Hazard Ranking System Issue Analysis:
      Containment Rating Factor
               MITRE

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Hazard  Ranking  System Issue Analysis:
        Containment Rating Factor
                    Stuart A. Haus
                      March 1987
                      MTR-86W199
                       SPONSOR:
                 U.S. Environmental Protection Agency
                     CONTRACT NO.:
                      EPA-68-01-7054
                   The MITRE Corporation
                     Civil Systems Division
                     7525 Colshire Drive
                   McLean, Virginia 22102-3481

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                   irmw
Department Approva
MITRE Protect Approval:  /<    LsCS <>J

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                              ABSTRACT
     This report addresses issues related to the modification of the
current HRS containment factor.  Advantages and disadvantages of
basing the containment factor on the RCRA Subtitle C land disposal
regulations are discussed.  A number of alternative approaches for
modifying the containment factor so as to base it on evaluation
criteria other than the RCRA Subtitle C regulations are identified
and briefly examined.  Two of these alternatives are recommended for
possible further development.  These two alternatives are:

     •  The integration of evidentiary and predictive criteria in
        the containment factor.

     •  The integration of a physical state factor into the
        containment factor.

Suggested Keywords:  Superfund, Hazardous waste, Hazard ranking,
Containment.
                                 iii

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                          ACKNOWLEDGEMENT
     The author wishes to acknowledge Greg Vogel for his valuable
contribution in the development and analysis of the options
presented in this report.
                                iv

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                          TABLE OF CONTENTS
LIST OF TABLES

1.0  INTRODUCTION

1.1  Background                                                    1
1.2  Issue Description                                             3
1.3  Scope and Approach                                            5
1.4  Organization of  the Report                                    6

2.0  REVIEW OF CURRENT HRS CONTAINMENT EVALUATION METHODOLOGY      9

2.1  Overview of HRS  Containment Factor                            9
2.2  Analysis of Current HRS  Containment Factor                   14
2.3  Issues Relevant  to the Revision of the HRS Containment       19
     Factor

     2.3.1  Screening Out Sites                                   20
     2.3.2  Differentiation of Sites                              22

2.4  Summary of Containment Factors in Other Ranking Systems      23

3.0  CONTAINMENT EVALUATION ALTERNATIVES                          27

3.1  Overview of Alternatives                                     27
3.2  Updating of Present RCRA-Based Criteria                      30
3.3  Integration of Containment Factor With a Factor Based        32
     on Waste Quantity
3.4  Development of Evidentiary Criteria With a Zero Value        33
3.5  Development of Evidentiary Criteria Without a Zero Value     36
3.6  Integration of Evidentiary and Predictive Criteria           37
3.7  Development of Time-Dependent Criteria                       38
3.8  Use of Criteria Based on Waste Disposal Location             41
3.9  Development of Criteria Based on Site Drainage               44
3.10 Integration of Containment and Physical State Factors        46

     3.10.1  Use of Evidentiary Criteria                          48
     3.10.2  Use of Predictive Criteria                           49

4.0  SUMMARY AND RECOMMENDATIONS                                  51

APPENDIX A - REVIEW OF CONTAINMENT FACTORS IN OTHER SITE          59
             RANKING SYSTEMS

APPENDIX B - BIBLIOGRAPHY                                         87

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                           LIST OF TABLES

Table Number                                                     Page

     2-1       HRS Containment Factor for Ground Water Route      12

     2-2       HRS Containment Factor for Surface Water Route     13

     2-3       Distribution of HRS Containment Factor Values      16
               for Facilities in the Automated NPL Technical
               Data Base

     3-1       Illustrative Containment Factor Values Based       43
               on Waste Disposal Location
                                 vii

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1.0  INTRODUCTION




1.1  Background




     The Comprehensive Environmental Response, Compensation, and




Liability Act of 1980 (CERCLA) (PL 96-510) requires the President to




identify national priorities for remedial action among releases or




threatened releases of hazardous substances.  These releases are to




be identified based on criteria promulgated in the National




Contingency Plan (NCP).  On July 16, 1982, the Environmental




Protection Agency (EPA) promulgated the Hazard Ranking System (HRS)




as Appendix A to the NCP (40 CFR 300; 47 FR 31180).  The HRS




comprises the criteria required under CERCLA and is used by EPA to




estimate the relative potential hazard posed by releases or




threatened releases of hazardous substances.




     The HRS is a means for applying uniform technical judgment




regarding the potential hazards presented by a release relative to




other releases.  The HRS is used in identifying releases as national




priorities for further investigation and possible remedial action by




assigning numerical values (according to prescribed guidelines) to




factors that characterize the potential of any given release to




cause harm.  The values are manipulated mathematically to yield a




single score that is designed to indicate the potential hazard posed




by each release relative to other releases.  This score is one of




the criteria used by EPA in determining whether the release should




be placed on the National Priorities List (NPL).

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     During the original NCP rulemaking process and the subsequent

application of the HRS to specific releases, a number of technical

issues have been raised regarding the HRS.  These issues concern the

desire for modifications to the HRS to further improve its

capability to estimate the relative potential hazard of releases.

The issues include:

     •  Review of other existing ranking systems suitable for
        ranking hazardous waste sites for the NPL.

     •  Feasibility of considering ground water flow direction and
        distance, as well as defining "aquifer of concern," in
        determining potentially affected targets.

     •  Development of a human food chain exposure evaluation
        methodology.

     •  Development of a potential for air release factor category
        in the HRS air pathway.

     •  Review of the adequacy of the target distance specified in
        the air pathway.

     •  Feasibility of considering the accumulation of hazardous
        substances in indoor environments.

     •  Feasibility of developing factors to account for
        environmental attenuation of hazardous substances in ground
        and surface water.

     •  Feasibility of developing a more discriminating toxicity
        factor.

     •  Refinement of the definition of "significance" as it relates
        to observed releases.

     •  Suitability of the current HRS default value for an unknown
        waste quantity.

     •  Feasibility of determining and using hazardous substance
        concentration data.

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     •  Feasibility of evaluating waste quantity on a hazardous
        constituent basis.

     •  Review of the adequacy of the target distance specified in
        the surface water pathway.

     •  Development of a sensitive environment evaluation
        methodology.

     •  Feasibility of revising the containment factors to increase
        discrimination among facilities.

     •  Review of the potential for future changes in laboratory
        detection limits to affect the types of sites considered for
        the NPL.

     Each technical issue is the subject of one or more separate but

related reports.  These reports, although providing background,

analysis, conclusions, and recommendations regarding the technical

issue, may not directly affect the HRS.  Rather, these reports will

be used by an EPA working group that will assess and integrate the

results and prepare recommendations to EPA management regarding

future changes to the HRS.  Any changes will then be proposed in

Federal Register notice and comment rulemaking as formal changes to

the NCP.  The following section describes the specific issue that is

the subject of this report.

1.2  Issue Description

     The HRS containment factor is currently a measure of the

methods (either engineered or natural) that have been employed to

minimize or prevent the migration of hazardous substances to ground

water or surface water.  Examples of engineered containment methods

include landfill liners, leachate collection systems, diversion

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structures, and diking.  Examples of natural containment methods

include locating waste management sites in areas where the terrain

precludes the overland migration* of hazardous substances to surface

water or in areas where there is no ground water or surface water in

the vicinity of the site.

     The criteria in the current HRS containment factor are based

upon those land disposal regulations developed, as of early 1982,

under Subtitle C of the Resource Conservation and Recovery Act

(RCRA).  Since that time, there have been significant changes in the

RCRA Subtitle C land disposal regulations, and further modifications

are currently being developed in response to requirements mandated

by the Hazardous and Solid Waste Amendments of 1984 (HSWA).

Consequently, concerns have been raised within EPA that the HRS

containment factor should be modified to be more consistent with the

current RCRA Subtitle C land disposal regulations.

     Public commenters have not raised technical issues about the

HRS containment factor in either NCP or NPL rulemakings.  Those

comments that have been received from the public have been related

to site-specific applications of the containment factor (e.g.,

whether a specific site should have been assigned a containment

factor value of 2 or 3).
*For reasons beyond the scope of this discussion, the HRS does not
 assess the potential for hazardous substances to be released to
 surface water via the ground water.  Consequently, containment
 methods relating to ground water discharges to surface water are not
 included in this discussion.

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1-3  Scope and Approach




     In the absence of public comments on the MRS containment




factor, the original objective of this effort was the development of




options for modifying the MRS containment factor to make it more




consistent with the current RCRA Subtitle C land disposal




regulations.  This objective did not include the examination and




development of additional alternative technical approaches for




evaluating containment in the HRS.  However, the analysis presented




in Chapter 2 indicates that few, if any, sites currently eligible




for the NPL are likely to have employed containment measures that




even come remotely close to meeting the requirements of the 1982




RCRA Subtitle C regulations, let alone those currently in effect.




For this reason, as well as for other reasons discussed in Chapter 2,




modification of the HRS containment factor to ensure more consistency




with the current RCRA regulations is considered to be primarily a




policy issue rather than a technical issue.




     Consequently, the primary focus of this paper has been




redirected toward a discussion of the issues related to any




modification of the containment factor, rather than the development




of specific options for modifying the containment factor.  Advantages




and disadvantages of basing the containment factor on the RCRA land




disposal regulations are discussed.  A number of alternative




approaches for modifying the containment factor so as to base it on




evaluation criteria other than the RCRA Subtitle C regulations are

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identified.  The advantages and disadvantages of each approach are




discussed.  One option for the development of a containment factor




under each of the alternative approaches is briefly outlined to




illustrate the types of options possible under each of these




alternative approaches.  The full development of options under




any of the alternative approaches will, however, require the




identification, by EPA, of the preferred options and the resolution




of specific issues (both policy and technical) discussed under each




alternative.  For example, decisions on whether data will be




collected for determining environmental concentrations of




contaminants greatly influence the types of MRS containment




evaluation criteria that can be developed (see discussion in




Chapter 3).




     The discussion in this paper is limited to the development of




containment options for the current HRS surface water and ground




water pathways because the current HRS has no air pathway




containment factor.  Options for containment factors for the air




pathway are discussed in a companion paper that addresses the




development of a potential for air release factor category




(Wolfinger, 1986).




1.4  Organization of the Report




     The current HRS containment evaluation criteria are presented




and analyzed in Chapter 2.  Issues associated with any modifications




to the current HRS containment evaluation criteria (including

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modifications to ensure more consistency with the current RCRA




Subtitle C land disposal regulations) are discussed.  Several




possible objectives to be considered in the development of




alternatives to the containment factor are identified.  Important




similarities and differences between the current HRS containment




factor and the containment factors in ten other site ranking systems




and three EPA hazardous waste policy analysis models are also




summarized in Chapter 2.  (Appendix A presents a detailed review of




the use of containment in these other hazardous waste site ranking




systems and the EPA policy analysis models.)  Chapter 3 outlines




nine options for modifying the containment factor to meet the




various objectives discussed in Chapter 2.  Advantages and




disadvantages of each option are described.  Chapter 4 presents a




summary and recommendations.  Appendix B contains the bibliography.

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2.0  REVIEW OF CURRENT HRS CONTAINMENT EVALUATION METHODOLOGY




     This chapter presents a summary of the current HRS containment




evaluation methodology.  This is followed by an analysis of the




current containment factor.  The analysis identifies several issues




associated with the containment factor that need to be considered in




any modification of the containment factor.  Other issues generic to




modification of the containment factor are then identified and




discussed.  This chapter concludes with a summary of the important




similarities and differences between the current HRS containment




factor and the containment factors incorporated in ten other systems




used to rank hazardous waste sites and in three EPA hazardous waste




policy analysis models.  A more detailed review of these systems is




provided in Appendix A.




2.1  Overview of HRS Containment Factor




     The HRS migration score currently reflects the potential threat to




humans or the environment from the migration of a hazardous substance




away from a site by three possible routes—ground water, surface water,




and air.  A migration score for each applicable route is calculated by




rating the site with respect to a number of factors that characterize




a) the potential for hazardous substances to migrate from the site by




that route, b) the hazardous substances present at the site, and




c) the presence and proximity of targets (e.g., human populations).




     The potential for migration along a route may be evaluated in one




of two ways—either through direct evidence of a release (i.e.,

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an observed release) or through the use of factors that evaluate the




potential for a release in terms of route characteristics and




containment.  If there is a documented observed release for any




route, a rating value of 45 is assigned for that route and the route




characteristics and containment are not evaluated.  If there is no




evidence of an observed release, the observed release is assigned a




value of zero.  In this case, route characteristics and containment




are evaluated for the ground water or surface water routes, but not




for the air route.  The route characteristics score and the




containment score are multiplied to assign a rating to the potential




for a release; their product has a maximum value of 45, the same as




the value for an observed release.  The migration score for a route




is then determined by multiplying either the observed release score




or the potential for a release score (for ground water or surface




water) by scores for waste characteristics and targets and




normalizing the product so that it ranges from 0 to 100.  The




individual route scores are combined to obtain the overall migration




score for the site.




