Dense Nonaqueous Phase Liquids (DNAPLs)

Solidification/Stabilization

Multi-Component Waste

S/S treatment has been applied successfully at wood preservation and former manufactured gas plant (MGP) sites to address creosote and coal tar DNAPL.

General Resources: Multi-Component Waste

Applying Solidification/Stabilization Treatment to Brownfield Projects
C.M. Wilk.
EM Magazine, p 25-32, Mar 2004

Describes the principles and field application of S/S treatment in brownfield redevelopment and presents examples of S/S use at four brownfield sites: a former wood preserving facility, a manufactured gas plant, an electric generating station, and a shopping mall development.

Technology Performance Review: Selecting and Using Solidification/Stabilization Treatment for Site Remediation
U.S. EPA, National Risk Management Research Laboratory, Cincinnati, OH.
EPA 600-R-09-148, 28 pp, 2009

Solidification/stabilization (S/S) is used to prevent migration of contaminants from contaminated soil, sludge, and sediment. Solidification refers to a process that binds a contaminated medium with a reagent, such as Portland cement, changing its physical properties. Stabilization involves a chemical reaction that reduces the leachability of a waste. The effectiveness of S/S has been demonstrated for non-volatile metals (e.g., arsenic, chromium), radioactive materials, halogenated semivolatiles, non-halogenated nonvolatiles and semivolatiles, PCBs, and pesticides, and potentially dioxins/furans. For treating organic contaminants (e.g., creosote), the use of certain materials such as organophilic clay and activated carbon, either as a pretreatment or as additives in cement, can improve contaminant immobilization. This review addresses important factors to consider in the selection of S/S treatment and discusses its implementation at seven sites.

General Resources: Coal Tar

A Resource for MGP Site Characterization and Remediation: Expedited Site Characterization and Source Remediation at Former Manufactured Gas Plant Sites
EPA 542-R-99-005, 103 + 44 + pp, 1999

Chapter 5 presents brief technology descriptions accompanied by short case studies for each of the following technologies: co-burning, thermal treatment processes, asphalt batching (essentially an ex situ S/S process), bioremediation/chemically enhanced bioremediation, containment, S/S (both in situ and ex situ), soil washing, and soil vapor extraction.

Case Studies: Coal Tar

Augusta Manufactured Gas Plant Cleanup Using Cement-Based Solidification/Stabilization
C.M. Wilk.
Portland Cement Association, SR998, 2003

After the removal of surface soil, deeper soils impacted by coal tars, oils, and other organic and inorganic compounds resulting from MGP operations were treated in situ by mixing cement into the soils with a crane-mounted auger system. Soils were treated to a depth of 30 feet below grade. Within the treated area, tar-like source material in the impacted soil was solidified in place. S/S changed the physical properties of the treated soil, creating an impervious mass to infiltrating precipitation and passing groundwater while further inhibiting leaching and transport of source material.

A Case Study: Manufactured Gas Plant Site, Troy, NY
Sherman, A.
MGP 2012: International Symposium and Exhibition on the Redevelopment of Manufactured Gas Plant Sites, 27-30 March 2012, Chicago, Illinois. Poster, 2012

Past industrial operations at this former MGP site situated on the Hudson River contaminated the site with coal tar, purifier waste, and petroleum. Although the state had selected a remedy of large-scale excavation and in situ chemical oxidation, additional site characterization supported a revised remedy that maintains a substantial excavation component but also includes in situ solidification, which works with the site geology to provide long-term containment of MGP residuals on site.

In Situ Soil Stabilization of a Former MGP Site
V. Jayaram, M.D. Marks, R.M. Schindler, T.J. Olean, and E. Walsh.
2001 International Containment & Remediation Technology Conference, Orlando, FL, June 2001.

The shallow soil mixing (SSM) technique consists of using a single large-diameter auger, generally 5 to 10 ft in diameter and capable of mixing to depths of 30 or 40 feet. The hollow-stemmed mixing shaft, known as the kelly bar, is attached to a single-flight auger that breaks the soil loose and lifts it slightly to six beater bars on the mixing shaft. As the auger penetrates the soil, a slurried reagent is pumped through the mixing shaft and exits through jets located on the auger flighting. The SSM technique was used to stabilize ~103,500 cubic yards of NAPL-contaminated soils at the Cambridge Research Park site in Cambridge, MA, the location of a former MGP. The site was divided into zones in which DNAPL (coal tar) and LNAPL (similar to weathered diesel oil or #2 fuel oil) or both were present. Downward migration of the DNAPL was restricted by the clay layer located ~22 ft bgs. The LNAPL floated atop the water table, exceeding a thickness of 2 feet in some monitoring wells. Stabilization in zones containing DNAPL only or DNAPL/LNAPL was performed by mixing to a depth of 2 feet below the clay layer. The LNAPL zones were stabilized to a depth of 12 ft bgs. SVE equipment was placed over the area being mixed to capture potentially hazardous vapors and fugitive dust released from the soils.

