M. Channel1, J. Wakeman2, and H. Craig3, 1U.S. Army Corps of Engineers, Waterways Experiment Station, 3909 Halls Ferry Road, Vicksburg, MS, 39180-6199, Phone: 601-634-2386; 2U.S. Army Corps of Engineers, Seattle District, Seattle, WA; and 3U.S. EPA Region 10, Oregon Operations Office, Portland, OR

ABSTRACT This paper describes two treatability studies for concurrent stabilization/solidification (S/S) of metals and explosives in soils from Open Burning/Open Detonation (OB/OD) activities at an Army site in eastern Oregon. These treatability studies address the destruction and removal efficiencies (DRE), a CERCLA measure of treatment feasibility, and also the ability of the formulations to meet site-specific leachate remediation goals for the treated soils. The untreated site soils exceeded the leachate remediation goals (measured on Toxicity Characteristic Leachate Procedure extracts) for the following compounds: cadmium, lead, Royal Demolition Explosive (RDX), 2,4,6-trinitrotoluene (2,4,6-TNT), and 1,3,5-trinitrobenzene (1,3,5-TNB). Treatability study results indicate that S/S is effective for cadmium and lead by a 30% cement + 10% flyash + 40% soil formulation. However, the explosives compounds, RDX and 2,4,6-TNT, met neither DRE goals nor leachability requirements. Success in removing explosives was achieved by modifying the cement/flyash mixture with an organic binding agent (granular activated carbon) in a slurry with the soil prior to addition of the cement/flyash. The amount of carbon required to achieve the leachate and DRE goals was greater for the more soluble nitramine compounds (e.g., RDX) than for the nitroaromatic compounds (e.g., 2,4,6-TNT). Over the range of tested formulations, all compounds were able to meet the CERCLA guideline of >90% DRE and the site-specific leachability goals. DREs of >99% were achievable for all metals and all explosives by one or another of the formulations tested, except for 1,3,5-TNB, which was not initially highly concentrated in site soils and which reached 90% DRE and met leachability goals. The distribution of 2,4,6-TNT at OB/OD site soils is commonly found to be extremely heterogeneous, possibly due to incomplete combustion during the burning activities. Flecks of solid compound give rise to outlier results during leachate extractions. A compositing technique for sampling and extraction of solidified soils was developed to better represent the average condition of the stabilized soils. The remedial activity will also sift and blend site soils to assure the process meets performance-based leachate goals. Costs for S/S technology application to soils at this site (based on initial contract award costs) are approximately $70/cubic yard, which includes placement in an onsite Army-run landfill. Mix design optimization studies were run subsequent to contract award by OHM Remediation Services, Inc. The study concluded that a mixture of 10% Portland cement + 2.5% activated carbon + 77.5% soil would stabilize soils with explosives in a manner adequate to meet cleanup requirements, taking into account site concentrations and materials handling (screening and blending) prior to S/S. The mix design also tested several other amendments to the cement component, which did not significantly improve performance for explosives above cement/activated carbon. These additions included soluble silicates, ash from rice hulls, and organophilic clays.

KEYWORDS: explosives, metals, stabilization, solidification

This paper is from the Proceedings of the HSRC/WERC Joint Conference on the Environment, May 1996, published in hard copy and on the Web by the Great Plains/Rocky Mountain Hazardous Substance Research Center.

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