The Clean Water Act gives the U.S. EPA and the Michigan DEQ responsibility for ensuring that surface water quality meets the standards appropriate to a particular water body.   For example, it gives the DEQ responsibility for addressing potential flows of contaminants into the stream (and eventually the Portage) from the old landfill.   The construction of the leachage collection system stems from DEQ concerns associated with that site.  Linked below is a document from the US EPA giving water quality criteria for surface waters for priority pollutants, non priority pollutants, and pollutants for organoleptic effects.  

        Water Quality Criteria

Developing the Huron Creek Watershed Management Plan