Raster dataset showing the probability of elevated concentrations of nitrate in ground water in Colorado, hydrogeomorphic regions and fertilizer use estimates not included.

Metadata Updated: November 12, 2020

This dataset is one of eight datasets produced by this study. Four of the datasets predict the probability of detecting atrazine and(or) desethyl-atrazine (a breakdown product of atrazine) in ground water in Colorado; the other four predict the probability of detecting elevated concentrations of nitrate in ground water in Colorado. The four datasets that predict the probability of atrazine and (or) desethyl-atrazine (atrazine/DEA) are differentiated by whether or not they incorporated atrazine use and whether or not they incorporated hydrogeomorphic regions. The four datasets that predict the probability of elevated concentrations of nitrate are differentiated by whether or not they incorporated fertilizer use and whether or not they incorporated hydrogeomorphic regions. Each of the eight datasets has its own unique strengths and weaknesses. The user is cautioned to read Rupert (2003, Probability of detecting atrazine/desethyl-atrazine and elevated concentrations of nitrate in ground water in Colorado: U.S. Geological Survey Water-Resources Investigations Report 02-4269, 35 p., http://water.usgs.gov/pubs/wri/wri02-4269/) to determine if he(she) is using the most appropriate dataset for his(her) particular needs. This dataset specifically predicts the probability of detecting elevated concentrations of nitrate in ground water in Colorado with hydrogeomorphic regions and fertilizer use not included. The following text was extracted from Rupert (2003). Draft Federal regulations may require that each State develop a State Pesticide Management Plan for the herbicides atrazine, alachlor, metolachlor, and simazine. Maps were developed that the State of Colorado could use to predict the probability of detecting atrazine/DEA in ground water in Colorado. These maps can be incorporated into the State Pesticide Management Plan and can help provide a sound hydrogeologic basis for atrazine management in Colorado. Maps showing the probability of detecting elevated nitrite plus nitrate as nitrogen (nitrate) concentrations in ground water in Colorado also were developed because nitrate is a contaminant of concern in many areas of Colorado. Maps showing the probability of detecting atrazine/DEA at or greater than concentrations of 0.1 microgram per liter and nitrate concentrations in ground water greater than 5 milligrams per liter were developed as follows: (1) Ground-water quality data were overlaid with anthropogenic and hydrogeologic data by using a geographic information system (GIS) to produce a dataset in which each well had corresponding data on atrazine use, fertilizer use, geology, hydrogeomorphic regions, land cover, precipitation, soils, and well construction. These data then were downloaded to a statistical software package for analysis by logistic regression. (2) Relations were observed between ground-water quality and the percentage of land-cover categories within circular regions (buffers) around wells. Several buffer sizes were evaluated; the buffer size that provided the strongest relation was selected for use in the logistic regression models. (3) Relations between concentrations of atrazine/DEA and nitrate in ground water and atrazine use, fertilizer use, geology, hydrogeomorphic regions, land cover, precipitation, soils, and well-construction data were evaluated, and several preliminary multivariate models with various combinations of independent variables were constructed. (4) The multivariate models that best predicted the presence of atrazine/DEA and elevated concentrations of nitrate in ground water were selected. (5) The accuracy of the multivariate models was confirmed by validating the models with an independent set of ground-water quality data. (6) The multivariate models were entered into a geographic information system and the probability GRIDS were constructed.

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License: No license information was provided. If this work was prepared by an officer or employee of the United States government as part of that person's official duties it is considered a U.S. Government Work.

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Dates

Metadata Date November 8, 2004
Metadata Created Date November 12, 2020
Metadata Updated Date November 12, 2020
Reference Date(s) June 9, 2003 (publication)
Frequency Of Update notPlanned

Metadata Source

Harvested from DOI Open Data

Additional Metadata

Resource Type Dataset
Metadata Date November 8, 2004
Metadata Created Date November 12, 2020
Metadata Updated Date November 12, 2020
Reference Date(s) June 9, 2003 (publication)
Responsible Party U.S. Geological Survey (Point of Contact)
Contact Email
Guid
Access Constraints Use Constraints: This dataset should not be used at a scale any larger than 1:250,000, which is the scale of the soils data used to construct the probability GRIDS. Soils data at a larger scale were not available for all regions of Colorado. This dataset is one of eight datasets produced by this study. The user is cautioned to read Rupert (2003) to ensure that they are using the correct dataset for their particular needs. The probability GRIDS developed by this study are designed to portray the potential for contamination of ground water in Colorado. These GRIDS do not show areas that are actually (currently) contaminated; rather, these GRIDS show the areas that have a potential (or likelihood) for being contaminated if a contaminant was released to the environment. More specifically, each GRID shows the probability of detection (in terms of a percent) of a particular chemical compound (the contaminant) in ground water. Probability is not the same as certainty; a well in a high probability area is not necessarily contaminated because contamination also can depend on well depth and other local factors not taken into account by the models used to produce these probability GRIDS. The atrazine/DEA and nitrate probability GRIDS were specifically developed for use by the State of Colorado in its Pesticide Management Plan to help provide a sound hydrogeologic basis for the management of atrazine and nitrogen in Colorado. The GRIDS are intended to be a first approximation at developing a consistent rating method for the entire State. Additional site-specific data are needed before site-specific decisions are made, such as pesticide-use restrictions. The most appropriate uses of these GRIDS are to focus prevention programs in areas of greatest concern, to focus ground-water sampling programs in areas of greatest potential for contamination, and to assist educational programs for ground-water quality protection. The accuracy of the probability GRIDS would be improved if (1) larger scale soils data were available in digital form, (2) more complete and detailed chemical-use data were available, and (3) a larger number and wider distribution of ground-water quality data, particularly in rangeland areas, were available. Data differentiating between sprinkler and flood irrigation methods would probably improve the accuracy in agricultural areas. Some site-specific variables, such as improper well construction and local spills of contaminants, were not accounted for in the models. Accounting for ground-water flow direction was beyond the scope of this study. Depth to ground water was not evaluated by this study because a large-scale statewide coverage was not available. Depth to ground water may be an important coverage to develop for future studies., Access Constraints: None
Bbox East Long -101.475
Bbox North Lat 41.574
Bbox South Lat 36.424
Bbox West Long -109.813
Coupled Resource
Frequency Of Update notPlanned
Licence Although this data set has been used by the U.S. Geological Survey, U.S. Department of the Interior, no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data and related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of this data, software, or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Metadata Language
Metadata Type geospatial
Progress completed
Spatial Data Service Type
Spatial Reference System
Spatial Harvester True

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