Scientific Investigations Report 2007–5179
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2007–5179
Table 7. Nitrate occurrence in shallow ground water beneath agricultural and urban areas within regional National Water-Quality Assessment Program study units in the arid to semiarid Western United States, 1993–2004.
[Abbreviations: LRL, laboratory reporting limit; MCL, maximum contaminant level; USEPA, U.S. Environmental Protection Agency; mg/L, milligram per liter. Symbol: <, less than]
| Land use | Number of wells |
Range in nitrate concentration (mg/L) |
Median nitrate concentration (mg/L) |
Percent of wells exceeding USEPA MCL (10 mg/L) |
Important factors relating to exceedence of USEPA MCL |
|---|---|---|---|---|---|
| Agricultural | 272 | <LRL to 74.6 | 0.27 | 25 | Irrigation practices, fertilizer application rate, general soil permeability characteristics, aquifer-redox condition. |
| Urban | 179 | <LRL to 53.3 | 0.22 | 10 | General soil permeability characteristics.1 |
1A sufficiently strong predictive model could not be developed for the exceedence of the nitrate MCL in urban areas. The only variable that provided any significant contribution was soil hydrologic group (p = 0.044).
U.S. Department of the Interior | U.S. Geological Survey
URL: https://pubs.usgs.gov/sir/2007/5179
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