In-Situ Solidification of Contaminated Sediments: A Technology Demonstration Project
Electric Power Research Institute (EPRI), Palo Alto, CA. Project 3002005216, 1086 pp, 2014

As an alternative to dredging and capping sediments affected by historical MGP operations, a pilot demonstration was performed to determine if in situ solidification (ISS) and support equipment contained on a barge could solidify tar-contaminated sediments through a column of water using readily available grout components while meeting U.S. EPA performance goals. Project elements included the control of turbidity, pH, and sheen using a dual-turbidity curtain system, and results showed that rigid controls such as steel sheet piling may not be required for good performance. The report covers the site characterization and treatability study of the pilot area; permitting and mobilization; ISS operations in December 2013; sampling and testing; monitoring; and pilot and estimated full-scale costs. The primary result of the project was proof of concept that ISS of submerged sediments is achievable and is ready to be tested at a larger scale. Additional information: Connecticut River ISS update by Jansen et al. in Remediation Journal 26(2):25-49(2016)

Solidification/Stabilization Treatment at a Former Manufactured Gas Plant Site
V. Jayaram, M.D. Marks, R. M. Schindler, T. J. Olean, E. Walsh, and C. M. Wilk.
Portland Cement Association, Skokie, IL. SR996, 4 pp, 2002

The Cambridge Research Park in Cambridge, MA, is a former brownfield site. To reclaim it, cement was mixed into 103,500 cubic yards of NAPL-impacted soils using a specialty auger system in a shallow in situ soil mixing technique. Light and dense NAPL was present in different zones. As the auger penetrated the soil, cement grout was pumped through the mixing shaft, exiting through jets located on the auger flighting and mixing cement into the contaminated soil. An overlapping drilling (auger) pattern was used to ensure complete mixing and treatment of the area. Cement-based S/S successfully treated the soil for MGP contaminants and improved the physical properties of the soil for property redevelopment.

St. Louis River Superfund Site, Duluth, St. Louis County, Minnesota: Five Year Review Report
U.S. EPA Region 5, 182 pp, 2003

From the 1880s to the early 1960s, operations at the St. Louis River/Interlake/Duluth Tar site included coal tar refining, tar product manufacturing, coking and byproduct recovery, iron making, and gas making. The remediation of the site's Operable Unit J was completed as required by the ROD: ~10,000 cubic yards of coal tar and tar-contaminated soil were solidified in place, and a 7-ft engineered cap designed to reject 90% of precipitation was placed over the unit. On-site borrow was used for all layers but topsoil.

Abstracts of Journal Articles

Effectiveness of In Situ Cement Stabilization for Remediation of Sediment Containing Coal Tar Derived Hydrocarbons
T. Thornburg, C. Leuteritz, D. Templeton, T. Metcalf, T. Bell, and K. Paschl.
The 22nd Annual Conference on Soils, Sediments and Water, University of Massachusetts, Amherst, 2005.

Sediments adjacent to a former coal tar processing facility are associated with intermittent releases of hydrocarbon droplets and sheen to the overlying marine water column, particularly during low tide. In situ sediment stabilization with Portland cement was one of the alternatives considered for a response action to control sheen in accordance with Surface Water Quality Standards; however, bench-scale test results indicated that in situ stabilization as a stand-alone technology would not be effective at controlling sheen. Performing the appropriate bench-scale tests cost-effectively demonstrated the need for a different approach to designing and implementing an effective remedial solution for this site.

In Situ Stabilisation/Solidification: Project Lifecycle
M.A. Fleri and G.T. Whetstone.
Journal of Hazardous Materials, Vol 141 No 2, p 441-456, 15 Mar 2007

Follows the lifecycle of S/S projects from a site investigation at a former MGP through the completion of full-scale work. A 10-year post-remediation sampling event also provides evidence of the long-term viability of the technology.

NAPL Containment Using In Situ Solidification
J.R. Greacen and E.J. Walsh.
Contaminated Soils, Sediments and Water: Science in the Real World, Vol 9. Springer, ISBN: 978-0-387-23036-8, p 477-483, 2005

DNAPL at 20 ft below grade covered a 3-acre area of a former MGP site, preventing site closure and inhibiting development of the property. As part of site closure, soil and DNAPL were stabilized in situ using a crane-mounted, 10-ft-diameter auger capable of injecting a 7% cement grout mixture. The auger was advanced ~22 feet below grade to extend beneath the DNAPL and key the stabilized mass into the underlying clay layer, advancing 2,256 overlapping columns over an area covering ~144,000 square feet. This remedy allowed site closure to proceed.

