A model standardized risk assessment protocol for use with hazardous waste sites.

This paper presents a model standardized risk assessment protocol (SRAP) for use with hazardous waste sites. The proposed SRAP focuses on the degree and patterns of evidence that exist for a significant risk to human populations from exposure to a hazardous waste site. The SRAP was designed with at least four specific goals in mind: to organize the available scientific data on a specific site and to highlight important gaps in this knowledge; to facilitate rational, cost-effective decision making about the best distribution of available manpower and resources; to systematically classify sites roughly according to the level of risk they pose to surrounding human populations; and to promote an improved level of communication among professionals working in the area of waste site management and between decision makers and the local population.


Introduction
Estimating the potential hazards to human populations from waste site exposures has become a central topic of debate and concern among scientists, public health administrators, politicians, trade representatives, environmentalists, community interest groups, and the general public. Given this growing level ofconcern from so many quarters ofour society and the need to develop a viable consensus regrding priorities for fuure action, it is striking that professionals working in this field have yet to develop a commonly accepted, scientifically defenslble approach to the classification oftoxic waste sites and their associated health hazards. This paper puts forward a model stndardized risk assessment protocol (SRAP) for use with hazardous waste sites. It must be emphasized from the outset that we do not view the protocol presented here as being in any sense final. Instead, it is meant to serve as a model protocol, that is to say, as a prototype or an example to illustrate an approach to the fundamental problems of classifying the health risks posed by potentially hazardous waste sites and organizing appropriate remedial action in a responsive and efficient manner. Background Before presenting the SRAP, it is important to clarify certain basic terminology that will be used in this paper. When one examines the literature on hazardous waste sites, it becomes clear that terms such as "risk assessment" and "risk analysis" are used clear from the context in which they occur. In order to prevent confusion, there are three primary terms that we will define: health risk assessment, standardized risk assessment protocol, and risk analysis.
For the purposes of this paper, a health risk assessment is a generic term covering a broad group of laboratory, environmental, and epidemiological investigations designed to evaluate the health implications of exposures to hazardous waste materials. In contrast, a standardized risk assessment protocol refers to a set ofoperationally defined criteria that are used as the basis for for site classification and decision making with regard to potential remedial actions. Finally, risk analysis is defined as the calculation of expected numbers of excess cases using exposure and health effects data derived from existng human (e.g., epidemiological) and animal (i.e., laboratory) studies. It will become clear as we proceed that a formal risk analysis is simply one part of a complete health risk assessment and that the model SRAP presented in this paper is an operationally defined set of rules for organizing, classifying, and acting upon the evidence (or lack of evidence) of human health risks derived from health risk assessments. Figure 1 presents a simple three-phase classification ofthe activities routinely carried out by public health agencies responsible for dealing with potentially hazardous toxic waste sites. This classification ofactivities was adapted, in part, from materials published by the Environmental Protection Agency (I) and the Agency for lbxic Substans and Disease Registry (ATSDR) (2).
In Figure 1, the discovery phase covers the process ofthe identification oftoxic waste sites that pose a potential threat to human populations. The identification ofrelevant releases may proceed from any one of a broad range of sources, e.g., the National Priority List ofSuperfumd sites, state and local agencies, licensed physicians, lawyers, or community interest groups. Once a site has been identified, an investigatory phase ofwork may be initiated. This phase ofwork usually involves a more or less complete health risk assessment and refers to the process of determining whether it is likely that a significant health risk to human populations exists due to a waste site exposure. Under ATSDR guidelines (2), for example, the investigatory phase of work encompasses three hierarchical research components: a) health assessments, site characterizations and toxicological profiles; b) pilot studies, including biological exposure studies, symptom/disease prevalence studies and cluster studies; and c) epidemiological studies, including classic research designs, health surveillance studies, and disease registries.
We have added to this a risk analysis component as a fourth possible aspect ofthe investigatory phase. As noted earlier, this component would draw upon existing animal and human studies to attempt to estimate the number of excess cases of specific health outcomes that may be expected to occur within the population exposed to the site.
Due to restrictions on space, we have simply enumerated and briefly described the components of a complete health risk assessment. Readers interested in obtaining a more complete review of methodological and other difficulties involved in the actual conduct of these investigative activities should refer to previous works (3,4).
The intervention phase covers activities undertaken to reduce the demonstrable risk from known releases oftoxic substances.

Under current federal law [Comprehensive Enviroumental
Response Compensation Act of 1980 (5) and Superfund Amendments and Reauthorization Act of 1986 (6)], this phase covers a variety ofpotential ameliorative activities that range from a simple site clean-up to the o ion oft mt programs for the members of exposed populations to the power to recommend more extreme steps, such as the provision of alternative community water supplies or the permanent relocation ofexposed individuals. Figure 1 shows that, depending upon the characteristics ofa site and the imediacyofthe evidence regarding a significant risk to human health, it is possible for an administrator tomove direcdy tothe implenentation ofan intervention program from any one of the earlier phases of work.
