The Wisconsin Groundwater Flow System in Pierce, Polk and St. Croix Counties is an important aquifer system that supplies groundwater to the region. This system consists of two main types of aquifers: glacial-drift aquifers and bedrock aquifers. Glacial-drift aquifers are composed of glacial deposits, which are unconsolidated sediments that were deposited during the last glaciation. These deposits are typically sand and gravel, and provide excellent conditions for groundwater flow. The most productive glacial-drift aquifer in the region is the St. Croix Valley Aquifer, which is located in St. Croix County. Bedrock aquifers are composed of consolidated sedimentary rocks, such as sandstone and limestone. These aquifers have lower permeability than glacial-drift aquifers, but can still provide groundwater resources. The most productive bedrock aquifer in the region is the Kinnickinnic Formation, which is located in Pierce and Polk Counties. The Wisconsin Groundwater Flow System in Pierce, Polk and St. Croix Counties provides an important source of groundwater for the region, and is managed by the Wisconsin Department of Natural Resources. This system is monitored to ensure that groundwater resources are used sustainably, and to protect water quality.