UNITEDSTATESENVIRONMENTALPROTECTIONAGENCY WASHINGTON. D.C. 20460 "o\.B-EC-88-008 January 14, 1988

OFt="ICE OF THE ADMI"'tSTr<

...TOR Honorable Lee M. Thoma·s Administrator 

## u.s. Environmental ProtectionAgency 401 MStreet,

## s.w. Washington, D.C. 20460
Dear Mr. Thomas:
The Hazard Ranking SystemReview Subcommittee of the Science Advisory Boardhas completed its review of a number of issues related to the Superfund Hazard Ranking System (HRS). The Hazard Ranking System is the principalmechanismused by EPA to determinewhether anuncontrolled waste site should be placed on the National Priorities List.
Besides evaluating the**questio~s** referred by the Office of Emergency and Remedial Response (OERR), the Subcommitteehas also chosento address: the overall algorithm for the HRS, the inclusion of exposure in the HRS, how theHRS could be evaluated in the future, and work which couldbe done to provide better documentation for the next revision of theHRS.
The Subcommitteehas suggested changes that will allow the HRS to provide a more accurate and scientifically based estimate of the relative risk of candidateuncontrolled waste sites. Ideally, theHRS scores should accuratelyassess the relative degree of risk at a site. However, we recognize this is not always feasible due to scientific and data limitations and to value and policy decisions implicit when considering .· and balancinghuman health and environmental impacts, Arevised HRS, better designed to evaluate sites by relative risk, will provide an improved mechanism for determiningwhich sites shouldbe included on the National Priorities List (NPL), and can potentially provideuseful input to the subsequent prioritizationof NPL si·tes. However, the Agency must continue to base this prioritizationonmany factors in addition to the HRS. Most of the changes needed to improve the currentHRS are changes in the riskvariables assessed and in the overall algorithm, not changes with vast new data requirements.
The Office of Emergency and Remedial Response referred three issues to the Subcommittee: the types of toxicity theHRS shoMld address and how it should do so; distances from an uncontrolled hazardouswasteIt. •

..."• 

### ••

- 2 ­ site that are relevant when consideringairpollutants fromthe site; the feasibility of including waste concentrationin theHRS and whether large volumewaste sites had been treated differently than other sites by theHRS. The Subcommittee finds that all the options OERR proposed for revising the toxicity factor are improvements over the current approach. The Subcommitteebelieves, given the difficulty of ambient airmonitoring, that the inclusion of potential release via the air pathway is an important improvement to the HRS. The Subcommittee also believes that improved characterization of the source and of exposure/mobility will improve the functioning of the HRS for all sites, notjust large volume waste sites.
With respect to the three issues posed to theSAB,,the Subcommittee recommends the following:
1. In order to improve the discriminating power of theHRS, the currentlyused Sax rating scale should be replaced bymultiplemeasures of toxicity. In addition, exposure measures need to be improved.
2. Modification of the HRS to include the potential for air release seems both appropriate and possible." Ascoring systemthat weights**populatio~** exposure in concentric rings is recommended.
3. EPA's experience in applying the HR$ to mining sites has not proven biased against such sites, that is, ithas not treated such sites with systematic error; however, it has that potential. Our recommendation for improvement includes incorporatinghazardous-constituent concentration ina tiered system, modifying the toxicity factor to reflect metal speciation, incorporating a mobility factor, and adding additional transformation factors.
The Subcommittee also recommends that more attempts be made to learn·· from subsequent experience so that when the HRS is next revised, a better basis for those revisions will be available. These recommendations are detailed in Appendix 6.
The Subcommittee's evaluationof these and other issues, and its conclusions and recommendations, are discussed in greater detail in the attached report. Because of their cross cutting nature, certainissues, such as exposure and the overall algorithm, appear inmore than one area. The Subcommitteewould like to call to your attention the high**q~ality** efforts of the staff from the Office of Emergency and Remedial Response that briefed and worked with the Subcommittee. 'Theywere professional, well.:.prepared, and responsive to the Subcommittee's requests for information.

### -3­

We

### appreciatethisopportunitytopresentourscientificviewsand look forward toanofficialwrittenresponsefranthellgencyconcerning thecomments and recommendations intheattachedreport.

Sincerely,

# "A~**v\cJ~** NortonNelson, Olairman ExecutiveCommittee



# .. SCienceAdvisory

### Board

Hazard

# !x:::~ Ranking SystemReviewSubcommittee ScienceAdvisoryBoard

cc: 

## w. POrter H. 

### f.Dngest T. 

### YosieUnitedStates EnvironmentalProtection Agency OfficeoftheAdministrator ScienceAdvisory6oard Washington,DC 20460**S.!.S~EC·S8-008** January1988



# ReviewoftheSuperfund HazardRankingSystem

ReviewbytheHazard RankingSystemReview ·" 

# Subcommitteeofthe ScienceAdvisoryBoard

### SAB-EC-88-008

SCIENCE ADVISORY BOARD HAZARD RANKING SYSTEM REVIEW SUBCOMMITTEE

REVIEW
of the 

### SUPERFUND HAZARD RANKING SYSTEM

January 1988



### ..ii

NOTICE
This report has beenwritten as a part of the activities of the ScienceAdvisory Board, a public advisorygroup providingextramural scientific information and advice to theAdministrator and other officials of the Environmental ProtectionAgency. The Board is structured to provide a balanced expert assessment of scientific issues related to problems facing the Agency. This report has not beenreviewed for approval by the Agency and, hence, the contents of the report do not necessarily represent the views and policies of the Environmental ProtectionAgency, nor of otheragencies in the Executive Branch of the Federal government, nor does mention of trade names or commercial products constitute endorsement or recommendation foruse.iii
U, S. ENVIRONMENTAL PROTECTION AGENcY SCIENCE ADVISORY BOARD HAZARD RANKING SYSTEM REVIEW SUBCOMMITTEE
ROSTER CHAIRMAN
Dr.Raymond C. Loehr, Professor, Civil EngineeringDepartment, 8.614 ECJ Hall, University of Texas, Austin, Texas 78712
VICE CHAIRMAN
Dr.Warner North, Principal, Decision Focus Inc., Los Altos Office Center, Suite 200, 4984 El Camino Real, Los Altos, California 94022
MEMBERS AND CONSULTANTS Dr, Stephen L. Brown, ProjectManager, EnvironCorporation, 1000 Potomac Street, N.W., Washington, DC 20007
Dr. Thomas Burke, Deputy Commission·er, New Jersey Department of Health, Room 805, State Health, CN360, Trenton, New Jersey 08625
Dr. Shepherd Burton, Systems Applications, 101 Lucas Valley Road, San Rafael, California 94903
Mr. George F, Carpenter, MichiganDepartment of Natural Resources, Environmental Response Division, Post Office Box 30028, Lansing, Michigan 48909
Mr. Richard Conway, Corporate Development Fellow, Union Carbide Corporation, Post Office Box 8361 (770/342), South**Charle~ton,** West Virginia 25303
Dr.Paul Deisler, 11215 Wilding Lane, Houston, Texas 77025
Dr. John Doull, Professor of Pharmacologyand Toxicology, University of Kansas Medical Center, Kansas City, Kansas 66103
Dr.Naihua Duan, Statistician, Rand Corporation, 1700 Main Street, SantaMonica, California 90406

### iv Dr, KeithFerguson, Environmental Protection, Environment Canada, Kapilano 100, ParkRoyal, West Vancouver, BritishColumbia CANADAV7TlA2 Dr, c. Daniel Kealy, U, S. Bureau ofMines, SpokaneResearch Center, East 315 Montgomery Avenue, Spokane, Washington 99207
Dr. James 0. Leckie, Department of Civil Engineering, StanfordUniversity, Stanford, California 94305-4020 Dr, Donald Mackay, Department of Chemical Engineering and Applied Chemistry and Institute for Environmental Studies, University ofToronto, Toronto, Canada M5S 1A4
Mr. Bruce Napier, BattelleNW, Post Office Box 999, Richland, Washington99352
Dr. David Pollock, U.S. Geological Survey, National Center, 

### Mail Stop411, Reston, Virginia 22092 Dr, Josephv. Rodricks, EnvironCorporation, 1000 Potomac Street, N.W., Washington, DC 20007
Dr. Ellen Silbergeld, Chief Toxics Scientist, Toxic Chemicals Program, Environmental Defense Fund, 1616 PStreet, N,W,, Room 150, Washington, D.C. 20036
Dr. Mitchel+ Small, Department of Civil Engineering, CarnegieMellon University, SchenleyPark, Pittsburgh, Pennsylvania 15213 Dr, Rebecca T. Zagraniski, Divisionof BirthDefects and Developmental Disabilities, Center for Environmental Health and InjuryControl, .• 

### Centers for Disease Control, Koger CenterRoom 2008 (F-37) 1600 CliftonRoad, N.E., Atlanta, Georgia 30333

Executive Secretary
Mrs. Kathleen

## w. Conway, Deputy Director, Science AdvisoryBoard (A-101F), 

## u.s. EnvironmentalprotectionAgency, 401 MStreet,

## s.w., Washington, D.C. 20460 Staff Secretary Mrs, DorothyM.·cl.ark, Secretary, Science AdvisoryBoard (A-101F), U.S. Environmental ProtectionAgency, 401 MStreet, S,W, Washington, D.C. 20460TABLEOF CONTENTS
PAGE
EXECUTIVE SUMMARY 1
Fa.ctor 1 Toxi.city Air Target Distance 2 Large Volume Waste 3 ExposUI:e 4 Algorithm 5 Recommendations To Evaluate and Improve the HRS 5
INTRODUCTION 7
The Current HRS: Purpose and PriorReviews 7 Required Revisions to the HRS 7 S.cien.ce Advisory Board Review 8 Structure and Practi.ce of the Current HRS 9 SUMMARY OF THE ISSUES 11 roxicity Factor 11 Air Target Distance 13 Large Volume Waste 15 Exposure 18 Algorithm 19 Recommendations to Evaluate and Improve the HRS 21
APPENDICES
1. Report of the Toxicity FactorWork Group 2. Report of the Air Target Distance Work Group 3. Report of the Large Volume.Waste Work Group 4 Comments on Exposure 

## s. Comments on Algorithm 6. Recommendations to Evaluate and Improve the HRS 

### 7. Requests from the Office of Emergencyand Remedial Response (SUPERFUND) 8. References CitedEXECUTIVE SUMMARY
The Hazard Ranking System (HRS) is the principalmechanismused by EPA to determinewhether anuncontrolled waste site should be placed on the National Priorities List (NPL), The Office ofEmergency and Remedial Response (OERR) requested that the Science AdvisoryBoard (SAB) review certain aspects of the technical basis for revising the HRS, The major issues identified by OERR.dealt with the toxicity factor, air target distance, and large volume wastes. (See Appendix 7 for the full text of this request). Overall, the Subcommittee is generally supportive of the changes OERR presented and found no fatal flaws in the approach to theHRS that OERR presented; however, the Subcommitteehas made recommendations in this report thatwould further improve theHRS, ToxicityFactor Toxicity should be an important component of a site ranking scheme. Because the toxicity factor in the currentHRS makes virtuallyno distinctions among sites listed orproposed to be on theNPL, and becauseEPA did not present evidence that it had examined the ability of the various factors to discriminate between sites·--including sites not on theNPL--the Subcommittee questions whether the existing toxicity factorhas the power to discriminate "very toxic" from "not so toxic" sites, The Sax chemical toxicityratings are a crude basis for setting priorities since they address only the acute toxicity of one constituent of thewaste. The Subcommittee recommends replacing Sax ratings and using multiplemeasures of toxicity for ranking sites. All of the options presented by OERR are substantial improvements, These options are described inOERR's Discussionof Options for Revising the Hazard Ranking System (HRS) Toxicity Factor (12).
Scientific techniques exist whichwould permit theHRS to consider several endpoints that are revelant to human health and the environment. Multiplemeasures of toxicity.shouldbe considered, any one of which, if sufficiently seve·re, could, by pLicing the site on the NPL, trigger a more detailed evaluation. By multiple measures, the Subcommitteemeans acute human health effects, human cancer, non-cancer chronic disease in humans, and impact on the non-human natural environment, However, a system of weighting the severity of different health endpoints, as is done in the Reportable Quantities (RQ) approach, is not encouraged because a single composite score obscures the valuejudgments implicit in such an approach,
It is possibie.that sites containinghazardous chemicals whose toxicities are notwell orwidely known might be omitted from the NPL, thus creating false negatives. Measures to counter this probleminclude- 2 ­
the continued development of toxicity profiles on additional chemicals and the keeping of good records so that sites can later be re-evaluated when additional toxicity data become available,
Air Target Distance
The Subcommittee supports efforts to modify the air pathway so that it considers the potential for release instead of relying only on a score for observed releases. Air emissions are often episodic and/or narrowly focused along a particular wind direction and, therefore,**~re** difficult to detect. Furthermore, time and site activities (such as excavation in the course of site remediation) can markedly change the potential for air emi$sions**~** Methods are currently available which can be simplified to calculate approximate, order-of-magnitude emission rates for impoundments and landfills. Using them requires information on the chemical identities at the site. When such information is totally lacking, it is impossible to even estimate the quantity of the chemical present, and volatile air emissions can not be predicted. The subsequent consideration of air exposure routes is very weak, Aminimum data requirement which mandates contaminant identification by record_reviewor direct sampling (either within containment structure or of emissions) would greatly improve the HRS' validity in all pathways. In the absence of an inventory, direct sampling methods such as soil gas analysis or contained surface sampling complement estimated emissions and provide a more effective estimate than the estimated emissions alone, Such methods normally will yield samples of much higher concentration than ambient air samples, and chemical analyses will'be more informative.
The Subcommittee recommends that the Agency derive a scoring system which weights the number of exposed people in a "ring" according to the distance from the site at which they live, (ThiS approach is described in·· greater detail in Appendix 2 and illustrated by the figure on page A2-12.) The widths of the rings can be determined to account for the decrease in air concentrations with distance.
This ring-weighting method does not account for risks to the maximally exposed individual (MEI), but it does explicitly account for the higher exposures that will occur closest to the site. The Subcommittee does not consider a separate or additional evaluation of MEl air risks as part of the HRS to be necessary. The recommended ring-weighting method will essentially set:ve the same purpose by weighting most heavily the nearest and 1nost exposed population.- 3 ­ The ring-weighting method should be calibrated on the basis of the variation of concentrationwithdistance. The influence of pollutants borne on particles will likelybe concentrated at lesser distances which would change the ring weights, but would not often lead tomarkedly different scores. Large Volume Waste
The issues before the Subcommitteewere the "applicabilityof the HRS in scoring mining waste sites" and the "feasibilityof usingwaste concentrationdata in a revised HRS."
The Subcommittee finds that the studies conducted thus far regarding the adequacy of the HRS listing process-for mining sites have been limited and inconclusive. Sufficient evidence based on experience has not been evaluated and presented to show an inadequacy of theHRS in regard to mining sites. However, the present scoring systemhas a potential to treat miningwastes with systematic error. The Subcommittee believes the present HRS is not well suited for scoring potential releases from mining sitewastes becausemobility is not included. Improved ways of considering the concentration (often low), toxicity release (mobilityinvarious matrices), and information on the transport and transformation of chemicals would make theHRS more accurate. Mobility is amore discriminating concept for both inorganic and organic substances than is persistence in the subsurface, especially with respect to inorganic compounds. The Subcommittee recommends that, during the development of a structured-value representation of themobility concept, a means of incorporating important matrix characteristics be explored. Significant matrix characteristics are extreme acidity or alkalinity (as expressed by both high and low pH), crystalline phase modifications of miningwastes that differ from native geologic materials, and the sorptive.capacityof**surr~unding** geologic materials (influencing migration tendency).

tn regard to the surfacewater route, EPA is consideringkeeping persistence as the parameter to includewith toxicity in thewaste characteristics portionof theHRS, butwould consider other transformation parameters along with the current use of biodegradation. Inclusion of these additional parameters would improve the existingHRS because itwould more closely correspondwithwhat happens in the realworld.
It appears from the presentations that OERRwould also include mobility in the air route score. Mobility and waste quantityare important factors indetermining exposure. Because of this importance, the basic approach o£ including mobilityin the HRS should be pursued. (See also Appendix.2.)

### - 4 ­ Modifying the current HRS to incorporate factors which capture some measure of both the physical-chemical characteristics of the hazardous constituents and the waste matrix, as well as those site characteristics responsible for risk, is clearly an improvement,
EPA presented two approaches for incorporating concentration into the HRS. While the direct measurement approach provides the soundest scientific basis for the HRS, inmost cases, it will not be practical-­ because of safety and cost considerations--to requirewaste constituent concentration data for every site at the site inspection stage. In contrast, the tiered approach used hazardous constituent concentration data where available and default values where theywere not, The Subcommittee supports the use of the tiered approach because it encourages the gathering and use of concentration data and provides for the use of indirect estimates where datagathering is impractical.
Both approaches translate waste constituent concentration data into an estimate of the total mass of a hazardous constituent at the site, which is thenused to compute the waste quantity score for the HRS. The approach that uses the "total mass" of hazardous constituent, without relevant information on metal speciation and. mobility, would produce false positives for some large volume wastes and pathways.
For the ground water pathway, the total concentration ormass of a constituent is of much less importance than the leachate concentration produced at the site. Consequently, more emphasis should be placed on the partitioning of hazardous constituents between the solid waste and the leachate•. Actual or estimated leachate concentration should then be factored into the waste quantity term in the HRS. For wastes that are in liquid form, total contaminant mass quantity should continue to be used.



### .. Exposure
The Subcommittee believes that toxicity issues are integrally linked to dose, i.e., migration and exposure (see Appendix 4).
Consideration of exposure in the evaluation of relative risk is vital. If there is no exposure, there is no risk and where there is exposure, risk varies with exposure. While the current HRS gives some consideration to exposure, often through the use of proxies such as persistence, distance to nearest well and target populations, the Subcommittee concludes that adnitional chemical-specific consideration of.routes of exposure, particularly with respect to the Toxicity Factor, would strengthen the HRS.
The Subcommittee is mindful of the difficulties in characterizing exposures to chemicals at waste sites that have undergone only preliminary inv@Stigation. It does not propose the implemention of expensive and- 5 ­ time-consuming sampling programs to measure actual concentrations in ambient mediawhere pollutant levels may be near orbelowdetection limits. However, additional surrogates for eKposure--e.g., a calculation of quantity estimates withmobility'considerations--will provide better rankings than does the current system, Without appropriate estimates
of mobility, consideration of toKicity in the algorithmis tantamount to assuming that the eKposures to every detected chemical at everywaste site are equal. The Subcommittee recommends adoption of a tiered approach for exposure similar to OptionW3 EPA developed for concentration (discussed inAppendix 3of this report). Algorithm
Revisions to the HRS should beginwith the development of a chainof logic, without regard for the ease or difficulty of collectingdata, that would lead to a risk assessment for each site. This framework, but not the underlying logic, would be simplified to account for the very real difficulties of data collection.
This chain of logic, which is termed the algorithminthis report, should lead to a situation in which an increased score reflects an increased risk presented by a site. Without this consistencyinthemeaning of a score it is impossible to assess the relative degree of risk posed by a site:
..The Subcommitteeplaces special emphasis on the algorithmissue because it is,impossible to reviewthe components of theHRS without consideringhow the components fit together. If theHRS is to evaluate sites by relative risk, then theHRS must be consistent with the underlying, quantitative relationships of the factors involved, Specific recommendations concerning this issue are presented inAppendix S. 

## .­ Consistency interms of relative risk and score does not exist between sites in the current HRS, although for a single sitea larger score represents"a larger risk, ·changes in theHRS algorithmmean that a score of 28.5 ina revised HRS will almost certainlymean something different than a score of 28,5 in the current HRS,
Recommendations To Evaluate and Improve the HRS Grapplingwith a difficult problem like the HRS clarifies the need for additional data, studies, and evaluations. The Subcommittee assumes that theHRS will again be revised, Results from the following would be most helpful at that time. Peer reviewof the plans for·such studies is recommended,.,

o The evaluation of the relative riskof sites as estimated by a HRS score should be compared with the results of riskassessments based on the Remedial Investigation/ Feasibility Studies (RI/FS).- 6 ­ Advance planning is needed so that additional RI/FS-like data is gathered on some sites with scores below 28.5; these can be selected using an a priori sampling scheme. Similarly, since the success of the-HRS at ranking by relative risk depends, in part, on the consistency and completeness of the scoring, at least some sites scnring above 28.5 may require additional datagathering. Such work would provide the basis for a meaningful retrospective study of the HRS and a better understanding of the basic parameters that are important in the use of the HRS scoring model,

o EPA should determine, based on results of RI/FS studies, whether the health risk associated with a sitewas likely to be dominated by one or a few chemicals (for each pathway) or by a larger number of chemicals. Such a reviewwould provide an objective basis for recommending how many chemicals should be selected for toxicity (or site) ranking. The two Agency studies of this issue presented to the Subcommittee were limited in the number and types of sites evaluated, and the sites studied were not selected for representativeness, but for convenience. Abetter evaluation is warranted.
" EPA should consider, how the scores through the various pathways relate to relative risk. With this information, the algorithm can be calibrated appropriately.
o 	 Avigorous effort should be made to improve the overall quality of analytical data collected at sites, Standardized collection and laboratory methods currently exist for only a small fraction of substances potentially present, Expanded chemical characterization of all media, coupled with a strong laboratory certification program will improve not only the HRS but all aspects of the Superfund

.. process.

o Screening models like the HRS must be simple. They do not have much resolving power and therefore, some false positives and false negatives are inevitable. Because of this limitation, HRS scores should not be overemphasized. Aprocess should be established either to review sites subject to scoring or to reviewHRS scores in an attempt to spot false positives and negatives, Such a scientific review process could involve the use of additional models; inmany cases, however, obvious false negatives or positives might be best handled by a "manual" review. The important point is that the system be flexible enough to allow**fo~** a variety of approaches to be used, as needed, during the scientific review process.- 7 ­ INTRODUCTION The Current Hazard Ranking System: Purpose and Prior**Revie~s** The Hazard Ranking System (HRS) is the principalmechanismused by EPA to determine**~hether** to place sites on theNational PrioritiesList (NPL), The HRS**~as** made available for public comment on**t~o** occassions. On March 12, 1982 a draft of the current version**~as** placed in the Superfund Docket and a notice was published inthe Federal Register. EPA summarized the public comments and addressed themin the preamble to the final HRS rule onJuly 16, 1982. On April 9, 1987 EPA published anAdvance Notice of ProposedRulemaking in the Federal Register requesting comments and information related to revising the currentHRS. TheAgency subsequently held a**t~o-day** publicmeeting to solicit public testimony. The issues referred to the Science AdvisoryBoard (toxicity factor, air target distance, and concentration) are ones that the publichadpreviously identified, Required Revisions to the Hazard Ranking System
Section l05(c)(1) of the Superfund Amendments and Reauthorization Act of 1986 (SARA) requires that the-Agency modify theHazardRanking System so that, "to the maximum extent feasible, it accuratelyassesses the relative degree of risk to human health and the environment posed by sites and facilities subject to review." The amendments require an:

oAssessment of the human health risks associated withcontamination or potential contamination of surfacewaters, either directly oras the result of run-off from a site.

oEvaluation of the damage to natural resources whichmay effect the human food chainand which isassociated with any release or threatened release,

oAssessment of the contamination orpotential contamination of the ambient air which is associated with a release or threatened release. Section 125 of SARA also requires that for certainwastes generated primarily from combustion of coal, EPA consider the following: "(l) The quantity, toxicity, and concentrations of hazardous constituents which are present in such waste and a comparisonwith otherwastes; (2) The extent of, and potential for, release of such hazardous constituents into the environment; and (3) The degree of risk to human health and the environment posed by such constituents,"- 8 ­ Section 1187 requires that EPA give a high priority to facilities where the release of hazardous substances has resulted in the closing of drinking water wells or has contaminated a principal drinking water supply.
Science Advisory Board Review
Three memoranda from the Office of Emergency and Remedial Response constitute the request for the review, (Appendix 7 contains copies ·of these memoranda,) In response to the first memorandum requesting an

independent outside scientific review of the technical basis supporting revisions of the HRS the Executive Committee of the Science Advisory Board formed the Hazard Ranking System Review Subcommittee, (The Subcommittee roster appears at the beginning of this report.) The members were chosen for their special expertise and experience in the hazardous waste area. The Subcommittee first met**~ay** 19-20, 1987 inWashington, DC for background briefings on the Superfund programand on the current HRS. OERR provided the Subcommittee and \lark Group with briefings on the toxicity factor and air target distance issues, issue papers, and key references. At the July 16-17, 1987 Subcommitteemeeting inWashington the Office of Policy Planning and Evaluation (OPPE) orally presented its Site Ranking Panel Study, four ranking systems and expert panel to rank 20 hazardous waste sites.
The Subcommittee formed threework groups to address issues referred by the OERR. These were the Toxicity FactorWork Group, the**~ir** Target DistanceWork Group and the Large Volume Waste Work Group. (Rosters for these Work Groups can be found in the front of Appendices 1, 2, and 3, respectively). Each work group reviewed documents on that issue prepared by OERR and reported to the full Subcommittee. (Review and important background documents are listed in Appendix 8.) 