Solidification/Stabilization Pilot Study for the Treatment of Coal Tar Contaminated Soils and River Sediments
M.A. Lawson, J.G. Venn, L.B. Pugh, and T. Vallis.
Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes: 3rd Volume.
American Society of Civil Engineers, Publication STP1240-EB, Paper STP14146S, 15 pp, 1996

Coal tar contamination was encountered at a former coal gasification site in soils below the groundwater table and in the sediments of the adjacent river. S/S treatability testing was performed to evaluate a Portland cement/fly ash binder system with added stabilizing agents. Results were sufficiently promising to warrant pilot testing. Grout containing Portland cement, fly ash, organically modified clay, and granular activated carbon was pilot tested at the site. Evaluation of durability, compressive strength, and permeability indicated acceptable physical characteristics and a decrease in leachable concentrations of most PAHs.

General Resources: Creosote

Contaminants and Remedial Options at Wood Preserving Sites
G. Sudell, A. Selvakumar, and G. Wolf.
EPA 600-R-92-182, 149 pp, 1992

Identifies the sources and types of wood preserving contaminants, characterizes them, and defines their behavior in the environment; describes the principal remedial options (i.e., technologies for immobilization, destruction, and separation/concentration) for contaminated soil at wood preserving sites; considers ways to combine technologies to increase treatment efficiency.

Presumptive Remedies for Soils, Sediments, and Sludges at Wood Treater Sites
U.S. EPA, Washington, DC. Office of Emergency and Remedial Response.
EPA 540-R-95-028, OSWER 9200.5-162, 61 pp, 1995

Describes the contaminants generally found at wood treater sites; presents the presumptive remedies for contaminated soils, sediments, and sludges at wood treater sites (i.e., bioremediation, thermal desorption, incineration, and immobilization); describes the presumptive remedy process concerning the site characterization and technology screening steps; and outlines the data that should be used to select a presumptive remedy.

Presumptive Remedies for Soils, Sediments, and Sludges at Wood Treater Sites, Appendix A: Summary of Screening and Detailed Analysis for Wood Treater Sites with Contaminated Soils, Sediments, and Sludges
U.S. EPA, Washington, DC. Office of Emergency and Remedial Response. 43 pp, 1995

The Feasibility Study/Record of Decision Analysis for Wood Treater Sites with Contaminated Soils, Sediments, and Sludges
U.S. EPA, 71 pp, 1997

Contains an evaluation of technologies considered in the feasibility studies (FSs) and records of decision (RODs) of 25 contaminated wood treater sites. Certain technologies were routinely screened out based on effectiveness, implementability, or cost. This evaluation provides the basis for limiting the analysis of technologies and alternatives when applying the presumptive remedy approach.

Case Studies: Creosote

EPA Superfund Explanation of Significant Differences: Koppers Co., Inc. (Charleston Plant), OU 1
U.S. EPA Region 4.
34 pp, 2012

The Koppers Company operated a wood-treatment facility from 1940 to 1978 to treat raw lumber, utility poles, and crossties with creosote. PCP and copper chromium arsenate also were used briefly as wood preservatives. The NAPL will be immobilized via S/S to reduce future costs associated with long-term operation, maintenance, and monitoring of a NAPL recovery system. Results of bench and field pilot studies indicate S/S will provide a 99% reduction in contaminant mass transport to the Ashley River. Due to the small size (roughly 0.30 acre) and shallow depth of observed NAPL (generally < 12 feet bgs), EPA believes that immobilization of NAPL via S/S applications is more robust than recovery via extraction wells. The ROD did not separate costs of the groundwater/NAPL remedy component by source area, but total estimated present worth was $3,074,000. The current cost estimate for S/S in the Northwest Corner is approximately $750,000, which accounts for solidification of the area using a 9% Portland Cement mix and disposal of debris encountered during the mixing process.

OW-5/55R Area In-Situ Geochemical Stabilization Remediation Pilot Test, Former Koppers Company Inc. Site, Nashua, New Hampshire
New Hampshire Department of Environmental Services, 96 pp, 2014

In situ geochemical stabilization (ISGS) technology comprises the injection of an enhanced permanganate-based reagent (RemOx EC) into NAPL-impacted zones to achieve containment or stabilization and solute flux reduction. Silica-based precipitates are deposited around NAPL ganglia and droplets following reagent injection, which leaves a mineral shell that reduces overall permeability in the treated area, thereby reducing the volumetric flux of upgradient groundwater into and through the impacted area. The oxidation of dissolved-phase constituents also "hardens" or chemically weathers the NAPL as it loses its more labile SVOCs. This report describes the results of an ISGS pilot test conducted November 11-13, 2014, to isolate creosote NAPL in a treatment area ~45 ft by 75 ft.

