Microcomputer Implementation of Risk Assessment for Hazardous Waste Technologies

Aaron A. Jennings and P. Suresh

Department of Civil Engineering, University of Notre Dame, Notre Dame, IN 46556, USA

ABSTRACT

Two user-interactive microcomputer codes have been developed to automate a relative risk assessment of alternative hazardous waste management technologies. RISKI conducts a deterministic assessment based on the Decision Alternative Ratio Evaluation(DARE) procedure. RISK2 implements a probabilistic analysis

designed to accommodate user uncertainty and imprecise information. Both codes offer extensive user support

including default analyses and "expert systems" tohelp select management technologies and maintain assessment consistency. Both aPproachessre capableof generating cardinalscale risk penalty functions necessary for quantitative optimization planning.

KEYWORDS

risk, risk assessment, hazardous waste, expert systems, management planning, microcomputers,

user-interactive, IBM PC.

INTRODUCTION

Hazardous waste management involves a great many technological difficulties. The kinds of industrial wastes currently being classified as "hazardous" under the Resource Conservation and Recovery act of 1970 (RCRA, Pi . 9=1-580) represent a tremendous diversity of physical and chemical properties. Because of this, it is extremely unlikely that any single management technology wi l l be able to service the needs of a community or large industry. Experience has indicated that a complementary mixture of management capabilities (phgsical/chem ica l treatment, resource recovery, biological treatment, incineration, land disposal, etc.) is required to alleviate most hazardous waste generation problems. The design of these facilities remains a challenging task. However, we nave begun to accumulate enough actual design and operational experience to overcome most existing design problems. New hazardous waste technologies are rapidly emerging.

If a major fault remains inour response to the hazardous waste problem, it lies in our ability (or lack of ability) to address the issue of risk. Hazardous wastes represent a tremendously diverse set of human and

environmental dangers. The failure to successfully address this issue has been a lingering criticism of the whole RCRA program. This failure has also plagued many proposed hazardous waste fac i l i ty plans. Exl)erience has demonstrated that plans that would easily improve the state of hazardous waste management can (and often do) fail because of the public's perception of risk. Initially this was a predictable r ~ whenever the term "hazardous waste" was mentlomO. More recently, the contrivances (if not their fundamental source) of these concerns have become much more sophisticated. Hazardous waste litigation can now hinge on very specific, mechanistic questions about danger levels.

Quantification of cumulative hazardous waste management risks (as opposed to the "simple" chemical toxicology dangers) was once considered to be too elusive and very difficult to accomplish. However, new assessment procedures ate also rapidly emerging. Begor~l assessment for individual process risks, procedures are being developed to quantify the relative technological risks of alternative management schemes, and the public perception of these risks. Here "technological" risks are defined as the actual risks posed by the pr~Oabllity or failure of a treatment or disposal operation to the extent they can be estimated bg

0266-9838/86/010016 - 09 $2.00 0 COF~UTATIONAL HECHANICS PUBLICATIONS 1986

Paper received September 6, 1985. Referees: M~ John L. Oeuble and Dr Piero Melli

Environmental Software, 1986, Vol 1, No. 1 1 7

Microcomputer Implementation of Risk Assessment: AA. Jennings and P. Suresh

the "expert" scientific community In contrast, public perception of risks is the purely subjective evaluation made by the parties-at-risk This public perception is very diff icult to quantify, but can be extremely important If public concern is ignored, it wi l l be vigorously expressed in modes that often prove fatal Lo proposed plans

In this paper, we wi l l describe two microcomputer- based, user-friendly programs (RISK I and RISK2) that have been designed to implement the risk assessment of an arbitrary set of hazardous waste technologies The underlying algorithms are capable of quantifying both types of risks described above However, the programs have been designed with the inexperienced user in mind Both supply the user with all necessary instructions, and both protect themselves from non sequltur information. The intent of both is to encourage the consideration of a mixture of management capabilities, and to facil itate the assessment of risks evaluated across this broad technology spectrum

RISK I and RISK2 have also been equipped with unique user-support features. RISK I conducts a deterministic assessment capable of instructing and supporting the user with Its own "default" analysis of the user's problem RISK2 conducts a probabilistic analysis that accounts for uncertainty in the user's information In addition, RISK2 offers "Expert System" subroutines to help select appropriate treatment and disposal technologies, and to help accomplish cocsistefcg Finally, RISK2 has been equipped with the capability to learn from its past users and to use what i t has learned to hell) advise its current user