     The components of the route characteristics rating category for




the ground water route are the depth to the aquifer of concern, the




net precipitation,  the permeability of the unsaturated zone,  and the




physical state of the waste.   The components of the route



characteristics rating category for the surface  water  route are the




facility slope and  intervening  terrain,  24-hour  rainfall, the






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distance to the nearest surface water, and the physical state of the




waste.  For both routes, the values assigned to the component factors




of the route characteristics category are weighted and then added




prior to being multiplied by the containment factor value.




     The HRS containment factor is currently a measure of the methods



(either natural or engineered) that have been used to minimize or




prevent the migration of hazardous substances to ground water or




surface water.  The containment factor is assigned a value for either




route by applying criteria that are specific both to the route and to




the type of waste management method being evaluated for that route.




The specific criteria for rating containment are presented in Table 2-1




for the ground water route and in Table 2-2 for the surface water




route.  The containment factor value assigned to a route is the




highest containment value (i.e., value for the least effective




containment measure) assigned to any of the containment measures




applicable to that route.




     The evaluation criteria in Tables 2-1 and 2-2 are based on the




technical requirements of the RCRA Subtitle C land disposal regulations




(40 CFR 264 and 265) promulgated or proposed prior to mid-1982.  Wastes




whose containment meets the specified RCRA technical requirements are




considered to pose a lesser threat to human health and the environment




than wastes whose containment does not meet the specified requirements




and are currently assigned the lowest relative containment factor value




of zero.  A containment factor value of zero for a route, in the






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                                                        TABLE 2-1
                             HRS  CONTAINMENT  FACTOR FOR GROUND  WATER ROUTE
Assign containment a value of 0 if:  (1) all the hazardous substances at  the  facility are underlain by an essentially
non-permeable surface (natural or artificial) and adequate leachate  collection systems and diversion systems are present; or (2)
there la no ground water in the vicinity.  The value "0"  does not Indicate no risk.  Rather, it indicates a significantly lower
relative risk when compared with more serious sites on a  national level.  Otherwise, evaluate the containment for each of the
different means of storage or disposal at the facility using the following guidance.

                                                                                                                      Assigned
                                                                                                                       Value

••  Surface Impoundment

    Sound run-on diversion structure, essentially non-permeable  liner (natural or artificial) compatible with the           0
    waste, and adequate leachate collection system

    Essentially non-permeable compatible liner with no leachate  collection system; or inadequate freeboard                 1

    Potentially unsound run-on diversion structure; or moderately permeable compatible liner                               2

    Unsound run-on diversion structure; no liner; or incompatible liner                                                   3

B.  Containers

    Containers sealed and In sound condition, adequate liner, and adequate leachate collection system                      "

    Containers sealed and In sound condition, no liner or moderately permeable liner                                       1

    Containers leaking, moderately permeable liner                                                                        2

    Containers leaking and no liner or Incompatible liner                                                                 3

C.  Piles

    Piles uncovered and waste stabilized; or piles covered,  waste uns tabilized , and essentially non-permeable liner         0

    Pilea uncovered, waste unstabllced, moderately permeable liner,  and leachate collection system                         1

    Piles uncovered, waste uns tabilized , moderately permeable liner,  and no leachate collection system                     2

    Piles uncovered, waste unstabillzed, and no liner                                                                     3

D.  Landfill

    Essentially non-permeable liner, liner compatible with waste,  and adequate leachate collection system                  0

    Essentially non-permeable compatible liner, no leachate  collection  system, and landfill surface precludes  ponding       1

    Moderately permeable, compatible liner, and landfill  surface precludes ponding                                         2

    No liner or incompatible liner; moderately permeable  compatible  liner; landfill surface encourages ponding; no          3
    run-on control

Source:  47 PR 31180, July 1982.

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                                                                         TABLE  2-2

                                              HRS  CONTAINMENT  FACTOR FOR  SURFACE  WATER  ROUTE



                 A»lgn containment a value of 0  If:  (1) all the waste at the site Is surrounded by diversion structures that are In sound
                 condition and adequate to contain all runoff, spills,  or leaks fron  the waste; or (2) Intervening  terrain precludes runoff fron
                 entering surface water.  Otherwise, evaluate the containment for each of the different Beans  of  storage or disposal at the site
                 and assign a value as follows:

                                                                                                                                       Assigned
                                                                                                                                        Value

                 A.  Surface Impoundment

                     Sound diking or diversion structure, adequate freeboard, and no  erosion evident                                        0

                     Sound diking or diversion structure. Inadequate freeboard                                                             1

                     Diking not leaking, but potentially unsound                                                                           2

                     Diking unsound, leaking, or  In danger of collapse                                                                      3

                 B.  Containers

                     Containers sealed, In sound  condition, and surrounded by sound diversion or containment system                         0

!_.                   Containers sealed and In sound condition, but not  surrounded by  sound diversion or containment system                   1
U>
                     Containers leaking and diversion or containment structures potentially unsound                                         2

                     Containers leaking, and no diversion or containment structures or diversion structures leaking or In danger of          3
                     collapse

                 C.  Haste Piles

                     Files are covered and surrounded by sound diversion or containment system                                              0

                     Piles covered, waste unconsolldated, diversion or  containment system not adequate                                      1

                     Piles not covered, waste unconsolldated, and diversion or containment system potentially  unsound                        2

                     Piles not covered, waste unconsolldated, and no diversion or containment structures or diversion system                 3
                     leaking or in danger or collapse

                 D.  Landfill

                     Landfill slope precludes runoff, landfill surrounded by sound diversion system,  or landfill has adequate cover          0
                     material

                     Landfill not adequately covered and diversion system sound                                                            1

                     Landfill not covered and diversion system potentially unsound                                                          2

                     Landfill not covered and no  diversion system present, or diversion system unsound                                      3

                 Sourcei  47 PR 31180, July 16, 1982.

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absence of an observed release, results in the route receiving a




migration score of zero because the other rating factor values are




multiplied by the containment factor to obtain the migration score.




     Because of this multiplicative property, the containment factor is




one of the two most influential rating factors in the HRS (along with




observed release) for the ground water and surface water route scores.




Accordingly, very specific criteria have been established for assigning




the containment factor value.  For example, a surface impoundment




having a sound run-on diversion structure, an adequate leachate




collection system, and an essentially non-permeable liner that is




compatible with the waste in the impoundment is assigned a zero value




for the containment factor for the ground water route.  A zero value




can also be assigned for the ground water route if there is no ground




water in the vicinity.  If no waste containment is attempted, the




containment factor is assigned a value of three.  Containment factor




values of 1 or 2 are assigned for various intermediate levels of




containment.




2.2  Analysis of Current HRS Containment Factor




     This section presents an analysis of the current HRS containment




factor.  The analysis identifies several issues that need to be




considered in any subsequent modification of the containment factor.




     Although data are not available to determine the actual




distribution of containment factor values that have been assigned to




all wastes sites ranked using the HRS, it is apparent from data for






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sites in the automated NPL technical data base that there is little




variation in the containment values assigned among these sites.




Table 2-3 presents the distribution of the containment factor values




(for ground water and surface water migration routes)  that have  been




assigned to the approximately 600 sites in the automated NPL




technical data base that do not have an observed release and for




which a containment value has been reported.  Approximately




99 percent of the relevant NPL sites, 93 percent of the relevant




"other sites," and 96 percent of all such sites in the automated NPL




technical data base have been assigned the maximum containment




factor value for the ground water pathway.  For the surface water




pathway, these numbers are 87, 80, and 84 percent, respectively.




Not one site has been assigned a containment factor value of zero




for either pathway.  This is not especially surprising since sites




with a containment factor value of zero would have a route score of




zero; only sites with migration scores of 25 or higher are required




to be forwarded to EPA Headquarters for review.




     The data in Table 2-3 illustrate that the current HRS




containment factor provides little discrimination, based on




containment practices, among those sites submitted to  EPA




Headquarters for quality assurance review.  For these  sites,




the primary function of the containment factor appears to be the




screening out of those few sites that have relatively  high levels




of containment.  For example, about 65 to 85 percent of sites in the






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                              TABLE 2-3

     DISTRIBUTION  OF  HRS  CONTAINMENT FACTOR VALUES FOR FACILITIES
              IN THE AUTOMATED NPL TECHNICAL DATA BASE*
                                  Number of NPL Facilities**
Containment Value
      0
      1
      2
      3
            Total
Ground Water
No.        %
Surface Water
No.         %
0 0
1 2
2 1
3 216
Total 219
0
1
1
99
100
0
19
16
252
287
0
7
6
87
100
                                 Number of Other Facilities***
Ground Water
No. %
0 0
10 3
12 4
300 93
322 100
Surface Water
No. %
0 0
35 11
29 9
256 80
320 100
                                Total Number of Facilities****
Ground Water
No. %
0 00
1 12 2
2 13 2
3 516 96
Total 541 100
Surface Water
No. %
0 0
54 9
45 7
508 84
607 100
   *This distribution applies to facilities in the automated NPL
    technical base that do not have an observed release and for
    which a containment value has been reported.
  **Based on the 888 facilities listed on or proposed for NPL as of
    August 1986.
 ***Based on facilities in the automated NPL technical data base that
    have not been proposed for or listed on the NPL as of August
    1986; containment values for these facilities have not all been
    subjected to a quality assurance review.
****Summation of the NPL and other facilities identified  above.
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 automated NPL technical data base assigned a containment  value  of  1

 for any route are not on the NPL.*

      No conclusions can be drawn from the data  in  Table 2-3 about  how

 containment factor values affect the overall ability of the current

 HRS to discriminate between NPL and non-NPL sites.  Low scoring sites

 (i.e., those with migration scores less  than 25) are not  generally

 submitted to EPA Headquarters for quality assurance review.  It is

 possible that low containment factor values are much more prevalent

 among  these sites and do,  in fact,  assist in discriminating such

 non-NPL sites from NPL sites.   Data to prove or disprove this are not

 available.

     One observation possible from the data in Table 2-3 is that

 wastes at many CERCLA sites  are  not  well  contained** and that the use

 of  technical criteria based  on  the  RCRA  Subtitle C land disposal

 regulations  may not  provide much  differentiation among containment

 practices at these sites.  For most  sites eligible for the NPL,  this

 is even more likely  to be true if the HRS containment factor is

 modified to  reflect  the current RCRA regulations which are

 considerably more stringent than those in effect during early 1982.

     Another consideration with regard to the present containment

evaluation criteria is that the criteria may lead to the assignment
 *Some of these sites are still under quality assurance review for
  placement on the NPL and may ultimately be placed on the NPL.
**A containment factor value of 3, which most sites appear to receive,
  indicates that there is essentially no containment provided at the
  sites for at least some of the wastes present at the site.

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of containment ratings values that are based, to a large extent, on

subjective judgments.  The evaluation criteria currently require a

determination of whether the relevant containment technologies

(e.g., liners) exist at a site and, if so, an assessment of the

effectiveness of each containment technology.  For example, the HRS

user needs to differentiate between sound, potentially unsound, and

unsound diversion structures.  Similarly, assessments are required

as to whether liners are essentially non-permeable or moderately

permeable and whether they are compatible or incompatible with

wastes.  Hie adequacy of covers and leachate collection systems must

also be assessed.  In light of the type of containment likely to be

present at CERCLA sites, it may be more meaningful for HRS screening

purposes just to distinguish whether a containment technology is

present at a site and not to try to make fine distinctions about how

effective it is.  For example, with regard to liners, the containment

could be ranked on whether a liner is present, not on whether it is

permeable or compatible with wastes.  Data to make such distinctions

are not generally available from current site inspections.

     The above analysis suggests a need for examining whether

alternatives exist for modifying the current containment factor that:

     •  Meaningfully provide greater differentiation among sites by
        including evaluation criteria other than RCRA-based technical
        requirements and/or

     •  Reduce the subjectivity of the containment evaluation
        criteria
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2.3  Issues Relevant to the Revision of the HRS Containment Factor




     One issue that needs to be considered is whether the containment




factor should continue to be included in the HRS.   The containment




factor currently appears to be effective in screening out sites that




have relatively high levels of containment.  However, the number of




such sites appears to be relatively small, at least based on data for




the sites in the automated NPL technical data base.  Of the sites in




the automated NPL technical data base that have containment values




assigned, only 4 percent do not receive the maximum factor value for




the ground water route and about 16 percent do not receive the maximum




factor value for the surface water route.




     Chapter 3 examines several alternative approaches for evaluating




containment in the HRS.  A further alternative is  to replace or




integrate the current containment factor with another factor that




addresses the retardation (e.g., geochemical removal) of containments




in the subsurface environment and in surface water.  The development




of options for considering retardation in the HRS  is currently being




examined in two companion studies (Sayala, 1986; Wang, 1986).   Once




the development of these options is completed, it  will be possible to




assess how they could most effectively be used in  the HRS.




