Formatted Title

Challenges When Remediation Timeline is Driven by Construction: A Phased Approach to Address Commingled Contamination in Vadose and Saturated Zones

Background/Objectives

The investigation and remediation of a historic industrial site in New Jersey used for former auto salvage and railcar cleaning operations has been ongoing for several decades.  Groundwater at the site is impacted by volatile organic compounds (VOCs) including chlorinated compounds (CVOCs), semi-volatile organic compounds (SVOCs) including polyaromatic hydrocarbons (PAHs), metals, and per- and polyfluoroalkyl substances (PFAS). The complex nature of this multi-bedded geological setting required comprehensive evaluation and profiling to build a conceptual site model (CSM) and identify source areas and groundwater plumes. Site characterization and delineation identified impacts in overburden, shallow bedrock, and deep bedrock zones.  The CSM indicated that a tiered in-situ approach was essential to address vadose and groundwater impacts, accelerate the remediation timeline, and meet site-specific goals. Near- and long-term remedial goals at the site included containing free/residual product and soil source mass leaching, reduction in groundwater concentrations to attain plume stability for monitored natural attenuation (MNA), and reduce potential vapor pathway prior to development of the site warehouse building.

Approach/Activities

The first phase of the remedial approach involved addressing the vadose zone impacted with free/residual product, VOCs, SVOCs, extractable petroleum hydrocarbons (EPH), polychlorinated biphenyls (PCBs), radionuclides, and metals.  Remedies included a combination of soil excavations and in situ soil stabilization and solidification (ISS) to stabilize free/residual product and contaminants. Due to the complexity of the soil impacts at the site, the ISS activities were preformed to contain/encapsulate contamination within hundreds of concrete cells creating a site-wide monolith. ISS treatment was implemented with the mixing of soil and the addition of several amendments which included specified quantities of Portland Cement, Ground Granular Blast Furnace Slag, and/or Quicklime. Vadose zone remediation was completed with the site-wide redevelopment which included the installation and establishment of engineering and institutional controls.

Once the soil source mass was addressed, in-situ injections were selected for remediation of overburden and bedrock aquifers using in situ chemical oxidation (ISCO) with activated persulfate and in situ chemical reduction (ISCR) technologies based on carbon/iron synergistic mechanisms. Depending on the contamination present in specific zones, the approach was engineered to provide chemical, biological and/or biogeochemical pathways for contaminant degradation to ultimately transition into MNA.

This presentation will illustrate the “cradle to grave approach” of the entire remedial process. We will also present the challenges of meeting remedial objectives within an acceptable timeframe while managing client expectations and demands.

Results/Lessons Learned

Comprehensive evaluation of the phased approach to address the contaminants will be presented. Key points of focus include:

• Significance of pre-remediation characterization and understanding of complex comingled plumes.
• Importance of a pilot test program to understand site constraints and develop a full-scale remedy.
• Design, application, and monitoring of a successful ISCO application that reduced source mass by 30 to >50%.
• Benefits of reductive technologies in bedrock aquifers that reduced source mass by 95%.
• Understanding the implications of using opposing chemistries to address mixed plumes.
• Challenges and lessons learned in injecting large volumes of chemical reagents in overburden aquifers using direct push technologies.
• Managing injection rate and evaluating distribution of reagents in fractured bedrock zones.
• Working within close proximity of active construction areas.