Water-quality assessment of part of the Upper Mississippi River Basin, Minnesota and Wisconsin — Ground-water quality along a flow system in the Twin Cities metropolitan area, Minnesota, 1997-98

Abstract

The U.S. Geological Survey (USGS) is committed to serve the Nation with accurate and timely scientific information that helps enhance and protect the overall quality of life, and facilitates effective management of water, biological, energy, and mineral resources. (http://www.usgs. gov/). Information on the quality of the Nation's water resources is of critical interest to the USGS because it is so integrally linked to the long-term availability of water that is clean and safe for drinking and recreation and that is suitable for industry, irrigation, and habitat for fish and wildlife. Escalating population growth and increasing demands for the multiple water uses make water availability, now measured in terms of quantity and quality, even more critical to the long-term sustainability of our communities and ecosystems. The USGS implemented the National Water-Quality Assessment (NAWQA) Program to support national, regional, and local information needs and decisions related to water-quality management and policy. (http://water.usgs.gov/nawqa/). Shaped by and coordinated with ongoing efforts of other Federal, State, and local agencies, the NAWQA Program is designed to answer: What is the condition of our Nation's streams and ground water? How are the conditions changing over time? How do natural features and human activities affect the quality of streams and ground water, and where are those effects most pronounced? By combining information on water chemistry, physical characteristics, stream habitat, and aquatic life, the NAWQA Program aims to provide science-based insights for current and emerging water issues and priorities. NAWQA results can contribute to informed decisions that result in practical and effective waterresource management and strategies that protect and restore water quality. The NAWQA Program recognizes that a national assessment by a single program cannot address all water-resource issues of interest. External coordination at all levels is critical for a fully integrated understanding of watersheds and for cost-effective management, regulation, and conservation of our Nation's water resources. The Program, therefore, depends extensively on the advice, cooperation, and information from other Federal, State, interstate, Tribal, and local agencies, non-government organizations, industry, academia, and other stakeholder groups. The assistance and suggestions of all are greatly appreciated.

Chloride ion transport and mass balance in a metropolitan area using road salt

“…Median chloride values of 46 mg/L were found in urban areas, 17 mg/L in agricultural areas, and 1.2 mg/L in forested area [ Fong , 2000]; 3% of the water samples taken from wells in the TCMA were found to exceed the USEPA secondary chloride standard of 250 mg/L [ Fong , 2000]. In a cross section of the surficial aquifer in a northwestern suburb of Minneapolis directly down gradient from a high‐traffic roadway, chloride concentrations ranged from 200 mg/L at the water table 3 m below the soil surface, to 590 mg/L at a depth of 13.5 m below the soil surface [ Andrews et al , 2005]. Concentrations of 380–470 mg/L were also measured down gradient from a major Interstate Highway (I‐94) in summer and late fall pointing toward a long‐term storage of road salt in the surficial aquifer [ Andrews et al , 2005].…”

“…In a cross section of the surficial aquifer in a northwestern suburb of Minneapolis directly down gradient from a high‐traffic roadway, chloride concentrations ranged from 200 mg/L at the water table 3 m below the soil surface, to 590 mg/L at a depth of 13.5 m below the soil surface [ Andrews et al , 2005]. Concentrations of 380–470 mg/L were also measured down gradient from a major Interstate Highway (I‐94) in summer and late fall pointing toward a long‐term storage of road salt in the surficial aquifer [ Andrews et al , 2005]. Data collected by the Minnesota Pollution Control Agency (MPCA) throughout the seven‐county TCMA showed that the highest chloride concentrations in groundwater, up to 2000 mg/L, were found in shallow wells (Figure 9).…”

“…Evidence of chloride retention is widespread in the TCMA. Four streams in the TCMA are on the MPCA's 2008 list of Cl − impaired waters, 38 lakes in the TCMA had a rising mean annual Cl − concentration over a 22 year period [ Novotny et al , 2008], and elevated Cl − concentrations in groundwater have been measured [ Andrews et al , 2005; Fong , 2000]. Chloride retention in urban areas where road salt (NaCl) is applied should cause much concern.…”

“…Elevated and/or increasing chloride concentrations attributable to road salt applications are present in groundwater and surface waters in urban environments in northern climate regions [ Andrews et al , 1997; Andrews et al , 2005; Bowen and Hinton , 1998; Fong , 2000; Godwin et al , 2003; Kaushal et al , 2005; Kelly , 2008; Lofgren , 2001; Marsalek , 2003; Novotny et al , 2008; Thunquist , 2004]. Mass balance studies on individual streams with watershed areas less than 450 km 2 indicate that between 27% and 65% of the road salt applied was retained within the individual urban watersheds [ Bubeck et al , 1971; Howard and Hayes , 1993; Huling and Hollocher , 1972; Ruth , 2003; Wulkowicz and Saleem , 1974].…”