Arsenic in Ground Water of the United States

Metadata:

• Identification_Information
• Data_Quality_Information
• Spatial_Data_Organization_Information
• Spatial_Reference_Information
• Entity_and_Attribute_Information
• Distribution_Information
• Metadata_Reference_Information

Identification_Information:

Citation:

Citation_Information:

Originator: U.S. Geological Survey

Publication_Date: 200212

Title: Arsenic in Ground Water of the United States

Publication_Information:

Publication_Place: Reston, VA

Publisher: National Atlas of the United States

Online_Linkage: <http://nationalatlas.gov/atlasftp.html>

Description:

Abstract:

This image shows national-scale patterns of naturally occurring arsenic in potable ground-water resources of the continental United States. The image was generated from the most recent arsenic measurement available for each of 31,350 wells and springs across the United States. Over 20,000 of the water samples were collected by the U.S. Geological Survey between 1973 and 2001. The remainder of the samples were collected by State agencies and analyzed by comparable laboratory techniques. The data set shows a moving 75th percentile, which can also be described as the maximum arsenic concentration found in 75% of samples within a moving 50 km radius (the median size of a U.S. county). In other words, for any given 50-km-radius region in the data, lower concentrations of arsenic were found in 75% of sampled wells, while higher concentrations of arsenic were found in 25% of sampled wells. This is a revised version of the August 2002 map layer, with a corrected shoreline for Greenland.

Purpose:

This map layer is intended to provide national-scale, broad-brush answers to questions such as, "Where in the country might at least 25 percent of wells have high arsenic concentrations?" The data should be displayed and analyzed at scales appropriate for 1:2,000,000-scale data.

The data should not be used to infer an arsenic concentration for an individual well. Although the data set shows that concentrations of arsenic are likely to be higher in certain geographic regions relative to others, there can be a high degree of local variability because of factors such as the well’s depth, the type of aquifer used by the well, and local geology and water chemistry. The only way to be certain of the arsenic concentration in the water supplied by any given well is to have the water tested.

No responsibility is assumed by the U.S. Geological Survey in the use of these data.

Supplemental_Information:

Some of the samples came from individual homeowner wells used, without treatment, for drinking water. Other samples came from wells supplying water for irrigation and other purposes. The data set does not include samples of saline or thermal water; all the samples represent aquifers used for drinking water supply, even if the specific well was not used to supply drinking water.

The intent of this study was to describe the quality of the untreated ground-water resource itself, rather than to directly measure the quality of drinking water by monitoring water from taps and other "finished" water. Comparisons of these findings with those from previous drinking-water studies indicate that the concentrations reported here are comparable on a national scale to concentrations in untreated ground water tapped by water utilities across the Nation. These findings also reflect the quality of the ground-water tapped without treatment by homeowners and small community water systems.

Arsenic concentrations are measured in units of micrograms per liter (ug/L), which is equivalent to parts per billion.

The following table describes the display of the 75th percentile of arsenic concentrations in the GeoTIFF image:

 Arsenic              Color         RGB values
 Concentration
----------------------------------------------------------------
  1 ug/L or less      dark green     50.67328 150.3464   0.67328
  3 ug/L              light green   152       251      152
  5 ug/L              yellow        255       255        0
 10 ug/L              orange        255       165        0
 50 ug/L or greater   red           255         0        0
 Insufficient data    white         255       255      255
 Non-US land          grey          204       204      204
 Water                light blue    132       193      255

Further information on arsenic in ground water is available from the USGS Water Resources Discipline page about Arsenic in ground water in the United States, at <http://water.usgs.gov/nawqa/trace/arsenic/>.