Solidification/Stabilization for Remediation of Wood Preserving Sites: Treatment for Dioxins, PCP, Creosote, and Metals
E.R. Bates, E. Sahle-Demessie, and D.W. Grosse.
Remediation Journal, Vol 10 No 3, p 51-65, 2000

Presents data from the successful remediation of a site with mixed organic/inorganic contaminants, remediation of a site with organic contaminants, and detailed treatability study results from four sites for which successful S/S formulations were developed. Includes pre- and post-treatment soil characterization data, site names, vendor names (in some cases), treatment formulas used (generic and proprietary), costs, recommendations, and citations to more detailed references. The data indicate that dioxins, PCP, creosote, PAHs, and metals can be treated at moderate cost by the use of S/S technology.

Solidification/Stabilization Treatment and Examples of Use at Port Facilities
C.M. Wilk.
Ports 2004: Port Development in the Changing World, 23-26 May, Houston, Texas.
American Society of Civil Engineers, Reston, VA, 2004

At a former wood treating facility in Port Newark, NJ, 8 acres of site soils were contaminated with PAHs resulting from the use of creosote, arsenic, and chromium. Two types of mixing techniques were used to treat the contaminated soils. In situ soil mixing was used on 22,000 cu yds of soil from 2 ft to 12 ft. Treatment involved pre-excavation of contaminated material, placement of the stockpiled material back into the excavated area in lifts, and S/S treatment of each lift with an in situ blender head. Another 26,000 cu yds of contaminated soil were addressed ex situ, using a pugmill to mix Portland cement into the soil. The pugmill mixture was placed on top of the in situ treated soils in a 2-ft layer, which was compacted to have structural properties similar to those of soil-cement, achieving unconfined compressive strengths greater than 250 psi and providing an excellent base for pavement placed over the entire site.

Solidification/Stabilization Treatment of Arsenic- and Creosote-Impacted Soil at a Former Wood-Treating Site
C.M. Wilk and R. DeLisio.
Portland Cement Association, Skokie, IL, SR997, 4 pp, 2002

Describes the use of cement-based S/S to treat arsenic- and creosote-impacted soil at the site of a former wood-treating facility in Port Newark, NJ. The treated soil was re-used as base for new pavement at this brownfields site.

Stabilization of DNAPL at a Former Creosote Wood Treating Site
D. Cervenak, P. Sawchuck, M. Brourman, R. Fisher, K. Mullins, and S. Radel.
2001 International Containment & Remediation Technology Conference, Orlando, FL, June 2001.

In-place stabilization of soils containing DNAPL was performed at a former creosote wood treating site in New Jersey to immobilize the DNAPL, minimize future dissolution of constituents to groundwater, and expedite natural attenuation. A total of 15,000 cubic yards of soils containing DNAPL was stabilized in accordance with the NJDEP-approved Remedial Action Work Plan. The soils were stabilized to a depth of up to 7 feet. Groundwater was encountered from 2 to 5 feet bgs. Portland cement was added to the soils containing DNAPL and blended using specialized excavator-mounted mixing equipment to create a solid, homogeneous soil/cement mass. Confirmatory test pits verified the effectiveness of the stabilization.

Treatment Technology Performance and Cost Data for Remediation of Wood Preserving Sites
S. Krietemeyer, J. Tillman, G. Wahl, and K. Whitford.
EPA 625-R-97-009, 122 pp, 1997

Advantages and limitations associated with implementation of S/S, soil washing, thermal desorption, incineration, solvent extraction, base-catalyzed decomposition, and bioremediation are discussed, with treatability and/or case studies for each technology.

Abstracts of Journal Articles

American Creosote Site Case Study: Solidification/Stabilization of Dioxins, PCP, and Creosote for $64 per Cubic Yard
E.R. Bates, F. Akindele, and D. Sprinkle.
Environmental Progress, Vol 21 No 2, p 79-84, 2002

Describes the development of S/S formulas and their application to remediate the American Creosote site in Jackson, TN. During 1998 and 1999, 45,000 cubic yards of soil contaminated with creosote, PCP, and dioxins were treated using S/S at a total cost of $64 per cubic yard. Formulations, design, specifications, and costs are presented.