### ' The Toxicity Factor Work Group met June 29-30, 1987 inWashington, DC to review Discussion of Options for Revising the Hazard Ranking System (HRS) Toxicity Factor (12). The Work Group reported its conclusions and recommendations to the full SubcommitteeJuly 16-17, 1987.
The AirTarget DistanceWork Group met July 27-28, 1987 inWashington to reviewAnalysis of the Air Target Distance Limit in the Hazard Ranking System (9).
The Large Volume WasteGroup met August 20-21, 1987 inDenver to review two documents, The Superfund Hazard Ranking System (HRS): Applicability to Mining Waste Sites, and The Superfund Hazard Ranking System (HRS): Feasibility of Using Concentration Data in a Revised HRS (13, 14). OERR briefed the Large Volume Waste Work Group, Two members of the public were invited to give presentations to the Work Group. Dr. Ishwar Murarka of the Electric Power Research Institute presented EPRI's utility- 9 ­

waste research program (1, 2, 3, 4, 5, 6, 7). Mr. WilliamBluke ofCH2M Hillspoke on his experiences at Superfund mining waste sites. Two members of the public, Dr. BrianMurphy of Gradient CorporationandMs. SusanSawtelle representing the EdisonElectric Institute and other utility organizations, provided oral comment. The latter two work groups reported their conclusions and recommendations at the final.full Subcommitteemeetingheld on September 14-15, 1987 inWashington, DC.
Materials given to the Subcommitteeweremade available to the public through the SuperfundDocket. All meetings were announced in the Federal Register and opportunity for bothwrittenand oralpublic comment was provided at eachmeeting.
The Subcommittee's report was approved by theExecutive Committee of the ScienceAdvisory Board onJanuary 14, 1988 prior to transmittal to the Administrator.
Structure and Practice of the CurrentHRS The current HRS uses a technique called structuredvalueanalysis (or scoring) to rank sites. In the HRS structured value analysis, a set of rules is developed which parallel what is thought to be occurringin the real world. The rules address what factors shouldbe considered, and how they, should be scored and combined. The combinationrules for the current HRS have been adjusted on the basis of professionaljudgment--that is, weights have been introduced to make theHRS output match a subjectively ranked test set of sites.
The current HRS, described inUncontrolled HazardousWaste Site Ranking System: AUsers Manual (8), assigns three scores to a site. Two are used primarily to identify facilities requiring emergency attention.**~** These are the score for Fire andExplosionand for Direct Contact. The .third, orMigration score, is.the primarybasis for inclusionon the NPL.
Threepathways (air, surfacewater, and groundwater) are considered in developing theMigration score. For each pathway, various factors are considered. These fall into three broad categories: likelihood of release, waste characteristics, and targets. The actual factors considered can varywith the pathway. For example, distance to the nearestwell applies to the ground water pathway but not to the air pathway.- 10

­ Aftera numerical value is assigned to each factor, it is multiplied by a weight to obtain a factor score. Factor scores within the same categoryare added. Scores for the categories are multiplied together. This procedure yields a score for the pathway, The pathways are then combined through a method called quadratic averaging. Each step in this process affects the final score and, therefore, how well the HRS discriminates between sites of greater and lesser risk to human health and the environment.
EPA and the states use the HRS to calculate a site score, from 0 to 100, based on the actual or potential release of hazardous substances from a site through air, surface water or ground water that may affect people. This score is the primary technical factor used to decide if a hazardous waste site should be placed on the National Priorities List. EPA, the states and other public agencies have used the HRS to evaluate several thousand sites. The scores and supporting documentation of these sites are submitted to EPA Headquarters where they are reviewed to ensure correct and consistent application of the system. Sites having scores above 28.5 are proposed in the Federal Register for the National Priorities List. Based"on public comment and all available information EPA develops a final score for each site and places it on the NPL if the score is still above 28.5.- 11

­ SUMMARY OF THE ISSUES Toxic::!tyFactor
The Subcommitteebelieves that toxicity to human health and the environment is an important considerationin siteranking. To beuseful, the toxicity factor should disc:rimate between "very toxic" and "not so toxic:" sites. If the objective of the !IRS is to generate estimates of relative risk, itmust.·address both toxicity and exposure. Although toxicityis part of the currentHRS, the toxicity factor makes distinctions among only a few of the 951 sites listed orproposed for theNPL.
The Sax chemical toxicityratings have provided the currentHRS with a crude basis for prioritizing sites. The Sax systemis insufficient because (a) it focuses on acute adverse outcomes instead of the range of toxicologic endpoints that need to be addressed intheHRS, and (b) it does not provide citations so that toxicologic: ratings canbe reevaluated and verified for the purposes of the HRS. All of the options (El, E2, E3) discussed in Discussionof Options for Revising the Hazard Ranking System (HRS) Toxicity Factor (12) represent improvements overthe Sax rating method.
The Subcommittee recommends the Sax rating method be replaced with a toxicity factor which addresses multiplemeasures of toxicitybecause most known toxic chemicals are associated with a range of healthand environmental effects. Therefore, to protecthuman health and the environment, the HRS needs to incorporate the potential for a wide range of adverse effects. Ahigh score for any of these endpointscould mot·ivate a more detailed evaluationof a site at the RI/FS stage.
To the extent that scientifically legitimate techniques exist for the considerationof various toxic: effects inhumans and innature, the decision of which endpoints to address is more of a policyrather than**~** a scientific choice. Nevertheless, because there are so many endpoints relevant to human health and the environment for which good methods exist, the Subcommittee encourages EPA to address multiple endpoints as part: of the toxicity factor. The multiple measures of human toxicityEPA should consideraddressingwith the revised toxicity factor include carcinogenicity, other chronichealthendpoints used to establishreference doses, and acute toxicity.
The three options presented inEPA-s Discussionof Options for Revising the l!azard Ranking System (HRS) Toxicity Factor (12) make use of essentially the same databases for toxicity, and none of the options is overwhelmingly superior to the others. However, because there isno sc;entifically credible basis fo·rweighting the severity.of differenthealth endpoints, as is currentlydone for calculatingReportable Quantities (RQs), the Subcommitteediscourages use of the RQ method. Suchweightings are subjective;- 12

­ subsequently, the subjectivitymay be obscured by the final numerical score, The strengths and weaknesses of the options are summarized here (see Appendix l for more detail).
For acute toxicity, the Subcommittee prefers use of the Registry of Toxic Effects of Chemical Substances (RTECS) method rather than the Reportable Quantity (RQ) method, because RTECS facilitates route-specific toxicity ratings and closer attention to the raw toxicity data.
For non-cancer chronic effects, the Subcommittee prefers use of the Reference Dose (RfD) method because the RQ method involves weighting the severity of various endpoints, and the modified ADI method has not received extensive reviewand may differ from the RfD method in rating individual chemicals,
For carcinogenic potency the Subcommittee sees little difference between the two options presented (qt* vs. ED!O) and suggests that other measures, e.g., ED(l)and ED(O.!), be investigated.
EPA addressed the question, "How Many Chemicals Should Be Evaluated?" ·sased on information presented to the Subcommittee orally and in writing (10)

it appears that the studies of this topic, while generally indicating only a few chemicals would dominate the health risk associatedwith a site, were limited in the number and type of sites evaluated and the sites were selected for convenience rather than representativeness. Because of this, and the fact that toxicological information is missing or scanty for many chemicals, the Subcommittee cannot recommend a fixed number of chemicals for OERR to examine at each site. Astudy to address this question·is one of the Subcommittee's recommendations (see page 6).
The Subcommittee recommends that EPA consider the risk represented by the numbers of chemicals known to be present, All things being equal, and because the toxicological effects of so many chemicals are unknown, a·· site with more chemicals should receive a higher priority in the Preliminary Assessment/Site Investigation (PA/SI) stages for further evaluation, Another approach is the assignment of discretionary points (see Appendix 5).
The Subcommittee could not formulate an absolute recommendation on the question of whether separate toxicity ratings for a chemical should be developed for various exposure routes, Such a route-specific approach has appeal because toxicity is known to vary by exposure route for some chemicals. However, this toxic!ty question cannot be addressed indepe·ndently-­ it is inextricably tied to how the HRS deals with migration and exposure issues. If the revised HRS aggregates route-specific exposure scores, this total exposure score could be multiplied by a net toxicity score which would not need' to be route-specific, (The cruder the scheme, the less need for route-specific factors,)- 13

­ Alternatively, a more accurate analysis would independentlyevaluate risks byroutebefore aggregating. Route-specific toxicity factors would improve the accuracy of such an approach. Althoughsuch toxicityfactors are not yet available for a large number of compounds, differences in toxicitybetween routes is potentially important. EPA may find consideration of route-specific toxicity on an exception basis to 

### be a practical solution

.especially applicable to compounds such as asbestos wherea particular

route, in this case inhalation, iswellknown to be of great importance. Whether ornot route-specific toxicityis addressed inthe HRS, it is of potential·utility in the subsequent RI/FS stage because themore detailed information supports more realistic analyses of risks,
The Subcommitteehas discussed the need for two additional steps in the NPL process. First, some type of consistentmethodologyor guidelines is needed to select chemicals during the preliminary assessment and site investigation foruse in the site ranking**process~** Second, the option of using more detailed riskinformation, if available, could be used as a supplement to the HRS process (seeAppendix 5).
AirTarget Distance
The basis for this sectionof the reviewwas Analysis of theAir Target Distance Limit in the Hazard Ranking System (9),
The.Subcommittee is very supportive of OERR's efforts tomodify the air pathway so that it considers the potential forreleases, instead of relying solely on a score for observed releases,
The air pathwayin the current Hazard Ranking Systemevaluates population risks to derive a score for "airtargets" using a matrix of population versus distance for four concentric circles withradii of l/4, 1/2, l, and 4 miles.
The Subcommittee recommends thatEPA consideralternatives to the**~** use of a single air target distance limit for all sites and derive a scoring system which uses site-specific population rings, The widths of these rings may •Tary by size'Sod type of site to account for the decrease in air concentra.tionwithdistance. (SeeAppendix 2, especiallythe illustrations inAttachment B.) The Subcommitteefavors such a refinement because the ring-weighting method relates more directly to riskat a site thandoes the current air target approach. The ringweighting method should be able to address risk more accuratelybecause it considers both the population exposure experienced near the siteand the toxicity factor
... In the ri.ng-:weighting approach, informationon the chemicals present is used to estimateemissions factors, These emissions factors and information about the health effects that can be expected to occur at variouslevels of exposure canbeused to develop ring-widths that relate to the exposure people livingin those locations canexpect to experience.- 14

­ Although this method**do~s** not evaluate maximally exposed individual (MEI)**risks~~·** itdoes explicitly account for the higher exposures that**~ill** occur**~!thin** the ring closest to the site. These higher exposures would receive an appropriately weighted score. The Subcommittee was asked to address approaches to assessing health risks from**airborn~** contaminants and has suggested a variety of approaches for EPA-s consideration. All of these approaches employ the following assumptions: carcinogens are non-threshold contaminants; there are thresholds for other toxic effects; concentrations of contaminants decrease with distance from the site; this decrease is more marked for particulates than for volatile chemicals; and acute toxicity and toxic effects from direct contact with particulates are the over-ridinghealth concerns in the area closest to an uncontrolled waste site.
Acute effects are addressed by Superfund-s emergency program and by the**curr~nt** HRS toxicity factor which is based on the Sax ratings (see Appendix 1). The Subcommittee favors a toxicity factor which includes multiple endpoints of toxicity including acute effects because some nearby populations around uncontrolled waste sites report symptoms consistent with acute toxicity (headaches, nausea, irritation, and respiratory effects) and because of the possibility of acute effects occuring in the event of a catastrophic release. Because of**t~e** weight given the inner-ring such acute effects could be well addressed with the ring-weighting approach or by a ring-weighting approach modified to account for the existence of a threshold concentration belowwhich no acute effects should occur. However, other scientifically supportable options include: considering acute toxicity in a separate assessment outside the HRS (such as under the emergency program); assigning discretionary points to the HRS score for the confirmed presence of local odors orhealth effects reasonably associated with materials found at the site; a separate assessment of the probability of a release of materials from a catastrophic event; and treatment of acute effects in a direct-contact pathway. 

### .· Chronic npn-cancer effects could also be addressed with the ring-weighting approach or by one modified to account for the existence of a threshold concentration below**~ich** no chronic effects should occur. In the modified ring-weighting approach this threshold concentration can be converted to a distance from the 

### site beyond which no adverse chronic effects would be expected. Chronic effects, particularly of particulate pollutants, could also be treated in a direct contact pathway. Carcinogens are dealt with in a reasonably precise manner by the ring-weighting approach, given the usual assumption that risk is directly related to average lifetime concentration in air. While the Subcommittee favors this approach, it is complex and EPA may want to·evaluate the effects of different diameters to see if the use of a single diameter for all sites is reasonable.- 15

­ The ring-weighting approach described inAppendix 2is best suited to carcinogenic effects

### of volatile chemicals. While concentrationof particulatesdecreases more sharplywith distance thandoes the concentration of volatile chemicals, the Subcommittee believes that this difference is not largeenough to require separateestimationmethods for volatile and particulate emissions in the HRS.
In assessing exposure, considerationof eachmedia pathway is recommended, includingair, water, food and direct contact. Measurement of exposure should also consider the route of exposure throughwhich substances exert their effects, While the relationship**bet~en** eXposure level and the biologicallyeffective dose is different for different pathways, not all compounds are toxicologically well characterized. As a result, EPAmay onlybe able to deal with route-specific toxicity on an exception basis; e.g., in the case of asbestos;inhalationismore important than ingestion. Many of the Subcommittee's recommendations hinge onknowing the identities of the chemicals at the site, Aminimum data requirement which mandates contaminant identificationby record reviewordirect samplingwould greatly improve the validityof theHRS inall pathways and is particularlyhelpful inestimating exposures to air pollutants and in addressing toxicity. For example, when the chemical identities areknown, it should be possible to modify and simplify theTreatment Storage and Disposal Facilities (TSDF) procedures to calculatean approximate, order-of-magnitude emissionrate for impoundments and landfills.
Both the identity of chemicals at the siteand emissionrates can be confirmedusing other investigative techniques, the most obvious of which is air concentrationmeasurement. Because ambientmonitoring is subject to the problemof dilution, to detect the presence and amount of emissions it isdesirable to analyze at the source, or as close to the

.. source as possible. There is, thus, anincentive touse methods of "probing" sources using such techniques as soil gas analysis.
Large Volume Waste
The large volumewaste issues before the Subcommitteewere the applicabilityof t.he HRS in scoringminingwaste sites and the feasibility of using waste concentrationdata ina revised HRS.
OERR provided The Superfund Hazard Ranking System (HRS): Applicability toMiningWaste Sites (13) and The SuperfundHazard Ranking System (HRS): Feasibilityof Using ConcentrationData in a Revised HRS (14) as the basis for the review,- 16

­ There are two ways to evaluate the applicability of the HRS to mining sites. The Superfund Hazard Ranking System (HRS): Applicability to Mining Waste Sites (13) presents EPA's experience in ranking mining sites with the HRS system in terms of false positives and false negatives and then distinguishes between the sites according to potential danger (determined by othermeans). In its evaluation, the Subcommittee coupled this approach with an examination of the scientific issues independent of the HRS experience.
In addressing large**~olume** waste (LVW) issues, it is useful to note that clearqualitative differences exist betweenmany LVW and the more numerous hazardous waste sites containing mixed synthetic organic/inorganic hazardous constituents in both liquid and solid form. LVW monofills are materials of a single type. Specific sites may have multiple types of wastes (e.g., mill tailings, smelting slags, etc,). Sites where these wastes are spatially separate are more easily characterized than sites where they are mixed. LVW are commonly contain low concentrations of hazardous trace elements (HTE) in the waste matrix which are**~;-eleased** by**ve~;-y** specific geochemical proc.,ss"s and subject to migration constraints that are increasingly better understood.
With r"spect to the question of the applicability of the current HRS to mining waste sites, the Subcommittee finds that the studies conducted**rega~;-ding** the adequacy of the HRS listing process for mining sites have been limited and inconclusive. The reports reviewed included the TRC (27, 28, 29) and MITRE (24, 25) reports contained inThe Superfund Hazard Ranking System (HRS): Applicability to Mining Waste Sites (13) as well as EPA's own studies. Sufficient experiential evidence has not been presented to show an inadequacy of the HRS in regard to mining sites. The present system has possiblyrated mining sites no worse than otherwaste sites. Some of the findings supporting this conclusion follow.



### .. (l) While the TRC (27, 28, 29) and MITRE reports (24, 25) reported that mining waste sites scored higher in waste quantity compared to non-mining sites (as expected given the large volume of wastes generated by themining industry), TRC did not conclude that this bias caused false positives or false negatives for mining sites. Both sets of reports found that waste quantity contributed relatively little to the final HRS score. (2) Although the TRC reports (27, 28, 29) suggested the degree of information available was a major factor in**~PL** listing of mining sites, they presented no data showing that the relatively larger data bases for certainmining sites**~;-esulted** inunfair**scoring~** · (3) The TRC reports (27, 28, 29) also suggested the final HRS score for mining sites could be predicted by population alone. Since the TRC reports only addressed·mining sites, they could not prove a bias against mining waste sites.- 17

­ Nevertheless, the Subcommittee believes the presentHRS is not well suited for scoring potential releases from mining sitewastes because mobilityand concentration are not included, Therefore, the present scoring systemhas a P?tential to treatmining wastes with systematic et"t'or.
For the ground waterpathway, the concentrationof a constituent in a waste is ofmuch less importance than the concentration of that constituent inthe leachate produced at the site. Consequently, more emphasis should be placed on the partitioning of hazardous constituents between the waste and the leachate, Leachate concentrationor interstitialpore water concentration, eitherknown or estimated, should then be factored into the waste quantity term in theHRS, Forwasees which are not in solid form, total contaminant mass quantity should continue tobeused, Improved ways of considering the concentration, toxicity (inorganics have special characteristics), release (mobilityinvarious matrixes), and informationon the transport/transformation of chemicals wouldmake the HRS more accurate. The area of contact of the sitewith the environmental compartments (air, water, humans, etc.) is also an important factor.
The issue of mobilityis especiallyimportant atmining sites because the large.volume of mining wastes oftenmeans largemasses of the contaminant are available for release. However, certain conditions must exist for these releases to occur, The current HRS does not address specific ionic form of inorganic metals, and ion form affectsmobility. Because·mobility is 

### amore discriminating concept than persistence in the subsurface, the Subcommittee suggests that OERR exploremeans of incorporating important matrix characteristics in a revisedHRS. Such characteristics include extreme acidity or alkalinity (as expressed by 

### .• bothhigh and low pH), any crystallinephase modifications ofmining wastes that differ fromnative geologic materials, and the sorptive capacityof surrounding geologic materials. The latter influences migration tenden.cy.
With respect to the feasibility ofusingconcentrationdatainthe revisedHRS, the Subcommittee finds that includinghazardous constituent concentrationisdesirable because both the severity of observed releases and the riskof potential releases are related to concentration.
EPA has proposed two options formodifying the HRS to account for the concentration of hazardous constituents. Both approaches translate waste constituent concentrationdata into an estimate of·the total mass of a hazardous constituent at the site, which is thenused to compute the waste quantity ·score for the HRS. Even the approach which uses "total mass" of hazardous constituent could contribute to produce false positives for some largevolume wastes and pathways.- 18

­ The Subcommittee-s preferred approach (Option 3) encourages the use of concentrationdata and provides the flexibility to substitute indirect estimates such as default concentrations to estimate a constituent-s total mass when direct measurements of concentrations are not**available~** While the direct measurement approach (Option W2) provides the soundest scientific hasis for the HRS is most cases, itmay not be practical, due to safetyand cost considerations for every site at the site inspection stage. The Subcommittee suggests the direct use of concentration rather than conversion to a mass value.
Amethod of determining a "representative concentration" for a site based on a stratified sampling strategywould be useful. In this approach, a complex site could be subdivided into a set of more homogeneous regions or strata, and a representative value for each stratumdetermined through limited sampling. Statistical techniques exist for manipulating stratified data, which could then be recombined with appropriate weighting into a final single HRS score for the site. Exposure
To the extent that the HRS is intended to assess relative risk, it must address both toxicity and exposure sufficiently. Exposure occurs when there is contact between pollutants and receptors. It is important to address exposure when there are toxic chemicals present in order to determinewhether there is any actual or potential risk to health or the environment. Where there are no toxic substances orwhere there is no exposure, there is no risk, even though there may be release or contamination. (However, determining the existence of a release or of environmental contamination is often the first step in evaluating actual exposure,) Where there is incomplete information on either toxicity or exposure, risk cannot be fully assessed. Risk can be evaluated by assessing four parameters: (a) the presence of chemicals, (b) their potential for release and mobility, (c) the probability of contact with humans, plants or animals and (d) their intrinsic toxicity.
Much could be gained by adding a chemical-specific exposure score that could be combined with chemical-specific toxicity scores to evaluate which chemicals dominate the risk at a single site and how the risk might compare across sites that are otherwise similar,
Given some minimal**info~ation** about a site and its chemical inventory, it may be possible to make crude estimates of partitioning among environmental media and, therefore, of emissions by routewhich could ,be used to generate part of a**chemical~specific** exposure score. The following information would support development of a chemical-specific exposure score: 1. An estimate of the total mass or source concentration of important chemicals at the site.- 19

­ 2. Adescription of the site-specific factors influencing release, e.g.; impoundment vs. landfill.
3. Partition factors applicable to the chemical, e.g.**Henry~s** Law constant and organic carbonpartitioncoefficient.
Some· characterization of the potential for migration also allows better consideration of time as a factor in sitemanagement, Environmental pathways include air, water (bothground and surface water), soil, and plants and animals that become part of the human food chain. The potential for release and mobility of chemicals through these pathways affects risk.'estimates. Chemicals- behave'differentlyin different environmental pathways, so all pathways need to be evaluated to estimate risk effectively,
The maindifficulty of dealing withexposuredirectlyis thatwe are dealingwith potential exposure as well as actual exposure, There are two aspects of exposure to be considered--the concentrationof contaminants in the environment around the site snd .the number of people potentially exposed to these concentrations.**A~tual** release may be demonstrated by environmental sampling, Potential release may be addressed byconsidering properties of the site and characterisitics of the chemicals present, such as distance to ground water and volatility. Similarly, the number of people (receptors) present and actuallyexposed today canbe counted, while the number of people who might be present at the location inthe future can only be estimated from .studies of populationdynamics.
Measurement of exposuremay be person-based or community-based.
While estimates of individual person-based exposures canbe developed from biological samples, from personalhousehold samples, from self-reported exposures, and from self-reported symptoms, each approach has its limitations. Community-based exposures can be developed from ambient pathway measurements, from sitemeasurements, and from modeled exposures. Numerous assumptions about targets and behavior are needed to impute exposure from ambient pathwaymeasurements, However, evenmore assumptions are needed to impute exposure from sitemeasurements. Incorporating concentration and mobility could produce a more comprehensive site assessment procedure. One way to do this is by using concentration as a weighting factor for thewaste quantity. The resulting effective waste quantities for lowvolumes of high concentrationwaste might be similar

# to. those for large volumes of low concentrationwastes. Similarly, the scores for toxicity/persistence and for effectivewaste quantity could be adjusted by considerations of mobility.- 20

­ Algorithm Improving the algorithm could potentially do more to improve the HRS than fine-tuning individual components. The Subcommittee has recommended changes that will allow the HRS to provide a more accurate and scientifically based estimate of the relative risk of candidate sites, To the extent possible, the HRS scores should correspond to an objective analysis of relative risk at sites. However, this is not always feasible due to both scientific and data limitations, as well as the value and policy decisions implicit when considering and balancing human health and environmental impacts.
Arevised HRS, better designed to evaluate sites by relative risk, will provide an improved mechanism for determining which sites should be included on the NPL, and can potentially providemeaningful input to the subsequent prioritization of NPL sites. However, the Agency must continue to base this prioritization on many factors in addition to the HRS. Most of the changes needed to transform the current HRS into a systemmore reliably related to riskare changes in the overall algorithm and not changes withvast new data requirements,
Internal consistency is important. Making rules that are consistent requires little up-front investment and no additional costs in the scoring of specific sites. These changes can be more cost-effective than some improvements to portions of the HRS alone, especially ones requiring additional data collection.
The way'that various components of the score are combined should reflect how their real world counterparts interrelate. The approach for accomplishing this is to beginwith a physically-based exposure assessment model for each exposure pathway, structured to properly translate expected nr potential releases into environmental concentrations and subsequent ·· exposures and effects. These models would, of necessity, be highly simplified for a screening assessment. Even a simplified exposure assessment model may not be, feasible given the time, resource and data limitations associated with the HRS process. However, the manner inwhich the pathway scores are estimated and combined should be consistent with the fundamental material balance and exposure principles of such an underlying model. This can be accomplished in the context of the structured value approach used in the current HRS system. When there isn't "enough" data for the HRS, it iS necessary to have a default value that encourages data collection (also termed missing value replacement), Lacking complete information on chemical inventory and concentration at a site may well be the rule rather than the exception, Therefore, a minimum data requirement will reduce the inconsistencies that are otherwise inevitable when different people perform the scoring.- 21

