computer techniques in environmental studies 585 · pdf fileof the software has been developed...

Creation of a concept for advanced use of

ecological risk assessment in environmental

management

G. Lefebvre, L. Houde

Environment Branch, Hydro-Quebec, 75 W. Rene-Levesque Blvd,

16th Floor, Montreal, Quebec, Canada

Abstract

In order to manage the environmental risks related to its installations, Hydro-Quebec has done many studies and built a number of computing tools. Mostof the software has been developed in a shell which allows easy data input andgraphical representation of the results, which can be georeferenced andsuperimposed on maps. The shell also allows comparison and reuse of resultsbetween models.

The most recent software is designed for ecological risk assessment forwhich Hydro-Quebec is developing a framework involving the use ofmathematical models. The ultimate aim is to provide a tool which canestimate the fate of pollutants in some compartments of an ecosystem andevaluate the potential effects of chemicals at levels of biological organizations.

1 Introduction

Hydro-Quebec is a government-owned electrical utility in the province ofQuebec, Canada. It generates electricity mainly from hydro sources (96%)with minor contributions from nuclear and conventional thermal plants. Theutility's generating capacity in 1994 was close to 30 GW.

The Hydro-Quebec transmission system is unusual in that most of theenergy is produced in northern areas whereas the customers are mainlyconcentrated hundreds kilometers to the south. The territory served coversroughly 1.54 million knf with more than 160,000 ha of rights-of-way to bemanaged and vegetation control to be done on 75% of these.

Hydro-Quebec also distributes electricity, operating an extensive networkof lines and more than 500 substations. With approximately 2.2 million woodpoles, most of them PCP-treated, the utility has to manage wood pole storage

Transactions on Ecology and the Environment vol 10, © 1996 WIT Press, www.witpress.com, ISSN 1743-3541

584 Computer Techniques in Environmental Studies

sites as well as dangerous-waste storage sites.

2 An ecosystemic approach

Assessing the ecological risks inherent in Hydro-Quebec's operations isimportant. For this reason the utility has developed a general frameworkallowing this exercice to be done systematically. The framework is intended toserve as the guideline for an iterative approach to each of the specific activitiesidentified. For each case, the goal in applying the framework is to helpspecialists characterize specific threats to ecological resources and selecteffective solutions for mitigating unacceptable risks.

With respect to Hydro-Quebec operations, we have identified sevenspecific installations and activities where an ecological risk assessment couldbe usefully performed:• Yard storage for PCP-treated poles• Potential use of soil moderately or slightly contaminated with PCP or oil• Hazardous-material storage sites• Rural and urban substations• Thermal generating stations• Herbicide spraying• Mercury contamination in hydroelectric reservoirs.

In most of these cases, the primary contaminated media are site soils,nearby surface waters, and groundwater. The main pathways of contaminanttransport are infiltration of soils and groundwater, and water runoff toreceiving surface waters. Quantifying exposure entails measuring or modeling.Since sampling and chemical analysis are very expensive, computer simulationmodels of contaminant transport and distribution can be used to estimatecontaminant concentrations in soils, surface waters, sediments andgroundwater at lower cost.

The sequential assessment of risks could proceed through the use of moredetailed, process-level ecological models which focusing on populationprojections based on demographic or bioenergetics models. These predictivemodels offer support to assessors who have to deal with very complexproblems when predicting the probability of adverse effects resulting fromexposure to contaminants.

To conclude this section, we present one of the problems mentionedabove, the potential reuse of soil moderately or slightly contaminated withhydrocarbons. When land is transferred or reassigned, its purpose or use oftenchanges. In some cases, Hydro-Quebec wants to reuse the excavated soil atother sites. An ecological risk assessment (ERA) study could ensure that theuse of contaminated soil at a specific site does not pose a threat to theenvironment. Such study depends on mathematical modeling.


Computer Techniques in Environmental Studies 585

3 Computing tools

In order to help specialists in their work, Hydro-Quebec, in cooperation withdifferent partners, has developed a number of computing tools in the 1980s.These are composed mainly of mathematical models, expert system, artificial-intelligence system, decision support systems, and a wide variety of databases.On the whole, this software is based on the use of a development shell.

