[an error occurred while processing this directive] [an error occurred while processing this directive] [an error occurred while processing this directive]
[an error occurred while processing this directive]inher_gw | |
Data format: Raster Dataset File or table name: inher_gw Coordinate system: State Plane Coordinate System 1983 Theme keywords: Inherenent Vulnerability, soils, land use, land cover, ground water, slope, elevation |
|
Abstract:
This data set represents the ratings applied to the unsaturated
zone for North Carolina. It is one of 6 data
sets updated for the North Carolina Public Water Supply, Source
Water Assessment Program. These data are used to rate the susceptibility of
public water supplies in North Carolina to contamination.
The original dataset was produced in 2000. This version is updated to reflect new data sources.
The selected factors contributing to the unsaturated zone rating
for ground-water supplies include vertical series hydraulic conductance,
land-surface slope, land cover, and land use. For ground-water systems,
the higher the inherent vulnerability of the unsaturated zone, the
higher the rating applied on a scale of 10 to 100. |
Metadata elements shown with blue text are defined in the Federal Geographic Data Committee's (FGDC) Content Standard for Digital Geospatial Metadata (CSDGM). Elements shown with green text are defined in the ESRI Profile of the CSDGM. Elements shown with a green asterisk (*) will be automatically updated by ArcCatalog. ArcCatalog adds hints indicating which FGDC elements are mandatory; these are shown with gray text.
This data set represents the ratings applied to the unsaturated zone for North Carolina. It is one of 6 data sets updated for the North Carolina Public Water Supply, Source Water Assessment Program. These data are used to rate the susceptibility of public water supplies in North Carolina to contamination. The original dataset was produced in 2000. This version is updated to reflect new data sources. The selected factors contributing to the unsaturated zone rating for ground-water supplies include vertical series hydraulic conductance, land-surface slope, land cover, and land use. For ground-water systems, the higher the inherent vulnerability of the unsaturated zone, the higher the rating applied on a scale of 10 to 100.
The purpose of this data set is to rate the susceptibility to contamination of the unsaturated zone for public ground-water supplies.
The 1996 Amendments to the Safe Drinking Water Act require that each state prepare a source-water assessment for all public water supplies. States are required to (1) delineate source areas supplying wells and surface-water intakes, (2) inventory potential contaminant sources within the delineated source areas, and (3) determine the susceptibility of wells or intakes to the inventoried potential contaminant sources. In North Carolina, the lead agency charged with this task is the Public Water Supply Section (PWSS) of the Division of Environmental Health, Department of Environment and Natural Resources (DENR). North Carolina's Source Water Assessment Program (SWAP) provides assessments of each public drinking water intake in North Carolina. These assessments provide a relative susceptibility rating calculated using state-wide data. The U.S. Geological Survey (USGS) cooperated with the PWSS to provide components of the inherent vulnerability rating that was used with the contaminant rating to determine the overall susceptibility rating of source water supplies. To assist the PWSS with rating ground water inherent vulnerability, the USGS compiled the unsaturated zone rating based on the following characteristics: vertical hydraulic conductance, depth to water, land surface slope, land use and land cover. The watershed characteristic rating includes average annual precipitation, land surface slope, land use, land cover and groundwater contribution. The SWAP program has planned for updates to the initial ratings as conditions change and new data sources become available. The initial data used to calculate the unsaturated zone ratings and watershed characteristics ratings were compiled from sources from the late 1990's. Critical data layers have been updated since the ratings were calculated. These improved data layers need to be used in the ongoing update of the susceptibility ratings. Overlay and index methods for rating susceptibility to contamination of the unsaturated zone for ground-water suppplies, and watershed characteristics for surface-water supplies were derived for use by the State of North Carolina in assessing more than 11,000 public water-supply wells and approximately 245 public surface-water intakes. Factors that influence the inherent vulnerability of ground water and surface water were selected and assigned ratings on a scale of 1 to 10. These factors were then assigned weight to reflect their relative influence on inherent vulnerability and the reliability of the data. The values for each factor were obtained from geographic information system (GIS) data layers that were transformed into ARC/INFO raster data sets known as grids. These raster data sets have 30-meter by 30-meter cells, and each cell is assigned a weighted- factor value. Limitations -- The overlay and index methods of unsaturated zone and watershed characteristics ratings are broad-stroke methods that assess vulnerability on the basis of expert opinion. The methods aslo have limitations in the age and scale of the hydrologic and geographic data. But the most significant limitation of the methods used is that no statistical confirmation of the results have been performed. UNSATURATED ZONE