The associated world file is included as part of the GeoTIFF. The contents of the world file are:

1000.0000
0.000000
0.000000
-1000.0000
-6086629.0000
4488761.0000

Time_Period_of_Content:

Time_Period_Information:

Range_of_Dates/Times:

Beginning_Date: 1973

Ending_Date: 200111

Currentness_Reference: Ground condition

Status:

Progress: Complete

Maintenance_and_Update_Frequency: None planned

Spatial_Domain:

Bounding_Coordinates:

West_Bounding_Coordinate: 166

East_Bounding_Coordinate: -4

North_Bounding_Coordinate: 83

South_Bounding_Coordinate: 15

Keywords:

Theme:

Theme_Keyword_Thesaurus: ISO 19115 Topic Category

Theme_Keyword: Geoscientific Information

Theme_Keyword: Environment

Theme:

Theme_Keyword_Thesaurus: None

Theme_Keyword: Arsenic

Theme_Keyword: Water

Theme_Keyword: Ground water

Theme_Keyword: Groundwater

Theme_Keyword: Well

Theme_Keyword: Drinking water

Theme_Keyword: Environment

Theme_Keyword: Water quality

Place:

Place_Keyword_Thesaurus: None

Place_Keyword: North America

Place_Keyword: United States

Place_Keyword: Puerto Rico

Place_Keyword: Alabama

Place_Keyword: Alaska

Place_Keyword: Arizona

Place_Keyword: Arkansas

Place_Keyword: California

Place_Keyword: Colorado

Place_Keyword: Connecticut

Place_Keyword: Delaware

Place_Keyword: District of Columbia

Place_Keyword: Florida

Place_Keyword: Georgia

Place_Keyword: Idaho

Place_Keyword: Illinois

Place_Keyword: Indiana

Place_Keyword: Iowa

Place_Keyword: Kansas

Place_Keyword: Kentucky

Place_Keyword: Louisiana

Place_Keyword: Maine

Place_Keyword: Maryland

Place_Keyword: Massachusetts

Place_Keyword: Michigan

Place_Keyword: Minnesota

Place_Keyword: Mississippi

Place_Keyword: Missouri

Place_Keyword: Montana

Place_Keyword: Nebraska

Place_Keyword: Nevada

Place_Keyword: New Hampshire

Place_Keyword: New Jersey

Place_Keyword: New Mexico

Place_Keyword: New York

Place_Keyword: North Carolina

Place_Keyword: North Dakota

Place_Keyword: Ohio

Place_Keyword: Oklahoma

Place_Keyword: Oregon

Place_Keyword: Pennsylvania

Place_Keyword: Rhode Island

Place_Keyword: South Carolina

Place_Keyword: South Dakota

Place_Keyword: Tennessee

Place_Keyword: Texas

Place_Keyword: Utah

Place_Keyword: Vermont

Place_Keyword: Virginia

Place_Keyword: Washington

Place_Keyword: West Virginia

Place_Keyword: Wisconsin

Place_Keyword: Wyoming

Access_Constraints: None.

Use_Constraints:

None. Acknowledgment of the National Atlas of the United States and (or) the U.S. Geological Survey would be appreciated in products derived from these data.

Point_of_Contact:

Contact_Information:

Contact_Organization_Primary:

Contact_Organization:

National Water-Quality Assessment Program, 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: 703-648-5716

Contact_Electronic_Mail_Address: nawqa_whq@usgs.gov

Data_Set_Credit:

This image incorporates field data collected by the U.S. Geological Survey, the Maine Department of Health, the Massachusetts Department of Environmental Protection, the Minnesota Pollution Control Agency, the New Hampshire Department of Environmental Services, the Rhode Island Department of Health, the Texas Water Development Board, and the Wisconsin Department of Natural Resources.

Native_Data_Set_Environment:

RGB (24-bit) compressed TIFF format created using Arc/INFO 8.0.2.

Data_Quality_Information:

Logical_Consistency_Report:

No tests for logical consistency have been performed on this map layer. The data samples were collected from a variety of agencies over a span of 28 years, but were all processed with comparable laboratory techniques.

Completeness_Report:

This map layer includes arsenic measurements from ground water in 49 States and Puerto Rico. Arsenic data were not available for the Hawaiian Islands.

Lineage:

Source_Information:

Source_Citation:

Citation_Information:

Originator: Ryker, S.J.

