Hazard Ranking System Issue Analysis: Options for Revising the Air Pathway MITRE ------- Hazard Ranking System Issue Analysis: Options for Revising the Air Pathway Thomas F. Wolfinger August 1987 MTR-86W53 SPONSOR: U.S. Environmental Protection Agency CONTRACT NO.: EPA-68-01-7054 The MITRE Corporation Civil Systems Division 7525 Colshire Drive McLean, Virginia 22102-3481 ------- Department Approval: MITRE Project Approval: ii ------- ABSTKACT This report presents two options for revising the air pathway of the EPA Hazard Ranking System (HRS). The HRS is used by EPA to rank uncontrolled wastes sites based on their relative threat to human health and the environment. Highly ranked sites are placed on the National Priorities List for further investigation and possible remedial action. The options focus on the incorporation of a "potential-to-release" option within the HRS air pathway. Inclusion of such an option would make the air pathway consistent with the other HRS migration pathways. The options also include recommended changes to other components of the air pathway to increase the ability of the HRS to discriminate the threat between sites. These changes arise from an analysis of weaknesses in the HRS and advances in the science of air emissions from hazardous wastes sites. Suggested Keywords: Superfund, Hazard ranking, Hazardous waste, Air emissions. iii ------- TABLE OF CONTENTS Page LIST OF ILLUSTRATIONS vii LIST OF TABLES viil 1.0 INTRODUCTION 1 I.I Background 1 1.2 Issue Description 3 1.3 Organization of Report 5 2.0 OVERVIEW OF AIR POLLUTION FROM HAZARDOUS WASTES SITES 7 2.1 Emission Processes 7 2.2 Factors Determining Emission Rates and Duration 9 2.3 Contaminant Transport and Transformation 13 3.0 ISSUES IN THE HRS AIR PATHWAY 19 3.1 Background on the Hazard Ranking System 19 3.2 Issues in the Current HRS Air Pathway 22 3.3 Options for Revising the HRS Air Pathway 30 4.0 MULTIPLE SOURCE, PROBABILISTIC APPROACHES 31 (OPTIONS 1 AND 1A) 4.1 Release Category 33 4.1.1 Observed Release 34 4.1.2 Potential to Release 41 4.2 Waste Characteristics Category 78 4.3 Targets Category 81 4.4 The Overall Pathway Score 86 5.0 SINGLE, "WORST" SOURCE APPROACH (OPTION 2) 89 5.1 The Option 2 Potential to Release Evaluation Mechanism 90 5.1.1 Emission Source Descriptors 93 5.1.2 Contaminant Mobility 97 5.1.3 Containment 99 ------- TABLE OF CONTENTS (Concluded) Page 6.0 IMPLICATIONS 105 6.1 Improvements in the HRS and the NPL 105 6.2 Cost Implications 107 6.3 Potential Implications for Other HRS Pathways 109 7.0 SUMMARY AND CONCLUSIONS 111 8.0 REFERENCES AND BIBLIOGRAPHY 113 8.1 Selected References on Emission Processes 113 8.2 Selected References Addressing Air Monitoring Guidance 114 8.3 Principal References Used in Developing Containment 115 Factors 8.4 General Bibliography 116 APPENDIX A - SUMMARY OF AIR MONITORING DATA AT SELECTED 141 WASTES SITES APPENDIX B - DISCUSSION OF REJECTED OPTIONS 147 APPENDIX C - STEP-BY-STEP INSTRUCTIONS AND EXAMPLES 181 APPENDIX D - ADDITIONAL TABLES 229 vi ------- LIST OF ILLUSTRATIONS Figure Number Page 1 Basic HRS Structure 23 2 Map of PE Index for State Climatic Divisions 70 vii ------- LIST OF TABLES Table Number 1 Ambient Air Monitoring Results for Selected 10 Wastes Sites 2 Atmospheric Residence Times for Selected 16 Contaminants Detected at Hazardous Wastes Sites 3 Ranges of Estimated Levels of Organic Vapors 17 in Ambient Air of Household Basements in Niagara Falls, NY 4 HRS Scoring Factors 21 5 Overview of Important Features of Air 32 Pathway Options 1 and LA 6 Site Conditions That Make It Difficult to 40 Demonstrate an Observed Release 7 Time Needed for 75 Percent of Selected Compounds 44 to Volatilize for Various Disposal Methods 8 Data on Mobility of Phenol and Dichloroethylene 46 9 Option 1 Emission Source Descriptors 50 10 Option 1A Emission Source Descriptors 52 11 Option 1 Size Ranges 55 12 Option LA Size Ranges 57 13 Option 1 Emission Source Descriptors and Values 60 14 Option 1A Emission Source Descriptors and Values 62 15 Gas Mobility Values 64 16 Method for Evaluating Gas Mobility 66 17 Alternate Metnod for Assigning Particulate 71 Mobility Factor Values viii ------- LIST OF TABLES (Concluded) Table Number Page 18 Combined Mobility Factor Matrix 73 19 Examples of Containment Factors and Values 75 20 Combined Containment Factor Matrix 76 21 Method of Calculating Overall Site Release 79 Value 22 Combined Toxicity-Mobility Factor Matrix 82 23 Current HRS Target Population Factor Matrix 84 24 Method of Calculating Air Pathway Score 87 25 Illustration of Option 2 Potential to Release 92 Evaluation Procedure 26 Option 2 Emission Source Descriptors and 94 Definitions 27 Option 2 Minimum Size Requirements 95 28 Option 2 Emission Source Descriptor Values 96 29 Option 2 Particulate Mobility Factor 98 30 Option 2 Particulate Containment Factors 100 31 Option 2 Gas Containment Factors 102 32 HRS Scoring Distribution for "Marginal" Sites 108 Lacking Observed Air Releases ix ------- 1.0 INTRODUCTION 1.1 Background The Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA) (PL 96-510) requires the President to identify national priorities for remedial action among releases or threatened releases of hazardous substances. These releases are to be identified based on criteria promulgated in the National Contingency Plan (NCP). On July 16, 1982, EPA promulgated the Hazard Ranking System (HRS) as Appendix A to the NCP (40 CFR 300; 47 FR 31180). The HRS comprises the criteria required under CERCLA and is used by EPA to estimate the relative potential hazard posed by releases or threatened releases of hazardous substances. The HRS is a means for applying uniform technical judgment regarding the potential hazards presented by a release relative to other releases. The HRS is used in identifying releases as national priorities for further investigation and possible remedial action by assigning numerical values (according to prescribed guidelines) to factors that characterize the potential of any given release to cause harm. The values are manipulated mathematically to yield a single score that is designed to indicate the potential hazard posed by each release relative to other releases. This score is one of the criteria used by EPA in determining whether the release should be placed on the National Priorities List (NPL). ------- During the original NCP rulemaking process and the subsequent application of the HRS to specific releases, a number of technical issues have been raised regarding the HRS. These issues concern the desire for modifications to the HRS to further improve its capability to estimate the relative potential hazard of releases. The issues include: • Review of other existing ranking systems suitable for ranking hazardous waste sites for the NPL. • Feasibility of considering ground water flow direction and distance, as well as defining "aquifer of concern," in determining potentially affected targets. • Development of a human food chain exposure evaluation methodology. • Development of a potential for air release factor category in the HRS air pathway. • Review of the adequacy of the target distance specified in the air pathway. • Feasibility of considering the accumulation of hazardous substances in indoor environments. • Feasibility of developing factors to account for environmental attenuation of hazardous substances in ground and surface water. • Feasibility of developing a more discriminating toxicity factor. • Refinement of the definition of "significance" as it relates to observed releases. • Suitability of the current HRS default value for an unknown waste quantity. • Feasibility of determining and using hazardous substance concentration data. ------- • Feasibility of evaluating waste quantity on a hazardous constituent basis. • Review of the adequacy of the target distance specified in the surface water pathway. • Development of a sensitive environment evaluation methodology. • Feasibility of revising the containment factors to increase discrimination among facilities. • Review of the potential for future changes in laboratory detection limits to affect the types of sites considered for the NPL. Each technical issue is the subject of one or more separate but related reports. These reports, although providing background, analysis, conclusions and recommendations regarding the technical issue, will not directly affect the HRS. Rather, these reports will be used by an EPA working group that will assess and integrate the results and prepare recommendations to EPA management regarding future changes to the HRS. Any changes will then be proposed in Federal notice and comment rulemaking as formal changes to the NCP. The following section describes the specific issue that is the subject of this report. 1.2 Issue Description Several issues relevant to the HRS air pathway have been raised by Congress and by public comments on the NPL and NPL rulemaking actions. Some of these issues have been the subject of discussions in Congress as it debates extending and revising CERCLA. Because of these comments and discussions, EPA has decided to re-examine the ------- desirability and feasibility of including an option within the air pathway release category that would allow sites lacking data documenting a release of contaminants into the air, to be scored based on their "potential to release". Currently, the air pathway is scored only when a release of air contaminants into the atmosphere can be documented. The inclusion of such an option would make the structure of the air pathway consistent with both the ground water and surface water pathways. The principal purpose of this report is to define alternate mechanisms for scoring sites for the air pathway. The principal emphasis is on modifications to allow sites to be scored based on their potential to release CERCLA contaminants into the air, in the absence of observed releases. The approach embodied in the options is different from that used in the other HRS migration pathways. The approach is based on the use of subjective probability to assess the potential of a site to release a significant quantity of contaminant as indicated by selected physical characteristics of the site. Additional modifications were investigated that arose either as logical extensions of the potential to release modifications or from perceived weak points in the HRS as discussed by commenters. Overall, the intent is to provide options that would generally improve the degree to which the HRS reflects the potential threat from uncontrolled waste sites. This report also addresses the additional costs that would be associated with the incorporation of ------- such a mechanism in the HRS. Additionally, the report addresses limited testing of the options for validity, feasibility and completeness. The report presents the options and supporting documentation to EPA to assist the Agency in determining if and how it would modify the air route of the HRS. 1.3 Organization of Report The body of the report is organized in six main sections with accompanying appendices. Section 2 presents an overview of the phenomena of air pollution from waste sites. Section 3 presents an overview of the HRS and discusses the principal air pathway issues addressed by the options. Section 4 discusses two multiple source, probabilistic approaches to evaluating potential to release, as well as other proposed revisions to the air pathway. The options discussed in this chapter constitute alternate air pathways. A simple, single-source potential to release option is discussed in Section 5. Section 6 discusses the implications for the HRS and NPL as well as program costs that might arise if the revision options are adopted. Section 7 presents a summary of the options and recommendations on revising the HRS air pathway. Appendix A presents summaries of the limited data available on air contaminant emissions from waste sites. A discussion of revision options that were rejected during the study is presented in Appendix B. Appendix C presents step-by-step instructions for ------- employing the most complex option (Option 1), as well as an example of its application to a hypothetical site. This appendix also contains an example of the application of the simpler option (Option 2) to the same site. Appendix D contains definitions of the basic emission source descriptors used in the options, as well as detailed containment factor descriptors for Options 1 and 1A. ------- 2.0 OVERVIEW OF AIR POLLUTION FROM HAZARDOUS WASTES SITES A review of the processes that could result in the release of air contaminants from waste disposal sites leads to the conclusion that nearly all disposal facilities either currently emit, have emitted, or will emit air pollutants. The exceptions are those sites whose containment is such that it forms (and will continue to form) an impermeable barrier between the contaminants and the atmosphere. Whether the pollutants are emitted in sufficient concentration to merit concern, or even be detected, depends on numerous site-specific factors. The following discussion presents an overview of current knowledge about emissions from uncontrolled hazardous wastes sites. The discussion is intended to provide background information pertaining to the options presented in Sections 4 and 5. A list of the principal references supporting this discussion is presented in Section 8.1. 2.1 Emission Processes Once wastes are deposited in a site, they become subject to numerous physiochemical processes. Some of these processes result in the creation of new contaminants. Other processes, arising from the pressure within the waste system to achieve equilibrium with the environment, can cause contaminants to migrate through pores in the soil, or diffuse through liquids, resulting in a release of contaminants from the site. The contaminants may then escape into ------- the atmosphere, if conditions are suitable, through processes such as volatilization or particle suspension. Emissions can occur directly from the site itself or after transport off-site in ground water or surface water. Two general types of air contaminants are emitted from waste disposal sites: gases and participate matter. Gases may be organic, such as methane or chloroform, or inorganic, such as hydrogen sulfide. Gaseous emissions may arise as a result of volatilization of liquids such as benzene or toluene, or from reactions involving chemicals disposed of on the site (e.g., the formation of hydrogen sulfide). A less common source of gaseous emissions is gas containers disposed of on the site. In general, the volatilization of organic liquids is the most common source of gaseous emissions from disposal sites, although at least one death has occurred from exposure to gases generated as a result of the interaction of improperly co-disposed chemicals. Like gases, particulate contaminants may be either organic or inorganic. The particulate matter itself may pose a hazard, as in the case of asbestos particles. Alternately, a hazardous compound can be absorbed or adsorbed onto the particle. The principal factors responsible for particulate emissions from wastes sites are wind and atmospheric turbulence. They can result in resuspension of surface soil and particulate wastes, and the release of liquid aerosols. Escaping gases may also carry contaminated particles with them. 8 ------- Table 1 summarizes the result of ambient air monitoring studies conducted around several wastes disposal sites. Additional monitoring data are summarized in Appendix A. As can be seen from Table 1, ambient concentrations of many hazardous substances are elevated in the areas surrounding major wastes sites. These elevated hydrocarbon concentrations indicate that uncontrolled wastes sites may have an adverse impact on the surrounding atmospheric environment. Further, they indicate, as well, the potential hazard associated with air emissions from wastes sites. As an example, the benzene concentrations listed for Love Canal are equivalent to a _3 lifetime probability of about 10 that a continuously exposed individual will develop cancer due to the exposure.* 2.2 Factors Determining Emission Rates and Duration The rate and duration of particulate and gaseous emissions are influenced by many factors. The importance of each factor differs from site to site. Two general categories of factors can be identified: the physical characteristics of the site and the nature of the wastes in the site. Within the first category, the most important and easily assessed factors that distinguish the relative *The benzene risk values are based on a benzene potency factor of 7.4 x 10 per (ug/m ). This value assumes that the exposed individual weighs 70 kilograms, breathes 20 cubic meters of contaminated air per day continuously for 70 years. These assumptions are derived taken from the approach suggested for use in CERCLA public health evaluations (U.S. Environmental Protection Agency, 1986). The risk value is intended solely to illustrate the degree of risk that may be associated with exposure to the concentrations of certain waste site contaminants. ------- TABLE 1 AMBIENT AIR MONITORING RESULTS FOR SELECTED WASTES SITES Site Type of Kin Buc Contaminant (ng/m3) Benzene Carbon 111-13687 Tetrachloride Chlorobenzene T-1127 Chloroform T-6389 Chi oro toluene Dichloro- T-33783 benzene (o,m,p) Love Canal Sylvester Midco I BKK (ug/m3) (ppb) (ppb) (ppb) 522.7 0.03-3.56 10-2000* 270.0 3.0-4.8 5.0 0.1-172 ND-500* 240.0 0.5-24.0 10.0 5100 0.2-1.0 0.008-7650 0.3-100.5 Chem Dyne (ppb) 19.2 *ppm **ug/m3 T: Trace. ND: Not detected. Source: Adapted from James, Kinman, and Nutini, 1985, ------- TABLE 1 (Continued) Type of Contaminant Kin Buc (ng/m3) Site Love Canal (ug/m3) Sylvester (ppb) Midco I (ppb) BKK (ppb) Chem Dyne (ppb) 1,1-Dichloro- ethane 1,2-Dichloro- ethane 1,2-Dichloro- ethylene Ethlybenzene Methylene Chloride Tetrachloro- ethane Tetrachloro- ethylene 364-470 T-2173 T-5263 T-1000 32-54 T-2896 334 0.7-11.6 1140 0.2-52 95.0 0.03-0.43 0.03-4.89 0.04-0.24 1.4-3.7 ND-5000* 0.4-3.0 ND-1500* 0.62 *ppm **ug/m3 T: Trace. ND: Not detected. Source: Adapted from James, Kinman, and Nutini, 1985. ------- TABLE 1 (Concluded) Type of Contaminant Toluene Kin Buc (ng/m3) Love Canal (ug/m3) 0.1-6.2 570 Site Sylvester (ppb) Midco I (ppb) BKK (ppb) Chem Dyne (ppb) Trichloro- ethanes Trichloro- ethylene Vinyl Chloride Vinylidene Chloride Xylenes T (1,1,1) 294-357 (1,1,2) T-10052 15-48.75** 454-555 73 73 1.54 0.05-0.58 ND-1000 0.2-1.8 83-12800* 2-7.3 RD-1200* 0.3-1.3 140 73 1.8 *ppm **ug/m3 T: Trace. ND: Not detected. Source: Adapted from James, Kinman, and Nutini, 1985, ------- propensity of sites to emit contaminants are: the type of site (e.g., landfill, surface impoundment), the size of the site (including both the quantity of waste deposited and the surface area of the site), the characteristics of the soil on the site, and the containment provided by natural and manmade barriers to emissions. The age of the site is also very important but cannot usually be readily assessed. Older sites with poor containment have probably released nearly all of their contaminants while newer sites with poor containment are probably currently emitting. Additional site characteristics of lesser importance include: wind speed, surrounding topography, precipitation, temperature, humidity, and atmospheric pressure. The most important factors relating to the nature of the waste are the contaminant concentrations in the waste and the inherent physiochemical characteristics of the contaminant that influence its propensity to migrate through and out of the site to the atmosphere. 