RISK A L 6 O R I T H i ~

RISKI and RISK2 are based on the Decision Alternative Ratio Evaluation (DARE) algorithm of Kles [11. The DARE algorithm may be used to resolve an arbitrary multiple criteria, multiple alternative selection problem. The approach involves a series of pairwise comparisons of alternatives considering, in turn, each of the decision criteria. The algorithm ultimately produces a normalized cardinal, relative preference scale for the evaluated alternatives.

In RISKI, the relative risks of an arbitrary set of hazardous waste technologies are calCUlated using a simple additive ut i l i ty relationship of equation (I) .

Ri = Z FiJWJ V i=l,N ; i=I,H ( I ) J

T. W I = 1.O (2)

where; R i = relative risk of the i th alternative tecflnologg,

FIj = individual factor score for the i th technology

considering the jth decision criterion,

Wj = we i~ t assigned to the jth decision criterion,

N : number of teclT~logles being evaluate(],

M : number of decision criteria being considered.

The individual factor sc~es (Fij) are normalized values of

decision criterion hierarchy ratings (Hij), and are generated

rrom the ratio evaluations as follows.

Hij = ]1 Utj V i=l,N ; j=I,H (3) I

Fij = Hij/~.Hij V i=l,N ; j=I,H (4) J

Here Uij is the set of user assigned ratings indicating

the quantitative evaluation assigned to the relative risks of specified te~-~logy pairs. Additional information on the development and impl~mentatlon of the RISK I algorithm may be found in Jennings and Suresh [2].

RISK2 provides for a more complex user-supplied information structure. In this algorithm it is assumed that the user assigned ratings (UIj) cannot be known explicitly.

Rather. i t is assumed that all input information can only be taken to belong to a set or possible values defined by finite, known bounds. This approach allows the algorithm to accommodate user uncertainty or imprecision (i.e. fuzziness) in decision variable weights and in all ratio evaluations.

Obviously, the selection of different values from any of the assumed sets would yield a different final risk ratings for the whole evaluation problem. However, Jennings and 5~JreSh [3] have shown that by a proper manipulation or set bounds, absolute bounds may be computed for the final ratings. Furthermore, this may be (lone by means or an explicit, analytical solution that avoids the necessity of numerical procedures such as Monte Carlo simulatioR This greatly ~ the microcomputer implementation possibilities of the me~md.

The RISK2 algorithm proceeds as follows:

I~i =E ~i j~j (5)

18 Environmental Software, 1986, Vol 1, No. 1

Microcomputer Implementation of Risk Assessment: A.A. Jennings and P..Suresh

where: ~1 = bounded set or final relative risk ratings for

the i th technology alternative,

F'ij = bounded set of factor scores for the i th

technology oorsldering the jth criterion,

~tj : fuzzy weight set for the jth criterion.

Here again,

~'ij = I~ij/~- ~ij V I=I,N ; j=l,I1 (6)

PI'Ij = TIOIj Y i=I.N; j=I.M. (7)

It should be obvious that there exists at least (me combination of values of the "fuzzy" user-assigned ratings (i.e. individual elements of 011) that wi l l extremize the

factor score matrix (i~ i j) for each technology. Because of the

structure of the hierarchy calculations (see equations 6 and 7) the value Implied by tills Selection can be no greater than that given bg the following combinations of 0"ij extremes

[31.

To obtain the upper bound for ~'ij :

U kj(max) V k=i,N ; j=I,M

ou: t [ Ukj(min) V k=l .( j - I ) ; j=I,M

(8)

To obtain the lower bound for ~ij :

[ ~ j (min) Vk=I ,N; j=I ,M

o0j :

Ukj(max) V k=l.( i - I ) ; j=I.M

(g)

For deterministic weights (i.e. Wj rather than ~#j) these

selections wo~ld (by equation I) yield maximum bounds for the implied risk ratings. In the presence of "fuzzy" weights, a particular selection must also be made for each element of ~/j. The appropriate selection for weights is less obvious

since the weight vector must also satisfy the constraint ~Wl =I.e.