It is important to note that decision making with regard to the activities outlined in Figure 1 generally takes place in an ad hoc manner. That is to say, public health administrators usually have to make decisions without the support of explicit, operationally defined criteria to determine the nature or the timing of the various activities to be undertaken. Consider, for example, the fact that the evidence uncovered during the course of an initial ATSDR health assessment (2) may serve as the basis for a wide range of recommendations, including the initiation of further pilot research or a full-scale epidemiological study, the implementation ofan intervention program, or some combination of all ofthe above. At the present time, it is not at all clear how these various alternatives should be evaluated within the context of specific health risk situations, a dilemma that inevitably results in ad hoc (or case-by-case) sorts ofdecision making, which all too often places undue emphasis on unscientific, exhtaneous, or momentary considerations. This potential for a less than rational expenditure of valuable manpower and resources is magnified when, as is often the case, the investigation ofa potentially hazardous case must take place in a highly charged public atmosphere characterized by deeply felt emotions of anger, suspicion, and fear. It might even be suggested that ad hoc styles of decision making, since they are open to such a broad range ofpotential influences, may serve to further stimulate public suspicion and frelings ofanger, in turn, making it even more difficult for public health officials to carry out their duties in a fillly reasonable and efficient manner.

A Model Standardized Risk Assessment Protocol
The SRAP was designed as a model protocol for dealing with the types of situations described previously. The SRAP would come into use immediately following the identification of a potentially hazardous waste site and might be updated on several occasions during the investigatory phase ofwork. Underlying the SRAP is the action-oriented assumption that the primary goal is to make a rational, consistent, and cost-effective decision about the level ofrisk to human populations and the most appropriate irdized rsk assesm procol significant risk: evideniary chain (7). available response at the earliest possible point in the process. In this regard, the SRAP was designed with at least four specific goals in mind: a) to organize the available scientific data on a specific site and to highlight important gaps in this knowledge; b) to facilitate rational cost-effective decision making about the best distribution of available manpower and resources; c) to systematically classify sites roughly according to the level of risk they pose to surrounding human populations; and d) to promote an improved level of communication among professionals working in the area of waste site management and between decision makers and the members of the local population. The SRAP focuses on the degree and patterns of evidence that exist for a significant risk to human populations from exposure to a hazardous waste site. Figure 2 shows the four specific categories of evidence that are considered: evidence that toxic substances exist on the site, evidence that environmental pathways exist for the substances to get offsite, evidence for human absorbtion of the toxic materials, and evidence of relevant health outcomes occurring in the exposed population. It should be noted that, together, these four evidentiary components make up a causal chain linking the toxic substances on a waste site to observed health outcomes in the exposed population. In other words, the SRAP attempts to estimate the extent to which the totality of scientific information available at any particular point in time does or does not support a classic cause-and-effect statement concerning the relevance of the toxic materials on a waste site for the health of the surrounding population.
A SRAP checklist has been developed for rating each one of the four categories of evidence in the causal chain. The content of the checklist was adapted in part, from the S.P.A.C.E. for Health document originally developed by the U.S. Public Health Service (7). The S.P.A.C.E. document, like a number of other proposed rating systems, attempts to produce a single overall priority score as its primary output. In developing our own checklist, we rejected this earlier approach for two important reasons. First, the true meaning of overall priority scores are often deceptive because the evidence from one or two areas of concern may unduly affect the final raing. This creates situations in which the hierarchy of sites, interms of numerical rtins, may not fit with common sense notions concerning relative levels of risk to human populations. Second, our desire to link levels and patterns of risk to a variety of potential rm;edial actions led us to focus on the strength of the data for each one of the specific evidenfiary components raher than a summ ry atn. A version of this checklist is provided in Table 1.
The checklist in Table 1 provides a four-point scale (0-3) for each rateable item and a space for indicng missing data. The final ratings for each evidentiary component (i.e., toxic substances, exposure pathways, human absorption, and health outcomes) are binary in character (strong or weak evidence). Ratings of strong or weak evidence are obtained from a specific set of SRAP rules (Fig. 3) that summarize the information collected in the checklist.
The current rules proposed in Figure 3 are weighted in a relatively conservative direction. In order to receive a strong rating, all ofthe relevant checklist items for an evidentiary component must jointly meet certain minimum standards. Otherwise, a weak rating is assigned to that evidentiary component. To illustrate, a strong rating for the evidence of human absorption would require both a minimum combined score of5 for the presence of a potentially exposed population and basis of evidence for human exposure/absorption and a minimum score of2 for levels of substances found through biological sampling.
