The Waterloo Coal Gasification Plant operated along the Cedar River in Waterloo, Iowa from 1901 to 1956. It is listed on the National Priorities List and contaminated soil and groundwater with polynuclear aromatic hydrocarbons (PAHs, a family of chemicals found in coal tar), benzene, cyanide, arsenic, lead, chromium, and other metals. Thirty contaminants of concern have been identified in total. The Cedar River, which runs adjacent to the site, shows no apparent adverse impact from the contamination.
MidAmerican Energy Company has led cleanup work under EPA oversight. From 1994 to 2001, a three-phase removal action excavated and incinerated about 93,000 pounds of contaminated soil. In 1997, 14,000 tons of soil were treated using thermal methods, and surface soil was removed again in 2003. Because fully cleaning up the groundwater was not feasible, EPA designated a technical impracticability zone where some contamination is expected to remain long-term. Outside that zone, EPA is using monitored natural attenuation, meaning contaminants are breaking down on their own while groundwater is tracked to make sure contamination does not spread. Groundwater is sampled twice a year, in March and September. Elevated manganese levels in three wells at the edge of the zone are being evaluated.
The site is protected by institutional controls. These include a ban on residential use, restrictions on drilling new wells, and a requirement that any new buildings be designed to block vapor intrusion from volatile organic compounds, or that testing confirm no health risk to occupants. Property owners must notify the Iowa Department of Natural Resources and EPA within 30 days of any land-use change or property transfer. EPA's Five-Year Review, completed August 7, 2023, confirmed that the cleanup remedy is functioning as intended and remains protective of human health and the environment. Human exposure is currently under control, and contaminated groundwater migration is stabilized. Physical construction is not yet complete, and remedial action is estimated to continue through late 2026 or early 2027. The next Five-Year Review is scheduled for August 7, 2028.
Two businesses currently operate on-site. Community members who want to follow the site's progress can contact the EPA Community Involvement Coordinator or Remedial Project Manager. Groundwater monitoring results and review documents are available through EPA's public records for the site.
