Principal Investigators:
Suleiman A. Ashur, Ph.D, P.E.
Hadi Baaj, Ph.D., P.E.
Heather O'connell
Ramon Carrasco
Department of Civil Engineering
University of Texas at El Paso
El Paso, Texas 79968-0516
and
K. David Pijawka, Ph.D.
Shuhbro Guhathakurta, Ph.D.
School of Planning and Landscape Architecture
Arizona State University
Tempe, Arizona 85287-2005
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Research Objectives
The objectives of this research project are:
1. To Create a database of the amount, type, and flows of hazardous
waste from Mexico to the US.
2. To Develop a risk assessment model applicable to the border region
implemented on a GIS platform and apply it to Sonora-Arizona case study.
3. To Analyze different management scenarios that will affect the transportation
risks.
Research Methodology
To achieve the goals of this research project, the following tasks were undertaken:
Task 1: Literature review of all problem components.
Task 2: Data collection and analysis: Several data set are needed
in this research:
Problems Encountered During the Research
The only problem encountered in this research was the difficulty in collecting data from Mexico. We have contacted several institutions in Mexico and requested information on the amount of hazardous wastes generated by the Maquiladora. However, the information were not available to us because it was classified in Mexico or due the fact that it does not exists. In addition, a major problem was finding an existing GIS database for the highways in Mexico at the border region.
Research Findings and Conclusions
The anticipated growth of US industries in the northern part of Mexico render this research urgent. As the number of US industries in Mexico continues to grow, an increase in hazardous materials shipments will occur from the US to Mexico. This will create a specific pattern of hazardous material shipments that will impose risks for the population in the US, in general, and the population in the states of Arizona, California, New Mexico, and Texas, in particular.
The US-Mexico border region is a growing source of hazardous waste. The research has provided information showing a substantial increase in the number of shipments of hazardous wastes over the last several years from Mexico to the US.
There is an urgent need to better manage the hazardous waste generated in Mexico by either building new disposal facilities or recycling plants. This will enable the development of policies dealing with the mitigation and reduction of risks of transporting hazardous waste in the border region.
The actual quantities of hazardous waste generated by the maquiladora plants are still unknown. The majority of the waste is not likely being shipped to the US or receiving proper treatment, recycling, or disposal in Mexico. The problem will become more severe as the maquila plants grow. Increasing hazardous waste shipments will dramatically increase risk levels.
Following are some conclusions pertaining to the test case. These conclusions may or may not be applicable to the whole US-Mexico border region. First, most of the Maquiladoras plants that shipped hazardous waste from Sonora to Arizona were concentrated in the city of Nogales (17 plants). Most of these Maquiladoras have recorded one shipment, only six plants have recorded two or three shipments. This turnout of shipments is very low. However, it is consistent with the turnout of shipments of all Maquiladoras in general. This pattern reinforces the need for strict and better management for the compliance of the Maquiladoras with hazardous waste shipment regulations.
Studying several management scenarios was a successful tool for helping to develop new policies in the border region. The United States has a plan to upgrade some ports of entry in the border region to accommodate the anticipated influx of shipments under NAFTA. This step may reduce the congestion at the ports of entry, but it will increase the risk factors along the existing shipment routes.
Some management scenarios had little effect on reducing risk. However, this could be limited to this test case only. A major reduction of risk occurred when building a new treatment, storage, or disposal facility in the border region, specifically in Mexico. A better scenario would be developing more than one TSD facility. A major risk and cost increase were generated from Maquiladoras located away from the border cities.
The major concentration of maquiladora plants is at the border cities and border states. The rest of plants are located in the middle and southern part of Mexico. The USEPA and Arizona Department of Environmental Quality databases have recorded shipments only from the border states. These unconsidered plants should be studied closely to find out the way these plants manage their hazardous waste.