2.3 Contaminant Transport and Transformation The most common air contaminant release situation is the emission of contaminants directly into the atmosphere. Once in the air, the contaminants become subject to atmospheric transport and transformation processes which dilute the contaminant concentration as the emissions are "spread out" over an increasing area. The size of this area effected by an emission is determined by many factors, 13 ------- some which simply reduce the contaminant concentration (dilution and removal) and others that transform the contaminant into other chemicals (transformation). Together, dilution, removal, and transformation play a major role in determining the distance from the site at which the concentration of a contaminant released from the site into the atmosphere becomes insignificant. The mechanics of dilution in the atmosphere are generally well known. There are two principal dilution processes; advection and diffusion. Advection refers to the transport of contaminants arising from wind. Diffusion arises as a result of turbulence in the atmosphere, either thermal or mechanical. These processes are generally rapid phenomena and are usually modeled in terms of an exponential function of distance or time (Hanna, Briggs, and Hosker, 1982). The processes that give rise to dilution are also largely independent of the particular chemicals of concern. The remaining processes of contaminant removal and transformation in the atmosphere are more complex and less well known. One measure of the speed of contaminant removal and transformation (which in turn would indicate the limit of the potential exposure area) is the "atmospheric residence time" of the contaminant of concern. This contaminant-specific parameter is defined as the amount of time it takes 1-1/e (about 63 percent) of an initial quantity of a contaminant to be removed from the atmosphere by physiochemical processes such as photochemical 14 ------- oxidation and deposition. Atmospheric residence times for toxic and hazardous contaminants generally range between 3 and 70 days but may reach as high as 11,000 days (Cupitt, 1980). Table 2 lists the atmospheric residence times for typical waste site contaminants. Many of the common waste constituents, therefore, remain in the atmosphere for a long period of time and, considering common wind speeds in the United States, may be transported over long distances. Because of this, the geographic extent of potential exposure to air releases from a particular waste site is much greater than that of any other transport route. However, the magnitude of this exposure decreases rapidly as the concentration declines due to dilution. Therefore, although the number of exposed individuals may be large, the degree of exposure will be low over most of the geographic area concerned. A. less common phenomena is the transport of gases through the soil (sometimes dissolved in ground water) resulting in eventual emission into the interior of buildings. Once inside the buildings, these contaminants may become trapped, resulting in the buildup of contaminant concentrations. Contaminant concentrations in such instances may reach relatively high levels, as shown in Table 3. The contaminant concentrations illustrated in this table probably arose from wastes sites in the Niagara Falls area, such as the Love Canal disposal site. Thus, situations of low population, high dosage exposure may occur due to the emissions of air contaminants 15 ------- TABLE 2 ATMOSPHERIC RESIDENCE TIMES* FOR SELECTED CONTAMINANTS DETECTED AT HAZARDOUS WASTES SITES Compound Residence Time (days) Carbon Tetrachloride Greater than 11,000 Chlorobenzene 28 Chloroform 120 Dichlorobenzene 39 Dioxane 3.9 Methyl Chloroform 970 Methylene Chloride 83 Nitrobenzene 190 PCB Greater than 11 Toluene 1.9 Trichloroethylene 5.2 Xylenes 0.7 *Time required for a quantity of the individual compound to be reduced to 1/e of its original value by deposition, chemical transformation, or similar processes. Source: Adapted from Cupitt, Larry T., Fate of Toxic and Hazardous Materials in the Air Environment, (EPA-600/3-80-084), U.S. Environmental Protection Agency, Research Triangle Park, NC, August 1980. 16 ------- TABLE 3 RANGES OF ESTIMATED LEVELS OF ORGANIC VAPORS IN AMBIENT AIR OF HOUSEHOLD BASEMENTS IN NIAGARA FALLS, NY (ug/m3) Chemical Concentration Range Chlorobenzene Dichlorobenzene Isomers (3)* Trichlorobenzene Isomers (3) Tetrachlorobenzene Isomers (2) Pentachlorobenzene Chloro toluene Isomers (2) Dichlorotoluene Isomers (3) Trichloro toluene Isomers (4) Tetrachlorotoluene Isomer Bromotoluene Isomer Chloronaphthalene Isomer 1,2 - Dichloropropane Pentachlorobutadlene Isomer 1,3 - Hexachlorobutadiene Benzene ND - 0.65 - 0.07 - 0.03 - T - 1.7 - 0.13 - 0.06 - 0.03 - T - 0.08 - 1.4 T 0.03 - T - 4.2 190 33 20 0.49 490 370 0.157 4.1 4.4 3.4 0.41 520 *Values are the sum of the individual isomers detected. ND: Not detected. T: Trace. Source: Pellizzari, Edo D., "Analysis of Organic Vapor Emissions Near Industrial and Chemical Waste Disposal Sites," Environmental Science and Technology, Vol. 16, No. 11, 1982, pp. 781-785. 17 ------- from wastes sites. This type of situation is in contrast to the high population, low dosage exposure situations found as a result of emissions directly into the atmosphere. This difference in exposure situation requires differences in scoring mechanisms to account for the different threats. This phenomenon is not reflected in the current HRS air pathway, nor in the options discussed in Section 3. A separate report addresses the situation where building interior air contamination exists (Wolfinger, I987b).* *Currently, situations of indoor air contamination are considered for NPL listing when the contaminated buildings themselves are considered "sites," (see, for example, Monticello Radiation Contaminated Properties, NPL Ranking 502, 51 FR 20153). 18 ------- 3.0 ISSUES IN THE HRS AIR PATHWAY This chapter presents a discussion of the issues that have been identified concerning the HRS air pathway. A description of the overall structure of the HRS and the current air pathway is also provided. 3.1 Background on the Hazard Ranking System The HRS is designed to assess a site based on the information compiled in a site inspection. The system is intended to "estimate the potential hazard presented by releases or threatened releases of hazardous substances, pollutants and contaminants," and to score the site based on the risk posed by releases from the site (47 FR 31187). The HRS addresses three hazard modes: migration, fire and explosion, and direct contact. The latter two are not used in computing the site score but are included in the HRS as indicators of the need for emergency response. The migration mode consists of three potential migration pathways representing the major routes of environmental transport common to hazardous wastes sites: ground water, surface water, and air. Each pathway is structured similarly using three factor categories: release, waste characteristics, and targets. The release category reflects the likelihood that the site has, is, or will release contaminants to the environment. If available monitoring data indicate that the site is releasing contaminants, then an "observed release" has been demonstrated.* If no such observed Information other than ambient monitoring data can be used to establish an "observed release" in certain situations. These situations are addressed on a case-by-case basis. 19 ------- release can be demonstrated, then the release category is evaluated using route characteristics and containment factors. These factors are largely physical characteristics of the sites and their surrounding environments. It is important to note that the ground water and surface water routes contain factors for route characteristics while the air route does not. This permits sites to be evaluated for their potential to release contaminants to these two pathways in cases where documentation of a release is lacking. The current HRS requires that ambient air monitoring data support the conclusions that the site is, or has been, emitting contaminants before the site can receive a nonzero air route score. The waste characteristics category reflects the implicit hazard of the contaminants that have been or might be released. The factors included in the waste characteristics categories address qualitative and quantitative characteristics of the wastes and waste contaminants found on the sites. The targets category constitutes a measure of the population and resources that might be adversely affected by a release. The factor categories and the factors contained in them are illustrated in Table 4. Within each pathway, the site is assigned a value for each applicable factor. The factor values are then multiplied by weighting factors and summed within factor categories. The resulting factor category values are then multiplied and normalized to form a migration route score. Thus, for each site, three migration route 20 ------- TABLE 4 HRS SCORING FACTORS Factor Category Pathway Ground Water Surface Release Category Waste Characteristics Targets Monitoring data or Depth to aquifer of concern Net precipitation Permeability Physical state Containment Toxicity/persistence Quantity Ground water use Distance/population Monitoring data or Facility slope and terrain Rainfall Distance to receiving water Physical state Containment Toxicity/persistence Quantity Surface water use Distance/population Distance to sensitive environment Monitoring data Reactivity/ incompatibility Toxicity Quantity Land use Distance/population Distance to sensitive environment ------- scores are produced, each on a scale of 0 to 100. These route scores are referred to as follows: • Ground water (S ) gw • Surface water (S ) sw • Air (S) a The overall site migration score (S ) is then calculated as the m root mean square (RMS) of the pathway scores: 7 7 9 1/2 s - (i/i.73)[(s r + (s r + (s r] m gw sw a The RMS procedure was chosen to emphasize the highest scoring route while giving some consideration to secondary and tertiary routes. This procedure is illustrated in Figure 1. 3.2 Issues in the Current HRS Air Pathway The principal air pathway issue concerns an apparent Inconsistency in the release category among the three migration pathways. Currently, air pathway release category is evaluated solely on the basis of sampling data, or occasionally other types of information that indicate contaminants have escaped from the site into the air (e.g., photographs coupled with soil contamination samples). If the data indicate that an "observed release" has occurred, then a release category value of 45 is assigned. Otherwise, the site is assigned an air pathway release category value of 0. This latter assignment, combined with the multiplicative structure of the air pathway, results in the site being assigned an air route score of 0. In contrast, within the ground water and 22 ------- Observed Release 0 or 45 pts or Route Characteristics & Containment* 0-45 pts GW SW A Waste Characteristics — 0-26 pts — 0-26 pts — 0-20 pts *Not Included in Air Pathway GW = Ground Water Pathway SW = Surface Water Pathway A = Air Pathway Targets GW — SW — A — 0-49 pts 0-55 pts 0-39 pts Pathway Score 0-100 pts Normalized FIGURE 1 BASIC MRS STRUCTURE ------- surface water pathways, an option Is provided for evaluating the release category based either on sampling data, ££ on the physical characteristics of the site and its surrounding environment. These latter characteristics reflect the potential of the site to release deposited contaminants. The inclusion of a potential to release option within the migration pathways improves the degree to which the HRS score reflects the relative risk posed by a site. This conclusion is based on several reasons. First, it is not always possible to determine that a site is releasing contaminants based on monitoring data. The contribution of the site to ambient contaminant concentrations may be masked by the contributions of other sources. Alternately, adverse environmental conditions (e.g., high wind in the air pathway) may make the detection of contaminants in the surrounding media infeasible. Thus, relying solely on monitoring data may result in sites being assigned scores of zero, even though they pose a threat (albeit an undetected threat). Second, even if the site is not currently releasing contaminants, it may begin to release material in the near future. Relying solely on past information may result in a site being assigned a zero score, even though that site may pose a significant threat in the near future. Drum sites are an example of this possibility. Drums provide adequate, temporary containment for many wastes but can not generally be relied upon to contain the wastes over time. Finally, the site may have released 24 ------- contaminants in the past that were undetected in the site investigation, that still pose a threat to the surrounding population and environment. Examples of this possibility are large air emitting facilities that are currently inactive or abandoned but that caused area wide soil contamination from contaminant deposition. As a result of the review of current knowledge on air releases from hazardous wastes sites, known criticisms of the HRS and the collective years of experience with the implementation of the HRS, five additional issues were identified within the context of the air pathway during development of these options. These issues were deemed to be sufficiently important to be addressed in the development of the proposed modifications. First, the air pathway toxicity value for a site is based on the toxicity characteristics of the single, most toxic contaminant known to be present on the site and available for migration. In this context, contaminants are "available for migration" if they are not contained on the site by some physical barrier (e.g., the containment factor value for the portion of the site in which the contaminants is found is nonzero). This approach is employed regardless of whether the physiochemical characteristics of the contaminant would prevent it from escaping in a quantity sufficient to pose a significant threat to the surrounding area. Second, concern has been raised about the adequacy of the current approach to assessing the potential of waste materials to 25 ------- Interact on a site, either Increasing the rate (or probability) of air releases or causing the formation of more toxic contaminants than were originally deposited on the site. The air pathway currently employs a waste reactivity and incompatibility factor to reflect this potential. This issue is addressed in a separate report (DeSesso et al., 1986). The third issue arises from the way in which population is estimated in the air pathway targets category. These population estimates are developed in two ways. In the first, population data is acquired from the local governments in the areas surrounding the site. This method is most commonly employed when the target radii encompass entire jurisdictions. In the second method, population is estimated using estimates of the number of houses in the applicable areas. These house counts may be provided by local governments or may be made using maps of the area such as USGS topographic maps. The number of houses is converted to equivalent population using an estimate of 3.8 persons per house. This estimation procedure suffers from several weaknesses. First, the accuracy of the information is degraded in cases where the target radii do not encompass entire jurisdictions. The problem of determining the fraction of the population that resides within the area defined by the target radii is a serious problem. In these circumstances, emphasis is often placed on the house counts. The second weakness lies in the way the house counts are developed. These counts are often provided by local jurisdictions or 26 ------- developed from recent local planning maps. In such cases, the house counts themselves may be very accurate. However, in other instances, they may be based on outdated maps, such as USGS topographic maps, and hence may be very inaccurate. The third weakness arises whenever house counts (accurate or not) are converted into equivalent population. The use of a uniform value of 3.8 persons per house ignores spatial and other variations in household demographics. The availability of 1980 Census data as an alternative to these data source highlights these weaknesses. The fourth issue concerns the geographic extent of potential exposure to air contaminants from a site. The current HRS employs a radial distance limit of four miles in evaluating the population exposure factor and distance limit of two miles in evaluating the land use and sensitive environment factors. Given the potential geographic extent of exposure indicated by the available information on atmospheric residence times and long-range transport phenomena (see, for example, National Research Council, 1983), a re-evaluation of these "target distance" limits is indicated. A separate report addressing the question of target distance limits is being prepared (Wolfinger, 1986a). The final issue arises from the underlying assumptions embedded in the current air pathway about the nature of air contaminant migration. The pathway is designed to rank sites based on the potential hazard they pose through direct emission of contaminants 27 ------- to the ambient air, subsequent transport, and eventual inhalation. As stated previously, situations of indoor air contamination are generally scored using the air pathway only when the buildings in question are considered the "wastes site". Due to its underlying assumptions, the HRS air pathway does not address the potential hazard posed by migration of air contaminants from a wastes site, through the soil, and into buildings. This is evident in the definition of observed release used in evaluating monitoring data. The data used to establish an observed release must be based on outdoor, ambient air monitoring. Data from monitoring performed indoors can not be used to establish an "observed release" unless the contaminated building itself is the site. Situations may arise in which a significant threat is posed by a site due to the migration and potential inhalation of air contaminants that, nonetheless, will not receive a nonzero air pathway score unless those emissions are sufficient to induce an elevation in outdoor contaminant concentrations above background. Due to differences in dispersion characteristics between indoor and outdoor air, it is possible that indoor air concentrations may reach significant levels while outdoor air concentration remains relatively unaffected. Thus, the air pathway observed release assumptions effectively preclude assigning a positive score to many sites experiencing indoor air contamination problems. Further, the current HRS air pathway is somewhat biased against such sites in the approach taken to evaluate the size of the exposed 28 ------- population. The target population factor approach requires that a fairly large population reside near the site to achieve a high value. A population of at least 1,001 persons residing within 1/4 mile of the site (3,001 within 1/2 mile or 10,001 within 1 mile) is required to assign 24 out of a possible 30 points for the population target factor. This is moderated by the medium values assigned to low populations near the site (e.g., one person residing within 1/4 mile of the site permits a site to receive at least 18 out of a possible 30 points). The approach currently employed reflects the perception that the average dose to the population, will be small, while the exposed population will be relatively large. This approach is not consistent with the high dose, low population exposure situation that would be characteristic of indoor air contamination sites. Because of this inconsistency, the HRS air pathway score assigned to a site associated with indoor air contamination may understate the relative risk posed by the site by underemphasizing the importance of exposures to small populations. Thus, the current HRS air pathway may not be adequate for assessing the relative threat of these sites. A scoring mechanism for indoor contamination sites is presented in Wolfinger, 1987b. The air pathway options, discussed in Sections 4 and 5, address the potential to release issue and the first three of the additional issues discussed above: evaluation mobility as part of the toxicity factor, use of waste reactivity and incompatibility data, and population evaluation. 29 ------- 3-3 Options for Revising the HRS Air Pathway The following two chapters describe three options for revising the HRS air pathway, in response to the issues discussed above. The principal focus of the options is on methods for evaluating the potential of a site to release contaminants. The first two Options (1 and 1A) are very similar, they differ only in the particular descriptors used in evaluating sites. Both of these options employ a multiple emission source descriptor approach, using probabilistic combinatorics to combine the values associated with each descriptor into an overall value for the site. The third option (Option 2) is a simpler approach, again employing a choice among several emission source descriptors, although only the highest scoring applicable descriptor is used to evaluate the site. This latter approach is similar to that used in the ground water and surface water pathway. Numerous additional options were developed, discussed with EPA, and rejected. These options are summarized in Appendix B. 30 ------- 4.0 MULTIPLE SOURCE, PROBABILISTIC APPROACHES (OPTIONS 1 AND 1A) Two similar options for revising the HRS air pathway are presented in this chapter. The options are consistent in structure with the ground water and surface water migration pathways of the current HRS. However, these options use a very different approach to evaluating the overall potential of a site to release contaminants than is used in the other pathways. The other pathways evaluate the overall site release potential based on the potential of that portion of the site that is most likely to release contaminants (i.e., a single, "worst" source approach). The options described in this chapter employ probabilistic combinatorics to assess the site potential as the aggregate potential of up to three source areas on the site. The important features of the options are summarized in Table 5. An alternate, single, "worst" source approach, for the air pathway is presented in Section 5. In each option, the analyst evaluates available ambient air monitoring data to determine if an observed release has occurred. If the data do not demonstrate an observed release, the analyst may then evaluate the site based on its potential to release. In either case, the waste characteristics and targets factors are then evaluated as indicated. The release, waste characteristics and targets factor evaluations are next multiplied together and normalized on a scale of 0 to 100 to form the air pathway score. 