University of Florida

Suwannee Hydrologic Observatory University of Florida - IFAS

Base Layers and Information: Geology/Soils Topography

Risk of nitrate contamination in groundwaters of the United States-- A national perspective

Metadata:

Identification Information:
Citation:
Citation Information:
Originator: Nolan, B.T., Ruddy, B.C., Hitt, K.J., and Helsel, D.R.
Publication Date: 1997
Title:
Risk of nitrate contamination in groundwaters of the United States-- A national perspective
Edition: 2
Geospatial Data Presentation Form: Map
Series Information:
Series Name: Environmental Science and Technology [Hard copy]
Issue Identification: Volume 31, Number 8, Pages 2229-2236
Publication Information:
Publication Place: Reston, Virginia, USA [Digital spatial data]
Publisher: U.S. Geological Survey [Digital spatial data]
Online Linkage: <URL:http://water.usgs.gov/lookup/getspatial?gwrisk>
Description:
Abstract:

Nitrate contamination of ground water occurs in patterns based on "input" factors (population density and nitrate contribution from fertilizer, manure, and atmospheric deposition) and "aquifer vulnerability" factors (soil drainage characteristic and woodland/cropland ratio in agricultural areas). Areas with high nitrogen input, well-drained soils, and low woodland to cropland ratio have the highest potential for contamination of ground water. The patterns of risk for nitrate contamination of ground water were compiled in a national map as described in Nolan and others (1997). The digital version of the national map is included here.

The risk patterns still are being refined as better data sets become available, and this map should not be considered to be the "final" version of the patterns.

Purpose:

This map was designed to present patterns of risk for nitrate contamination at large regional or national scales. Knowing where and what type of risks to ground water exist can alert water-resources managers and private users of the need to protect water supplies. By targeting regions with the highest risk of nitrate contamination, resources can be directed to areas most likely to benefit from pollution-prevention programs and long-term monitoring.

Supplemental Information:

Procedures Used:

Soil drainage characteristic was determined from data on soil hydrologic group in the STATSGO (State Soil Geographic) data base (U.S. Soil Conservation Service, 1994a,b). The STATSGO categorical values for hydrologic group were converted to numbers in order to generalize (by area-weighted average) the hydrologic group for each soil map unit. The threshold level of 2.5 was determined; soils with a value less than 2.5 were considered to be well-drained soils (similar to the STATSGO hydrologic group values of A or B) and soils with a value greater than or equal to 2.5 were considered to be poorly-drained soils (similar to the STATSGO hydrologic group values of C or D). The original map unit level data was converted from a coverage (vector data) to a grid in order to facilitate overlaying the data layers using ARC/INFO GRID processing. The grid was divided into 2 groups, those cells having a hydrologic group value less than 2.5 and those cells having a hydrologic group value greater than or equal to 2.5.

The extent of woodland and cropland in agricultural areas was compiled from the 1992 Census of Agriculture (U.S. Bureau of the Census, 1995) in which the acres of woodland and cropland are compiled by county. The woodland to cropland ratio was calculated by dividing the acres of woodland by the acres of cropland. The ratio represents the extent of woodland in relation to cropland in agricultural areas of the Southeast, where dilution, denitrification, and vegetative uptake likely attenuate nitrate concentration in ground water. This county level information was converted from a coverage to a grid in order to facilitate overlaying the data layers. The grid was divided into 2 groups, those cells having a woodland/cropland ratio less than 0.3 and those cells having a woodland/cropland ratio greater than or equal to 0.3.

Population density was determined from 1990 population data compiled by census block group (U.S. Bureau of the Census, 1991) and was calculated for each census block group by dividing the number of people in the block group by the land area of the block group. This census block group information was converted from a coverage to a grid in order to facilitate overlaying the data layers. The grid was divided into 2 groups, those cells having greater than 386 people per square kilometer and those cells having less than or equal to 386 people per square kilometer.

Nitrogen loading was determined by combining nitrogen input from fertilizer (Battaglin and Goolsby, 1994), manure (Smith and others, 1997), and atmospheric deposition (Smith and others, 1997). This county level nitrogen data was converted from a coverage to a grid in order to facilitate overlaying the data layers. The grid was divided into 2 groups, those cells having greater than 2,100 kilograms per square kilometer and those cells have less than or equal to 2,100 kilograms per square kilometer.