3.1 Simulation system

The architecture of the simulation system is presented at figure 1. It is in facta set of software tools which allow users to structure and pilot a problem-solving process in the environmental field. The system facilitates theacquisition, analysis, synthesis and transmission of environmental informationrequired to assess impacts on the environment. It includes several models witha common user-friendly interface. The simulation system offers high-performance visual tools and a data management system which allows easycomparison and reuse of results between models. Description ofhydrodynamic characteristics of a river, for instance, which might represent amajor time-consuming step, can be used either for the hydrodynamic modeland the mass pollutant dispersion in surface water model.

Data acquisition can be done in various ways: graphical informationsystems (GIS), laser videodisk, satellite images, topographical maps, etc. Anautomatic finite-element mesh builder is available for all the computing tools,which substantially reducer's the user's task in the discretization process.

Figure 1 - Simulation system



3.2 Mathematical models

A firm believer in the concept of sustainable development, Hydro-Quebec hascommitted itself to pursuing a more efficient approach to managing thedifferent sources of risk inherent in the operation of its facilities andequipment. Better risk management calls for greater understanding and moreaccurate assessment of the sources of danger. In order to reach this objectiveand allow the potential impact mentioned in section 2 to be adequatelyassessed, the utility has developed or incorporated a number of mathematicalmodels for contaminant dispersal in air, water, and soil. It has also developeda model for simulating the hydrodynamic characteristics of a body of water(lake, river, etc.). Some of these models will be described in more detail insection 4.

3.3 Expert system and Artificial Intelligence system

An expert system has been developed to provide a learning tool for thoseresponsible for taking action when accidental spills occur at a substation. Inorder to simulate the expert's behavior as closely as possible, the interventionprocess was broken down into four stages:• characterization of the site and the spill conditions and identification of the

possible paths that the contaminants could follow;• visual reconnoitering of the probable contamination sites;• prioritization of the potential intervention points;• determination of the most suitable means of containing and recovering the

contaminants at each site.Another system, which has been developed in collaboration with Carnegie-

Melon University concerns impact assessment by automated learning.

3.4 Decision support systems

In order to help managers in their decision-making task in critical situations orto better manage existing facilities and develop environmental standards, anumber of administrative units at Hydro-Quebec have jointly developedseveral computerized tools using decision support systems.

These decision support systems are designed specifically for themanagement of nuclear crises and assessment of the repercussions oftechnological accidents at certain installations, e.g. explosion of an oil tank,failure of a turbine in operation at a thermal generating station, etc. Anotherdecision support system was developed for assessing the consequences ofenvironmental accidents that could occur at or near hazardous-waste storagesites. To improve the management and location of PCP-treated wood poles,the utility is now in the process of developing another system comprising fourmathematical modules specifically for that purpose. The most recent decision



support system is for ecological risk assessment. The remainder of this paperwill focus on this system.

4 Decision support system

In order to resolve some of the problems identified above, we neededmathematical models that could assess problems different from those we couldassess with our existing models. We also needed models that could completethose already available in the shell. Many models are neither user-friendly noravailable in a same platform. We therefore decided to integrate four newmodels in our shell and to transfer our simulation system to an OLE 2.0Windows-based format.

4.1 Choice of the models

We developed a number of model selection criteria which included:• Accepted physical equations: the models had to be based on accepted

physical equations.• Input data requirements: a model might be very interesting but, if it requires

a lot of complex input data, it will be neither useful nor easy to use.• Validated/recommended models: as we have to use the models in our

studies, we looked for standard models. Discussions with authorities andthe scientific community often oriented us to some specific models.

• Number of product classes: the more product classes (organic compounds,metals, etc.) the models can take into account, the more advantageous theyare.

• Uncertainty analysis: Monte Carlo simulation or other uncertainty analysiswas a primary characteristic sought.Other criteria such as cost, access to source codes and availability of a

designer to modify the model were also considered.In order to establish a preliminary list, we based our research on different

software databases and conducted a bibliographical review. This first stepallowed us to identify a list of 76 potential models which we then classifiedinto four groups according to the area of application: atmospheric dispersion,surface water dispersion, soil and groundwater dispersion, multimedia andecological risk. Then, according to the information we were able to gather onthese models and by consulting recognized specialists, we reduced the listfrom 76 to 27. Since most of our production is hydroelectric, atmosphericdispersion is not a major stake for Hydro-Quebec and, in any case, we alreadyhad our own model, we decided to focus on the other groups.

