--> Abstract: Groundwater and Soil Remediation at a Timber Products Facility in Northwestern Montana, by L. Lottman-Craigg and K. A. Wallace; #90993 (1993).

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LOTTMAN-CRAIGG, LINDA, and KENNETH A. WALLACE, Woodward-Clyde Consultants, Helena, MT

ABSTRACT: Groundwater and Soil Remediation at a Timber Products Facility in Northwestern Montana

The field area is located in Lincoln County in northwestern Montana. The region has been a timber and mining area since the late 1800s, and from 1946-1969, the mill at the site produced telephone poles that were treated with wood preservatives, including creosote, pentachlorophenol in a carrier oil, and an inorganic salt solution. Groundwater contamination was discovered in 1979, when a local resident installed a shallow well downgradient of the facility and detected creosote in the water. In 1983, after further investigations, the site was placed on the Environmental Protection Agency's (EPA's) Superfund list. The chemical constituents from wood-treating processes contaminated soils and migrated through the unsaturated zone into the underlying groundwater.

An extensive soil cleanup program was initiated, consisting of the excavation of contaminated soils followed by waste degradation in two land-treatment units. Soils are placed in lifts, tilled frequently to assure adequate oxygen is supplied to microbes, and amended with nutrients and moisture. After EPA-mandated cleanup levels are reached, a cap will be installed to prevent water infiltration.

Glacial, glacio-fluvial, and alluvial deposits form a complex of water-bearing and nonwater-bearing units below the site. Two

aquifers have been distinguished, with groundwater located from less than 10 ft to over 100 ft below the surface. Both aquifers have been impacted by the migration of wood-treating wastes. Because of the rapid and prolific groundwater system, conventional pump and treat cleanup systems would be largely ineffective, other than to control plume migration. An innovative biorestoration system has been employed that stimulates native microbes to speed up contaminant oxidation. A surface bioreactor system is used to collect, separate, and degrade contaminants the locations containing free product.

AAPG Search and Discovery Article #90993©1993 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah, September 12-15, 1993.