Recommendations for Further Research
The following areas could be considered for future research:
Problem Background
The maquiladora industry or Maquiladoras has grown substantially over the last decade. Maquiladoras is the name of the US-owned assembly plants in Mexico. Most of these industrial plants are located in the northern part of Mexico in an area known as the US-Mexico border region. The number of these industries grew from 585 in 1982 to 2,153 plants in 1993 (1). There is also growing evidence that these industrial plants produce substantial amounts of hazardous waste as byproducts of their industrial processes. It is estimated that the Baja California Maquiladora industry generates about 100,000 tons of hazardous waste per year, the equivalent of 12% of California's 1989 estimate of in-state hazardous waste generation (2,3). Under 1988 Mexican environmental law, hazardous waste generated by US companies must be returned to the US for treatment and disposal (1). However, only 10% of the companies in the Mexican states of Baja California and Sonora have requested official shipments of hazardous waste to the US (3). The remaining hazardous waste was either recycled, stored on site, or illegally dumped in the border region.
The problem of transboundary movement of hazardous materials surfaced after the Environmental Cooperation Agreement (La Paz Agreement) in 1983 between the US and Mexico. This agreement established an area of 100 kilometers on both sides of the US-Mexico border within which parties agreed to cooperate "for protection, improvement and conservation of the environment." Each government designated its national coordinator to implement the agreement by its environmental authority: the United State Environmental Protection Agency (USEPA) and the Secretariat of Ecology and Urban Development (SEDUE). Since the La Paz 1983 agreement, there have been five annexes, each dealing with a specific transborder problem. Most importantly, for the purpose of this research, Annex III deals with the transborder shipment of hazardous waste and hazardous substances between the two countries.
The problem addressed for Mexico in Annex III with respect to the transboundary movement of hazardous waste is two-fold: (1) the need to prevent illegal and unregulated dumping in Mexico from the US sources; and, (2) the lack of infrastructure (i.e. landfills, recycling plants) in Mexico to treat and dispose of hazardous waste produced by the maquiladora industry. The US agreed that hazardous waste generated by the Maquiladoras would continue to be returned to the US, as required by Mexican law (4).
Environmental Transportation Issues in the Border Region
Generally speaking, most of the hazardous waste generated by the maquiladora industry should be shipped back to the US, for treatment and storage, or adequate treatment capacity should be developed in Mexico. These shipments contain constituents that are hazardous to human health and to the environment. For example, 1,215 tons of ignitable waste and 411 tons of corrosive waste were shipped from Mexico to the US in 1992. These wastes have high risks in case of traffic accidents, especially if such events occur in highly populated areas in Mexico or in the US (5).
The more worrisome part of this problem is the lack of knowledge of
the pattern of movement regarding the remaining hazardous waste. Authorities
on both sides of the border has been ignoring the problem for a long time
as if it did not exist. Serious enforcement activity of Mexico's environmental
regulations pertaining to hazardous waste is only now beginning to be recognized.
With the amount of hazardous waste shipments expected to increase dramatically
in a short period of time, the transportation risk problem will become
difficult to manage. Currently, in the US, the disposal of hazardous waste
is a serious challenge because of escalating amounts and decreasing capacity
for treatment and disposal. The capacity of landfill disposal is reaching
its maximum because of increasing restrictions that have to be met with
this option and the closure of existing facilities. The potential for opening
new disposal facilities is very limited. With the implementation of the
North American Free Trade Agreement and the continuing growth of industries
in the border region, the transportation of hazardous waste has become
a serious policy issue. It is now, more than ever, necessary to study the
problem and propose solutions under different management scenarios that
may exist in the near future.
Problem Description
Hazardous material is defined as any material that could present a danger during shipment by ground, air, sea or any other mode of transportation such as pipe line. An example would be the transporting of explosives from one place to another. Hazardous waste, on the other hand, is defined by the Resource Conservation and Recovery Act (RCRA) legislation (1976) as "a solid waste, or combination of solid wastes, which because of its quantity, concentration, or physical, chemical, or infectious characteristics may: (1) cause, or significantly contribute to, an increase in mortality or an increase in serious irreversible or incapacitating reversible illness or (2) pose a substantial present or potential hazard to human health or the environment when improperly treated, stored, transported or disposed of or otherwise managed." While the definition refers to "solids," it has been interpreted to include semisolids and liquids. Hazardous waste account for 0.2% of all hazardous material traveled yearly in the US (6).
