National Water-Quality Assessment (NAWQA) Project

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Variations in Groundwater Quality among Principal Aquifers

Map showing principal aquifers (opens in new window)

Graphs showing water quality in select principal aquifers

The following graphs are from Circular 1337. Explanation of how to read the graphs

Maps showing groundwater quality from select published studies

Publications about principal aquifers

Select findings

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  • From 'Microbial Quality of the Nation’s Ground-Water Resources, 1993–2004':
    The waters most affected by the presence of coliform bacteria were those in the Valley and Ridge, the Floridan, and the Piedmont and Blue Ridge aquifers, where more than 50 percent of the study wells tested positive for these bacteria. The numbers of wells with detections of coliform bacteria were significantly lower for the Glacial Deposits, Stream and River Valley, Columbia Plateau, Basin and Range, High Plains, Southeastern Coastal Plain, and Coastal Lowlands aquifers. (Download report SIR 2006-5290)
  • From 'Quality of Water from Domestic Wells in Principal Aquifers of the United States, 1991–2004':
    The occurrence of some contaminants varied regionally and by principal aquifer and therefore may be of greater potential concern for human health or aesthetic water quality in some locations or regions than nationally. The occurrence of anthropogenic organic compounds is widespread in principal aquifers, although at concentrations well below human-health benchmarks. The widespread occurrence demonstrates that all aquifers require some level of consideration to prevent or mitigate contamination. (Download report SIR 2008–5227)
  • From 'Factors Affecting Water Quality in Selected Carbonate Aquifers in the United States,1993–2005':
    Water quality in the 12 carbonate aquifers was highly variable. Most of the samples met drinking-water standards. The occurrence of anthropogenic contaminants was related to contaminant sources but also was affected by degree of aquifer confinement, ground-water age, and redox status. Areas with higher amounts of agricultural or urban land in unconfined aquifers were the most likely to have elevated concentrations 'of anthropogenic contaminants. (Download report SIR 2008-5240)

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