Publication_Date: 2001

Title: Mapping arsenic in ground water

Series_Information:

Series_Name: Geotimes Newsmagazine of the Earth Sciences

Issue_Identification: v. 46, no. 11, p. 34-36

Publication_Information:

Publication_Place: Richmond, VA

Publisher: American Geological Institute

Type_of_Source_Media: Journal article

Source_Time_Period_of_Content:

Time_Period_Information:

Single_Date/Time:

Calendar_Date: 2002

Source_Currentness_Reference: Publication date

Source_Citation_Abbreviation: USARSENIC

Source_Contribution:

National distribution of arsenic concentrations in ground water.

Source_Information:

Source_Citation:

Citation_Information:

Originator: USDA Forest Service

Originator: U.S. Geological Survey

Publication_Date: 200205

Title: Forest Cover Types

Publication_Information:

Publication_Place: Reston, VA

Publisher: National Atlas of the United States

Type_of_Source_Media: Online

Source_Time_Period_of_Content:

Time_Period_Information:

Single_Date/Time:

Calendar_Date: 2000

Source_Currentness_Reference: Publication date

Source_Citation_Abbreviation: Atlas-FCT

Source_Contribution: Background and shoreline.

Source_Information:

Source_Citation:

Citation_Information:

Originator: U.S. Geological Survey

Publication_Date: 200208

Title: Arsenic in Ground Water of the United States

Publication_Information:

Publication_Place: Reston, VA

Publisher: National Atlas of the United States

Type_of_Source_Media: Online

Source_Time_Period_of_Content:

Time_Period_Information:

Range_of_Dates/Times:

Beginning_Date: 1973

Ending_Date: 200111

Source_Currentness_Reference: Ground condition

Source_Citation_Abbreviation: Atlas-AR200208

Source_Contribution: Spatial and attribute information.

Source_Information:

Source_Citation:

Citation_Information:

Originator: National Imagery and Mapping Agency

Publication_Date: 1990

Title: World Vector Shoreline

Publication_Information:

Publication_Place: Bethesda, MD

Publisher: National Imagery and Mapping Agency

Online_Linkage: <http://www.ngdc.noaa.gov/mgg/shorelines/shorelines.html>

Type_of_Source_Media: Online

Source_Time_Period_of_Content:

Time_Period_Information:

Single_Date/Time:

Calendar_Date: 1990

Source_Currentness_Reference: Publication date

Source_Citation_Abbreviation: WVS

Source_Contribution: Shoreline information.

Process_Step:

Process_Description:

A detailed description of how this map layer was created, and discussion on interpreting the map layer, may be found in USARSENIC. Information on sources is included under Data Set Credit, above.

The area of the United States was divided into a grid using equal-area hexagons 100 kilometers across (the median size of a U.S. county). For areas with a minimum data density of five wells per hexagon, the 75th percentile of arsenic concentration was computed. A moving 75th percentile was then approximated by "smoothing" across hexagon boundaries based on neighboring values.

Source_Used_Citation_Abbreviation: USARSENIC

Process_Date: 2001

Process_Step:

Process_Description:

The map layer was projected to a Lambert Azimuthal Equal Area projection, merged with the background information from Atlas- FCT, and converted to a GeoTIFF image.

Source_Used_Citation_Abbreviation: USARSENIC

Source_Used_Citation_Abbreviation: Atlas-FCT

Process_Date: 2002

Source_Produced_Citation_Abbreviation: Atlas-AR200208

Process_Step:

Process_Description:

The coastline of Greenland was replaced by a new, corrected version derived from World Vector Shoreline (WVS). This image contains no thematic data for Greenland; the new data were inserted only to maintain consistency with other National Atlas data layers.