In order to obtain the true upper and lower bounds for ~ij, let F(max)i T and F(min)iT be vectors of extreme values

of P'ij written In a decreasing order of magnitude for the i th

decision criterion. Let ~#(max) I and ~(min)l be the appropriately reordered vectors of "fuzzy" minimum weights It is also convenient to define the following:

& w I = wi(max) - wi (min) V i=l ,M (10)

r(max) = ~Wi(max) - I.O (11)

Y(min) = 1.0 - ~.Wj(min) 02)

where Wj(max) and Wj(min) are the extreme values of ~j . The AWj values must also be reordered appropriately for the

I th Oeclslon criterion to yield ~wj(mex) I and ~Wj(mln) I.

Given these, the weights that wi l l extremize the ultimate risk ratings may be o0mputed by the procedme of equations (13) and (14) [3].

To yield upper bound risk ratings:

I r,-- 1 I rj z z~wi(max) i -~ Wj(max)ii = AWj(mex) I I t r I < AWj(max)i -P Wj(max)ii " rj ~ ( l ] )

I r}+ I = r j - wj(max)il I I r j , i < 0.0 -* Wj(max)ii = 0.0 I tl v i=l.N ; I=I,M J

To yield

I t I I I t

lower bound risk ratings:

1 r M : r(mln) I l'k -> ~Wk(min)i -~ Wk(min)ii = Z~Wk(min)i I

F k < AWk(min) i -~ Wk(mln}li = r k ~ (14)

l'k-1 = Fk - Wk(min)ii I rk_ i < 0.0 -~ Wk(min)ii = 0.0 I

V I = I , N ; k = M , I I J

Note that the resulting vectors (Wj(max)i i and

Wk(min)li) wil l be in the order necessary to minimize R i for

the i th alternative. Given these selections, extreme bounds for the final technology ratings may be computed by the following vector operations.

Environmental Software, 1986, Vol 1, No. 1 19

Miorocomputer Implementation of Risk Assessment: A.A. Jennings and P. Suresh

Rl(mex)= [ F(max)lT [ W(max)i * Wj(mex)|l ] } V i=l,X (IS)

Rl(min)= { F(min)lT[ W(min) i ÷ Wj(min)li I } V i=l,N (16)

This completes one pass of the RISK2 algorithm. If a probability distribution or membership function is assumed for values within the user-supplied ranges, bounds may be ger~'atsd for risk ratings at any ccnfid=-,=~ or membership level. These bounds converge to the deterministic rating (Ri)

given by equation (1) as confidence decreases to zero. The currant version of I]151{2 generates risks for five confidence levels (99Z, cjs~ 90~, 50~, 0~') based on a normal distributioR

ALGORITHM IHPt.IEHENTATION

The risk assessment programs described here do much more than simply execute calculations. They also assist the user in defining and developing the required information, and in understanding the consquences of the implied value judgments. An assessment session using either program can be briefly summarized by the following four steps.

STEP I :

STEP 2:

STEP 3:

STEP 4:

A set of M potential consequences is developed to serve as the decision criteria by which hazardous waste treatment and/or disposal technologies are compared. These must be well posed (i.e. independent) contrivances and must embody the user's corc~-F=~ about potential failure consequences.

Weights are assigned to the selected consequences. These values (Wj of ~#j) define the degree of

Importance to be associated with eac~ decision criteria.

A set of N management alternatives to be evaluated is developed. These may be relatively crude disposal strategies, or detailed unit operation designs. However, cumulatively they must represent at least one disposal alternative for each of the waste types being considered.

A directed series of N-1 pairwlse comparison of the selected marmcjement alternatives cc,-~idering, in turn, each of the M potential consequences is conducted. These palrwise evaluatlens yield the Uij

or Oij data necessary to compute the implied

relative risk scale (R i or lq'i).

In addition to executing these basic steps, RISK I and RISK2 offer unique features to support the user and protect the integrity of the risk computations. Both have been programmed in an extremely user-friendly style making it convenient for even a first time user to ccxx/uct a successful analysis. In addition, logic and blunder traps have been liberally seeded througtmut both codes making it very difficult for unintentional errors or non sequitor information to sabotage the analysis session.