     Assuming that containment is to remain a component of the HRS and




that the HRS is to remain a screening tool, there  are several other




important issues that are generic to any modification of the current




HRS containment factor.  These issues are reviewed in this section.






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     The first issue that needs to be resolved is the specification

of the primary function that a containment factor is to serve in the

HRS.  There are two different functions that a containment factor can

provide.  It can be used primarily to screen out (assign low rating

values to) those relatively few sites that have adequate containment*

or it can be used primarily to provide differentiation among all sites

without an observed release, through modifications designed to provide

a more uniform distribution of containment rating values.  Based on the

data presented above, it is unlikely that any single containment factor

(especially one based on technical requirements for containment

structure design)** can be developed to do both effectively.  For

those sites in the automated NPL technical data base, the current HRS

containment factor appears to be serving the former function rather

than the latter function.  Data are not available to determine which

function it actually serves for all sites ranked with the HRS; however,

for reasons discussed above, it is likely to serve the former function.

     2.3.1  Screening Out Sites

     Because containment is currently one of only two multiplicative

factors in the HRS (the other is observed release), it can be

extremely effective as a factor for screening out sites that exhibit
 *Issues related to the definition of adequate containment are
  discussed below.
**Technical requirements for containment structure design include such
  requirements as covers, liners, and leachate collection systems
  rather than the specification of performance objectives for the
  containment structure.


                                 20

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specified levels of containment.  If it is decided to use the

containment factor primarily to screen out those sites that have

adequate containment, the basic structure of the containment factor

would likely be:

     •  No containment—assign maximum value

     •  Limited containment*—assign intermediate value

     •  Adequate containment—assign minimum value

     The main issue that would need to be resolved is how the concept

of adequate containment is to be defined and evaluated for HRS

purposes.  Ideally, it would be defined such that, at sites meeting

the definition, there would be little or no potential for hazardous

substances to migrate from the site via the route being evaluated.

This would tend to argue for basing the definition of adequate

containment on RCRA technical requirements since they provide, for

screening purposes, the clearest definition of adequate containment.

However, to be effective, the definition must also be consistent

with the site characteristics that would actually be encountered in

the universe of sites being evaluated for the NPL.  If no sites meet

the definition of adequate containment, then there is likely to be

little or no benefit, for ranking purposes, to such a definition.

Chapter 3 identifies and examines several possible alternatives that
*There could be one or more levels of limited containment defined,
 depending on how fine a distinction can realistically be developed
 from available data.
                                 21

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 could  be  further  developed  for  screening  out  sites,  if  this  is  the




 desired approach.




     A further  issue  that needs to  be  considered is  whether  or  not  the




 minimum value to  be assigned  for adequate containment should be zero.




 With a multiplicative containment factor,  a zero value  would result in




 a zero score for  that migration route.  A non-zero  (but relatively  low




 value) would result in a low  score  for  the migration route and  would




 reflect the  fact  that almost  no containment is likely to be  100 percent




 effective over  a  sufficiently long  period of  time.   This issue  is




 primarily a  policy issue, not a technical  issue.




     2.3.2  Differentiation of  Sites




     If,  on  the other hand, a primary objective  is to provide greater




 differentiation within the  types  of containment  practices likely to be




 present at most sites eligible  for the  NPL, the  issues  are more




 technical in nature.   (One  reason for such an objective  might be to




 provide some greater  differentiation among those  sites whose scores




 are high  enough for placement on the NPL.)  The primary  issue in this




 case is the  definition  of containment characteristics that meaningfully




 delineate  actual, but likely  small,  differences in containment




 effectiveness and that at the same time are representative of the




 containment  technologies likely to be present at most sites eligible




 for NPL listing.  Based on Tables 2-1 through 2-3, most sites in the




automated NPL technical data base have no containment for at  least a




portion of the  wastes present at the site.  Thus, it is  unlikely that






                                 22

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any useful definition could be based solely on technical requirements
for land disposal.  Chapter 3 identifies and examines several possible
alternatives for non-RCRA based criteria that could be further
developed for differentiating among sites, if this is the desired
approach.
2.4  Summary of Containment Factors in Other Ranking Systems
     In addition to the above analysis, ten ranking systems that
consider containment in rating the threat posed by hazardous waste
sites have been identified along with three EPA hazardous waste policy
analysis models that also account for waste containment.   The
containment factors in these systems have been reviewed.   The review
focuses on how containment is used in the various systems and how
containment effectiveness is defined and evaluated.  Important
similarities and differences between these factors and the HRS
containment factor have been identified.  The findings of this review
are presented in Appendix A and are summarized below.  The ten ranking
systems reviewed are:
     •  HARM                    •  S.P.A.C.E. for Health
     •  HARM II                 •  PERCO
     •  GSR                     •  Illinois Rating Scheme
     •  ADL                     •  Rating Methodology Model
     •  SAS                     •  Dames and Moore Methodology
The three EPA hazardous waste policy analysis models reviewed are:
     •  Liner Location Risk and Cost Analysis Model
     •  Hazardous Waste Tank Failure Model
     •  RCRA Risk-Cost Analysis Model
                                 23

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     Of  the 10 ranking systems  reviewed, one  (S.P.A.C.E. for Health)




has a containment factor that is  identical to the HRS containment




factor and four  (HARM, HARM  II, CSR, and ADL) have multiplicative




containment factors that are very similar to  the HRS containment factor




in concept and application.  There are two major differences between




these latter  four systems and the HRS.  Three of these systems  (HARM,




HARM II, and  CSR) have a non-zero lower limit for the containment  score




to indicate that no containment is likely to  be 100 percent effective.




Three of the  systems  (HARM,  CSR,  ADL) also employ fewer intermediate




containment levels  (either one  or none) than  the HRS to avoid making




fine distinctions about the  degree of containment present at a  site.




     Two other ranking systems  (SAS and PERCO) do not explicitly use




containment in rating a site.   SAS uses containment only as a means of




evaluating waste quantity.   PERCO uses containment only for identifying




sites similar to the site being evaluated.




     One other ranking system (Illinois Rating System) considers




operational history, rather  than  containment  effectiveness, in  the




ranking of sites.  This approach  does not appear practical to apply to




CERCLA sites where information about the operational history of the




site is extremely limited and often unavailable.




     The remaining two ranking systems (Rating Methodology Model and




Dames and Moore Methodology) have containment factors that are additive




rather than multiplicative and that are rated on the same scale




(0 to 3)  as the HRS containment factor.  These factors were considered






                                 24

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in the original development of the HRS and were judged not to be




comprehensive, nor well defined.




     Consequently, we have concluded that these other ranking systems




do not provide any further basis for developing modifications to the



HRS containment factor.




     The three EPA hazardous waste policy analysis models address




containment in a very different manner than the HRS.   Two of  the models




(the Liner Location Risk and Cost Analysis Model and  the Hazardous




Waste Tank Failure Model) use fault tree analysis and Monte Carlo




simulation (see Appendix A) to estimate both the probability  and timing




of containment failure events that lead to releases of hazardous




substances and the release volumes associated with the failure events.




The failure and release components of the two models  are currently




developed for application to a limited number of facility designs




(e.g., several specified containment configurations)  and operating




conditions, most of which are not likely to be representative of CERCLA




sites.




     The third model (RCRA Risk-Cost Analysis Model)  is a more




deterministic model than the other two with regard to the




consideration of containment failure.  In this model, all synthetic




liners are assumed to fail within 35 years and to have a linear failure




rate over this 35-year period; leachate collection systems are assumed




to release a fixed fraction of the leachate they handle; and  surface




releases from storm-water management units and surface impoundments are






                                 25

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assumed to occur solely from overtopping during storm events, and




overtopping is assumed to have a constant probability of occurrence in




any year.




     As currently structured, these three models are intended primarily




for use in analyzing the risks and costs associated with alternative




regulatory strategies (e.g., alternative standards for waste




containment).  They are not meant for, nor are they applicable to,




site-specific comparisons of containment effectiveness among different




facilities, especially among abandoned, uncontrolled waste disposal




sites.  Consequently, we have concluded that the models themselves do




not provide any further basis for developing modifications to the HRS




containment factor.




     However, some results from regulatory analyses conducted with




these models may be useful in developing portions of various




containment rating scales to be incorporated in the HRS containment




rating factor.  This will depend, in part,  on the nature of the




containment rating factor alternatives that are developed.  (Chapter 3




identifies various alternative approaches for evaluating containment




in the HRS.)  Limitations in the release pathways and facility types




and designs accounted for in the three models will, however, limit any




such application.
                                 26

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3.0  CONTAINMENT EVALUATION ALTERNATIVES

     Nine alternative approaches for evaluating containment in the

HRS are identified and examined in this chapter.   These alternative

approaches have been developed to collectively illustrate ways that

the current HRS containment factor could be modified to:

     •  Increase its consistency with RCRA Subtitle C land disposal
        regulation

     •  Include criteria other than RCRA-based technical requirements

     •  Provide greater differentiation among sites, or

     •  Reduce the subjectivity of the current containment
        evaluation criteria

No one alternative approach does all four.  However, depending on

data availability, several of the alternative approaches could be

combined to encompass various objectives.

     One option for the development of a containment factor under

each alternative approach is briefly outlined to  illustrate the

types of containment options possible under each  alternative.  The

advantages and disadvantages of each alternative  are discussed, and

issues that need to be resolved before more complete options can be

developed under the alternative are identified.

3.1  Overview of Alternatives

     The nine alternatives are as follows:

     1.  Modify the present criteria to incorporate changes in the
         RCRA technical requirements since 1982 (Section 3.2).

     2.  Integrate the containment rating factor  with a rating
         factor based on waste quantity (Section  3.3).


                                 27

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     3.  Revise the evaluation criteria to be evidentiary rather
         than predictive, and retain the zero factor value
         (Section 3.4).

     4.  Revise the evaluation criteria to be evidentiary rather
         than predictive, and eliminate the zero factor value
         (Section 3.5).

     5.  Integrate evidentiary and predictive criteria (Section 3.6).

     6.  Develop time-dependent evaluation criteria to replace the
         present criteria (Section 3.7).

     7.  Develop evaluation criteria based on waste disposal
         location rather than on waste management technology
         (Section 3.8).

     8.  Develop evaluation criteria based on site drainage to
         replace the present criteria (Section 3.9).

     9.  Integrate the containment rating factor with the physical
         state rating factor (Section 3.10).

     The first alternative provides an illustration of the criteria

that would be developed if the containment factor was modified to be

more consistent with current RCRA Subtitle C land disposal

regulations.

     Two other alternatives examine methods for providing a more

uniform distribution of containment values.  One of these

alternatives (Alternative 9) considers the integration of the

current HRS physical state factor into the containment factor.  As

discussed in Section 3.10, most sites in the automated NPL technical

data base have been assigned values of 3 for both of these factors.

This approach seeks to provide a more uniform distribution of

assigned values by integrating these factors into a revised
                                 28

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containment factor.  The other alternative (Alternative 2) considers




the integration of the current containment factor with a factor




based on the quantity of waste present in the various waste




management areas at a site.  The current HRS containment value




assigned to a route is the highest rating value assigned to any




waste management area for that route.  This alternative attempts  to




define a more representative containment value by weighting the




containment value for each waste management area by the portion of




the waste at the site that is present in that waste management unit.




     Two additional alternatives (Alternatives 3 and 4) examine the




use of evidentiary criteria, instead of RCRA-based criteria, in




evaluating containment.  The criteria in the present HRS containment




factor, which are based on RCRA requirements, are predictive,




equating the application of good containment technology to the




existence of good containment.  These two alternatives consider




criteria based on evidence of containment efficiency at a site




rather than on the predictive technical requirements.  Such




evidentiary criteria would equate the visual or analytical evidence




of hazardous substances in contact with the environment with the




existence of poor containment.  Good containment would also need  to




be proven through analytical evidence.  A third alternative




(Alternative 5) then considers the integration of evidentiary and




predictive criteria in evaluating containment.
                                 29

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     Another alternative (Alternative 6) addresses the use of




time-dependent criteria, rather than RCRA-based criteria, in




evaluating containment.  This alternative examines whether




containment values could be assigned based on the time elapsed since




waste deposition, recognizing that no containment is likely to be




100 percent effective over time.




     Two other alternatives examine ways to reduce the subjectivity




in the current containment evaluation criteria and to make the




criteria more applicable to the differences in containment likely to




be present at CERCLA sites.  One alternative (Alternative 7) examines




the use of containment factors based on waste location (i.e., above




ground or below ground) rather than on the type of waste management




unit in which the wastes are placed.  The second alternative




(Alternative 8) equates good containment with good site drainage and




bases the evaluation criteria on site drainage.