Currently, there is no complete database providing information on the pattern of shipments of waste from the maquiladora industries as well as the shipment routes to disposal facilities. Furthermore, it is widely expected that the amount of hazardous waste will increase substantially as a result of the North American Free Trade Agreement (NAFTA) and the accompanying anticipated relocation of US industries to Mexico. In addition, binational environmental regulations and those in Mexico are beginning to be seriously implemented. That will result in substantial flows in hazardous waste from generator sources to the treatment and disposal facilities in the border region. The nature of the risks in transporting hazardous materials and waste requires study to provide management options to reduce risk and respond to transportation accidents involving hazardous waste.
Moreover, environmental compliance is taking on new urgency in Mexico as a result of inspections by the Secretariat of Social Development (SEDESOL), the federal successor agency to SEDUE. For example, in the mid-July of 1992, an inspection took place at one Mexicali environmental treatment firm, Mexaco, which resulted in a shutdown warrant of the company and jailing of its general manager. The company had been storing drums full of hazardous waste in its site from various maquiladora, and was unable to accurately report on the contents of some drums (7).
In general, there are two types of shipments of hazardous substances across the US-Mexico border region: 1) shipments of hazardous materials (raw materials) from the US to Mexico as part of the industrial process, which can be classified as many-origins-to-many-destinations shipments, as shown in Figure 2.1 (a) (8). This pattern is a complex one because of the substantial amount and diversity of hazardous materials shipments which render it extremely difficult to track; the lack of a regulatory tracking system adds to the problem; 2) shipments of hazardous waste from Mexico to US as a by product of US industries in Mexico. This pattern is less complex and is classified as many-origins-to-few-destinations, as shown in Figure 2.1 (b) (8).
The goal of this USEPA-sponsored research is to develop an analytical
framework for environmental transportation issues by assessing the transportation
risks of shipping hazardous waste in the border region. The solution will
be approached by utilizing the Geographic Information System (GIS) technology.
GIS is defined as a system for collecting, storing, manipulating, and presenting
geographic data. System refers to the integration of computer hardware,
software, and data.
In 1992, Perry et al. conducted a major and comprehensive research study on the hazardous waste generated by the Maquiladora industry in the US-Mexico border region. Based on data from the state of Baja California in Mexico, the quantities of hazardous waste generated by Baja maquiladora were estimated based on the amounts of raw material utilized by a sample of 34 assembly companies (1,2,3). Perry et al. assumed that because most of these hazardous substances were used to facilitate assembly rather than in manufacturing, the amount of hazardous waste generated would be close to the volume or weight of the imported hazardous substances.
In total, there were 117 different hazardous materials imported annually. The study reported that approximately 9,592 metric tons of solids and 2,063,606 liters of liquid substances were imported to these sample plants. When extrapolated, the 318 Baja maquiladora generated 100,000 tons of waste in 1988. On this basis, an individual plant would generate 315 tons of hazardous waste per year. These materials can be classified into three major categories: (1) a wide range of solvents such as acetone and methylene chloride; (2) acids and alkaline substance such as sulfuric and hydrochloric acids; and (3) heavy metals such as lead and nickel (3).
2.4 PROBLEM DEFINITION
The study estimated the total quantity of hazardous waste generated, by assuming that such quantities were equal to the amount of raw material imported by the sample plants. Determining the quantities generated by the 34 sample plants and the total number of plants, the study calculated the total quantities of hazardous waste generated by the Maquiladora industry. Another major finding was the detection of traces of Volatile Organic Chemicals (VOCs) used in printed circuit board assembly process in New River at the US-Mexico border.