A. RISK I - An Overview

RISKI generates a deterministic, relative risk scale for the user-definad management technologies based on the user-defined consequences to human health and the environment. UP to 10 potential ~ e n c e s may he selected from an internal menu (refer to Table I). Alternative consequences may also defined by the direct text entry. Similarly, hazardous waste technologies may he selected from an internal menu of 30 alternatives (refer to Table 2) or inl~Jt directly. Technical documentation is provided on all menu entries [4]. Provisions have also been made for the user to permanently modify the program's menu information.

Once the evaluation pro01em has been defined, the complete DARE assessment is executed. This is accomplished by indicating the appropriate response to simple program queries, and entering the required data as instructed by the code. Upon completion of the deterministic analysis, the user is offered the opportunity to conduct a check of result consistency. This is accomplished by repeating theOAREanalysls on the reor0ered set of technologies until quantitative transitivity has been achieved 15].

Table I. - Internal Menu of Potential Hazardous Waste Activity Consequences

1. Site Worker Occupational Hazard 2. Off-Site Acute Human Health Hazard 3. Off-Site Chronic Human Health Hazard 4. Acute Environmental Damage Potential 5. Chronic Environmental Damage Potential 6. CBlat)" 7. (Blank) 8. CBlar~) 9. (Blank)

m. (Blank)

w Empty storage for additional user-defined consequences.

2 0 Environmental Software, 1986, Vol 1, No. 1.

Microcomputer Implementation of Risk Assessment: A.A. Jennings and P.. Suresh

Table 2. - Internal Menu of Hazardous Waste Technologies

I . Inc inerat ion (Genera l } 2. Halogenated Hydrocarbon Incineration 3. Rotary Kiln Incineration 4. Liquid Injection Incineration 5. Multiple Hearth Inclnaratlon 6. Multiple Chamber Incineration 7. Ocean Incineration 8. Fluldized Bed Incineration 9. Wet Air Oxidation

10. Molten Salt Incineration I t . Land Disposal (6eneral) 12. Secure Landfill 13. Land Treatment 14. Deep Well Injection 15. Surface Impoundment 16. Deep Secure Storage 17. Ocean Floor Disposal 18. Deep Salt Bed Disposal 19. (Blank)" 2o. (stark) 2 t. Biological Treatment. (Genera l ) 22. Aerobic Biological Stabilization 25. Anaerobic Biological Stabilization 24. Physical/Chemfcal Treatment (General) 25. Acid-Base Neutralization 26. Organic Liquids Treatment 27. Metals Solution Treatment 28. Oil Recovery Ixj Redistillation 29. Solvent Recovery bg Redistillation 30. 5olidif ication/F ixat ion

" Empty storage for additional user-defined consequences.

RISK I also provides a novel alternative to a complete DARE analysis. If the user has restricted tectw~logg and consequence selections to those of the internal menus (i.e. those the code has prior knowledge of), the user is offered a "Default Evaluation" optiorL If selected, RISK I reads a predetermined evaluation matrix and reduces it (1~ deleting inappropriate rows and columns) to the set of alternatives and c~-~equences selected. This default matrix replaces the hierarcl~ matrix (Hi j) of equation (5) and allows for the

computation of R i in the absence of a user-supplied factor

scores. The default option has been provided for a rapid initial analysis of the user's problem. Hopefully, this will then catalyze for a more thorough assessment by the user.

It shsuld probably be emphasized that the relative risk of alternative depends on the number and type of

alternatives considered. Although fixed default hierarchy

values arestored in the RISK I 's database, the implied risl( rating for any alternative will very with the set of competing alternatives. This behavior is reproduced I~l executing equation (4) (the hierard'~j normalization) on the reduced default matrix. It should also be noted that since default hlerard~j values have been assigned I~j the authors, they represent the auther's own opinions and bias about hazardous waste teu==-=~iogles. However. provisions have been made to allow knowledgeable users to modify the data that yields the default evaluatio~

Figure I illustrates the major steps in a RISKI analysis session.

B. RISK2 - An "Expert" Probabilistic Rtsk Assessment

RISK2 does not support the default evaluation option. RISK2 is designed to accu-=-=modate uncertainty in the raw information. This "fuzziness" may be due to unfamiliarity with a particular technolo~j or conse~-=ce scenario. It matj also be an exact expression of the true stale of knowledge about the various hazardous waste ozm-=~'<lU~-ces.

