Hazardous Waste Logistics: Strategic and Tactical Decisions

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Hazardous Waste Logistics Strategic and
Tactical Decisions
Department of Transport Engineering Pontificia
Universidad Católica de Chile
Rodrigo A. Garrido
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Starting with an easier problem...Design of an
Urban Waste Transport System

• Santiago is the capital of Chile with 6 million
  inhabitants.
• 1980s Santiago generated 0.63 kg/Inhab-day of
  residential solid waste today it reaches 1.4
  kg/Inhab-day.
• Currently 95,000 tons of RSW are generated in
  Santiago, which are disposed into 2 Sanitary
  Landfills

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Problem Definition

• Logistics management of a RSW collection and
  disposal system with the following stages
• Collection picking up waste from generation
  points
• Hauling transporting it from generation points
  or Transfer Centers to landfill
• Final disposal dropping off the load into the
  landfill

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Simplification Zoning the City

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Simplification Assuming fixed routing cost

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The problem to solve is to...

• Locate unknown number of Transfer Centers and
  Landfills legal regulation
• Distribute the waste to TC and from these to the
  Landfills
• Choose type of trucks for both journeys
• These decisions are simultaneously made to
  minimize the total system cost

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Proposed Solution Mixed integer programming
model

• Objective Function includes installation and
  operating costs for both stages
• Subjected to capacity constraints, available
  technology, demand satisfaction and non
  negativity.

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Application to Santiago

• Planning horizon year 2020
• Annual growth rate of 3
• Centroids reflect demographic density
• 14 possible landfill sites and 5 for TC
• 240 Integer variables, 19 Binary variables
• 240 Continuous variables, 589 Constraints

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Heuristic Solution Network partition and
penalties

• But...If the waste was dangerous?

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Why do we need to move Hazmat?

• Hazmat include explosives, flammable, oxidant,
  poisonous, infectious, radioactive, or corrosive
  substances among others
• Industrial production processes use hazmat as
  manufacturing components and often generate
  hazmat by-products.
• Hazmat must be safely transported from their
  origin to special facilities to be used in a
  production process, modified to decrease their
  degree of danger, or properly disposed.

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Generation and Distribution of Hazardous Waste in
an Urban Context

• Objectives
• To estimate the generation of hazwaste in a
  metropolitan area
• To develop a model for routing hazwaste in the
  urban transportation network
• To locate treatment plants

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How to proceed...?

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The Generation Model

• Industrial classification into 28 Categories
• Standard hazmat 14 categories
• - Corrosive, Toxic, Reactive, Flammable.
• Current generation ???
• Forecasting aggregated ARIMA model
• Desegregation at county level, Land Use
• Hazwaste to be transported per county

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Disaggregation at county level

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How much of that is transported?

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What is the cost of an incident with hazmat?

• Potential to provoke fatalities or injuries to
  the inhabitants in the vicinity of the event
• Impact area defined by a dispersion radius ?
  that depends substance properties and topography

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An accident in an arc and its consequence
Probability of an accident in route R
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Now, lets route!!!

Sherali et al (1997)
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Problems with that formulation

• If we had several hazmat types?
• How much of m, h is too much? not yet...
• If we find an optimal route,
• what happens when used daily?
• What is the meaning of a fair solution?

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Routing multiple hazmat frequently transported

• Each with different degree of danger

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But... did you forget about the people?

• Consider an arc a and a hazmat with radius l

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How to incorporate equity on routing?

• Control the difference in risk for any two zones

• Lets call it the Gopalans constraint
• Gopalans constraint can be included in the
  routing model we have so far

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How can we improve Gopalans constraint?

• It assumes a fixed acceptable risk for each zone
  How high that risk could be? not yet...
• It assumes that the hazmat movement will produce
  the same maximum risk on each zone
• Do all the zones have the same baseline risk?

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The Relative Degree of Risk

• Degree of Risk for given hazmat r

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A practical value for the risk function

• Assuming a constant risk function w/r to space in
  Gopalans expression

people

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Risk acceptability and equity

• Each zone has a basline risk Bk

We can modify P1 with this new equity constraint
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Multiobjective Routing of Multiple Hazmat

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How else could we improve the system?

• So far we have found a set of non dominated paths
  to route hazmat
• Each shipment travels from the generation point
  to a fixed and known treatment plant
• How many plants should we have?
• Where should they be located?

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OK, but Not in my backyard!

• Locating hazmat treatment plants require at
  least
• Low accident probabilities at each site
• Low acc prob during transportation to each site
• Low consequences if an accident occurs
• Low total logistics cost
• High social acceptability
• High equity
• Clearly a multiobjective location problem

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Some Definitions

• In a directed graph, let O be the set of hazmat
  generators and D the set of potential plants

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Objectives of our Model

• Minimum assignment cost
• Minimum setup cost
• Min catastrophic consequences
• Expected number of affected trucks
• Cost of catastrophic accident in site j Caj
• Expected consequence in j

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The Model
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Multicriteria Analysis Multiobjective
Programming

• Proceed in two steps
• Search for a set of feasible solutions Pareto
  optimal
• Multicriteria function to find Best Solution

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First Step Finding the Pareto Optimal Set

• For a given vector (a1, a2, a3) solve

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Second Step The best compromise-solution

• For a given metric p solve
• L1 gives the best compromise solution for
  linear deviation
• L2 gives the Euclidean distance
• L8 gives the most equitable

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Application Hazwaste in Santiago
Chile(ongoing!!!)

• Santiago has 39 boroughs.
• The strategic transportation network has 6,000
  arcs and 2,000 nodes.
• Generation in 24 centroids, with 6 potential
  treatment plants
• Four types of hazwaste

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Santiagos Hazwaste CaseEstimation of Accident
Probabilities

• Summary of estimated conditional probabilities at
  network level 

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Santiagos Hazwaste CaseEstimation of the
Consequences
Impact area for each category of hazmat
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Santiagos Hazwaste CaseEstimation of the
Consequences
Summary of registered accidents by type of
hazmat between years 1993-1999
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The probability of an accident

• Identify and evaluate scenarios for the
  occurrence of an incident involving hazmat
• Scenarios can be described as a sequence of
  events. The events can be represented in a tree
  structure, showing a sequential progression of
  branched options event tree

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Outcome of the event treeProb of a
catastrophic accident in arc a
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Final Remarks

• A lot of unresolved issues in literature
• Risk measurement
• Equity
• Routing and location jointly?
• Bi-level optimization problem?
• Interactions between hazmat?
• Non-constant costs?
• Road pricing for hazmat, what to charge?

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Any questions?
whos that guy?