Although the above study was a major step in bringing the hazardous waste issue to surface, it lacked precision by its emphasis on a small sample of industries, and did not address the problem of transportation risk.
This research is an attempt to address two overriding issues regarding
the transport of hazardous waste in the US-Mexico border area. The first
issue concerns the lack of a current comprehensive database that tracks
the amount and flows of hazardous waste shipments, determines the risks
to population and the environment based on actual hazardous waste shipment
data, and identifies of the patterns of shipments (their origins, destinations,
and transport routes). The second issue is the growing need for a risk
assessment transportation model that can readily be used for the border
region and serve as a valuable tool for formulating different management
scenarios aimed at transportation risk reduction and/or equity. The need
for such tool is further emphasized by the anticipated growth in hazardous
waste shipments due to the NAFTA-related industrial growth.
Chapter 3 - Methodology
Introduction
To achieve the goals of the research, the accomplishment of the following tasks are to undertaken:
Task 1: Literature review of the different problem components.
Task 2: Data collection and analysis: Several data set are needed in this research:
Task 4: Development and analysis of different management scenarios:
a major contribution of this research is to identify the impacts of different
risk management scenarios. There are two sets of scenarios: the first set
of scenarios focuses on changes in the demand pattern (and amounts) such
as (1) existing conditions, (2) increases in hazardous flows due to strict
enforcement of environmental laws in Mexico, and (3) reduction hazardous
flows due to construction of new recycling facilities in Sonora and/or
Arizona. The second set of scenarios focuses on the impacts of routing
hazardous waste under different preferences (such as minimum cost, minimum
risk, risk equity, and/or a combination of thereof).
Risk Assessment Model
The solution methodology relies on the development of a suitable risk
assessment model. This is accomplished in three steps: (1) selecting a
general category under which the risk assessment model will be implemented;
(2) review of different risk assessment models in the selected area; and
(3) selecting a risk assessment model appropriate for the border region.
To select a suitable model one may either choose an existing model (or
a combination of existing models) from the literature, or develop a new
risk assessment model.
Selecting Model's Category
After extensive review of all risk models and their advantages and
disadvantages (Table 2.1), the category of probabilistic risk assessment
models was selected as the appropriate area of investigation. This selection
was based largely on the fact that all data required for the analysis was
not complete or available.
In probabilistic risk assessment, risk is calculated as the product
of the probability of occurrence of a hazardous waste accident (or incident)
and the consequences of that accident. The outcome of the risk estimation
process is the calculated risk associated with each link in the transportation
network model. If the objective is to minimize the risk in a network, the
calculated risk will be the input to the proposed routing model (9).
Alternatively, if the objective is to minimize cost, transportation cost
will be the attribute of each route segment. However, in this type of research,
most of the time both cost and risk need to optimized to construct a risk
profile.
Review of Probabilistic Risk Assessment Models
A key component in probabilistic risk assessment models is the calculation
of truck accident probabilities and the probability of different outcomes
of each accident. In the following sections, the development of truck accident
probabilities is presented.
Truck Accident Probabilities
In the current United States Department of Transportation (USDOT) guidelines, the probability of a hazardous materials accident is computed as follows (10,11):
Based on equation (3.2), default truck accident rates and release probabilities for the use in hazardous materials routing and analysis were calculated in Table 3.3. These default values were calculated as shown in Tables 3.1 and 3.2 Table 3.3 (37) presents typical values of truck accident rates and release probabilities that can be used as default values in equation (3.2). A key aspect of Table 3.3 is that both truck accident rates and release probabilities vary with area type (urban or rural) and roadway type. The data in Table 3.3 could be used as national default values, however, these data limit the analysis to the level of release of hazardous materials given an accident. In reality, the outcome of the accident could be: (1) spill, (2) fire, (3) explosion, and (4) threat.