These thresholds, of course, are not fixed, and they may be adjusted to reflect levels ofacceptable risk established by responsible expert committees.
Given a completed checklist (i.e., no missing data) and the rules in Figure 3, a final rating ofstrong or weak may be obtained for the evidence in each component ofthe risk assessment protocol. These final ratings will produce 1 of 16 possible outcomes ( Fig. 4) or patterns of risk. A site, for example, that has strong ratings for both toxic substances and exposure pathways, and weak or indeterminate (i.e., incomplete data) ratings for human absorption and health outcomes would get at least an interim rating of site class 13. In the case of the checklist items having missing data, further investigations regarding human absorption and/or health outcomes might change the initial site class from a 13 to a 14, 15, or, perhaps, even to a 16 Figure 4 also shows how these 16 site classes can be given an action level rating of0 to 4 depending on the number of evidentiary components receiving a strong rating. Figure 5 illustrates how these 16 site classes can be roughly organized according to the level ofpotential risk to human health and can serve as a basis for planning remedial action. In this figure, the 16 site classes are ordered according their action level and cross-classified by appropriate remedial responses. Notice that these responses range from no further action in the case of an action level of 0 to an intensive program of community intervention inthe case ofaction level 4. With regardtothe example of the class 13 site discussed above, its action level would be 2 (strong, strong, weak, weak). In such a case, Figure 5 recommends that the following activities be at least considered by the administrator in charge ofwork on the site: improve site control to block the further discharge of toxic substances; renew biological and pilot health outcome testing to be sure that toxic substances from the site are not being absorbed at significant levels or promoting identifiable health problems among community residents; and initiate an exposure registry to trace any ptential health problems that may appear in exposed individuals at a future date. As noted earlier, the additional evidence from the renewed biological and health outcome investigations may ultimately lead to the recategorization of the site at a higher actio level and to the implemntation ofan even more comprehensive program of community intervention.
In reviewing Figures 3 togh 5, it should be kept in mind that the tenn '"eak evidence" does not mean "no evidence." A rating ofweak evidence simply means dat this risk component does not reach the highest level of concern. When pla potential remedial action the content of the information regarding each componenlt with a weak rating should be carefully considered on an individual basis.  This checklist approach was designed to be flexible in nature and to be filled out on more than a single occasion during the investigative phase of work. Within the context ofthe investigative phase, the checklist serves as both a mnemonic and a planning device, ensuring the comprehensiveness ofthe health risk assessment procedure and systematically highlighting important gaps in the available data.
Under the model developed here, the fundamental goal ofthe investigatory phase ofwork should be to complete, to the extent possible, the full health risk assessment procedure for a given site. Ideally, the work in this phase continues until sufficient information is collected to determine whether or not remedial action is required and, if so, the kind ofintervention program that is most appropriate to the situation.
Once a full set ofratings ofthis kind has been completed, the agency staffhas a rational basis for assessing the level ofpotential risk to human health involved in a specific release and deciding upon the most appropriate recommendations to be made in a given situation. Even ifa limited amount ofdata on the checklist remains unknown or ifthe missing information is confined to a single evidentiary component (e.g., human absorption), it still may be possible to make decisions concerning initial remedial activities on the basis ofthe data collected in other components ofthe checklist (e.g., substance, exposure pathway, and health outcomes) while planning further investigatory activities. For example, ifstrong evidence were available concerning both a poorly controlled toxic substanceon a siteand theoccurrence of relevant health outcomes in a nearby population and weakbut still significantevidence regarding an exposure pathway, it probably would not be necessary to await the results ofhuman testing before beginning to plan an intervention program.

Summary and Conclusions
It should again be emphasized that the standardized risk assessment protocol outlined in this paper is simply a model system. It was constructed to illustrate the kind ofprocedure that might be developed to reduce the ad hoc quality that characterizes much of the decision making that occurs with regard to hazardous waste sites. In this sense, the underlying message of this paper is the importance ofdeveloping some type ofgenerally accepted, scientifically defensible procedure for classifying toxic waste sites and selecting remedial activities appropriate to the established health risks to human populations.