I Select ion of ~ Addi t ion of Menu Consequences User-Defined

Consequences

I neve'opment of Consequence I Weight s (by 1 of 3 Options)

I Select ion of ~ Addi t ion of User-Def ined

Menu Technologies Technologies

I User's DARE Analysis I Default Analysis I

I I

I Report Ouality Output

I p°st DARE c°nsistency check .1

st°_PP _)

Figure I - Major Steps of a RISKI Assessment Session

|

Environmental Software, 1986, Vol 1, No. 1 21

Microcomputer Implementation of Risk Assessment: AJC Jennings and P. Suresh

Bg definition, risk embodies not only the severitg or consequences, but also tt~ pro0abilitg that these consequences will be exertS. Therefore, the onlg risks that can be known absolutely are those determined in retrospect. As 5age and White [6] have observed, future risks must be divided into Real (unknowable), Statistical (implied bg the correct use of the information population), Predicted (proposed based on an available information sample) and Perceived risk. Since RISK2 is designed to assess Predicted and Perceived risks, the accommodation or a substantial degree or unsuretg seems appreprlate. This 0ass, r~wever, eliminate the possibilitg of a meaningful default evaluation. Us~'s desiring this feature may run RISK I as precursor to the probebilistic analysis.

In place of the default option, RISK2 has been armed with "expert systems" that make the code trulg unique. The first of these is the program's abilitg to suggest appropriate treatment and/or disposal tecrmologles based on the user's wasLe inventory. RISK I requires the user to select alternatives from the program's internal menu, or input alternative technologies. Experience has indicated that users occasionally have difficulty in making these selections or specify technologies that are not well suited to the hazardous wastes being c~-=~idered. RISK2 appears to have overcome t~ls pr~lem.

The second unique feature of RISK2 is a 0gnamlc database that "learns" from its previous users remembering statistics about tl~ir responses. When sufficient information has been assembled on a particular tecltnologg evaluation (for ang one consequence), the code checks the plausibilitg and o~-,sistenc'g of the current user's reslX=-w. This feature allows the code to continue to learn and to overo~;-.a anlJ residual bias trmt may have been imparted MI its authors.

Figure 2 illustrates the major steps in the RISK2 assessment session. Algorithm details of the additional special features are discussed in the following sections.

RISK2 SPECIAL FEATURES

A. Tecl-cplogg 5election Advisor

RISK2 suggests appropriate technologies to the user based on the phgsical and chemical properties of the wastes being considered. A very general first level and more detailed second level classification scheme have been built into the program (refer to Table 3). Recent studies [7,8] have indicated that these are of sufficient detail to define the viable disposal alternatives for hazardous waste tgpes.

Waste technologies are associated with the classifications bg a mapping matrix. Once information has been provided on the tgpes of waste being considered, the program reduces Its menu offerings to the most suitable technologies. The user meg then delete from or add to this suggested list.

The waste/technologg mapping and search routine proceeds as follows. Let I1 be the BxD matrix mapping B waste categories into D management teclx~logg. A zero map element (lllxi) indicates that the b th waste tgpe mag

not be accommodated ~ the d th technologg. Let V be vector of D elements storing the serial numbers of the D internal menu technologies. Also, let S be a resultant vector of D elements to store indexes for selected technologies.

Selection of ~ Addi t ion of Menu Consequences ~ User-Defined

Consequences

~ s DevelopmenL of Consequence l

S e~ i imgll iJr (obf Yi nlf :;~ai~i °i~z zi In e s s ,,

Technology ~ Enter Waste I Selection Composit ion Data

Help ??

_ ~ Selection of ~ Addi t ion of User-Defined

Menu Technologies Technologies

I Ac t i va te Database yes Interface ?? /

. . . . . . . . ~l . . . . . . . . .

q User's DARE Analysis

Report Quality Output

I

advice Analysis data ) Response I

IC°mputeand I Save Sta t is t ics

t . . . . . . . . . . . . . . . . . j

Post DARE Consistency Check I

J,

Figure 2 - Major Steps of a RISK2 Assessment Session

2 2 Environmental Software, 1986, Vol 1, No. 1

Microcomputer Implementation of Risk Assessment: A.A. Jennlngsand P..Suresh

For arcj waste categorg the following dot product mag be computed.