These four grids were combined into one output grid. The sixteen values from the input grids were consolidated into four risk categories for nitrate contamination of ground water in the conterminous United States:

Group 4 -- high -- nitrogen loading greater than 2,100 kilograms per square kilometer or population density greater than 386 people per square kilometer; hydrologic group less than 2.5 and woodland to cropland ratio less than 0.3.

Group 3 -- moderately high -- nitrogen loading greater than 2,100 kilograms per square kilometer or population density greater than 386 people per square kilometer; hydrologic group greater than or equal to 2.5 or woodland to cropland ratio greater than or equal to 0.3.

Group 2 -- moderately low -- nitrogen loading less than or equal to 2,100 kilograms per square kilometer and population density less than or equal to 386 people per square kilometer; hydrologic group less than or equal to 2.5 and woodland to cropland ratio less than 0.3.

Group 1 -- low -- nitrogen loading less than or equal to 2,100 kilograms per square kilometer and population density less than or equal to 386 people per square kilometer; hydrologic group greater than or equal to 2.5 or woodland to cropland ratio greater than or equal to 0.3.

Revisions:

The previous version of this map was published in Nolan and Ruddy (1996).

Reviews Applied to Data:

The procedures were reviewed internally. The report was colleague reviewed.

Ground water nitrate data collected through 1992 from wells less than 100 feet deep generally verified the risk patterns shown in the national map.

Related Spatial and Tabular Data Sets:

The data set is provided in ascii format as well as exported ARC/INFO GRID format. In the ascii file, only the field called "S1" is included. The field called "VALUE" is not included. The projection file needed for the ascii format of the data set is: 

Projection    ALBERS
Datum         NAD27
Zunits        NO
Units         METERS
Spheroid      CLARKE1866
Xshift        0.0000000000
Yshift        0.0000000000
Parameters
 29 30  0.000 /* 1st standard parallel
 45 30  0.000 /* 2nd standard parallel
-96  0  0.000 /* central meridian
 23  0  0.000 /* latitude of projection's origin
0.00000 /* false easting (meters)
0.00000 /* false northing (meters)
The retrospective database for nutrients in ground water and surface water is available through the internet at <URL:http://wwwrvares.er.usgs.gov/nawqa/nutrients/datasets/retrodata.html>.

The current version of the map also appears in Nolan and others (1998), which is available through the internet at <URL:http://wwwrvares.er.usgs.gov/nawqa/wcp/index.html>.

Other References Cited:

Battaglin, W.A., and Goolsby, D.A., 1994, Spatial data in GIS format on agricultural chemical use, land use, and cropping practices in the United States. Available through the internet at <URL:http://water.usgs.gov/lookup/getmeta?nit87>.

Nolan, B.T., and Ruddy, B.C., 1996, Nitrate in ground waters of the United States--Assessing the risk: U.S. Geological Survey Fact Sheet FS-092-96, Reston, Va. Available through the internet at <URL:http://wwwrvares.er.usgs.gov/nawqa/FS-092-96.html>.

Nolan, B.T., Ruddy, B.C., Hitt, K.J., and Helsel, D.R., 1997, Risk of nitrate contamination in groundwaters of the United States--A national perspective: Environmental Science and Technology, v. 31, no. 8, pages 2229-2236.

----- 1998, A national look at nitrate contamination of groundwater: Water conditioning and purification, v. 39, no. 12, pages 76-79. Available through the internet at <URL:http://wwwrvares.er.usgs.gov/nawqa/wcp/index.html>.

Smith, R.A,. Schwartz, G.E., and Alexander, R.B., 1997, Regional interpretation of water-quality monitoring data: Water Resources Research, v. 33, no. 12 [in press].

U.S. Bureau of the Census, 1991, 1990 Census of Population and Housing, Public Law 94-171 Data (United States): The Bureau, Washington D.C. (machine-readable files)

----- 1995, 1992 Census of Agriculture: The Bureau, Washington, D.C. (machine-readable files).

U.S. Soil Conservation Service, 1994a, State Soil Geographic (STATSGO) data base for the United States and Puerto Rico (CDROM): U.S. Department of Agriculture, Soil Conservation Service, Ft. Worth, Texas. Available through the internet at <URL:http://www.ftw.nrcs.usda.gov/stat data.html>.

----- 1994b, State Soil Geographic (STATSGO) data base--Data use information: Misc. Publication No. 1492, National Soil Survey Center, Lincoln, Nebraska. Available through the internet at <URL:http://www.ftw.nrcs.usda.gov/stat data.html>.

