Hydrogeologic characteristics of the St. Croix River basin, Minnesota and Wisconsin: Implications for the susceptibility of ground water to potential contamination

Abstract

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88). Elevation, as used in this report, refers to distance above the vertical datum. *Hydraulic conductivity: the standard unit for hydraulic conductivity is cubic foot per day per square foot of aquifer cross-sectional area (ft 3 /d/ft 2). In this report, the mathematically reduced form, foot per day (ft/d), is used for convenience. **Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times foot of aquifer thickness [(ft 3 /d)/ft 2 ]ft. In this report, the mathematically reduced form, foot squared per day (ft 2 /d), is used for convenience. Physical Setting The St. Croix River (fig. 1) originates near Solon Springs, Wis., and flows approximately 154 mi south to its confluence with the Mississippi River at Prescott, Wis. The St. Croix National Scenic Riverway includes the St. Croix River and the Namekagon River that together amount to 252 river miles for recreational use. The St. Croix River Basin encompasses 7,730 mi 2 in Minnesota and Wiscon sin (Lenz and others, 2001) and includes all or part of 19 counties. Land cover is varied, grading from predomi nantly forest cover upstream in the basin to a mixture of forest, agriculture, and urban land use further downstream. Glacial deposits overlie igneous and sedimentary bedrock in the basin. Feinstein and others (2006) give a detailed description of hydrogeologic properties of the basin.

Simulation of the Groundwater-Flow System in Pierce, Polk, and St. Croix Counties, Wisconsin

“…Of the 65 active wells, 9 withdraw water from Quaternary sand and gravel aquifers, whereas the remaining 56 municipal wells withdraw water from bedrock aquifers. These aquifers are susceptible to contamination (Juckem, 2007) as indicated by local areas with high concentrations of nitrates in groundwater samples (Masarik and others, 2006). In addition, the counties are experiencing population growth because of their proximity to the Twin Cities metropolitan area in Minnesota.…”

Development of regression equations to revise estimates of historical streamflows for the St. Croix River at Stillwater, Minnesota (water years 1910-2011), and Prescott, Wisconsin (water years 1910-2007)

“…Croix River at Stillwater, Minn. (water years 1910-2011), and at Prescott, Wisc. (water years 1910-2007.…”

“…In addition, the constant may better account for geologic differences between St. Croix Falls and Stillwater. Downstream from St. Croix Falls, increased soil and bedrock permeability may allow the surrounding watershed to capture a greater portion of the water budget (Juckem, 2007), resulting in less peak runoff and greater base flow. However, the hydrograph separation analyses needed to quantify base flow and peak flows at St. Croix Falls and Stillwater are beyond the scope of this report.…”

“…In addition, the constant may better account for geologic differences between St. Croix Falls and Prescott. Downstream from St. Croix Falls, increased soil and bedrock permeability may allow the surrounding watershed to capture a greater portion of the water budget (Juckem, 2007), resulting in less peak runoff and greater low flows. Furthermore, the difference between previous and revised mean streamflow values may be lower at Prescott than Stillwater because of the effects of water storage in Lake St. Croix and because of larger groundwater contributions to Lake St. Croix from the Willow and Kinnickinnic Rivers.…”