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[an error occurred while processing this directive]condgw | |
Data format: Raster Dataset File or table name: condgw Coordinate system: State Plane Coordinate System 1983 Theme keywords: Vertical Series Hydraulic Conductance, Soils, Permeability, Vulnerability |
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Abstract:
Vertical series hydraulic conductance classes 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.
This data set represents the ratings applied to conductance classes
for use in the rating of the unsaturated zone for public ground-water
suppliers.
The harmonic mean hydraulic conductance 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.
For ground-water systems, the higher the conductance of the
unsaturated zone, the higher the rating applied on a scale of
1 to 10. |
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.
Vertical series hydraulic conductance classes 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. This data set represents the ratings applied to conductance classes for use in the rating of the unsaturated zone for public ground-water suppliers. The harmonic mean hydraulic conductance 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. For ground-water systems, the higher the conductance of the unsaturated zone, the higher the rating applied on a scale of 1 to 10.
This data set is to be used in a hydrologic analysis with other data sets to rate the unsaturated zone for public ground-water supplies and watershed characteristics for public surface-water supplies in North Carolina. For ground-water supplies, the factors used to rate susceptibility to contamination include vertical hydraulic conductance, land-surface slope, land cover, and land use. The selected factors used to devise ratings for surface-water supplies' susceptibility to contamination are average annual precipitation, land-surface slope, land cover, land use, and ground-water contribution.
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. VERTICAL SERIES HYDRAULIC CONDUCTANCE: The vertical series hydraulic conductance (also referred to as conductance) layer is calculated for the entire thickness of the unsaturated zone. The entire thickness of the unsaturated zone includes a soil layer, and may include a saprolite and crystalline bedrock layer depending on the depth to water at any point. To calculate the conductance value, thickness of soils, depth to bedrock and soil conductance are necessary. The conductance of the saprolite and bedrock layers are also needed. County-level soil information from the Natural Resources Conservation Service (NRCS) Soil Survey Geographic Database (SSURGO) database for North Carolina was used where available. The SSURGO data provides an estimate for conductance of the soil layer, thickness of the soil layer, and depth to the bedrock of a soil layer. This was combined with the depth to water layer, and the conductance values for saprolite and bedrock that were created for the 2000 compilation of conductance. Detailed soils were available for 73 counties in the 2000 release of the data. For the update of the conductance layer, twenty additional detailed soil surveys were available to refine the conductance of the soil layer statewide. SSURGO data for Anson, Avery, Buncombe, Burke, Catawba, Chatham, Clay, Cleveland, Graham, Henderson, Lee, Lincoln, Madison, Montgomery, Stokes, Surry, Transylvania, Vance, Watauga, Yadkin and part of Haywood County were included in this update. The counties of Caswell, Cherokee, Iredell, Rowan, Rutherford, Swain, and Warren were not available at the time of processing. The less detailed State Soil Geographic (STATSGO) database was used in these counties. In 2004, NRCS implemented a new database and access system to the SSURGO spatial and tabular data. Because of this, methods developed in 2000 for the original compilation of unsaturated zone data were modified. The fields from the SSURGO soils database used in 2000 were no longer available. Permeability of soil fields, PERML and PERMH, have been replaced by Ksat in the SSURGO database. The SSURGO Metadata table column descriptions define Ksat as ?the amount of water that would move vertically through a unit area of saturated soil in unit time under unit hydraulic gradient.? (http://soils.usda.gov/survey/geography/ssurgo/). Verbal communication with Soil Scientists at NRCS confirmed that the Ksat variable should be used as a substitute for perml and permh (cite, date). The NRCS also distributes software to calculate one Ksat value per soil type, as a weighted average over the soil layers. This value for each soil is multiplied by .1417 to convert it to an inch per hour ratio, comparable to the values used in 2000. Soil thickness and depth to bedrock were also updated from the SSURGO data for the 21 counties that were updated. New conductance values were calculated separately for the new county data, and merged with the 2000 layer. One additional change was made from the 2000 compilation. The categories were rescaled to better represent the conductance through a smaller area represented by a 30 by 30 foot cell size. The new categories and ratings for Vertical series hydraulic conductance are: >Table 1 -- Vertical series hydraulic conductance categories and rating values for unsaturated zone rating > Vertical series hydraulic Percent of area Rating > conductance categories in North Carolina > (feet-squared per day) > <= 50 33 1 > > 50 to <= 100 14 2 > >100 to <= 200 9 3 > >200 to <= 400 11 4 > >400 to <=800 8 5 > >800 to <= 1,600 3 6 > >1,600 to <= 3,200 3 7 > >3,200 to <= 6,400 5 8 > >6,400 to <= 12,800 2 9 > >12,800 12 10 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. 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]. O'Hara, C. G., 1994, Permeability of soils in Mississippi: U.S. Geological Survey Water-Resources Investigations Report 94-4088, 1 sheet. O'Hara, C.G., 1996, Susceptibility of ground water to surface and shallow sources of contamination in Mississippi: U.S. Geological Survey Hydrologic Investigations Atlas HA-739, 4 sheets. More information on STATSGO, SSURGO, and the MUIR database can be found at the USDA-NRCS, National Soils Survey Center, National Soil Data Access Facility website, http://soils.usda.gov/ STATSGO data can be accessed from: http://soils.usda.gov/survey/geography/statsgo/ Information on the SSURGO data available through NC Center for Geographic Information and Analysis can be viewed at: http://cgia.cgia.state.nc.us/corpmeta.dir/corplayer.html NRCS has all certified SSURGO data online at: http://soildatamart.nrcs.usda.gov/Default.aspx NRCS distributes a Soil Data Viewer for ArcGIS applications, used to display and aggregate soil properties by soil unit. http://soildataviewer.nrcs.usda.gov/download50.aspx 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.