Evaluation of the models and many discussions with specialists led us toidentify four models of potential use.



4.1.1 Qwasi Model (Mackay[l,9J)The Qwasi (Quantitative Water Air Sediment Interaction) model is typicallybased on the concept of fugacity, which expresses the tendency of a chemicalto escape from one chemical phase to another. This model was developed byMackay from the University of Trent (Ontario).

The model treats four bulk compartments: air, water, soil and sediment.Each of these is considered to consist of subcompartments of varying fractionsof air, water and organic matter. Equilibrium is assumed to exist within, butnot between, compartments. The model calculates the steady-statedistribution and concentration of chemicals and the persistence in theenvironment. The accumulation media and dominant pathways of transfer aredetermined.

4.1.2 FRAC3DVS Model (Therrien[2,5], MacQuarrie[3], Schafer[4])This model provides a three-dimensional solution of the flow equations forgroundwater and mass transport in porous media. The program wasdeveloped by Therrien at the Laval University in Quebec city. The solutioncan be obtained using either the finite-element or the finite-differenceapproach; both steady-state and transient situations can be simulated. Theporous medium can be completely or partially saturated, which means that thezone above the water table can be simulated explicitly.

Three-dimensional simulation of the transport of one or several dissolvedsubstances is also possible. The transport processes considered are:advection, dispersion, adsorption and degradation, represented by a first-orderlaw of kinetics. Specific or diffused sources of pollution, whose intensity canvary over time, can be considered for the simulation.

The use of numerical solution approaches allows heteregeneous porousmedia to be taken into account. The model has already been used in aprobabilistic approach (Monte Carlo) where the hydraulic conductivity of themedium varies from one element to another.

Another feature of this model is that it can simulate the presence ofpumping or injection boreholes, observation shafts, surfaces allowing seepageabove the water table and recharge by infiltration. The model has already beenused and validated by researchers at universities across North America.

4.1.3 SOILFUG Model (Di Guardo[6,7])This model is a fugacity-based model developed by Di Guardo et al. from theInstitute for Environmental Studies at the University of Toronto, to describethe unsteady-state behavior following application of agricultural chemicals. Itevaluates the importance of different phenomena (degradation, volatilization,runoff/leaching) and the possibility of a build-up of concentrations afterprolonged use of chemicals. It is an unsteady-state but equilibrium eventmodel.

The simulation is performed by computing the amount of organic matterpresent in the soil over a period of time according to slow and fast degrading



fractions. The model can take into account different soil types and differentrainfall scenarios (steady rainfall or sporadic storms).

Many validation exercices, in the form of field experiments, for instance,have been performed with pesticides such as chlorobenzene,hexachlorobenzene, atrazine, carbofiiran, lindane, simazine, etc. in Canada, theUnited States and the United Kingdom. Most produced conclusive results.

4.1.4 CASM Model (Bartell[8], Suter[10])The Comprehensive Aquatic Simulation Model (CASM), developed by Bartellfrom SENES Oak Ridge (USA), simulates daily changes in the biomass ofaquatic food web populations. The aquatic food web consists of tenfunctionally defined populations of phytoplankton, five zooplanktonpopulations, three planktivorous fish populations and a single population ofpiscivores. The model uses difference equations to simulate daily changes inbiomasss of the food web populations. Input requirements include daily valuesof light, temperature, and nutrients. This model requires good knowledge ofthe effects of toxic substances in order to estimate changes in biomass thatresult from exposure to a constant chemical concentration.

The model itself has been subjected to detailed numerical sensitivityanalyses. Predicted toxic effects on selected model components have beencompared to effects measured for phenolic compounds in experimental ponds.

4.2 Results of the project

The integration of recognized models in the same environment allows us tosimulate the behavior of pollutants in different compartments of an ecosystem.As shown in Figure 2, users can build their own set of models.

In the case of aerial application of herbicides in rights-of-way, for instance,the user can identify the area to be sprayed by defining the herbicidecharacteristics, soil characteristics, etc. which completes the description of thepreprocessing. The user can then choose the compartments to be simulated,which corresponds to choosing different solvers. Lastly, the user selects theway the results should be presented. The input data, e.g. preprocessing inputsand results of one model, are then passed from one model to the otherautomatically.