Source_Used_Citation_Abbreviation: Atlas-AR200208

Source_Used_Citation_Abbreviation: WVS

Process_Date: 200212

Spatial_Data_Organization_Information:

Direct_Spatial_Reference_Method: Raster

Raster_Object_Information:

Raster_Object_Type: Grid Cell

Row_Count: 7273

Column_Count: 10366

Spatial_Reference_Information:

Horizontal_Coordinate_System_Definition:

Planar:

Map_Projection:

Map_Projection_Name: Lambert Azimuthal Equal Area

Lambert_Azimuthal_Equal_Area:

Longitude_of_Projection_Center: -100.00

Latitude_of_Projection_Center: 45.00

False_Easting: 0.0

False_Northing: 0.0

Planar_Coordinate_Information:

Planar_Coordinate_Encoding_Method: Row and column

Coordinate_Representation:

Abscissa_Resolution: 1000.0

Ordinate_Resolution: 1000.0

Planar_Distance_Units: Meters

Geodetic_Model:

Horizontal_Datum_Name: None

Ellipsoid_Name: Sphere

Semi-major_Axis: 6370997.0

Denominator_of_Flattening_Ratio: 1.0

Entity_and_Attribute_Information:

Detailed_Description:

Entity_Type:

Entity_Type_Label: Arsenic concentration grid cell

Entity_Type_Definition:

Any of the grid cell elements in the arsenic concentration raster file.

Entity_Type_Definition_Source: U.S. Geological Survey

Attribute:

Attribute_Label: Arsenic concentration grid cell value.

Attribute_Definition:

Each grid cell value is a color definition that represents an estimate of the 75th percentile of arsenic concentration in that region. The concentrations were recorded in micrograms per liter (ug/L; equivalent to parts per billion), and were converted to colors according to the following table. All arsenic concentrations greater than 50 micrograms per liter were recoded as 50 micrograms per liter. There may be intermediate colors in the image that are not included in this table.

 Arsenic             Color        RGB values
 Concentration
--------------------------------------------------------------
  1 ug/L or less     dark green    50.67328 150.3464   0.67328
  3 ug/L             light green  152       251      152
  5 ug/L             yellow       255       255        0
 10 ug/L             orange       255       165        0
 50 ug/L or greater  red          255         0        0
 Insufficient data   white        255       255      255
 Non-US land         grey         204       204      204
 Water               light blue   132       193      255

Attribute_Definition_Source: U.S. Geological Survey

Attribute_Domain_Values:

Range_Domain:

Range_Domain_Minimum: 0

Range_Domain_Maximum: 255

Distribution_Information:

Distributor:

Contact_Information:

Contact_Organization_Primary:

Contact_Organization: Earth Science Information Center, U.S. Geological Survey

Contact_Address:

Address_Type: Mailing address

Address: 507 National Center

City: Reston

State_or_Province: VA

Postal_Code: 20192

Country: USA

Contact_Voice_Telephone: 1-888-ASK-USGS (1-888-275-8747)

Contact_Voice_Telephone: 703-648-5920

Contact_Instructions:

In addition to the address above there are other ESIC offices throughout the country. A full list of these offices is at <http://geography.usgs.gov/esic/esic_index.html>.

Distribution_Liability:

Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made by the U.S. Geological Survey regarding the utility of the data on any other system, nor shall the act of distribution constitute any such warranty. No responsibility is assumed by the U.S. Geological Survey in the use of these data.

Standard_Order_Process:

Digital_Form:

Digital_Transfer_Information:

Format_Name: TIFF

Digital_Transfer_Option:

Online_Option:

Computer_Contact_Information:

Network_Address:

Network_Resource_Name: <http://nationalatlas.gov/atlasftp.html>

Fees:

There is no charge for the map layer.

Metadata_Reference_Information:

Metadata_Date: 20050923

Metadata_Contact:

Contact_Information:

Contact_Person_Primary:

Contact_Person: Peg Rawson

Contact_Address:

Address_Type: Mailing address

Address: 12201 Sunrise Valley Drive

Address: MS-561

City: Reston

State_or_Province: VA

Postal_Code: 20192

Country: USA

Contact_Voice_Telephone: 703-648-4183

Contact_Electronic_Mail_Address: atlasmail@usgs.gov

Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata

Metadata_Standard_Version: FGDC-STD-001-1998

Metadata_Security_Information:

Metadata_Security_Classification_System: None

Metadata_Security_Classification: Unclassified

Metadata_Security_Handling_Description: None