Final Report
Project Title: Geographic Information Systems Development
SCERP Project Number: HW93-21
Principal Investigator: George F. Hepner, Department of Geography, University of
Utah
Goals: The goals of this project are: 1) geographic information systems (GIS) database
creation for locales on the border, 2) use the GIS for modeling the geographic location
and potential movement pathways of industrial contaminants and their relationships to
human populations, 3) provide information and technology transfer to other investigators
and agencies.
Rationale: Recent advancements in geographic information science and technology have
de it possible to use a geographic information systems approach for complex, multimedia
environmental assessments. Geographic space provides the framework for the integration
of diverse environmental data sets. Analysis of environmental change over space, as well
as time is possible. The border region is a diverse, binational setting where the location
and movement of environmental contaminants are especially critical to ecosystem
maintenance and environmental policy issues.
The unique topography and the present land use patterns of the Ambos Nogales area
make the environmental risk of contamination by liquid and airborne hazardous materials
released from one of many industrial firms an issue of great concern to local residents on
both sides of the border. The primary surface and sub-surface flows are from the higher
elevation south toward the north and the Santa Cruz River channel. The approximate
elevations of the major industrial zones in Nogales, Sonora are 1250-1300 meters. The
approximate elevations of the primary business and residential areas of both Nogales' are
1150-1200 meters. Most hazardous contaminants released into the air or water will
follow pathways from the higher elevation industrial areas to the lower elevation
commercial and residential areas. The steep-sided valley configuration will likely contain
airborne contaminants within the populated area for a longer duration, thereby, increasing
the potential risk to human health. The eventual destination of many liquid contaminants
is the aquifers along the Santa Cruz River channel from which thousands of people
farther north in Arizona pump their potable water. This nexus of human settlement and
activities with an unusual set of environmental conditions is the foundation of our GIS
research project.
Approach: This research addresses these issues with fundamental research in the
development of alternative contaminant dispersion models that are usable in the complex
terrain of the border region. A component of our research is the development of a GISbased methodology for the delineation of surface protection zones for ground water
resources. These methodologies are applied to actual test sites in Ambos Nogales where
the results are applicable to emergency response and land planning policy.
The basis of our GIS research effort is a regional ecological characterization and database
development for the Nogales Sonora/Arizona area. The ecological database processed in
a GIS provides the foundation for the primary research foci which include: 1) analysis
and modeling of the effects of land use change in Nogales on hazardous materials
sources, 2)the identification of surface and subsurface contaminant migration pathways,
and 3) the estimation of vulnerability of human populations to hazardous materials
incidents. Essentially, land use studies are identifying industrial locations and the
potential hazardous contaminants at these sites. The populations at risk and the possible
pathways for exposure of these populations to hazardous materials are being investigated
and modeled using a GIS.
Status: Surface Contaminant Model- Most attempts at modeling the dispersion of denserthan-air contaminant clouds focus on the fluid mechanics and atmospheric dynamics of
the advection-dispersion problem with minimal attention given to the effects of complex
terrain on dense gas movement. This is acceptable for many regions of the earth and for
many airborne contaminant typologies. In areas with very complex terrain, however, the
character of the terrain dominates flow of the contaminants, and models built for flat
terrain do not provide adequate results.
This research develops two approaches that focus explicitly on the characteristics of the
terrain to delineate pathways for dense gas dispersion. A distance buffer approach is used
to delineate contaminant pathways and potential impact areas. An impedance surface
approach is a second approach used to integrate terrain factors that impede or enhance the
flow across the surface. Simulation results under differing conditions are presented to
provide insights into contaminant pathways and areas of possible elevated human
exposure.
Environmental characteristics include information about the complexity of the terrain and
meteorological conditions. Unique to this model is the inclusion of terrain as a dominant
factor in gas cloud movement. Most publicly and commercially available dense gas
dispersion models require the assumption that the dispersion occurs over flat,
unobstructed terrain where surface roughness is not significant.
The dispersion model assigns to each cell in an accumulated impedance layer the total
accumulated impedance for the path between that cell and the nearest (in impedance
measure) contaminant source cell. In dispersion terms, this makes the cell locations with
higher impedance more difficult to reach by a contaminant source.
