Nutrients in groundwaters of the conterminous United States, 1992–1995

Summary

This national water quality assessment characterises nitrate contamination in United States groundwater from 1992–1995, finding nitrate detected in 71% of samples with substantially higher concentrations beneath agricultural land than urban or deeper aquifer settings. The study identifies key hydrogeological and land management factors that increase or mitigate nitrate contamination, including soil drainage, aquifer permeability, recharge rates, and irrigation practice, demonstrating the complex interaction between nitrogen loading and subsurface conditions in determining groundwater quality.

Regional applicability

This United States national study provides a useful comparative baseline and methodological precedent for United Kingdom groundwater quality assessments, particularly given the importance of agricultural intensification and nitrate leaching in similar temperate European contexts. However, direct applicability is limited by differences in hydrogeology, climate, and agricultural practices; UK-specific assessments would be needed to establish comparable risk profiles for chalk and sandstone aquifers relied upon for drinking water supply.

Key measures

Nitrate concentration (mg/L); detection frequency; maximum contaminant level exceedance; comparison across land use types (agricultural, urban, major aquifers); depth to groundwater; soil drainage class; aquifer permeability; groundwater recharge rate

Outcomes reported

The study detected nitrate in 71% of groundwater samples nationally, with highest concentrations (3.4 mg/L median) in shallow groundwater beneath agricultural land. Nitrate exceeded the maximum contaminant level of 10 mg/L in more than 15% of samples from 4 of 33 major aquifers used for drinking water.

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