$d = Mbd" Vd 'v'b (I 7)

The resulting elements of S are zero or non-zero indicating suitable alternatives for the bth waste cateoorg. Equation (I 7) Is executed once for each categorlJ, replaCing onlg zero elements of 5. The final result is the union of appropriate Ledmologies.

The details of this operation are of slgnific&-ce for two reasons. First, i t sllould be obvious that the map data represent opinions about desirable teGe~loglas. The authors have specificallg designed this to collapse the rather long tedlnologg menu into a manageable number of alternatives. Users may find it desirable to modifg this map to suit their own preferences, current federal regulations, or state disposal practices. Secondly, since the knowledgeable user

the opportunitg to alter the techoologg set or classification scheme, It Is Imperative that appropriate adjustments be made in the map matrix.

B. Plauslbilit 9 and Comistem!l Advisor

The second expert mjstem of RISK2 is embodied in the generation and use of a dgnamic information base. This retains knowledge alx~Jt user responses In the form or statistics on all possible (menu) compurlsons. Each time the i th tec~nolog~j is compared with ang other menu Lechoolngg considering the jth consequence, the result is remembered. This Is accompl i~ed bg recomputing the mean of all such previous ratings. This requires the storage or two statistics (the mean, p and the number of oOservations) for each of the 30x30xlO = 9,000 possible comparisons. However, this mag be accomplished in a single 9.000 element arratJ since each of the ten (30x30) matrices are reciprocallg stjmmetric (ZabZba = 1.0) and information need

not be stored on the diagonal. It would be desirable to store enough information to support a more detailed trend analysis. Unfortunatelg, for the microcomputer applications envisioned, the vast storage requirements made this unfeasible.

In a database of this tgpe U'mre is some question of when and how to preserve information. Obviouslg, it is desirable to protect the database from bad information. On the other hand, shielding it from a wide varietg of users supresses information on the true diversitg of opinion. The hazardous waste field derinitelg does not need another biased, narrow-minded "expert".

Table 5. - RISK2 Hazardous Waste Classification Scheme

L iqu id V a s t e s ( 6 e n e r a l ) Concentrated Inorganic Liquids (Acids/Bases) Heavg Metal 5olutions Concentrated Organic Liquids Halogenated Organic Liqulde Dilute Aqueous Organics Oils and OillJ Wastes Unknown Liquid Wastes

Sludges (Genera l ) Organic Sludge Inorganic Sludge Caustic Sludge Heavy Metal Sludge Urknown Sludge

Specia l So l id WNtes (General) Metal Oxides 5lag Organic Solids Inorganic Solids Unknown Solids

This question has been addressed (if not completely resolved) in RISK2 bY providing an option to suppress database updating. This option is presented to the user once at the beginning of the analysis session, and pertains to the whole session. This provides a "no-fault" innovation mode that does not alter the program's knowledge stale. First Lime users should probably activate this option until theg are familiar with the basic program functions. All user's must realize that when this option is bgpassed the program wil l remember and continue to the provided information.

RISK2 uses the dynamic database to help maintain plausibilltlJ and consistencg. The code checks its memor U after each ratio evaluation or menu alternatives. If i t determines that it has "sufficient information" on this evaluation, and the response is "sufficientlg different" from the current central tendencg, the program wi l l warn the user. When this occurs, the user is provided with information on the apparent i rL~ is tmcg and asked to verlrg the value. It remains at the user's discretion whether or not to alter the entrlJ. If not revised, the apparentlg extreme value wi l l be accepted and subsequentlg redefine "extreme" for this comparison. %ufficlent information" is defined as previous knowledge of at least two such evaluations. "Sufficientlg different" is defined as deviation in excess or one-half order of magnitude.