­ One concernwith the use of default data is that the fact of data limitations couldindicate that the sitemight be different from otherwise comparable sites. The definition of comparable sites is crucial and may depend on the scoring component, When data are available that exceed wh.ft is needed for theHRS, there is the question of how to use all of it. The default or tiered approach OERRpresented on concentrationis onemechanism for using additional-datain the revised HRS. Another approach is the assignment of discretionary points. The Subcommitteediscussed several scenarios where discretionary points could be assigned including sites where: a very large number·of chemicals were identified, the presence of the toxic materials in the surrounding populationhad been demonstrated, and toxic particulate air emissions were anticipated. For theHRS score to reflect relative risk, the extra points assigned must be proportional to the extra risk the situationpresents. (SeeAppendix 5.)
Recommendations to Evaluate and Improve the HRS
The current HRS is appropriate for theoriginal purposes OERRhas ·described because most of the factors scored are related to risk, and

higher scores for those factors reflect higher risks, Thus, the current HRS is plausible, However, it is both possible and desirable to revise the HRS to relatemore closely to the relative risk posed by uncontrolled waste sites.
The HRS performance should be judged by an·empirical retrospective evaluation of how successfully the HRS predicts riskor onhow successfully its components predict phenomena (such as release) which contribute to risk. this evaluation should be based onan in-depth technical review. Whatever the definition of risk, theRRS shouldbejudged on how well it approximates that definition, not on how well itmatches a subjective notion of the relative importance of the sites ina test set. .· The Subcommittee recognhes the possibility that sites containing hazardous chemicals whose toxicity is not widely known will be omitted from the NPL 11st.1ng, thus possibly creating false negatives. Measures to counterthis probleminclude continuingto develop toxicity profiles on more chemicals and keeping good records so that sites with currently unstudied chemicals canbe re-evaluated as toxicity information on these chemicals becomes available,
The Subcommittee recognizes the need for some flexibility inthe HRS to allow for the wide range of physical and chemical characteristics of sites, Being flexible is compatiblewith reducing the possibility of error in theHRS, EPA must reduce this possibilityof error ineach component (or "factor") of the system and, evenmore importantly, inthe algorithmused to relate these components into a score that is intended to reflect relative risk,

### - 22

­ To adequately evaluate the current or modified HRS, in-depth studies should be conducted to determine the effectiveness of the HRS to assess risk and to identifyareas for improvement, One goal of these studies would be to improve the algorithm so that it can be defended as risk-related. Another goal is to to determine at least a crude method for estimating the quantity of specific chemicals present. Any HRS evaluation studies should be thoroughly peer reviewed before their initiation,
Future evaluation of the HRS should consider the possibility of incorporating detailed numerical geochemical transport/fate models which are currently under development, The advantage of using such models in a future HRS is the explicit inclusion of quantitative representation of specific processes and mechanisms reponsible for the release, transport, transformation, and retention of hazardous compounds. In comparison to structured value (or "scoring") approaches, themodels increase data requirements, but can yield less ambiguous, more detailed simulations appropriate for pathway calculations and, ultimately, exposure estimates.
As m<!ntioned in the Oth"r Comments portion·Of Appendix 3, EPA should develop studies both to review**large-~olume** waste sites ranked under the

.model and to examine basic: parameters of the model,

.•

### APPEND!X 1

REPORT OF THE TOXICITY FACTORWORK GROUP • 

### TO THE 

### HAZARD RANKING SYSTEM SUBCOMMITTEE OF THE SCIENCE ADVISORY BOARDU, S. ENVIRONMENTAL PROTECTION AGENCY SCIENCE ADVISORY BOARD HAZARD RANKING SYSTEM REVIEW SUBCoMMITTEE TOXICITY FACTOR WORK GROUP
ROSTER
CHAIRMAN
Dr. Warner North, Principal, Decision Focus Inc. Los Altos Office Center Suite 200, 4984 El Camino Real, Los Altos, California 94022

MEMBERS/CONSULTANTS
Dr. Paul Deisler, 11215 Wilding Lane, Houston, Texas 77025

Dr. John Doull, Professor of Pharmacology and Toxicology, University of Kansas Medical Center, Kansas City, Kansas 66103

Or. Joseph V. Rodricks, Environ Corporation, 1000 Potomac Street, N.W,, Washington, DC 20007

Dr. EllenSilbergeld, Chief Taxies Scientist, Toxic Chemicals Program, Environmental Defense Fund, 1616 P Street, N.W., Room 150, Washington, D.C. 20036

Dr, Rebecca T, Zagraniski, Division of BirthDefects and Developmental Disabilities, Center for Environmental Health and Injury Control, Centers for Disease Control, Koger Center, Room 2008 (F-37), 1600 Clifton Road, N.E., Atlanta, Georgia 30333
EXECUTIVE SECRETARY (Until August 31, 1987)
Mr. Eric Males, Executive Secretary, Science Advisory Board (A-101F), 

## u.s, Environmental ProtectionAgency, 401 MStreet, S.W., Washington, DC 20460 (Until August 31, 1987)
EXECUTIVE SECRETARY (After August 31, 1987)**~rs.** KathleenW, Conway, Deputy Director, ScienceAdvisory Board, (A-101F), 

## u.s, Environmental ProtectionAgency, 401 MSt., S.W.,**~ashington,** D.C. 20460
STAFF SECRETARY**~rs,** DorothyM. Clark, Staff Secretary, Science Advisory Board, (A-101F) U.S. ,Environmental ProtectionAgency, 401 MStreet, S,W,, Washington, DC 20460

### TABLE OF CONTENTS Page Number
GENERAL COMMENTS 

### Al-l
RESPONSES TO SPECIFIC TOXICITY ISSUES POSED BY OERR Al-3 HowMany Chemicals Should Be Evaluated? 

### Al-3 Route-specific Toxicity Scores Al-4
NoncancerEffects of Carcinogens and Acute Toxicity 

### Al-4 Advantages and Disadvantages of CertainToxicity Ranking Options 

### Al-6
Default Values 

### Al-6 CombiningToxicityScores 

### Al-6
OTHER COMMENTS 

### Al-6 Flexibilityand Common Sense 

### Al-6 General Support for a Structured Value Approach to the HRS 

### Al-6
Two Additional Steps in the NPL Process 

### Al-6 Migration 

### Al-7**~** 

### Dose 

### Al-7
Future Studies 

### Al-7 ATTACHMENT: Discussionof Options for Revising the HazardRanking System(HRS) Toxicity Factor, May 4, 1987 pages 4Q-41Al-l

GENERAL COMMENTS
The Toxicity FactorWork Group reviewed Discussions of Options for Revision of the Hazard Ranking System (HRS) Toxicity Factor (12).
The Toxicity FactorWork Group believes that toxicity is an important consideration in assessing sites because, if the objective of the HRS is to generate estimates of relative risk, the HRS must deal with toxicity and exposure. The toxicity factor in the current HRS makes distinctions among only a few of the 951 current and proposed site on the NPL. By pathway, fully 85% (ground water), 87% (surface water), and 97% (air) of these sites received the maximum toxicity/persistence score, Because the Agency did not present information on sites that are not on the NPL, the Work Group was unable to determinewhether the current toxicity factor is adequate to distinguish between "very toxic" and "not so toxic" sites.**~ot** only is it unlikely that the most toxic substances at different sites are equally toxic, it is inconceivable that theyoccur at equal concentrations even if total quantity of waste is**id~ntical, Ther~fore,**  in revising the HRS, the EPA should consider approaches that would better discriminate between sites of differing toxicities and subsequently examine how well the new toxicity**f~ctor** actually performs,
Some toxicity decisions are made in the Preliminary Assessment/Site Investigation (PA/SI) stage. For example, specific chemicals are selected for scoring in the HRS, while other chemicals are dropped from the process, The bases for these selections do not appear to be standardized at this time. As a result, while the toxicity data that is handled by the HRS is already a subset of the full information, additional (perhaps important) toxicologic data are not part of the quantitative process, The exposure factors are addressed in various ways in the HRS and most are handled quantitatively in the HRS. Consequently, the HRS score actually reflects a disproportionate amount of information on exposure and less on toxicity, thus deewphasizirig toxicity in the final score. Therefore, EPA should consider the development of some type of consistent methodology or guidelines for evaluatingthe toxicity of chemicals at a site during the PA/SI stages, The Toxicity Factor Work Group reviewed the following methods (12) for evaluating the toxicity of individual chemicals:

oChronic Toxicity (Noncancer)

- Reference Dose Method

- Reportable Quantity (or Composite Score) Method

- Modified Acceptable Daily Intake (ADI) Method oCarcinogenicity

- Cancer Potency FactorMethod

- Reportable Quantitites (RQ) or Effective Dose10 Method

- EPA Weight-of-Evidence Method oAcute Toxicity

- Reportable Quantities (RQ) Method

- Registry of Toxic Effects of Chemical Substances (RTECS) Method

### Al-2
The Sax chemical toxicity ratings have provided a very crude basis for prioritizing sites because theyare largelybased only on the acute toxicity of one constituent of thewaste. The Sax systemis insufficient because it focuses on acute adverse outcomes instead of the range of toxicological endpoints that need to be addressed in the HRS and because itdoes not provide citations so that toxicologic ratings canbe reevaluated and verified f.or the purpose of theHRS.
OERR presented three options for evaluating and scoring toxicity inthe revised HRS (12), These are a reportable-quantities-based option (El), an optionbased on reference doses and potency factors (E2), and anoptionbased on modified acceptable daily intake and 1Neight-of-the-evidenceapproaches. Each of these options takes into account several types of toxicity and uses quantitative measures of substance potency, 1Nhereas the Saxmethod is unidimensional and developed for protection against poisoning. The three options presented by OERR are much better than the Sax rating method, and theWork Group recommends thatEPA replace the Saxmethod.
BecauseOERR's three options make use of essentially the same data bases for toxicity (although the data are processed differently), the Work Group does not believe any of the options is overvhelmingly superior to the others. The options do have different strengths and weaknesses, however, and theWork Group has addressed these belowin (page Al-5). Although this is really a policy decision rather thana scientific one, theWork Group does not encourage a system for weighting the severity of different health endpoints, as is currently'done for calculating reportable quantities (RQs), bothbecause suchweightings are subjective, and because they are subsequently obscured by the final numerical score. Similarly, to the extent that scientifically legitimate techniques exist for the considerationof various toxic effects inman and innature, the decision of whichendpoints to address is primarilya science policy·• decision rather than a purely scientific one. Nevertheless, because there are many endpoints relevant to human health and the environment for 1Nhich good methods exist;theWork Groupencourages the Agency to address multiple endpoints as part of the HRS toxicity factor.
TheWork Group's efforts to review the toxicity issues were complicated by the follo1Ning factors.

o It is difficult to translate the objectives of theHRS (that is, a scheme that separates sites into those with risks greater or lesser than an arbitrary threshold, with a desire to avoid false negatives [false placement ofhigh risk sites·into the low risk category], and to the extent possible, that ranks all sites by their relative risk) into operational criteria to design the scheme.Al-3

o The Agency has presented the toxicity issues in a somewhat theoretical manner. Few real world examples and few test cases such as example rankings of chemicals or sites, were presented to theWork Group.

o Lastly, and probably most important, the Work Groupbelieves that toxicity issues are integrally linked to dose (i,e., migration and exposure) issues. The existing HRS system deals with exposure by using surrogates to address the question of whether people (receptors) will be exposed, and if so, how many will be exposed, and to what concentrations, via ground**wate~,** surface, and air routes. RESPONSES TO SPECIFIC TOXICITY ISSUES POSED BY OERR
The full text of the specific questions can be found in the attachment to this report. They are repeated in abbreviated form here for the convenience of the reader.
How Many Chemicals Should Be Evaluated?
Areview of past Superfund risk assessments were undertaken byOERR (10) to determinewhether the health risk associated with a site is likely to be dominated by one or a few chemicals (for each pathway), or by a larger number of chemicals. The study, which was limited in the number and type of sites considered and because sites were selected for convenience rather than for representativeness, generally indicated that only a few chemicals would dominate at any given site. However, the Work Groupdid not review this study in detail and cannot recommend a fixed number,of chemicals for OERR to examine at each site. Instead, the Work Group offers the following gene(al guidance.
EPA appropriately considers toxicity early in the site evaluation process. Identification of known toxic substances occurs in the PA/SI stages prior to the HRS evaluation. Indeed, only sites containing toxic' substances currently identified by the Superfund Laboratory Programare likely to be candidates for HRS evaluationand listing, In addition, the chemical rec·eiving the highest score in the toxicity-persistence matrix (8) is selected by field staff for scoring purposes in the HRS, The Work Group has concerns about the procedure now used to identify chemicals in the PA/SI stages and to select a single "most toxic" chemical for the HRS evaluation,
Because so few chemicals have been toxicologicallywell characterized, the Agency should consider a factor fo( sheer numbers of chemicals known te> be present (in addition to developing scores based ona smaller number of chemicals of known toxicity). All things being equal, a sitewith more chemicals should receive a higher priority for further evaluation, most probably in the RI/FS. (See discussion of discretionary points in Appendix 5 of the HRS Subcommittee's report.)

### Al-4 Should SeparateToxicityRatings for a Chemical beDeveloped for VariousExposureRoutes?
Because this questionis inextricably related tohow theHRS deals withmigrationand exposure issues, theWorkGroup has chosen to discuss the advantages and disadvantages of three approaches rather than tomake a single recommendation.
One approach is to aggregate route-specific exposure scores into a net (total) exposure score for a site. This total exposure score could be multiplied by a net toxicity score. The toxicity scoremay not need to be route-specific because the cruder the scheme, the less theneed for route-specific factors. Amore accurate analysis would independentlyevaluate route-specific risks before aggregating, Because the relationshipbetweenexposure level and the biologicallyeffective dose is different for different pathways, route-specific toxicity factors would improve the accuracy of such an approach,
Athird approach, which recognhes that route-specific toxicity factors are not yet available for a large number of compounds, is touse route-specific informationwhen it is available and relevant--such as in the case of asbestos where the inhalationroutehas far greater biological effect than the ingestion route--and to aggregate exposure scoreswhere such informationis lackingor the route-specific differences are small.
Whether or not route-specific toxicity is addressed in theHRS, it should be considered intheRemedial Investigation/Feasibility Study (RI/FS) stage because themore detailed information supports more realistic analysis of risks.
How should potential carcinogens, noncancer effects and acute toxicity 

# .. be evaluated as part of a scoring systemused todetermine listingon the NPL? TheWork Group concludes thatmultiplemeasures of toxicity should be usedin the process of evaluatingwaste sitesbecause a varietyof toxic effects may be experienced by the exposedhuman and natural populations. Which endpoints are of concern to EPA is primarilya science policy decision, However, scientific techniques existwhichwould permit the HRS to consider several endpoints whichare relevant tohuman healthand the environment,
The Work Groupbelieves the importanceof acute effects in theHRS should be decreased relative to chronic effects because, given the likelihood for long-term low-level exposures around uncontrolled waste sites, chronic effects appear more relevant. Futhermore theWork Group understands that EPA has a separate emergency response program to respond quickly to those**uncontr~lled** 

### waste sites where acutely toxic exposure levels are thoughtAl-5 possible. As a result, the Work Group recommends replacing the Sax method with any of several OERR-developed approaches which include measures of chronic toxicity.
Acute effects are important when they occur, and some Subcommittee members conclude that, since the emergency program suffices to address them, acute effects need not be considered in the revised HRS. However, because of reports of acute effects such as odors, nausea, headache, and respiratory irritation around unremediated and uncontrolled hazardous waste sites and because of the potential for catastrophic releases, or releases during remediationwhich may result in exposures sufficient to cause acute effects, the Work Group recommends that the revised HRS include acute effects among the multiple endpoints considered.
Besides carcinogenicity, the health endpoints should include those used to establish reference doses (including at a minimum, fetotoxic, teratogenic, and neurotoxic effects); and acute toxicity (including not only lethality, but endpoints such as irritation, allergic sensitization, and neurotoxicity). The major concerns for most sites will be for chronic health effects (cancer and non-cancer). While acute toxicity should be examined, it will generally be less important than chronic toxicity in the site ranking process. Any of the variety of health and environmental endpoints considered could motivate·a more detailed evaluation of a site.
For acute taxies, the Work Group prefers the Registry of Toxic Effects of Chemical Substances (RTECS) method to the Reportable Quantity (RQ) method because RTECS facilitates route-specific toxicity ratings and closer attention to the raw toxicity data. If a more sophisticated use of the toxicological data is envisioned, use of the RQ evaluations of RTECS may be helpful to identify the preferred animal studies for toxicity ratings. Use of Threshold Limit Values (TLVs), which are contained in RTECS, may be one means of expanding the acute toxicity, including not only lethality but also other endpoints. , For non-cancer chronic effects the Work Group prefers the Reference Dose (RfD) method because the RQ method involves subjectivelyweighting the severity of various endpoints and the modified ADI method has not received extensive reviewand may differ from the RfD method in rating individual chemicals.
For carcinogenic potency the Work Groupdoes not perceivemuch gross difference between the two options presented (q1

## * vs. EDIO). Other measures (e.g., ED [I) and ED [0.1]) should be investigated because they refer to a more realisticallymeaningful risk range for human exposures and, where the dose-response is known to be concave upwards, they would offer an automatic correction to potency for this fact. In evaluating relative risk for carcinogens, both weight-of-evidence and potency should be considered in determining relative risk for carcinogens.
The Work Groupjudges that the Agency's procedure in the RQ calculation

### Al-6 for combiningweight-of-evidence and potencyinformationis reasonable for purposes of ranking different carcinogens.
Are There ScientificAdvantages/Disadvantages to Basinga Toxicity RankingMethod on a No-Adverse-Effect Level? The WorkGroup chose to address the advantages and disadvantages of the options presented rather than enter into an abstract discussion on NOAELs and alternatives. Fornon-cancer chronic effects theWork Group prefers the Reference Dose (RfD) method to the Reportable Quantities (RQ) method (which involves weighting the severityof various endpoints), and to themodified Acceptable Daily Intake (ADI) method (whichhas not received extensive reviewand may differ from theRfD method inrating individual chemicals).
Is 1t

### Necessary to Attempt to Deve.lop DefaultValues for Ratinga Substance's ToxicityWhen its ToxicityDataBase is Limited? The WorkGroup has no recommendation on this issue. Having little patiencewith "invented toxicology" theWorkGroup wishes to encourage the Agency to develop data rather than relying on default values. In cases where toxicological data become available after a sitehasbeen scored, theWork Groupencourages theAgency to re-evaluate the site in the light·of the new findings.
What Quantitative Procedures areMost Reasonable for Combining IndividualToxicity Ratings forMultiple Substances at a Site?
The Work Groupdoes not encourage a systemforweighting the severity of different healthendpoints, as is currentlydone for calculating Reportable Quantities (RQs). The Work Groupbelieves that a varietyof endpoints should beused to rank sites for further study. In the context of an on/off switch, anyhealth effect may be an adequate criterionfor "' further studyof a site.
OtllER COMMENTS Flexibilityand Common Sense
rheHRS isdesigned to 

### be a simple, workable, mechanistic procedure that generates reliable estimates of relative risk. However, considering the state of information available at the PA/SI stage, the complexityof risk, and the variabilityamong sites, this may bean impossiblegoal. In light of these uncertainties, there aremany opportunities for errors in both overestimatingand underestimating relative risk. Thus, theWork Groupbelieves thac any systemmust offerflexibility and the opportunity for common sense.Al-7
General Support for a Structured Value Approach to the HRS,
Even though, in theWork Group's view, itmay not be possible to develop an HRS that provides reliable estimates of relative risk, the Work Group is supportive of a HRS concept and role which attempts to rank sites by relative risk. That is, the Work Group supports the use of a structured value analysis that includes (even if crudely) factors related to risk. The estimates generated by such a scheme may be simply one mechanism for evaluating sites.
Two Additional Steps in the NPL Process
The Work Group has discussed the need for two additional steps in the NPL process: (a) some type of consistent methodology or guidelines to select chemicals during the preliminary assessment and site investigation should be developed for use in the site evaluation process, and (b) the option of using more detailed risk information, if available, should be considered as a supplement to the HRS process., One approach, for example,· is to allow adjustment of point scores to take into account special knowledge, as discussed in Appendix 5 to the Subcommittee's report. Migration Migration of pollutants from a site to a receptor (considering both time and kinetics) is an important part of the exposure assessment, Where there is no contact between pollutants and receptors, there is no risk. The current HRS does not evaluate mobility at all and does not sufficiently evaluatemigration (which the current HRS addresses in the ground water,' surface water·and air pathways) and, thus, can be expected to misclassify some sites with respect to relative risks,
Dose 

### .· Dose information is included in the HRS evaluation only through the very crude surrogate of total waste quantity, Concentration information for specific substances, if available, is not used in the HRS. The Work Group is concerned about dose as it relates to the types and severity of effect. It is an important element for predicting risk, but it is not apparent that any effective surrogates exist to address it in the current HRS.
Future Studies
Some members of the Work Group are concerned that si.tes containing hazardous chemicals.whose toxicity is not widely known will be omitted from the NPL listing, thus creating false negatives. Measures to counter this problem include continuing to develop toxicity profiles on more chemicals and record keeping so that sites with "unknown chemicals" can be re-eva.luated as toxicity information on these chemicals becomes available.Al-8
The lack of toxicological informationon many chemicals ishardly a problemunique to the Superfund programand theWork Groupdoes not wish to imply that this difficultycanbe solved by Superfund, orindeed theAgency, alone.SPECIFIC QUESTIONS FOR THE SCIENCE ADVISORY BOARD
This section lists a few specific unresolved questions about scientific issues involved in the development of a revised toxicity factor for the HRS. EPA believes that these questions are significant and need to be addressed before a revised toxicity factor can be developed. (1) How many chemicals per site (or exposure medium) should be evaluated to serve as the basis for an overall toxicity factor score? If less than all chemicals detected, how should they be selected? Should selection be based on the most toxic substances, the most frequently detected, or those that appear to be present in the greatest quantities? (2) Should separate toxicity ratings for a chemical be developed for various exposure routes (i.e., should chemicals have three or four different ratings, depending on exposure route?) , or is a single route-independent toxicity rating adequate for HRS ranking purpose? [Note: It is assumed that separate media-specific toxicity factor scores would be developed for a site under any HRS revision option based on the chemicals evaluated for that medium, regardless of whether route specificity is accounted for in individual chemical toxicity ratings.] (3) Should potential carcinogens be evaluated for noncancer effects also, or can it be assumed that the carcinogenicity potential should dominate the overall toxicity rating? (4) Is it advisable to include acute toxicity evaluation as part of a scoring system used to determine listing on the National Priorities List (NPL)? If so, how should it be weighted? (5) Should more specific noncancer toxicity types, such as teratogenicityand mutagenicity, be broken out and rated separately? If so, how should they be weighted relative to other effect types so that single overall rating could be derived for each chemical? (6) Are there scientific advantages/disadvantages to basing a toxicity ranking method on a no-effect level NOAEL, such as in Options E2 and E3 versus an effect level (MED, such as in OptionEl)?- 2 ­ (7) It is necessary to attempt to develop default values for rating a substance's toxicity when its toxicity data base is limited, or should site scores be developed based only on chemicals having "better" toxicity data? (8) What quantitative procedures aremost reasonable for combining individual toxicityratings for multiple substances at a site?

