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Dames & Moore, 1999 - USDA Forest Service

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9.3.4 Maintenance Yard<br />

9.3.5 Lagoon Soils<br />

approximately 34 degrees appear to be at risk. The maximum depth of a failure has been<br />

estimated to be 15 feet. The failure of a slope would likely result in the delivery of tailings<br />

material to Railroad Creek.<br />

The base of the tailings piles is at increased risk over time of erosion during storm events due<br />

to the continued breakdown and insufficient size of some of the rigrap streambank protection.<br />

The erosion of the toes of the piles during a major storm event may result in the delivery of<br />

tailings materials to the cqk.<br />

The surface soil within the maintenance yard area exceeds MTCA levels for arsenic, cadmium,<br />

copper, iron, lead, and total petroleum hydrocarbons.<br />

The subsurface soil within the maintenance yard area exceeds current MTCA levels for total<br />

petroleum hydrocarbons only.<br />

The surface soil within the lagoon exceeds levels for total petroleum hydrocarbons; the<br />

subsurface soil exceed MTCA levels for cadmium, copper, lead, and total petroleum<br />

hydrocarbons.<br />

The following scope of work has been identified by the Agencies as a data need which will require additional<br />

sampling and analysis:<br />

9.4.1 Lucerne Bar Sampling<br />

Additional sediment sampling will be conducted in Lake Chelan near the mouth of Railroad<br />

Creek and to the east of the area sampled during the Phase 111 RI. The objective of the<br />

sampling and analysis will be to further characterize the nature and extent of metals<br />

concentrations in near-shore sediment. The sampling is scheduled to be completed between<br />

August and October <strong>1999</strong>.<br />

G:\WPDATA\OOJWPORTSWOLDEN-2W9-0.d~ 9-1 1<br />

17693-005-019Wuly 28, <strong>1999</strong>;10:07 AM;DW\FT FINAL RI REPORT

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