3.2  Updating of Present RCRA-Based Criteria




     HSWA imposes additional technical requirements for RCRA




Subtitle C hazardous waste management facilities, particularly land




disposal units.  The containment evaluation methodology could be




revised to incorporate these additional requirements, as well as




additional requirements promulgated under RCRA in the period after




1981.   For example, HSWA requires double liners, leachate collection




systems,  and ground water monitoring at surface Impoundments,




disposal  piles, and landfills, although waivers are allowed.  The






                                 30

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revised evaluation criteria applicable to surface impoundments for

the ground water route might be the following:

   Rating*                      Criteria

     0   =   Sound run-on diversion structure, non-permeable and
             compatible double liners, functioning leachate
             collection and ground water monitoring systems, sound
             diking with cover, adequate freeboard, weekly
             inspection.

     1   =   Sound run-on diversion structure, non-permeable and
             compatible liner, no leachate collection or ground
             water monitoring systems, sound diking, adequate
             freeboard.

     2   =   Potentially unsound run-on diversion structure or
             diking, liner installed but integrity unknown, or
             inadequate freeboard.

     3   =   Unsound or no run-on diversion structure, no liner, or
             unsound diking.

Similar criteria could be developed for landfills, waste piles, tanks

and containers under both the ground water and surface water routes.

     These revisions would have similar characteristics to the

present methodology.  Specifically, they may not result in

differentiation among sites considered for placement on the NPL.

Hie major advantage of using these criteria is that for screening

purposes they do provide a clear definition of adequate containment,

and sites that are well engineered to contain the wastes would

likely be assigned very low scores.
*Note the rating values indicated here and throughout the remainder
 of Chapter 3 are meant only to illustrate relative rankings of
 containment.  They are not specifically being recommended for use
 in the HRS.
                                 31

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3.3  Integration of Containment Factor With a Factor Based on Waste
     Quantity

     In the current HRS each containment area is assigned a

containment factor value for each of the two water routes.  The

containment value for each route is the highest rating value assigned

to any waste management area for that route.

     A more representative measure of containment at the site may be

obtainable by weighting the containment factor rating value for each

waste management area by the portion of the hazardous waste at the

site that is present in that waste management area.  This weighted

value could then be used to assign the overall containment rating

value to the route.  In addition to providing a more representative

containment value, this approach would also provide increased

differentiation among sites that have some degree of containment for

at least some of the wastes at the site.

     However, this alternative does not appear to be practical to

implement unless current data acquisition problems can be overcome.

Presently, hazardous waste quantity estimates cannot be derived for

about 20 percent of the sites in the automated NPL technical data

base (Kushner, 1986).  For many of the remaining sites, waste

quantity estimates can be derived only for a fraction of the

hazardous wastes deposited at the site.  Unless more complete

estimates of hazardous waste quantities can be obtained for CERCLA

sites, this is not a viable alternative.  To derive more complete

estimates of hazardous waste quantity, the current site inspection

                                 32

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program would have to be expanded considerably.  (A companion report

[Wolfinger, 1986] discusses issues involved in the collection of waste

concentration data which could be used to estimate waste quantity at

CERCLA sites.)  Because of the data limitations, this alternative is

not developed further in this report.

3.4  Development of Evidentiary Criteria With a Zero Value

     The present containment evaluation criteria are based on the

presumption that if a waste is contained using technology specified by

the RCRA regulations, it poses a lesser threat to human health and the

environment than waste not contained using such technology; this level

of containment is currently assigned a value of zero.  Reductions in

the containment technologies present at a site or in their operating

efficiencies result in higher containment factor values being assigned.

Several subjective evaluations are presently required to assign a

containment factor value, such as liner permeability, diversion

structure soundness, and container condition.  The information required

to make these evaluations may be difficult to obtain.  For example,

the presence of a liner may be established through design drawings or

site inspections, but the condition or permeability may be difficult

to determine without laboratory testing or on-site monitoring that

disturbs the site.

     The approach under this alternative is to base the containment

factor value primarily on criteria that can be evaluated through

observation and limited site sampling and analysis, such as the

following:
                                 33

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   Rating                       Criteria

     0   =   Demonstrated compliance with current RCRA waste
             containment requirements, such as impermeable and
             compatible double liners, covers, functioning diversion
             and leachate collection systems, and non-leaching waste
             stabilization.

     1   =   Evidence of waste containment measures, efficiency
             unknown, no evidence of uncontained waste.

     2   =   Evidence of waste containment measures and presumptive
             evidence of uncontained waste.

     3   =   Visual or analytical evidence of uncontained waste, or
             no evidence of waste containment present.

The above criteria for assigning a zero value are similar to the

present criteria for assigning a zero containment value,  except that

they reflect the current RCRA regulations.  If compliance with RCRA

requirements cannot be documented, but waste containment  measures of

unknown efficiency exist, a higher value (e.g., 1) could  be assigned

under this alternative.  This category would include sites at which

a liner or cover is installed but at which the liner's  compatibility

and integrity were not evaluated, or at which a diversion structure

or leachate collection system is present, but at which  its operating

efficiency was not determined.

     A still higher value (e.g., 2) could be assigned when there

is analytical evidence of uncontained waste, even if some waste

containment measures exist.  The analytical evidence could include

contaminated soil, ponded water, or leachate where the  contaminants

can be attributed to the wastes disposed at a site.   While this
                                 34

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analytical evidence would be insufficient to score an observed




release, it does indicate that containment is poor and that waste




constituents have a higher potential for entering the environment.




     The criteria for assigning the highest value (e.g.,  3) are




similar to the present containment factor criteria.  Sites at which




no waste containment measures are evident, or at which waste contact




with the environment can be visually observed, would be assigned




this highest value.




     This alternative illustrates the use of evidentiary criteria,




rather than RCRA-based technical criteria, to rate most levels of




waste containment.  RCRA-based criteria, not evidentiary criteria




are, however, used to rate the highest level of containment because




the lack of analytical evidence of uncontained waste does not




necessarily indicate that a release has not or will not occur.  It




may just mean that the evidence has not been found.  For example,




where monitoring has been done, the lack of such evidence may be




the result of temporal or spacial variations in environmental




concentrations or faulty monitoring procedures.  It may also mean




that substances being released were not those tested for in the




sample analysis.  This is discussed further in Wolfinger (1986).




Consequently, it is possible for sites with identical wastes and




identical containment measures to be assigned different containment




ratings under this alternative because evidence has been found at




one site but not at the other.






                                 35

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     It should be noted that this evidentiary approach may be more




applicable to the surface water route than to the ground water route,




Certain types of evidence that would be of extreme importance in the




ground water route (e.g., leachate or soil samples from below




landfills, surface impoundments, etc.) are not easily obtainable or




have risks inherent in their collection (e.g., drilling through a




landfill could open conduits for waste migration).  The collection




of these additional data would likely require an expansion of the




current site inspection program.  Without further analysis, it is




not possible to determine whether the data required to use the above




criteria or the data required to use the current ground water




containment factor are more costly to obtain.




     This approach is not likely to result in any significant shift




in the distribution of containment factor scores.  The highest and




lowest evaluation criteria under this alternative are essentially




the same as those of the current containment  factor.   As a result,




there would likely be little change in the distribution of these two




values.  There would be some limited shift in the distribution of




the two intermediate values, but probably almost no shift in the




absolute number of sites being assigned an intermediate value.




3.5  Development of Evidentiary Criteria Without a Zero Value




     This alternative is the same as that in  Section  3.4, except




that the zero rating value is eliminated.   The following evaluation




criteria illustrate this approach:






                                 36

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   Rating                       Criteria

     1   =   Waste containment measures evident, no evidence of
             uncontained waste.

     2   =   Waste containment measures evident with presumptive
             evidence of uncontained waste.

     3   =   No waste containment present, or visual or analytical
             evidence of uncontained waste.

     The zero rating value has been eliminated both to remove

dependence of the criteria on RCRA land disposal requirements and

to indicate that complete waste containment over time cannot be

absolutely assured even with measures that comply with RCRA

requirements.  (This latter consideration could also be incorporated

in the alternative in Section 3.4 by assigning a value of 1, not

zero, to containment that meets RCRA requirements and by adjusting

all other values accordingly.)  The advantages and disadvantages of

this alternative are essentially the same as those discussed in

Section 3.4.  However, no differentiation is made for different

levels of containment when there is no evidence of uncontained

wastes.  This is addressed in Section 3.6.

3.6  Integration of Evidentiary and Predictive Criteria

     This alternative illustrates the integration of evidentiary

and predictive criteria in the rating of containment.  Under this

approach, sites at which there is evidence that hazardous substances

have been released from a containment area would be assigned a

higher value than sites at which there is no evidence of release.

Where there is no evidence, the rating would be based on predictive

                                 37

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technical requirements.   It is  anticipated  that  the  type of evidence

that would be used under this alternative would  be evidence that

shows migration from a waste containment  area, but which is not

adequate for demonstrating an observed release to surface  or  ground

water (e.g., contaminated soil, leachate, erosion  trails).

     This alternative would have essentially  the same advantages  and

disadvantages as the alternative presented  in Section 3.4. However,

it would have the added  advantage of being  able  to differentiate

among sites at which there was  no evidence  of uncontained  waste.

One possible option under this  alternative  is illustrated  below  (for

the ground water route for a landfill):

   Rating                       Criteria

     0   =   Demonstrated compliance with RCRA-based land  disposal
             requirements.

     1   =   No evidence of uncontained waste; single liner and
             functioning leachate collection  system.

     2   =   No evidence of uncontained waste; single liner,  no
             functioning leachate collection  system.

     3   =   Presumptive evidence of uncontained waste.

     4   =   Visual or analytical evidence  of uncontained  waste,  or
             no evidence of waste containment present.

3.7  Development of Time-Dependent Criteria

     Since the physical, chemical, and biological  processes that

result in contaminants being released  from  waste sites are

continuous, the duration of time these processes have been in

operation affects the integrity of containment structures  at  the
                                 38

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site, the quantity of any constituents released from the site, and the

nature of the wastes that remain at the site.  The longer wastes are

at a site, the greater the overall potential for there to be a release

from the site, especially if the site is abandoned or not maintained.

     The approach under this alternative is to use criteria that are

based on the elapsed time since waste deposition to evaluate the

containment at a site.  Such criteria would likely result in a more

uniform distribution of containment values.  The following evaluation

criteria are an example of criteria that could be developed (they are

presented solely for illustration purposes; they are not based on an

analysis of containment failure data):

   Rating                       Criteria

     0   =   Less than two years elapsed time since the initial
             disposal of hazardous substances.

     1   ™   At least two years, but less than ten years, since
             initial disposal.

     2   =   At least ten years, but less than twenty years, since
             initial disposal.

     3   =   Twenty years or more since initial disposal or no
             evidence of waste containment.

     The use of time-dependent criteria would, by its very nature,

tend to differentiate sites on the basis of the timing of a potential

release (i.e., how soon is it likely to occur).  For example, under

this approach, older sites would be assigned higher rating values

than those newer sites where releases are equally likely to occur

within the same period of time from waste deposition.  Consequently,


                                 39

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newer sites would, in general, tend to have lower HRS  migration




scores than older equivalent sites.  The net effect would be that




sites that are close to (or are already) releasing hazardous




substances would be more likely to be placed on the NPL than sites




that are equally likely to, but further away in time from, releasing




hazardous substances.  The desirability of such an impact is a




policy issue.



     Furthermore, there would be several drawbacks to the application




of time-dependent criteria.  First, it would be necessary to define




a viable measure of time.  Documentation of the wastes managed at a




site has proven difficult (see Section 3.3); documentation of the




dates of deposition would be even more difficult.  Disposal dates




are often unavailable because of poor or non-existent recordkeeping.




Further, wastes were often deposited at different times and in




different amounts and mixtures at a site.  Surrogate measures, such




as years since site opening or site closing, suffer from similar




information collection problems and may differ significantly from




the actual years since waste deposition.




     Second, the interactions between site age, containment structure




integrity, and contaminant mobility are very complex.   It is not




clear that they could be adequately defined or be simplified enough




to be incorporated in the HRS.  Site-specific and waste-specific




characteristics would be very important and would have to be




considered.  For example, buried drums in a desert environment






                                 40

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generally corrode more slowly than those buried in locations with




high ground water tables where the drums are continually in contact




with water and quickly corrode.  Furthermore, waste characteristics,




such as corrosivity and reactivity, also strongly affect the drum




life.




     For these reasons, time-dependent criteria do not appear to be




a viable alternative for use in the HRS containment factor.




3.8  Use of Criteria Based on Waste Disposal Location




     This alternative illustrates the use of criteria that are based




on waste location rather than on the type of waste management unit




in which wastes are deposited.  For each water route, the criteria




are differentiated by whether the wastes are deposited below the




ground surface or deposited at or above the ground surface.  The




assumption is that waste containment requirements are similar for




wastes deposited in similar locations (i.e., above or below ground),




regardless of the type of unit in which they are placed.  For




example, for the surface water route diking is important for wastes




deposited above ground, but is not important for wastes deposited




below ground.