•"

### APPENDIX 2

REPORT OF
THE AIR TARGET DISTANCE WORK GROUP TO THE
HAZARD RANKING SYSTEM REVIEW SUBCOMMITTEE OF THE SCIENCE ADVISORY BOARD



### .·

### U. S. ENVIRONMENTAL PROTECTION AGENCY SCIENCE ADVISORY BOARD HAZARD RANKING SYSTEM REVIEW SUBCOMMITTEE AIRTARGET DISTANCE WORK GROUP ROSTER CHAIRMAN
Dr. Thomas Burke, Deputy Commissioner, NewJerseyDepartment ofHealth Room 805, StateHealthCN360, Trenton, NewJersey 08625 MEMBERS/CONSULTANTS Dr. StephenL. Brown, ProjectManager, EnvironCorporation 1000 Potomac Street, N.W., Washington, DC 20007 Dr. Shepherd Burton, Systems Applications, 101 Lucas ValleyRoad San Rafael, California 94903 Mr. George F. Carpenter, MichiganDepartment of Natural Resources, Environmental Response Division, Post OfficeBox 30028 Lansing, Michigan 48909
Dr. Naihua Duan, Statistician, Rand Corporation, 1700 Main Street, SantaMonica, California 90406
Dr. DonaldMackay, Department of Chemical Engineeringand Applied Chemistryand Institute for Environmental Studies, University of Toronto, Toronto, CanadaMSS 1A4
Dr. Mitchell Small, Department ofCivilEngineering, CarnegieMellon University, SchenleyPark, Pittsburgh, Pennsylvania 15213 .•


### EXECUTIVE SECRETARY (Until August 31, 1987)
Mr. EricMales, Executive Secretary, ScienceAdvisoryBoard, (A-101F), 

## u.s. Environmental ProtectionAgency, 401 MStreet,

## s.w., Washington, DC 20460 (Until August 31, 1987) EXECUTIVE SECRETARY (AfterAugust 31, 1987) Mrs. Kathleen

### w. Conway, DeputyDirectot", ScienceAdvisoryBoard, (A-101F), U.S. Environmental ProtectionAgency, 401 MSt., S.W., Washington, D.C. 20460 STAFF SECRETARY
Mrs. DorothyM. Clark, Staff Secretary, ScienceAdvisoryBoard, (A-lOlF), U.S. Environmental ProtectionAgency, 401 MStreet,

## s.w., Washington, OC 20460

### ATTACHMENT A

POINTS FOR SAB CONSIDERATION

o Use of a Single TargetDistanceLimit at all Sites

o Applicability of AirEmissions Information**fro~** 

### TSDF to Superfund Sites

o Approach to assessingHealthRisks (Is cancermost Conservative?)

o Range of Emissions Est.imatesused



### .·



### •TABLE OF CONTENTS
PAGE
GENERAL COMMENTS A2-l COMMENTS ON THE ISSUES RAISED BY OERR A2-2
An Alternative to the Use of a SingleTarget A2-2 Distance Limit at All Sites Approach to Assessing Health Risks A2-4 Applicability or Air Emissions Information from TSDFs to A2-5 Superfund Sites and the Range of Emissions Estimates Calculated
Other Factors Affecting the Potential for Release A2-8
OTHER COMMENTS A2-8 Relationship of the Air Pathway to the Rest of the HRS A2-8
Determination of Actual Release A2-9

ATTACHMENT A: Points for SAB Consideration
ATTACHMENT B: Derivation of the Air Target Score

### • Al-l 

### GENERAL COMMENTS The AirTarged DistanceWork Group.reviewed OERR's Analysis of the Air Target DistanceLimit in the Hazard Ranking System (9), The airpathway in the current Hazard Ranking System (HRS) uses an evaluation of exposed population at risk to derive a score for "airtargets," The scheme uses amatrix of populationversus distance for four concentric circles (with radii of 1/4, l/2, l, and 4miles), Publiccomments have suggested that the four mile distancemay be too large, EPA studies, by contrast, have suggested that, for siteswithlarge emission rates of careinogens, individual Ufetime risks may remain above 10-6for even greater distances, The Work Group considered this and otherquestions related to the airpathway (seeAttachment A). · In general, theremay not be significant air risks atmany potential Superfund siees, but the HRS needs to address themwhen theyare present, The Work Group is very supportive of OERR's efforts to modify the air pathway so that it considers potential releases, instead of relying solelyon a score for observed releases. Because air emissions are oftenepisodic ornarrowly focused along a particularwind direction, theyare difficult to observe, In-addition, there canbe a decliningor changing risk depending on the nature or integrity of containment or the site type·, Theremay have occurr!.d a significant releaseearlyina site's history which has resulted in a lossof contaminants and decreasing emissions at the time when sites are evaluatedand scored. Lastly, future activities at a site (such as excavation) may create thepotential for new air**~missions.** 

### For these reasons, inclusion of a potential for release is an important modificationof the HRS. Ideally, 

### if comprehensive informationwas available, air emission models developed for otherpurposes could be 

### used to estimate potential •· releases. These estimations, however, may require informationwhich isnot available to the Agency during the preliminary assessment/site investigation (PA/SI) stage. With informationon the identities of chemicals present, an emission rate can be 

### calculated for volatile chemicals or the presence of volatile emissions established on a crude yes/no basis. When such informationis lacking, volatile air emissions cannot be predicted at all, and the subsequent consideration of air exposure routes is veryweak,
If 

### the identities of chemicals areknown, it shouldbe possible to modify and simplify the procedures for modeling air emissions fromhazardous waste transport, storage and disposal facilities (TSDFs) to calculatean approximate, order-of-magnitude emissionrate for impoundments and landfills, Other**investigativ~** 

### techniques could be 

### used to confirmemission rates, the most obvious ofwhich is air concentrationmeasurement in the illllllediate vicinity of the source, Because of the dificulties inmeasuring variable low-level ambient air concentrations, more direct sampling, such as soil gas analysis or"inverted dishpan" surface sampling, should be considered.A2-2
COMMENTS ON THE ISSUES RAISED BY OERR
Th@ full**te~t** of the issues raised by OERR**~an** b@ found in**Atta~hment** A. Abbt"eviated versions are used here for the convenience of the read"'·
An Alternative to the Use of a Single Target Distance Limit at All Sites.
The Work Group recommends that EPA consider an alternative to the use of a single air tar:get distance limit for all sites.
To evaluate the exposed population at risk mo•e accurately, the Work Group recommends that the Agency derive a scoring system that will properly weight the number of exposed people according to the distance from the site at**whi~h** they live. The weighting factor should be proportional to individual risk, as determined by concentrations that decrease with distance from the site. In otherwords, the system should use population rings that are based on distances from a site at which air concentrations decrease by a constant factor. These distances may vary by size and type of site. oor illustrative purposes a method of developing these rings is presented in Attachment B. Although this method does not evaluate maximally exposed individual (ME!) risks per se, it does explicitly**a~count** for the higher exposures that willoccur within the ring closest to the site. Therefore, the Work Group concludes that a separate or additional evaluation of MEI risks as part of the HRS is unnecessary. These rings could be incorporated into the scoring systemas a simple refinement of the current matrix, as illustrated in table 1.

Table 1 Suggested Matrix for Air Pathway Population Scores



### .. Generalized Target Distance Score Distance from Center of Site Population a-ba ba-b2a



# -­ b2a-b3a



# --­ b3a-b4a



# --­ !06-107 10 9 8 7



### • 105-106
1o4-105 9
8 8
7 7
6 6
5 103-1o4 7 6 5 4 J02-1o3 6 5 4 3 10l-Joz 5 4 3 

### 2

### • A2-3 Thematrixis interpretedas follows. The distance "a" is the radiusof the site itself. (In practice, siteswill not be circularand "a"must be takenas a typical dimension--derived, for example, by taking "a" as equsl to the square root of the areaof the sitedivided by pi,) The dimensionless constant "b"is a multiplier of the order of 2 to4, determined as shown inAttachment B. Forexample, if the site was 200 yards in diameter (about 1/9mile), and themultiplierwas 3, the rings would be 1/9 to 1/3mile, 1/3 to 1mile, 1to 3miles, and 3 to 9miles, The populationused is that ineachannular ring (between "a" and "ba", etc.), determined to one significant figure. Once scores are assigned for each ring, the largest score is takenas adequately representing the site. The scores are all logarithmicallyrelated to populationrisk, so that they should be added toother scores representing logarithms of variables that enter risk linearly, such as the carcinogenic potencyor thequantityofwaste or emissionrate. As shown, the scores for a large site("a" islarge) willbe greater

. than for a small site ("a" is small) for the same populationdistribution because each of the four rings will be 

### largerand incorporatemore population. The populationineach ringwillincrease as a2, so if a increasesby a factor of 3, the populationwill expand by a factor of 9, andthe scorewill go up byone point. Thisbehaviorimplies incorporationof a factor related to emission strength (in turn, proportional to a2) inthe score. Thismay not be appropriate. Perhaps itwould be better to definea standard value far a, takenfrom a typical site. After deriving such a ring-weighted system, the Agencymay want to evaluate the effects of different diameters to see if theuse of a single diameter for allsites is reasonable because a ringwidth that varies between sites, based.on their diameters, may be too complex for the

### HRS.

.• 

### To place the scores from the ring-weighting process on the same scale as ather scores inthe

### HRS withwhich theymight be combined, the scores could be 

### increased indirect proportionbymultiplying by a constant. For example, ifonewishes tohavea score of 30 inthe top leftcorner, one canmultiply

# all the Scores·by3 thusobtaining, for example, 3 in the lower right: corner and 12 inthe lower left corner. But if this is done, anorderofmagnitude change in carcinogenic potency shouldalso be represented by 3points change in score, and so on. The above scoringsystemis reasonably precise for cancerfor which individual risk, given theusual assumption that risk is directly related to average lifetime concentrationinair, isdirectlyrelated to average lifetime concentrationinthe air. Fornoncancer effects, EPA ordinarilyassumes a threshold of concentrationfor anydamage to occur. Thus, outside some critical distance (different for siteswith different emission rates or different threshold toxicities), no effects will occur, and inside that distance one could assume conservativelyA2-4 that 100% incidence of the effect occurs, There seems to be no simple scoring schem

.. to take this property into account in a population score, but the practical effect is that population beyond perhaps one mile (for example) is simply irrelevant to the air target score for noncancer endpoints. If, in the toxicity score, a noncancer effect is responsible for the greaterpart or the score, then the choice of points from Table 1 should be restricted to the**t~o** left columns (for example). As before, the degree of danger for an individual in these**t~o** rings**~111** have already been captured in the toxicity score and**~hatever** score is used as a surrogate for exposure, Approach to Assessing Health Risks
As implied above, toxic!ty considerations may also be different for the air**path~ay** than for surface or ground**~aters,** An exclusive evaluation of a contaminant from the standpoint of carcinogenicity is inadequate, Many compounds detected at contamination sites are not currentlyconsidered carcirwgens or suspected carcinogens. Acute toxicity is generallymeant to be considered in emergency or interimresponse procedures prior to HRS scoring, In reality, sites may not pass some threshold of acute toxicity considered in this way snd, yet, still exhibit some subacute or chronic health effect. This is ·particularly true for the late-history site,**~here** average emissions may be relatively low,**but--~ith** breaching of a**fe~** drums, deterioration of

## a building, or removal of cover--a short-term, acute emission is again possible. If acute toxicity conditions were discovered at a site during site inspection orHRS scoring, the site should be automaticallyreferred to emergencyresponse. This seemingly would elimingte the need for considering acute toxicity in the HRS. !t does not appear that this complete separation is appropriate,**ho~ever,** given the threshold nature of emergency response or changeable site conditions,
In addition, other subacute or chronic effects of noncarcinogens must be considered, Neurotoxicityand chemosensory effects of air pollutants, while occurring at differing levels of concern, are real responses to airborne contami-nants, and environmental toxicity is occasionally important. The public is also often concerned about nuisance effects, such as odor
or nausea. The Work Group favors separate consideration of acute toxicity in a • direct contact**path~ay, Ho~ever,**  acute toxicity could instead be included among the multiple measures of toxicity in a revised toxicity factor, In addition, the exposure of the near-site population exposure to air contaminants could be separatelyassessed, or discretionary points could be added to the HRS score for smells or symptoms reasonably related to exposures to chemicals**kno~** to 

### be at the site (providing that these are confirmed in some suitable manner), The direct contact pathwaymay be especially useful if EPA**~!shes** to eliminate or reduce the importance of scoring acute toxicity for the surface and ground**~ater path~ays,** • 

### A2-S Inassessingexposure, consideration of eachmedia**path~ay** 

### is recommended includingair, water, food, and direct contact. Measurement of exposure should also considerthe route of exposure throughwhich substances exert their effects, For example, inhalationismore important thaningestionin the case of asbestos. ApplicabilityorAirEmissions Informationfrom TSDFs to Superfund Sites and the Range of Emissions Estimates Calculated
Because air emissions are oftenepisodic or**narro~ly** 

### focused along a particularwind direction, theyare difficult to detect, Forthis reason, inclusion of a potential for release is animportant priority formodification of theHRS. The procedures givenintheAnalysis of theAirTarget Distance Limit in the Hazard Ranking System (6) for estimatingair emissions from sudace impoundments and landfillsat Superfund sites are based onmodel equations developed forRCRA Facilities (TSDFs), These procedures are appropriate for thepurpose towhich they · are applied: to determine the range of possible (long-term) emissionrates at Superfund sites. The model equations represent the state-of-the-art inthis relatively new area of environmental science. There are, however, some limitations identifiedbelowand suggestions for additional analysis that canresult ina clearerand more defensible analysis. These include the need to illustrate previous validation studies of themodels, particular:ly those presented inpeer-reviewed scientificjournals, the need to better illustratethemodel comparisons at existing landfills, and betterid.entificationof the potential applicabilityof the models to particular sites. Despite the difficulties indata collection, validationstudies with the surface impoundment and landfillmodels have beenattempted. ·• Using these studies inthe documentationfor proposed changes to theHRS would provide theuserwitha sense of the reliabilityand accuracy of the procedures, which we s.uspect is 

### about one-half to one orderof magnitude. These studieshave

.been presentedinpeer-reviewed articles injournals such as Environmental Progress and theJournal of theAir PollutionControlAssociation.
In addition, the comparisonof predicted and measured emission rates (inSection4.4.1.4 of Analysis of theAirTarget DistanceLimit in the Hazard Ranking System, July6, 1987) would be strengthed by inclusion of a plot of predicted vs. observed rates, This comparisonmay indicate significant variabilityon a site-by-sitebasis, Thisvariability is, 

### in·part, due to the simplifications·inherent inthemodels, but is also largelya result of the difficulties in identifyingmodel parameters at a given site, even for the most basic of inputs, suchas the identification of chemicals in thewaste. These difficulties are pertinent to theuse of these, orrelated model equations, as.part ofanHRS scheme that considers'potential air emissions,A2-6 Ideally, if comprehensive information was available, the emission models for TSOFs could be used. Abrief reviewof these procedures is presented belowin order to highlight important variables.
Emissions from surface impoundments depend on the concentration of chemicals in the water. Methods to estimate such emissions apply the tradicional "two phase resistance" transport equations which include an estimate of the chemical's air-water partition coefficient or Henry's Law Constant. The resistances depend on factors such as wind speed, fetch, diffusivities, and the presence of oily films but, to a first approximation, itwould probably be acceptable to adopt mean values of the resistances and apply them to all chemicals. The key items of information are chemical identity, chemical Henry's Law Constant, and chemical concentrations. In the long-term the chemical will be depleted from inactive sites unless there is migration from sediments to replace it.
Air emissions from landfills depend on the resistance to**transfe~** from the soil cover depth and porosity, coupled to the chemical's vapor pressure as the driving force for diffusion. The key items are chemical identity, chemical vapor pressure, and soil cover depth and porosity.
Emission rates can be estimated readily for tanks and drums given a knowledge of the geometry and**co~tents.** Waste piles and other accumulations of waste will require separate treatment. In all cases, the keyvariables to estimate volatile emissions are chemical identity and vapor pressure. Information on the chemical identities is valuable because it allows the presence of emissions to be established and the calculation of emission rates for volatile chemicals. When such information is lacking, air emissions can not be predicted and the subsequent consideration of air exposure routes is impossible These may be evidence of emissions as a .• result of odors, for example.
If the chemical identities are known, it should be possible to modify and**simp~ify** the TSDF procedures to calculate an approximate, order-of-magnitude emission rate for impoundments and landfills. A score could then be assigned based on the logarithm of the emission rate. The populationdistance matrix discussed earlier includes the effects of dispersion.

• Otherinvestigative techniques could be used to confirm the emission rates, the moat obvious of which is air concentrationmeasurement. Ambient monitoring, however, is subject to the problem of dilution, as the three examples on the next page show.

### A2-7 If we 

### considera site 100 mby 100 memitting 100 kg/year into a wind of average speed Sm/s, and assume that the airiswellmixed at the downstream sampling site to a height of 5

### m, then the concentration at that sitewill be C

### g/m3 givenby: 100kg/yr

### x 1000 g/kg• 5

### m/s x 100 m x 5

### m x 31.5x 106 s/yrx

## c or C • 

### 1.3

### x 10-6 g/m3 or 1.3 ugJm3, This lowconcentrationmay be difficult to detect quantitatively.
For surface impoundments, it is 

### preferable tomeasure thewater concentrationand infer an emission rate. For example, intheabove esse an emissionof 100 kg/yr over 104 m2 would require a concentration of 0.023 g/m3, assuming an overall watermass transfercoefficient of 0.05m/h, i.e., 

### toS g/y • 104m2 x0.05m/h x 8760 h/yrx0.023g/m3, • 

### This concentrationis a factor of 18,000greaterthanthe airconcentration. Likewise, if the emissionis from soilandwe assume aneffective diffusivity (corrected for**porosity~** 

### of0.01 cm2/s or0.0036m2/h and a path length of 1 mandarea 104 m , thenthe effectivediffusion volume exchanged is 0.0036m2Jh'x 104m2/1mor 36m3/h. This is essentiallythe volume of soil porevapor released perhour. If the emission ratewas 100 kg/yr the concentrations would be 0.32g/m3, i.e., 1D5 g/y• 36 m3/h x 8760 h/yrx0.32 g/m3, Again, this concentrationis a factor of250,000 greaterthan in the ambient air and ismuch easier to measure, 

### .· Based on these examples and theWork**Group~s** 

### experience, to detect the presence and amount of emissions it isdesirable to analyze at the**sou~ce,** 

### or as close to the source as possible. Once the chemicalmixes with the ambient· air, itsuffe·rs a concentrationdropby a factor on the order of 104 to 106, This may produce ambient concentrationsbelow detection limits, Thus, there is thus anincentive to usemethods of "probing" 

### • sources by using, for example, soil gas analysis or "inverteddishpan" surface emissionsamples. We 

### believe thatvaluable confirmatorydata would be obtained at quitemodest cost. Theseinvestigativetechniques could give direct.measurements of emissions rates.

# ..

A2-8 Site investigations of soil, ground water and**surfa~e** water have been aided by the prior existence of sound analytical protocols for sample collection, storage, and analysis. It appears that insufficient effort has been devoted to developing protocols which are appropriate for air sampling at waste sites, The traditionalhigh volume sampler is often effective, but it is, to an extent, misapplied, More effort should be devoted to developing more subtle,**e~onomic** and useful air sampling procedures which are**spe~ifi~** to the conditions prevailing around waste sites. Other Factors Affecting the Potential for Release
The following additional factors should be considered in developing the air pathway component of the HRS:
l. The type of containment, i.e,, impoundment vs, tanks, and drums vs, encapsulation, should be**~onsidered,** Also included should be an assessment of the extent to which the containment is likely to be disturbed as part of the remediation process at the site, Sites where more excavationand handling of wastes are required may gresent a higher potential for air releases. 2. Catastrophic releases may create air emissions. This category could include the susceptibilityof the site to flooding, the seismic activity of the area, and the frequency of severe weather, e.g., extremelyhigh winds which can lead to fugitive particulate emissions.
3. Reported incidents by surrounding residents, such as complaints concerning odors, eye irritation, or nausea, may result from**a~r** emissions. While, in the absence of air monitoring data, these reports may not be sufficient evidence of a "confirmed" release, such sites should be scored for their potential-to-release,
OTHER COMMENTS Relationship of Air Pathway to the Rest of the HRS
As part of its revision of the HRS air pathway, the Work Group • recommends that OERR assure that the scores assigned for populationand distance are consistent with one another and with other scores with which they must be combined, for example, scores for to,xicity, waste quantity, or release potentiaL If the HRS is to represent the relative risk of sites, it.must be consistent with the underlying, quantitative relationships of the factors evaluated, Weighting the risk among pathways on**an~** priori basis where, for example, the air pathwaymight be worth one-half the ground water pathway, is not scientificallyjustified.AZ-9 

### Two aspects of riskneed to be addressed. First, riskmaybe declining or changing depending on the nature or integrityof containment or the site type. Theremay have been a significant releaseearlyin a site's history "hich has resulted ina loss of contaminants and decreasing emissions in laterhistory ("hich often coincides "ithsiteevaluation and scoring). This earlier release may have been of an acute nature "hichno longer is detectable or representative of the site. The second aspect is that the near-site populationmay be considered to be at greaterrisk from the air pathway than from thewater pathways. Because of the nature of migration of aircontaminants (speed ofmovement and plume entrainment) the populationat highest riskmay change as atmospheric conditions change. Theremay be a need to considerthe near-site populationas exposed to anindependent direct-contact pathwayrather thanas a subset of the airpathwaybecause acute rather.thanchronic to>:icitymay be more relevant and because of the known presence at some sites of chronic to>:icants in the form of particulates (such as dusts containing lead). Exposure to the larger respirable particulates canbe a verynear-sitephenomenon, which may be de-emphasized by inclusioninthe airpathwaywith its focus on greater distances. On-siteworkers (not cleanup staff, but employees at activemanufacturing or landfillsites) arealso at risk in manners different from long distance populations. E>:posures may last for fractions of days but be intensewhen theyoccur. Near-sitepopulations are continuallyexposed to a varietyof routes incomparison to single route**e>:pos~re** 

### of remote populations. E>:posure also changes with the nature of contaminant migration. Near a site, the contaminants aremorevaried as wellas atgreater concentrations, and therearemore routes of e>:posure. Volatile organic compounds are present and are subject to inhalation. Inaddition, particulatescontainingeithermetals or adsorbed organics tend to deposit near site boundaries and are subject to ingestionand dermal absorption as "ellas inhalation, Remot·e from the site, concentrationand variety of contaminants areless, and e>:posure ismore limited to thevolatile compounds and the inhalationroute. DeterminationofActual Release 

### • One of the important scoringfactors inthe currentHRS is anon-off switch for the presence of actual release of hazardous material into the ambient air. The determinationof actual release isusuallybased on a limited amount of·airmonitoring, The data providedby the program office indicate that 14.2% of the951 NPL sites have shown observed release, compared to41.6% for surfacewaterand 73.0% for groundwater. These statisticsmay bemisleading and couldresult from differences in detecti?n efficiencyrather than true dominance of thewaterroutes.A2-!0 The differences in detection efficiencyare also thought to result in a reluctance to collect data for this route, a problem**~hich** could

### be addressed by a minimum data requirement for the HRS.
Air releases are often intermittent,**~ith** a substantial temporal variation, Let "r" denote the fraction of days during**~hich** a release occurs at a site. If r>O, the site should be classified (in the current HRS) as having an actual release. Strictly speaking, both the release fraction and the pr.,sence of actual release are relative to the time frame under consideration. If longitudinal air monitoring is available for a long time period, and measurement error is negligible, the release**~ould** be observed, In the absence of longitudinal monitoring, there can be a substantial probsbility that a site**~ith** intermittent release**~ould** not**sho~** an observed release, If one assumes that air monitoring is conducted for one day, such as the day of site inspection (chosen randomly), For a site with release fraction,''r", (say40%) the probability of not observing the release is 1-r, or 60%, Therefore, the prevalence of air. release for the NPL sites can be substantiallyhigher than the value of !4.2%, which is based on the available data on observed air releases, For**e~ample,** if the release fraction fot all NPL sites with actual release is 40%, the prevalence of air releases would be about 35% (14.2%/40%), among which only a small fraction. 1S identHied by the available data as showing an observed release, Lt is likely that air releases can be substantiallymore prevalent than what the available data indicate,

one possible remedy for the underestimation of actual releases is to increase the frequency of air monitoring, For a site with release fraction r·**~** 40%, if airmonitoring is conducted for three instead of one days, chosen randomly (because of possibl"' intertemporal correlation, three consecutive days cannot be regarded as being random), the probability**of~**observing the release would be 21.6% instead of 60%. However, .· the amount of resources required to increase the airmonitoring frequency would be substantial, and might not be cost effective.
As discus.sed above, alternative sampling ""'thods such as soil gas monitoring may be easier than ambient air monitoring,



### •1 

### (this works for n "' 

### 2also) 

# ---------------------

--------------------- 

# -

# S x Pk

(21Tr 

### dr) (D ----) 

### rn**~** 

### 2iT

### PkD · [ (bx)2-n

- xZ-n] (2-n)


### 2 

### Tf Pk N 

### (b2-n-1) 

### x2-n



# .. (2

# -n) (b2-t)1Tx2

2 p 

### k N (b2-n -1) 

### " (2

## - n) (b2


## - 1) 

### xn ATTACHMENT B Derivationof the Air

### Target Score
suppose populationNis distributed uniformly in a ring between distance x and bx, The populationdensity is given by
N N**~-----** 

### Suppose further that concentration, averaged over all directions, declines as 

### an inverse power of distance:

If excess risk is proportional to concentration (as usually assumed for carcinogens)., the proportional!tyconstant is P,·and excess risk•PC,.P(k/rn), then the population riskin the ringis given by