A standardized protocol of the type presented permits an administratortosystematicallyanswertwocriticalquestionsinvolved in the investigation ofany potentially hazardous toxic waste site: Has all the information required for a complete health risk assessment been collected? Does the information that has been collected support a specific recommendation offurther action in this case? A protocol of this sort also provides a simple system that classifies sites roughly according to the level ofhealth risk posed to human populations and provides guidelines that relate patterns ofriskto available types ofremedial activities. The flexible nature ofthe system permits a site's classification to be updated as new evidence is obtained and allows it to serve as a means of facilitating ongoing communication with other involved professionals, as well as with concerned members ofthe general public. Finally, it is our beliefthat the existence this kind of standardized method for the classification of hazardous wastes stites, that is, one that logically relates patterns ofhealth risk to potential ameliorative actions, may play an important role in reducing or controlling expressed levels of public anger and suspicion. If potentially exposed communities perceive that public health officials have stndardized and reliable methods for assessing the extentofthe health risksposedby hazardous waste sites, and ifthe results ofsuch investigations can be communicated to the public on a routine and timely basis, it may be possible in the future to achieve improvedpublic cooperation andconfidence, and to promoteanatmospheremoreconducivetotheconductofthescientific activities necessary to measure truepotential risks fromtherelease oftoxic substances.

Appendix SRAP Checklist Tables
In general, substances in Table A-1 classified as having slight toxicity produce changes in the human body that are readily reversible and disappear following termination of exposure, either with or without medical treatment. Those substances classified as having moderate toxicity may produce irreversible as well as reversible changes in the human body. These changes are not of such severity as to threaten life or to produce serious physical impairment.
Assigncontainmentin Table A-5 avalueofOifallthehazardous substances at the facility are underlaid by an essentially nonpermeablesurface(naturalorartificial)andadequateleachate collectionsystemsanddiversionsystemsarepresentorifthere is no groundwater in the vicinity. The value 0 does not indicate absence ofrisk. Rather, 0 indicates a significantly lower relative risk when compared with more serious sites on a national level. Otherwise, evaluate the containment for each of the different means of storage or disposal at the facility, using the guidelines in Table A -5. Assign containment in Table A-6 a value of0 ifall the waste at the site is surrounded by diversion structures that are in sound condition and adequate to contain all runoff, spills, or leaks from the waste or if intervening terrain precludes runoff from entering surface water. Otherwise, evaluate the containment for each ofthe different means of storage or disposal at the site and assign a value as outlined in Table A-6.
In Table A-7, check the applicable rating scale level for each rating factorlisted intheleftcolumn. (You willneedtorefertoTable A-5 to determine which levels tocheckfor the rating factor "containment.") Considering the interrelationships ofthe rating factors and the level checked foreach onedetermine and overall level (0, 1, 2, or3) forexposurepotential fromthesiteffiroughgroundwater.
Site slope and intervening terrain are indicators ofthe potential for contaminated runoffor spills at a site to be transported to surface water. The site slope is an indicator of the potential for runoffor spills to leave the site. Intervening terrain refers to the average slope of the shortest path that would be followed by runoff between the site boundary and the nearest downhill surface water. Table A-8 shows values assigned to various combinations ofslope conditions. Transfer the value applicable to a particular site to Table A-9 to determine the overall exposure potential from the site through surface water.
In Table A-9, check the applicable rating scale level for each rating factor listed in the left column. (You will need to refer to Tables A-6 and A-8 to determine which levels to check for the rating factors "containment" and "site slope and intervening terrain.") Considering the interrelationships ofthe rating factors and the level check for each one, determine an overall level (0, 1, 2, or 3) for exposure potential from the site trough surface waters.
'Ible A-. Sax toxicity rating (7)(8)(9) aNumbered toxicity ratings are from Sax (8). Toxicity ratings in parentheses are from Sax (9).  3   3  0  3  1  3  1  3  3  3  3  2  2  3  3  3  1  3  1  2  2  3  3  2  1  3  0  3  0  3  0  3  1  3  3  1  1  2  0   Ignitability   (I)   3  aOn occassion it may be necessary to convert data to a common unit to combinethem. In such cases, 1 ton = I cubic yard = 4druns, and forthepurposes of converting bulk storage, 1 drum = 50 gallons.  Containers sealed, in sound condition, and surrounded by sound diversion or containment system Containers sealed and in sound condition, but not surrounded by sound siversion or containment system Containers leaking and diversion or containment structures potentially unsound Containers leaking, and no diversion or containment structures or diversion structures leaking or in danger of collapse Waste piles Piles are covered and surrounded by sound diversion or containment system Piles covered, wastes unconsolidated, diversion or containment system not adequate Piles not covered, wastes unconsolidated, and diversion or containment system potentially unsound Piles not covered, wastes unconsolidated, and no diversion or containment or diversion system leaking or in danger of collapse Landfill Landfill slope precludes runoff, landfill surrounded by sound diversion system, or landfill has adequate cover material Landfill not adequately covered and diversion system sound Landfill not covered and diversion system potentially unsound Landfill not covered and no diversion system present, or diversion system unsound  aTerrain average slope < 3 % or site separated from water body by areas of higher elevation. water of concern for drinking aSite slope and intervening level determined by the use of Table A-8. bContainment level determined by use of Table A-6.