GIS in environmental contamination
Encyclopedia
GIS in environmental contamination is the use of ArcGIS
software in mapping out the contaminants in soil and water using the spatial interpolation tools from ArcGIS. Soil and water contamination by metals and other contaminants have become a major environmental problem after the industrialization across many parts of the world. As a result, environmental agencies are placed in charge in remediating, monitoring, and mitigating the soil contamination sites. GIS is used to monitor the sites for metal contaminants in the soil, and based on the GIS analysis, highest risk sites are identified in which majority of the remediation and monitoring takes place. GIS is used in making spatial interpolations of contaminants in the soil and water. Spatial interpolation allows for more efficient approach to remediation and monitoring of soil and water contaminants.
from heavy elements can be found in the urban environments, which can be attributed to the transportation and industries along with the background levels (minerals-leaching heavy elements from weathering). Also, some of the most soil contaminated areas are around the mines such as the ones in Slovenia
, Bosnia and Herzegovina
, and in United States (Sulphur Bank Superfund Site, in California). In a study area, GIS is used for the analysis of spatial relationship of the contaminants within the soil.
, Slovenia, where the world’s second largest Hg mine operated has a significant amount of Hg emissions into the atmosphere by a surface process of adsorption of Hg from and to soil particles surfaces, which results in a diffusion of Hg through the pores of soil. To calculate the emission flux for Hg, a Hg emission model was developed:
lnFHg=Ea/(R*Ts )+n*ln[Hg]s+m+0.003*Rz Equation 1
in which the FHg is the flux of Hg emission, Ea is the activation energy, R is the gas constant, Ts is the soil temperature, n and m are constants, [Hg]s is the Hg concentration, and 0.003* Rz accounts for the solar radiation since the solar radiation has the effect on the temperature, hence the solar radiation has the effect on the emission flux of Hg.
Once the Hg concentration data was gathered, a schematic model has been prepared for GIS input, which consisted of a digital elevation model (DEM), a satellite land use map, and EARS data. Using the inverse distance weighted (IDW) method from geostatistical tools in ArcGIS 9.3, a raster model of the Hg concentration has been produced for the Idrija area.
and groundwater
, with groundwater being the more difficult scenario to remediate since the residence time of water is much longer than the surface water. Some of GIS applications that can be used in analysis of water related problems will be covered in the next couple of sections.
(factor t), impact of the vadose zone
(factor i), and the hydraulic conductivity
(factor c), which together spell out DRASTIC.Furthermore, there is a weighting factor associated with each of the parameters that can range from one to five. In addition, the lower the numbers for the DRASTIC index after the assessment of the aquifer, than the lower the risk of aquifer contamination in that area. These seven parameters derive DRASTIC summary index score, which determines which are more prone to contamination than other. The significance of the DRASTIC summary index score is that it shows areas that are more prone; as a result, the state or local authorities depending on the scale will place necessary measures in place that would prevent or mitigate contamination of the water supply.
Using GIS, a map was developed for the seven counties (Hillsborough, Polk, Manatee, Hardee, Sarasota, DeSoto, and Charlotte) in Florida, which shows the DRASTIC summary index score for the Floridan Aquifer System, Surficial Aquifer System, and Other Rocks aquifer. The development was not difficult and intricate; instead, the map is only a combination of multiple layers that had been stacked on top of each other as shown in Figure 1.
ArcGIS
ArcGIS is a suite consisting of a group of geographic information system software products produced by Esri.ArcGIS is a system for working with maps and geographic information...
software in mapping out the contaminants in soil and water using the spatial interpolation tools from ArcGIS. Soil and water contamination by metals and other contaminants have become a major environmental problem after the industrialization across many parts of the world. As a result, environmental agencies are placed in charge in remediating, monitoring, and mitigating the soil contamination sites. GIS is used to monitor the sites for metal contaminants in the soil, and based on the GIS analysis, highest risk sites are identified in which majority of the remediation and monitoring takes place. GIS is used in making spatial interpolations of contaminants in the soil and water. Spatial interpolation allows for more efficient approach to remediation and monitoring of soil and water contaminants.
GIS in soil contamination
Soil contaminationSoil contamination
Soil contamination or soil pollution is caused by the presence of xenobiotic chemicals or other alteration in the natural soil environment....
from heavy elements can be found in the urban environments, which can be attributed to the transportation and industries along with the background levels (minerals-leaching heavy elements from weathering). Also, some of the most soil contaminated areas are around the mines such as the ones in Slovenia
Slovenia
Slovenia , officially the Republic of Slovenia , is a country in Central and Southeastern Europe touching the Alps and bordering the Mediterranean. Slovenia borders Italy to the west, Croatia to the south and east, Hungary to the northeast, and Austria to the north, and also has a small portion of...