Assuming the same population, N, the populationin the next larger ring isgivenby



# -

The ratio of the two risks is



### • If we want this ratio to be 1/10, 

### then
10 

### and b

# "-vro

Forexample, if n • 2, b • 

### 3.16. Note that 

### if Dis constant from ring to ring, the ratio of population risks is

/11 

### b2-n Rbx -.,., " and will be greater thsn 1 if

### n

## <2, implying that there is 

### no "natural" limit for the air target distance,• Both atmospheric diffusion theory, available data, and current diffusion modeling practiced by EPA support a value for n of less than or equal to 2 for ground-level sources. At close-indistances, less than 10 km for**e~ample,** the decay in the ring-averaged concentration is inversely proportional to the square of the radial distan'"" from the source for average meteorological conditions. At distances greater than 10 km, the decay for average meteorological conditions is slower than quadratic, EPA models used in performing risk assessments, such as the Human**E~posure** Model (HEM), use formulas for diffusion that have the ringaveraged concentration decaying approximately as r-1.7, for distances out to approximately 10 km for average meterological conditions.
As an**e~ample,** one can refer to the table when a**~** 0.09 mile and b**~** 3,33 (n is about !.9), Figure B-1 shows the rings for these assumptions and Table B-1 shows the matrix of scores, TABLE B-1 Air Target score for b - 3.33 Ring Boundaries (miles) PoEulation 0.09

- 0.3 0.3

- !.0 !.0

- 3.3 3.3

- 11.1

!06

- 1o7 10 9 8 7 !05 106 9 8 7 6 

# I t04

- !OS 8 7 6 5 1oJ 104 7 6 5 4 t02

- 103 6 5 

### 4 3 1ol

- 'to2 5 4 3 

### 2 !00

- 101 

### 4 3 2
(The scores above the line imply population densities greater than 30,000/miZ, which are rare.)
rf one assumes that population is uniformly distributed at density 0**~** l,OOO/mi2, then the populations in the rings are about 260, 2900, 32,000, and 390,000people. Each ring would score 6 points; the overall score would, therefore, also be 6.
The decline iaindividual risk per ring is by definition one orderof-magnitude, Therefore, if one arbitrarily defines risk to equal !o-3 for the innermost ring, then the corresponding population risk iS 260 x lo-3 "0.26 (less than one case in a lifetime), In ring 2 it is 2900 x !0-4 or0.29, in ring 3 it is 0.32 and in ring 4 it 1S 0,39. Thus, total population risk continues to increase as long as the population density remains constant. Practically, individual risk has declined to 10-6 in ring 4 and would be negligible (lo-7) in a fifth ring.F'l.GURE B-1



### ·Air Target Distance Score (not to scale)



### • Ring 4

Ring 

### 3

i

### 11 miles



# I

Site Area (radius about 0.09 miles)

### APPENDIX 3

REPORT OF THE LARGE VOLUME WASTEWORK GROUP TO THE 

### HAZARD RANKING SYSTEM REVIEW 

### SUBCOMMITTEE OFTHE SCIENCE ADVISORY BOARD



### •• 

### U. S. ENVIRONMENTAL PROTECTION AGENcY SCIENCE ADVISORY BOARD HAZARD RANKING SYSTEM REVIEW SUBCOMMITTEE LARGE VOLUME WASTE WORK GROUP ROSTER
CHAIRMAN

Mr. Richard Conway, CorporateDevelopment Fellow, Union Carbide Corporation, Post Office Box 8361 (770/342), SouthCharleston, West Virginia 25303

XEMBERS/CONSULTANTS

Dr. Keith Ferguson, Environmental Protection, Environment Canada, Kapilano 100, Park Royal, West Vancouver, BritishColumbia, CANADA V7TlA2

Dr. C. Daniel Kealy, U. S. Bureau of Mines, Spokane Research Center, East 315 Montgomery Avenue, Spokane, Washington 99207

Dr. James 0. Leckie, Department of Civil Engineering, Stanford University, Stanford, California 94305-4020**~r.** 

### Bruce Napier, Battelle NW, Post Office Box 999, Richland, Washington99352

Dr,David Pollock, U.S. Geological Survey, National Center, Mail Stop411, Reston, Virginia 22092

EXECUTIVE SECRETARY**~rs,** 

### KathleenW, Conway, Deputy Director, Science Advisory Board, (A-lOIF), 

## u.s. Environmental ProtectionAgency, 401 MStreet, 

## s.w., Washington, D.C. 20460
STAFF SECRETARY
Mrs.DorothyM. Clark, Secretary, Science Advisory Board, (A-IOlF), 

## u.s. Environmental ProtectionAgency, 401 MStreet,

## s.w., Washington,

## D.c. 20460

### TABLE OF CONTENTS

BACKGROUND RESPONSES TO ISSUES/QUESTIONS RAISED BY OERR ApplicabilityofHRS toMiningWaste Sites Bias AgainstMining Sites Not Demonstrated Inadequacyof theHRS forMining Site Evaluations Not Proved Inappropriatenessof theExistingHRS for Mining SitesNot Demonstrated, But Has that Potential Factors to Modify theHRS forLargeVolume Wastes FeasibilityofUsing**Concentrat~on** 

### Value of Incorporating a Concentration. Factor Desirabilityof IncludingHazardous Constituent ConcentrationDataintheHRS Options for IncorporatingConcentrationData IntheHRS OtherComments onConcentration OTHERCOMMENTS Long-TermConsiderations Need forAdditional Studies 

### • Search forFalseNegatives and FalsePositives SuMMARY PageNumber A3-l A3-3 A3-3 A3-3 A3-4

A3-S

A3-S

A3-6 A3-6

A3-7

A3-8 

### .·

A3-9 A3-ll A3-11 A3-12 A3-12 A3-l2 ATTACHMENT A--Issues fromThe Superfund Hazard Ranking System (HRS): ApplicabilitytoMiningWaste Sites, July22, 1987 ATTACHMENT B--Issues fromThe Superfund Hazard Ranking System (HRS): FeasibilityofUsingConcentrationData ina RevisedHRS, July27, 1987

# ..

A3-1
BACKGROUND
Mr. Henry L. Longest, Director of the Office of Emergency and Remedial Response (OERR), referred the large volume waste issue, "whether large volume wastes should be considerE!d differE!ntly from otherwastes," to the Science Advisory Board for review inhis June 25, 1987 memorandum (22). The issues as stated more specifically in the July 28, 1987 memorandum (20) of**~r.** StephenA. Lingle, Director of the Hazardous Site EvaluationDivision (OERR) are: "1) Applicability of the HRS in sco<ing mining waste sites; and

2) Feasibility of using waste concent<ation.data in a <evised HRS."
This memo<andum also states, ";,e (OERR) believe that the Subcommittee findings will be equally applicable to both miningand fly ash sites." The Work Group concentrated on mining sites and assume OERR will translate its findings to utility ;,aste sites.
The primary EPA document addressing the first issue, The Superfund Hazard Ranking SystE!m (HRS): Applicability to MiningWaste Sites (13) was reviewed at the Work Group's August 20, 1987 meeting. Besides providing background on the HRS, it presents an overviewof mining waste site charactedstics, summa<izes five·previous studies on the application of the HRS to mining waste sites, and provides "n assessment of "potential dangers" at six such sites rated by the HRS.
In the·overvie;,of mining ;,aste site cha<,.cteristics, four major categories of wastes from the extraction of ores "nd minerals were add<essed: mine waste, mill tailings, dump and heap leach waste, "nd mine water. (The Work Group had the Office of Solid Wastes' Management of MiningWastes (!7) and chapters 1-5 of the Draft Report to Congress: Wastes from the Combustion of Coal by Electric Utility Power Plants (16) as additional sources of information on the characte<istics of large volume wastes). Metals, radionuclides, asbestos, and cyanides (but not organics) ;,ere identified as the contaminants of conce<n at large volume ;,aste sites. The acidity (pH) was identified as a key factor in the mobility of metals, and the ground water and surface water pathways were those usuallyof concern at these sites.


### • Three of the five papers summarized and evaluated in the issue pape<were prepared by TRC Environmental Consultants, Inc. for the Ame<ican Mining Congress (27, 28, 29). The other two were Agency contractor reports developed by MITRE Co<poration (24, 25) in <esponse to issues raised by TRC. The TRC pape<s assert that the HRS does not adequatelydiscriminate risks posed by various mining waste sites as well as it does for non-mining sites; the MITRE papers respond that TRC's conclusions a<e not supported by their analysis, or by further MITRE analysis.A3-2 

### OERRbriefedtheWork Group on its comparison of scores for six actual miningwaste sites with the results of an assessment of the qualitative overall risk to human health and the environment (potential danger) at those sites (11), Ratings for four pathways were derived: ground water, surfacewater, air and direct contact. For these six study sites, higherHRS scores were associated withhigherpotential danger ratings.
In itsJulybriefing of the Subcommittee, the Officeof Policy, Planning, and Evaluation reported that its SiteRanking Panel (an in-house groupof EPA personnel withvarying degrees of expertised on Superfund issues), usinga differentgroup of sites and experts, apparently found virtuallyno correlationbetween the experts• ranking of sites and theHRS scores (18). Since theunpublishedOPPE study (23) was not reviewed by the Subcommittee nor otherwise peer-reviewed, the Work Group is unable to judgewhat credencemay be 

### placedupon its findings. Taking the study at face value, itwould appear that becausemost of the sites chosenwere alreadyon the NPL, thismay indicate that theHRS discriminates poorly between listed sites, butdoes not necessarilymean theHRS does not discriminate between those that shouldbe andshould not be listed,
There.are two ways to evaluate the applicabilityof theHRS to mining sites. The July 22, 1987 issue paper, The SuperfundHazardRanking System (HRS): ApplicabilitytoMiningWaste Sites, uses the approach of "valuating the experience in ranking miningsites with theHRS systemin terms of false positives and false negatives and differentiating according to th1! potential danger as determined by othermeans, Inits evaluation, theWork Group coupled this approachwith anexaminationof the scientific issues independent of theHRS experience.
The second issue paper is The SuperfundHazard Ranking System (HRS):·• Feasibilityof Using ConcentrationData ina Revised HRS, July 27, 1987, Besides providinggeneral background on the HRS, the paperdiscusses the (non)use of waste concentration intheHRS, describes theuse ofwaste concentrationdat·a inothersiteranking models, and presents three options for using waste concentrationin a revisedHRS, Basically, theinherentdifficulties of sampling and analyzing hazardous wastes, theheterogeneityof waste sites, cost, and the need • 

### to quicklydevelop a NPL dissuaded the Agency from includingconcentration in the originalHRS. Four.systems which address concentrationinvarious ways were described: the SiteRanking System (SRS), HARM II, SiteAssessment System, and Remedi.al ActionPrioritySystem (RAPS). OERR'viewed the SRS approach, a linear s·coring systemwhich fallsjust short of being a quantitative riskmodel, as having components of potentialutility, but cautioned that any of the systems relyheavily on the professionaljudgement of field personnel.A.3-3 The three options pr<>sented by the Agency for using waste concentration data in th<> revised HRS are: Wl Retain the current HRS approach where waste concentrationdata are used only to identify the most toxic waste constituent.
W2 Mandate the use of waste concentration at all sites to determine a total mass of constituent to be used in the revised HRS, much as the waste quantity score is currently applied.
W3 Adopt a tiered approach to encourage the use of constituent concentrationdata, where available, and reliance on default values of concentration to estimate the total mass of a constituent at other sites.
The detailed questions posed to the Work Group on large volume waste issue are presented inAttachments Aand B.
RESPONSES TO ISSUES/QUESTIONS RAISED BY OERR Applicability of HRS to MiningWaste Sites
The full text of the questions posed by OERR can be found in Attachment A. An abbreviated formis used here to assist the reader.
Bias Against Mining Sites Not Demonstrated. The TRC and Mitre reports showed that mining waste sites scored higher inwaste quantity compared to non-mining sites. This is expected given the large volume of wastes generated by the mining industry. TRC did not show this bias caused false-positives or false-negatives for mining sites. BothTRC and Mitre found waste quantity contributed relatively little to the 

### .· final HRS score. TRC addressed whether the degree of site information available was a major factor in.NPL listing. Since some mining sites have more extensive data bases thando others, TRC concluded that these may be more likely to have higher scores and, therefore, to be placed on the NPL, compared with sites of equal risk but with less available information. Most rnajor industrial facilities also will have more extensive data bases than smaller sites (especially "orphan chemical dumps"). Extensive data • bases and a regulatoryhistorymay highlight major industrial sites before others. Moreover, more frequent and "denser" I!IOnitoring has a better chance to find environmental problems and observed releases; also, sites with serious problems may be more thoroughly studied. In any event, no data were'presented by TRC showing that the relatively larger data bases formining sites resulted inunfair scoring. On the contrary, smaller data bases could theoretically be biased. Use of default values for scores where data are missing would be a better solution to the alleged umderscoring of sites with lesser data bases.A3-4 

### Analysis of the relativeweights of components intheHazardRanking Systemmay suggestbias if

### one. kind of waste, such as mining wastes, always scores highinan important component irrespective of environmentalhazard. TRC stated the final HRS score formining sites could be predictedby population alone. Since theTRC studiedonlymining sites, it did not prove a bias againstmining waste sites. Also, themore completeMitre analysis indicated that population is the second-most important factor (after observed release) for scoring of all types of waste sites and, therefore, is a critical factor for all sites, notjustmining sites.
In two areas, theWork Group concurs withTRC. First, inorganic metals have certain characteristics not addressed ina systemthatdoes not take into account differences inmobilitybetween specific ionic forms. The Work Group assumes that OJ':RRwill conSiderthese differences in the revisions to the toxicity/persistence score. Second, the large volume ofminingwastes oftenmeans largemasses of the contaminantare available for release, but certainconditions must exist for these releases to occur.-.



### rn summary, while theTRC analysis ide.ntified some important ranking priorities of the HRS system, its findings do not present a strongargument indicatinga bias againstmining sites. Inadequacyof the HRS forMining SiteEvaluations Not Proven. After reviewing theTRC and MITRE studies as addressed in theJuly22, 1987 issue paperThe SuperfundHazardRanking System: ApplicabilitytoMining Waste Sites, theWork Group finds that the studies conducted regarding the HRS listingprocess are preliminaryin that theyhave examined only small subsetsof thedatabase, and are inconclusive. Therefore, sufficient experiential evidencehas not accumulated and bee'n presented to showan inadequacy of the HRS inregard tomining sites. The OPPE study (18) presentationat theJuly 16thSubcommitteemeeting, "Preliminary**Analysts~** 

### ofAlternativeModels to Support Revisions of the CJ':RCLA, HazardRanking System," also·provided some data. That studyinvolvedmining sites and 16 nonmining sites and used a panel of in-houseEPA personnel (with varying degrees of expertise inSuperfund issues) to evaluate risk for comparisonwith thevarious existingrankingmodels. Withinits limited study, OPPI': found no consistencybetweenits**panel~s** 

### ranking of risk and ratings from anyof themodels, including theHRS model. This data set formining sites seems limitedand cannot support a conclusion about the adequacyof theHRS scoring system• 

### • In summary, sufficient evidence was not presented to theworkGroup to 

### conclude that the current HRS hasbeenadequateor inadequate for mining sites (or**ev~n·for** 

### non-mining sites).

### • A3-5 Inapptopriateness of the Existing HRS for Mining Sites Not Demonstrated, But Has That Potential. As stated above, the Work Group was unable to find sufficient evidence that the HRS has treated mining sites with systematic error. Further, although only a small subset of mining sites was available for analysis, the Work Group was unable to identify any sites currently listed that should not have been on the NPL. The present systeu has possibly rat<'!d mining sites no worse than otherwaste sites. However, the present scoring systemhas a potential to treat mining wastes (and others) with systematic error, The vast majority of listed mining sites and, to a slightly lesser degree non-mining sites, have observed releases. SinceTRC reported (25, page 9) that 95% of listed mining sites had an observed release and sine<'! observed releases require l<'!ss judgement in scoring, there was a lower risk of false positives,
The Work Group believes the present HRS is not well suited for scoring potential rdeases from mining waste si,tes because mobility is not included, as discuss<'!d below,
Factors to Modify to Make the HRS for Large Volume Wastes, tn regard to improving the HRS, the following points should be considered:

oMine wastes (one of four types of mining wastes) tend to be solid rather than liquid, and contaminants may be less mobile.

oWhere mining wastes contain low concentrations of hazardous substances in large waste volumes only partiallyisolated from the environment, environmental conditions instead of the extent of isolationmay control contaminant release,

oNatural geochemical processes are often required to mobilize

.. hazardous substances in mining wastes, such as acid generation by the biochemical oxidation of metal sulfides,

oThe concentration of hazardous substances and the potential for release can often be estimated for mining wastes, i.e., acid mine drainage (AMD) potential and leachingtests, More generally, the HRS doel! not adequately consider the nature of the source, release, transport, and transformation• Improved ways of considering the concentration, toxicity (inorganics have special characteristics), release (mobility in various matrices), and transport/transformation factors would make the HRS more accurate. The concentration issue is addressed in the latter part of this report and Appendices 1 and 2 address the toxicity issue. OERR's briefing of the Work GroupAugust 19-20, 1987 inDenver indicated that it is considering ways to incorporate mobility factors within the HRS that may have considerable pr0111ise (26).AJ-6 Revisions of the HRS.then under considerationbyOERR included substitutinga**~ability** factor for the persistence factor in theground water and surfacewater pathways. In theground water pathway**para~eters** representative of the tendency for**conta~inant ~ability**  and the sorptive capacityof the geologic**~edia** would replace the persistence**para~eter,** The Work Group supports such changes becausemobility is a more discriminatingconcept for both inorganics and organics than is persistence in the subsurface, especiallywith respect to inorganic**co~pounds,** The Work Group recommends that, during the development of a structured value representation of themobility concept, OERR should explore a means of incorporating important matrix characteristics. These include extreme pH, any crystalline phase modifications of miningwastes that differ from native geologic materials, and the sorptive capacityof surrounding geologic materials (influencingmigrationtendency),
Extreme pH is a particularlyattractive characteristicbecause itis meaningful and because the pH of mining wastes can be determined relatively simplyand accurately, Mining wastes tend to be highly buffered, either acid or alkaline. All fluids on a mining sites couldbe tested forpH and solids. could be tested for paste pH, particularlynear the surface (30). The pH of pathwaymedia and receiving waters aremore difficult to determine accurately, However, evenhere, samples should be obtained and measured for pH in.both the field and the laboratory,
In regard to the surfacewater route, OERR favors retaining persistence as the parameter to couple with toxicity inthewaste characteristics portion of the HRS, butwould consider four additional transformationprocesses along with the current biodegradationone. The Work Group concludes that inclusion of these additional factors would improve the existingHRS because itmore closely corresponds withwhat happens in the real world. Mobility would be included in the air route; a gas mobility factor value and a particulatemobility factor valuewould be combined, Details were unavailable; but the basic approach of including mobility should be pursued due to its importance alongwithwastequantityinthe exposure potential scenario, (Seealso Appendix·2 on exposures through the air.) Feasibilityof Using ConcentrationData in a Revised HRS
• The full text of the questions posed to the Subcommittee by OERR can be found inAttachment B, Abbreviated versions areused below.
Value of Incorporating a ConcentrationFactor. The following discussion assumes that the structured value model construct ofHRS will be maintained in the short-term.A3-7 Modifying the current HRS to incorporate factors which capture some measure of both the physical-chemical characteristics of the hazardous constituents and the nature of the waste matrix, as well as those site characteristics responsible for risk, is clearly an improvement. Modifications relating to the form and concentration of the hazardous constituents (HC) would add a degree of sensitivity to the HRS and possibly capture some measure of mobilityand potential for exposure, Possible factors include HC concentration in the waste material, total mass of the HC, potential for release of the HC, mobility of the HC in the ground water, and concentration of the HC in the ground water.
It appears that the most useful way to implement a modification of the HRS to facilitate inclusion of additional factors, as well as create flexibility to accommodate a range of site data qualityand quantity, is to augment the HRS with a multi-tiered default approach for use of HC concentration orquantity data, Such a multi-tiered structure would provide alternative routes for use of data differing inquality and quantity, as well as provide the opportunity for inclusion of a**d~cision** point on the question of acquiring new, additional data for the HRS scoring process. Perhaps the concept of using the most appropriate tier for a specific situation is more important than assuming that the top tier is best, and only defaulting to a lower tier.**~hat** is, for solid and semi-solid wastes at mining sites total quantity of hazardous waste makes little sense in the absence of mobility factors; rather, the concentration of the contaminants is important. For drum and other liquid wastes, the total quantity of hazardous material is probably important. Desirablity of Including Hazardous Constituent Concentration Data in the HRS, Because both the impact of observed releases and the risk of potential releases are related to source concentration, particularly 

### .· for the direct contact and air pathway, including hazardous constituent concentration in the HRS would be desirable.
At present,·theHR.S h only a screening tool used by OERR, in combinationwith other science policy considerations for deciding if detailed (RI/FS) studies are required. SARA encourages thedevelopment of a more accurate and comprehensive ranking system. Addition of concentrationdata could improve the accuracy of the HRS• • EPA has proposed 

### two options (W2 and W3) for modifying the HRS to account for the concentration of hazardous constituents, Both approaches translate waste constituent concentration data into an estimate of the total mass of a hazardous constituent at the site, which is thenused to compute the waste quantity score for the HR.S. Both approaches represent improvements over the current HRS. However, if mobility is not addressed, even the approach which uses "total mass" of hazardous constituent could contribute to produce false positives for·some large volume wastes and some pathways,A3-8 For theground water pathway, the concentration of a constituent in a solidwaste is of much less importance than the concentration that constituent may attain in·the leachate migrating away from a site. Consequently, more emphasis should be placed on the partitioningof hazardous constituents between the solidwaste and the leachate. Leachate concentration (at least estimated) should then be factored into the HRS waste quantityterm, Forwastes that are not in solid form, total contaminant mass quantity should continue to be used. Options for Incorporating ConcentrationData Inthe HRS. OptionW2 would require thatwaste constituent concentrationdatabe collected at a site before it could be scored. In contrast, OptionW3 (theWork Group's. preferred approach) is a tiered system that would encourage the use of concentrationdata, but would also provide the flexibility touse indirect estimates, or default concentrations, to estimate a constituent's total mass when direct measurements ofconcentrations are not available. The direct measurement approach of optionW2, modified for solidwastes to account for partitioning betweenwaterand solid, would provide the soundest scientific basis for the revised HRS. Inmost cases, however, it will not be practical due to safetyand cost considerations to require waste constituent concentrationdata for every siteat the site inspection stage. Furthermore, theWork Group-recommends the directuse of concentration rather than conversion to a mass value for wastes insolid or semi-solid form.
One of themostdifficult tasks will be to decidewhich tier to use. In the case of optionW3, there is a need to decidewhether to use measured concentrations or indirect estimates of mass. It is likely that economic and safetyconsiderationswill determine the decision as to which tierwill be used. If a site is relatively uniformand sufficientwaste constituent.data can be obtained at 

### .· reasonable cost to characterize thewaste, tierone (concentration) could be used. On the otherhand, if a site is non-uniformand costs of obtaining the necessary concentrationdata (or time and safety requirements) are prohibitive, itwould be reasonable to usea higher tier. In**effect~** this approach may effectivelydistinguishbetween inorganic (miningand utility) and organicwaste sites because of the greaterheterogeneity of organicwaste sites and the large expense of organic analyses. Inorganicanalyses are relativelyinexpensive (assuming speciationi$ calculated, not measured); therefore, this approachwould encourage 

### the collection of waste constituent concentrationdata at • mining sites, where concentrationdata isoften a critically important factor, as discussed above.
In conjunctionwith using concentrationdata inthe HRS, a method of determining a "representative concentration" for a sitebased on a stratified sampling strategywould be useful. In.this approach, a complex site could be subdivided into a set of more homogeneous regions or strata,A3-9 and a representative value for each stratum determined through more limited sampling. Statistical techniques exist for manipulating stratified data, which could then be recombined with appropriate weighting into a final single HRS score for the site.
To define a factor for converting quantity of hazardous constituents to quantity of hazardous waste, from a scientific point of view, the median concentration obtained in the September 1986 MITRE report by Arlene R. Wusterbarth, Hazard Ranking System Issue Analysis: Relationship Between Waste Quantity and Hazardous Constituent Quantity (32) should be used. OERR reported orally that this median concentration of all HCs at all sites is 450 mg/kg, but there was wide variation, This value relates to aggregates of constituents and onlymaterials on certain lists of hazardous coru>tituents were sought. Hence, risk management or policy considerations might cause EPA to select another value for the default concentration. One alternative is to convert HC to toxicity units (concentration times a relative toxicity factor) rather than concentratio?•
Aspecific rule for moving between levels (tiers) in optionW3 might be considered, The first level (total amount or concentration of hazardous constituent) should be used where data are sufficient to support an estimate of hazardous waste constituent quantity. This would occur where there are data to determine the hazardous waste quantity accurately. What data are available clearly show the quantity is significantly above the amount necessary to receive the maximum score, or significantly below the amount necessary for the next-to-minimum score. Where the quantity of hazardous constituent(s) is not known, scores could be calculated using the procedures of each of the first three levels, Then, scores for level 1 and level 2 would be compared, If the scores were within 25% of one another, the score for level 1would be used. If the scores weregreater than 25% apart, the score from level 2·· would be compared to that from level 3. If level 2 and level 3 scores were within 25% of one another, then the level 2 score would be used; if not, the level 3 score would be used in the HRS. The final level 4 score would be used where data onwaste quantity were virtually absent (especially for

### well fields).
Other Comments on Concentration. The Work Groupcommented on five additional issues related to the use of concentration data in the HRS• • 1. Some Technical and Practical Considerations, OERR-s issue paper on the feasibility of using concentration (14) addresses only waste concentration data, The Work Group recommends that concentration in the receiving environment, and perhaps population densities, also be considered as discussed in the Wolfinger report (31). Data on receiving water concentration data would aid in scoring observed releases. Fishbioassay data may be useful at times in ranking toxicity of releases in the absence of, or in addition to, chemical concentration data.A3-10 

### Siteswillhave databases of differing completeness and accuracy, as occurs now in site evaluation. Modified scoring syatems l!IUS

### t use lacge databases effectively to producel!lore accurate scores while handling with equal fairness sites with fewer data.
Sollie toxic contal!linants, such as metals, canbel!leasured in both solids and liquids at rea·sonable cost. All site inspections at mining sites couldgathervaluable data on the quantity of metals in the liquid and solid phases of thewaste, 2. EvaluationTechniques. The revised HRS shouldbe tested for both·high strength concentration/lowvolume wastes (drums) and low strengthconcentration/highvolume wastes (mine tailings), withboth observed releases and potential releases of contaminants. The sensitivityof the new ranking system to concentration. should be tested to determine the importance ofconcentration inlisting on the NFL and, thus, the need to obtainl!lore complete and accuratehazardous waste consitituent data. The analysis would also be 

### a first step inexamining possible false positives and false negatives. J, 

### W2/W3 Modification. Anon-linear scale such as that currently used for waste quantitymay be appropriate, Such a scalewould give low scores to small, less significant sites, while not unduly penalizing large sites, In a properlyconstructed algorithm, sites which are less significant in terms of riskwill score lower than those sites which present greater risks.
Forunknown waste quantit.ies, the default scheme suggested by Kushner inHazard Ranking SystemIssueAnalysis: Sites with ' UnknownWaste Quantity (19) is prefered over a minimumdefault value,. 

