 Between 1990 and 2000, under an agreement with the EPA and the State of Michigan, several of the current and past owners of plants that had been responsible for the contamination investigated the Portage Creek site.Polychlorinated biphenyls constitute a wide array of now-banned organic chemicals with a variety of industrial applications.At the Kalamazoo River site, most polychlorinated biphenyls are a result of the recycling of carbonless copy paper during the 1970s, the waste products from which were dumped into the river.