Glickman in 1992, used the same procedure in a more detailed analysis for risk assessment of transporting flammable liquids in bulk (13). He used the following equation in his analysis:
| Highway Class | Truck accident rate, TARi
(accidents per million veh-mi) |
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| Area Type | Roadway Type | California | Illinois | Michigan | Average * |
| Rural | Two-Lane | 1.73 | 3.13 | 2.22 | 2.19 |
| Rural | Multilane undivided | 5.44 | 2.13 | 9.50 | 4.49 |
| Rural | Multilane divided | 1.23 | 4.80 | 5.66 | 2.15 |
| Rural | Freeway | 0.53 | 0.46 | 1.18 | 0.64 |
| Urban | Two-Lane | 4.23 | 11.10 | 10.93 | 8.66 |
| Urban | Multilane undivided | 13.02 | 17.05 | 10.37 | 13.92 |
| Urban | Multilane divided | 3.50 | 14.80 | 10.60 | 12.47 |
| Urban | One-way street | 6.60 | 26.36 | 8.08 | 9.70 |
| Urban | Freeway | 1.59 | 5.82 | 2.80 | 2.18 |
| Highway Class | Probability of hazardous materials release given an accident, P(R/A)i | ||||
| Area Type | Roadway Type | California | Illinois | Michigan | Average * |
| Rural | Two-Lane | 0.10 | 0.071 | 0.073 | 0.086 |
| Rural | Multilane undivided | 0.10 | 0.071 | 0.064 | 0.081 |
| Rural | Multilane divided | 0.09 | 0.064 | 0.062 | 0.082 |
| Rural | Freeway | 0.08 | 0.111 | 0.095 | 0.090 |
| Urban | Two-Lane | 0.08 | 0.059 | 0.069 | 0.069 |
| Urban | Multilane undivided | 0.06 | 0.052 | 0.055 | 0.055 |
| Urban | Multilane divided | 0.07 | 0.048 | 0.058 | 0.062 |
| Urban | One-way street | 0.07 | 0.050 | 0.056 | 0.056 |
| Urban | Freeway | 0.06 | 0.055 | 0.067 | 0.062 |
| Highway Class | ||||
| Area Type | Roadway Type | Truck accident
rate (accidents per million veh-mi) TARi* |
Probability of
release given an accident P(R/A)i** |
Releasing accident
rate (releases per million veh-mi) |
| Rural | Two-Lane | 2.19 | 0.086 | 0.19 |
| Rural | Multilane undivided | 4.49 | 0.081 | 0.36 |
| Rural | Multilane divided | 2.15 | 0.082 | 0.18 |
| Rural | Freeway | 0.64 | 0.090 | 0.06 |
| Urban | Two-Lane | 8.66 | 0.069 | 0.60 |
| Urban | Multilane undivided | 13.02 | 0.055 | 0.77 |
| Urban | Multilane divided | 12.47 | 0.062 | 0.77 |
| Urban | One-way street | 9.70 | 0.056 | 0.54 |
| Urban | Freeway | 2.18 | 0.062 | 0.14 |
* : Calculated from Table 3.1
** : Calculated from Table 3.2
where:
Each term on the right hand side of equation (3.5) can be replaced with the product of two probabilities, based on the operative definition of conditional probability:
Selecting the Probabilistic Risk Assessment Model
The model in equation (3.7) is considered an acceptable probabilistic
risk model for the assessment of hazardous materials shipments. This model
can be used in calculating the risks associated with the shipment of hazardous
waste in the border region. However, it requires an extensive data availability
and analysis in order to evaluate the different variables in the model.
These specific data are very difficult to obtain. Moreover, one main goal
of this research is to study the transportation issues related to the hazardous
waste shipments based on considering both risk and cost rather than developing
a risk model only.
Developing a Risk Assessment Model for the Border Region
It is important to present a complete picture of different patterns
of hazardous materials and hazardous waste shipments generated by the Maquiladoras.
To achieve this goal, it is necessary to introduce transportation risk
pathways generated by the shipments of hazardous materials from/to different
maquiladora plants in Mexico.