     For each pathway under this alternative, containment is




evaluated for both locations using predictive criteria similar to




those in the current containment factor.  The criteria are modified,




however, to make them more applicable to the differences in




containment likely to be present at CERCLA sites and to remove some






                                 41

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of the subjectivity that results from use of current site inspection




data.  For example, under this alternative distinctions are made as




to whether or not liners are present, not on how permeable the liners




are or whether they are compatible with the wastes at the site.  Such




distinction may not be appropriate for CERCLA sites since it appears




that the vast majority of these sites do not have liners.  Further,




based on current site inspection data, asssessments of liner




integrity, permeability, and compatibility are often subjective.




     Illustrative criteria for this alternative are presented in




Table 3-1.  It should be noted that the values listed in Table 3-1




are based on engineering judgments, not an analysis of modeling




results or site data.  Such analysis may be necessary if this




approach is to be considered further.  In using the criteria in




Table 3-1, it is recommended that evidence of properly functioning




waste containment measures be required to assign values corresponding




to excellent or good containment.  A lack of evidence would result




in a rating of poor containment if containment measures were present.




When both types of disposal locations are present at a site, rating




values would be assigned to each and the highest rating value would




be used to compute the route score.




     One advantage of this approach is that it can be applied to any




type of waste containment unit at a site; it is not limited to the




four types in Tables 2-1 and 2-2.  It also eliminates some of the




subjectivity present in the current containment factor.   Further, it






                                 42

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                              TABLE 3-1

           ILLUSTRATIVE CONTAINMENT FACTOR VALUES  BASED ON
                       WASTE DISPOSAL LOCATION
                                                   Rating Value
         Criteria
     Ground
      Water
Surface
 Water
Below-Grade Disposal

  Excellent containment
  (4 of 5 technologies functioning)

  Good containment
  (2 of 5 technologies functioning)

  Poor containment
  (1 of 5 technologies functioning
  or efficiency unknown)

  No containment

Above-Grade or Surface Disposal

  Excellent containment
  (4 of 5 technologies functioning)

  Good containment
  (2 of 5 technologies functioning)

  Poor containment
  (1 of 5 technologies functioning
  or efficiency unknown)

  No containment
        2

        3
        2

        3
   0


   0



   1

   2
   2

   3
                      Containment Technologies

           •  Engineered Cover        •  Leachate collection

           •  Double liner

           •  Run-on diversion
Diking with adequate
freeboard
                                 43

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may provide a somewhat more uniform distribution of containment


values since only one containment technology needs to be present to


achieve a value of 1.


     One major disadvantage of this approach is that it assumes that


each containment technology in Table 3-1 is of equal importance.


This may not be the case.  For example, leachate collection may be


more important than run-on diversion.  A further disadvantage of the


approach is that the five listed containment technologies may not be


applicable, nor even meaningful, for every type of waste management


unit.  For example, surface impoundments are not likely to have


covers, while almost all landfills would have some limited cover.


Additional refinements would thus be necessary if this approach was


deemed to warrant further investigation.


3.9  Development of Criteria Based on Site Drainage


     This alternative represents a further simplification of the


approach in Section 3.8.  The simplification is directed at providing


a more uniform distribution of containment values and further
                                               i

reducing subjectivity in the evaluation of containment.  To do this,


the evaluation criteria are based on those containment technologies


more likely to be present at CERCLA sites (i.e., some type of cover


material or cap and drainage or diversion structures).  Technologies


(e.g., liners, leachate collection systems) not likely to be present


or whose evaluations are likely to be subjective are not included.
                                 44

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     Under this alternative, the level of waste containment could be

equated with good site drainage using criteria similar to the

following:

   Rating                       Criteria

     0   =   Cap or cover, functioning drainage or diversion
             structure with collection system.

     1   =   Cap or cover, functioning drainage or diversion
             structure.

     2   =   No or non-functioning drainage or diversion structure,
             no ponding observed.

     3   =   No or non-functioning drainage or diversion structure,
             ponding observed.

These criteria are similar to the current surface water route

containment evaluation methodology and, except for liner and leachate

collection system evaluations, they are also similar to the ground

water criteria.

     This approach eliminates the evaluations of liner permeability

and leachate collection system operation from the present HRS

criteria because accurate information on their effectiveness is

difficult to obtain without extensive monitoring programs.  For

example, the presence of a clay or synthetic liner is not by itself

evidence that the waste is contained.  The synthetic liner may be

torn or the clay may be cracked or channeled such that the liner is

quite permeable.  There is no way of making this determination

without more extensive monitoring data than is presently available

from site inspections.
                                 45

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     The primary advantage of this approach is that it would provide




a more uniform distribution of site scores, if this is desired.   In




addition, the proposed criteria should be simpler to implement than




the existing criteria because they are not specific to each waste




management technology.  The necessary evaluations could be based on



visual evidence; evaluations of liner permeability or compatibility




are not required.  The criteria could also be integrated with the




evidentiary criteria discussed in Sections 3.4 to 3.6 to obtain a




more uniform distribution among containment values than presently



exists and to incorporate other factors affecting waste containment.




     The major disadvantage with this alternative is that it ignores




elements (e.g., liners) that are important to good containment.   It




is structured to provide a more uniform distribution of values,  not




to meaningfully evaluate the overall effectiveness of containment at




a site.




3.10  Integration of Containment and Physical State Factors




     The physical state of a waste is included as a rating factor




under the current HRS route characteristics category.  It is




evaluated when there is no evidence of an observed release for the




ground water or surface water routes.  The following criteria are




presently used to assign a value to physical state:




   Rating                       Criteria




     0   =   Consolidated or stabilized solid.



     1   =   Unconsolidated or unstabilized solid.





                                 46

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   Rating                       Criteria

     2   =   Powder or fine material.

     3   =   Liquid, sludge or gas.

     The physical state of a waste affects the potential for the

waste (or its hazardous constituents) to migrate from a site or

alternatively for it to be contained at a site.  Physical state can

thus be used as a measure of either waste containment or waste

migration potential.  It is currently used as a measure of waste

migration potential in the ground water and surface water route

characteristics factor category of the HRS.  Physical state could,

however, be integrated with the current containment factor (or a

revised containment factor) and deleted from the route

characteristics factor category.  The advantages and disadvantages

of this are discussed below.

     Most of the sites in the automated NPL technical data base for

which there are physical state and containment values have a value

of 3 assigned to both factors, indicating that there are at least

some uncontained liquids, sludges, or gases present at most of these

sites.*  Of the 698 sites in the automated NPL technical data base

for which a value was assigned to the physical state factor, 617 of

the sites (88 percent) received a value of 3.  Eighteen sites
*The physical state factor value assigned to a route is the highest
 physical state factor value assigned to any of the substances at the
 site that can migrate along that route.  Thus, there could be solids,
 in addition to liquids, sludges, or gases, present at a site that
 receives a factor value of 3.

                                 47

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(3 percent) were assigned a value of zero, 32 sites (5 percent) a 1,




and 31 sites (4 percent) a value of 2.




     Based on the above data, it appears that the primary function




that physical state currently serves in the HRS is to assist in




screening out (i.e., lowering scores) of sites that do not contain




at least some liquids, sludges, or gases.  If this is the objective,




it could most likely be carried out more effectively by integrating




physical state into the containment factor, since this would place




greater weight on physical state in the overall route score.  Under




this approach for each waste management unit, both the type of




containment and the physical state of the wastes in that unit would




be considered in assigning a rating value to that waste management




unit.  This integration could at the same time provide some further




differentiation among the vast majority of CERCLA sites at which




uncontained liquids, sludges, and gases are present in some, but not




all, waste management units at the site.  This would, however, have




to be verified by further analysis if this alternative was deemed to




warrant further investigation.




     There are numerous ways in which physical state could be




integrated into the containment factor.  Two examples are illustrated




below, using both evidentiary and predictive approaches.




     3.10.1  Use of Evidentiary Criteria




     The physical state and containment factors could be integrated




for each waste management unit using evidentiary criteria similar to






                                 48

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those presented in Section 3.4.   The following criteria  illustrate

this approach for rating a waste management unit:

   Rating                       Criteria

     0   =   Evidence of only stabilized or contained solid in the
             waste management unit

     1   =   Unstabilized, contained solid in the  waste  management
             unit with presumptive evidence of containment  failure,
             or containment efficiency unknown
                                -or-
             Evidence of contained liquid or sludge in the  waste
             management unit

     2   =   Uncontained solid in the waste management unit
                                -or-
             Contained liquid or sludge in the waste management unit
             with presumptive evidence of containment failure,  or
             containment efficiency unknown

     3   =   Uncontained liquid, sludge, or gas in the waste
             management unit

     The effective use of these criteria focuses on the  determination

of containment.  For example, a solid must be stabilized or contained

for the waste management unit to be assigned a zero value.

Containment or stabilization must be supported by  evidence  similar  to

that discussed in Section 3.4.  The advantages and disadvantages of

this approach would be similar to those advantages and disadvantages

discussed for the evidentiary approach in Section  3.4.

     3.10.2  Use of Predictive Criteria

     The physical state and containment rating factors could also be

integrated for each waste management unit using predictive  criteria

similar to those of the current containment factor or to those

illustrated in the alternatives.  The following criteria illustrate

                                 49

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how some of the waste location criteria in Section 3.8 could be

integrated with the physical state factor:

   Rating                       Criteria

     0   =   Stabilized solid, or solid disposed with four of the
             five functioning containment technologies.*

     1   =   Unstabilized solid disposed with two of the five
             functioning containment technologies
                                -or-
             Liquid or sludge disposal with four of the five
             functioning containment technologies

     2   =   Unstabilized solid disposal with one of the five
             functioning containment technologies
                                -or-
             Liquid or sludge disposal with two of the five
             functioning containment technologies
                                -or-
             Analytical evidence of leaking containment

     3   =   No waste containment for solids, liquids, sludges,  or
             gases

Evidence of functioning containment technologies, similar to that

discussed in Section 3.8, would be required to ensure consistent

evaluation.  The advantages and disadvantages of the above criteria

would be similar to those discussed in Section 3.8.
*From Section 3.8,  the five containment technologies  are:
 dike with adequate freeboard,  run-on diversion structure,  double
 liner,  engineered  cover,  and leachate collection  system.
                                 50

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4.0  SUMMARY AND RECOMMENDATIONS




     The current HRS containment factor uses evaluation criteria




that are based on the requirements of the RCRA Subtitle C land




disposal regulations as of early 1982.  The analysis in Chapter 2




indicates that many wastes at CERCLA sites are not well contained




and that the use of evaluation criteria based on the RCRA Subtitle C




regulations may not provide much differentiation between sites.




This is even more likely to be true if the HRS containment factor is




modified to reflect the current land disposal regulations.




Furthermore, the current HRS containment evaluation criteria may be




more complex and subjective than is warranted.  In light of the type




of containment likely to be present at CERCLA sites, it may be more




meaningful for HRS screening purposes just to distinguish whether a




containment technology is present at a site and not to try to make




fine distinctions about how effective it is.




     Based upon the analysis in Chapter 2, several issues that need




to be considered in any modification of the HRS containment factor




have been identified.  One issue is whether the containment factor




should continue to be included in the HRS.  While the containment




factor appears to be effective in screening out sites that have




relatively high levels of containment, the number of sites receiving




less than the maximum containment factor value appears to be small.




Assuming that containment is to remain a factor in the HRS, the




primary issue that needs to be addressed is whether the containment






                                 51

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factor is to be used primarily to screen out those relatively few

sites that have adequate containment or to provide increased

differentiation among all sites without an observed release.  For

reasons discussed in Chapter 2, it is unlikely that any single

containment factor can be developed to do both effectively.

     If it is decided to use the containment factor to screen out

sites with adequate containment, there are two basic issues  that

need to be addressed:

     •  How adequate containment is to be defined and evaluated for
        HRS purposes.

     •  Whether the rating assigned for adequate containment is to
        be a zero or a non-zero value.

     If it is decided to use the containment factor to differentiate

among all sites without observed releases, the primary issue is more

technical.  The primary issue is defining containment characteristics

that meaningfully delineate actual, but likely small, differences

in containment effectiveness and that at the same time are

representative of the containment technologies likely to be  present

at most sites eligible for NPL listing.  For reasons discussed in

Chapter 2, it is unlikely that any useful definition could be based

solely on technical requirements for land disposal.

     Nine alternative approaches for evaluating containment  in the

HRS are identified and examined.  These alternatives have been

developed to collectively illustrate ways that the current HRS

containment factor could be modified to:


                                 52

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     •  Increase its consistency with RCRA Subtitle C land disposal
        regulations

     •  Include criteria other than RCRA-based technical requirements

     •  Provide greater differentiation among sites, and/or

     •  Reduce the subjectivity of the current containment
        evaluation criteria

     No one alternative approach does all four.   One option for the

development of containment factors under each alternative approach

is briefly outlined to illustrate the types of containment options

possible under each alternative.  The advantages and disadvantages

of each alternative are discussed, and issues that need to be

resolved before more complete options can be developed under the

alternative are identified.

