Mapping Environmental Risk on the Bolivian Altiplano

By Gary Ostroff

Mapping Environmental Risk on the Bolivian Altiplano
Gary Ostroff, P.E.
HydroQual, Inc.

The Bolivian Altiplano is a flat region high in the Andes, lying between the eastern and western cordilleras of that great mountain chain. Mining gold and silver began here in the time of the Inca, and was vastly expanded under the rule of the Spanish Empire. Today, the Bolivian economy is heavily dependent on the continued exploitation of the region, although gold and silver are no longer the only natural resources that are sought. The environmental impact of these mining sites, some of them more than four centuries old, has been significant, and comprises heavy-metal pollution of the air, soil, and water. HydroQual developed a GIS application to support the Bolivian Ministry of Mining and Metallurgy in assessing the health risks of mining sites, and developing appropriate remediation measures.

The full-scale application was developed on an ESRI ArcView 3x platform, and employed extensive scripting in AVENUE to create a seamless link between the GIS display and several environmental modeling packages that analyze the fate and transport of environmental contaminants. These models run as externally compiled FORTRAN routines - they are widely used models with established track records and credibility. The results are returned as ASCII files, and incorporated into the GIS display.

As with any GIS/Modeling interface, the data types employed are of great importance, and they structure the type of analysis that can be done. This application uses points, lines, and raster data structures, but not polygons. This is modeling with rasters (using ESRI Spatial Analyst) makes the computation extremely efficient and rapid.

The table at the right indicates how the various risk factors and contaminant pathways were modeled: Point sources of pollution, e.g.discharges or smelters, were represented as points; rivers and streams, which both transport and are subject to pollution, were shown as lines; while the effects of air pollution from smelter plumes, were modeled with raster data sets. The Avenue scripting software automatically formats the data input and output appropriately - the users have only to contend with data input and interpretation. The image to the right shows an initial view of the area around Ouroro, one of the most intensively mined regions of the Altiplano. Settlements, rivers, mining areas, lakes are displayed as standard ArcView themes. The image on the left below shows the result of one analysis of air pollution in the vicinity of the city. The area has several large and aging smelting facilities that discharge a great many pollutants into the atmosphere, which then drift over the plain and are deposited in plumes determined largely by wind direction and the height of the discharge stack. The EPA air pollution model that produces the analysis is formatted for display as a raster data set in Spatial Analyst.

A great deal of data generation was required to support the construction of this application. For example, the air quality model requires meteorological data and a complete digital elevation model. The water quality models require a fully developed stream network. While some data was available, much of it had to be created specifically for this application. The Bolivian government possessed detailed CAD drawings of their hardcopy geological maps, but they had not been created for GIS applications, so they were not attributed, and the network suffered from many discontinuities. Comprehensive elevation models were not available at an appropriate resolution, and CAD files of contour lines were also not suitable for mass conversion to GIS formats. A period of intensive review and modification of these data was required to create the base data on which the final application rests.

The nature of the final application is shown in the schematic pyramid below. The GIS software is the link between the base data, and the higher-level modeling routines that have been grafted seamlessly to it. Once impacts and alternative mitigation strategies have been identified, the application can apply a simple cost/benefit analysis to support decision making on appropriate measures. This application was distributed to several government ministries with responsibilities for mining and environment, and was also loaded on field stations in several mining regions of the Altiplano.

Published Thursday, April 3rd, 2003

Written by Gary Ostroff

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