Transportation Risk Pathways
The analysis of the risks of transporting hazardous substances and waste in the US-Mexico border region is a complex task. Achieving this task requires the ability to separate the various patterns of shipments into transportation pathways.
The first pattern of transportation pathways is characterized by shipments of hazardous substances to individual maquiladora for processing and assembly purposes (Figure 3.1). The majority of these substances are imported from the US industries as raw materials to be used in treatment, degreasing, cleaning materials in assembly oriented industrial processes. However, some of these transboundary shipments maybe regenerated by in-state Mexican shipments of these substances. These shipments will create two groups of pathways as shown in Figure 3.1: 1) pathways from the US to the maquiladora plants in Mexico, and 2) pathways within Mexico (i.e., pathways of shipment
from Mexico industries to the Maquiladoras). Most importantly, there are transportation risks associated with transboundary shipments of raw material to the maquiladora plants both in the US and in Mexico.
The USEPA database shows that of the 2,153 Maquiladoras producing hazardous waste in 1992, only 329 industries have records of shipments to the US. This means that only 15% of Maquiladoras have actually transported waste to the US.
As shown in Figure 3.2, two risk pathways are apparent from these shipments: waste may go directly to a disposal facility in the US for incineration or landfilling, or may be re-imported by a US recycling facility for treatment. In addition, two additional indirect risk pathways are apparent from recycled hazardous waste: a) the transport of residual hazardous waste from the recycled facility to a point of disposition, and b) shipments of re-used and treated waste for industrial purposes.
At this point, Mexican environmental law provides a safe haven by allowing the storage of hazardous waste at a maquiladora facility indefinitely, based on technical storage standards that are being developed. Moreover, some of none-RCRA hazardous waste generated at the plants can and are being shipped to recycling and reuse plants in Mexico. In addition, some waste is also sent either to disposal facilities (i.e., landfills) or to the off-site storage facilities in Mexico.
Transboundary shipments of hazardous waste from Mexico to the US have several pathways. According to Mexican law, hazardous waste generated by the Maquiladoras should be shipped back to the US for treatment, storage, or disposal (TSD).
The number of such shipments on a yearly basis is unknown but a handful of hazardous waste recycling plants in northern Mexico are operating. The Titisa recycling facility in Baja California has a capacity of recycling 15,000 tons of hazardous waste, representing an estimated 15% of the waste produced by Baja maquiladoras (3).
Transportation risks are also incurred by shipments from these recycling facilities either through the transport of usable byproducts from recycling or the transport of residual
hazardous waste requiring disposal. Information on shipment patterns of residual waste to disposal facilities is not available at this time. Substantial growth is anticipated in recycling facilities that utilize hazardous waste generated from the maquiladora industry.
Although a fairly robust database of generation-to-destination flows
of hazardous waste has been generated, the database is limited to reported
waste streams from generators in Mexico to first-line TSD facilities in
the US. The pattern of shipments and the amount of hazardous waste shipped
from the Maquiladoras to different Mexican facilities remain unclear. Moreover,
the amounts of hazardous waste from Mexico that are not recorded in RCRA
manifests but nevertheless do enter the US are also not available. At this
juncture in the research, the available data will permit a reasonable picture
of direct transboundary shipments of hazardous waste to TSD facilities
in the US.
Mathematical Development of the Risk Assessment Model
In general, any hazardous material shipment has the potential of generating risk at two possible locations: at the facility during loading and unloading and at any point along the shipment route. Transportation risk results from equipment failure during shipment or by traffic accident. In this research it is assumed that the risk generated by loading and unloading at different facilities and the possible risk generated by equipment failure is minimal.
