Theme: 08. Metals

Topic Area: 8c. Precipitation and Stabilization of Metals

Formatted Title:

Optimization of a Combined Active and Passive In Situ Stabilization Approach for High Concentration Metals in Groundwater

Background/Objectives:

Often, groundwater and saturated soils impacted with high concentrations of metals are remediated through excavation with off-site disposal and groundwater pump and treat (GWPT). These approaches are generally disruptive, costly, and energy intensive. Moreover, the geochemical behavior of metals tends to result in extremely long remediation timeframes in the case of GWPT. Alternative technologies include in situ treatment via geochemical stabilization, permeable reactive barriers (PRBs), and in situ solidification and stabilization (ISS), representing a suite of passive, more sustainable, and less costly remedies. Key to implementing a strategy based on using these alternative technologies is conducting pre-design investigation and bench- and/or field pilot-testing to select and design an appropriate technology and remedy. Through a case study, we present a holistic predesign investigation, remediation technology bench- and field pilot-testing, and remedy optimization approach.

Approach/Activities:

A large-scale urban fill site in the northeastern United States is mainly impacted with cadmium, copper, and zinc and requires remediation to reduce the flux of metals in groundwater, discharging to an adjacent river. Dissolved phase cadmium, copper and zinc have been detected in groundwater at concentrations up to 0.4, 36, and 1,000 mg/L, respectively. The pH of the impacted groundwater ranges from 4.6 to 6.4. The zones of highest mass flux and distribution of geochemical conditions were assessed through sampling of monitoring wells, high resolution site characterization of soil and groundwater, groundwater hydraulic testing, and groundwater-surface water interaction assessment.

Results/Lessons Learned:

A decision matrix was used to holistically assess the results of the predesign investigation and bench testing for the selection of a site remedy. Key considerations included reduction of mass flux in groundwater, geochemical effects, long-term performance, cost effectiveness, resiliency, and sustainability. The selected remedial approach incorporated a combination of source area in situ remediation, soil stabilization/solidification, and down-gradient permeable reactive barriers applied in a phased and flexible manner.

Bench-testing indicated that two to nearly three orders of magnitude concentration reduction of metals in groundwater and leachable metals could be achieved. The solidified/stabilized soils resulted in hydraulic permeabilities several orders of magnitude lower than adjacent site soils and sufficient geotechnical strength. The results of bench testing were then scaled up to a set of field pilot tests for soil and groundwater. An optimized full-scale approach was developed based on the pilot testing results. The results from the bench- and field pilot-testing will be reviewed in the context of how the full-scale approach was optimized.

Menu

Nick Hastings