     As part of the development of the alternatives, ten existing

ranking systems that consider containment in rating the threat posed

by hazardous waste sites were reviewed along with three EPA hazardous

waste policy analysis models that also account for containment.  Five

of the ranking systems were found to have containment factors that

are very similar in concept and application to that of the HRS.  Two

ranking systems were found not to explicitly evaluate containment in

ranking a site.  The other three ranking systems were found to have

containment factors that are not comprehensive nor well defined.  The

three EPA hazardous waste policy analysis models were found not to be

applicable for use in making site-specific comparisons of containment

effectiveness.
                                 53

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     Of the nine alternatives developed, one focuses on updating the

current RCRA-based containment evaluation criteria.   One examines the

use of time-dependent, rather than RCRA-based, criteria.  Two others

examine the use of evidentiary criteria rather than  RCRA-based

criteria.  Three others examine the integration of waste quantity,

physical state, or evidentiary criteria into the containment factor.

The remaining two examine ways to reduce the subjectivity in the

current evaluation criteria and to make the current  criteria more

applicable to the differences in containment likely  to be present at

CERCLA sites.

     It is recommended that two of these alternatives be considered

for possible further development and that six others be eliminated

from further consideration.  Further development of  the ninth

alternative, Updating of the Current Containment Factor, is entirely

a policy issue.

     The two alternatives that are recommended for possible further

development are the following:

     •  Integration of Evidentiary and Predictive Criteria in the
        Containment Factor.

     •  Integration of the Physical State Factor Into the Containment
        Factor.

     The integration of evidentiary and predictive criteria offers

several possible advantages.  First, it could be used to assign

higher rating values to sites at which there is evidence that

hazardous substances are leaving waste management areas than to sites


                                 54

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at which there is no detected evidence that hazardous substances are




leaving the waste management area.  Such evidence is currently not



considered in the HRS unless it can be used to document an observed




release.  Second, where there is no detected evidence of a release,




predictive criteria could also be used to assign containment factor




values based on differences in containment technologies.  For reasons




previously discussed, it is recommended that such criteria only




distinguish whether a technology is present and not whether there are




differences in the effectiveness of the technology.  Third, this




approach would likely result in a slightly more uniform distribution




of containment values; however, any such change is not expected to be




large.  The major disadvantage of this approach is that sites that




have releases that are not detected, due for example to environmental




variations in concentrations, would receive a lower rating than they



should.  However, the same problem can also occur with the current




observed release factor.




     From the analysis presented in Section 3.10, it appears that




there is not much differentiation of sites based on the current




physical state factor.  Instead, the physical state factor appears




to assist in screening out sites that do not contain at least some




liquids, sludges, or gases.  Regardless of which containment




alternative, if any, is selected for further development,  it is




recommended that the integration of the physical state and




containment factors be evaluated further.  Such an integration may






                                 55

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increase the effectiveness of the HRS in screening out those sites




that have an adequate level of containment for the types  of wastes




present at the site.   It may also increase the differentiation among




the vast majority of  CERCLA sites that have at least some uncontained




liquids, sludges, or  gases.




     The other six alternatives are not recommended for further




development for a variety of reasons.  The integration of the waste




quantity and containment factor is not recommended for further




development because of significant problems with data availability.




If these could be resolved, this alternative would be the preferred




approach because it could be used to both screen out sites with




adequate containment  and to provide a considerably more uniform




distribution of containment values.




     The use of time-dependent criteria is not recommended because




it is unlikely that the complex relationships between site age,




containment integrity, and contaminant mobility could be adequately




defined or simplified for effective use in the HRS.  This approach




also suffers from data acquisition problems.




     The two evidentiary approaches that are not integrated with




predictive criteria are not recommended because the integrated




approach offers several advantages over these two.




     The other two approaches are not recommended because many of




their simplifications either ignore or equate differences in




containment that may  be significant for certain types of  containment






                                 56

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structures.  Further, some of the more meaningful simplifications




can still be incorporated into whatever containment factor is




ultimately used in the HRS.  However,  it should be noted that,  if it




is decided to modify the containment factor to provide a more uniform




distribution of containment values, these latter two approaches are




the only ones identified that are likely to be able to achieve  this.
                                 57

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                             APPENDIX A
     REVIEW OF CONTAINMENT FACTORS  IN OTHER SITE  RANKING  SYSTEMS

     This appendix reviews the containment factors that have been
incorporated in other systems.  Ten ranking systems that consider
containment in rating the threat posed by hazardous wastes sites  have
been identified along with three EPA hazardous waste policy analysis
models that also account for containment.  The review of these systems
focuses on how containment is used in each system and how containment
effectiveness is defined and evaluated.  Important similarities and
differences between these factors and the HRS containment factor  are
identified.  The ten ranking systems reviewed are:
     •  HARM                    •  SAS
     •  HARM II                 •  PERCO
     •  GSR                     •  Illinois Rating Scheme
     •  ADL                     •  Rating Methodology Model
     •  S.P.A.C.E. for Health   •  Dames and Moore Methodology
The three EPA hazardous waste policy analysis models reviewed are:
     •  Liner Location Risk and Cost Analysis Model
     •  Hazardous Waste Tank Failure Model
     •  RCRA Risk-Cost Analysis Model
     Before reviewing these systems, it should be noted that the  HRS
containment factor is a multiplicative factor that is rated on a
scale of 0, 1, 2 or 3.  Since it is a multiplicative factor, if it
were to be divided by three and the divisors used to normalize the
corresponding HRS pathway scores were also to be divided by three,
                                 59

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there would be no change in the HRS pathway scores.  In this case, the




HRS containment factor would be rated on a scale of 0 to 1 and would




have values of 0, 0.33, 0.67- and 1.




A.I  HARM




     Hie Hazard Assessment Rating Methodology (HARM) is used by the




U.S. Air Force to rank hazardous substance sites for priority attention




for follow-on site investigations and confirmation activities under




Phase II of the Air Force's Installation Restoration Program (IRP).




HARM is designed to use data developed during the Record Search




(Phase I) portion of the IRP (Engineering-Science, 1983).  Record




Searches are essentially equivalent to EPA Preliminary Assessments.




     The HARM score is developed from four subscores:  Receptors,




Pathways, Waste Characteristics, and Waste Management Practices.  A




total risk score is determined by averaging and normalizing the first




three subscores.  The total risk score is then multiplied by the Waste




Management Practices subscore to produce the HARM score.




     The Waste Management Practices subscore is a measure of the




containment at the site and ranges from 0.1 to 1 as follows:




     •  No containment                              1.0




     •  Limited containment                         0.95




     •  Fully contained and in full compliance      0.10




Table A-l shows the guidelines for a determination of fully




contained.  These guidelines are quite similar to those used to




assign a zero rating to the current HRS containment factor.






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                              TABLE A-l

               FULLY CONTAINED SITES—HARM GUIDELINES
Landfills;

     •  Clay cap or other impermeable cover
     •  Leachate collection system
     •  Liners in good condition
     •  Adequate monitoring walls

Surface Impoundments;

     •  Liners in good condition
     •  Sound dikes and adequate freeboard
     •  Adequate monitoring wells

Spills;

     •  Quick spill cleanup action taken
     •  Contaminated soil removed
     •  Soil and/or water samples confirm total cleanup of the spill

Fire Protection Training Areas;

     •  Concrete surface and berms
     •  Oil/water separator for pretreatment of runoff
     •  Effluent from oil/water separator to treatment plant
Source:  Engineering-Science, Comparison of U.S. Air Force Hazard
         Assessment Rating Methodology (HARM) with U.S. Environmental
         Protection Agency Hazard Ranking System (HRS) at Four Air
         Force Bases Evaluated under the Phase I Installation
         Restoration Program, Engineering-Science, Atlanta, GA,
         April 1983.
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     The HARM Waste Management Practices subscore is thus very




similar in concept and application to the HRS Containment Factor.




The main differences are that its lower limit is 0.1, rather than




zero, and that it has one, rather than two, intermediate rating




categories.  The primary disadvantage of the HARM factor is that




it does not address route-specific differences in containment.




A.2  HARM II




     The Hazard Assessment Rating Methodology II (HARM II) is a




modification and extension of the HARM system that is intended to




permit the use of site-specific monitoring data in setting




priorities.  HARM II is used by the U.S. Air Force in Phase II of the




IRP program to set priorities for detailed site investigations and




possible remedial action (Barnthouse et al., 1986).




     HARM II has a Waste Containment Effectiveness factor that is




based on the HRS containment factor (Barnthouse et al., 1986) and




that is consequently very similar in concept and application to the




HRS containment factor.  The Waste Containment Effectiveness factor




is a multiplicative factor used to determine surface water or ground




water pathway subscores.  Tables A-2 and A-3 present the Waste




Containment Effectiveness factor for the surface water and ground




water pathways, respectively.  Again, the main difference compared




to the HRS, is that the lower limit is 0.1, not zero.
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                             TABLE A-2

               HARM  II WASTE  CONTAINMENT EFFECTIVENESS
                  FACTORS  FOR SURFACE WATER PATHWAY
Containment Structure	Score

Landfills

     Clay or other cover in sound condition without evidence     0.1
     of severe erosion; if in floodplain, diked effectively
     to prevent floodwater encroachment

     Some problems with cover or dike/diversion systems;          0.5
     no wastes exposed

     Problems with both cover and dike/diversion system;          0.8
     or serious problem with one of these; no exposure of
     wastes yet

     Cover and/or diking system (if needed) absent; wastes       1.0
     exposed

Surface Impoundments

     Sound dikes, adequate freeboard, and no erosion evident     0.1

     Inadequate freeboard                                        0.5

     Potentially unsound dike                                    0.8

     Dikes unsound, leaking, or in danger of collapse, or        1.0
     evidence of past spillover
Spills
     Contaminants material apparently removed completely;         0.1
     but possible occurrence of a spill

     Contaminated area covered with impervious material          0.5

     Contaminants completely covered with soil, area             0.8
     revegetated

     No cleanup action or covering done                          1.0
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                       TABLE A-2  (Concluded)
Containment Structure	Score

Tanks

     Tanks in sound condition and inspected regularly; tank      0.1
     area effectively bermed to contain any spills (and
     subsequent rainfall)

     Tanks in sound condition and bermed, but berm system        0.5
     or inspection system possibly insufficient

     Tanks in sound condition, but not bermed                    0.8

     Tanks unsound                                               1.0

Fire Protection Areas

     Berms; oil-water separator for treatment of runoff;          0.1
     oil-water separator effluent to treatment plant

     Some deficiency in the above                                0.8

     None of the above                                           1.0


Source:  Barnthouse, L.W. et al., Development and Demonstration of a
         Hazard Assessment Rating Methodology for Phase II of the
         Installation Restoration Program,  (ORNL/TM-9857), Oak Ridge
         National Laboratory, TN, 1986.
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                              TABLE  A-3

               HARM II  WASTE  CONTAINMENT  EFFECTIVENESS
                  FACTORS FOR GROUND WATER PATHWAY
Containment Structure	Score

Landfills

     Liner essentially impermeable, intact, and compatible       0.1
     with waste; cover of low permeability, and intact;
     leachate collection system; adequate monitoring wells

     Physical containment system suitable; no monitoring         0.5

     Deficiencies in physical containment system (e.g.,           0.8
     moderately permeable liner, no leachate collection,
     or defective cover)

     Cover and/or diking system (if needed) absent; wastes       1.0
     exposed

Surface Impoundments

     Liner essentially impermeable and compatible with           0.1
     waste; double liner or leakage detection system

     System essentially sound, but no double liner or            0.5
     leakage detection system

     Liner moderately permeable or in deteriorating condition    0.8

     No liner or incompatible liner; soil contaminated           1.0
     by leakage from impoundment
Spills
     Contaminated material apparently removed completely;        0.1
     but possible occurrence of a spill

     Contaminated area covered with impervious material          0.5

     No cleanup action or covering done                          1.0
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                        TABLE A-3  (Concluded)
Containment Structure	Score

Tanks

     Tanks in sound condition and inspected regularly; tank      0.1
     area lined adequately

     Tanks in sound condition;  no liner                          0.5

     Tanks leaking                                               1.0

Fire Protection Areas

     Concrete surface                                            0.1

     No concrete surface                                         1.0
Source:  Barnthouse, L.W.  et al.,  Development and Demonstration of a
         Hazard Assessment Rating  Methodology for Phase II of the
         Installation Restoration  Program,  (ORNL/TM-9857), Oak Ridge
         National Laboratory,  TN,  1986.
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A.3  GSR




     The Confirmation Study Rating (GSR) model is used by the U.S. Navy




in the Navy Assessment and Control of Installation Pollutants (NACIP)




Program to assign priorities for further study to hazardous substance




sites.  The GSR model is based on the HARM system (Luecker, 1982).




     In the GSR model, Receptor, Pathway, and Waste Characteristics




rating factors are multiplied by a Waste Management factor to obtain




the site score.  The Waste Management factor is a measure of the




containment at the site and is identical to the Waste Management




Practices subscore of HARM, with one exception.  The one difference is




that limited containment is given a value of 0.8 in the CSR model




rather than 0.95 as in HARM.