The total quantity of risk generated by hazardous material shipments is equal to the risk of hazardous material shipped to the US industries in Mexico plus the risk of hazardous wastes shipped out from these industries. This can be expressed by the following equation:
The risk of hazardous materials shipped to the US industries in Mexico
is equal to the risk generated from the shipment of hazardous material
from the US and Mexican sources of raw materials to the Maquiladoras in
Mexico. By ignoring the stop-over at ports of entry, the transportation
risk associated with these shipments can be presented in the following
equation:
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3.3.2.2 Transportation Risk of Hazardous Waste
The risk of transporting hazardous wastes is defined as the many-origin-to-few-destination
problem as shown in Figure 3.2. This can be calculated using the following
equation:
| M | |
| Risk(HW) = | Risk
(HW)m |
| m=1 |
whereby Risk(HW)m is defined as:
| RJ | SI | DJ | |||||
| Risk(HW)m |
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TR(mrj) |
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TR(mli) |
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TRi | |||
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TR(rjdj)} |
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A major goal in developing this model is to capture the risk associated with the shipments of hazardous waste from the maquiladora industries to the US, on humans and on the environment.
The human factor is typically measured by population exposure to hazardous waste. The population exposure can be measured by the number of people living within a one mile along the transportation routes. With respect to measuring environmental impacts, one approach is to obtain the costs of site clean-up of hazardous waste as a result of an accident. A second approach that may be considered is the cost of traffic delay due to an accident involving a hazardous waste shipments. In this case, the delay cost consist of direct cost (fuel cost) and indirect cost (pollution to the environment) due to the temporarily closure of a highway to clean up the accident site.
As stated previously, transportation risk is calculated as the product of the probability of occurrence of a hazardous material accident and the consequences of that accident. i.e.,
As stated before, the first two components are given in Table 3.2, while the third term, Lk, is the length of the route segment.
Since hazardous waste consists of liquid and solids, the outcome of an accident could be a spill or a threat only. However, some hazardous waste are ignitable and could catch fire, but these outcomes are ignored in this research because of: 1) the hazardous waste is usually shipped in drums which reduces the probability of an explosion, and 2) hazardous waste in the drums consist mostly of a mixed waste. This will reduce the concentration of the ignitable material and the probability of having an explosion.
The quantity of release given an accident is calculated as the average amount of hazardous waste released in different hazardous waste accidents. A second approach to estimate these values is by assuming that the quantity released in an accident is equal to 10% of the average load per shipment. Furthermore, the impacted area V(R) is assumed to be 1 square foot per gallon of hazardous waste released.
Using these averages, equation (3.16) can be written as:
In the literature, there are three components of risk: population risk, environmental risk, and property risk. The FHWA guildlines measured the first two components, but did not specify when to consider both risks and how to combine or weight these risks when both are considered (14). Most routing studies have avoided these issues by considering only population risk. However, a 1987 Canadian screening method suggested some specific weights for use in combining the three component of risks. The weight factors for population, property and environmental risk were 60%, 10%, and 30% respectively. It is unlikely that all users would agree on a single set of weight factors appropriate for all circumstances.
The method used in this research largely follows the risk assessment
method in the FHWA routing guide. Environmental risk was calculated as
the probability of an accident times the consequences of the accident.
In this research, consequences were calculated as the clean-up cost per
square footage as shown in equation (3.19). Although this method follows
the steps of the FHWA report, it provides an approxy procedure for measuring
the adverse effect of an accident of the environment. Another direct approach
could be by creating an index to measure the direct consequence of a release
to the environment. This index can be introduced as a function of the depth
of the ground water table at the location of potential accidents and be
a function of the nature of the hazared. However, this method was not considered
in this research.
Accident Consequences on Population
In the earlier FHWA guidelines (15), population exposure for a given route segment was determined as the total number of persons exposed in the impact area. The impact area was defined as a band of equal width, usually 1/2 miles, on either side of the roadway segment. That approach had drawbacks because it assumes that the entire population along a route segment is exposed to the same amount of risk. Actually, only the population within a specific distance, say 1/2 mile, from the release location should have been considered. The first model has been modified and adjusted by dividing the population within the impact area along the entire route segment by the length of the route segment. This correction was suggested by Harwood and Russell and later incorporated in the updated guidelines published by the Department of Transportation Research and Special Programs Administration (RSPA) (11,16).