### 4. QualitYofWaste**Conce~tration** 

### Data. Samplingguidelines could be 

### developed for each waste type (i.e. drums, tanks, tailings, impoundments, etc,). These could be modified by site inspection staffbasedupon site specific factors, but a minimum sampling scheme should be 

### identified• 

### • Perhaps a relatively large numbeJ: of samples c::ould be collected, but onlya limited number analyzed initially. The initialresults and calculated HRS scores could be 

### used to decide on·the need for additional analyses, This approach would apply only to contaminants that couldbe preserved.• A3-ll
More datamay be required for sites with no observed release because they are more likely to score below the 28.5 boundary, and waste concentrationdata are critical in assessing the risk of potential releases. Composite samples should be obtained to reduce the number 

### ofanalyses, while providing estimates of average waste concentration.
5. Sampling Risk. Waste sampling schemes should be developed based on a thorough review of existing data on hazards to sampling personnel. Description of the waste, anecdotal evidence, and data on the receiving environment should indicate the hazards posed to site investigators, In suspected high-risk sites, the sampling scheme should begin around the perimeter where less contamination is expected, and progress towards the areas of expected higher concentrations (this is also consistent withgood sall!pling technique), Small test holes and gas sampling· equipment could be used on the actual site to test for hazardous conditions.
Data requirements could be Nlaxed where severe onsite health and safety hazards exist. In any case, these sites should probably be addressed by the Superfund Removal Program for their direct contact; fire and explosion capabilities.
OTHER COMMENTS Long-Terlll Considerations Although SARA mandates a re-evaluation of the HRS, and presumably a revision or alteration in a compressed time frame, it is nevertheless

.. us.,ful to consider both the long-term and short-term requirements of the HRS and subsequent site evaluation process. In that context, these remarks focus on the issues involved in development of quantitative representation of.concepts involving contaminant concentration in the waste materials, contaminant concentration inground water and mobility (a notion that combines release and transport).
Clearqualitative differences exist betweenmany large volume wast" (LVW) sites and the more numerous hazardous waste sites containing admixed synthetic organic/inorganic hazardous constituents in both liquid and solid form. LVW may be segregated into monofills of a single wast" type, Some sites have multiple types of wastes (e.g., mill tailings, smelting slag"s). Where these wastes are spatially separate, the sites may be r"lativ.,ly easy to characterize, Commonly, LVW sites contain low concentrations of hazardous trace elements (HTE) in the waste matrix,A3-12
The release of theseHIE is governed by very specific geochemical processes and is subject to migration constraints. Scientists and regulators increasingly understand the effects of these two factors on release. Long-term evolutionof the HRS should include considerationof detailed numerical geochemical transport/fatemodels currently under development. The advantage of eventually using transport/fatemodels in theHRS is the explicit inclusion of quantitative representation of specific processes and mechanisms responsible for the release, transport, transformation, and retention of hazardous compounds. The use of thesemodels entails with enlarged data requirements, but canyield less ambiguous, more detailed simulations appropriate for pathway calculations and, ultimately, exposure estimates. Considerable time and effort willbe required to integrate thesemore complex transport/fatemodels into the overall framework of theHRS and to test their performance,
Need for Additional Studies
The studies of large volume waste presented to theWork Group contained· little in theway of original investigation. Looking to future improvements in the HRS, OERR should plan thoroughly peerreviewed studies, both to review large volume waste sites ranked under theHRS and to examine basic parameters in themodel. Astud7of the first typewas suggested by Mr. R. Walline of EPA RegionVIII which could address the actual reasons why·release occurred at problemmining sites (reasons reportedly are different than those initiallyassumed). Astudy of the second type might address the characteristic(s) of mining was-te that control release (mobility) to ground water. Search for False Negatives and False Positives
Because it is difficult to designa systemthat caninall cases make the bestuse of allthe site-specific scientific information available,.. the Agency should consider the advantages ofutilizing additional scientific judgment outside of (or adjunct to) theHRS model inmaking decisions on whether to list sites on theNPL. Screening models like the HRS must be simple. They do not have mucb resolving power and therefore, some false positives and false negatives are inevitable. Because of this limitation, HRS scores should not be overemphasized. Aprocess should be established either to review sites subject to scoring or to reviewHRS scores inan attempt to spot false 

### • positives and negatives, Such a scientific review process could involve the use of additional models; inmany cases, however, obvious false**nega~ives** or positives might be besthandled by a "manual" J;eview. The importaut point is**th~t** the systembe flexible enough to allowfor a variety of approaches to be used, as needed, during the scientific review process.A3-l3 The extent of waste characterization data to be collected at the S I level is part of a cost/benefit calculation. The economic impact of being falsely included or not included on the NPL should be considered.
SUMMARY
Studies of the experience of applying the HRS to mining sites have not proved systematic error unique to such sites. However, the HRS has a potential to produce abnormally high scores for mining sites due to the manner inwhich toxicity, mass, release, and**transport/transfo~ation** processes are addressed.



### .·



### •

### ATTACHMENT A

The Superfund Hazard Ranking System (HRS): Applicability toMining Waste Sites, July 22, 1987, defines the issues for SAB considerationas follows:
1. "Does the series of TRC analyses indicate that the HRS is unfairly biased against mining waste sites (as compared to othertypes of po,tential Superfund sites)?
2. "Is there sufficient evidence that the existingHRS scoring/NPt listing process has been inadequatewith regard to mining sites evaluated to date (i.e., produced numerous false positives or false negatives)?
3. "Has it beendemonserated that the existingHRS is aninappropriate scoring system for determiningwhetherminingwaste sites should be 

### listed on the NPL (i.e., subjected to further investigations and analysis)? If so, what factors should EPA considermodifying to make the currentHRS more appropriate for mining sites?"



### .•



### •• ATTACHMENT B
The**Supe~fund** Hazard Ranking**Syst~w** (HRS): Feasibility ofUsing**Conc~ntratioa** Data in a Revised HRS, July 27, !987 defines the issues for SAB consideration as follows:

J, "Based on the information**pres~nted** and other data available, does it appear to be**desir~able** to include waste concentration data in**th~** HRS?
2. "What additional**t~chnical** and practical considerations ought to be factored into the decision as to whether or not waste concentration data should be included in the HRS? ), "Can the SAB suggest any systematic quantitative or**s~wi** quantitative methodology for deciding whether to include waste concentration data and for evaluating systems that do so in**th~** HRS that would consider effectiveness of the system at generating risk-based scores, the costa of data development, and potential improvements in decisionmaking?
4. "Which of the suggested new approachs (W2 or\o/3) appears to be more desireable?
5. "Can the SAB suggest any·changes in the structure of options \o/2 or W3 that would wake thew more desireable (e.g., changes in decision rules, parameter values)?
6. "What quality level of data on waste concentrations data quality (what types, amounts, and level of precision) should be required if such information is to be used in developing HRS scores? Is there a simple, robust way to specify data quality that could be easily applied by a wide range of field personnel at a wide variety of sites?
7. "With regard to alternative \o/3: --What general advice can be given regarding how to define rules for moving between tiers? How ·good· does waste concentration data need to be to allowita use?
--Does the approach taken to defining conversion factors • (particularly the assumption of 200 ppm typical waste concentration) appear to be reasonable? What alternatives could be suggested?
8. "What appr·oaches can be taken to mitigating risks to field personnel during waste sampling? Should data requirements be relaxed at sites where severe on-site health and safety hazards exist?"

### APPENDIX 4

COMMENTS ON EXPOSURE BY THE HAZARD RANKING SYSTEM REVIEW SUBCOMMITTEE
OF THE 

### SCIENCE ADVISORY BOARD

•

### TABLE OF CONTENTS

EXPOSURE Why is it ImportAnt to Address Actual and Potential Exposure Options for Assessing Exposure Relationship of Source Characteristics to Em·issions
How Comprehensive Should the HRS Be in Addressing Environmental Pathways and Routes of Exposure EnvironmentAl Pathways
Routes of Exposure
MEI and Population Risks
How Can the Revised HRS BetterAccount for Exposure, BothActual and Potential



### • PAGE

A4-l

A4-l
A4-2
A4-3

A4-3
A4-3
A4-3
A4-3



### .·A4-1 EXPOSURE Why is it Important to Address Actual and Potential Exposure Exposure occurs when there is contact betweenpollutants and receptors, Addressing exposure is important when there are toxic chemicals present because the determination of whether there is anyactual orpotential risk to health or the 'environment depends on bothexposure and toxicity Where there are no toxic substances orwhere there is no exposure to them, there is no risk. To the extent that the RRS is intended to assess relative risk, itmust address both toxicityand exposure sufficiently to determine risk, Where**infor~on** oneither toxicity orexposure is incomplete, risk cannot be fully assessed, Risk can be evaluated by assessing four factors: (a) the presence of chemicals, (b) their toxicity, (c) their potential for release and 1110b1l1ty, and (d) the probabilityof human and environmental contact. Options for AssessingExposure Ideally, a quantitative risk ranking,systemwould rely ondatafor all variables of the risk algorithm. Because it is not possible to obtainquantitative data for allthe necessary variables, semi-quantitative approaches must be considered. Surrogates for quantitative values may be developed through several**mea~.** They include identifying the appropriate measure of central tendency for theknown data values, modeling values from the few known data points for the site of, concern orfor comparable sites, ·using indirect measures (such as total waste volume as a substitute for concentration), or simply applying points in the algorithmbased on a subjective'evaluation of the available descriptive information for the site. An example of

## atiered approach for the use of waste quantity information is discussed inAppendix 3. Asimilar strategycould be developed which uses measured values inpreference to indirect estimat:es.· for a variable of exposure, When the ideal dataare not available, however, options to estimate the parameter can be used in s tiered process that moves away from actual measures toward increasinglyindirectmeasures, In this manner, ·themaximum value of the data is retained while the goal of evaluating a variable is met. Exposure should be assessed in a manner that is both chemical-specific and pathway-specific as noted inAppendix 2. The potential for release and mobilityis related not only to the chemical of concernbut also to 

### • the environmental media throughwhich it must travel before exposure can occur. Without this specificity, any attempt to address exposure is likely to result ininaccurate estimates of risk.
The most attractive option is to determine the presence of individual chemicals of known toxicityand then assess their potential for release, mobility, and contact withhumans and environmental receptors. Much could be gained by addinga chemical-specific exposure score that couldA4-2 be combined with chemical-specific**to~icity** scores to determine which chemicals dominate the risk at a single site and how the risk might compare across sites that are otherwise similar (e.g. in population distribution, existence of valued environmental resources, hydrogeology, meteorology, and containment), While little is**kno~** about the amounts of chemicals present and their concentrations in environmental media after only a site inspection, the insights to be gained from a chemicaland site-specific approach are so great that it should not be lightly dismissed, Relationship of Source Characteristics to Emissions
The HRS has been limited by not taking into account the potential for mobility of specific chemicals through specific pathways. Clearly, detailed estimates of pollutant emissions by pathway are not feasible with the information and resources available for scoring a typical candidate site with the HRS, (Here emissions should be taken to mean pollutant discharges generally, not just those to the air,) Given some minimal information about a siteand its chemical inventory,**howeve~,** it may be possible to make crude estimates of partitioning among environmental media and, therefore, of emissions by route which could be used to generate part of a chemical-specific exposure score. Informationneeded to derive-such estimates includes:
j, An estimate of the total mass or source concentration of important chemicals at the site.
2. Adescription of the site-specific factors influencing release, e.g.; impoundment vs, landfill. J, Partition factors applicable to the chemical, e,g,, Henry·s law·· constant and organic carbon partition coefficient,
Some characterizationof the potential for migration also allows better consideration of time as

## afactor in site management, Achemical that quickly moves off-site through air or surface watermay pose high risks to surrounding populations in the short-term, especially if it acts as a threshold toxicant, whereas an immobile (but persistent) chemical will remaina potential hazard for long periods, especially if it is a non-threshold toxicant, e.g,, a carcinogen. Estimates of the 

### • total mass deposited and the emission rates would permit an estimate of thesite•s "lifetime" if not remediated, Such estimates might provide a b,etter appreciation of the urgency for remedial actions·,
How Comprehensive Should the HRS Be in Addressing Environmental Pathways and Routes of Exposure?
Both toxicity and potential for exposure depend on environmental and biologic processes. An evaluation of environmental pathways addressesA4-3 

### the environmentalparameters that affect riskand an assessment of routes of entryprovides the informationneeded to estimate risk to**hu~ans** 

### and and theenvironment.**Environ~ental** 

### Pathways. Environmental pathways include air, water (bothground and surfacewaters), soiland**inter~ediate co~part~ents** 

### such as plants and animals thatbecome part of the human food chain. The potential for release and mobilityof chemicals throughthese pathways affects riskestimates. Factors to considerincludevapor pressure, time of transport from point of originto populations at risk, chemical transformations that may occurduring that**ti~e,** 

### and the toxicity of the chemicals that are expected at the point of exposure. Chemicals behave differentlyindifferent environmental pathways, so allpathways need to be evaluatedfully to estimate risk.
Routes ofExposure. Routes of exposure (entry) occurby ingestion (throughwater, food and soil), inhalation (throughairandwater vapors), and direct contact (throughwater and soil). Biological processes such as metabolismand pharmacokinetics affect thedose delivered to tissues thatmay experience adverse effects-. Biologicaluptake, deliveryto tissues and transformation of chemicals tomore toxic chemicalswithin the body areaspectsof risk that cannot be directly assessed inthe HRS. As.a result, whereroute-specific toxicityinformationexists, the toxicityand biological impact o!chemicals need to 

### be estimated by route ofentryand incorporated into the toxicity**fa~tor** 

### of thealgorithm. Without a syntheses of these**route-specifi~** 

### evaluations, risk**~Y**

### be eitherincorrectlyestimated orunder-estimated.
MEI and PopulationRisks. SARA Section 105(a)(8)(A) states that theHRS should take into account "thepopulationat risk." The Maximally Exposed Individual (MEI) isnot considered inCERCLA orSARA. While population risks**al~ays** 

### come into.playdue to the impact ofcollective .• 

### individual risks, so!De "mini!Dal" individual risks (such as birthdefects) associatedwith the ME! approachhave**~jor** 

### lifelongimpact. Furthermore, theMEI is a verywidelyused.measure of risk. The currentHRS addresses MEI in consideringdistance tonearest well and populationrisks inconsidering air target distance.
How can therevisedHRS betteraccount for exposure, bothactualand potential? 

### • Exposure requires contact betweenpersonand pollutantwithrisk focused on this point ofcontact. Sources; transportand fate; and the presence, nature,and activities of receptors are relevant to exposure. Measurement ofexposure**~ay** 

### be person-based or community-based.

### A4-4
The**cu~~ent** HRS finesses the assessment of**exposu~e** and instead uses the**p~obability** of release (and other factors such as persistence, waste quantity, distance to nearest well and population affected) as proxies for exposure. The main difficulty of accounting for direct exposure stems from the need to consider potential as well as actual exposure. There ate two aspects of exposure to be considered here--the concentration of contaminents in the environment around the site and the number of people around the site. Actual release may be demonstrated by environmental sampling. Potential release may be addressed by considering properties of the site and chemicals present such as distance to ground water and volatility. Similarly, the number of people (receptors) present and actually exposed today can be counted, while the number of people potentially present at the location in the future can onlybe estimated from studies of population dynamics.
While estimates of person-based exposures canbe developed from biological samples, from personal household samples,**f~om** self-reported exposures, and from self reported symptoms, each approach has its limitations. As a practical matter, biological samples are rarely available. The cost of personal or household samples are prohibitive and would allowonly limited opportunities to evaluate potential ambient exposur.,s. Because subjectivity c·an easily enter into self-reported exposures, objective measurements need to be used to limit the subjective variability. Subjectivity also enters into reports of symptoms (whether self-reported or based on medical record studies) which serve as a proxy for exposure. Nevertheless, the reporting (by nearby residents) of physical symptoms consistent with acute effects of contamination from the site could be considered as evidence of possible, but not confirmed releases, This is one of the situations which could be addressed by the .• assignment of discretionary points to the HRS score. (see Appendix 5) Community-based exposures can be developed from ambient pathway measurements, from sitemeasurements, or from modeled exposures. Numerous assumptions about targets (such as animals or humans) and their behavior are needed to impute exposure from ambient pathway measurements. However, even more assumptions are needed to impute exposure from site measurements (see also source**characteri~ation** discussion above) because the monitors are placed further from the potentially exposed population requiring • additional assumptions about the time and mobility factors that operate between the source and target population. Even more assumptions are required to model exposure from similar sites because no two sites are exactly the same•. Modeled exposures may be based on similar sites and can be used to predict rare events. The latter two approaches (site measurements and modeling) are discussed further below.

### A4-S
The way the current HRS addresses source characterization--including both the evaluation of the mobility and fate of chemicals and the consideration of concentrationorquantity of**chemical~s** insufficient to model exposure. Incorporating concentration and mobility could produce a more comprehensive ranking scheme. One way to do this is by using concentration as aweighting factor for thewaste quantity. The resulting effectivewaste quantities for low quantities of highconcentrationwastemight be similar to those for large quantities of low concentrationwastes. Similarly, the scores for toxicity/ persistence and for effectivewaste quantity couldbe adjusted by considerations of mobility.
From a scientific standpoint, exposuremay be modeled by imputing anexposure for a site based on what is known of similarbut more fully studied sites. If there are sufficient data on the actual exposures from sites with similar characteristics a potential exposure for the specific site could be imputed, but it ismore difficult to define sites which are comparable in this context than.to define sites which are comparable in terms of quantity and concentration, For exposure, the sites have to be comparable in geology (especially inmineralogy) as well•

•

### APPENDIX 5

COMMENTS ONTHE ALGORITHM BY THE



### HAZARD RANKING SYSTEM REVIEW SUBCOMMITTEE

OF 

### THE

SCIENCE ADVISORY BOARD



### .­



### •TABLE OF CONTENTS
PAGE ALGORITHM 

### AS-1 Background AS-1 Why is it Important to Pay Attention to the 

### AS-1 overall Alogrithw?
Can the Revised HRS Represent Relative Risk? Or 

### AS-2 Can it Only Serve as an "On-Off" Switch? What do These Choices Mean? What Methods are Available to Develop a Ranked List? 

### AS-4
What Rules Should be Used to Develop Scores Based on AS-5 on Risk? Aggregation of Pathway Scores AS-7
How Can the HRS Make Better Use of Temporal Analysis? 

### AS-8
What can Be Done About the Quality of the DataUsed in AS-8 the HRS? What Can Be Done When There Isn't "Enough Data" For AS-9 The HRS?
What Should Be Done When Data Are Available That Exceed AS-10 What Is Needed For The HRS?
Caveat AS-11



### •AS-! 

### ALGORITHM Background TheHazard Ranking Systemoperates through the following three steps: !. 

### To the extent,possible, specified informationregarding the ·properties of the siteand of the chemicals deposited there is gathered and described quantitativelyorqualitatively according to the needs of theHRS. 2. The informationismanipulated, usuallythrough comparison to categories intables provided in theHRS manual, to yield a series of factor scores. The specifications of the conversionfrom raw informationto factor scoresmay be called scoringrules.
J, 

### The individual factor scores are combined withincategories and then the category scores arefurther combined toyield route scores and eventually an overallmigrationscore for the site. The specifications of how the scores are to be combined may be called combining rules. Together the scoring rules attd the combining rules form the overall logic and procedure, oralgorithm, for the operationof theHRS. To a substantial extent, the methods for gatheringthe raw data·(step l above) and decidinghow much effort shouldbe expended on that stepareleft to the individuals doing the scoring. The algorithm, however, is a fixed procedure that undergoes OERR sponsored qualitycontrol. As such, it is thekey to how well theHRS will performinassessingrelative risk. Both the relationshipof the rsw data to the factor scores and theways inwhich the factor scores are combined must be treated carefullyand 

### .· consistentlyto optimize the performance of theHRS. Why is 

### it important topayattention to the overallalgorithm? Improving the algorithmcouldpotentiallydo more to improve the HRS thanfine-tuningindividual components. Thealgorithm shouldbe approached by thinkingabout the bestway • 

### to assess 

### risks for·a hazardous waste sitewithout regard to the availability of site-specific informationand then simplifyingthe rules (but not the logic) as needed to take into account real-world constraints --that is, to.identifythemost important variables and thendevelopdata (orsurrogates) and combining ruleS". The overallalgorithmneeds to meet the intendedpurposes of the HRS as stated by SARA. SARA requires EPA tomodify theHRS so that, ''toA5-2 the**ma~imum e~tent**  feasible, it**accu~ately** assess the**~elati~e deg~ee**  of <isk to human health and the**envi~onment** posed by sites and facilities under**re~iew,"** In Mt", Longest's June 15, 1987 memorandUlD (see Appendix 7 for full text) he states, "OERR believes that the purpose of the HRS is primarily a screening tool used to determine which sites will be candidates**fo~** Fund-financed remedial**~esponse,** To the degree possible, the model also needs to provide a**st~atification** of sites based on the relative risks posed to human health and the**envi~onment."** It is not clear that the**cur~ent** system**st~atifies** by risk, nor that it can serve as a successful on-off**sc~een** without**st~atifying** by**~isk** at least in the region of the cut-off score. At aminimum the HRS must discriminate sites into two risk groups--on or off the NPL. Ideally, the HRS would individually rank all sites based on accurate ascertainments of risk--resulting in as many**~elati~e** risk ranks as there are sites to be ranked, While the binary ranking is minimally sufficient, it is apparent that programmatic concerns**de~nd** a ranking that is more than binary. The decision about the level of**~ankirig** was not within the scope of the Subcommittee-s review, instead the Subcommittee focused on developing conclusions and recommendations for the scientific bases of an effective ranking system. The Subcommittee**p~oceeded** to evaluate the various components and structure of the algoritha to**wo~k** toward a scientificallyvalid approach to estimating risk.
One such component relating to risk is the toxicity score, The additive structure of the matrix weights the lower end of the two components (toxicity and persistence) and thus implies that any toxic effect**o~ p~rsistence**  ismore important than the probability or severity of the effect or the degree of persistence. These baseline assumptions have the effect of treating toxicity and persistence in a binary manner, but this method of assessment may not be sufficient to meet the goals of the HRS and the Subcommitteedid not find it to be an acceptable approach if the HRS outcome is expected to be more than binary. In addition--and as**e~idenced** by the very high percentages of sites receiving the maximum score for toxicity and persistence--the inability of the current toxicity module to rank substances effectively on relative risk puts a severe limitation on the entireHRS to discriminate between sites on the NPL and**the~eby** to prioritize appropriatelyon the bases of public health and environmental protection concerns. The scoring methodology needs to be re-evaluated in terms of the overall purposes of the HRS• 

