That's the typical method of removal. Rost said the DOT postponed the final pier removal because of the coal tar issue and the impact the resulting disturbance would have on the environment. In 1990, the coal tar was found during excavation for the first main support pier on the Iowa approach. While digging about six feet below the riverbed, construction workers noticed an unusual-looking substance coming up with scoopfuls of loose shale. Digging was halted June 27 and the DNR was called in to identify the substance and oversee the removal of about 350 cubic yards of contaminated riverbed.
Coal tar is a known carcinogen.
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