Pollution Engineering - January 2009 - (Page 29)

The selected remedy for OU1 utilized a containment strategy to encapsulate contaminants remaining onsite. The chosen remedy components included the construction of subsurface barrier walls around the old creosote ponds, which were located on the eastern and western ends of the site. These consisted of trenches that would need to be filled with a soil/bentonite mix and keyed into the weathered limestone aquitard, located 50 to 65 feet below grade. The proposal called for engineered caps to be placed over the areas contained within the barrier wall. Groundwater outside each of the cap/wall footprints would be treated in-situ with chemical oxidation to enhance natural degradation of contaminants. The caps would include subcaps consisting of approximately 75,000 cu. yards of solidified/stabilized (S/S) materials from the creosote impoundments, Burnett Creek, site soils above the performance standard of 1 part per billion set for dioxin, and the remaining waste cell onsite (which contain CCA-impacted soils). The S/S remedy component could be applied to these subcap materials. S/S-treated material mixed to a consistency of damp soil. hazardous constituents, the technology also can improve the construction properties of the treated materials, enabling their reuse. Treatment S/S treatment at the site was applied to 11,000 cu. yards of surface soils above the dioxin standard of 1 ppb; pond sediments of 55,000 cu. yards; 8,000 cu. yards of materials from the remaining waste cell, and 600 cu. yards of Burnett Creek sediments, for a total volume of approximately 75,000 cu. yards. These materials were excavated and staged for treatment. An excavator was used to preblend the staged material with a 10-percent addition by weight of fly ash. The pre- S/S treatment S/S treatment involves mixing a binding agent, commonly portland cement, into contaminated soil, sediment, sludge or waste. Successful treatment is accomplished through physical changes to the treated material and, often, chemical changes to the hazardous constituents themselves. S/S treatment operations may be conducted either ex- or in-situ. During exsitu treatment, the waste material is first excavated then mixed with the S/S binding agent, commonly with excavators or in pugmills. Ex-situ treatment can be performed entirely on site by a mobile treatment plant transported to the site. During in-situ treatment, contaminated material is mixed with S/S binding agents while the material remains in place , commonly with excavators, horizontal rotary soil mixers or deep soil mixing augers. S/S treatment technology contributes to greening their remediation processes through sustainable development of a contaminated property. While immobilizing “ Ex-situ treatment can be performed entirely on site by a mobile treatment plant transported to the site. will contribute to the long-term protectiveness of the remedy and facilitate possible future site redevelopment. Performance standards for the S/S treatment included: (1) unconfined compressive strength (UCS) of at least 100 psi at 28 days, (2) hydraulic conductivities of less than 1x10-6 cm/sec by the falling-head permeability test, and (3) no significant increased leaching of contaminants of concern by the Synthetic Precipitation Leaching Procedure. Quality control tests included UCS tests on every 500 cu. yards of treated material, and permeability and leachability tests on every 1,000 cu. yards. Full-scale mixing began after an initial pilot scale session lasting several weeks, which verified the achievement of performance standards using the mix design. Reuse of S/S-treated material in capping system The remedy includes the construction of caps over the former creosote impoundments on the eastern and western ends of the site. The caps will extend significantly beyond the pond footprints of these former impoundments. The footprints were established for an informal groundwater standard of 1,000 ug/L of total semi-volatile organic compounds to capture groundwater contamination within the barrier walls. The capping system consisted of subcaps, geosynthetic clay liners, and a 2.5-foot thick vegetative soil layer. S/S treated material was used as the construction material for the subcaps. 29 blended material was then run through a 2-inch screen to remove oversized material. After screening, the material was processed through a pugmill to mix a 10-percent addition of portland cement with the material. Water was added during pugmilling to result in a damp soil-like consistency. The S/S treatment reduced the permeability of the material for use in the cap while improving its structural properties, which ” JANUARY2009 www.pollutionengineering.com http://www.pollutionengineering.com

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Pollution Engineering - January 2009 Contents The Editor’s Desk EnviroNews PE Events Legal Lookout Green Connections Ten Top Technologies for 2009 Old Fashioned Chemistry Emitting Education NGWA Reports from Its Annual Meeting A Wood and a Pond Company Technical Profiles Filtration/Membrane Products Flow and Level Monitoring Equipment Classified Marketplace Advertisers Index State Rules

Pollution Engineering - January 2009

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