31 ------- TABLE 5 OVERVIEW OF IMPORTANT FEATURES OF AIR PATHWAY OPTIONS 1 AND 1A Option 1 Option 1A RELEASE CATEGORY Observed release Observed release based on monitoring based on monitoring data data Potential to release Potential to release based on: based on: - 30 size-dependent - 12 size-dependent emission source emission source descriptors descriptors (3 size classes) (3 size classes) - gas and particulate - gas and particulate mobility factors mobility factors - detailed gas - less detailed gas and particulate and particulate containment factors containment factors WASTE Combined toxicity- Combined toxicity- CHARACTERISTICS mobility factor mobility factor Waste quantity Waste quantity TARGETS Population Population Sensitive environment Sensitive environment Land use Land use 32 ------- The following sections discuss the three factor categories (release, waste characteristics, and targets) and the rating factors contained in them, for the two air pathway options. The relationship between the categories and the factors is illustrated in Table 5. Tables for all of the factors, except containment, are provided in the text. Tables of containment factors are provided in Appendix D. Step-by-step instructions for employing Option 1, with an example of its application, can be found in Appendix C. 4.1 Release Category The release category reflects the likelihood that the waste site was, is now, or will be, emitting a significant quantity of any air contaminant or combination of contaminants. If the available monitoring data indicate that the site has released hazardous substances to the air (i.e., an observed release has occurred), then the likelihood that the site is emitting a significant quantity of an air contaminant is deemed to be 100 percent (47 FR 31188). In these cases, a maximum release value would be assigned to the site. The maximum value possible has been set at 45, maintaining consistency among the pathways in the current HRS. If no observed release can be documented, then the site is evaluated based on its "potential to release". The maximum possible potential to release value is also 45. The potential to release factor value reflects the likelihood that the site has released contaminants in the past or will release contaminants sometime in 33 ------- the future, as well as the likelihood that the site is currently emitting undetected contaminants. This likelihood is formally a subjective probability.* It is "subjective" in that it is based on information about the site rather than a frequency of occurrence of releases at other sites with similar characteristics. It represents, therefore, the judgment of a group of experts rather than the results of a statistical sampling program. The options for evaluating potential to release, discussed below, establish a procedure for translating information about the physical characteristics of a wastes site into a subjective probability that the site has, is, or will emit a significant quantity of contaminant. 4.1.1 Observed Release Several factors contribute to the determination that an "observed release" has occurred at a site. Given the wide variety of emission sources contributing to air pollution, it is nearly always possible to detect air contaminants near a wastes disposal site. However, the detected contaminants may not have been released from the site, but may have originated from numerous sources nearby or even a long distance away. For example, sulfate originating in the Ohio River Basin has been detected in Upstate New York, while indium from Ontario has been detected in Rhode Island (National Research Council, 1983; Rahn, Lowenthal, and Lewis, 1982). *For detailed discussions on subjective probability, the reader is directed to Jaynes, 1958; Kyberg and Smokier, 1964; Raiffa, 1970, and Stael von Holstein and Matheson, 1978. 34 ------- It is essential, therefore, to determine that a significant portion of the detected contamination arose from the site. A sample of the "background" air is required to make this determination. The background sample should be taken close enough to the site to include the contributions of all other major sources of potential contaminants but far enough away from the site to exclude contributions from the site itself. This generally implies that the background sample be taken upwind from the site and that the "site sample" be taken downwind of the site. The difference or ratio of the site and background samples can be used to determine if an observed release has occurred. If the ratio or difference is "significant," then the site is considered to be emitting and an observed release value of 45 is assigned. Otherwise, an observed release value of 0 is assigned and the potential to release rating factors are evaluated. 4.1.1.1 Definition of Significant Difference. The question of "significance" in the context of the HRS air pathway is complex. It is complicated by the highly variable nature of the atmospheric environment and the effects of such variations on site emission characteristics. A release is considered significant if it results in an elevation in the ambient concentration of any contaminant above that which would occur if the site were not present. Furthermore, there must be a reasonable certainty that any elevation in concentration indicated by the data arose from the site and is 35 ------- not simply the result of factors Independent of the site, e.g., meteorological conditions and nearby sources. Significance is thus defined in terms of demonstrating that a release has occurred, not in terms of the degree of hazard posed by the release. A complete discussion of the question of significance in the context of the HRS can be found in Brown, 1986. 4.1.1.2 Implications for Sampling. These considerations place requirements on the procedures used in sampling. It is imperative that the site samples not be taken in such a fashion as to artificially elevate the measured concentrations. This imperative precludes, for example, the use of samples taken inside of drums or vents, or samples taken immediately above pools of liquid wastes, as site samples. The overriding principle concerning a site sample is that it represent the concentration that an individual might reasonably be exposed to from the site. In practice, this principle leads to an operational "rule of thumb" that the site sample should be taken at least 20 feet away from the emission sources on the site and that the sample be taken "in the breathing zone". The background and site samples can then be compared and the release category evaluated. An obvious problem arises in practice, however, with this approach. Financial constraints usually restrict the number of air samples taken. In most cases, the emphasis in air sampling has been placed on investigator safety rather than site characterization. Typically, only a few ambient samples are 36 ------- available for any particular site for use in assessing observed releases. An additional problem arises regardless of the thoroughness of the sampling plan, the sophistication of the sampling equipment employed and the care taken during actual sampling. Because the emissions characteristics of many sites generally depend on highly variable atmospheric conditions (including temperature, pressure, wind speed, and stability), it is possible that many sites may not be releasing a sufficient quantity of contaminants to affect an observed release during the sampling period. Alternately, the sampling stations may not be in the "emissions plume" due to unforeseeable meteorological conditions. Thus, it is all too likely that air sampling will miss an observed release unless the site emissions rate is high and sustained, or unless the sampling was performed at an advantageous time and place. 4.1.1.3 Improvements in the Current Approach. The options presented here envision a somewhat different approach than is currently used to evaluate whether an observed release has occurred. The practice in the current MRS is that a statistically significant difference between contaminant concentrations in background and site samples, or an order of magnitude difference between background and site samples, is sufficient, but not necessary, to achieve an "observed release". There are numerous problems with the statistical approach. It is problematic whether the samples taken during a site 37 ------- investigation meet the requirements for statistical hypothesis testing of significant difference, e.g., representativeness and independence. The "order of magnitude" approach, as it is currently employed, is also weak. There is little scientific basis for requiring a 10-fold difference to demonstrate an observed release (as opposed to, for example, a 5-fold or 20-fold difference). This aspect of determining observed releases is discussed in Brown, 1986. Currently, there are few restrictions on the samples; the only uniformly binding requirements being that the samples be taken "in the breathing zone," i.e., at a height of about five feet and that they be taken with an instrument that will screen out methane. No other restrictions apply uniformly and no consideration is given to the conditions under which the samples are taken. Because of the problems routinely encountered by investigators in establishing an observed air release based on current sampling practices, stricter requirements on monitoring data would be imposed in these options making it more difficult for a site to achieve an "observed release". However, the atmospheric conditions under which the monitoring occurred would be considered, potentially reducing the level at which a difference between the the background and site samples would be considered significant. This approach is described below. The approach employs the ratio of the background and site samples as the measure of interest. A similar approach can be developed using the difference between the samples. The thresholds 38 ------- for significance employed below are provided for illustrative purposes only and will be further evaluated. Under "normal" atmospheric conditions, the ratio of the concentration of any CERCLA contaminant in the site and background samples would be required to exceed a uniform threshold (e.g., 10) to achieve an observed release. "Normal" atmospheric conditions are considered to be those that do not suppress emission from the site. If atmospheric conditions are such that detected concentrations would be lowered relative to the site's potential to emit, or if emissions levels would be suppressed relative to average conditions, then conditions would be considered "abnormal". Under these conditions a lower significance threshold would be used, for example, a ratio of 1.5. If either threshold is achieved, as applicable, then a release value of 45 would be assigned. Information describing the sampling conditions, including average wind speed and direction during sampling, must be provided in support of the sampling data. Identification of other potential, nearby sources of the detected contaminants is also desirable. Atmospheric conditions deemed to meet the criteria for a lower threshold value are listed in Table 6. This list is intended to be fairly exhaustive, although other circumstances should be treated on a case-by-case basis. If implemented, this list of conditions would require further refinement. Consideration must be given to the trade-off between the increased flexibility in determining an observed release 39 ------- TABLE b SITE CONDITIONS THAT MAKE IT DIFFICULT TO DEMONSTRATE AN OBSERVED RELEASE High wind speeds Low temperature High relative humidity, including precipitation Flat and open surrounding terrain Unstable atmosphere 40 ------- envisioned here, and the increase in difficulty in assuring the quality of the data that such a subjective approach entails. Further guidance on site sampling can be found in the reports listed in Section 8.2. 4.1.2 Potential to Release As implied in the above discussions, there are numerous reasons why an observed release from a site may be difficult to demonstrate even though a release has occurred. The potential to release portion of the air pathway is intended to provide for the scoring of sites when no observed release can be demonstrated. The approach reflected in the options discussed below uses information on the physical and chemical characteristics of the site and the wastes in the site to assess the subjective probability that the site has, is, or will emit a significant quantity of contaminants. This subjective probability is implicitly translated into a scale of 0 to 45 in the tables and worksheets. The characteristics of a site that indicate its potential to release are evaluated and the resulting values combined in an algorithm that reflects the probabilistic aspects of the release category. This algorithm is discussed in detail below. This approach differs from the approach currently embodied in the ground water and surface water pathways, although the potential to release values in these pathways can be interpreted probabilistically. Currently, in the other pathways, the evaluation 41 ------- of the release potential of a site employs a single, "worst" source approach. In these pathways, different areas of the site are evaluated according to particular criteria (e.g., physical state and containment) and the value for the highest scoring area (i.e., the single, "worst" source) is used as the release value. Interpreted probabilistically, the release category in the ground water and surface water pathways reflect the maximum probability that some portion of the site will release contaminants. This "maximum" value is actually less than the combined probability that some portion of the site will release contaminants. The combined probability is employed in Options 1 and 1A discussed below. The option discussed in Section 4 (Option 2) employs the approach embodied in the current ground water and surface water pathways. The overall approach discussed below was chosen for two fundamental reasons. First, the principal alternate approaches (those based on emission estimation equations) were deemed to be too complex and required data that would be impossible to gather in a site investigation (e.g., mass transfer coefficients for contaminants in site-specific waste mixtures). Second, this approach is consistent with the probabilistic nature of the potential to release component of the pathway and employs most of the principal factors that determine site emission characteristics. This approach better reflects the probability that the overall site will emit contaminants, in comparison to the single maximum approach currently 42 ------- employed in the other pathways, and hence, results in a site score that better reflects the risk posed by the site. The principal negative aspect of the approach taken is its computational complexity. This complexity is mitigated, however, by the development and use of descriptive tables and easily used references (e.g., Versar, 1984). As indicated in Table 5, four site characteristics are employed in assessing the potential of a site to emit air contaminants: • Emission source descriptor • Size • Overall contaminant mobility • Containment The first two characteristics are combined into a single factor. The size-dependent emission source descriptors constitute a simple classification of sites according to type of "disposal" employed on the site (e.g., landfill or surface impoundment). The use of these descriptors reflects the belief of the author that the type of site is important in determining the rate and duration of emissions. The importance of the type of disposal practice employed on the site in determining organic compound emissions is indicated in Table 7. This table indicates that the disposal practice is one of the principal determinants of the rate of volatilization of organic compounds from a site. For example, the data indicate that emission rates from landspreading will be greater for a shorter 43 ------- TABLE 7 TIME NEEDED FOR 75 PERCENT OF SELECTED COMPOUNDS TO VOLATILIZE FOR VARIOUS DISPOSAL METHODS Contaminant Phenol Tetrachloroethylene Benzene Ethanol Methyl Ethyl Ketone Ethylactetate Tricolor oethylene Chloroform Carbon tetrachloride Dichloroethane Dimethylamine Ethylene Pentane Dichloroethylene Landspreadlng 39 days * 5 days 16 hours 7 hours * 7 hours * * 3 hours 0.7 hours * * * Disposal Method Surface Impoundment * 12.4 days 11.6 days * * * 11.4 days 11.3 days 10.3 days 9.1 days * 7.4 days * * Covered Landfill 333 years * 41 years * * 2.6 years 2 years 11 months * 11.7 months * * 7.8 months 4.2 months *Data not available to calculate rate for this substance. Source: Scheible et al., 1982. 44 ------- period than those of covered landfills, all other characteristics being the same. Contaminant mobility refers to the overall propensity of the contaminants on the site to migrate to the surface and escape into the atmosphere, based on their physiochemical characteristics. Contaminant mobility is reflected with separate factors for gaseous and particulate contaminants. Table 7 also illustrates the importance of the characteristics of the contaminants in the site. As indicated in Table 8, phenol is generally less mobile than dichloroethane. This relative mobility is evident as well in the longer retention time indicated for phenol in a landfill (333 years) as compared with dichloroethylene (4.2 months). Containment refers to the physical characteristics of the site, either manmade or natural, that act to restrict emissions and contain the contaminants on the site. Containment is also reflected with separate gaseous and particulate factors. Containment is the single most important factor determining potential to release, hence its employment as a multiplicative rather than an additive factor. The overall approach to evaluating the potential of a site to release contaminants is as follows. The emission sources on the site are identified and classified using the emission source descriptors. The size of each emission source is assessed and a size class assigned to each emission source descriptor. From this 45 ------- TABLE 8 DATA ON MOBILITY OF PHENOL AND DICHLOROETHYLENE Contaminant Phenol Dichlorethylene (1,1) VP* 0.62 630.1 AQ* 1.3 E-6 1.5 E-2 RS* 2.0 E-l 202 *VP: Vapor pressure In units of mmHg at 25° C. AQ: Henry's constant in units of atm-m^/mol. RS: Relative soil volatility as defined in Versar, 46 ------- information, a size-dependent emission source descriptor value is assigned to up to three of the selected descriptors. The contaminants present in the areas represented by the descriptors are identified and used to calculate a gaseous contaminant mobility value for each descriptor. The particulate mobility value for each selected descriptor is calculated based on characteristics of the climate surrounding the site (primarily wind speeds, precipitation, and temperature). The two mobility values are combined and added to the emissions source descriptor value, for each descriptor selected. The gas and particulate containment aspects of the areas represented by each of the three selected descriptors are evaluated and their values combined into a single containment value for each selected descriptor. The sum of the descriptor and mobility values are then multiplied by the containment value to form an overall value for each of the three selected descriptors. This value represents the probability that the sources represented by the selected descriptor has, is, or will emit a significant amount of contaminant. The three descriptor-specific values are then combined into an overall potential to release value for the site using the appropriate probability formula (see Section 4.1.2.4). The relationship of the potential to release value to the probability that a site will emit a significant quantity of air 47 ------- contaminants (i.e., the emissions probability) is as follows. The size-dependent site descriptor value reflects the subjective probability that an uncontained site (containment value equivalent to 3) with relatively immobile contaminants (mobility value equivalent to 0) could release a significant quantity of air contaminants. The emission probability is equal to the value divided by 15. For example, the emission source descriptor value assigned to a small landfarm is 6.* Thus, the probability that such a source, poorly containing relatively immobile contaminants, would emit a significant quantity of air contaminants is estimated at 6/15 (or, equivalently, 18/45). The mobility factor serves to increase the emission probability based on the overall mobility of the contaminants associated with the emission source descriptor in question. Continuing the example, the emission probability for a similar landfarm with very mobile contaminants (mobility value of 5) would be 11/15 (or [6 + 5]/15). The containment value serves to decrease the probability based on the degree to which physical barriers present on the site would reduce emissions. Thus, the emission probability for a small, relatively uncontained (containment value of 2) landfarm with very mobile contaminants would be 22/45 (or 11/15 x 2/3). This corresponds to an overall value for the landfarm of 22 on a scale of 0 to 45. *This example employs the value given in Table 13 for a small landfarm. 48 ------- Values based on any other scale can be readily developed by multiplying the probabilities by the desired scale. The following discussion describes the factors and this approach in greater detail. 4.1.2.1 Size-Dependent Emission Source Descriptors. A list of emission source descriptors and associated definitions was developed based on the results of the literature review, an examination of the descriptors used by investigators in describing candidate NPL sites and a review of the definitions promulgated under RCRA. Lists of the descriptors for Option 1 and 1A are provided in Table 9 and Table 10, respectively. Complete definitions are provided in Appendix D. The differences in the number and definitions of the emission source descriptors listed in Tables 9 and 10 constitute the principal differences between the options.