### • Can the revised HRS represent relative risk? Or can it only serve as an "on-off" switch? What do these choices mean?
The Subcommlt.tee has suggested changes that will allow the HRS to provide a more accurate and scientifically based estimate of the**~elative** risk of candidate sites. To the extent possible, the HRS scores should

### AS-3 correspond to an objective evaluationof relative riskat sites. E:owever, this is not always feasible due to both scientific and data limitations, as well as the value and policy decisions implicit when consideringand balancing human health and environmental impacts.
While recognizing that the Agencymust continue tobase NPL listing decisions onmany factors in addition to the HRS, the Subcommittee believes that a revised HRS, better designed to evaluate sites by relative risk, will provide an improved mechanism for determining which sites should be included on the NPL, and can potentiallyprovide meaningful input to the subsequent assessment of NPL.sites. Most of the changes needed to revise the HRS are changes in the overall algorithmand not changes with vast new data requirements, (Pages AS-5 throughAS-8 discussdesirable changes in the algor!thm.)
If the HRS is to be used to set priorities based on relative degree of risk, many factors need to be considered systematicallyinsetting priorities. Although it is possible to talk about anon-off switch and evaluate theHRS by whether it rates most sites onwhen theyshouldbe "on" and vice-versa, in fact there is a continuous range of scores with anarbitrary cut-off level designed simply to.get400+ sites on the original list. Unless the list is in reasonably good orderboth above and below the cutoff, its fidelity indistinguishinghigh and lesser risk sites will depend markedly on the choice of the cutoff, i.e., onhow many sites (or what percent of sites) are wanted on the list.
There are costs associated withmisclassification. If the HRS will be used to decide whether ornot to spend $850,000onan RI/FS, the economic cost of a false positive is 

### approximately$850,000to the fund .• (although less to society because eventhe low-risk sitemight need remediation and would benefit from the RI/FS). The social cost of a false positive may be reflected indecreased propertyvalues, increased physical stress.and community·.concern, and inextensive time and effort expended by publicand private officials attempting to address these concerns. The social cost of a false negative is the difference in average riskbetweenthe sites that shouldbe onand those that should not, less anybenefit of attention,independent of Superfund. Unfortunately, the average risk of Superfund sites is not known, let alone the riskof 

### • those thatwere scored but whichdid not make the NPL.
The difficulty remains that therehas beenno analysis to determine wnether the current HRS score is a good predictorof the riskultimately generated by the formal risk assessment process conducted during the RI/FS phase. This evaluationneeds eo be done as a guide to future modifications of theHRS.• A5-4 The question remains, "tisk of what and to whom?" To create a risk-based RRS that evaluates sites, EPA would first need to reach an acceptable definition of risk which combines the health, ecological, and economic damages expected over the life of the facility. The Subcommittee favor multiple measures including a human population risk measure, The latter is especially important because quantitative techniques are available to assess it, Some subjective increases or decreases in score could be used to account for severity of human health effects and likelihood of effects on non-human biota,
What methods are available to develop a ranked list?
There are three common methods for developing ranked lists,
One way is to devise a highly simplified mathematical model that produces a number that is approximately proportional to the true ranking variable--in this case, some agreed-upon definition of risk. (Actually, all that is required is that the number increase monotonically with risk,) The system referred to as "RAPS" is such a model. Although simplified modeling has the advantage of being related to risk, it has the disadvantage of being a very substantial departure from the current HRS. RAPS is probably too complex·to work well with the limited data available formost HRS candidate sites, even though it has worked well for DOE sites.
Anothermethod is to devise a series of screens that successively divide the list of all sites into categories, which are later ordered in some fashion that is approximately the same order as risk.
The third major technique, often simplyreferred to as "scoring", is structured value analysis, of which the current HRS is an example. Although the other two approaches have their virtues, it is reasonable to concentrate on variationa .of the structured value approach because the current HRS uses it, Even here, two different approaches are possible.
The curren't HRS appears to take a so-called "empirical" approach. That is, a superficially plausible set of rules was developed and then modified "empirically" to match a subjectively ranked test set of sites. If the subjective ranking was truly what the HRS was supposed to achieve, and if the test setwas adequately representative of all sites to be scored, then this method is perfectly satisfactory• The other approach, a risk assessment approach, is to beginwith a clear understanding of how to rank the list quantitatively if all the needed informationand resources to process it were available. Then the risk assessment. is simplified until it is obvious how to transform it into a scoring system. The scoring system is further simplified until it can operate at a reasonable cost on the often very sparse informationA5-5 

### available. Forexample, the populationriskat a sitemight be represented by the sumoverallroutes of risk by route, and eachroute-specific riskmight be represented by ,the sum of all chemical-specificrisks by route. Each chemical-specific riskmightbe represented by anintegral overpopulation at riskof the product of toxic potencyand timeintegrated exposure. 

### What rules shouldbe used todevelop scores based on risk? First of all, internal consistencyis important. Making rules that are consistent requires little up-front investment and no additional costs inthe scoring of specific sites. These changes may be muchmore cost-effective thanadditional data collection. The way that the various pieces/components of the scorecompile should reflect how their real world counterparts interrelate. The approach for accomplishing this is to beginwitha physically-basedexposure assessment model for each exposure pathway, structured properlyto trans!ate expected orpotential releases intoenvironmental concentrations and subsequent exposures and effects. Thesemodels would, of necessity, be highly simplified for a screeningassessment. Even a simplifiedexposure assessment model may not be feasib·le giventhe time, resource and data limitations associatedwith theHRS process. Still, themanner inwhich the pathway scores are estimatedand combined shouldbe consistentwith the fundamental material balanceand exposure principles of suchan underlyingmodel. The following pointsdiscuss how this canbe accomplished in the**~ontext** 

### of the structuredvalue approachused inthecurrentHRS system. 

### !na scoring systemdesigned to reflect relative risk, the scores**~auld** 

### be added across routes and chemicals, witheach scorebeinga**produ~t** 

### of scores representing population, toxic potencyand exposure
.. potential. To work properly, the scores for these three factors would have to be 

### approximately proportional to the estimated values of the factors. For populationand potency theanswerwould be relatively easy, but the exposure scorewould probablyneed to be 

### constructed from scores representingvarious factors related to exposure, suchasmass of chemical deposited, containment efficacy, mobility, and persistence. Exactlyhow this isdone isnot as important as that the rules for sc6ringfactors are·consis

### tentwith the rules for combining scores, and 

### • that bothare reasonablyconsistent with how the factor enters the risk equationin a riskassessment. In**~ontrast,**

### .the rules for combining scores inthe currentHRS do not always reflect,relative risk. Scores oftenriseas the logarithmof the factor value being scored. Forexample, each order-of-magnitude increase in potencymay receive an additional point, andeachfactor**~f** 

### two or two-and-a-half increase,inpopulationat riskmay receivean 'AS-6 additional point. Using logarithmic scores is an appropriate way to account for a wide variation inmagnitude of the possible values for factor score9; furthermore, logarithmic scores can be added to simulate multiplication of the underlying factors. For example, when the HRS assesses a site with carcinogens, the population at risk can be estimated by multiplying the size of the population at risk by the risk per individual which can be estimated as the product of the exposure of each individual by the potency of the carcinogen. The combining rule should add the logarithmic scores corresponding to the three factors. In the case cited, however, the logarithms are to different bases; potency is scored by a logarithm to the base !0, but population is scored approximately to the base 2.3. Because (2.3)3 is approximately equal to 10, it takes 3 populationpoints to be equivalent to 1 potency point, and the potency scores must be multiplied by 3 (or population scores divided by 3) before they are added. In this case, the HRS "weighting factor" of 3 is exactly what is called for by the existing science. It is a natural**outco~e** of the simplification process and r10t a subjective "weight". In theHRS, the weights do not always conform to the science, and the**co~bining** rules are not always consistent with the scoring rules orwith one another.
The use of a scoring system to place sites on the NPL is certainly appropriate and, as scoring systems for priority setting go, the HRS is already better thanmost. Almost all of the factors scored are plausibly related to risk and generally or1e point means the same in different parts of each scale, usually a change of sn order-of-magnitude or a constant factor. However, the current HRS is not always internally consistent in the number of points which relate to a change in risk. For example: !) Asingle point does r10t have the same**mathe~atical** relationship to the final score in one part· of the algorithmas a single .• point has in another. This variation in scoring implies different assumptions about how the factors relate to risk. 2) Subjectiveweighting factors are included. For example, the route scores are combined by a route mean square rule so that when one routedominates, it alone is enough to place a site above the cut-off. (However, at many sites, the rislt through one routewill usually dominate the other two. Whether or not such weights should be used is debatable• • However, if weighting is used, it should be explicit.) 3) The rules for combining some scoJ:"eS in the curr.ent HRS do not rel.at.e properly to the observed behavior of those factors. For example, consider the way in which the total waste characteristics score is derived from its components. It is the sum of the component scores for quantity and toxicity/ persistence (toxicity and react·ivity for the sir route).A.S-7 

### Technically speaking, a sitewithmuch harmless material could be eligible for the NPL if it receives the**ma~imum** 

### scores for observed release/route characteristics containment, quantity, and targets.. 

### This is an extreme case, However, the combinationof summation and multiplication in the algorithmhas problems beyond this ratherartificial example. Auseful interpretationof the current HRS would be that since both toxicity/persistenceand quantity scores appear to be logarithmic, summing themwould be correct for assessing the totalwaste characteristic score on the logarithmic scale. However, the same interpretationdoes not hold for other pares of the algorithm. Forexample, the component scores for observed release/route characteristics-containment, totalwaste quantity characteristics, and targets --aremultiplied. If the same logarithmic interpretationis to be applied to these components, then all those multiplications should be changed to summations. Otherwise, the summation in the waste characteristics score should

### be changed to multiplication. The underlying question iswhether the entire score should be interpreted on the logarithmicscale.
For another important component, observed release/route characteristics. containment, the scale used for scoring appears to be the probabilityof release instead of its logarithm.

­ there are two important concepts here. First, theway the scores are combined should reflect theway those components relate to oneanother in the real world. Secondly, the final HRS score shouldbe on some kind of easily understood scale**(arith~etic,** 

### probability, logarithmic, etc.) so that the relative risks presented by various sites canbe easily understood.**"Normali~ing"** 

### scores among routes onlymakes senseif one believes that 100 points implies the same risk through each route. On the otherhsnd, there is no easily implementedway of interpreting



# .. any of the scores and the equalityassumption is not disprovable. Aggregation of Pathway Scores
Avariety of methods can

### be used to aggregate pathway-specific scores. If sufficient structural informationon the pathways scores is available, such information shouldbe used inchoosing the aggregation method. Forexample, if the pathway scores are constructedonthe logarithmic scale, the exponential averaging method shouldbe used. lf • 

### the pathwayscores are constructed on the arithmetic scale, the linear averagingmethod should

### be used. The quadratic averaging method used in the current H'RS is 

### not onlyarbitrarybut,'from a scientific viewpoint, arguablyincorrect. OPPE reported that its unpublished SiteRanking Panel studycompared three different aggregation rules: linearaveraging, quadratic averaging, and cubic averaging. 

### The results (within the limitations of the study) indicatedthat the panel's final rankingwas closest to cubic averaging.A5-8
In the absence of sufficient structural information on the**path~ay** scores, the choice of the aggregation method reflects the subjective judgment on the relative importance of single- and**multiple-path~ay** sites. An important class of aggregation rules is the k-th**po~er** averaging method in which the score for each pathway is raised to the power k, calculating the average across pathways, and then taking the k-th root, The linear averaging method is k**~** I and**k~2** is the quadratic averaging method. Large values of k give less prominence to the**path~ays** with lower scores, making it easier for**single-path~ay** sites to get on the NPL. Small values of k give more prominence to pathways**~ith** lower scores, making it easier for multi-pathway sites to get on the NPL.
There are two other important aggregation rules. The worst case method takes the worst of the**path~ay** scores, The**e~ponential** averaging method**e~ponentiates** the pathway scores, takes the average across the pathways, then takes the log, The two methods should yield very similar results, giving little prominence to pathways with**l~er** scores and making it easier for single-pathway sites to get on the NPL. Both methods can be viewed as generalizations of the k-th power averaging method with k approaching infinity.
How can the HRS make better use of temporal analysis? Analyzing how long it takes eo analyze a site through the various steps**bet~een** identification and remediation yields informationwhich has implications for parts of the HRS-especially the toxicity/persistence score and in considering population dynamics, If, for example (and this currently seems to be the rule rather than the exception), the site remains unremediated for a long period of time, then chronic effects become more important than acute and the HRS should address them, (See**Appendi~** 2 for a discussion of acute and chronic effects at unremediated sites.) By analyzing information about the source and migration (and also anything else that would remove wastes from the site, such as decomposition), it is possible to estimate the length of time a sitemay present a problem. Such an estimate has implications for remediation. Similarly demographic and other relevant changes which may be predicted over time could alter the nature and degree of risk posed by a site, Because such factors alter risk, the revised HRS should not ignore them• 

### • What can be done about the quality of the data used in the HRS?
Amajor effort·should be made to improve the overall quality of analytical data collected at sites. Standardized collection and laboratory methods currently exist for only a small fraction of substances potentiallyA5-9 

### present. Expanded chemical characterization of all media, coupled with a strong laboratorycertificationprogram, will improve not only theHRS but all aspects of the Superfund process. Similarly, acceptable data collectionprocedures should be established (or expanded upon) for non-analytical data (such as populationestimates, volume of

..wastes, etc.) so that the best quality datawill be 

### preferred. Mechanisms which could be used to encourage the collectionand use of quality data include: a tiered data quality approach such as the one OERR presented to the LargeVolume Waste Work Group, data collection "trees", and the weighting of final HRS scores to account for the quality of data used in generating it. What canbe done when there isn•t "enoughdata" for thel!RS?
It is necessary to have a method ofdefault (also termed missing value replacement values) when data are limitedornonexistent for chemicals. Lackingcompleteinformationon chemical inventoryand concentration at a sitemay well be the rule rather than the exception. Therefore, a standardized approach to the circumstancewill reduce the inconsistencies that are inevitable**~f** 

### suchdecisions are left to field staff or if only the "better" dataare somehow selected andused.
several approaches can be 

### used for assigning a value to a scoring component when data arenot available. One way is to assign a zero. This would be·a mistake. However, because itunderestimates risk. (However, on a logarithmic scale, assigning a zeromay, in fact, overestimate risk, If 

### the'risk should be very small, the logarithmic score should be 

### appropriatelynegative--evenminus infinity, if the riskis zero arithmetically.)



### .· From a scientific perspective, a betterway is touse auxiliary informationon the site to help impute themissing value.

one concernwith this approach iswhether the fact that the data aremissing might be an indication that the sitemight be different fromotherwise comparable sites,
The definition of comparable sites is crucial and may depend on the scoring component. Forquan.tity and concentration, gross categories of 

### • sites couldbeused (as a minimum), Stratificationby region is also possible, leading to a definition of comparable sites such as those of thesame categoryin the same geographic region. When possible, comparable sites shouldbe defined to allow the use of thegreatest amount of data.
There are two general statistical approaches for defining comparability in this situation. First, one candevelop a metric tomeasurehow comparable two sites are intenus of the auxilliaryc,harscteristics, then choose aA5-IO prespecified number of sites closest to the specific site in terms of the givenmetric. Second, one can use an empirical model to describe how the scoring component depends on the**au~illiary** characteristics, then use the prediction from the model to impute the missing value for the specific site.Incorporation of a large number of auxilliary characteristics is not a trivial task. It might not be worth the effort to go beyond the use of broad site categories and regions. The decision depends onwhether other characteristics could be powerful predictors of the scoring component being considered.
In some situations, limited data about the sitewill exist. Averaging those data is an easy measure of central tendency likely to represent the site better than any of the individual numbers. For example, if a few concentration measurements are available, even if variable and of uncertain quality, their average can be taken to show relative quantity in the absence of better infonnation. Alternatively, some sense of proportion can be gleaned from the types of wastes known to have been deposited at a site. For example, relatively low concentrations (compared with average wastematerials) of all hazardous chemicals are expected in fly ash, but metals and products of·incomplete combustion (dioxins and furans) would be more likely present than volatile organics.
Another approach may be used**~hen** some data is available. It is known to statisticians as the shrinkage formula and to the actuarial literature as the credibilitymethod, This approach uses data both from the site and from sites thought to·be comparable. The Subcommittee 1s not in a posftion to evaluate how difficult the field staff would find implementation of this approach,
What should be done when data are available that exceed what is needed for the HRS ?

one approach 1s the assignment of discretionary points (which the Subcorumittee has sometimes called the "Bump Factor"), The Subcolllmittee discussed severs! scenarios where such discretionary points could be usefully assigned such as in the case of a site where:
1. Many chemicals were identified (only some of which were data available for evaluating toxicity but where the presence of • other implied additional risk)• 2. The presence of the toxic materials in the surrounding target populationhad been demonstrated.
3. Acute exposures to air emissions were possible from catastrophic release or other changes in site conditions,

### AS-11
4. One ormore contaminants were known to be extremely toxic to indigenous natural populations.

S. Human effects had been confirmed and those effects could be reasonably linked to exposure to particular chemicals from the site.
6. Nuisance levels of chemicals in the air around the sitewere identified of and their presence confirmed (best analytically, but possibly by smell). This approach could also be used to take better account of non-human receptors. The idea is to assign extra points which are proportional to the extra risk the situation presents. Caveat
If the algorithm is changed, then the 28.5 cut-off score shouldbe re-evaluated. The threshold Sm, which determines whether a site is eligible for the NPL, needs to be adjusted wheneither the algorithmis changed or when more routes are incorporatedbecause the same score will not necessarilyhave the same meaning. For routes already used in the HRS, OERR should investigate from existing data what alternative threshold should be used in order to yield a pre-specified proportion of sites on the NPL, if the algorithm is changed•



## •

### APPENDIX 6

RECOMMENDATIONS TO EVALUATE AND IMPROVE THE HRS

B'l 

### THE



### HAZARD RANKING SYSTEMREVIEW SUBCOMMITTEE

OF 

### THE

SCIENCE ADVISORY BOARD



### .·

•• A6-I RECOMMENDATIONS TO EVALUATE AND IMPROVE THE HRS
How Good Is the HRS?
The HRS is appropriate for the purpose for which it is intended, As a scoring systems for priority setting, it is better than most, The factors scored (with possibly one or two exceptions) are related to risk, and higher scores for them reflect higher risks, Thus, the current HRS is plausible. The recommendations concerning the algorithm discussed in Appendix 5 should greatly improve it,
HOW CAN EPA LEARN FROM EXPERIENCE TO BETTER PREPARE FOR THE NEXT REVISIONS?
OPPE Study, In considering the HRS as a predictor for a comprehensive risk assessment, it is natural to clarify how well it performed in the past. The unpublished OPPE Site Ranking Panel study (18, 23) did not address this question but focused entirely on subjective evaluation, For parts of the HRS (route characteristics and containment), additional data are available, It should be possible to conduct an empirical evaluation using RI/FS and/or other data to evaluate the HRS score both for sites on the NPL and for those that did not score high enough for the NPL. Empirical Evaluation. The HRS performance should be judged by an empirical retrospective evaluation of how successfully the HRS predicts risk or by how successfully its components predict phenomena (such as release) which contribute to risk. This evaluation should be based on an in-depth technical review. Whatever the definition of risk, the HRS should be judged on how well it approximates that definition, not on how well it matches some subjective notion of the relative importance of the sites in a test set, With respect to empirical evaluations, the route characteristics and containment scores are estimates for the probablity of release when actual release is not detected. Two distinct probabilities need to be considered: (a) the probability that current releases are not detected, and (b) the probability that such releases will occur in the future. For the latter, the time horizon also needs to be considered. For the sites with sufficient RI/FS and/or data from studies by the states or other**parti~s,** it should be possible to search for the best way to predict release from the components of route characteristics and containment scores,A6-2 Comparisonof Data and Scores for the Same Site, Given the screening nature of 

### theHRS, as a screening tool, it does not appear cost-effective to attempt to establishconfidence intervals rigorously, However, some sefinition of uncertaintywould be useful for interpreting the scores, If re-evaluations are available for some available for some sites, it would be useful to compare the data obtained from the separate inspections of the site, State data, frequently used inHRS scoring, might also be used for this purpose. What Kinds of Data Should the Agency Collect and What Kinds of Studies Should it Conduct to Support Future HRS Revisions?
There are two goals for such studies. First, the Agency should improve the algorithm to be defended as risk-related and, second, the studies should develop at least a crude way to estimate thequantity of specific chemicals present. The planning of anyevaluative studies should be carefullypeer-reviewed before being implemented.
As mentioned in the Other Comments portion of Appendix 3, EPA also should develop studies to review large volume waste sites ranked under the model and to examine basic parameters of the model. Astudyinthe first category suggested by Mr. R. Walline of EPA RegionVIII could address the actual reasons why release occurred at problemmining sites (reasons reportedly are different**~han** those initiallyassumed) and a study in the second categorymight address the character1st1c(s) of miningw,aste that control release (mobility) to'ground water.



### .•

•

### APPENDIX 7
REQUESTS

FROMTHE

OFFICE OF EMERGENCY AND REMEDIAL RESPONSE (SUPERFUND) TO THE SCIENCE ADVISORY BOARD



# ..

•.-\7-1

UNITEDSTATESENVIRONMENTALPROTECTIONAGENCY WASHINGTON, D.C. Z0460 

## DEC 9

# 191!6

QFIOIC5OF SOLJO**'f'¥AST~ ~NO**  .!i:Mt:ACE:NCv**;;~£S,..nl\iS~** MEMORANDUM


### SUBJECT: Science Advisory Board Review of Hazard Ranking System

## i/,~ FROM: 

### Henry L 

### t,ongest tr, Director Office of Emergency and Remedi

### ~**s~onse** TO: Dr. Terry Yosie, Director Science Advisory Board

The Office of Emergency and Remedial Response (OERR) is conducting a review and possible revision of the Hazard Ranking [ System (HRS). OERR is requestinq that the Science Advisory BoarG review several issues in conjunction with this effort.
BACKGROUND
The HRS is the principal mechanism**use~** 

### by EPA to**deter~ine** 

### whether to place**site~** 

### on the**~ational** 

### Priorities List (NPL), promulgated under Section 105 

### of the Comprehensive Environmental Response,**Compen<>~t**

### ion and t,iability Act of 1980 (CERCLA). The HRS was promulgated on July 16, 1982 (47 FR 31219), as Appendix A of the National Continoency Plan (NCP). The current HRS evaluates the relative potential of uncontrolled hazardous substances to cause human health or safety problems, or ecological or environmental damaqe, hy**ta~ino** 

### into account "pathways" to human or environmental exposure in terms of numerical scores. Those sites that score 28.50 or qreater on the HRS, and which are otherwise eligible, have been ptacerl on the NPt. A site must be on the NPL for it to be eligible for remedial action financed by 

### the CERCLA trust fund.
On October 17, 1986, CERCLA was amended. The Superfund 

### •**~endment~**

### and Reauthorization Act of 1986 (SARA) requires E?A to promulgate changes to the HRS 18 months after enactment. The**a~endments ~equire**  

### EPA to modify the HRS so that, "to the**maximu~** 

### extent feasible, it**accu~ately** 

### assesses the relative**deg~ee** 

### of**ris~** 

### to human health and the environment posed by 

### sites and facilities subject t0**~eview.•** 

### Specifically, the amendments require:

### -2­

0 

### An·assessment of the human health risks associated with contamination or potential contamination of surface waters, eitherdirectly or as a result of the run-offof any**ha~ardous** 

### subatance, pollutant or contaminant. This assessment should take into account the use of these waters for recreation and the potentialmigration of any**ha~ardous** 

### substance, pollutant or contaminant through surface water to**downstrea~** 

### sources of drinking water ·

0 

### An evaluation of the damage to natural resources which may affect the human food chain and which is associated with any release or threatened release

0 

### An assessment of the contamination orpotential contamination of the ambient air which is associat·ed with a release or threatened release Section 125 of SA.RA requires EPA in its revision of the HRS, to 

### specifically assess those wastes described in section 300l(b)(3)(A)(l) of the solid waste Oisposal Act. These wastes , include fly ash waste, hattom ash waste, slag waste and flue gas[ emission control**'"'ast~>** 

### .,enerated primarily from the combustion of coal or other fossil fuels.**T~e** 

### amendments require EPA to consider: (1)**~he** 

### quantity,**to~icitv,** 

### and concentrations of hazardous const ituen·ts which are present in such waste and a**ca~aarison** 

### with other wastes: (2)The extent**~E,** 

### and potential for, release of such hazardous crJnstituents into the environment: and (3)The degree of risk to human health and the environment posed by such constituents.**~** 

### Additionally, section 118 of the SARA states that ePA shall aive a 

### high priority to facilities where the**~elease** 

### of hazardous substances**a~** 

### ppllutants or contaminants has resulted in the closing of drinking water wells,**o~** 

### has contaminated a principal drinking water supply. In the amendments to cr::RCLA, Congress has stated its intention that the 

### aRS remain a screeninq tool to enable EPA to list sites on the NPL as expeditiously as possible, using data from the 

### • Preliminary Assessment (PA) and Site Inspection (SI). The legislative history nf SARA makes**cl~ar** 

### that Congress did not intend that the .revised HRS become a mechanism for making detailed risk assessments;**·~at~er,** 

### it was intended to he consistent with thelimited purpose of the**~PL--sc~eening** 

### sites that might, after further**~tudy, wa~rant**  

### Fund-financed remedial action. In order to**i01:J~?'I"' ~he**  

### <'lccuracy of the fiRS, the Agency is considering**e~pandinr ~~e**  

### data collection performed**befo~e** 

### a site is**p~oposed** 

### for the ·:

### >:., t?**o~ov**

### ide**dat.~** 

### to i"'olement a revise•i fiRS. To maxill'i

### ze t·,**~** 

### use oE

### these 1**i•~**

### ite<i re
..**ou~ces,** 

### EPA mustA7-3 

### -3­

target its data collection activities to those specific areas that would most increase the accuracy of the HRS. ISSUES FOR REVIEW Based on the public comments received during the rulemakings for the initial NCP (47 FR 31180, July 16, 1982), the original NPL (48 FR 40658, September 8, 1983), and the subsequent NPL updates, as well as the intent of Congress and program experience, OERR has begun a review and revision of the HRS. In conjunction with this review, OERR has analyzed the HRS and developed technical issue papers on selected aspects of the ranking scheme. Specific issues we would like the Science Advisory Board to review at this time include:

• 

### A review of the scientific factors in the existing HRS to recommend how these might be modified to enhance its effectiveness

. 

