Attenuation Factor model results for Upper Floridan aquifer vulnerability to Bromacil and Ethylene Dibromide
This dataset includes Attenuation Factor (AF; Rao and others, 1985) model results for Upper Floridan aquifer vulnerability to Bromacil and 1,2-Dibromoethane or Ethylene Dibromide (EDB). The AF value serves as an index for assessing the transport of pesticide mass from the vadose zone. The AF model setup requires the input of raster soil bulk density, soil organic carbon content, soil field capacity, soil air filled porosity, recharge to the aquifer, depth to groundwater, the pesticide sorption coefficient, pesticide Henry's Law Constant, and pesticide half-life. These variables were entered into the AF equation using the raster calculator tool in ArcGIS. The resulting AF values are dimensionless and range between 0 and 1. A value of 1 indicates that all of the pesticides in the vadose zone will leach into the groundwater; conversely, a value of 0 suggests that no pesticides will leach into the groundwater.
A downloadable version of the final dataset is provided in GeoTIFF file format with 10-meter resolution.
Douglas, Steven H., 20170828, Attenuation Factor model results for Upper Floridan aquifer vulnerability to Bromacil and Ethylene Dibromide: U.S. Geological Survey Data Release doi:10.5066/F7S46QTV, U.S. Geological Survey, St. Petersburg, FL.
Planar coordinates are encoded using row and column
Abscissae (x-coordinates) are specified to the nearest 10.0
Ordinates (y-coordinates) are specified to the nearest 10.0
Planar coordinates are specified in meters
The horizontal datum used is North American Datum of 1983.
The ellipsoid used is Geodetic Reference System 1980.
The semi-major axis of the ellipsoid used is 6378137.0.
The flattening of the ellipsoid used is 1/298.257222101.
This dataset was generated from the Attenuation Factor model to test the model's ability to indicate groundwater vulnerability to pesticides in the Southwest Florida Water Management District (SWFWMD).
Water management district boundaries dataset was used as the study area extent that the other layers were clipped to.
SIM3182 (source 2 of 8)
U.S. Geological Survey, 20111117, Potentiometric Surface of the Upper Floridan Aquifer in Florida and in Parts of Georgia, South Carolina, and Alabama, May – June 2010: U.S. Geological Survey, Orlando, FL.
The EDB Henry's law constant was used as the Henry's law constant variable in the Attenuation Factor model equation.
Sorption Coefficient (Koc) (source 7 of 8)
Delle Site, A., 2001, Factors affecting sorption of organic compounds in natural sorbent/water systems and sorption coefficients for selected pollutants. A review..
The EDB sorption coefficient was used as the sorption coefficient of pesticides on organic matter variable in the Attenuation Factor model equation.
SSURGO (source 8 of 8)
U.S. Department of Agriculture, Natural Resources Conservation Service, 2015, USDA-NRCS Soil Survey Geographic (SSURGO 2.2): Bulk Density, Organic Carbon Content, Field Capacity, and Porosity: USDA/NRCS - National Geospatial Center of Excellence, Fort Worth, TX.
Tabular and map Soil Survey Geographic Database SSURGO data for Florida were downloaded through the U.S. Department of Agriculture (USDA) Geospatial Data Gateway. Descriptions for the SSURGO classes are available at the Soil Survey website http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/ref/?cid=nrcs142p2_054253. SSURGO metadata is available at: http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/home/?cid=nrcs142p2_053631. The polygon shapefiles were joined to the tabular files within the SSURGO file geodatabase. The first join to be made uses the “mukey” field as the common identifier to join the cokey field from the “component” table. The second join to be made uses the cokey field as the common identifier to join the om_r (organic carbon content), dbthirdbar_r (bulk density), awc_r (field capacity), and wsatiated_r (porosity) field from the “CHorizon” table. The Florida shapefiles were clipped to the SWFWMD boundaries, using the clip tool in ArcGIS and the polygon shapefile, DISTRICT, as the boundary. The variables are expressed as a percent or fraction of the total volume. If the original data from SSURGO is expressed as floating-point decimal values between 0 and 1 then they were converted to values between 1 and 100 by adding a new field to the raster in the attribute table and using the field calculator to multiply the original values by 100. Bulk density was converted from g/cm3 to kg/m3 using the field calculator and by multiplying the bulk density values by 1000. The final polygon shapefile was converted to 10 meter raster GeoTiffs using the Polygon to Raster tool and selecting the new field with values 1 to 100 as the new raster values.
Person who carried out this activity:
Steven H. Douglas
Cherokee Nation Technologies contracted to the U.S. Geological Survey
600 4th St S
St Petersburg, FL
Date: 2015 (process 2 of 5)
Depth to groundwater was created by clipping the USGS potentiometric well points shapefile (Kinnaman and Dixon, 2011) to the SWFWMD study area extent. The potentiometric surface was calculated by interpolating the points with the Inverse Distance Weighted tool in ArcGIS and using the default settings. Finally, depth to groundwater was created by subtracting the potentiometric surface from the FLIDAR_MOSAIC_M DEM value using the raster calculator tool.
Date: 2015 (process 3 of 5)
Henry's law constant, half-life, and sorption coefficient raster layers were created by making three copies of the bulk density raster from the SSURGO data-set. Using the ArcGIS field calculator the values for all cells in the study area were changed to the corresponding variable value to create the constant raster variable.
Date: 2015 (process 4 of 5)
The recharge polygon shapefile, SWFWMD, was converted to a 10-meter raster GeoTiff, using the Polygon to Raster tool in ArcGIS.
Date: 2015 (process 5 of 5)
The Attenuation Factor model equation described by Rao and others (1985), was constructed using the Raster Calculator tool in ArcMap. The resulting AF values range between 0 and 1 and were divided into 5 classes, using the reclassify tool in ArcGIS, based on the standard deviation: very low (less than 0.3), low (between 0.3 and 0.522), medium (between 0.522 and 0.742), high (between 0.742 and 0.962), and very high (greater than or equal to 0.962).
Rao, P.S.C., Hornsby, A.G., and Jesup, R.E., 1985, Indices for ranking the potential for pesticide contamination of groundwater: Proceedings of the Soil and Crop Science Society of Florida, Florida.
Douglas, S., Dixon, B., and Griffin, D., Unknown, Assessing intrinsic and specific vulnerability models ability to indicate groundwater vulnerability to groups of similar pesticides: a comparative study: Physical Geography, Philadelphia, PA.
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