* The selection of emission source descriptor is generally left up to the investigator evaluating the site. However, there are necessary restrictions in the selection process. First, the descriptors selected should be the ones that best describe the site. It contravenes the system to call a puddle of water a "surface impoundment," for example, simply to achieve a higher site score. Second, in order to use a descriptor, information indicating that hazardous contaminants have been located or deposited in the area *The only remaining differences between the options lie in the containment factor definitions. These differences arise largely from the differences in emission source descriptors, as well. 49 ------- TABLE 9 OPTION 1 EMISSION SOURCE DESCRIPTORS Code Descriptor Aboveground or Iaground Tanks: 01 • Tanks intact 02 • Tanks broken 03 Active Fire Site 04 Belowground Injection 05 Belowground Tanks Contaminated Surface Soil: • Background at or above analytical detection limit; 06 - Contamination level at or below background 07 - Contamination level above background but not significantly above background 08 - Contamination level significantly above background • Background below analytical detection limit; 09 - Contamination level below analytical detection limit 10 - Contamination level above analytical detection limit Exposed Drum Site: 11 • Drums broken 12 • Drums intact Inactive Aboveground Fire Site: 13 • Re-ignition expected 14 • Re-ignition not expected Inactive Belowground Fire Site: 15 • Re-ignition expected 16 • Re-ignition not expected 17 Landfarm/Landtreatment 50 ------- TABLE 9 (Concluded) Code Descriptor Landfill: 13 • With both biodegradable material and exposed drums 19 • With biodegradable material but without exposed drums 20 • All other situations 21 Open Pit Spill Site: .22 • Spill dry 23 • Spill wet Surface Impoundment: 24 • Dry; evidence of waste contamination near surface 25 • Dry; all other situations 26 • Wet; evidence of waste contamination near surface 27 • Wet; all other situations 28 Surface Water Body or Outfall 29 Waste Pile 30 Emission Sources Not Elsewhere Specified 51 ------- TABLE 10 OPTION 1A EMISSION SOURCE DESCRIPTORS Code Descriptors 01 Active Fire Site 02 Belowground/Buried Containers 03 Contaminated Soil 04 Dry Surface Impoundment 05 Inactive Fire Site 06 Intact Exposed/Aboveground Containers 07 Landfarm 08 Landfill 09 Nonintact Exposed/Aboveground Containers 10 Waste Pile 11 Wet Surface Impoundment 12 Emission Sources Not Elsewhere Specified 52 ------- covered by that descriptor is required before that descriptor can be used. Third, generally a descriptor can be used only once in describing a site. This principle applies unless it can be established that two different areas described by the same descriptor received different wastes or are otherwise dissimilar. Further, the area described by a selected descriptor should be as homogenous as possible. For example, if a site contains two different landfills with similar waste and containment characteristics, then the landfill descriptor may be used once, referring to both landfills simultaneously. However, if two dissimilar landfills are present on the site, the "landfill" descriptor should be employed twice. A fourth restriction associated with the size of the source described by the selected descriptor is discussed below. Three size categories are defined for emission source descriptors using data developed in 0'Sullivan, 1982 and Vogel and 0*Sullivan, 1983. Size category definitions were developed, for convenience, both in units of surface area and equivalent volume, as applicable. Different values of depth were employed following the assumptions in the aforementioned references. The size categories were developed using the percentiles of the distribution of RCRA Part A volume and surface area data as presented in the references. The RCRA Part A data was the only information source that could be identified for size-related data. The applicability of the data to CERCLA sites is problematic. 53 ------- For the purposes of evaluating the size of the area covered by a particular emission source descriptor, only the total area containing waste materials should be included. When two areas are covered by the same descriptor, then the sum of their respective areas is used in evaluating the overall area. For example, if a site contains two similar landfills (similar in waste and containment characteristics), the size associated with the "landfill" descriptor is the sum of the sizes of the landfills. If the "landfill" descriptor is used twice to reflect the presence of two dissimilar landfills, then the size associated with each use of the descriptor is the size of the applicable landfill. Size categories for the Option 1 and 1A emission source descriptors are presented in Tables 11 and 12, respectively. The use of these size categories places an additional restriction on the investigator's selection of emission source descriptors. In general, the areas covered by the descriptors selected must be larger than the minimum size in the "Small" size category. If this constraint cannot be met, then the investigator must use only the descriptor whose size is greatest relative to the minimum size in its "Small" category. A set of values were developed for the various size-dependent emission source descriptors based on the judgment of the author concerning the subjective probability that a generic emissions source of specified description and size would emit a significant 54 ------- TABLE 11 OPTION 1 SIZE RANGES Descriptor Belowground Tanks (cubic feet) Small Medium Large Contaminated Surface Soil (square feet) Small Medium Large Exposed Drum Site (number of drums) Small Medium Large Inground or Aboveground Tanks (cubic feet) Small Medium Large Inactive Aboveground Fire Site (square feet) Small Medium Large Inactive Belowground Fire Site (square feet) Small Medium Large Landfarm/Landtreatment (square feet) Small Medium Large Landfill (cubic feet) Small Medium Large Size Range 1,000 - 8,900 8,900+ - 470,000 greater than 470,000 11,000 - 200,000 200,000+ - 2,600,000 greater than 2,600,000 1 - 250 251 - 10,000 greater than 10,000 1,000 - 8,900 8,900+ - 470,000 greater than 470,000 11,000 - 200,000 200,000+ - 2,600,000 greater than 2,600,000 74,000 - 190,000 190,000+ - 21,000,000 greater than 21,000,000 11,000 - 200,000 200,000+ - 2,600,000 greater than 2,600,000 74,000 - 190,000 190,000+ - 21,000,000 greater than 21,000,000 55 ------- TABLE 11 (Concluded) Descriptor Landfill (square feet) Small Medium Large Open Pit (cubic feet) Small Medium Large Open Pit (square feet) Small Medium Large Spill Site (square feet) Small Medium Large Surface Impoundment (cubic feet) Small Medium Large Surface Impoundment (square feet) Small Medium Large Surface Water Body or Outfall (square feet) Small Medium Large Waste Pile (cubic feet) Small Medium Large Waste Pile (square feet) Small Medium Large Size Range 11,000 - 28,300 28,300+ - 790,000 greater than 790,000 74,000 - 190,000 190,000+ - 21,000,000 greater than 21,000,000 11,000 - 28,300 28,300+ - 790,000 greater than 790,000 11,000 - 200,000 200,000+ - 2,600,000 greater than 2,600,000 1,000 - 8,900 8,900+ - 470,000 greater than 470,000 300 - 2,700 2,700+ - 71,000 greater than 71,000 300 - 2,700 2,700+ - 71,000 greater than 71,000 130 - 1,300 1,300+ - 88,000 greater than 88,000 36 - 360 360 - 10,600 greater than 10,600 56 ------- TABLE 12 OPTION 1A SIZE RANGES Descriptor Belowground/Buried Containers (cubic feet) Small Medium Large Exposed/Aboveground Containers (cubic feet) Small Medium Large Contaminated Soil (square feet) Small Medium Large Inactive Fire Site (square feet) Small Medium Large Landfarm/Landtreatment (square feet) Small Medium Large Landfill (cubic feet) Small Medium Large Landfill (square feet) Small Medium Large Open Pit (cubic feet) Small Medium Large Size Range 1,000 - 8,900 8,900+ - 470,000 greater than 470,000 6 - 1,400 1,401 - 56,000 greater than 56,000 11,000 - 200,000 200,000+ - 2,600,000 greater than 2,600,000 74,000 - 190,000 190,000+ - 21,000,000 greater than 21,000,000 11,000 - 200,000 200,000+ - 2,600,000 greater than 2,600,000 74,000 - 190,000 190,000+ - 21,000,000 greater than 21,000,000 11,000 - 28,300 28,300+ - 790,000 greater than 790,000 74,000 - 190,000 190,000+ - 21,000,000 greater than 21,000,000 57 ------- TABLE 12 (Concluded) Descriptor Open Pit (square feet) Small Medium Large Spill Site (square feet) Small Medium Large Surface Impoundment (cubic feet) Small Medium Large Surface Impoundment (square feet) Small Medium Large Surface Water Body or Outfall (square feet) Small Medium Large Waste Pile (cubic feet) Small Medium Large Waste Pile (square feet) Small Medium Large Size Range 11,000 - 28,300 28,300+ - 790,000 greater than 790,000 11,000 - 200,000 200,000+ - 2,600,000 greater than 2,600,000 1,000 - 8,900 8,900+ - 470,000 greater than 470,000 300 - 2,700 2,700+ - 71,000 greater than 71,000 300 - 2,700 2,700+ - 71,000 greater than 71,000 130 - 1,300 1,300+ - 88,000 greater than 88,000 36 - 360 360 - 10,600 greater than 10,600 58 ------- amount of air contaminants. The author's opinion is based on the literature review and a review of the limited air monitoring data available in the NPL site files and remedial investigation reports. The quality and coverage of the available monitoring data preclude the calculation of "objective," frequency-based probabilities. The initial values were modified, as necessary, after consultation with personnel from the EPA Environmental Response Team, Hazardous Waste Engineering Research Laboratory, and Office of Air Quality Planning and Standards. Values for Option 1 and 1A emission source descriptors are presented in Tables 13 and 14, respectively. Values on any other desired scale can be developed by dividing the listed value by 15 and multiplying by the maximum of the desired scale. For example, the value for a small landfarm, evaluated on a scale of 0 to 20, would be 6/15 x 20 or 8.* 4.1.2.2 Contaminant Mobility. Contaminant mobility is evaluated using the combination of two mobility factors, one addressing gaseous contaminants, the other addressing particulate matter. The gas mobility factor reflects the potential of the contaminants in a site to migrate through the site to the surface/ air interface and escape as a gas. The factor is based on three physiochemical characteristics of the contaminants: vapor pressure, Henry's constant, and dry relative soil volatility. Vapor pressure *Such changes of scale would require adjustments in the mobility factor value scales and in the conversion factors used on the worksheets (i.e., 45 and 2,025). 59 ------- TABLE 13 OPTION 1 EMISSION SOURCE DESCRIPTORS AND VALUES Values ode Descriptors 01 Aboveground or Iaground Tanks: Tanks intact 02 Aboveground or Inground Tanks: Tanks broken 03 Active Fire Site 04 Belowground Injection 05 Belowground Tanks 06 Contaminated Surface Soil: Background at or above analytical detection limit; contamination level at or below background 07 Contaminated Surface Soil: Background at or above analytical detection limit; contamination level above background but not significantly above background 08 Contaminated Surface Soil: Background at or above analytical detection limit; contamination level significantly above background 09 Contaminated Surface Soil: Background below analytical detection limit; contamination level below analytical detection limit 10 Contaminated Surface Soil: Background below analytical detection limit; contamination level above analytical detection limit 11 Exposed Drum Site: Drums broken 12 Exposed Drum Site: Drums intact 13 Inactive Aboveground Fire Site: Re-ignition Expected 14 Inactive Aboveground Fire Site: Re-ignition Not Expected Medium 8 10 10 10 60 ------- TABLE 13 (Concluded) Values Code Descriptors Small Medium 15 Inactive Belowground Fire Site: 4 6 Re-ignition Expected 16 Inactive Belowground Fire Site: 2 4 Re-ignition Not Expected 17 Landfarm/Landtreatment 6 8 18 Landfill: 6_ 8_ With both biodegradable material and exposed drums 19 Landfill: 4_ 6_ With biodegradable material but without exposed drums 20 Landfill: All other situations 1_ 3_ 21 Open Pit 5 7_ 22 Spill Site: 4 6_ Spill dry 23 Spill Site: 6_ 8_ Spill wet 24 Surface Impoundment: 6 8 Dry; evidence of waste contamination near surface 25 Surface Impoundment: 2 4 6 Dry; all other situations 26 Surface Impoundment: 5 7 9 Wet; evidence of waste contamination near surface 27 Surface Impoundment: 1 3 5_ Wet; all other situations 28 Surface Water Body or Outfall 3_ 5_ 7_ 29 Waste Pile 5_ 7_ 9_ 30 Emission Sources Not Elsewhere: 3 3 3_ Specified 61 ------- TABLE 14 OPTION 1A EMISSION SOURCE DESCRIPTORS AND VALUES Code Descriptors 01 Active Fire Site 02 Belowground/Buried Containers 03 Contaminated Soil 04 Dry Surface Impoundment 05 Inactive Fire Site 06 Intact Exposed/Aboveground Containers 07 Landfarm 08 Landfill 10 Nonintact Exposed/Aboveground Containers 10 Waste Pile 11 Wet Surface Impoundment 12 Emission Sources Not Elsewhere Specified Values Small 10 1 6 5 5 1 6_ 5 8 5 5 3 Medium 10 3 8 7 7 1 8_ 7 9 7 7 3 Large 10 5 10 9 9 1 10 9 10 10 9 3 62 ------- provides a measure of the propensity of a contaminant to escape from a pure liquid or solid. Henry's constant (defined as the ratio of the partial pressure of a gas in solution to the mole fraction of the gas in solution) provides a measure of the propensity of a contaminant to escape from a solution. Relative soil volatility is a measure of the tendency of a gas to move through and escape from soil. The derivation of this complex factor is described in Versar, 1984. A vector of values for each of these characteristics can be assigned to a contaminant using the evaluation techniques developed by Versar and summarized in Table 15. Versar ranked wastes and contaminants based on their vapor pressures, Henry's constant and relative soil volatility in order to identify, for example, highly volatile wastes. The associated values were assigned by the author. Referring to the data presented in Table 8, the vector of mobility values for phenol would be (2,1,2), while that of dichloroethylene would be (3,3,3). An average of the three values for five contaminants present on the site is used in evaluating the gas mobility value. An average is used as an attempt to address the effects of co-disposal and resulting mixing of wastes and waste contaminants. In theory, the average of several contaminants characteristics would be a better estimator of the mobility of contaminants mixed in a matrix than the characteristics of any single contaminant. The value of five was 63 ------- TABLE 15 GAS MOBILITY VALUES Level High Medium Low Very Low Vapor Pressure Mobility (VP) Definition Above 10 torr* Above 10" 3 - 10 torr 10"5 - 10~3 torr Less than 10"^ torr Value 3 2 1 0 Level High Medium Low Very Low Aqueous Volatility (AQ) Definition** Above 10~3 Above ID"5 - 10"3 10~7 - 10~5 Less than 10~7 Value 3 2 1 0 Level High Medium Low Very Low Relative Soil Volatility (RS) Definition*** Above 1 Above 10~3 - 1 10-6 _ 10-3 Less than 10~"6 Value 3 2 1 0 *Torr is a unit of pressure equal to 1/760 of an atmosphere. **Based on Henry's constant. ***flased on dry relative soil volatility as defined in Versar, Inc., Physical-Chemical Properties and Categorization of RCRA Wastes According to Volatility, Final Draft Report, Versar, Inc., Springfield, VA, September 28, 1984. 64 ------- chosen as being large enough to meet the objective of better estimating overall mobility and as being small enough to be useable at most sites. Since different contaminants are found in different areas of a site, the choice of contaminants to be used in evaluating gas mobility should be consistent with the choice of emission source descriptor for the portion of the site in question to the extent possible given information about the site. For example, when evaluating the landfill portion of a site, only those contaminants found in the landfill portion should be used in evaluating the gas mobility value. As many contaminants as possible (up to five) should be used in this calculation. The methodology will accommodate less than five contaminants without penalizing the site, since the average of the nonzero values is used. The approach for evaluating gas mobility is summarized in Table 16. An example calculation of the gas mobility factors value for a hypothetical site is given in Appendix C (Table C-12). Particulate mobility reflects the potential for particles on the surface of a site to be formed and entrained in the atmosphere, escaping from the site. These particles may be contaminated soil, dry hazardous substances (such as asbestos), or liquid aerosols. The approach taken in the particulate mobility factor is based on the equation for fugitive dust emissions from a limited particle reservoir developed by Cowherd et al. (1985). The limited reservoir 65 ------- (1) (2) (3) (4) (5) TABLE 16 METHOD FOR EVALUATING GAS MOBILITY Emission Source Descriptor Code Contaminant VP AQ RS Code Value Value Value Sum (6) Average of nonzero values in last column of lines 1 through 5 GAS MOBILITY TABLE Range of Average Value Greater than or equal to Less than Value 0 30 3 5 1 5 7 2 7 10 3 66 ------- equation was chosen after consultation with Gregory Muleski (a co-author of the above report) as being most applicable to CERCLA sites. In simplifying this equation for use in these HRS options, the assumption is made that the three controlling factors in fugitive emissions (erosion force, threshold wind speed, and Thornthwaite PE Index) are equally applicable to both "solid" waste materials and liquid aerosols. The approach taken is a simplification of the Cowherd et al. equations. Other factors included in the equations but excluded here are frequency of disturbance and vegetative cover. The frequency of disturbance is not included as (1) not generally differentiating among CERCLA sites and (2) too difficult to estimate. Vegetative cover is addressed in the containment factor. Using the reduced form of the Cowherd et al. equation, the following particulate mobility index (I) is defined: I = (u+ - ut)/(PE)2 where: u = Fastest mile at nearest airport (meters per second) u = Threshold wind speed at 7 meters (meters per second) PE = Thornthwaite PE Index The fastest mile (u ) is defined as the velocity of the fastest wind the duration of which was equivalent to a travel distance of one mile. For example, in order for a wind speed of 120 miles per hour to be a fastest mile, the duration of the associated wind would have to exceed 30 seconds. In this equation, 67 ------- it is a measure of the force that the wind applies In eroding soil. For the purpose of determining site particulate mobility, the average of the monthly, historical fastest miles is used as u . This average is used rather the historical maximum, since the average is a better measure of the wind erosion force that would be routinely applied to the site. The historical fastest mile is simply the maximum of the monthly fastest miles and is potentially very sensitive to very rare events, e.g., tornados. As such, it is not as good a measure of routine wind erosion force as the average of the monthly fastest miles. Data on the fastest mile can be obtained from the Local Climatological Data Annual Summaries (LCD) for the latest available year, listed under the Normals, Means, and Extremes. Data for the weather station that is closest to the site and listed in the LCD should be used. The threshold wind speed (u ) is the minimum speed required to entrain particles. It can be estimated using the procedure in Cowherd et al. or it may be assumed to be 12.5 meters per second. This latter, worst-case value is based on a threshold friction velocity of 75 centimeters per second (the lowest for which the limited reservoir equation is applicable) and a roughness height of 1 centimeter (corresponding to a plowed field). Cowherd et al. describes the procedure for deriving the default threshold wind speed. 