Chloride and nitrate groundwater concentrations across hydrogeologic zones in the Lake Huron Basin from 1995 to 2023

This child item contains groundwater quality information, with respect to nitrate as N and chloride, for the hydrogeologic zones of the Lake Huron Basin, which are defined in the "Data used to characterize Lake Huron HUC-8s into hydrogeologic zones" child item of this data release. The dataset used in this analysis was from the Michigan Department of the Environment, Great Lakes, and Energy (EGLE) WaterChem database, which contains water quality information for drinking water wells across the state of Michigan. A Memorandum of Understanding (MOU) is in place between EGLE and the U.S. Geological Survey, which allows the U.S. Geological Survey to use the data from WaterChem database for hydrologic studies and prevents the U.S. Geological Survey from sharing individual point data on wells. Therefore, the data in this child item represents nitrate and chloride at the aggregate scale of the hydrogeologic zones. The WaterChem dataset from MI-EGLE contains geospatial locations where each of the groundwater samples were taken but does not contain the well information associated with the sample. Well information for the groundwater wells in the Lake Huron Basin was obtained from the Michigan Wellogic database (Michigan Department of the Environment, Great Lakes, and Energy, 2024). Quality control was performed on the well dataset, and then each well was determined to be in the bedrock or glacial aquifer based on the well depth reported in Wellogic and the thickness of the glacial deposits reported from Soller and Garrity (2018). A shapefile of the quality controlled wells from Wellogic and their associated aquifer designation are contained in a .zip file within this child item. The wells and water quality data were then spatially joined to determine whether the sample were from the bedrock or glacial aquifer and how groundwater contamination varied across the aquifer settings. The water quality tables in this child item summarize the total groundwater samples of nitrate and chloride within each hydrogeologic zone and aquifer, the number of detections, and the number of samples with concentrations above the EPA drinking water standards. This is one of three child items in the overall data release https://doi.org/10.5066/P133AHTG.

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