, Bosnia and Herzegovina
Bosnia and Herzegovina
Bosnia and Herzegovina , sometimes called Bosnia-Herzegovina or simply Bosnia, is a country in Southern Europe, on the Balkan Peninsula. Bordered by Croatia to the north, west and south, Serbia to the east, and Montenegro to the southeast, Bosnia and Herzegovina is almost landlocked, except for the...
, and in United States (Sulphur Bank Superfund Site, in California). In a study area, GIS is used for the analysis of spatial relationship of the contaminants within the soil.
Soil contamination in Slovenia
In IdrijaIdrija
Idrija is a small town and municipality in the Goriška region of Slovenia. It is known for its mercury mine and lace....
, Slovenia, where the world’s second largest Hg mine operated has a significant amount of Hg emissions into the atmosphere by a surface process of adsorption of Hg from and to soil particles surfaces, which results in a diffusion of Hg through the pores of soil. To calculate the emission flux for Hg, a Hg emission model was developed:
in which the FHg is the flux of Hg emission, Ea is the activation energy, R is the gas constant, Ts is the soil temperature, n and m are constants, [Hg]s is the Hg concentration, and 0.003* Rz accounts for the solar radiation since the solar radiation has the effect on the temperature, hence the solar radiation has the effect on the emission flux of Hg.
Once the Hg concentration data was gathered, a schematic model has been prepared for GIS input, which consisted of a digital elevation model (DEM), a satellite land use map, and EARS data. Using the inverse distance weighted (IDW) method from geostatistical tools in ArcGIS 9.3, a raster model of the Hg concentration has been produced for the Idrija area.
GIS in Water Contamination
Water contamination can occur in surface waterSurface water
Surface water is water collecting on the ground or in a stream, river, lake, wetland, or ocean; it is related to water collecting as groundwater or atmospheric water....
and groundwater
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...
, with groundwater being the more difficult scenario to remediate since the residence time of water is much longer than the surface water. Some of GIS applications that can be used in analysis of water related problems will be covered in the next couple of sections.
DRASTIC Summary Index Score modeled using GIS
Under certain hydrological parameters, some aquifers are more prone to contamination than other aquifers. The parameters that are taken into consideration when calculating the vulnerability of aquifers to contamination are: depth to water (factor d), net recharge (factor r), aquifer media (factor a), soil media (factor s), topographyTopography
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
(factor t), impact of the vadose zone
Vadose zone
The vadose zone, also termed the unsaturated zone, is the portion of Earth between the land surface and the top of the phreatic zone i.e. the position at which the groundwater is at atmospheric pressure . Hence the vadose zone extends from the top of the ground surface to the water table...
(factor i), and the hydraulic conductivity
Hydraulic conductivity
Hydraulic conductivity, symbolically represented as K, is a property of vascular plants, soil or rock, that describes the ease with which water can move through pore spaces or fractures. It depends on the intrinsic permeability of the material and on the degree of saturation...
(factor c), which together spell out DRASTIC.Furthermore, there is a weighting factor associated with each of the parameters that can range from one to five. In addition, the lower the numbers for the DRASTIC index after the assessment of the aquifer, than the lower the risk of aquifer contamination in that area. These seven parameters derive DRASTIC summary index score, which determines which are more prone to contamination than other. The significance of the DRASTIC summary index score is that it shows areas that are more prone; as a result, the state or local authorities depending on the scale will place necessary measures in place that would prevent or mitigate contamination of the water supply.
Using GIS, a map was developed for the seven counties (Hillsborough, Polk, Manatee, Hardee, Sarasota, DeSoto, and Charlotte) in Florida, which shows the DRASTIC summary index score for the Floridan Aquifer System, Surficial Aquifer System, and Other Rocks aquifer. The development was not difficult and intricate; instead, the map is only a combination of multiple layers that had been stacked on top of each other as shown in Figure 1.
Interpolating the water table in a coastal area using GIS
For areas near the coast, water elevation in the well is necessary information when determining if the area will be susceptible to salt water intrusion. Basically, if there is no confining unit, than that is categorized as unconfined aquifer, which would be susceptible to the saltwater intrusion at approximately 40:1 ratio, which is based on the Ghyben-Herzeberg equation. To interpolate the water table for the area, convert the point shapefile, which consists of water elevation for each of the measured groundwater wells, into a raster layer, which would provide small cells in place of a point. Then, using the spatial analyst from ArcToolbox in ArcGIS, use the new raster layer as the input raster layer in the interpolation tool. After the interpolation is complete, the area among the measured water elevation points will be filled, which will result in a smooth and continuous surface. Then, the newly created raster layer can be used to create contour lines by using the spatial analyst tool from ArcGIS. An example of spatial interpolation of water table is shown in Figure 2 in which a continuous map has been created from the point well data; then, the contious map was used to create the contour lines. The map in Figure 2 shows the cone of depression in the Chatham county extending out to other counties.External links
- http://www.usgs.gov/
- http://www.fgdl.org/