68 ------- The Thornthwaite PE Index is a surrogate measure of the relative moisture content of the soil. It can be read from Figure 2, or calculated as follows (Thornthwaite, 1931): 12 PE = 115 x [P/d - 10)]10/9 where: PE = Thornthwaite PE Index P. = Mean precipitation for month i in inches T. = Mean temperature for month i in degrees F Data on the mean precipitation and temperatures for each month can also be found in the LCD. Again, data for the weather station nearest to the site and listed in the LCD should be used. Once the particulate mobility index I has been calculated, the particulate mobility factor value is calculated as follows: Particulate Mobility Value = 4 + log1Q I rounded-off to the nearest whole number. If log,Q I exceeds 4, the factor is assigned a value of 0. If log-,Q I is less than 0.5 (i.e., the calculated value would exceed 3) then the factor is assigned a value of 3. The value of 4 in the formula is a scaling factor needed to adjust the value to a scale of 0 to 3. Table 17 provides an equivalent way to determine the particulate mobility value from the index without requiring the calculation o'f log,Q I. The alternate is derived directly from the above equation. An example of the calculation of the particulate mobility index, 69 ------- Source: Cowherd et al., 1985 FIGURE 2 MAP OF PE INDEX FOR STATE CLIMATIC DIVISIONS ------- TABLE 17 ALTERNATE METHOD FOR ASSIGNING PARTICULATE MOBILITY FACTOR VALUES Particulate Particulate Mobility Index (I) Mobility Value Less than 3.16 x 10~4 0 3.17 x 10~4 - 3.16 x 10~3 1 3.17 x 10~3 - 3.16 x 10~2 2 Greater than 3.17 x 10~2 3 71 ------- employing the equation for the Thornthwaite PE Index, is presented in Appendix C (Table C-13). The expected distribution of locations in the United States according to particulate mobility value is indicated below: Value Percent of Sites 0 6 1 47 2 31 3 16 This distribution was developed using data from a random selection of 30 airports across the country. To the extent that the geographic distribution of airports is indicative of the distribution of sites, this distribution of particulate mobility values reflects the distribution of hazardous wastes sites particulate mobility values, as well. The combined mobility value is calculated from the gas and particulate mobility values using Table 18. If a scale other than 0 to 5 is desired, it can be calculated by multiplying the values by the ratio of the maximum of the desired scale and 5.* 4.1.2.3 Containment. Containment refers to the physical characteristics of a site that inhibit or reduce emissions. It is generally the most important determinant of the emission rate at a site. Containment-related characteristics range from natural factors *In such cases, adjustments would also have to be made to the emission source descriptor and containment values as well as to the conversion factors employed on the worksheets. 72 ------- TABLE 18 COMBINED MOBILITY FACTOR MATRIX Gas Mobility Value 0 1 2 3 Particulate 0: 0 1 23 Mobility 1:1 2 34 Value 2: 2 3 45 3: 3 4 55 73 ------- such as vegetative cover to artificial, synthetic covers. Separate containment factors were developed for gas and particulate containment. There are also sufficient differences among the containment factors that might be associated with different types of sites to require that different containment descriptors be developed for each emission source descriptor. Many emission source descriptors share the same or similar containment descriptors. Numerous sources were examined to develop containment factors. The most important sources are listed in Section 8.3. Once the containment descriptors were developed, a subjective assessment of their efficiency in reducing potential emissions was made and values assigned. The descriptors and values were then reviewed in conjunction with the emission source descriptors and values and changes made as necessary. Table 19 lists examples of the gas and particulate containment factors and values. The combined containment value is calculated from the gas and particulate containment values using Table 20. Complete lists of containment factors for both options can be found in Appendix D. The choice of an applicable containment descriptor depends on the judgment of the analyst evaluating the site. Containment should be evaluated, however, in the area of the hazardous contaminants. It should reflect the barriers to contaminant migration present on the site. For example, assume a site contains two tanks; one containing hazardous waste, the other containing liquids of unknown composition. 74 ------- TABLE 19 EXAMPLES OF CONTAINMENT FACTORS AND VALUES Particulate C oatainment—Landfill Value • Site covered with an essentially impermeable and 0 maintained cover or heavily vegetated with no exposed soil or waste-bearing liquids (e.g., paved-over). • Site substantially vegetated or totally covered 1 with a maintained nonwater-based dust suppressing fluid. Little exposed soil or waste-bearing liquids. • Site lightly vegetated or partially covered with a 2 maintained nonwater-based dust suppressing fluid. Much exposed soil or waste-bearing liquids. • Site substantially devoid of vegetation with a large 2 percentage of exposed soil or waste-bearing liquids. No other cover. Facility slope less than 10 degrees or unknown. • Site substantially devoid of vegetation with a large 3 percentage of exposed soil or waste-bearing liquids. No other cover. Facility slope greater than 10 degrees. Gas Containment—Landfill Value • Uncontaminated soil cover in excess of six inches. 0 • Uncontaminated soil cover greater than one inch and 1 less than six inches; cover soil resistant to gas migration. • Uncontaminated soil cover less than six inches; cover 1 soil type unknown. • Uncontaminated soil cover greater than one inch and 2 less than six inches; cover soil not resistant to gas migration. • Uncontaminated soil cover less than one inch; cover soil 2 resistant to gas migration. • Uncontaminated soil cover less than one inch; cover soil 3 not resistant to gas migration. • Covering soil contaminated with waste contaminants at 3 surface and no synthetic cover between surface and bulk of waste materials. 75 ------- TABLE 20 COMBINED CONTAINMENT FACTOR MATRIX Gas Containment Value 0 1 2 3 Particulate 0: 0 1 2 3 Containment 1:1 1 2 3 Value 2: 2 2 2 3 3: 3 3 33 76 ------- Assume also that the tank with known contents is structurally intact while the other tank is not. The containment for the tanks should be evaluated based on the intact, known-waste tank, not the nonintact tank. 4.1.2.4 Potential to Release Scoring Algorithm. The algorithm used to combine the size-dependent emission source descriptor, mobility, and containment values is complex. In general, several emission source descriptors will apply to a given site. Given this consideration and the differences between emission source descriptor values, several descriptors are needed to adequately evaluate the potential of a site to release contaminants. Both Option 1 and 1A provide for the use of up to three descriptors for a site. The use of more than three descriptors would introduce a level of complexity into the resulting calculations that is not commensurate with possible gains in the site assessment results. The descriptors selected by the person evaluating the site, therefore, should be the three that best describe the emission potential of the site. Mobility and containment values are evaluated for each descriptor selected based on the characteristics of the site and its contaminants to which the descriptor applies. A total value for each descriptor is calculated as the sum of the size-dependent emission source descriptor value and the combined mobility value multiplied by the combined containment value. The three resulting values are then combined, using the equation for the probability of 77 ------- the union of three independent events,* to form a site potential to release value. This method of calculating site potential to release values is illustrated in Table 21. This approach is recommended since it is the only approach consistent with the underlying assumption that the release category reflects the probability that some portion of the site has, is, or will release a significant quantity of air contaminants. 4.2 Waste Characteristics Category The waste characteristics category reflects the degree of hazard posed by the contaminants that are, or might be, released from the site. In both Option 1 and 2, three waste characteristics are included in this category: contaminant toxicity, contaminant mobility, and waste quantity. The reactivity/incompatibility factor currently in the HRS is not included in these options. This factor was not included in the options pending the results of a separate analysis (DeSesso et al., 1986). It would be desirable to include a fourth characteristic, contaminant concentration. The incorporation of this factor is not feasible at this time and awaits completion of an independent review of the overall waste concentration issue. *The probability (Pr) of the union of three independent events (A, B, and C) is given by the following equation: Pr(A U B U C) - Pr(A) + Pr(B) + Pr(C) - Pr(A)Pr(B) - Pr(A)Pr(C) - Pr(fl)Pr(C) + Pr(A)Pr(B)Pr(C) 78 ------- TABLE 21 METHOD OF CALCULATING OVERALL SITE RELEASE VALUE Descriptor Code (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (D+ (1) x (1) x (2) x (1) x (4) - Des. Mobility Containment Size Value Value Sum Value Product (A) (B) (A+B) (C) ([A+B]xC) (2)+ (3) (2) / 45 (3) / 45 (3) / 45 (2) x (3) /2025 (5) - (6) - (7) + (8) Site Release Value Note: The values of 45 and 2025 used in this method arise from the conversion of the combined probability to a value on a scale of 0 to 45. If another scale is used, alternate values must be developed and employed. 79 ------- The current HRS uses the single most toxic contaminant on the site, available for migration, in assessing toxicity. Availability is based primarily on containment considerations. If the contaminant is not contained by a physical barrier, it is considered available. Both options presented here envision using the single most mobile and toxic contaminant on the site. To achieve this, a combined toxicity-mobility evaluation approach is used. This approach weighs toxicity and mobility nearly equally, although a slightly greater emphasis is placed on toxicity in the evaluation. The contaminant mobility evaluation approach used in this factor is similar to that used in the potential-to-release mobility factor. In the release category, however, mobilities of several contaminants were combined to form an overall site mobility value. Here, the Individual contaminant mobilities are used to identify and evaluate the most toxic, most mobile contaminant. In these options, contaminant toxicity is assessed using the same methods as the current HRS (47 FR 31219-31243). The proposed method can be readily modified to accommodate other methods of assessing toxicity, such as are proposed in OeSesso et al., 1986. Contaminant mobility is assessed as follows. If the contaminant has been identified as being emitted from the site in an observed release, it is assigned a mobility value of 3. If the contaminant has not been identified as part of an observed release, its mobility factor value is assigned differently. Mobility values for 80 ------- particulate contaminants that have not been identified as being emitted from the site are evaluated using the particulate mobility factor discussed previously. The assumption is made, therefore, that the particulate mobility factor value for the overall site applies to all particulate contaminants. The mobility value for a nonemitted gaseous contaminant is calculated as the average of its vapor pressure, Henry's constant and dry relative soil volatility values according to Table 15. The mobility value for a contaminant present as both a gas and a particle is the greater of the applicable gas and particle mobility values. The combined toxicity-mobility value for a particular contaminant is calculated using Table 22. The combined toxicity-mobility value for the site is the maximum of the combined toxicity-mobility values for the contaminants identified on the site. The waste quantity factor is identical to the factor in the current HRS (47 FR 31219-31243). The overall waste characteristics value is the sum of the toxicity-mobility value and the waste quantity value. 4.3 Targets Category The targets category reflects the extent of the population and resources potentially at risk from contaminants that might be released from the site. Three factors are included: population, land use, and sensitive environment. The tables used to assign values for each factor, in each option, are the same as are 81 ------- TABLE 22 COMBINED TOXICITY-MOBILITY FACTOR MATRIX Mobility Value 0 1 _2 _3 0: 0 0 0 0 Toxicity 1: 0 2 4 6 Value 2: 2 4 8 12 3: 4 6 12 18 82 ------- currently used in the HRS (47 FR 31219-31243). The changes envisioned in these options address the selection of location for the center of the circles used in evaluating population, the size of the radii of these circles, and the use of 1980 (or later, as available) Census data to determine population. The current HRS employs a simplistic approach to population estimation. As discussed previously, it relies routinely on house counts in the area surrounding the site and coverts these data into equivalent population assuming persons per household. The number of households is frequently derived from outdated maps of the area. The current HRS also calculates the target distance from the location of the wastes, or if that information is not available, from the site boundary, using fixed target distances. This approach is illustrated in Table 23, the current HRS air pathway population factor matrix. If, for example, 50 people live within 1/4 mile of a site (value = 18), while 2,000 people live within 1/2 mile of the site (value = 21), the site would be assigned a population factor value of 21. Improvements of this overall approach is embedded in both options. The improvements do not address the way the population factor is evaluated, rather they address the way the size of the target population is determined. The options envision that the following approach would be employed unless the local governmental authority can provide better data. The approach is based on the Bureau of the Census computer program, called RADII5. This publicly 83 ------- TABLE 23 CURRENT HRS TARGET POPULATION FACTOR MATRIX Distance to Population From Hazardous Substance (mile) Population 1 101 1,001 3,001 10, 0 - 100 - 1,000 - 3,000 - 10,000 000+ 0-4 0 9 12 15 18 21 0-1 0 12 15 18 21 24 0-1/2 0 15 18 21 24 27 0-1/4 0 18 21 24 27 30 84 ------- available computer program calculates the population reported in the 1980 Census in circles of user specified radii around any location in the United States. Both Options 1 and 1A envision that EPA. would acquire these programs, modify them as necessary, and provide results to persons evaluating sites as needed. The use of this data source would require a change in the way target distance is calculated in the air pathway. The easiest approach consistent with the requirements of the RADII5 program is to employ circles of varying radii, defined in terms of an effective source radius plus a target distance, centered at the "center of gravity" of the site. The effective source radius is defined as 1/2 of the greatest distance between any two identifiable emissions sources on the site.* Thus if the site contains only two identifiable sources, the effective source radius equals 1/2 of the distance between them. If the site contains more than two sources, then the radius equals 1/2 of the distance between the two that are furthest apart. Neither of these two modifications would affect the way targets are evaluated in the air pathway. The overall targets category value would remain the sum of the population, land use, and sensitive environment values in both Option 1 and 2. *ln evaluating the distance between identifiable emission sources, the distance should be calculated from the respective centers of the sources. 85 ------- 4.4 The Overall Pathway Score As discussed previously, the overall pathway score is the product of the release category, waste characteristics category and targets category scores, normalized to a scale of 0 to 100. The calculation of the release category score is discussed la Section 4.1. The waste characteristics category score is the sum of the toxicity-mobility value and the waste quantity value. Similarly, the targets category score is the sum of the population, land use and sensitive environment values. This approach is Illustrated in Table 24. 86 ------- TABLE 24 METHOD OF CALCULATING AIR PATHWAY SCORE 1. OBSERVED RELEASE VALUE3 2. POTENTIAL TO RELEASE VALUEb 3. TOXICITY-MOBILITYC 4. HAZARDOUS WASTE QUANTITYd 5. WASTE CHARACTERISTICS VALUE (Lines 3+4) 6. TARGETS 7. Population 8. Land Used 9. Sensitive Environment 10. TARGETS VALUE (Lines 7+8+9) 11. If line 1 is not equal to 0.0, multiply lines 1 x 5 x 10 If line 2 is not equal to 0.0, multiply lines 2 x 5 x 10 12. Divide line 11 by 351 S aFrom Worksheet 1. ^From Worksheet 2. cFrom Worksheet 7. dFrom HRS User's Manual. a 87 ------- 5.0 SINGLE, "WORST" SOURCE APPROACH (OPTION 2) The principal purpose of this section is to describe a simple mechanism for evaluating hazardous wastes sites based on their potential to release CERCLA contaminants into the air, in the absence of an observed release. The mechanism is closely related to the approach described in Section 4. This simple approach is designed to be consistent with the assumptions and approaches embodied in the current HRS. It is designed to be implemented with a minimum of change to the other components of the air pathway, as they currently exist. As such, it does not address any issues in the HRS other than the absence of a potential to release option in the current air pathway. Alternately, this mechanism can be integrated with the suggested revisions to the waste characteristics and targets categories discussed in Section 4 to form another overall revision option. The approach described in this section follows the same general approach as is used in the ground water and surface water pathways. If an observed release can not be demonstrated, then the site release category is evaluated based on the characteristics of that portion of the site that is most likely to release contaminants to the applicable medium. Thus, the Option 1 multiple source approach employing probabilistic combinatorics is replaced in Option 2 by a simpler, "worst" source approach. Additionally, in Option 2 the list of emission source descriptors is simplified with resulting 89 ------- simplifications in the containment descriptors. Further, size is reflected as a constraint on the selection of descriptors and does not affect the emissions source descriptor values. The following sections described this alternate approach to assessing potential to release in more detail. An example of the application of this approach to a hypothetical site is presented in Appendix C. 5.1 The Option 2 Potential to Release Evaluation Mechanism The approach reflected in the simplified mechanism discussed below uses information on the physical characteristics of the site and the waste in the site. Four site characteristics are employed in assessing the potential of a site to emit air contaminants: • Emission source descriptor • Size • Overall contaminant mobility • Containment The first two characteristics are reflected into a single factor, although in a somewhat different fashion than is used in Options 1 and 1A. These characteristics are discussed in detail in Section 4.1.2. The overall approach to evaluating the potential of a site to release contaminants using Option 2 is similar to that of Options 1 and 1A discussed previously. The emission sources on the site are classified using emission source descriptors. The size of each 90 ------- emission source is also assessed. From this information, a emission source descriptor factor value is calculated for each descriptor meeting the applicable minimum size requirement. Up to five contaminants present in the site are used to calculate a gaseous contaminant mobility value for each applicable emission source descriptor. This value is based on the average physiochemical characteristics of the contaminants associated with each descriptor. A particulate mobility value for the site is then calculated based on the Thornthwaite PS Index (Thornthwaite, 1931) for the area surrounding the site. The combined mobility value is the sum of the gaseous and particulate mobility values. This causes the mobility factor to play a slightly greater role, relative to the emission source descriptors, in determining the potential to release value in Option 2 than in Option 1. The gas and particulate containment aspects of the area represented by the selected descriptors are then assessed and evaluated separately. A combined containment value is then evaluated from the gas and particulate containment values. The sum of the descriptor and mobility values is then multiplied by the containment value to form the potential to release value for the selected descriptor. This procedure is illustrated in Table 25. The highest of the calculated descriptor factor values is taken as the potential to release value in the air pathway for the site. Thus, this approach employs the "worst" source in evaluating potential to release. 91 ------- TABLE 25 ILLUSTRATION OF OPTION 2 POTENTIAL TO RELEASE EVALUATION PROCEDURE A) Emission Source Descriptor Value B) Gas Mobility Value C) Particulate Mobility Value D) Subtotal (A + B + C) E) Particulate Containment Value F) Gas Containment Value G) Combined Containment Value Maximum of E and F H) Emission Source Potential to Release Value (D x G) 92 ------- 5.1.1 Emission Source Descriptors A basic list of emission source descriptors is presented in Table C-l. The relationship between the reduced list used in this simpler option and the original list is presented in Table 26. The choice of emission source descriptor is left up to the investigator evaluating the site. The restrictions to descriptor selection are generally the same as those discussed for Options 1 and 1A (see Section 4.1.2.1). However, since the emission source descriptor values do not vary according to size in Option 2, size is employed as a constraint on the selection of descriptors. Minimum size requirements were adapted from the three size categories defined in Section 4.1.2.1. These requirements are listed in Table 27. The size constraint imposed on the selection of emission source descriptors in Option 2 is similar to that used in the other options. Generally, the size of the source described by a selected descriptor must equal or exceed the minimum listed in Table 27, if that descriptor is to be used in evaluating the site. The sole exception to this rule applies when this constraint can not be met by any descriptor. In this case, the "largest" descriptor (relative to the size requirement) is used to evaluate the site, as in done in Options 1 and 1A. The emission source descriptors values presented in Table 28 are adapted from the larger list of size-dependent emission source descriptor values listed in Table 13. 