Three major factors have been incorporated into the dispersion model. They include
surface distance, slope impedance, and wind impedance. The impedance between cells is
increased in proportion to the angle between the "from" cell and "to" cell. Therefore, as
the angle increases downhill the velocity of the gas movement increases, or conversely
the impedance between cells decreases. The functional dependence between slope angle
and impedance is derived by vector decomposition of the gravitational force vector into
components parallel and perpendicular to the surface slope. The impedance is then
inversely proportional to the gravitational component parallel to the surface slope. Winds
are accounted for in a similar manner. The three factors, surface distance, slope
impedance, and wind impedance, multiplied together functionally define the overall
impedance.
Currently, this phase of the research has been finished and the results have been accepted
for publication in the Journal of Hazardous Materials. The next step is to validate the
simulation results with wind field analysis being done by the Berman and Brazel group at
Arizona State University. This will yield concentration profiles for specific dense gaseous
contaminants over time and space. Failure of the SEDESOL Institute of Ecology to
release to us promised results of a mass balance study of industrial wastes for Nogales
has hurt our validation efforts.
Subsurface Model- A two-dimensional finite-element groundwater flow and transport
model (FEFLOW) was obtained from the WASY Institute for Water Resources Research
in Germany for the purpose of simulating the subsurface hydrogeologic environment
beneath Nogales Wash, which is the unconfined aquifer from which water is drawn for
municipal use.
A test study area was identified for initial use of the model and a conceptual model for
the area defined. All pertinent data were digitized using ARC/INFO including geology
and well locations. FEFLOW has data interchange capabilities with ARC/INFO making
discretization of the study area straightforward and efficient. Once the finite-element
mesh was defined and flow boundary conditions were set, a theoretical contamination
source was placed upgradient of two known water wells in Nogales Wash and the model
was run for a simulated time of 5 years. The plume generated by the source reached both
wells in this time. A similar approach was taken for evaluation of wellhead protection
areas for municipal water supply wells in located in Nogales Wash for both Nogales,
Arizona and Nogales, Sonora.
The result has been the preliminary acceptance of a M.S. thesis titled, "Integrated GIS
and Ground water Modeling: An Approach to Wellhead Protection in the Nogales Wash
Study Site." This line of research will be discontinued due to the inability to find a
qualified student. This was caused, in part, by the delay in funding for next year until
after the start of the academic year.
Urban growth model for Nogales, Sonora/Arizona- Assessing environmental problems
along the U.S.-Mexico border requires data regarding the potential urban growth
scenarios in border communities with maquiladora activity. For example, GIS-based
community vulnerability model requires information on the location and activities of
maquiladoras and the distribution of sub populations and sensitive institutions in Ambos
Nogales (in addition to terrain and other physical data). More generally, assessing
environmental impacts on air quality and watersheds require these data as well. This is
because urban growth is a direct result of increased maquiladora activity and urban
growth can have substantial negative environmental impacts. Thus, increased economic
activity in border communities can have both first-order and second-order impacts on
environ-mental quality. The first order effect is direct environmental impacts from
maquiladora activity such as potential hazardous material releases. The second-order
effect is the urban growth stimulated by maquiladora and other basic economic activity.
The second order effects can be substantial, and therefore it is crucial to include potential
urban growth scenarios as input to environmental assessment. A major problem when
assessing the impacts of industrial activity on environmental quality in border
communities is the lack of data regarding potential urban growth scenarios. In order to
rectify this situation, we have initiated the development of an urban growth model for
Nogales, Sonora/Arizona. The urban growth model will use as input projections of
maquiladora or other basic economic activity in the Ambos Nogales region. The output
from the model will the likely spatial distribution of urban growth in response to the
increased basic economic activity. The urban growth scenario will serve as input to
environmental impacts analyses. During the period beginning with Year Four funding
and ending December 31,1994, we have conducted an initial literature review and have
identified a good, "first-cut" urban growth model. This model is the well-known Lowry
urban growth model (Lowry 1964; Webber 1984). Although the model is somewhat
dated, it serves well as an initial model for several reasons: i) There is a wealth of
published experience with the Lowry model that will provide valuable guidance for
developing the Nogales model; ii) The data requirements for the Lowry model are
modest. Data availability will be an important limiting factor in developing any urban
model for the U.S./Mexico border region; iii) The main factor driving urban growth in the
Lowry model is distance-based accessibility to basic economic activity (e.g.,
maquiladora activity). While distance as a controlling factor for urban growth has
become less important in developed countries due to high mobility levels, this factor is
still important in developing countries such as Mexico where mobility among average
citizens is still limited; iv) The Lowry model and other Lowry-like models have been
successfully integrated into GIS (e.g., Sui and Lo 1992). This is important given the
intended use of the model, i.e., combining model output with other physical data in a GIS
in order to conduct environmental impacts assessment. Initial experience with the Lowry
model will allow us to assess its goodness of fit for Ambos Nogales. Given this
experience, we will then be able to extend the basic Lowry model using GIS capabilities.
