application of the ZVI/clay technology to solve environmental remediation problems has seen significant increase over the last half decade, after a relatively quiet period since the initial applications in the early to mid-90s. The ZVI/clay soil mixing technology was used in 2011 to treat a TCE impacted source zone on the OMC Superfund Site in Waukegan, Ill. On the Waukegan project, the ZVI was delivered and mixed with the soils using a large diameter soil mixing rig that project, approximately 6,500 m (8,500 cu yds) of impacted soils were treated down to a maximum depth of 7.2 m (24 ft) BGS. Additionally, ISCR with the ZVI/clay technology was used in 2012 to treat PCE impacted soils at a former wastewater lagoon that contained wastes from a former industrial dry cleaning in a mixture with bentonite and water. On 3 project included soil mixing 7,500 m (9,800 cu yds) down to a maximum depth of 8 m (26 ft). Less common uses of IST include facility in Alberta, Canada. The Alberta 3 Close-up of soils mixed with potassium permanganate oxidizing chlorinated solvents and other volatile contaminants through adding oxidants with or without catalysts. ISCO performed with soil mixing has grown rapidly over the last half decade as engineers and owners have adapted the technology to solve problematic sites. Soil mixing offers numerous benefits over other methods of performing IST, including the potential for a reduced construction schedule, a reduced cost, a reduced carbon footprint, and improved contact between the reagent and contaminated media in a low permeability or fractured subsurface. with ISS for the ISCO and S/S of 5,700 m (7,500 cu yds) of TCE impacted soils down to a maximum depth of 5.8 m (19 ft) in East Rutherford, N.J. Potassium permanganate was used as the oxidant on that project. On another project, in Robbinsville, N.J., in 2011, a base-catalyzed sodium persulfate treatment was used on xylene and pesticide ville included treating 2,100 m (2,800 cu yds) down to 4.6 m (15 ft) BGS. ISCO was also used in Norwich, N.Y. (2012) in combination with hot air stripping to treat acetone impacted soils. The treatment reagent used in Norwich, N.Y. was calcium impacted soils. The soil mixing in Robbins- 3 58 • DEEP FOUNDATIONS • MAR/APR 2014 IST was used in combination in 2010 3 peroxide mixed with the soils, down to a maximum depth of 8.2 m (27 ft), in conjunction with fertilizer nutrients and phosphoric acid. Prior to the treatment “polishing step,” designed to enhance long term biodegradation, a significant amount of the acetone was stripped from the soils using hot air soil mixing. Potential Future Trends and Conclusions • Increased scrutiny of sustainability related metrics in remedial method evaluation. • A shift from S/S to treatment as regulators target gross concentration reduction rather than impact reduction. • Increased application of ISS to the in-place remediation of saturated sediments. (See recent EPRI research, including information on the recent pilot study completed in Springfield, Mass., in 2013). • Increased viability of ISS to more sites as more applicable leaching/diffusion tests are accepted. See the new EPA LEAF tests (methods 1313 – 1316) and the ITRC guidance document (2011). • Increased application of jet grouting to environmental remediation projects. • An increase in novel reagent combinations that will further expand the use of soil mixing to remediate historically difficult contaminants. • Additional equipment modification and development, including improved batch plants, drill rigs and quality control that will make soil mixing more cost effective. The current practices in the soil mixing of contaminated soils were developed over 30 plus years. The technology has been used to stabilize, treat and contain contaminated soils. The geoenvironmental industry has embraced this technology, particularly over the last 5 to 10 years, and should continue to support soil mixing for contaminated soil remediation. Better overall understanding of this technology by designers, acceptance of this technology by environmental regulators, the use of more realistic contaminant leaching methods, and the further refinement of equipment, technique, and quality control procedures will help further the growth of this technology.