93 ------- TABLE 26 OPTION 2 EMISSION SOURCE DESCRIPTORS AND DEFINITIONS Option 2 Emission Option 1 Emission Source Descriptor Source Descriptor Containers Aboveground or Inground: Tanks (All variations) Belowground Tanks Exposed Drum Site: (All variations) Contaminated Soil Contaminated Surface Soil: (All variations) Spill Site Fire Site Active Fire Site Inactive Aboveground Fire Site: (All variations) Inactive Belowground Fire Site: (All variations) Landfill Belowground Injection Landfarm/Landtreatment Landfill: (All variations) Open Pit Surface Impoundment Surface Impoundment: (All variations) Surface Water Body or Outfall Waste Pile Waste Pile 94 ------- TABLE 27 OPTION 2 MINIMUM SIZE REQUIREMENTS Descriptor Containers Belowground Tanks Drum Site Inground or Aboveground Tanks Contaminated Soil Fire Site Aboveground Fire Site Belowground Fire Site Landfill Surface Impoundment Waste Pile Minimum Size 1,000 cubic feet 1 drum 1,000 cubic feet 11,000 square feet 11,000 square feet 74,000 square feet 11,000 square feet 74,000 cubic feet 1,000 cubic feet 300 square feet 130 cubic feet 36 square feet 95 ------- TABLE 28 OPTION 2 EMISSION SOURCE DESCRIPTOR VALUES Code Descriptors Value 01 Containers 4 02 Contaminated Soil 7 03 Fire Site 5 04 Landfill 6_ 05 Surface Impoundment 8 06 Waste Pile 3 96 ------- 5.1.2 Contaminant Mobility As in Options 1 and 1A (see Section 4.1.2.2), contaminant mobility is reflected using the combination of two mobility factors, one addressing gaseous contaminants, the other addressing particulate matter. The value for the gas mobility factor is determined in the same manner as in Option 1. The particulate mobility factor in Option 1 is based on the equation for fugitive dust emissions from a limited particle reservoir. Three factors were retained for tne Option 1 mechanism: erosion force, threshold wind speed, and Thornthwaite PE Index. An analysis of the values for the particulate mobility factor in Option 1, based on data from randomly selected airports, indicated that the Thornthwaite PE Index dominates the particulate mobility evaluation. Thus, a simplified, single variable factor employing the PE index alone can be used, sacrificing only some of the resolution provided by the more complex approach. This simpler approach is summarized in Table 29. The PE index for a site can be determined from Figure 2, or from the complex equation described in Section 4.1.2.2. This simpler approach yields nearly the same result as the more complex approach in Option 1. The values for only 7 of the over 30 sites examined were significantly affected by the erosion force and wind speed values. The approach presented in Table 29 results in the same particulate mobility factor value for all but these 7 sites, and higher values for 5 of these 7. 97 ------- TABLE 29 OPTION 2 PARTICULATE MOBILITY FACTOR Paniculate Thornthwaite PE Index Mobility Value Greater than 100 0 70 to 100 1 34 to 69 2 Less than 34 3 98 ------- 5.1.3 Containment The factor value for containment is determined in Option 2 the same way as in Option 1 (see Section 4.1.2.3). The list of Option 2 containment descriptors is also adapted from the more extensive list prepared for Option 1. These descriptors are listed in Tables 30 and 31. The combined containment value is determined from the gas and particulate containment values using the Option 1 approach (Table 20). 99 ------- TABLE 30 OPTION 2 PARTICULATE CONTAINMENT FACTORS CONTAINERS C001P Belowground/buried containers: (see Landfill, etc.) C002P Intact, sealed aboveground containers; containers protected from the weather by a maintained cover C003P Intact, sealed aboveground containers; containers not protected from the weather by a maintained cover C004P Open, unsealed, or nonintact aboveground container; waste totally covered with an essentially impermeable, maintained cover C005P Open, unsealed, or nonintact aboveground container; waste partially covered with an essentially impermeable, maintained cover C006P Open, unsealed, or nonintact aboveground container; waste totally covered with an essentially impermeable, unmaintained cover C007P Open, unsealed, or nonintact aboveground container; waste otherwise covered or uncovered C008P Aboveground containers; other LANDFILL, CONTAMINATED SOIL, FIRE SITE, AND WASTE PILES LD01P Site covered with an essentially Impermeable and maintained cover or heavily vegetated with no exposed soil or waste-bearing liquids (e.g., paved-over) LD02P Site substantially vegetated or totally covered with a maintained nonwater-based dust suppressing fluid. Little exposed soil or waste-bearing liquids LD03P Site lightly vegetated or partially covered with a maintained nonwater-based dust suppressing fluid. Much exposed soil or waste-bearing liquids LD04P Site substantially devoid of vegetation with a large percentage of exposed soil or waste-bearing liquids. No other cover LD05P Totally enclosed in a structurally intact building 100 ------- TABLE 30 (Concluded) LANDFILL, CONTAMINATED SOIL, FIRE SITE, AND WASTE PILES (Concluded) LD06P Partially enclosed in a structurally intact 2_ building LD07P Totally enclosed in an nonintact building 2_ LD08P Partially enclosed in an nonintact building 3_ LD09P Substantially surrounded with windbreak 2_ (e.g., mesh or other fence, trees, etc.) LD10P Active fire site 3_ LD11P Other 1 SURFACE IMPOUNDMENT SI01P Enclosed* impoundment; impoundment totally covered with a maintained cover SI02P Enclosed impoundment; impoundment totally covered with an unmaintained cover SI03P Enclosed impoundment; impoundment partially covered with a maintained cover SI04P Enclosed impoundment; impoundment partially covered with an unmaintained cover SI05P Enclosed impoundment; uncovered, surface completely open to atmosphere SI06P Nonenclosed impoundment; impoundment totally covered with a maintained cover SI07P Nonenclosed impoundment; impoundment totally covered with an unmaintained cover SI08P Nonenclosed impoundment; impoundment partially covered with a maintained cover SI09P Nonenclosed impoundment; impoundment partially covered with an unmaintained cover SHOP Nonenclosed impoundment; uncovered, surface completely open to atmosphere SHIP Other *An enclosed impoundment is one with a freeboard exceeding two feet in height or one that is substantially surrounded by a wall, fence, trees, or other adequate windbreak. 101 ------- TABLE 31 OPTION 2 GAS CONTAINMENT FACTORS CONTAINERS C001G C002G C003G C004G C005G C006G C007G C008G FIRE SITE FS01G FS02G FS03G FS04G Belowground/burled containers: (see Landfill, etc.) Intact, sealed aboveground containers; containers protected from the weather by a maintained cover Intact, sealed aboveground containers; containers not protected from the weather by a maintained cover Open, unsealed, or nonintact aboveground container; waste totally covered with an essentially impermeable, maintained cover Open, unsealed, or nonintact aboveground container; waste partially covered with an essentially Impermeable, maintained cover Open, unsealed, or nonintact aboveground container; waste totally covered with an essentially impermeable, unmaintalned cover Open, unsealed, or nonintact aboveground container; waste otherwise covered or uncovered Aboveground containers; other Inactive fire site: (see Landfill, etc.) Active aboveground fire site Active belowground fire site: Uncontamlnated* soil cover in excess of two feet Active belowground fire site: Uncontamlnated* soil cover less than two feet, soil resistant to gas migration** ^Lacking contrary evidence, covering soils are assumed to be uncontamlnated. Soil cover contaminants must be attributable to the underlying waste materials and gaseous in origin. **USGS soil types GC, ML, CL, and CH. Source: Adapted from Lutton, R. J., Evaluating Cover Systems for Solid and Hazardous Wastes, (EPA-530/SW-867c), U.S. Environmental Protection Agency, Washington, DC, September 1980. 102 ------- TABLE 31 (Continued) FIRE SITE (Concluded) FS05G Active belowground fire site: Uncontaminated* soil cover less than two feet, soil not resistant to gas migration** LANDFILL. CONTAMINATED SOIL, AND WASTE PILES LD01G Functioning gas collection system LD02G Existing, malfunctioning gas collection system LD03G Intact synthetic cover plus uncontaminated soil cover over 0.5 inches in depth* LD04G Totally covered with an intact synthetic cover; surface soil contaminated* LD05G Totally covered with a nonintact synthetic cover; surface soil contaminated* LD06G Uncontaminated soil cover* in excess of six inches LD07G Uncontaminated soil cover* greater than one inch and less than six inches; cover soil resistant to gas migration** LD08G Uncontaminated soil cover* less than six inches; cover soil type unknown LD09G Uncontaminated soil cover* greater than one inch and less than six inches; cover soil not resistant to gas migration** LD10G Uncontaminated soil cover* less than one inch; cover soil resistant to gas migration** LD11G Uncontaminated soil cover* less than one inch; cover soil not resistant to gas migration** LD12G Covering soil contaminated* with waste contaminants at surface and no synthetic cover between surface and bulk of waste materials *Lacking contrary evidence, covering soils are assumed to be uncontaminated. Soil cover contaminants must be attributable to the underlying waste materials and gaseous in origin. **USGS soil types GC, ML, CL, and CH. Source: Adapted from Lutton, R. J., Evaluating Cover Systems for Solid and Hazardous Wastes, (EPA-530/SW-867c), U.S. Environmental Protection Agency, Washington, DC, September 1980. 103 ------- TABLE 31 (Concluded) LANDFILL, CONTAMINATED SOIL, AND WASTE PILES (Concluded) LD13G Totally enclosed in a structurally Intact building LD14G Totally enclosed in an nonintact building LD15G Waste uncovered or exposed LD16G Other SURFACE IMPOUNDMENTS SI01G Dry surface impoundment (see Landfill, etc.) SI02G Wet enclosed* impoundment; impoundment totally covered with a maintained, essentially impermeable cover SI03G Wet enclosed impoundment; impoundment totally covered with an unmaintained, essentially impermeable cover SI04G Wet enclosed impoundment; impoundment partially covered with a maintained, essentially impermeable cover SI05G Wet enclosed impoundment; impoundment partially covered with an unmaintained, essentially impermeable cover SI06G Wet enclosed impoundment; uncovered, surface completely open to atmosphere SI07G Wet nonenclosed impoundment; impoundment totally covered with a maintained, essentially impermeable cover SI08G Wet nonenclosed impoundment; impoundment totally covered with an unmaintained, essentially Impermeable cover SI09G Wet nonenclosed impoundment; impoundment partially covered with a maintained, essentially impermeable cover SI10G Wet nonenclosed impoundment; impoundment partially covered with an unmaintained, essentially impermeable cover SI11G Wet nonenclosed impoundment; uncovered, surface completely open to atmosphere SI12G , Other 0 *An enclosed Impoundment is one with a freeboard exceeding two feet in height or one that is substantially surrounded by a wall, fence, trees, or other adequate windbreak. 104 ------- 6.0 IMPLICATIONS This section discusses the potential implications of adopting the proposed revisions to the HRS air pathway. Implications for the cost of using the HRS and the listing of sites on the National Priorities List (NPL) are discussed. The testing and refinement of these options is expected to reveal further issues and may resolve some identified below. 6.1 Improvements in the HRS and the NPL The basic purpose in revising the HRS is to improve the capability of the HRS in identifying sites suitable for inclusion on the National Priorities List. This purpose is achieved whenever the scores for sites calculated using the HRS better reflect the risk posed by the sites. Such improvements in the quality of HRS scores serves to improve the NPL, ensuring that the sites identified as National Priorities are the sites that should be further investigated and, if necessary, cleaned up. The proposed revisions to the HRS air pathway improves the HRS in three ways. First, the revisions address the potential of a site to release air contaminants, a characteristic currently lacking in the HRS. The options account for many of the important factors that determine the potential to release, although some important characteristics of a site (e.g., age) are not included. The important factors included in the options are the type of emission source, size, overall contaminant mobility, and containment. As a 105 ------- result, the risks from potentially important sites at which air monitoring was not conducted, or proved equivocal, can now be reflected in a reasonable fashion by the HRS air route score. Second, these options resolve a criticism of the waste characteristics category of the current HRS. In the current system, a very toxic contaminant can be used to assign a toxicity value, whenever there are no physical barriers to contain it on the site, regardless of whether that contaminant is unable to migrate due to its chemical properties. The current approach does not address the physiochemical characteristics of the contaminant that determine whether it can migrate, irrespective of containment. The options presented propose a method of assigning a value for toxicity that includes an evaluation of the migration potential of the contaminant. Finally, the proposed revision in the approach used in estimating population should result in the use of more current and accurate population estimates, improving the quality of the target factor values. The adoption of any of the air pathway options would also affect the number of sites listed on the NPL. The inclusion of a potential to release option is expected to raise the average air pathway score since many sites that otherwise would receive a zero air pathway score under the current riRS (those lacking an observed release) would receive a positive score for potential to release under the options discussed previously. Thus, if the requirement 106 ------- that the site score equal or exceed 28.50 is maintained, then a greater number of sites would meet this requirement using the options than would under the current HRS. This would increase the size of the NPL. It is not possible to determine the fraction of sites that would be affected. However, it is possible that most if not all of the sites that received HRS scores marginally below the cut-off (e.g., those scoring between 25.0 and 28.49) may qualify for listing using the revised HRS. Table 32 provides the distribution of these marginal sites and the air pathway scores needed to achieve the 28.50 cut-off. This table illustrates that at least 58 sites currently not listed are potential candidates for listing using a revised HRS, if the cut-off is not changed. 6.2 Cost Implications The air pathway revision options were generally developed with the intent that their adoption would not add significantly to the costs of using the HRS. The inclusion of a potential to release option in the air pathway requires no additional monitoring data. A detailed site and containment description, supplemented by site photographs, should be sufficient to evaluate the site's potential to release. Whether this would result in an increase in site investigation costs is problematic. However, such a cost increase would likely be small. 107 ------- TABLE 32 HRS SCORING DISTRIBUTION FOR "MARGINAL" SITES LACKING OBSERVED AIR RELEASES Range of Maximum Points Needed Number of Sites Current Scores To Equal or Exceed 28.5 in Given Range 25.00 - 25.49 23.67 9 25.49 - 25.00 22.05 6 26.00 - 26.49 20.19 14 26.49 - 27.00 18.19 6 27.00 - 27.49 15.79 7 27.49 - 28.00 13.01 9 28.00 - 28.49 9.20 7 Total 58 Source: Based on scores for final and proposed NPL sites that lack observed air releases, proposed through Update 5. 108 ------- Further, the addition of the mobility factor in the waste characteristics category should have a negligible cost impact as it also requires no new data development. The recommended changes to the targets category may result in an increase in scoring costs as they require new data. If the RADI15 program is adopted, appropriately modified and made available to the analysts, the cost for providing population estimates should be no more than $100 per site. The costs of modifying the RAD1I5 program will also be small as the EPA Office of Air Quality Planning and Standards has already implemented a version of the program on EPA's computer. Thus, the only potentially significant program cost increase that might arise from incorporating the air revision is the additional analyst costs. This cost should not exceed the equivalent of 8 person-hours per site. These costs may be minimized by developing tables that would facilitate scoring, eliminating some of the worksheets described in the appendices. 6.3 Potential Implications for Other HRS Pathways Some of the changes to the air pathway envisioned in these options raise issues for the ground water and surface water pathways, In general, if the HRS is to remain internally consistent, should the other pathways be revised in the same fashion as suggested for the air pathway? For example, should the potential to release options currently employed in the other pathways be revised to reflect the presence of multiple potential sources using an approach 109 ------- based on probabilistic combinatorics? The following aspects of the revisions are of particular importance in this context: • Criteria for observed release • Use of multiple descriptors • Probabilistic scoring algorithm • Use of Census data in targets category • Combined toxicity-mobility factor • Multi-contaminant mobility factor in potential to release The nature and extent of changes in the other pathways that might arise from adoption of the air pathway options are unknown. 110 ------- 7.0 SUMMARY AND CONCLUSIONS This paper has presented three options for revising the HRS air pathway. The suggested revisions include a potential to release option in the release category, a combined toxicity-mobility factor in the waste characteristics category, and revisions in the target distance and population estimation procedures in the targets category. Adoption of the suggested revisions would improve the HRS and the NPL by increasing the degree to which HRS scores reflect the potential risks from hazardous wastes sites and, as a result, by providing better discrimination among potential NPL sites. Since these options would constitute an improvement in the HRS, one of the options should be proposed, as modified after testing, as a formal revision to the HRS in the National Contingency Plan. Of the options, Option 1 is preferred. This option employs more descriptors and should, therefore, provide greater discrimination among sites. Option 2 is simpler, consistent with the approach used in the other pathways, and would be an adequate procedure for evaluating potential to release. However, the use of Option 2 would discriminate against sites with multiple sources. Hence, it would understate the potential for such sites to release contaminants and would thus understate their relative risks. Regardless, if Option 2 were adopted, the adoption of the recommended changes to the waste characteristic category and targets estimation procedures would be indicated. Ill ------- 8.0 REFERENCES AND BIBLIOGRAPHY 8.1 Selected References on Emission Processes Anderson, David C. and Stephen G. Jones, "Fate of Organic Liquids on Soil," Proceedings of the National Conference and Exhibition on Hazardous Waste and Environmental Emergencies, Held on March 12-14, 1984 in Houston, TX, Hazardous Materials Control Research Institute, Silver Spring, MD, 1984, pp. 384-388. Bennett, Gary F. "Fate of Solvents in a Landfill," Proceedings of the National Conference on Hazardous Wastes and Environmental Emergencies, Held on May 14-16, 1985 in Cincinnati, OH, Hazardous Materials Control Research Institute, Silver Spring, MD, 1985, pp. 199-210. Brown, Kirk W., Gordon B. Evans, Jr., and Beth D. Frentrup, eds., Hazardous Waste Land Treatment, Butterworth Publishers, Woburn, MA, 1983. Cowherd, Chatten Jr. et al., Rapid Assessment of Exposure to Particulate Emissions from Surface Contamination Sites, Midwest Research Institute, Kansas City, MO, September 1984. Hwang, Seong T., "Toxic Emissions from Land Disposal Facilities," Environmental Progress, Vol. 1, No. 1, February 1982, pp. 46-52. James, S. C., R. N. Kinman, and D. L. Nutini, "Toxic and Flammable Gases," Contaminated Land; Reclamation and Treatment, Michael A. Smith, ed., Plenum Press, New York, NY, 1985. Kinman, Riley N. and David L. Nutini, "Production, Migration, and Hazards Associated with Toxic and Flammable Gases at Uncontrolled Hazardous Waste Sites," Land Disposal of Hazardous Waste: Proceedings of the Tenth Annual Research Symposium, (EPA-600/ 9-84-007), U.S. Environmental Protection Agency, Cincinnati, OH, August 1984, pp. 52-60. Shen, Thomas T., "Air Quality Assessment for Land Disposal of Industrial Wastes," Environmental Management, Vol. 6, No. 4, 1982, pp. 297-305. Shen, Thomas T., "Estimating Hazardous Air Emissions from Disposal Sites," Pollution Engineering, Vol. 13, No. 8, August 1981, pp. 31-371 Shen, Thomas T., "Estimation of Organic Compound Emissions from Waste Lagoons," Journal of the Air Pollution Control Association, Vol. 32, No. 1, January 1982, pp. 79-82. 