NOR_04_08 - Rib Lake


Rib Lake, Roesler Recent sediment sampling in Rib Lake found a substantial layer of petroleum product contaminated sediment off the mouth of Tannery Creek. The contaminated layer was distinctively blackened and had a petroleum product odor. It was about 1 foot thick and was overlain by about 1 foot of "cleaner" sediment. Additional monitoring is needed to determine the extent and nature of this contamination. Multiple sediment cores will be collected along several transects and visually examined to determine the distribution, depth and thickness of the contaminated layer. Representative cores will be saved for analysis. A three site composite of the contaminated layer will be developed for high, medium, and low areas of visually evident contamination. An additional composited sample will be developed for the overlying sediment layer from locations where it is less than 6 inches deep. A total of 4 samples will be analyzed. Sampling will be done by Craig Roesler with an LTE assistant during the winter of 2007-8.


To determine if this site should be added to the 303d list and to identify management options.


This lake was not added to the 303(d) list. If undisturbed, there is probably little movement of mercury, arsenic, copper and zinc out of the contaminated layer. It is currently capped with 1 ft or more of cleaner sediment. Overlying water depth is about 3-6 ft. Some disturbance by outboard motors and boat anchors may occur. An extreme windstorm could conceivably cause resuspension of the contaminants. If the lake level became lower, (the outlet dam has a 1 ft head) the potential for wind-induced resuspension would probably increase. Any sediment disturbing activities in the area should be avoided. The most desirable solution would be the removal of the contaminated material. However, the cost of removal may be prohibitive. A total of about 7,767 yd3 of material would need to be removed. There is some woody debris buried in the sediment, especially closest to the creek mouth, which might complicate sediment removal.

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