U.S. 12 diesel spill assessment, cleanup continues

Excavation along U.S. 12 should provide an environmental team with a better understanding of how deep and wide diesel has penetrated into the soil following a tanker crash about 136 miles east of Lewiston last week.

Cleanup crews finished excavation of a borrow pit on the north side of U.S. 12 Monday afternoon. Penetration still is evident at depth of about 10 feet. Environmental consultants from Tetra Tech of Boise estimate that about 700 cubic yards of material was removed from north of the highway where most of diesel initially pooled.

A laboratory analysis of the excavated material will help determine how much of the diesel was contained soil that has been removed.

An air rotary drill arrived at the scene Monday and completed the first of about five core samples from the westbound travel lane adjacent to the spill. Preliminary field screening results from the first cores showed no evidence of diesel under the highway surface.

The drill reached the water table at about 40 feet. Water samples from the first and subsequent cores will be sent to a lab for analysis and results could be available as early as Thursday.

The core samples will help identify a possible migration path of diesel and will help officials determine whether a portion of the highway and roadbed will need to be removed and rebuilt.

A small amount of “sheen” was discovered near the bank of the Lochsa River over the weekend. An aggressive effort to keep the sheen behind containment booms and absorbent pads appears to be working, experts indicate. A “miniscule” amount of additional sheen was detected late Sunday or early Monday, likely carried by rainfall.

Traffic through the area is reduced to a single lane and will be controlled by flaggers 24 hours per day until the cleanup operation is complete. Motorists are advised to use caution when traveling through the area, follow the directions of flaggers, reduce speed and watch for heavy equipment.

Intermittent rain in the area Sunday and Monday morning raised a concern about possible rock fall from the cliff immediately north of the highway. The hillside will be monitored constantly as crews work below.

A multi-agency response was initiated after a Keller Transport Inc. tanker and trailer carrying 9,500 gallons of diesel overturned Wednesday morning (Sept. 29). A tank ruptured when it hit a rock bluff north of the highway. Authorities indicate about 7,300 gallons of fuel spilled into a borrow pit.

Representatives from a number of state and federal agencies along with private consultants implemented intense containment and cleanup efforts to minimize impacts on the Lochsa River south of the highway. They will continue to monitor the river 24 hours a day for any signs of diesel.

Published 10-8-2010