113 ------- Shen, Thomas T. and Granvllle H. Sewell, "Air Pollution Problema of Uncontrolled Hazardous Waste Sites," Proceedings of the National Conference on Management of Uncontrolled Hazardous Waste Sites, Held on November 29-December 1, 1982 In Washington, DC, Hazardous Materials Control Research Institute, Silver Spring, MD, 1982, pp. 76-80. Shen, Thomas T. and James Tofflemire, "Air Pollution Aspects of Land Disposal of Toxic Waste," Journal of the Environmental Engineering Division of ASCE, Vol. 106, No. EE1, February 1980, pp. 211-226. Thibodeaux, Louis J., "Estimating The Air Emissions of Chemicals from Hazardous Waste Landfills," Journal of Hazardous Materials, Vol. 4, 1981, pp. 235-244. 8.2 Selected References Addressing Air Monitoring Guidance Ford, P. J., P. J. Turlna, and D. E. Seeley, Characterization of Hazardous Sites, A Methods Manual. Volume 2. Available Sampling Methods, (EPA-600/4-83-040), U.S. Environmental Protection Agency. Las Vegas, NV, September 1983. Hanlsch, Robert C. and Maureen A. McDevitt, Protocols for Sampling and Analysis of Surface Impoundments and Land Treatment/Disposal Sites for VOCs: Technical Note, (DCN 84-222-078-11-12), Radian Corporation, Austin, TX, September 28, 1984. Plumb, R. H., Jr., Characterization of Hazardous Sites, A Methods Manual. Volume 3. Available Laboratory Analytical Methods, (EPA-600/4-84-038), U.S. Environmental Protection Agency, Las Vegas, NV, May 1984. Rlggin, R. M., Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air, (EPA-600/4-84-041), U.S. Environmental Protection Agency, Research Triangle Park, NC, April 1984. U.S. Environmental Protection Agency, Field Standard Operating Procedures for Air Surveillance F.S.O.F. 8, (Draft), U.S. Environmental Protection Agency, Environmental Response Team, Washington, DC, 1985. U.S. Environmental Protection Agency, Standard Operating Safety Guides, U.S. Environmental Protection Agency, Washington, DC, November 1984. 114 ------- U.S. Environmental Protection Agency, Technical Assistance for Sampling and Analysis of Toxic Organic Compounds in Ambient Air, CEPA-600/ 4-83-027), U.S. Environmental Protection Agency, Research Triangle Park, NC, 1983. 8.3 Principal References Used in Developing Containment Factors Brown, D. et al., Techniques for Handling Landborne Spills of Volatile Hazardous' Substances, (EPA-600/ 2-81-207), U.S. Environmental Protection Agency, Cincinnati, OH, September 1981. Brown, Kirk W. , Gordon B. Evans, Jr., and Beth D. Frentrup, eds., Hazardous Waste Land Treatment, Butterworth Publishers, Woburn, MA, Ehrenfeld, John R. and Joo Hooi Ong, Evaluation of Emission Controls for Hazardous Waste Treatment, Storage, and Disposal Facilities, (EPA-450/ 3-84-017), U.S. Environmental Protection Agency, Research Triangle Park, NC, November 1984. Ehrenfeld, John R. and Joo Hooi Ong, "Control of Emissions from Hazardous Waste Treatment Facilities," (85-70.1), Presented at the 78th Annual Meeting of the Air Pollution Control Association, Held on June 16-21, 1985 in Detroit, MI, Air Pollution Control Association, Pittsburgh, PA, 1985. Farmer, Walter J. et al., Land Disposal of Hexachlorobenzene Waste - Controlling Vapor Movement in Soil, (EPA-600/2-80-119) , U.S. Environmental Protection Agency, Cincinnati, OH, August 1980. Genetelli, Emil J. and John Cirello, eds., Gas and Leachate from Landfills; Formation, Collection and Treatment, (EPA-600/ 9-76-004) U.S. Environmental Protection Agency, Cincinnati, OH, 1976. James, S. C. , R. N. Kinman, and D. L. Nutini, "Toxic and Flammable Gases," Contaminated Land; Reclamation and Treatment, Michael A. Smith, ed., Plenum Press, New York, NY, 1985. Lutton, R. J., Evaluating Cover Systems for Solid and Hazardous Wastes, (EPA-530/SW-867c), U.S. Environmental Protection Agency, Washington, DC, September 1980. Lutton, R. J., G. L. Regan, and L. W. Jones, Design and Construction of Covers for Solid Waste Landfills, (EPA-600/ 2- 79-165), U.S. Environmental Protection Agency, Cincinnati, OH, 1979. Moore, Charles A., "Landfill Gas Generation, Migration and Controls," CRC Critical Reviews in Environmental Control, Vol. 9, No. 2, November 1979, pp. 157-184. 115 ------- Patry, G. D. R. and R. M. Bell, "Covering Systems," Contaminated ^aud; Reclamation and Treatment, Michael A. Smith, ed., Plenum Press, New York, NY, 1985. Roabury, Keith D. and Stephen C. James, "The Control of Fugitive Dust Emissions at Hazardous Waste Cleanup Sites," Proceedings of the Fifth National Conference on Management of Uncontrolled Hazardous Waste Sites, Held on November 7-9, 1984 in Washington, DC, Hazardous Materials Control Research Institute, Silver Spring, MD, 198A, pp. 265-267. Ihibodeaux, Louis J., Charles Springer, and Rebecca S. Parker, "Design for Control of Volatile Chemical Emissions from Surface Impoundments," Hazardous Waste and Hazardous Materials, Vol. 2, No. 1, 1985, pp. 99-106. Vogel, Gregory A. and Denis F. 0'Sullivan, Air Emission Control Practices at Hazardous Waste Management Facilities, (MTR-83W89), The MITRE Corporation, McLean, VA7 June 1983. Walsh, Gary, "Control of Volatile Air Emissions from Hazardous Waste Land Disposal Facilities," Proceedings of the National Conference on Hazardous Wastes and Environmental Emergencies, Held on May 12-14, 1984 in Houston, TX, Hazardous Materials Control Research Institute, Silver Spring, MD, 1984, pp. 146-153. 8.4 General Bibliography Amoore, John E. and Earl Hautala, "Odor as an Aid to Chemical Safety: Odor Thresholds Compared with Threshold Limit Values and Volatilities for 214 Industrial Chemicals in Air and Water Dilution," Journal of Applied Toxicology, Vol. 3, No. 6, 1983, pp. 272-290. Amster, Michael B., Nasrat Hijazi, and Rosalind Chan, "Real Time Monitoring of Low Level Air Contaminants from Hazardous Waste Sites," Proceedings of the National Conference on Management of Uncontrolled Hazardous Waste Sites, Held on October 31-November 2, 1983 in Washington, DC, Hazardous Materials Control Research Institute, Silver Spring, MD, 1983, pp. 98-99. Anderson, David C. and Stephen G. Jones, "Fate of Organic Liquids on Soil," Proceedings of the National Conference and Exhibition on Hazardous Waste and Environmental Emergencies, Held on March 12-14, 1984 in Houston, TX, Hazardous Materials Control Research Institute, Silver Spring, MD, 1984, pp. 384-388. Arthur D. Little, Inc., Proposed Revisions to MITRE Model, Arthur D. Little, Inc., Cambridge, MA, September 23, 1981. 116 ------- Arthur D. Little, Inc., An Analysis of the Hazard Ranking System and the National Priority List. (Reference No. 88922), Arthur D. Little, Inc., Cambridge, MA, February 1983. Astle, Alice D., Richard A. Duffee, and Alexander R. Stankuas, Ph.D., "Estimating Vapor and Emission Rates from Hazardous Waste Sites," Proceedings of the National Conference on Management of Uncontrolled Hazardous Waste Sites, Held on November 29-December 1, 1982 in Washington, DC, Hazardous Materials Control Research Institute, Silver Spring, MD, 1982, pp. 326-330. Baker, Lynton W., An Evaluation of Screening Models for Assessing Toxic Air Pollution Downwind of Hazardous Waste Landfills, Masters Thesis, Office of Graduate Studies and Research, San Jose State University, San Jose, CA, May 1985. Baker/TSA, Tyson's Dump Site, Montgomery County, PA, Draft Remedial Investigation Report, Baker/ISA, Beaver, PA, August 1984. Balfour, W. David and Charles E. Schmidt, Sampling Approaches for Measuring Emission Rates from Hazardous Waste Disposal Facilities, (EPA-600/D-84-140), U.S. Environmental Protection Agency, Cincinnati, OH, May 1984. Balfour, W. D., R. G. Wetherold, and D. L. Lewis, Evaluation of Air Emissions from Hazardous Waste Treatment, Storage, and Disposal Facilities, (EPA-600/2-85-057), U.S. Environmental Protection Agency, Cincinnati, OH, May 1985. Balfour, W. D. et al., "Field Verification of Air Emission Models for Hazardous Waste Disposal Facilities," Land Disposal of Hazardous Waste; Proceedings of the Tenth Annual Research Symposium, (EPA-600/ 9-84-007), U.S. Environmental Protection Agency, Cincinnati, OH, August 1984, p. 197. Battye, William et al., Preliminary Source Assessment for Hazardous Waste Air Emissions from Treatment, Storage and Disposal Facilities (TSDFs), (Draft Final Report), GCA Corporation, Bedford, MA, February 1985. Bell, R. M. and G. D. R. Parry, "The Upward Migration of Contaminants Through Covering Systems," Proceedings of the Fifth National Conference on Management oflJncontrolled Hazardous Waste Sites, Held on November 7-9, 1984 in Washington, DC, Hazardous Materials Control Research Institute, Silver Spring, MD, 1984, pp. 588-591. 117 ------- Bennett, Gary F., "Fate of Solvents in a Landfill," Proceedings of the National Conference on Hazardous Wastes and Environmental Emergencies, Held on May 14-16, 1985 in Cincinnati, OH, Hazardous Materials Control Research Institute, Silver Spring, MD, 1985, pp. 199-210. Bilsky, I. L., "Air Pollution Aspects of Hazardous Waste Disposal in Texas," (85-79.3), Presented at the 78th Annual Meeting of the Air Pollution Control Association, Held on June 16-21, 1985 in Detroit, MI, Air Pollution Control Association, Pittsburgh, PA, 1985. Bradstreet, Jeffrey W., Richard A. Duffee, and James J. Zoldak, "Quantification of Odors from Waste Sites," (85-79.4), Presented at the 78th Annual Meeting of the Air Pollution Control Association, Held on June 16-21, 1985 in Detroit, MI, Air Pollution Control Association, Pittsburgh, PA, 1985. Breton, Marc et al., Assessment of Air Emissions from Hazardous Waste Treatment, Storage, and Disposal Facilities (TSDFs) - Preliminary National Emissions Estimates, (Draft Final Report), (GCA-TR-83-70-G), GCA Corporation, Bedford, MA, August 1983. Breton, Marc et al., Evaluation and Selection of Models for Estimating Air Emissions from Hazardous Waste Treatment, Storage, and Disposal Facilities, (FJPA-450/3-84-020), U.S. Environmental Protection Agency, Research Triangle Park, NC, December 1984. Brodzinsky, Richard and Hanwant B. Singh, Volatile Organic Chemicals in the Atmosphere; An Assessment of Available Data, (EPA-600/ 3-83-027a), U.S. Environmental Protection Agency, Research Triangle Park, April 1983. Brown, D. et al., Techniques for Handling Landborne Spills of Volatile Hazardous Substances, (EPA-bOO/2-81-207), U.S. Environmental Protection Agency, Cincinnati, OH, September 1981. Brown, Kirk W., Gordon B. Evans, Jr., and Beth D. Frentrup, eds., Hazardous Waste Land Treatment, Butterworth Publishers, Woburn, MA, TSBT: Brown, Richard D., Hazard Ranking System Issue Analysis; Use of Significance in Determining Observed Release, (MTR-86W101), The MITRE Corporation, McLean, VA, July 1986. Burkuard, Lawrence P., Anders W. Andren, and David K. Armstrong, "Estimation of Vapor Pressures for Polychlorinated Biphenyls: A Comparison of Eleven Predictive Methods," Environmental Science and Technology, Vol. 19, No. 6, 1985a, pp. 50CPW1: ~~ 118 ------- Burkhard, Lawrence P., Anders W. Andren, and David E. Armstrong, "Henry's Law Constants for the Polychlorinated Biphenyls," Environmental Science and Technology, Vol. 19, No. 7, 1985b, pp. 590-596. Caldwell, Steve, Kris W. Barrett, and S. Steven Chang, "Ranking System for Releases of Hazardous Substances," Proceedings of the National Conference on Management of Uncontrolled Hazardous Waste Sites, Held on October 28-30, 1981 in Washington, DC, Hazardous Materials Control Research Institute, Silver Spring, MD, 1981, pp. 14-20. Caravanos, Jack and Thomas T. Shen, "The Effect of Wind Speed on the Emission Rates of Volatile Chemicals from Open Hazardous Waste Dump Sites," Proceedings of the Fifth National Conference on Management of Uncontrolled Hazardous Waste Sites, Held on November 7-9, 1984 in Washington, DC, Hazardous Materials Control Research Institute, Silver Spring, MD, 1984, pp. 68-71. Caravanos, Jack, Granville H. Sewell, and Thomas T. 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Zegel, William C., "An Overview of Hazardous Waste Issues," Journal of the Air Pollution Control Association, Vol. 35, No. 1, January pp. 50-54. 139 ------- APPENDIX A SUMMARY OF AIR MONITORING DATA AT SELECTED WASTES SITES This appendix presents a compilation of available data on the ambient air contaminant concentrations arising from selected wastes sites. The data are limited in scope and are presented to indicate the magnitude of the air contamination problems that might arise from wastes sites. 141 ------- TABLE A-i PCB CONCENTRATIONS AT SELECTED SITES Site Concentration (ug/mr) Caputo 0.05 - 3 (winter) 246 - 300 (summer) Lehigh Elect 0.0075 New Bedford 0.021 (winter) 0.41 - 1.5 (summer) Source: Adapted from Smith, Michael A., ed., Contaminated Land: Reclamation and Treatment, Plenum Press, New York, NY, 1985, pp. 407-417. 142 ------- TABLE A-2 AMBIENT AIR CONCENTRATIONS OF SELECTED COMPOUNDS AT THREE CALIFORNIA HAZARDOUS WASTES DISPOSAL FACILITIES (ppb Carbon) BKK Kettleman Hills IT-Martinez Compound Upwind Downwind Upwind Downwind Upwind Downwind n-Hexane Benzene n-Heptane Toluene n-Octane Ethyl Benzene Xylenes Dichloro- benzene Total 12 10 8 52 5 10 46 0 143 139 115 86 952 158 37 157 0 1644 11 13 6 25 3 3 15 0 76 75 106 185 123 84 64 239 0 876 10 8 7 22 2 3 11 3 66 12 16 15 30 3 9 19 2 106 Note: Monitoring conducted by Illinois Institute of Technology for EPA during November and December 1979. Source: Scheible et al., 1982. 143 ------- TABLE A-3 AMBIENT AIR CONCENTRATIONS OF SELECTED COMPOUNDS AT THREE CALIFORNIA HAZARDOUS WASTES DISPOSAL FACILITIES (ppb Carbon) BKK Kettleman Hills IT-Martinez Compound Ethane Ethene Propane Acetylene 1-Butane n-Butane Propene Propadiene i-Pentane n-Pentane 1-Butene i-Butene Total Upwind Downwind Upwind Downwind Upwind Downwind 15 29 19 35 23 50 10 53 31 4 11 280 76 100 370 48 730 440 49 4 800 650 35 48 3350 28 18 29 18 11 26 5 30 19 8 192 27 15 27 14 11 67 4 170 140 2 11 488 28 23 88 20 80 93 11 110 56 7 16 532 15 18 13 14 86 21 5 23 14 209 Note: Monitoring conducted by State of California Air Resources Board during November and December 1979. Source: Scheible et al., 1982. 144 ------- TABLE A-4 POTENTIALLY CARCINOGENIC, TOXIC, MUTAGENIC, OR TERATOGENIC COMPOUNDS MEASURED AT THE BKK SITE (Maximum Detected Concentrations) Compound Benzene Vinyl Chloride Chloroform Carbon Tetrachloride Dioxane Tetrachlorethane Tetrachloroethylene Methyl Chloroform Trichloroethylene 36.0 Note: Monitoring conducted by University of Southern California during November 1979-June 1980; January 1981; and February 1981. Facility was in operation at this time. Source: State of California Air Resources Board, An Assessment of the Volatile and Toxic Organic Emissions from Hazardous Waste Disposal in California, Background Material for a Public Meeting, February 24, 1982, State of California Air Resources Board, Sacramento, CA, February 1982, p. 31. 145 ------- TABLE A-5 AVERAGE CONCENTRATIONS OF CONTAMINANTS DETECTED AT SELECTED NEW JERSEY DISPOSAL SITES (ppb volume) Compound Vinylidene Chloride Methylene Chloride Chloropyrene Chloroform 1-2 Dichloroethane 1-1-1 Trichl or oe thane Benzene Carbon Tetrachloride I richlor oe thylene Dioxane 1-1-2 Trichloroe thane Toluene 1-2 Dibromoethane Tetrachloroe thylene Chlorobenzene Ethylbenzene m&p Xylene Styrene o-Xyiene 1-1-2-2 Tetra- chloroe thane o-Chlorotoluene p-Chlorotoluene p-Dichlorobenzene o-Di chlorobenzene Nitrobenzene Naphthalene Site A 0 0.09 0 0.33 0.01 0.38 4.98 0.06 0.39 0 0.02 42.09 0.25 0.92 0.53 3.56 9.95 0.62 3.09 0.24 0.4 0.71 0.24 0.35 1.38 0.88 Site B 0.39 0.49 0 0.64 0 0.51 2.55 0.12 0.36 0 0.02 11.52 0.25 1.03 0.09 0.78 2.18 0.27 0.93 0.05 0.06 0.06 0.1 0.11 0.23 0.2 Site C 36.44 11.34 0.01 0.91 0.28 3.04 7.66 0.1 2.86 0.01 1.26 51.91 0.36 2.03 0.78 3.91 7.72 1.3 2.27 0.59 0.43 0.39 0.51 0.77 0.48 0.27 Site D 3.46 0.9 0 0.21 0.03 0.84 1.33 0.04 0.21 0 0.32 15.16 0.06 0.38 0.32 0.61 1.52 0.11 0.42 0.02 0.05 0.07 0.08 0.11 0.12 0.11 Site E 1.6 1.14 0 0.08 0 0.57 0.6 0.03 0.08 0 0.29 3.28 0.05 0.12 0.09 0.13 0.37 0.13 0.15 0.01 0.02 0.04 0.04 0.06 0.01 0.1 Landfill 2.61 1.58 0 0.12 0 1.29 3.33 0.02 0.34 0 0.11 27.79 0.02 1.53 0.15 1.53 3.35 0.41 0.9 0.01 0.01 0.03 0.06 0.06 0 0.08 Note: Detection limit of 0.01 substituted for values below detection limit. Source: Adapted from LaRegina, J. E. et al., 1984. 146 ------- APPENDIX B DISCUSSION OF REJECTED OPTIONS This appendix presents discussions of the scoring options that were developed and rejected. A short description of each option is presented, followed by the reasons for its rejection. B.I Evaluating Ambient Monitoring Data for Observed Releases Two basic options for evaluating ambient monitoring data for observed release were developed. These options would employ ambient measurements that might not "significantly" exceed background or may be surrogates for ambient air measurements in assigning an observed release value. This option would maintain the current approach: existence of data showing concentrations significantly above background results in a maximum value, 45. Other monitoring results would be evaluated as in Table B-l. The following relationship would hold between the values 0 < A < B < C < 45 Thus, a zero value would be assigned if and only if a comprehensive monitoring program showed no detectable levels of contamination. An alternate, similar option developed would allow data other than ambient air data to be used. For example, evidence of surface soil contamination, relative to background levels, could be utilized in a process similar to that for ambient air data suggested above. A minimum acceptable area of contamination would have to be set as well. 147 ------- TABLE fl-1 EVALUATING MONITORING RESULTS Monitoring Result Value No Contaminants Detected • Comprehensive monitoring program* 0 • Limited monitoring program* A Contaminants Detected • Background above analytical** detection limit B - Contamination level below analytical detection limit - Contamination level above analytical detection limit C but not significantly above background - Contamination level significantly above background 45 • Background below analytical detection limit C - Contamination level below analytical detection limit - Contamination level above analytical detection limit 45 *Guidance would be provided as to the definition of comprehensive and limited monitoring programs. **The analytical detection limit reflects the combination of instrument and laboratory detection limits. These differ for different instruments and laboratory methods. 