Oil leakage from a transformer represents another potential use of thesystem. For this simulation, the user can define the area to be simulated, usingthe GIS (Geographical Information System) component, and then definepreprocessing inputs. The user can choose the problems to be assessed byselecting the different models. In this case, the oil leakage can leach into thissoil or migrate at the soil surface toward a small pond located beside thesubstation. The user should then select FRAC3DVS, Soilfug, Qwasi andCasm.



r\L

Preprocessing Solution Postprocessing

Simulation models

Figure 2 - Composition of simulation by user

The foregoing examples represent just a few of the possibilities for thedifferent models. The next two figures show the preprocessing module for theQWASI model (Figure 3) and an example of postprocessing options for theQWASI-Fish model (Figure 4).

5 Conclusion and future work

As mentioned, Hydro-Quebec has to manage facilities and activities thatrepresent environmental risks and has therefore developed software to helpspecialists and managers in their work. The latest DSS represents a newapproach, since it allows the user to choose a specific problem and then buildup the expected application in order to assess the fate and transport of apollutant in different compartments of the environment.

The system described represents phase 1 of the project. In the nearfuture, Phase 2 of the DSS will begin. This consists in integrating at least oneother model and adapting the previously integrated ones to Hydro-Quebec'sspecific problems and needs, in collaboration with model designers. Interfaceswith databases on specific products, fish species native to Quebec and also onHydro-Quebec's installations, to name but a few, should be developed shortly.This kind of modifications can be done relatively easily and at reasonable costwith the architecture already developed.



mp,cdu*chmqutlp,,*,

Pretraltement; Donnees d'entree du modele QWASI

JT ( Metier )( Ajouter ]

u rrOu m]

Figure 3 - QWASI model (preprocessing)

Volume; 10 cm3Fecfeur de digestion: 3_Tauxdecfoissance: 1 flOE-03

Taux de consommmlion 2

Figure 4 - QWASI-Fish model (postprocessing)

6 References

1. Mackay, D , Multimedia Environmental Models - The fugacity approach,Lewis publishers, Michigan, 1991.

2. Therrien, R, Sudicky, E.A., Three-Dimensional Analysis of Variably-Saturated Flow and Solute Transport in Discretely-Fractured PorousMedia, Journal of Contaminant Hydrology, May 1995.

3. MacQuarrie, K.T.B., Sudicky, E.A., On the Incorporation of Drains intoThree-Dimensional Variably-Saturated Groundwater Flow Models, WaterResources Research, May 1995.



4. Schafer, W., Therrien, R, Simulating transport and removal of xyleneduring remediation of a sandy aquifer, Journal of ContaminantHydrology, February 1995.

5. Therrien, R, Sudicky, E.A., McLaren, R.G., User's Guide forFRAC3DVS : An Efficient Simulator for Three-dimensional, Saturated-Unsaturated Groundwater Flow and Chain-Decay Solute Transport inPorous or Discretely-fractured Porous Formations, September 1994.

6. Di Guardo, A., Mackay, D , Cowan, C.E., Calamari, D , A FugacityModel of Chemical Fate in Soil: Application to Amendment AssociatedChemicals, Poster presented at SETAC - 15th Annual Meeting, Denver,Colorado, U.S.A., October 1994.

7. Di Guardo, A., Williams, R.J., Matthiessen, P., Brooke, D.N., Calamari,D , Simulation of Pesticide Runoff at Rosemaund Farm (UK) Using theSoilfug Model, Environmental Science and Pollution Resources , 1994, 1(3) 151-160.

8. Bartell, S.M., Gardner, R.H., O'Neill, R.V., Ecological Risk Estimation,Lewis Publishers, Michigan, 1992.

9. Mackay, D , Paterson, S., Mathematical models of transport and fate,Chapter 5, Ecological risk assessment, ed. Glenn W. Suter II, pp 129-152, Lewis Publishers, Michigan, 1993.

10. Suter, G., Bartell, S., Ecosystem-Level Effects, Chapter 9, Ecologicalrisk assessment, ed. Glenn W Suter II, pp 275-308, Lewis Publishers,Michigan, 1993.


computer techniques in environmental studies 585 · pdf fileof the software has been developed...

Documents