For example, using a GIS to compute accessibility as a function of distance over terrain
should improve the Lowry model's predictive capabilities in a community such as Ambos
Nogales where high physical relief combined with limited mobility are major influences
on urban growth. We will also be able to use experience with the Lowry model as a basis
for developing a more elaborate urban growth model if necessary.
GIS-based Community Vulnerability Model- This project developed a GIS-based
modeling approach for assessing community vulnerability to potential hazardous
substance releases. The relationship between the location of human activity (population
and institutions) and the location of potential sources of hazardous material releases
determines community vulnerability. Due to the inherent spatial nature of the problem,
GIS provides an effective technique for modeling and ssessing community vulnerability.
The main technique used in GIS-based community vulnerability model is composite
mapping analysis (CMA). This methodology involves combining separate spatial data
layers in a meaningful manner to generate useful information regarding the spatial
relationship among these data. The GIS-based community vulnerability model combines
spatial data layers corresponding to potential hazardous material release sites and likely
contaminant pathways with other spatial data layers corresponding to human activity
such as residential density and sensitive institutions. Querying the resulting composite
layer provides the estimated vulnerability of different sub populations and sensitive
institutions to potential hazardous material releases. The CMA also requires assigning
weights to each spatial data layer that reflects the variable's contribution to community
vulnerability. For example, sub populations such as individuals under 18 years old or
over 65 years old may require special attention in the case of a hazardous material
release. Therefore, these sub populations should contribute more to the overall
community vulnerability assessment than the general population. The GIS-based
community vulnerability model considers these factors and derives the final composite
layer as a weighted linear combination of the input data layers. A potential problem with
assigning weights to the input spatial data layers is determining the exact values for these
weights (e.g., quantitatively assessing the sensitivity of the over 65 year old
subpopulation to hazardous material releases relative to the general population). In many
cases, these weights are a subjective judgment call. In order to structure this subjectivity,
this research project performed a sensitivity analysis with the input spatial data weights.
A series of vulnerability scenarios were developed by varying these weights on two
levels. At a "macro" level, the analysis varied relative weights between hazard factors as
a whole and human factors as a whole. At a "micro" level, the individual variables that
comprise each factor were also varied. This resulted in eighteen community vulnerability
scenarios. Experiments with the eighteen vulnerability scenarios indicated that the GISbased community vulnerability model is very robust. First, a statistical analysis indicated
that "high" and "very high" vulnerability estimates were very consistent across all
scenarios. This is important since estimates of these categories are the most significant
outputs from the model. Second, a GIS-based analysis compared spatial variation in the
"high" and "very high" vulnerability zones across scenarios. Again, results were
consistent. The robust results indicate that the GIS community vulnerability model can be
used effectively as a tool for policy analysis and planning responses to potential
hazardous material releases. Planners and policy makers can use the model output to
prepare for possible emergency situations, evaluate evacuation routes or determine
feasible locations for new emergency response facilities.
Potential Users/Technology Transfer:
Scientists from EPA, SEDESOL, and state agencies working toward improved
methodologies for modeling contaminant dispersion over space and time in area of
complex terrain, vulnerability assessment and ground water protection zone delineation.
Emergency response contingency planners for Ambos Nogales. Scientists, planners and
policy makers can use the database (terrain, land cover, demographic, etc. in ARC/INFO)
and analytical products for other applications relevant to their jobs.
We have provided data and GIS expertise to individuals in the SCERP Consortium and
interested governmental agencies.
Other Personnel:
We have relied on Duncan Patten, Tony Brazel and Neil Berman at Arizona State
University for logistical support of our field research in Nogales and for collaboration on
our dispersion pathways research.
We have collaborated with Carmen Maso (Region 9 EPA) and Dave Parrish (Region 6
EPA) for data sharing and presentation assistance to EPA personnel.