U.S. Geological Survey groundwater research in the Great Lakes Basin

Abstract

U.S. Geological Survey (USGS) conducts national and regional-scale investigations with relevance to the Great Lakes Basin as part of its Water Availability and Use Science Program and its National Water Quality Program. USGS also conducts local-scale investigations in the Great Lakes Basin that collectively have regional significance. From a groundwater perspective, major resource issues include finding adequate supplies, understanding the relation between groundwater and surface water, and understanding the effect of water quality on drinking water sources. At the national scale, USGS recently completed an assessment of brackish groundwater (dissolved-solids concentration between 1,000 and 10,000 milligrams per liter) that provides information on the potential for such groundwater to augment freshwater supplies, including in the Great Lakes Basin. USGS also recently completed a national assessment of the potential corrosivity of untreated groundwater. New York and Pennsylvania were classified as having a high prevalence of potentially corrosive groundwater; however, most Great Lakes states were classified as having a moderate prevalence of such water (<http://water.usgs.gov/nawqa/pubs/gw_corrosivity/>). A recent analysis of decadal-scale changes in groundwater quality at USGS well networks across the U.S. reveals an increase in chloride and total dissolved solids concentrations in groundwater in many areas, including in the Great Lakes Basin (<http://nawqatrends.wim.usgs.gov/decadal/>). At the regional scale, USGS work on the quantity and quality of groundwater in glacial aquifers has particular relevance to the Great Lakes Basin, because unconsolidated materials deposited at or near land surface as a result of glaciation make up the most productive aquifers in the Basin. USGS is developing an updated geologic framework for glacial deposits across the U.S. that includes the texture and thickness of glacial deposits, the depth to top of bedrock, the number of glacial aquifers beneath a given location, and the depth and degree of aquifer confinement. The distribution of domestic and public supply wells in glacial aquifers is being mapped. Over 15 million driller's logs were compiled and standardized to provide the desired level of spatial heterogeneity for these efforts. Generalized groundwater-flow models are being constructed for each HUC-8 watershed within the U.S. side of the Great Lakes Basin to estimate groundwater age and to provide insight into the time lag between nonpoint source contaminant loading at the water table and arrival at streams. Samples from glacial aquifer wells were collected and analyzed for tracers of groundwater age in support of this effort. Samples also were analyzed for a wide variety of water quality constituents to estimate the percentage of glacial deposits where constituent concentrations are high, moderate and low with respect to human-health benchmarks. Three-dimensional maps of manganese and arsenic are being developed for the glacial deposits by using a statistical modeling approach that incorporates information from the updated geologic framework and the measured and modeled information on groundwater age. Data from state ambient monitoring programs were procured in support of this water quality mapping effort. At the local scale, one topic of investigation with regional significance is the effect of stormwater management on groundwater beneath urban areas. Study areas include Buffalo, NY; Cleveland, OH; Detroit, MI; and Gary, IN.