Best scale available was used. 1:24,000 was used, and filled in with 1:250,000 scale soils.
Based on source data, 1:24,000 or 1:250,000 scale
permeability and soil thickness
permeability and soil thickness
Ksat, soil thickness and depth to bedrock
saprolite characteristics
saprolite characteristics
p. 409-423
p. 199
p. 593-96.
p. 1397-1407
methods
methods
generalized geology
methods for applying ratings
Several new counties were added to the dataset; Anson, Avery, Buncombe, Burke, Catawba, Chatham, Clay, Cleveland, Graham, Henderson, Lee, Lincoln, Madison, Montgomery, Stokes, Surry, Transylvania, Vance, Watauga, Yadkin and part of Haywood County were included in this update
Using the NRCS Soil Data Viewer 5.0, Load each county soil shapefile and database into the viewer.
For each new county, open the Soil Physical Properties Attribute Folder, and choose saturated Hydraulic Conductivity (Ksat) for analysis
As the Rating Option, Choose Weiighted Average aggregation method, and use the Dept Range of 0 to 100 inches. Choose MAP to display within ArcMap session.
Open the table and export it as a dbf table that contains the Musym and Ksat values for each county
Add a new field to the Ksat table, Ksat_inhr, and calculate it equal to Ksat * .1417 to convert it from um/s to in/hr
Join the tables to the shapefiles, and convert each county to a grid with Ksat_inhr as the value for the grid. Merge all new counties.
Do similar processes for soil thickness and depth to bedrock for the new counties.
Calculate the new conductivity values for the new counties, substituting in Ksat for HMP.
merge the new conductance grid with the old grid conductance grid so that the new values replace the old one. The areas outside of the new counties will retain the original values of the old conductance grid.
Remap the conductance grid into categories using the following remap table (Using the ARC/INFO command, SLICE, with the TABLE option): >50 : 1 >100 : 2 >200 : 3 >400 : 4 >800 : 5 >1600 : 6 >3200 : 7 >6400 : 8 >12800 : 9 >100000 : 10 >
First draft of metadata created by seterzio using FGDCMETA.AML ver. 1.33 07/15/99 on ARC/INFO data set h:\conductance\condgw
Metadata imported.
Metadata imported.
Internal feature number.
ESRI
> >Value Attribute Table, SOILSGW.VAT: > >COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME > 1 VALUE 4 10 B - > 5 COUNT 4 10 B - > 9 PCT_TOT 4 8 F 2 > 13 SQMI 4 8 F 2 > VALUE is the rating: valid values are integers 1 to 10, inclusive COUNT is the number of 30-meter by 30-meter cells in the entire data set that have the value. PCT_TOT is the percent of the total area JUST FOR the North Carolina portion of the study area SQMI area in square miles for that category WITHIN NORTH CAROLINA > >list condgw.vat >VALUE COUNT PCT_TOT SQMI >1 51100160 33.00 17756.81 >2 21891965 14.14 7607.24 >3 13801470 8.91 4795.88 >4 16552914 10.69 5751.98 >5 12036342 7.77 4182.51 >6 4644788 3.00 1614.02 >7 4811959 3.11 1672.11 >8 7653977 4.94 2659.68 >9 3498085 2.26 1215.55 >10 18850175 12.17 6550.25 > MIN is the minimum value (1 at the least) MAX is the maximum value (10 at the most) MEAN is the average value STDV is the standard deviation > >Statistics Summary Table, SOILSGW.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 > >list condgw.sta >Record MIN MAX MEAN STDV > 1 1.000 10.000 3.910 3.136 >
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