Environmental Software, 1986, Vol 1, No. 1 2 3

Microcomputer Implementation of Risk Assessment: A.A. Jennings and Po Suresh

It Is interesting to note that individual disk versions of RISK2 wi l l experience different histories of use. They wi l l , in a very real sense, learn from their environment and develop different states of wisdom. Currently, program disks are supplied with a blank memory. However, the authors are evaluating a procedure for gifting them with an optional memory to cushion their early responses. This would be developed by a panel of hazardous waste specialists assessing a series or disposal scenarios. This epproach has the disadvantage of introducing potential bias, but any such bias would eventually be overcome by continued use.

RISK ASSlESSMENT - A BRIEF EXAMPLE

The text of an interactive risk assessment session (CRT display and final report) is too extensive to reproduce here, and varies considerably given the diversity of the available options. There are also numerous warning messages instructions that the user (loss not see unless an error or illogical entry is made. In addition, illustrations of the functions of RISK I have appeared elsewhere (8.9]. For the purpose of this description, only the problem definition and final results of a RISK2 session wi l l he presented. The intent of this is to illustrate the role of relative risk analysis in resolving hazardous waste management problems.

Assume that a community is struggling with the management of hazardous wastes produced by local metal fininshlng industries. The community is Interested In a long-term solution to waste management. The industries are wil l ing to consider more than disposal costs i f the resulting plan wi l l have community support. No decision has been made about on-site versus off-site technologies. One of the interested parties might conduct the following assessment.

In Step I, all five potential consequences are selected. In Step 2 the user elects to specify unequal consequence weights and variable degrees of unsurety about their evaluation as follows;

Consequence ~lected

5peclfle(I Weight and Degree of Uncertainty

Site Work Occupational Hazard Off-Site Acute Human Health Hazard Off-Site Chronic Health Hazard Acute Environmetal Damage Potential Chronic Environmental Damage Potential

0.10 +_ I0 % 0.15 + _ 25% 0.30 *_ 40 % 0.15 + 2 5 ~ 0.30 *- 40

Note that the user has placed more Importance on long term consequences, but has also expressed a greater degree of uncertainty in his ability to evaluate these.

In Step 3, the user must select a set of appropriate technologies. The user elects to have RISK2 suggest these based on waste composition. The user indicates that. he is considering the disposal of concentrated inorganic liquids, heavy metal solutions, inorganic sludge and inorganic solids. Given these, the teohnologg advisor wi l l suggest 13 of the alternatives listed in Table 2, and present them to the user. Of these, the user decides to omit all thermal destruction options except Rotary Kiln Incineration. He also rejects Ocean Floor Disposal and Deep Salt Bed Disposal as being unfeasible. Analysis then proceeds using the following 8 alternatives:

I. Rotary Kiln Incineration 3. Deep Well Injection 5. Deep Secure Storage 7. Metal Solution Treatment

2. Secure Landfill 4. Surface Impoundment 6. Acid-Base Neutral izat ion 8. Sol idi f icat ion/F ixat ion

From this point on, RI5K2 guides the user t~ough the directed series of pairwise cor~arisons required to generate the ultimate risk rating scale (A'I). The outcome of these is

illustrated in Figure 3. The ranges of the "fuzzy" relative risk ratings (at 99% and 90% confidence level) and the deterministic results have been indicated. At this point, RISK2 generates a whole report on the analysis session including the developed ut i l i ty matrix (Oij) and the implied

consequence hierarchies (~'ij , A'Ij)" The program also

generates risk ratings for intermediate confidence levels.

Figure 3 clearly indicates that the user believes that Secure Landfill and surface Impoundment represent a significantly higher risk than the remaining alternatives. Based on risk alone, this user would favor Deep Secure Storage. The reader wi l l probably also observe that these results are quite debatable.

2 o.4 L

r ' -

.,~ 0.3 rv"

.~ o.2

-~ 0 .1

~ = = = :

z i 99% Confldence Range

,i ................. ................ i ................ / i ................ i .........

J i i Confidence I i I j / R°nge I i .... i ............................. ] ............................... ! ........

t I i ' Value / i

i ...... t ........................... .............................. i .......... T .............. T ............. ! ...... # #2 #3 #4 #5 #6 #7 #8

Hazardous Waste Technology Alternative

Figure3-Example Results ore RISK2 Assessment

24, Environmental Software, 1986, Vol 1, No. 1

Microcomputer Implementation of Risk Assessment: A.A. Jennings and P. Suresh

The fundamental role or RISK2 is to allow this debate to be conducted at a rational and quantitative level. The RISK2 report clearlg indicates how individual results are achieved. If the parties-at-risk do not agree, (and theg wi l l not ! ), the specific (and significant) points at which theg differ may be examined in greater detail. The infeasible alternatives are simplg rejected, and the debate mag be focused on the most viable management schemes. From this point, cost and risk optlmizations mag be used to produce a complete management plan [81.