### • An evaluation of the way the HRS evaluates waste 

# • • ' characteristics, particularly as it relates to**~** 

### mining waste sites, a critique of several reports on mining waste issues, and a review of a technical paper explorinq the potential use of concentration data in the HRS• 

### • An examination of the toxicity ranking scheme employed in the existing HRS and OERR's suggestions for modifying this scheme.


### • An analysis of the distance used to determine the target population potentially affected by 

### .· the release of hazardous substances to the air. OERR will outline each specific issue more fully to better focus the Science Advisory Board's review in a memo accompanyina each report. Review of The Scientific Factors in the HRS
We would like the Science Advisory Board to review the • 

### current HRS and those specific factors that make up each scoring pathway. As part of this review, we are requesting that the Science Advisory Board rank the existing HRS factors in order of th.eir impor:-tancEI in accur:-ately assessing r:-isk from a release of hazardous substances. We would also like the Science Advisory Board to evaluate the appropriateness of the weighting factors currently used in the HRS and recommend how these might be modified to enhance the effectiveness of the HRS. The intent of this is'to help**)ER~** 

### focus our HRS revisions effort, as well as our expanded data "•'\l<'!ction activities.

### -4­



### In the existing HRS, the score for a facility is based on the potential for harm to humans or the environment from migration of a 

### hazardous substance from a facility by routes involving ground water, 

### surface water or air. It is a compositeof separate scores for each of the three routes. The score for each route is obtained by considering a set of factors that characterize the potential of the facility to cause harm. Each factor is assigned a numerical value (on a scale of 0 to 3, 

### 5or 8) 

### according to prescribed_guidelines. This value is then multiplied by a weighting factor yielding the factor score. Waste Characteristics/Mining Waste Issues In scoring a site using the current HRS, EPA considers the quantity of hazardous waste deposited, rather than the quantity of hazardous constituents within these wastes. EPA alsodoes not consider the quantity of hazardous constituents released into the ground water, surface water, or air, but onlywhether that release is significantly above background, When**EP~** 

### developed the**HRS~** 

### the Agency believed that ,1eterrnining the quantityof hazardous constituents would require a significant amount of sampling and 

## .j**analysi~** 

### that would result in substantial delays in the ranking t 

### of sites. In its various rulemakings on the NPL, EPA has received public comments on this aspect of the HRS and how it is used to evaluate mining waste sites, The comrnenterc. have stated that the HRS is biased against i'tiqh-volume, low-toxicity wastes, such as mining wastes, because it does not take into account quantity, toxicity and concentration of the hazardous constituents, and that EPA is unable to provide evidence that the HRS is a rational basis by which to ran.k mining sites forinclusion on the NPL.
.• 

### OERR would liKethe Rcience Advisory Board to evaluate the HRS in light of**the~R** 

### criticisms, and to reviewboth a technical paper on the HRS developed by TRC, Inc. F.or the mining industry, and a critique.of the TRC mininr;**re:_:~ort** 

### conducted byOERR's contractors. As part of this**~eview,** 

### we would like the Science Advisory Board to examine the validity of the mining industry's concerns and to rec.ornmend**ar~3s** 

### for revision of the HRS, if warranted, to address these concerns, keeping inmind the use of the RRS 

### aa a screeninq tool for further studies• 

### • In addition,**w~** 

### woul1 like the**Sci~nce** 

### Advisory Board to review a technical i'"'>er developed by OERR that el(plores the use·of concentration :lata i'l**~valuating** 

### hazardous waste sites. This review**shout~** 

### focufi O'l 

### the Eeasibility ?f including waste**concent~~tions** 

### in the**H~S,** 

### the data requirements and resource implications of**ir"pl~·,enti~-)** 

### such a chanqe, as welt as the**~eliability** 

### of**">ii"~Pllrq** 

### ·lata to accurately**det~rmine** 

### the quantity·of**haza~1:)""' '"'~-stituents**  

### contained in wastes.**--~7.**

### 5


### -5­

Air Target Distance Limit Currently, the air pathway of the HRS relies on analytical data that shows level<> of a contaminant at or in the vicinity of a facility that significantly exceed the background levels. The air pathway provides a score based on the toxicity of the substance released via the air route, and the population within a four-mile radius of the site. This Population is used as an indicator of the population which**~ay** 

### be harmed should a hazardous substance be released to the air.
OERR has**analy~ed** 

### the distance used to determine the tarqet population potentially affected by a release of hazardous substances to the air and prepared a technical report detailing its findings. The report presents conclusions on the qeneral level of cancer risk arising from uncontrolled waste sites and examines the implications of the analysis for the distance factor of the air pathway. The study used an EPA model called Human Exposure Model (HEM) to make these estimates. · We would 1ike the Science Advisory Board to evaluate the 

# f target distance**li~it** 

### used in the air pathway of the existing t 

### HRS and review the technical Qaper developed on this subject. As part of this revi"''"'• we would like an assessment of the general methodology used 

### L1 the technical paper and the implications of these eindings on the air pathway factor of a revised HRS. In addition, we would '""'lco"le any 

### suggestions concerning general approaches for revising the air targets distance limit. Toxicity Many public comments have 

### been received 

### by EPA on the method used in the HRS to rank the toxicity of hazardous substances., The current method is based on a ratinq scheme developed 

### by N, Irving sax (1975, 1979, 1984) and**~~tes** 

### the toxicity of hazardous substances on a scala of 0 to 3. The rating is**prima~ily** 

### based on acute toxicity. Several technical issues have been**~aised** 

### by commenters that suggest**th~** 

### possible need for modification of the HRS is in order to ill'pr.'Jve its ability to discriminate among sites whose wastes have different toxicity**char~cteristics.** 

### As a result of**t~ese** 

### comments and the intent of Congress to •**~ake** 

### the HRS as**accu~~te** 

### as possible, OERR has evaluated the methon currently used in the HRS for**~stimatinq** 

### the relative toxicity of substances at hazarlous waste sites and the methods employed by**oth~r** 

### ranking**syst~<os** 

### to evaluate toxicity. Based on the review, OERR has**sugaest~~ l~prove~ents**  

### to the HRS toxicity eactor that**incoroo~ate ~easu~~~**  •Jf 

### acute,**suh-ch~onic** 

### and chronic toxicity.

we would like**t~·~** 

### Science Advi.sory Board to evaluate the toxicity·ranking ,;ch-"'"-"**e!'lploy~<l** 

### in the exi-<tina HRS, to review OERR's technical,,.,,., 1n 

### this subject,**>~nd** 

### to sugqest**imp~ovement;** 

### to the HRS that "'n;**'"t"~** 

### -1c::urately**as~ess th~**  

### toxicity of a hazardous substil'l.··.

### A;-6


### -6­

SCHEDULE The 

### specific technical**~epo~ts Eo~**  

### Science**Adviso~y Boa~d** **~eview** 

### will bemade available to you 30 days in advance of the Science Advisory**aoa~d** 

### meeting. We would be more than happy to meet with the Science Advisory**Boa~d** 

### to**b~ief** 

### them on the existing RRS, if**approp~iate.** 

### Thank you for**you~** 

### help in this**p~oject.** 

### If you have any questions concerning OERR's**~equests,** 

### please contact Jane Metcalfe at 382-7393. We**loo~ Eo~wa~d**  

### to**wor~ing** 

### with you on the HRS**~evisions** 

### effort.



## .f •



## •WASHINGTON, D.C. 20460


## JJN

## 2 51987**Of~ICE**010 SOLIDWASTE AND EMeRGENCY**~!:;SPOI'.!Sf;** 

### MEMORANDUM SUBJECT: Science

# Adviso~y Review of thei?i FROM:**Hen~y** 

### L. Longest II,**Di~ector** 

### Office of**Eme~gency** 

### and Remedi s onse TO: Dr.**Ter~y** 

### Yosie, Director Science Advisory**Boa~d**


### In December 1986, I requested the Science Advisory Board­**(S~B) ·~**  

### dssistance in reviewing several issues related to OERR's efforts to**~eview** 

### and revise the Hazard Ranking**Syste~** 

### (HRS) as**di~ected** 

### by Congress in the Superfund Amendments and Reauthorization Act of 1986 

### (SARA). In response to this**~equest,** 

### an Ad Hoc HRS Subcommittee was formed by the SAB. This Subcommittee met for the first time on May 

### 19 &

### 20, 1987. By this memorandum !'wish to express OERR's appreciation to the Subcommittee and SAB staff for their responsiveness to our request and the expressed willingness to work within the narrow time constraints for the revisions imposed by SARA. I 

### would also like to take this opportunity to confirm several**~ey** 

### points which should facilitate the Subcommittee review. Purpose of the HRS During the initial meeting on May 

### 19 

### &20, many members of the Subcommittee posed questions concerning the purpose of the HRS. As pointed out, the purpose of the HRS is a 

### major determinate of the structure and function of a model. Such a model is required to prioritize actual or potential hazards to public health and the environment posed by hazardous waste sit... 08M 

### believes that the purpose of the HRS is**primaril~~**

### screening tool used to determine which sites • 

### will be**~idates** 

### for Fund-financed remedial response. To the degr••possible, the model also needs to provide a stratification of sites based upon the relative risks posed to human health and the environment. OERR does not believe that the HRS is-intended to assess absolute risk, since it is to be applied early in the remedial site evaluation process. OERR intends to**~evise** 

### the HRS to the maximum extent feasible,A7-8 

### -2­



### to estimate more accurately the risks associated with a site. tn conducting these revisions, however, OERR will balance the benefits of increased accuracy against the associated costs, avoiding revisions that would require far more extensive data and, in so doing, impede the ability of the HRS to function expeditiously. OERR's Objective on Seeking SAB Review Congress, through SARA, requested that in our review of the HRS, we assess several specific areas. In reviewing these areas, OERR is particularly concerned that our decisions concerning the approaches used in revisions be supported by sound technical and scientific analyses. Peer review of the technical or scientific issues under considerationwill provide essential support for any proposed revisions. Specific Issues For SAB Review OERR requests that the Subcommittee examine three specific HRS revision issues: 1) 

### the method(s) used to assess toxicity, 2) the air target distance limit and 3) whether large volume wastes should be considered differently from other wastes. These issues are described brief1y·in the December 9, 1986 memorandum and will be developed more fully in issue papers to be presented to the Subcemmittee according to the schedule agreed to at the May 19 &

### 20, 1987 Subcomittee meeting. As I understand, the following schedule has been agreed to by all parties: 1. 

### Toxicolog.y Panel

-- June 29 & 

### 30 2- Meeting 2 of Subcommittee-- July 16 &

### 17 3. Air Panel-- July 27 &

### 28 (issue paper to be mailed July ll 4. Large Volume Waste Panel

-- Aug. 19 &

### 20 (issue paper availableJuly 17) 

# s. Final Subcommittee



### . .Meeting

-- Sept. 14 &

### 15 (tentative)



### . In my December 9, 1986 memorandum, I requested SAB review of the fourth 

## issue involving the reviewof scientific factors in the

# au. The scope of that review was to priorithe the various .._ing factors in terms of their importance to assessinirrisk and evaluate the appropriateness of the 

### • weightinffassigned to those factors.
As 

### explained by craigWolfe during theMay 19 & 

### 20, 1987 SAB meeting, OPPE has assembled a groupof Agency officials to discuss the importance and weighting of various risk related factors and rank order 20 hazardous waste sites. I believe that the work of this expertpanel will be most satisfactory in answering the questions related to the factors and weightings in the current HRS. consequently, I believe it would be duplicative to continue

### my request to the SAB for such a review and therefore, I withdraw this part of my request for review to the SAB.

### OERR believes that the issues**p~esented** 

### to the Subcommittee meet the·criteda identified in the Administe-ator's guidance concerning use of the SAB, and can be addressed as**disc~ete** 

### issues. While 

### we intend to provide updates to the Subcommittee 0n overall proge-ess with**~espect** 

### t0 cevist<)ns •)f**~·\'** 

### '•l':.i!."e model, we do not believe that ceview of the**ove~all** 

### model is eithec feasible o!." appropt:"iate foe the Subcommittee due to the need fo!." policy as well aN**~·:l~ntific** 

### considerations. OERR looks forward to continuing the open and focused review effort which was initiated at our first meeting. If you have any questions please contact Ms. Penny Hansen, Deputy Director of the**Haza~dous** 

### Site Evaluation Division at 475-8600

.



### •A7-10

UNITEDSTATESENVIRONMENTAL.PROTECTIONAGENCY WASHINGTON, D.C. 20460 

## JUL28

## 1987

·-

## ·­ OF.,:;t¢£OF SOt..IOW.Si'"£ANOeM£ACi£NCY**~E:SPOfltSE** 

### MEMORANDUM SUBJECT: Science**Adviso~y Boa~d**  

### (SAB) Review of Mining Waste/Concent=ation Issi<e**~** 1; ·

### r 	 , 

### !;'ROM: Stephen A. Lingle, Dil:'ectoe

## ~ , ·,

## ..._._.,U**Haza~dous** 

### Site Evaluation Division**~** 

### TO: Teel:'y tosie,**Di~ectol:'** 

### Science Advisoey Boaed

Thank you fot' the**oppo~tunity** 

### to introduce themining waste and concenteation issues to the full subcommittee. Mr. Richard Conway, chait:'l!lan of the HighVolume Waste Panel expt'essed his**desi~e** 

### to**hav~**

### OERR further define the issues foe SAB consideeation. The purpose of thismemorandum is to provide this**clat'ification~** 

### As :esented in the July 16, 1987 

### subcommittee meeting, the two 4Ssues**~:"elated** 

### to mining waste sites are: 1)

### Applicability of the HRS in scoring mining waste sites1 and 2) Feasibility of using waste concentration data in a , revised HRS. The fit'st issue has been eaised by the mining induStl:'y during publi·c comlllents on·various NPL rulemakings. The commentees have stated that the HRS is biased against highvolume, lowconcentrationwastes, because it does not take' into account quantity, toxicity, and**concent~:"ation** 

### of the hazardous constituents. The commentatOI:'S also stated that EPA is unable to**p~:"ovide** 

### evidence that the HRS is a rational 

### • basis by 

### which to**~:"ank** 

### mining sites for inclusion on the NPL.

. OERR would like the SAB to evaluate the HRS in light of these comments., and to eeview th!:'ee technical papel:'s on the HRS developed by TRC, Inc. fo= the mining industry, and two l:'epol:'ts peepaeed by OERR's contl:'actors. As part of this l:'eview, we would like the SAB to examine the validityof the**minin~** 

### industry's**conce~:"ns** 

### with**~espect** 

### to high volume waste• 

### A7-ll 

### -2­

sites**s~ch** 

### as mining sites. Although the**pape~s** 

### discussed in the first issue**pe~tained** 

### to mining waste, OERR believes thatthe issue is equally**~elevant** 

### to sites containing othe• highvolu.a wastes such as fly ash. The ·s@cond issue is •elated to the**fi~st** 

### as it**add~esses** 

### the feasibility of using the**concent~ation** 

### of the**ha%a~dous** 

### constituents of wastes. In**~esponse** 

### to public comments that concent•ation data**a~e** 

### not used in the**cu~~ent** 

### HRS to**dete~ine** 

### the quantity of haza•dous waste, and the**•equi~ements** 

### of SARA Section 125(a), EPA developed an option that specifies**th~ee tie~ed**  

### methodology that allows the use of waste**concent~ation** 

### data. This methodology is**desc~ibed** 

### in the**concent~ation** 

### issue**papa~ p~esented**  

### to the SAB. In •evising the HRS, Section 125(a) of SARA**~equires** 

### EPA to**add~ess** 

### quantity, toxicity and**concent~ation** 

### of**ha~a•dous** 

### constituents**fo~** 

### RCRA Section 300l(b)(3)(A)(i) special study wastes (fly ash, bottom ash wastes, and flue gas emission**cont~ol** 

### waste**gene~ated p~ima~ily** 

### f•om the combustion of coal**o~ othe~**  

### fossil fuels). Although, SARA Section lOS(g) does not**~equi•e ~evisions**  

### to the HRS, it does require that !PA**conside~** 

### the same factors (quantity, toxicity, and concentration) in the decision to**p~opose** 

### new mining waste sites to the NPL using the current HRS until the HRS is revised. EPA believes. that the methodology desciibed in the third option of the concentration issue paper could be employed to satisfy Section 125(a) and would also address concerns about scoring other high volume waste sites such as mining waste sites as well. Consequently, we believe that the subcommittee findings will be equally applicable to both mining and fly ash sites. I hope that this discussion**p~ovidea** 

### the desired**cla~ification** 

### of this issue. In addition, we are in the**p~ocess** 

### of gathering available information on costs of waste sampling and analysis at large volume waste sites. This information.will be**p~ovided** 

### to the SAB**membe~s** 

### as soon as possible. OERR appreciates the time and effort the subcommittee members have**e~pended** 

### and we look forward to our**ne~t** 

### meetinq in Denver. If you have any additional questions, please contact Aqnea Ortiz of 

### my staff, at (202) 475-9700• Attachments

cc: Kathleen

## ·w. Conway SAB Subcommittee**Membe~s**

### APPENDIX 8 REFERRENCES CITED



### •

# ..

REFERENCES CITED

!. 

### Electric Power Research Institute. Inorganic and Organic Constituents in Fossil Fuel Wastes. EPRI EA-5176, Vl. August 1987.
2. Electric Power Research Institute. Leaching Studies of Utility Solid Wastes. EPRI EA-4215. August 1985 

### 3. Electric Power Research Institute,**Physical-Che~ical** 

### Characteristics of Solid wastes. EPRI EA-3236.**Septe~ber** 

### 1983. 4, 

### Electric Power Research Institute. Round-Robin Evaluationof Regulatory ExtractionMethods, EPRI EA-4740.**Dece~ber** 

### 1986.
5. 

### Electric Power Research Institute,**Mobili~ation** 

### and Attenuation of Trace**Ele~ents** 

### in FlyAsh. EPRI EA-4747. August 1986, 

### 6. Electric Power Research Institute. Evaluationof**tnstr~ents** 

### in Unsaturated FlyAsh, EPR! EA-5011, April 1987.
7. Electric Power Research Institute. 

### SWES: Description, Status and Available Results. EPRI**EA-532~2~-~S~R-.--A~u~g~u~s~t~1~9~8~7~.~~~~~** 8. 

### Environmental ProtectionAgency. Uncontrolled Hazardous Waste Site Ranking System: AUsers Manual (HW-10), originally published in the July 16, 1982. Federal Register, 1984.
9. 

### Environmental ProtectionAgency, Office of Emergency and Remedial Response, Analysis of the Air Target Distance**Li~it** 

### in the Hazard Ranking**Syste~.** 

### Prepared 

### by ICF Incorporated, July 1987•



### . • 

### 10. Environmental Protection Agency, Office ofEmergency and Remedial Response. Chemicals Contributing to Estimated Risks at Superfund Sites: ALimited Study. July 16, 1987,
11. Environmental ProtectionAgency. Office of Emergency and Remedial Response. Comparison of Available Dataon the Concentration of Hazardous Constituents inMiningWaste and Non-MiningWaste, pages 

### 5-10. Received August 1987•
• 

### 12. Environ-ental ProtectionAgency, Office of Emergency and Remedial Response, Discussion of Options for Revising the Hazard Ranking System (HRS) Toxicity Factor, Prepared by ICF Incorporated, May 4, 1987.
!3. Environmental ProtectionAgency. Office of Emergencyand Remedial Response. The Superfund Hazard Ranking System (HRS): Applicability toMiningWaste Sites, Prepared by ICF Incorporated. July 22, 1987,

### - 2 ­ 14,**Enviro~ental** 

### ProtectionAgency, OfficeofEmergency and Remedial Response, Report on the FeasibilityofUsing Concentration Dataina Revised Hazard Ranking System, Preparedby ICF Incorporated, July27, 1987, 15. Environmental ProtectionAgency, OfficeofPolicyPlanningand Evaluation, Views/Approach toHazard Ranking SystemRevisions, July 1987. 16, Environmental ProtectionAgency, Officeof SolidWaste. Report to Congress: Wastes from theCombustion ofCoal by Electric UtilityPower Plants, Chapters 1-5. June 1987. 17, Environmental ProtectionAgency. Office ofSolidWaste, Management ofMiningWastes, June 22, 1987. 18. IndustrialEconomics, Incorporated. PreliminaryAnalysisofAlternative Models to Support Revision to 

### theCERCLAHazard Ranking System, · Prepared for theEnvironmentalProtectionAgency's OfficeofPolicy, Planning and Evaluation, Presented to theScienceAdvisoryBoard. July 16, 1987. 19. Kushner, L. M, Hazard Ranking System IssueAnalysis: Siteswith UnknownWaste quantity,_August 1986. 20. Lingle, S. A., Director, Hazardous SiteEvaluationDivision, Memorandum: ScienceAdvisoryBoard (SAB) ReviewofMining Waste/ConcentrationIssues to

### TerryYosie, Director, Science Advisory Board, July28, 1987. 21. Longest, H. L., Director, OfficeofEmergency and Remedial Response. Memorandum: ScienceAdvisoryBoardReview ofHazardRanking SystemtoTerryYosie, Director, ScienceAdvisoryBoard, December 9, 1986•. 22. Longest, !{,

### .L., Director; OfficeofEmergencyand Remedial Response. Memorandum: ScienceAdvisoryBoard Review oftheHRS toTerry Yosie, Director, ScienceAdvisoryBoard, June25, 1987. 23. Merkhofer, L, H., et al. ASite-RankingPanelEvaluationof the RelativeRiskPosed byTwenty**Superf~nd** 

### Sites. Keystone, • 

### Colorado: The KeystoneCenter. Prepared for the

## u.s• EnvironmentalProtectionAgency's Officeof Policy, Planning and Evaluation, DraftReceived September 1987,.PP• 1-17.- 3 ­ 24. MITRE Corpo.-ation. Analysis of EPA Hazard Ranlting Systelll Scoring of Mining Sites on the National Priorities List. Prepared for U.S. EPA, 1985.
25. MITRE Corporation. Estimates of the Quantity of Hazardous Substances Present inMining Waste at NPL Sites. Prepared for: the U.S, Environmental ProtectionAgency's Office of Policy, Planning and Evaluation. January 9, 1986,
26. Ortiz, A,, Incorporating Mobility Factors into the Hazard Ranking System, Office of Solid Waste and Emergency and Re=edial Response. August 20, 1987,
27. TRC Environmental Consultants, Analysis of Mining Sites on the National Priorities List, Prepared for theAmericanMining Congress, !983,
28. TRC Environmental Consultants, Analysis ofMining Sites on the National Priorities List: Score Changes and Newly Proposed Sites, Prepared for AmericanMining Congress, 1984a.
29. TRC Environmental Consultants. Review ofMining Sites on the National Priorities List: Comparisonwith Non-Mining Sites, ?repared for the**Ameri~an** MiningCongress. 1984b,
30. Sobek, 

### A. A., et a1. Field and LaboratoryMethods Applicable to Overburden and Mine Soils. EPA/600-2-78-054, March 1978.
3J. Wolf1nge,r, T. F. Hazard Ranking System Iasues Analysis: The trse of Concentration Data, EPA/68-01-7054, April 1987. 

### J2, Wusterbarth, A, R. Hazard Ranking System Issue Analysis: 

### .· Relationship BetweenWaste quantityand Hazardous Constituent Quantity. EPA/68-Ql-7054, September 1987.