To understand the differences between the two approaches, assume a route segment (k) in the transportation network has a population density of Pd in the impacted area Ia. As shown in Figure 3.3(a), representative of the first method, the total number of persons within the specified impact zone width are exposed to a hazardous waste release along segment k [C(P)k]. This is calculated as follows:
Pd = population density given in persons per square miles.
Ia = impact area in square miles.
Figure 3.3(c) represents the population exposure area that will be considered in this research. The suggested model assumes that the personal injury consequences of a hazardous waste release are proportional to the population potentially exposed to the releases. Moreover, people in the exposed area are within equal distances from the release point. It is important to note that in case of gaseous release (which is ignored in the case of hazardous wastes, the wind conditions must be considered. Therefore, the impact area is (0.25 x W2 x ) and the population exposure is given by:
)
x PdTransportation Routing Algorithm (TRA)
In routing, the total population risk and/or total environmental risk for each alternative route is computed by summing all individual risk components along each route. No attempt is made to combine or weight the population and environmental risks of a given route, so these risks must be considered separately.
Figure 3.4 shows the flow chart of the Transportation Routing Algorithm (TRA) implemented in this research. First, the quantities of hazardous waste (or demand) is calculated for a selected scenario. Second, a flow matrix is developed which assigns the demand of each Origin-Destination (O-D) pair in the transportation network. Third, TRA computes the different link attributes for all links. These attributes are: 1) the population risk, 2) the environmental risk, and 3) the transportation shipping cost. The first two link attributes are computed using equations (3.20) and (3.19). The transport cost is calculated assuming an overall average cost of $1 per mile of travel. This assumption, while robust, is valid because the cost is approximately proportional to the travel distance. It is a simplifying assumption given that the research focus is not on transport cost, but on the risk side of the coin. The risk profile is a necessary tool which facilitates decision-making regarding different management scenarios.
Fourth, utilizing a shortest path algorithm, different routes are generated for each O-D pairs in the transportation networks (each having a specific set of values for the three different route attributes). Based on the decision makers objective and the scenario structure, if the objective of optimization is to minimize the population risk, transport paths are identified which minimize the risk. For each route, the corresponding environmental risk and the transportation cost will be calculated. The same procedure is repeated for different objectives. It is important here to note the direct optimizing of all the three attributes requires that the decision maker identify the trade-off between them. Having identified the risk and cost values for each selected routes, a risk profile can be developed which helps us in study this particular scenario. .
(a) Method used by earlier FHWA guideline (1980) (15)
The goal of this problem is to optimize the following three objective
functions:
To illustrate the risk assessment procedures for hazardous waste routing analyses, a numerical example of the calculations will be provided. The example will address the routing problem of a single origin-destination node pair (AE) shipment, on the highway network shown in Figure 3.5. Calculations are summarized in Table 3.4.
In table 3.4, the values in columns (5) and (6) were from Table 3.3. Column (8) was calculated as the product of (5), (6), and (7) using equation (3.2). Total persons exposed (column 10) was calculated from equation (3.25). Population risk was calculated as in equation (3.20). The environmental risk was calculated as in equation (3.19) assuming that only 1% of the average number of shipments and that each shipment carried an average of 10 tons. The average quantity released V(R)k is equal to:
The results of three risk models (achieving the minimization of the three different objectives: population risk, environmental risk, and transport cost) are listed in columns (11-13). These results used to develop a risk profile as shown in Figure 3.6. This risk profile will help in making different management decisions.
The population risk, environment risk, and transport cost computations are valid for one node pair only (AE). To determine the yearly population risk, yearly environment risk, and yearly transport cost for a given network consisting of many origin-destination node pairs, each node pair's attributes (population risk, environmental risk, and transport cost) has to be multiplied by the number of yearly shipments of that node pair.
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Last updated 6/10/99