RATING -- The relative unsaturated zone rating is based on a combination of factors that contribute to the likelihood that contaminants from surface and shallow sources will reach the water table by following the path of aquifer recharge. The selected factors, which are represented by GIS spatial-data layers, include vertical series conductance of the unsaturated zone, land-surface slope, land cover, and land use. The values of each of these four factors are categorized, and the categories are assigned a rating on a scale of 1 to 10. A rating of 1 reflects a low contribution to inherent vulnerability and 10 reflects a high contribution. For example, the rating for land-surface slope is low (1) in areas of high slope (greater than 50 percent) and high (10) in areas of low slope (less than 2 percent) because increased infiltration potential in flatter terrain leads to an increased likelihood of ground-water contamination. With the exception of land use, these factors describe influences on the physical transport of water, with or without contaminants. The land-use factor is included as a measure of the potential for generating nonpoint-source contamination at land surface. For the purpose of calculating the unsaturated zone rating, each of these four factors is weighted on the basis of importance of the factor in determining vulnerability. Vertical series conductance and land use are weighted more heavily than are land-surface slope and land cover. For each cell, the product of the factor weights and ratings are summed to determine the total rating for the cell, resulting in a relative numerical unsaturated zone rating that ranges from 10 to 100 for each cell. >Factors contributing to the unsaturated zone rating. > >Description Weight > >Vertical series conductance of the unsaturated zone 3 >The harmonic mean of a series of layers of unsaturated >material provides a single value for the capacity of the >entire sequence of the unsaturated zone to transmit water >(with or without contaminants) from the land surface to >the water table. > >Land-surface slope 2 >The inclination or slope of the land surface indicates >the likelihood that precipitation will infiltrate or >run off. > >Land cover 2 >The type of material covering the land surface >influences the likelihood that precipitation will >infiltrate into the ground or run off the land surface. > >Land use 3 >The type of land use influences the likelihood of >potential nonpoint-source contamination. > SELECTED REFERENCES: Eimers, J. L., Weaver, J. C., Terziotti, S., and Midgette, R. W., 2000, Methods of rating unsaturated zone and watershed characteristics of public water supplies in North Carolina: U. S. Geological Survey Water-Resources Investigations Report 99-4283, 31 p. Heath, R. C., 1994, Ground water recharge in North Carolina: Groundwater Section, North Carolina Department of Environmental Management, informal report, 52 p. North Carolina Department of Environment and Natural Resources, 1999, North Carolina source water assessment program plan: Raleigh, North Carolina Department of Environment and Natural Resources, Division of Environmental Health, Public Water Supply Section, [variously paged]. DISCLAIMER: Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this Federal Geographic Data Committee-compliant metadata file is intended to document the data set in nonproprietary form, as well as in ARC/INFO format, this metadata file may include some ARC/INFO-specific terminology.
Ground Condition
Not to be used for site specific analysis
3916 Sunset Ridge Road
The authors are grateful to colleagues in the Public Water Supply Section of the Division of Environmental Health, North Carolina Department of Environment and Natural Resources (DENR) for their assistance in this collaborative project: thanks to Robert Midgette, Protection and Enforcement Branch Head; Amy Axon,hydrogeologist - Source Water Protection; and David Hammermann, Geographic Information Systems Specialist. The authors also thank the USGS report review team for their review of the update procedures: Jeanne Robbins, Surface-water Specialist; Melinda Chapman, Ground-water Specialist; Mary Giorgino, Water-quality Specialist; and Douglas Harned, ALBE-National Water Quality Assessment Project Chief
visually verified against original source
Not applicable for raster data.
Completed for the State of North Carolina.
visually verified
methods for applying ratings
Create a grid based on the weighted values of the contributing factors. inher_gw = ( ..\landcover\landcovergw * 2 ) + ( ..\landuse\landusegw * 3 ) + ( ..\soils\condgw * 3 ) + ( ..\slope\slopegw * 2 )
First draft of metadata created by seterzio using FGDCMETA.AML ver. 1.33 07/15/99 on ARC/INFO data set h:\gw_layers\inher_gw
Metadata imported.
Internal feature number.
ESRI
> >Value attribute table, INHER_GW.VAT: > >COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME > 1 VALUE 4 10 B - > 5 COUNT 4 10 B - > VALUE is rating between 10 and 100. COUNT is the number of 30 meter by 30 meter cells that have the value in positive integers. In the final data set, the values range from 12 to 84. >Summary statistics table, INHER_GW.STA: > >COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME > 1 MIN 8 15 F 3 > 9 MAX 8 15 F 3 > 17 MEAN 8 15 F 3 > 25 STDV 8 15 F 3 MIN is the minimum value. MAX is the maximum value. MEAN is the average value. STDV is the standard deviation. > MIN MAX MEAN STDV >12.000 84.000 52.873 10.973
none
3916 Sunset Ridge Rd.
Contact via email
Although these data have 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. 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.
3916 Sunset Ridge Road