Theme: 01. Remediation Technology Innovations

Topic Area: 01m. In Situ Technologies: Lessons Learned

Formatted Title:

Adaptive Recirculation System Design for ISCR Cycling of Metal Plating Releases

Background/Objectives:

Historical releases resulted in a 7-acre, 60-foot deep metals groundwater plume within the interlayered beds of sand, silt and clay of the Potomac-Raritan-Magothy aquifer, the most heavily pumped aquifer in New Jersey. Hexavalent chromium [Cr(VI)] impacts are present in the vadose and saturated zones in a strongly acidic environment (pH=1.5-4 s.u.). Soil impacts are detected just below surface and extend below the water table to depths of 35 to 40 feet. The source areas are located beneath active operational areas of the plant where minimal business interruptions were essential. A comprehensive laboratory treatability study and field pilot tests program was implemented to evaluate the effectiveness of an innovative chemical reagent suite for in-situ remediation of elevated Cr(VI) impacts (>1,000 ppm in soil and groundwater) as previously presented. The objective of the next phase of work was to develop and implement remedial actions for the source areas beneath the building with numerous access constraints.

Approach/Activities:

This study builds upon the prior work focusing on the remedial design investigation and full-scale design and implementation of an injection-extraction recirculation system for in-situ chemical reduction (ISCR) of Cr(VI), chromium, nickel, and copper. To remediate the source areas and address annual budget constraints, a remedial strategy that incorporated a sequenced and adaptive approach where system infrastructure could initially target one source area, and then easily be connected to subsequent phases (more downgradient source areas) of work was critical. As such, a network of injection and extraction wells was installed and connected with various system elements to permit a modular and semi-autonomous system operation. Throughout system expansion, the system was upgraded to expand the footprint of remediation and to improve safety and remote operation capabilities. In Area 1, greater than 210,000 gallons of groundwater were recirculated and dosed with 4,250 gallons of 29% calcium polysulfide over two injection cycles. Area 2 is being implemented in the Fall of 2023.

Results/Lessons Learned:

In the sequential build and operation of the system, lessons were learned related to chemical dosing, hydraulic balancing, management of varying groundwater concentrations, hydraulic and geochemical responses, automation features, and safety measures. Injection operations and performance were assessed via hydraulic and geochemical responses. Performance monitoring of the groundwater concentrations has demonstrated effective treatment with 95% to 99.9% reductions in Cr(VI) concentrations of targeted areas. Lessons learned related to impacts from acidic and concentrated metallic solutions, remedial design investigations and amendment design and distribution will be presented.

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Nidal Rabah