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Ramsey County Multi-Hazard Mitigation Plan, 2018 Page | 18 tissue, perfluorooctane sulfonate (PFOS) in fish tissue, PCB in fish tissue, turbidity, and poor biological conditions according to aquatic macroinvertebrate bioassessments. Basic hydrography in Ramsey County is mapped in Figure A-1 in Appendix A, while aquifer vulnerability (using 2011 data from the Minnesota Department of Agriculture) and public wells are mapped in Figure A - 14. 3.3.1 Groundwater Ramsey County is located over the Prairie Du Chien-Jordan Aquifer, which is the major source of groundwater for the Minneapolis & Saint Paul Twin Cities Metropolitan Area. Over the last 80 years, the level of the Prairie du Chien has steadily declined as the area has become more populated and the primary source of drinking water has shifted to groundwater (MPCA, 2018). Other aquifers that supply groundwater to Ramsey County are the St. Peter Aquifer, Franconia-Ironton-Galesville Aquifer and the Mt. Simon Aquifer. The Prairie du Chien Group and Jordan Sandstone together form the most heavily used aquifer in the county. This aquifer is present throughout the county except in a narrow bedrock valley in the northwest (the Phalen channel), where the first bedrock is the St. Lawrence or Franconia Formation. The aquifer is overlain by the shaly basal part of the St. Peter Sandstone in much of the county. The Prairie du Chien Group is composed predominantly of dolostone; water flows mainly through fractures, joints, and solution cavities. Its total thickness is about 120 to 130 feet. The Jordan Sandstone (70 to 100 feet thick) consists of highly permeable, fine- to coarse-grained quartzose sandstone, and most water movement is intergranular. Despite their difference in rock type, the Prairie du Chien Group and Jordan Sandstone function as a single aquifer because no regional confining bed separates them. Locally, however, small water-level differences may exist, owing to relatively impermeable beds of shale of limited extent. In general, the groundwater flows from areas with the highest hydraulic head in northeastern Ramsey County toward the Mississippi River. This flow pattern indicates that the Prairie du Chien-Jordan aquifer discharges into the river. The flow pattern may be altered by localized pumping of high-capacity wells, especially during the summer when heavy demands are placed on it. The Prairie du Chien-Jordan aquifer is a confined aquifer except for the southeastern comer of the county. 3.3.2 Lakes There are 82 lake basins in Ramsey County, 23 of which are accessible to the public for recreational use. 3.3.3 Rivers The Mississippi originates from Lake Itasca, stretching all the way to the Gulf of Mexico, and forms a portion of the southern border of Ramsey County. The Minnesota River originates from Big Stone Lake and connects to the Mississippi in the southwest corner of Ramsey County. 3.3.4 Wetlands Due to the urbanization of Ramsey County, few natural wetlands remain. According to the Ramsey Conservation District Comprehensive Plan, over 80% of Ramsey County's pre-settlement wetlands have been destroyed. Wetlands provide critical water quality and flood control, recharge groundwater, and provide habitat for wildlife. The plan notes that the Jones wetland in New Brighton is biologically