A.4  ADL




     The Arthur D. Little, Inc. (ADL) system is an adaption of the




HRS that was developed for the Chemical Manufacturers Association




(Arthur D. Little, Inc., 1981).




     Like the HRS, the ADL system contains a multiplicative containment




factor that is used only when there is no observed release for the




ground water or surface water pathway.  The containment factor is




scored as either a 0 or a 1.  For both pathways, it is scored 0 if the




site is certified to have an impermeable liner (natural or artificial),




the high water table is below the liner, and an impermeable cover has




been installed.  Otherwise, it is scored 1.
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     The major difference between the HRS containment factor and the
ADL containment factor is that the ADL containment factor does not
attempt to evaluate intermediate levels of containment.   It is based
on the assumption that the rater should not try to make fine
distinctions in the degree of containment present at a site.  The
site is scored as either being contained or not contained.
A.5  S.P.A.C.E. for Health
     The System for Prevention, Assessment, and Control of Exposures
and Health Effect from hazardous sites (S.P.A.C.E. for Health) was
developed by the Centers for Disease Control (CDC) for use in public
health assessments of hazardous sites (French et al., 1984; Kay and
Tate, 1984).  The system is used to assign priorities to sites,
based on the potential of the site to endanger human health.
     Site Characteristics is one of four factors used in S.P.A.C.E.
for Health for determining the site priority.  There are seven
elements used to rate Site Characteristics.  One element, Site
Management and Containment, provides a measure of the containment at
the site.  Site Management and Containment is evaluated through the
use of criteria that are identical to those of the HRS containment
factor (see Tables 2-1 and 2-2).
A.6  SAS
     The Site Assessment System (Michigan, 1983) is used to assess
and prioritize release sites for further investigation and possible
remedial action.

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     SAS considers containment through a Release Potential




Category.  All containment structures (e.g., landfill) are first




rated for each pathway as to whether their containment effectiveness




is unquestionably adequate, inadequate, or unknown for that




pathway.  A rating of unquestionably adequate containment for a




pathway must be based on information that indicates the structure




was designed, constructed, and is operating so that emissions of




hazardous substances are effectively prevented from entering the




environment through that pathway.  Limited guidelines are provided




for this determination.




     The Release Potential Category is scored for each containment




structure that is not rated unquestionably adequate.   This is done




by first determining the fraction of the total waste quantity at the




site that is present in each containment structure (this results in




a value between 0 and 1 for each structure).  The physical state of




the waste in each containment structure without unquestionably




adequate containment is then scored as follows:  solid—1.0,




semi-solid—1.5, liquid or gas—2.0.  The quantity fraction and the




physical state score are then multiplied to give a release potential




score for each structure.  The release potential scores for each




structure without adequate containment for a specific pathway are




then summed to obtain the release potential score for the pathway.




The aggregated pathway release potential scores may not exceed 2.
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The aggregated pathway release potential score is then used as a




multiplicative factor in determining the overall pathway score.




     SAS thus differs from the HRS in that it uses the concept of




containment strictly as a means of measuring the quantity of waste




that can migrate along a pathway and not as a measure of the




relative effectiveness of the containment structure at a site.  In




the HRS containment is used for both purposes.  Any waste in a




containment structure receiving an HRS containment score of zero for




a pathway is not considered in the rating of the HRS waste quantity




factor for that pathway.




A.7  PERCO




     The Prioritization of Environmental Risks and Control Options




(PERCO) model (Arthur D. Little, Inc., 1983) was developed for the




Massachusetts Department of Environmental Quality Engineering for




use in ranking contaminated sites in terms of immediate and




long-term environmental and human health hazards.  The ranking is




used to provide a rationale for allocation of state remedial action



funds.




     Containment is not explicitly considered in ranking a site with




PERCO.   Rather containment is used in the following manner.  PERCO




contains a multiplicative factor called contaminant severity.  It is




calculated based on the measured concentrations of contaminants in




the environment of a site and acceptable ambient levels of those




contaminants, using relationships defined in PERCO.  Contaminant






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severity is assigned a value ranging from zero to 100.  If monitoring




data are not available for a site, then the contaminant severity is




approximated for the site, using information from other similar




sites for which monitoring data are available.  To do this, at least




ten similar sites, whose contaminant severity scores fall within an




acceptable range, are identified; the contaminant severity scores




for those sites are then averaged.  This average contaminant




severity score is used as the contaminant severity score for the




site.




     As one option, similar sites may be identified through




professional judgment.  For two pathways (air and surface water),




there is also an option for identifying similar sites through the




calculation of a similarity score.  One of the factors used to




calculate the similarity score is containment integrity.  Containment




integrity is a measure of the potential for leakage from three types




of containment structures:  drums; tanks; and pools, pits, or




lagoons.  Drum integrity is scored as follows:  many drums




leaking—8; a few widely separated drums leaking—4; all drums




intact—2; no drums on surface—0.  Tank integrity is scored as




follows:  at least one tank leaking—10; all tanks intact—6; no




tanks on site—0.  Pools, pits and lagoons are scored as follows:




large pools or lagoons evident, but not associated with leaking




drums or tanks—10; no such pools evident—0.
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     For the air pathway, there is one further option for  calculating




similarity scores to identify similar sites.   This involves




calculating a release potential score for sites that may be  similar.




The release potential score is calculated for each site, based on




the condition of drums and tanks at the site; the volume of  liquids




in pools, pits, and lagoons at the site; and the areal extent over




which liquid wastes are buried at the site.   The condition of drums




is scored on a scale of 0 to 40, primarily based on the percent of




drums present that are corroded, damaged, have loose covers, or are




otherwise capable of leaking contents to the environment.  The




condition of tanks is scored for each tank on a scale of 0 to 7,




based on whether the tank is leaking, has air vents to the outside,




and/or has an open top.  The liquid volume,  the surface area, and




the two scores for drum and tank condition are manipulated




mathematically and then added to obtain the  release potential score.




     PERCO thus differs from the HRS in that it does not consider




waste containment in the rating of a site.  Each site is rated




solely on monitoring data obtained either from that site or  from at




least ten similar sites.  Containment is considered only in  the




identification of the sites that are similar to the one being




rated.  The containment evaluation factors used in PERCO are




appropriate only for this purpose; they are  not intended for, nor




are they appropriate for, rating the relative effectiveness  of




containment structures.






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A.8  Illinois Rating Scheme




     The Illinois Rating Scheme is used by the State of Illinois as




a screening tool, for regional planning, to identify and prioritize




sites or areas potentially affecting ground water for more detailed




study and evaluation (Gibb et al., 1983).




     The Illinois Rating Scheme consists of four additive factor




categories, each of which is made up of several additive elements.




One of these factor categories, Health Risk of Waste and Handling




Mode, contains an element that is a measure of site containment.




This element, Recorded Management of Waste, is evaluated differently




for active industrial sites, active landfills, and abandoned sites



as indicated in Table A-4.  In using the criteria in the table,  no




guidance is provided as to what constitutes controlled or




uncontrolled operation,  a violation, or a site being well operated.




     The Illinois Rating Scheme differs from the HRS (and the nine




other ranking systems reviewed) in that it considers limited features




of a site's operational history (e.g., source of waste, types of



violations) rather than its waste management characteristics in the




ranking of the site.  While containment effectiveness is related to




operational history to a limited extent, this kind of approach does




not appear practical to apply to CERCLA sites where information




about the operational history of the site is extremely limited and




often unavailable.
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                              TABLE A-4

     ILLINOIS RATING SCHEME RATING RECORDED MANAGEMENT OF WASTE



           Criteria                                            Rating

Active Industrial Sites

   Principal On-site Storage or Disposal Method

       Incineration                                              0
       Secure Containers                                         2
       Treatment/Discharge                                       4
       Land Application                                          6
       Landfill                                                  8
       Surface Impoundments                                     10

Active Landfills

   Operational History

       No violations whatsoever; operated up to best             0
         expectations
       No violations; generally well operated                    2
       No violations of a serious nature; generally well         4
         operated
       Some violations of a serious nature; history doubtful     6
       Selected violations of a serious nature; past history     8
         unknown
       History of serious violations; essentially               10
         uncontrolled for periods of time

Abandoned Waste Sites

   Operational History

       Controlled operation; solely municipal wastes             0
         involved
       Controlled operation; predominantly municipal wastes      2
         involved
       Controlled operation; municipal and industrial wastes     4
         involved
       Uncontrolled operation; municipal and industrial          5
         wastes involved
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                       TABLE A-4  (Concluded)
  	Criteria	Rating

   Operational History (Concluded)

       Uncontrolled operation;  predominantly industrial          8
         wastes involved
       Uncontrolled operation;  wastes of all types probably     10
         present
Source:  Gibb, J. et al., Hazardous Waste in Ogle and Winnebago  Counties;
         Potential Risk via Groundwater Due to Past and Present
         Activities, Illinois Department of Energy and Natural Resources,
         Document No. 83/26, Springfield, Illinois, 1983.
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A. 9  Rating Methodology Model




     The Methodology for Rating the Hazard Potential of Waste




Disposal Sites (Rating Methodology Model) was developed for use by




the EPA Office of Enforcement and the Oil and Special Materials




Division in setting priorities for sites based upon preliminary




assessment data (JRB Associates, Inc., 1980).




     The Rating Methodology model consists of four rating areas




whose scores are added to obtain an overall site score.  One of the




four rating areas is Waste Management Practices which consists of




eight rating factors, four of which are related to waste containment.




These four rating factors are:




     •  Use of liners




     •  Use of leachate collection systems




     •  Use of gas collection systems




     •  Use and conditions of containers




The criteria and rating scales used to evaluate each of these four




rating factors are shown in Table A-5.  The eight Waste Management




Practices rating factors are weighted and summed to determine the




score for the Waste Management Practices rating area.




     The rating factors in the Rating Methodology model were




considered in the original development of the HRS.  The rating




factors for containment were found not to be suitable for inclusion




in the HRS, in part because they were not comprehensive enough, nor




well enough defined, for use in evaluating site containment.






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                                TABLE  A-5

       CONTAINMENT RATING FACTORS IN THE RATING METHODOLOGY MODEL
  Rating Factors
           Criteria
Rating
Scale
Levels
Use of Liners
Use of Leachate
Collection Systems
Use of Gas
Collection Systems
Use and Condition
of Containers
Clay or other liner resistant to organic      0
compounds

Synthetic or concrete liner                   1

Asphalt-base liner                            2

No liner used                                 3

Adequate collection and treatment             0

Inadequate collection or treatment            1

Inadequate collection and treatment           2

No collection or treatment                    3

Adequate collection and treatment             0

Collection and controlled flaring             1

Venting or inadequate treatment               2

No collection or treatment                    3

Containers are used and appear to be          0
in good condition

Containers are used but a few are leaking     1

Containers are used but many are leaking      2

No containers are used                        3
Source:  JRB Associates, Inc., Methodology for Rating the Hazard
         Potential of Waste Disposal Sites (Draft Final Report),
         McLean, VA, 1980.
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Furthermore, the use of an additive containment factor was judged




unsuitable because with an additive factor, a site could have total




containment and still receive a high score.  This is not the case




with a multiplicative containment factor.




A. 10  Dames and Moore Methodology




     The Dames and Moore Methodology was developed to evaluate waste



disposal sites with respect to their potential for ground water and




surface water contamination (Dames and Moore, undated).




     The Dames and Moore Methodology was adapted from the Rating




Methodology model and consists of four rating areas.  One of these




rating areas is Spill Potential.  Spill Potential applies only to



landfills and consists of ten rating factors, four of which are




related to waste containment.  These four rating factors are:




     •  Cover condition



     •  Leachate management




     •  Gas management




     •  Personnel training



The criteria and rating scales used to evaluate each of these four




rating factors are shown in Table A-6.  The ten Spill Potential




rating factors are weighted and summed to determine the score for




the Spill Potential rating area.




     These four rating factors have the same limitations as the




rating factors in the Rating Methodology model from which they were




derived.






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                                TABLE A-6

   CONTAINMENT RATING  FACTORS  IN THE DAMES AND MOORE METHODOLOGY MODEL
   Containment
  Rating Factors
                                               Rating
                                               Scale
Multiplier	        Criteria               Levels
Cover Condition
Leachate Management
    10       Well contoured, no cracking or
             vigorous vegetative cover, no
             signs of subsidence

             Signs of cover failure
             visible at 25% of site area

             Signs of cover failure
             visible at 50% of site area

             Large areas of subsidence,
             poor contouring, no vegetative
             cover in most of the site,
             exposed waste

     8       Arid region; or leachate
             monitors installed but none
             detected

             No leachate monitoring, but
             leachate generation unlikely
             (arid weather, good cover, etc.)

