WRD Colorado District

Ground-Water Quality Beneath Irrigated Agriculture in the Central High Plains Aquifer, 1999–2000

By Breton W. Bruce, Mark F. Becker, Larry M. Pope, and Jason J. Gurdak

Available from the U.S. Geological Survey, Branch of Information Services, Box 25286, Denver Federal Center, Denver, CO 80225, USGS Water-Resources Investigations Report 03-4219, 39 p., 14 figs.

This document also is available in pdf format: Adobe Acrobat Icon WRIR 03-4219.pdf (2.9 MB) (Requires Adobe Acrobat Reader)

The citation for this report, in USGS format, is as follows:
Bruce, Breton W., Becker, Mark F., Pope, Larry M., and Gurdak, Jason J., 2003, Ground-Water Quality Beneath Irrigated Agriculture in the Central High Plains Aquifer, 1999–2000: U.S. Geological Survey Water-Resources Investigations Report 03-4219, 39 p.


In 1999 and 2000, 30 water-quality monitoring wells wereinstalled in the central High Plains aquifer to evaluate thequality of recently recharged ground water in areas of irrigatedagriculture and to identify the factors affecting ground-waterquality. Wells were installed adjacent to irrigated agriculturalfields with 10- or 20-foot screened intervals placed near thewater table. Each well was sampled once for about 100 waterqualityconstituents associated with agricultural practices.Water samples from 70 percent of the wells (21 of 30 sites) containednitrate concentrations larger than expected backgroundconcentrations (about 3 mg/L as N) and detectable pesticides.Atrazine or its metabolite, deethylatrazine, were detected withgreater frequency than other pesticides and were present in all21 samples where pesticides were detected. The 21 sampleswith detectable pesticides also contained tritium concentrationslarge enough to indicate that at least some part of the watersample had been recharged within about the last 50 years. These21 ground-water samples are considered to show water-qualityeffects related to irrigated agriculture. The remaining 9 groundwatersamples contained no pesticides, small tritium concentrations,and nitrate concentrations less than 3.45 milligrams perliter as nitrogen. These samples are considered unaffected bythe irrigated agricultural land-use setting. Nitrogen isotoperatios indicate that commercial fertilizer was the dominantsource of nitrate in 13 of the 21 samples affected by irrigatedagriculture. Nitrogen isotope ratios for 4 of these 21 sampleswere indicative of an animal waste source. Dissolved-solidsconcentrations were larger in samples affected by irrigatedagriculture, with large sulfate concentrations having strongcorrelation with large dissolved solids concentrations in thesesamples. A strong statistical correlation is shown between samplesaffected by irrigated agriculture and sites with large ratesof pesticide and nitrogen applications and shallow depths toground water.





Purpose and Scope


Description of Study Area

Hydrogeologic Setting

Land Use

Fertilizer and Pesticide Use

Water Use

Study Design and Methods

Site Selection

Well Installation

Sample Collection

Land-Use Classification

Quality Control

Ground-Water Quality Beneath Irrigated Fields

Major Dissolved Ions and Water Properties

Nutrients and Pesticides


Dissolved Organic Carbon

Relation Between Land Use and Water Quality

Nutrients, Pesticides, and Tritium

Nitrogen Isotopes

Dissolved Solids and Major Ions

Land-Use and Hydrogeologic Factors Affecting Ground-Water Quality

Summary and Conclusions

References Cited

Supplemental Information

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