as a result the metals contamination in the shallow zone has not migrated. During remedial trench installation, the approach for addressing the elevated dissolved Cd and Zn in the intermediate groundwater zone was to precipitate the dissolved metals in situ by raising the groundwater pH from ~4 to ~9.5-10 via addition of alkaline reagents into groundwater zone at select high concentration areas. Excavated soils were replaced with alkaline charges that react with acidic groundwater to create slightly alkaline conditions within the aquifer and remove the dissolved metals from solution. The alkaline charges utilized a combination of fast-acting TerrabondMG (40% by weight) in conjunction with limestone aggregate (60% by weight) emplaced in the trenches in a staggered/offset alignment perpendicular to the anticipated groundwater flow. The interim groundwater treatment goals are to increase the pH above 7 to effect a > 90% reduction in dissolved Cd and Zn concentrations within the source areas as compared to existing conditions. https://mde.maryland.gov/programs/LAND/MarylandBrownfieldVCP/Documents/RWM%20IM%20Progress%20Report%20August%202018%20Rev0%2011-2-2018%20(1).pdf