             Some evidence of leachate
             generation at only certain
             portions of the site

             No leachate monitoring, or
             positive proof of leachate
             generation
0
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                         TABLE A-6  (Concluded)
   Containment
  Rating Factors
Multiplier
Criteria
Rating
Scale
Levels
Gas Management
Personnel Training
             No gases are generated or
             generated gases are
             successfully managed.

             Inadequate information.  Gas
             generation anticipated.  Some
             venting measures Installed.

             Inadequate information.  Gas
             generation anticipated.  No
             venting measures installed.

             Gas generation is evident or
             anticipated.  Signs of cap
             distress visible.

             All waste disposal related
             personnel are formally trained
             in safety and environmental
             control.

             Only waste disposal supervisory
             personnel are formally trained
             in safety and environmental
             control.

             Some informal training of waste
             disposal supervisory personnel.

             None
                         0
Source:   Dames and Moore,  Overview of  Methodology  for Rating  Potential
         for and Significance of Ground and  Surface Water  Contamination
         from Waste Disposal Sites,  Bethesda, Maryland,  Undated.
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A.11  Liner Location Risk and Cost Analysis Model




     The Liner Location Risk and Cost Analysis Model is designed




to be used by EPA to investigate cost/risk and cost/effectiveness




implications of the land disposal of hazardous wastes under different




technology, location, and waste stream scenarios.  The model




estimates the relative chronic risk to human health from land




disposal facilities with different design technology, location, and




waste stream characteristics.  The model also estimates the cost of




facilities with differing technologies and sizes.  The model uses a




series of submodels to predict contaminant releases, subsurface and




atmospheric transport, human exposure, and health risk based upon




dose-response factors (U.S. Environmental Protection Agency, 1985).




     Containment is taken into account within the Failure and Release




Submodel of the Liner Location Model.  For land disposal facilities




(i.e., landfills, surface impoundments, waste piles, and land




treatment), this submodel estimates both the probability of various




types of failures (i.e., release of leachate) at selected times for




different facility designs in different climates and the quantity of




leachate released by the failures.  Various combinations of liners




and cover types and materials are used to define the different




facility types.  The model does not consider failure events that




result in overland surface run-off releases.




     The Failure Analysis Submodel utilizes a "fault tree" approach




to evaluate the frequency of occurrence of a failure event at a






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facility due to various elementary failure events (e.g.,  liner aging,

infiltration of liquid, drum failure, cover consolidation,  liner

breach due to rise of ground water table).  The fault tree  approach

traces a failure event backwards to identify all relevant elementary

failure events which could combine to cause the failure.  Each

elementary failure event is given a probability distribution based

upon theoretical and empirical data.  The volume of liquid  entering

or exiting the facility if the elementary failure event occurs is

also given a probability distribution.  (Each elementary  failure

event is assumed to occur at random and is given either a triangular,

binomial or time-dependent binomial distribution.  The volume of

liquids associated with an event is given a uniform distribution.)

This submodel uses the fault tree structure to compute the

probabilities of failure events which occur if some sequence of

prerequisite elementary events have occurred.

     Monte Carlo simulation* is then used to estimate the cumulative

probability of occurrence of each failure event for each  facility

type and climate and to estimate the volume of leachate released by

the failure event.  The volume of leachate released is estimated by

incorporating a series of hydrologic inputs (e.g.,  infiltration from
*Monte Carlo simulation consists of sampling from the probability
 distribution of the elementary events.   The sampling is  done through the
 use of a random number generator.   After all the elementary failure
 events in a fault tree are evaluated,  the model determines  whether a
 failure event occurs and the volume released if it  occurs.   This process
 is repeated a large number of times using a computer to  obtain  an
 estimate of the relative frequency of  occurrence of each failure event.

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precipitation) in the elementary failure events and tracking them with




a mass balance analysis.




     The Liner Location Risk and Cost Analysis Model thus addresses




containment in a very different manner than the HRS.  However, as




currently structured, it is not meant for, nor is it applicable to,




site-specific comparisons of containment effectiveness.  Rather it is




intended primarily for use in analyzing the risks and costs associated




with alternative regulatory strategies (e.g., alternative standards




for waste containment at land disposal facilities).




A.12  Hazardous Waste Tank Failure Model




     The Hazardous Waste Tank Failure (HWTF) Model is one of the models




being used by the EPA Office of Solid Waste to support the development




of regulations for hazardous waste tanks (IGF Incorporated and




Pope-Reid Associates, Inc., 1986; Pope-Reid Associates, Inc., 1986).



     The HWTF model uses fault trees and Monte Carlo simulation (see




Section A.11) to predict the timing of failure events (e.g., leaks,




ruptures) for hazardous waste tank systems and to estimate release




volumes associated with these failure events over a 20-year operating




life.




     The HWTF model is currently designed to analyze four types of




tanks:  RCRA-permitted treatment tanks, RCRA-permitted storage tanks,




accumulation tanks (storage for less then 90 days), and small-quantity




generator tanks.   For each type of tank, the HWTF estimates the timing




of failure events and the magnitude of associated releases for five






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regulatory (containment) scenarios:  a baseline scenario that assumes




all tanks are managed and operated in compliance with existing RCRA




Subtitle C regulations and four alternatives that are more stringent




than the baseline scenario.




     As structured, the HWTF model is not meant for,  nor is it




applicable to, site-specific comparison of containment effectiveness.




Rather it is intended for use in analyzing alternative regulatory




strategies.




A. 13  RCRA Risk-Cost Analysis Model




     The RCRA Risk-Cost Analysis Model is used by the EPA Office of




Soild Waste to support the development of regulations under RCRA.  The




model produces relative risk and cost estimates for different




management configurations of waste streams; waste transportation,




treatment and disposal technologies;  and environments.  The model




estimates human health, ecosystem and sensory risks from steady state




releases of RCRA contaminants (and selected other contaminants) to




ground water, surface water, and air.  The model also calculates the




costs of each technology in a management configuration as an annual




revenue requirement.  The model treats each management configuration




in a generic fashion employing standard risk assessment methods (e.g.,




emissions estimates coupled with transport and fate models aligned




with dose response models) and numerous simplifying assumptions (ICF




Incorporated, 1984; Males, 1984).
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     Containment is taken into account in the RCRA Risk-Cost Analysis




Model in the Waste Disposal Technologies component of the model.




This component contains six kinds of disposal technologies:




landfills, surface impoundments, waste piles, land treatment,




incineration, and deep well injection.  To represent a wide  range




of designs, the model includes a number of different configurations




for each kind of disposal technology.  For landfills and surface




impoundments, the configurations differ primarily in the type of




liner system used, ranging from unlined to double liners.  Except




for the unlined configuration, all configurations include leachate




collection, monitoring wells, and collection of surface run-off.   A




number of the configurations that employ liners comply with  the RCRA




Subtitle C requirements for landfills and surface impoundments.




With regard to the other four disposal technologies, the various




configurations in the model all comply with the RCRA Subtitle C




regulations appropriate to the technology.




     In general, the model accounts for leachate migration to ground




water by first estimating leachate generation rates over time and




combining these with estimates of liner failure probabilities and




saturated flow limitations imposed by underlying clays and soils.




Synthetic liners are assumed to have a life of 35 years and  to have




a uniform failure rate over this period.  When a synthetic liner




fails, it is assumed to disintegrate (i.e., leak everywhere).  Clay
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liners are assumed to retain their integrity and low permeability over




the operating life of the waste disposal technology.




     Leachate collection and treatment systems are assumed to release




a fixed portion of the leachate they handle.  All leachate released by




the system is assumed to be lost to the environment.  The leachate is



distributed among air, surface water, and ground water by first




estimating the amount of constituents that evaporate (based on




volatility), and then assuming that 70 percent of the remainder moves




toward surface water and 30 percent moves toward ground water.




     Overland run-off to surface water is also assumed to occur from




storm events exceeding the holding capacities of surface impoundments




and/or storm water run-off management systems.  Overtopping is assumed




to have a constant probability of occurrence in any year.  The model




does not account for other overland run-off release mechanisms (e.g.,




leaks or dike failures).  The model also does not account for the




transport of contaminants by ground water to surface water.




     As structured, the RCRA Risk-Cost Analysis Model is not meant




for, nor is it applicable to, site-specific comparisons of containment




effectiveness.  Rather it is intended for use in analyzing alternative




regulatory strategies.
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                             APPENDIX  B

                             BIBLIOGRAPHY
Arthur D. Little,  Inc.,  Proposed Revisions  to MITRE Model, Arthur D.
Little, Inc., Cambridge, MA, September  23,  1981.

Arthur D. Little,  Inc.,  PERCO;  A Model for Prioritization of
Environmental Risks and  Control Options at  Hazardous Waste Sites,
Arthur D. Little,  Inc.,  Cambridge, MA,  September 12, 1983.

Barnthouse, L.W. et al., Development  and Demonstration of a Hazard
Assessment Rating  Methodology for Phase II  of the  Installation
Restoration Program,  (ORNL/TM-9857),  Oak Ridge National Laboratory,
TN, 1986.

Dames and Moore, Overview of Methodology for Rating the Potential
for and Significance  of  Ground and Surface  Water Containment from
Waste Disposal Sites, Bethesda, MD, Undated.

Engineering-Science,  Comparison of U.S. Air Force  hazard Assessment
Rating Methodology (HARM) with U.S. Environmental  Protection Agency
Hazard Ranking System (HRS) at Four Air Force Bases Evaluated Under
the Phase I Installation Restoration  Program, Engineering-Science,
Atlanta, GA, April 1983.

French, Jean G. et al., A System for  Prevention, Assessment, and
Control of Exposures  and Health Effects from Hazardous Sites
(S.P.A.C.E. for Health), Centers for  Disease Control, Atlanta, GA,
January 1984.

Gibb, J., Barcelona,  M., Schock, S.,  and Hampton,  M., Hazardous
Waste in Ogle and Winnebago Counties;   Potential Risk via
Groundwater Due to Past and Present Activities, Illinois Department
of Energy and Natural Resources, Document No. 83/26, Springfield,
IL, 1983.

ICF Incorporated, The RCRA Risk-Cost  Analysis Model Phase III Report
and Report Appendices, Washington, DC,  1984.

ICF Incorporated and  Pope-Reid Associates,  Inc., Hazardous Waste
Tanks Risk Analysis (Draft Report), prepared for the U.S.
Environmental Protection Agency: Office of  Soild Waste, Washington,
DC, 1986.

JRB Associates, Inc., Methodology for Rating the Hazard Potential of
Waste Disposal Sites  (Draft Final Report),  McLean, VA, 1980.

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Kay, Robert L., Jr. and Chester L. Tate, Jr., "Public Health
Significance of Hazardous Waste Sites," Proceedings of the Fifth
National Conference on Management of Uncontrolled Hazardous Waste
Sites, held on November 7-9, 1984 in Washington, DC, Hazardous
Materials Control Research Institute, Silver Spring, MD, 1984,
pp. 232-238.

Kushner, L., Hazard Ranking System Issue Analysis;  Superfund Sites
With Unknown Waste Quantity; MTR-86W83, The MITRE Corporation, McLean,
VA, 1986.

Luecker, Elizabeth B., "Navy Assessment and Control of Installation
Pollutant (NACIP) Confirmation Study Ranking Model," Proceedings of
the Twelfth Annual Environmental Systems Symposium, held on May 20-21,
1982, at Langley Air Force Base, Langley, VA, American Defense
Preparedness Association, Arlington, VA, 1982.

Males, E., RCRA Risk-Cost Analysis Model, presented at the AICHE
Conference held on August 21, 1984, U.S Environmental Protection
Agency, Washington, DC, 1984.

Michigan Department of Natural Resources, Site Assessment System (SAS)
for the Michigan Priority Ranking System Under the Michigan
Environmental Response Act (Act 307, P.A., 1982), Lansing, MI, 1983.

Pope-Reid Associates, Inc., Hazardous Waste Tank Failure Model;
Description of Methodology and Appendices A-E, prepared for the U.S.
Environmental Protection Agency, Office of Soild Waste, Washington,
DC, 1986.

Sayala, D., Hazard Ranking System Issue Analysis;  Subsurface
Geochemical Processes (Draft Report), MIR-86W171, The MITRE
Corporation, McLean, VA, 1986.

U.S. Environmental Protection Agency, Liner Location Risk and Cost
Analysis Model (Draft Report and Draft Appendices), Office of Solid
Waste, Washington, DC, 1985.

Wang, M., Hazard Ranking System Issue Analysis;  Alternative Methods
for Ranking the Persistence of Hazardous Substances in Surface Water
(Draft Report), MTR-86W172, The MITRE Corporation, McLean, VA. 1986.

Wolfinger, T., Hazard Ranking System Issue Analysis;  Options for
Revising the AirTathway (Draft Report), MTR-86W53, The MITRE
Corporation, McLean, VA, 1986.

Wolfinger, T., Hazard Ranking System Issue Analysis;  The Use of
Concentration Data (Draft Report), MTR-36W40, The MITRE Corporation,
McLean, VA,  1986.
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