A Seepage Control Cutoff in an Extreme Saline Environment-Paper

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Ciner Wyoming constructed a 5,500-foot seepage cutoff wall at its Pond 2 tailings facility near Green River, Wyoming, to enable expanded storage while limiting highly saline seepage toward groundwater and the Green River. The site includes permeable fractured bedrock beneath overburden, so investigations used borings, rock coring, permeability tests, drilling data, and geophysical surveys to locate competent bedrock. The wall was designed to extend at least 5 feet into competent rock.<br /><br />The 30-inch-thick wall was built using hydromill and clamshell excavation under self-hardening slurry (SHS), which remained in the trench as the finished wall. The slurry used sulfate-resistant cement, slag, bentonite, and filtered Green River water rather than saline pond water. Design targets were a minimum compressive strength of 60 psi and maximum hydraulic conductivity of 1 × 10⁻⁶ cm/s.<br /><br />The owner, engineer, contractor, and expert panel collaborated on design and quality assurance. An offset test section was constructed, tested, and deconstructed to verify wall continuity, dimensions, and material performance before proceeding with the main wall. All 135 strength tests and 132 permeability tests met acceptance criteria. Average strength was 164.6 psi, and average permeability was 1.66 × 10⁻⁸ cm/s. In a long-term test, SHS exposed to pond water remained intact and its permeability declined.<br /><br />Piezometer monitoring confirmed that the wall substantially altered groundwater flow. At one location, the head difference across the wall increased from about 2.7 feet in bedrock before construction to 13.6 feet afterward. Groundwater contours showed flow backing up on the upstream side, and groundwater levels rose about 8 feet before tailings deposition began. The results indicate that the wall effectively limits seepage in the extreme saline environment.

Keywords

seepage cutoff wall

tailings facility

groundwater seepage

saline seepage

fractured bedrock

self-hardening slurry

hydromill excavation

hydraulic conductivity

quality assurance

piezometer monitoring