A federal review of cleanup operations at a Superfund toxic waste site in rural Missouri has raised questions about whether excess levels of pollutants — which may present a health risk even in minuscule amounts — have migrated off-site.

The 200-acre Wheeling Disposal site near Amazonia served until 1986 as a dump for pesticides, asbestos, leather tanning sludge, and waste from laboratories, batteries and cyanide. It is being cleaned up by the companies responsible for the contamination, under the supervision of the Environmental Protection Agency. The cleanup includes long-term monitoring of ground and surface water.

But according to a review by the EPA’s inspector-general, the agency’s regional managers have “inadvertently allowed” the companies funding the cleanup to use incorrect methods to measure contamination and “did not always require the [companies’] laboratories to properly analyze some contaminants.” As a result, the report found, the EPA “has limited assurance that unsafe levels of contaminants are not migrating off-site and creating risk to human health and the environment.”

Surface runoff from the dump flows to tributaries and creeks that discharge into the Missouri River two miles south of the dump. By relying on incorrect standards, the EPA officials “may not have detected unacceptable levels of  contaminants in the site’s surface and ground water,” the inspector-general said.

The report recommends that agency officials ensure that accurate standards are used to assess conditions at the site and that laboratories use the correct analytic methods. It also calls for assessment of risks to wildlife, since the site is “habitat for wildlife and birds and is also a recreational hunting and fishing area.”