CONCLUSIONS

The combined RISK I/RISK2 approach appears to be a verg powerful tool for developing hazardous waste technologg risk penaltg functions. RISK I allows the user to define the scope of the required assessment, and to generate a preliminarg analgsis. RISK2 supports a much more thorough assessment considering the degree of unsuretg that must accompa~ the raw data. Raw data mag be detai led technological Information entered I)g a hazardOUS waste professional, or simplg opinions and perceptions entered bg the partiee-at-risk. Both programs offer extensive user- support and "Expert Sgstems" that allow inexperienced users to particlpete in the assessment of risks. It is hoped that this approach wi l l be capable of brokering the productive dialog necessarg to resolve our current hazardous waste d i lemmas.

PRO6~AM AVAILABILITY

The source codes for RI5K I-and RI5K2 are written in FORTRAN 77 specifically for microcomputer implementation. Versions of both are currently available for the IBM Personal Computer. RISKI requires 710 lines of source code and is approximately 25 kb in size. RISK2 involves t 270 lines of code (approximately 41kb). Compiled, executible versions require 70 kb and 90 kb respectivelg. The required attendant data sets require 20 kb. Both programs mag be edited using EDLIN, the line editor of IBM DO5 2.0, compiled using Microsoft FORt and PA52, and linked using Microsoft LINKER and EXEPACK.

The RISKI code and documentation are not copgrighted and wi l l be supplied bg the authors for a nominal handling charge. RISK2 is a copgrighted software package. The authors wil l also be glad to supplg academic users with RISK I/RISK2 documentation and program disk for a handling charge. Potential commercial users should contact the authors about an acquisition agreement.

ACKNOWLEDGEMENT

The authors gratefullg acknowledge the Charles A. Lindbergh Fund, Inc. for providing the financial support necessarg to develop RISK I and to conduct research on effective methods of Ilazardous waste management planning.

REFERENCES

I. Klee, A.J.,'The role of Decision Models in Evaluation of Environmental Health Alternatives', Manaaement Science. 16(2), B52-B67, 1971.

2. Jennlngs, A.~, and Suresh, P., "Interactive Risk Analgsis for Hazardous Waste Disposal Alternatives', in Prnceedina_s of the 2rid National Conference on Iliorocomeuters in Civi l Enainesrina. (ed.) W.E. Carroll, Orlando, FI., 1984.

3. Jennings, A.A. and 5uresh, P., "Risk Penaltg Functions for Hazardous Waste Management', Journal of Environmental Enairmarina. (in review), 1985.

4. Jannings, A,A. and 5uresh. P., Risk I , A User- Interactive Mior_nc__nmputer Program to Ouantifll the Risk of Hazardous Waste Management Technologies; User's Marmal for the II]11 Personal Camllmter, Department of Civil Engineering, University of Notre Dame, 1984, I ! l p.

5. Klee, A.J. "Models for Evaluation of Hazardous Waste', Journal of Lhe Environmental Enain~rirm Division. ASCE. 102(EEl) I I 1-125, 1976.

6. Sage, A.P. and White, E.B., "Methodologies for Risk and Hazard Assessment: A 5urveg and Status Report', IEEE Transactions of Sestems. Man. and Cabernetics, ,SMC-IO(8). 425-446, 1980.

7. Jennings, A.A., "Profiling Hazardous Waste Generation for Marmgernent Planning', Journal of HazardOus Materials. 8, 69-83, 1983.

8. Jeflnings, AJ~. and 5holar, R.L., *Hazardous Waste Disposal Network Analysis', J_gg[l]aLg[ Environmental Enaineerlng. 110(2), 325-342, 1984.

9. Jennings, A.A., "Risk Assessment for Hazardous Waste Management Planning', Great Lakes Waste and Pollution Review Ma?azinL 2(I), 5-9,1984.

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