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clean-up. Locations of these sites need to be considered when locating new wells. Municipalities are required by the Minnesota Department of Health to identify these potential sources of groundwater contamination in their Wellhead Protection Plans There are three known areas of groundwater contamination [hat have affected municipal water supplies in the metropolitan area: the Riley Tar Site in St. Louis Park; the U.S. Army TCAAP [richloroethene (TCE) plume in Arden Hills and New Brighton; and the extensive perfluorocarbon (PF) contamination in southern Washington County that has been linked to three landfills that received perfuorocazbo^ wastes from 3M. The Riley Tar Site and the TCAAP Site were discovered many years ago and are actively managed. The PF contamination in southern Washington County was first discovered in 2004-2005 and has been the object of intense evaluation since [hen. The PF contamination appears to be very widespread and may have permanent impacts on groundwater supplies in Oakdale, Lake Elmo, Woodbury, Cottage Grove, and St. Paul Park. Studies by the MPCA and MDH suggest the PF compounds may also enter groundwater from more widespread locations associated with municipal landfills and fire-fighting and fire-training sites (PF compounds are associated with fire-fighting materials). Naturally occurring constituents in aquifers can impact the water quality of municipal groundwater supplies. It is not unusual for municipalities to treat for the removal of iron and manganese from groundwater before distributing. Many bedrock aquifers and some glacial aquifers have naturally high levels of iron and manganese. Arsenic concentrations above health limits are a problem in out- state groundwater supplies but are less frequently an issue in the metropolitan area. Arsenic is a naturally occurring [race metal in shaley rocks that were deposits in marine environments. Higher levels of arsenic are occasionally found associated with the Eau Claire Formation. Arsenic is a known human carcinogen and is difficult to remove at very low concentrations. Radium and other trace radio-nuclides are commonly found slightly above health limits in sandstones such as the Jordan Sandstone, the Ironton-Galesville Sandstones, and the Mt. Simon and Hinckley Sandstones. Elk River treats groundwater to remove radium. 2.5 Available Aquifers in the Elk River Area Because Elk River is located along the periphery of the Hollandale Embayment, it does not have available to i[ [he important Prairie du Chien-Jordan Aquifer System. In the southeastern portion of the city limits, the Franconia-Ironton-Galesville Aquifer is likely present and does likely have above- average permeability because it is not overlain by the St. Lawrence Formation. However, the primary P:\Mpls\23 MN\71\2371105 Water Supply Alternative Smdy\FinalDeliverables\Alternatives_Report_final.doc 1f