Deep Soil Mixing for Contaminated Soil Remediation at a Superfund Site-Paper

Paper

Pdf Summary

The paper describes in-situ solidification/stabilization (ISS), a deep soil mixing method used to remediate contaminated soil without excavating and transporting it off site. Cementitious grout is mixed into soil to immobilize contaminants and improve strength, reduce hydraulic conductivity, and limit contaminant leaching. Compared with off-site disposal, ISS can reduce costs, construction impacts, and exposure risks.<br /><br />The case study involved a heavily industrialized, 16-acre Superfund site in northern New Jersey contaminated with VOCs, PAHs, coal tar, and metals. Approximately 150,000 cubic yards of soil were treated using excavator-mounted bucket mixing. GPS-based machine guidance tracked treatment depths and captured as-built data, supporting real-time quality control.<br /><br />Treatability testing identified a grout blend of 2% Portland cement and 6% ground granulated blast furnace slag (slag cement), by wet soil weight. The mix achieved average 28-day unconfined compressive strength of 369 psi and hydraulic conductivity of 3.54 × 10⁻⁷ cm/sec, exceeding project requirements of at least 40 psi and below 1.0 × 10⁻⁶ cm/sec. Higher slag proportions reduced permeability, while excessive Portland cement increased metal leachability.<br /><br />Replacing much of the Portland cement with slag cement also reduced environmental impacts. For the project, estimated savings included about 12,800 metric tons of CO₂-equivalent emissions, 45 million MJ of energy, and 127.6 million liters of fresh water, alongside reduced use of nonrenewable materials.<br /><br />The authors conclude that bucket mixing can be a cost-effective option for treatment depths up to roughly 40 feet. GPS guidance and cloud-based data collection improve precision and documentation, while slag cement can enhance treatment performance and sustainability.

Keywords

in-situ solidification

soil stabilization

deep soil mixing

contaminated soil remediation

cementitious grout

ground granulated blast furnace slag

hydraulic conductivity

Superfund site

VOC contamination

carbon footprint reduction