FIELD DOCUMENTS AND WORK PLANS 1990

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apparently is the result of contact of contaminated storm water runoff or wood preservative solution with the surface soils. The majority of contamination is contained within the top 1 foot of soil in isolated areas and only in areas immediately adjacent to the facility. Pipe and Culvert Contamination Contaminated sediments exist in some of the drainage pipes and ditch culverts. The pipes and culverts which need remediation are adjacent to areas requiring soil remediation. Subsurface Soil Contamination Subsurface soils beneath the retort pit area on MCTC' s North Yard have been affected by wood treating activities conducted at the site. The subsurface soils can be divided into .two subunits - the shallow soils and the deep soils. The upper 15 feet of subsurface soils are termed the shallow soils and contain copper and arsenic. Hexavalent chromium exists in the pore water in the soils from below the shallow soils to the groundwater table. These soils are referred to as the deep soils. Groundwater Contamination The quality of groundwater underlying the MCTC facility has been impacted by wood treatment and treated wood storage operations. The direction of groundwater flow is approximately south to southwest with the water table at approximately 60 feet below land surface (bls) . Contamination appears to be limited to the shallow and intermediate zones of the aquifer or to about 200 feet bls. The attached Figures 3-5 and 3-6 (taken from the full volume draft RAP) shows the known extent of groundwater contamination. SUMMARY OF FEASIBILITY STUDY ALTERNATIVES Several remedial alternatives were identified and evaluated in the Feasibility Study. To facilitate evaluation of the alternatives, each operable unit was considered independently. The range of alternatives considered is summarized below: ES-3