The U.S. Environmental Protection Agency (EPA) has ordered Norfolk Southern to conduct more testing in East Palestine.

According to the release, the EPA ordered Norfolk Southern to do additional cleanup and sheen investigations focusing on oily sheens and sediments in Sulphur Run and Leslie Run creeks.

The order was made under the EPA's Clean Water Act authority and will build on the cleanup work that's already been done in the creeks over the last few months. The work will determine if more cleanup is needed to make sure any potential long-term impacts are addressed.

"As many folks have seen, the sediment in the creeks in some areas may generate a sheen when disturbed or agitated," EPA Regional Administrator Debra Shore said. "In addition to the sampling and clean-up work over the last eight months, EPA will require that contamination from the derailment is identified along the impacted length of the creeks. Through this order, Norfolk Southern will take a thorough look at the waterways to ensure there are no lasting impacts from the derailment."

Through the order, surface water sampling will continue to happen weekly and visual water inspections will continue. The sheen investigation will be done along a 5-mile portion of impacted areas of both Sulphur and Leslie Runs. According to the EPA, a sediment agitation technique will be done in the creeks where the sheening occurs and both sheen and sediment samples will be collected.

The creek cleanup also includes removing impacted sediment in Sulphur Run downstream from the derailment site.

The latest order comes after U.S. EPA Administrator Michael Regan made his fourth visit to East Palestine this week.

Norfolk Southern released the following statement following the EPA order:

Echoing the EPA, this order formalizes the continuation of work that has been ongoing since the derailment under a different regulatory scheme. Norfolk Southern remains cooperative, working with EPA and Ohio EPA at the site, and will continue to address derailment-related impacts in the waterways of Sulphur and Leslie Runs. The work under this new order will complement and build upon our prior cleanup and assessment efforts. We remain committed to cleaning up the site safely and thoroughly.