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ENVIRONMENTAL CONSTRUCTION AND REMEDIATION Shallow Soil Mixing A refinery adjacent to Lake Michigan was required to close a pond which was previously used to contain refinery sludge as well as storm water and other wastes. Contaminants of concern included refinery related products; petroleum hydrocarbons, and BETX. The seven-acre pond was up to 25 ft deep and the sandy soils beneath the pond also required treatment. Off-site disposal was cost- prohibitive, therefore an on-site closure was engineered which included stabilization of the pond and containment using a slurry wall and cap.
Technical requirements for the stabilization specified an unconfined compressive strength of 35 psi in 14 days. Geo-Con performed a bench scale study prior to mobilization and a pilot project immediately prior to construction to evaluate the most cost-effective cement addition rate.
The SSM method was chosen as the most cost-effective method for mixing cement with the sludges for stabilization. SSM provided superior mixing quality and the power required to blend the underlying soils and cement with the oily sludges. Geo-Con utilized a 12 ft diameter SSM mixing rig for the project. Dry cement was conveyed pneumatically to the rig where it was metered into the sludge and blended.
The SSM work was performed around the clock for three months to stabilize about 100,000 cy of sludge and soil. A three-ft wide cement-bentonite slurry wall about 40 ft deep and a jet grout curtain were installed around the pond to isolate the area from the groundwater. The slurry wall was constructed through inactive utility lines and debris. Finally, an impermeable cap of clay and synthetic liners was placed over the entire site. After final grading, the area supports new oil storage tanks.
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