The Illinois Environmental Protection Agency, which is now overseeing the site, observed asphalt in the canal and along the shoreline after the cleanup was reported complete, said IEPA spokesperson Kim Biggs in a statement last week.

Nearly a half-million gallons of non-road-grade liquid asphalt spilled into the canal this year. Under normal circumstances, this would be troubling, but federal resources could help address the problem quickly and effectively.

The find has been championed by MWRD officials as a significant positive indicator for water quality and ecosystem health.