Time Period of Content:
Time Period Information:
Single Date/Time:
Calendar Date: 1997
Currentness Reference:

Current as of publication date.

Status:
Progress: Complete
Maintenance and Update Frequency:

The risk patterns still are being refined as better data sets become available, and this map should not be considered to be the "final" version of the patterns. The map will be updated as necessary to reflect continual improvements in the procedures to define the risk patterns.

Spatial Domain:
Bounding Coordinates:
West Bounding Coordinate: -129.49561904
East Bounding Coordinate: -64.43926745
North Bounding Coordinate: 48.6335631
South Bounding Coordinate: 21.80790306
Keywords:
Theme:
Theme Keyword Thesaurus: None
Theme Keyword: Ground water contamination
Theme Keyword: Ground water pollution
Theme Keyword: Nutrients
Theme Keyword: Nitrates
Theme Keyword: Ground water vulnerability
Theme Keyword: National Water-Quality Assessment (NAWQA)
Place:
Place Keyword Thesaurus: None
Place Keyword: Conterminous United States
Stratum:
Stratum Keyword Thesaurus: None
Stratum Keyword: None
Temporal:
Temporal Keyword Thesaurus: None
Temporal Keyword: None
Access Constraints:

None.

Use Constraints:

None.

Browse Graphic:
Browse Graphic File Name: < URL:http://wwwrvares.er.usgs.gov/nawqa/wcp/wcpfig1.html>
Browse Graphic File Description:
This is an image (95 KB) of the national map showing the patterns of risk for nitrate contamination of ground water that appears in Nolan and others (1998).
Browse Graphic File Type: GIF
Point of Contact:
Contact Information:
Contact Person Primary:
Contact Person: Barbara C. Ruddy
Contact Organization: U.S. Geological Survey
Contact Address:
Address Type: mailing address
Address: Bldg. 53, Denver Federal Center, Mail Stop 415, Box 25046
City: Lakewood
State or Province: CO
Postal Code: 80225
Country: USA
Contact Voice Telephone: 303-236-2101 x273
Contact Facsimile Telephone: 303-236-4912
Contact Electronic Mail Address: bcruddy@usgs.gov
Hours of Service: 8:00am-4:30pm MST
Contact Instructions: Please contact thru email
Native Data Set Environment:
dgux, 5.4R3.10, AViiON UNIX, ARC/INFO version 7.0.4
Data Quality Information:
Logical Consistency Report: Not applicable for raster data.
Completeness Report: See supplemental information.
Lineage:
Process Step:
Process Description:
Version 1 of the ground water risk map published in USGS fact sheet FS-092-96.
Process Date: 1996
Process Step:
Process Description:
Version 2 of the ground water risk map published in ES&T article.
Process Date: 1997
Spatial Data Organization Information:
Direct Spatial Reference Method: Raster
Raster Object Information:
Raster Object Type: Grid Cell
Row Count: 3058
Column Count: 4771
Spatial Reference Information:
Horizontal Coordinate System Definition:
Planar:
Map Projection:
Map Projection Name: Albers Conical Equal Area
Albers Conical Equal Area:
Standard Parallel: 45.5
Standard Parallel: 45.5
Longitude of Central Meridian: -96
Latitude of Projection Origin: 23
False Easting: 0.00000
False Northing: 0.00000
Planar Coordinate Information:
Planar Coordinate Encoding Method: coordinate pair
Coordinate Representation:
Abscissa Resolution: 1.0
Ordinate Resolution: 1.0
Planar Distance Units: METERS
Geodetic Model:
Horizontal Datum Name: North American Datum of 1927
Ellipsoid Name: Clarke 1866
Semi-major Axis: 6378206.4
Denominator of Flattening Ratio: 294.98
Entity and Attribute Information:
Detailed Description:
Entity Type:
Entity Type Label: ESTGRD.VAT
Entity Type Definition: Value attribute table
Entity Type Definition Source: GIS software
Attribute:
Attribute Label: VALUE
Attribute Definition:
Value from 1-16 assigned according to values in original 4 input grids
Attribute Definition Source: Assigned
Attribute Domain Values:
Enumerated Domain:
Enumerated Domain Value: 1-16
Enumerated Domain Value Definition: Thresholds
Enumerated Domain Value Definition Source:
Computed from 4 input grids each with 2 values
Attribute:
Attribute Label: COUNT
Attribute Definition: Number of GRID cells that contain each VALUE
Attribute Definition Source: Computed
Attribute Domain Values:
Enumerated Domain:
Enumerated Domain Value: Integer
Enumerated Domain Value Definition: Postive number
Enumerated Domain Value Definition Source: n/a
Attribute:
Attribute Label: S1
Attribute Definition: Risk group
Attribute Definition Source: Computed
Attribute Domain Values:
Enumerated Domain:
Enumerated Domain Value:
1 = low; 2 = moderately low; 3 = moderately high; 4 = high.
Enumerated Domain Value Definition:
The 4 risk groups were consolidated from the 16 original values.
Enumerated Domain Value Definition Source: See "Procedures Used"
Entity Type:
Entity Type Label: ESTGRD.STA
Entity Type Definition: Statistics table
Entity Type Definition Source: GRID
Attribute:
Attribute Label: MIN
Attribute Definition: Minimum GRID cell VALUE
Attribute Definition Source: Computed
Attribute Domain Values:
Enumerated Domain:
Enumerated Domain Value: 1
Enumerated Domain Value Definition: Computed
Enumerated Domain Value Definition Source: n/a
Attribute:
Attribute Label: MAX
Attribute Definition: Maximum GRID cell VALUE
Attribute Definition Source: Computed
Attribute Domain Values:
Enumerated Domain:
Enumerated Domain Value: 16
Enumerated Domain Value Definition: Computed
Enumerated Domain Value Definition Source: n/a
Attribute:
Attribute Label: MEAN
Attribute Definition: Mean GRID cell VALUE
Attribute Definition Source: Computed
Attribute Domain Values:
Enumerated Domain:
Enumerated Domain Value: 5.617
Enumerated Domain Value Definition: Computed
Enumerated Domain Value Definition Source: n/a
Attribute:
Attribute Label: STDV
Attribute Definition: Standard Deviation of GRID cell VALUEs
Attribute Definition Source: Computed
Attribute Domain Values:
Enumerated Domain:
Enumerated Domain Value: 3.536
Enumerated Domain Value Definition: Computed
Enumerated Domain Value Definition Source: n/a
Overview Description:
Entity and Attribute Overview:

The attributes in the VAT (value attribute table) are: 

VALUE
COUNT
S1
VALUE is a number from 1-16 assigned according to values in the original four input grids (soil drainage characteristic, woodland/cropland ratio, population density, and nitrogen loading). Each input grid had two values - one value for "above" the threshold and the other value for "below" the threshold.

COUNT is the number of grid cells having a particular value.

S1 is the risk group. Four risk groups were consolidated from the 16 values. 1 = low; 2 = moderately low; 3 = moderately high; 4 = high.

Entity and Attribute Detail Citation: Not Available
Distribution Information:
Distributor:
Contact Information:
Contact Organization Primary:
Contact Organization: U.S. Geological Survey
Contact Person: Kerie J. Hitt
Contact Address:
Address Type: mailing address
Address: 12201 Sunrise Valley Drive, MS 413
City: Reston
State or Province: VA
Postal Code: 20192
Country: USA
Contact Voice Telephone: 703-648-6854
Contact Electronic Mail Address: kjhitt@usgs.gov
Contact Instructions: Please use email.
Distribution Liability: None.
Standard Order Process:
Digital Form:
Digital Transfer Information:
Format Name: ARCE and ASCII
File Decompression Technique: gzip -d; gunzip
Digital Transfer Option:
Ordering Instructions: Available via ftp.
Fees: None
Metadata Reference Information:
Metadata Date: 19980402
Metadata Contact:
Contact Information:
Contact Person Primary:
Contact Person: Kerie J. Hitt
Contact Organization: U.S. Geological Survey
Contact Address:
Address Type: mailing address
Address: 12201 Sunrise Valley Drive, MS-413
City: Reston
State or Province: VA
Postal Code: 20192
Country: USA
Contact Voice Telephone: 703-648-6854
Contact Facsimile Telephone: 703-648-5295
Contact Electronic Mail Address: kjhitt@usgs.gov
Hours of Service: 9:00am-5:30pm EST
Contact Instructions: Please contact thru email
Metadata Standard Name:
FGDC Content Standards for Digital Geospatial Metadata
Metadata Standard Version: 19940608
Metadata Time Convention: Local Time
Metadata Security Information:
Metadata Security Classification System: None
Metadata Security Classification: Unclassified
Metadata Security Handling Description: None

Generated by mp on Thu Apr 2 16:55:30 1998