148 ------- Further minor variations might be developed using alternate values and data categories such as vegetation injury. The above options were rejected since in the interest of maintaining simplicity in the observed release category and as placing too much emphasis on data of questionable quality and meaning. The basic concept led to the development of the also rejected "inconclusive monitoring" emission source descriptors (see Section B.2.2) and the adopted exceptions in the mobility factor (see Section 3.3.2). B.2 Potential to Release Options B.2.1 Emissions Estimation Approach The principal alternative to the engineering factors approach adopted in the two options discussed previously is the emissions estimation approach. In this approach, emissions equations would be used to estimate the emissions from a site and a value assigned based on the magnitude of the emissions estimate. Several emissions equations are available for generic waste disposal and treatment processes. Breton, et al. (1984) and Balfour, Wetherold and Lewis (1985) present fairly comprehensive discussions and evaluations of the emissions models currently available. Durham (1985) presents a discussion of ongoing EPA efforts to improve these models. Some of the models have been verified in field studies with good success (Balfour, W. D., et al., 1984, Caravanos, Sewell, and Shen, 1985). Many of these models have also been employed by EPA in policy 149 ------- studies (Breton, et al., 1983; Battye, et al., 1985). A review of this and related literature indicates that an emissions estimation approach would probably be feasible. The approach, however, was rejected for several reasons. First, many of tne equations are complex and require a fairly high level of sophistication to employ them properly. It was believed that the requisite high level of expertise would not be readily available in the field. Further; the equations require data that are not generally available. Some of the data are available in standard references, for standard conditions. The principal data of this type are the mass transfer coefficients, which are available for only a limited number of chemicals in idealized environments. It is possible to incorporate methods to calculate tnese factors from readily available data (e.g., vapor pressure) in many cases. However, these methods further complicate the calculations, do not always account for important, difficult to evaluate site characteristics, and generally lower the confidence in the final result. Of particular importance in this context is the effect of waste mingling on equation parameter values. Additional data that are necessary in many of the equations include site-specific data on detailed soil characteristics and meteorological factors. Second, the equations are not available addressing many of the situations encountered in CERCLA sites. Of particular importance are sites containing broken drums or tanks, either exposed or 150 ------- buried. Equations applicable to this common circumstance are not currently available. Further, the equations are idealized and do not reflect the deviations from design that are encountered in uncontrolled sites. Finally, many of the emissions estimation approaches require air monitoring data to back-calculate emissions rates. If such data were available, then the potential to release option would not have to be employed at all. In summary, the emissions estimation approach is probably technically feasible, but would be very difficult to implement. B.2.2 Inconclusive Monitoring Descriptors During the course of refining Options 1 and 2, five emission source descriptors were developed for monitoring results that did not indicate an observed release. The idea behind these "inconclusive monitoring" descriptors was to make use of monitoring results that, even though they did not indicate an observed release, would affect a subjective judgment of the probability that the site was or would soon release a significant amount of contaminants. These descriptors are listed in Table B-2. After much discussion, these five descriptors were deleted for two reasons. First, it was believed that if the air data collected at the site do not indicate an observed release, then they are also not of sufficient quality to use as emission source descriptors. Second, the information contained in these data would be better used 151 ------- TABLE B-2 "INCONCLUSIVE MONITORING" EMISSION SOURCE DESCRIPTORS Code Descriptor Ambient air monitoring results: Background at or above analytical detection limit: 30 - Contamination level below analytical detection limit 31 - Contamination level at or above analytical detection limit but not significantly above background 32 - Contamination level significantly above background but of insufficient quality to constitute an observed release Background below analytical detection limit: 33 - Contamination level below analytical detection limit 34 - Contamination level significantly above background but of Insufficient quality to constitute an observed release 152 ------- in assessing contaminant mobility and, hence, the exceptions to the contaminant mobility factor discussed in Section 3.3. B.2.3 Site Age A review of the processes that lead to air releases indicates that the dominant factors in determining release potential are the nature (e.g., mobility) and quantity of the waste in the site and the site containment. Since the processes that determine emission levels are continuous, the duration of time these processes have been in operation determines the quantity of waste remaining on the site and to a lesser extent, the nature of the waste. Thus, the time between disposal and site investigation, or the site age, is a crucial factor in determining emission potential that is not addressed in Options 1 and 2. There are two reasons for this apparent omission. First, no viable measure of the time between investigation and disposal could be defined. It is generally not possible to determine the date at which wastes were deposited at a site. Further, wastes were often deposited at different times and in different amounts and mixtures over a long period of time. Surrogate measures, such as years since site opening and years since site closing, suffer from similar information collection problems and may differ significantly from the actual years since disposal. Second, the interaction between site age and contaminant mobility is very complex and could not be simplified enough to allow both to be incorporated in the options. 153 ------- B.2.4 Mobility Factors Two alternate approaches to the Versar approach for evaluating contaminant mobility were investigated: partition coefficients and fugacity. Partition coefficients (Leo, Hansch and Elkins, 1971; Chiou, Schmedding, and Manes, 1982; Mingelgrin and Gerstl, 1983; Miller, et al., 1985) reflect the propensity of a compound to distribute between two other compounds or solution phases. For example, the octanol-water partition coefficient of a compound reflects the propensity of that compound to distribute between octanol and water within a combined solution. The octanol-water partition coefficient has been suggested as a measure of bioaccumulation (Saari and Goldfarb, 1986). They are also potentially useful in managing waste disposal, as an indication of the mobility of contaminants in various solutions (Prasad and Whang, 1985). The fugacity of a compound is somewhat similar to a partition coefficient (Mackay, 1979; Mackay and Paterson, 1981, 1982, and 1984). However, fugacity reflects the long-term propensity of a compound to distribute among environmental media rather than between two solutes such as octanol and water, for example. The media of concern, for example, can include air, water, sediment, aquatic biota, and soil. Fugacity can be used to calculate the long-term equilibrium distribution of a chemical in the environment. 154 ------- The use of partition coefficients were rejected for several reasons. In both Options 1 and 2, contaminant mobility reflects the ability of a contaminant to move offsite due to the contaminant physiochemical characteristics. Partition coefficients measure the propensity of the contaminant to distribute among solutions. They do not reflect the propensity of a contaminant to volatilize, only the possibility to migrate to the air-surface interface. These coefficients are applicable to mobility only to the extent that the distribution between solutions indicate ability to migrate. This, in turn, depends on the migration potential of the solute, which is generally unknown. Further, the partition coefficient depends on the contaminant in question and the two solutes. The same compound may have very different octanol-water and organic carbon partition coefficients. The choice of the best applicable coefficient at a site depends on the actual site waste composition, information that is generally unavailable. Finally, only octanol-water partition coefficients are available for the contaminants generally encountered at wastes sites. The use of fugacity was rejected primarily because of a lack of available fugacity data for the contaminants of interest and the complexity of the fugacity calculation approaches. It was felt that these calculations were too complex to be employed in the field. Less important reasons include the concern that fugacity reflects long-term equilibrium behavior rather that short-term transport 155 ------- phenomena. Fugacity would be a misleading measure of mobility whenever the long-term distribution of a chemical differed significantly from its short-term local distribution. B.2.5 Alternate Methods for Combining Containment Values Several alternate methods for combining containment values were considered. The first option developed employs a single containment factor approach, combining the particulate matter and gas containment aspects of a site. The containment descriptors and values are listed in Table B-3. This approach was rejected as being inferior to the two-factor approach presented in Options 1 and 2, while not really representing a significant simplification (see the matrix approaches in Table B-3). Additional options for combining the two containment values are as follows: • Three-level containment scale (0-2) for gases and particulate matter, combined value is the sum of the two values with a maximum value of 3. • Four-level containment scale (0-3) for gases and particulate matter, combined value is the maximum of the two values. • Four-level containment scale (0-3) for gases and particulate matter, combined value is the sum of the two values with a maximum value of 3. • Three-level containment scale (0-2), the combined value is the maximum of the two values unless both are equal to two, in which case the combined value is J. The adopted approach, which reflects the viewpoint that emissions are determined by the least restrictive containment, was deemed superior to these alternatives. 156 ------- TABLE B-3 SINGLE CONTAINMENT FACTOR APPROACH ACTIVE FIRE SITE 3_ BURIED TANKS • Depth to tanks at least six inches; soil resistant 1_ to gas migration • Depth to tanks at least six inches; soil not 2_ resistant to gas migration • Other 0_ CONTAMINATED SURFACE SOIL See Matrix Procedure 1 EXPOSED DRUMS Drums intact 1 Drums broken 3 EXPOSED TANKS • Open Roof Tanks - Dome intact; seals intact 0_ - Dome intact; seals broken; waste covered with 1_ a stable immiscible fluid - Dome intact; seals broken; waste covered with 1_ floating spheres - Undomed or dome not intact; waste covered with 2_ a stable immiscible fluid - Undomed or dome not intact; waste covered with 2_ floating spheres - Other 0_ • Fixed and Floating Roofs - Structurally intact; seals intact — Conservation vents intact and functioning 0_ — Conservation vents intact but not functioning 1 157 ------- TABLE B-3 (Continued) EXPOSED TANKS (Concluded) - Structurally intact; seals intact (Concluded) — Waste covered with a stable inert gas — Waste covered with floating spheres — Insulated — Waste covered with a stable immiscible fluid — Other - Structurally intact; seals broken — Conservation vents intact and functioning — Conservation vents intact but not functioning — Waste covered with a stable inert gas — Waste covered with floating spheres — Insulated — Waste covered with a stable immiscible fluid 2 — Other ? - Structurally not intact — Conservation vents intact and functioning 0 — Conservation vents intact but not functioning 1 — Waste covered with a stable inert gas 1 — Waste covered with floating spheres 1 — Insulated 2 — Waste covered with a stable immiscible fluid — Other - Other INACTIVE ABOVEGROUND FI&E SITE See Matrix Procedure 2 LANDFARM/LANPTREATMENT See Matrix Procedure 3 LANDFILL See Matrix Procedure 4 OPEN PIT SPILL SITE See Matrix Procedure 5 158 ------- TABLE B-3 (Continued) SURFACE IMPOUNDMENTS • Enclosed Impoundment* - Synthetic cover intact - Impoundment covered with floating spheres - Stable surfactant layer covering impoundment Synthetic cover torn 2_ Unstable or incomplete surfactant layer 2 Other D~ • Open impoundment (not enclosed) - Impoundment covered with floating spheres - Stable surfactant layer covering impoundment - Synthetic cover intact - Synthetic cover torn - Other SURFACE WATER BODY OR OUTFALL UNDERGROUND INJECTION • Depth of injection at least x inches • Depth of injection less than x inches WASTE PILE See Matrix Procedure b *An enclosed impoundment is one with a freeboard exceeding two feet in height or one that is substantially surrounded by a wall, fence, trees or other adequate windbreak. 159 ------- TABLE B-3 (Continued) MATRIX PROCEDURE 1 CONTAMINATED SURFACE SOIL Evaluate the site separately for the following containment factors: Particulate Containment (choose applicable characteristic with lowest value): • Site covered with an essentially impermeable cover 0_ or heavily vegetated. No exposed soil or liquids (e.g., paved-over) • Enclosed in an intact building 1_ • Site substantially vegetated or covered with a 1_ nonwater based dust suppressing fluid. Little exposed soil or liquids • Enclosed in an nonintact building 2_ • Site lightly vegetated or lightly covered with a 2_ nonwater dust suppressing fluid. Much exposed soil or liquids • Slope average less than 10 degrees 2_ • Substantially surrounded with mesh fence 2 • Site substantially devoid of vegetation. Large 3 percentage of exposed soil or liquids • Other 0 Gas Containment: • Enclosed in an intact building 1 • Covered with an intact synthetic cover 1 • Covered with a nonintact synthetic cover 2 • Enclosed in a nonintact building 2 • Other 0 160 ------- TABLE B-3 (Continued) Combine the two containment values as follows: Level of Gas Containment Level of Particulate Containment 0: 1: 2: 3: 0 0 1 2 3 1 1 1 2 3 2 2 2 2 3 ,3 3 3 3 3 161 ------- TABLE B-3 (Continued) MATRIX PROCEDURE 2 INACTIVE ABOVEGROUND FIRE SITE Evaluate the site separately for the following containment factors: Particulate Containment (choose applicable characteristic with lowest value): • Site covered with an essentially impermeable cover 0_ or heavily vegetated. No exposed soil or liquids (e.g., paved-over) • Enclosed in an intact building 1 • Site substantially vegetated or covered with a 1_ nonwater-based dust suppressing fluid. Little exposed soil or liquids • Enclosed in a nonintact building 2_ • Site lightly vegetated or lightly covered with a 2_ a nonwater dust-suppressing fluid. Much exposed soil or liquids • Slope average less than 10 degrees 2 • Substantially surrounded with mesh fence 2 • Site substantially devoid of vegetation. Large 3 percentage of exposed soil or liquids • Other 0 Gas Containment: • Enclosed in an intact building 1 • Enclosed in a nonintact building 2 • Other 0 162 ------- TABLE B-3 (Continued) Combine the two containment values as follows: Level of Gas Containment 0 1 2 3 Level of 0: 0 1 23 Particulate 1:1 1 2 3 Containment 2: 2 2 2 3 3: 3 3 33 163 ------- TABLE B-3 (Continued) MATRIX PROCEDURE 3 LANDFARM/LANDTREATMENT Evaluate the site separately for the following containment factors: Particulate Containment (choose applicable characteristic with lowest value): • Site covered with an essentially impermeable cover 0_ or heavily vegetated. No exposed soU or liquids (e.g., paved-over) • Site substantially vegetated or covered with a 1_ nonwater—based dust-suppressing fluid. Little exposed soil or liquids • Site lightly vegetated or lightly covered with a 2_ nonwater dust-suppressing fluid. Much exposed soil or liquids • Slope average less than 10 degrees 2_ • Substantially surrounded with mesh fence 2 • Site substantially devoid of vegetation. Large percentage of exposed soil or liquids 3 • Other 0 Gas Containment: • Synthetic cover with soil cover over 0.4 inches 0 • Soil cover in excess of one inch; soil resistant 1 to gas migration • Soil cover in excess of one inch; soil not resistant 2 to gas migration • Other 0 164 ------- TABLE B-3 (Continued) Combine the two containment values as follows: 9 Level of Gas Containment Level of Particulate Containment 0: 1: 2: 3: 0 0 1 2 3 1 1 1 2 3 2 2 2 2 3 3 3 3 3 3 165 ------- TABLE B-3 (Continued) MATRIX PROCEDURE 4 LANDFILL Evaluate the site separately for the following containment factors: Particulate Containment (choose applicable characteristic with lowest value): • Site covered with an essentially impermeable cover 0 or heavily vegetated. No exposed soil or liquids (e.g., paved-over) • Site substantially vegetated or covered with a nonwater based-dust-suppressing fluid. Little exposed soil or liquids 1 • Site lightly vegetated or lightly covered with a 2 nonwater dust-suppressing fluid. Much exposed soil or liquids • Slope average less than 10 degrees 2 • Substantially surrounded with mesh fence 2 • Site substantially devoid of vegetation. Large 3 percentage of exposed soil or liquids • Other 0 Gas Containment: • Functioning gas collection system 0 • Depth to waste at least six inches; soil cover 1 resistant to gas migration • Depth to waste at least six inches; soil cover not 1 resistant to gas migration —— • Nonfunctioning gas collection system 3 • Other 0 166 ------- TABLE B-3 (Continued) Combine the two containment values as follows: Level of Gas Containment 0123 Level of 0: 0 1 23 Particulate 1:1 1 2 3 Containment 2: 2 2 2 3 3: 3 3 33 167 ------- TABLE B-3 (Continued) MATRIX PROCEDURE 5 SPILL SITE Evaluate the site separately for the following containment factors: Particulate Containment (choose applicable characteristic with lowest value): • Site covered with an essentially impermeable cover 0_ or heavily vegetated. No exposed soil or liquids (e.g., paved-over) • Enclosed in an intact building 1_ • Site substantially vegetated or covered with a 1_ nonwater-based-dust suppressing fluid. Little exposed soil or liquids • Enclosed in an nonlntact building 2_ • Site lightly vegetated or lightly covered with a 2_ nonwater-dust-suppressing fluid. Much exposed soil or liquids • Slope average less than 10 degrees 2 • Substantially surrounded with mesh fence 2 • Site substantially devoid of vegetation. Large 3_ percentage of exposed soil or liquids • Other 0_ Gas Containment: • Synthetic cover with soil cover over 0.4 inches 0 • Covered with an intact synthetic cover; surface 1 contamination • Soil cover in excess of one inch 1 • Covered with a nonlntact synthetic cover; surface 2 contamination • Other 0 168 ------- TABLE B-3 (Continued) Combine the two containment values as follows: Level of Gas Containment 0123 Level of 0: 0 1 23 Particulate 1:1 1 2 3 Containment 2: 2 2 2 3 3: 3 3 33 169 ------- TABLE B-3 (Continued) MATRIX PROCEDURE 6 WASTE PILE Evaluate the site separately for the following containment factors: Particulate Containment (choose applicable characteristic with lowest value): • Site covered with an essentially impermeable cover 0_ or heavily vegetated. No exposed soil or liquids (e.g., paved-over) • Enclosed in an intact building 1_ • Site substantially vegetated or covered with a 1_ nonwater-based-dust-suppressing fluid. Little exposed soil or liquids • Enclosed in an nonlntact building 2_ • Slope average less than 10 degrees 2_ • Substantially surrounded with mesh fence 2_ • Site lightly vegetated or lightly covered with a 3 nonwater-dust-suppressing fluid. Much exposed soil or liquids • Site substantially devoid of vegetation. Large 3_ percentage of exposed soil or liquids • Other 0_ Gas Containment: , • Covered with an intact synthetic cover 1 • Covered with a nonintact synthetic cover 2 • Enclosed in an intact building 2 • Other 0 170 ------- TABLE B-3 (Concluded) Combine the two containment values as follows: Level of Gas Containment Level of Particulate Containment 0: 1: 2: 3: 0 0 1 2 3 1 1 1 2 3 2 2 2 2 3 3 3 3 3 3 171 ------- B.2.6 Alternate Release Potential Algorithms Options 1 and 1A use an algorithm to evaluate a site's release potential that combines values based on three emission source descriptors using probabilistic combinatorics. In Option 2, the single emission source descriptor that best describes the entire site is chosen and the site evaluated accordingly, considering size, mobility, and containment. Numerous alternate algorithms were considered as follows: • Assign a minimum nonzero value (e.g., 5) to each site lacking an observed release. • Choose the emission source descriptor with the highest overall value considering descriptor values, size, mobility and containment. • Choose all the applicable emission source descriptors and sum the resulting values, considering size, mobility and containment, using the minimum of this sum and 45 as the site value. • Choose all the applicable emission source descriptors and sum the resulting values, considering size, mobility and containment, truncating the sum of the size dependent emission source descriptor and mobility values to 15 before multiplying by the containment value. The minimum of this sum and 45 would be the site value. These options were rejected in favor of the probabilistic combinatorics since the latter approach better reflects the probabilistic nature of the potential-to-release option. A potentially viable alternative, however, may be to use two rather than three emission source descriptors. 172 ------- B.3 Targets Category Options These options envision alterations in the target distance limit used in the HRS, currently four miles. As stated previously, the actual target distance limit is yet to be chosen for Options 1 and 2, pending completion of a special analysis. The options are listed in Tables B-4 through B-ll. Further options can be defined employing a minimum value of 3 (for example). B.4 Alternate Air Pathways A total of six complete air pathway options were developed and presented to EPA for consideration. Four of these options were rejected in favor of the two options presented in Section 3. The remaining options are simplifications of the first two. Successive simplifications were made in the release category addressing emission source descriptors, containment factors, and mobility factors. The waste characteristics and targets categories were unchanged from Option 1. These four options are summarized in Table B-12. 173 ------- TABLE fl-4 ALTERNATE POPULATION-AT-RISK FACTOR MATRIX (Variation 1) Distance (miles) Population 0-50 0-15 0-4 0-1 1, 1 101 001 3,001 1, 3, 10 Popi 1 101 001 001 10, 0 6666 - 100 6 9 12 15 - 1,000 9 12 15 18 - 3,000 12 15 18 21 - 10,000 15 18 21 24 ,000+ 18 21 24 27 TABLE B-5 ALTERNATE POPULATION-AT-RISK FACTOR MATRIX (Variation 2) Distance (miles) ilation 0-15 0-4 0-1 0-1/2 0 6666 - 100 9 12 15 18 - 1,000 12 15 18 21 - 3,000 15 18 21 24 - 10,000 18 21 24 27 000+ 21 24 27 30 0-1/2 6 18 21 24 27 30 174 ------- TABLE B-6 ALTERNATE POPULATION-AT-RISK FACTOR MATRIX (Variation 3) Distance (miles) Population 1 101 1,001 3,001 10 0 - 100 - 1,000 - 3,000 - 10,000 ,000+ 0-15 6 6 9 12 15 18 0-4 6 9 12 15 18 21 0-1 6 12 15 18 21 24 0-1/2 6 15 18 21 24 27 0-1/4 6 18 21 24 27 30 175 ------- TABLE 3-7 ALTERNATE VALUES FOR LAND USE (Variation 1) ASSIGNED VALUE - Distance (miles) to Commercial/Industrial Distance (miles) to Nat./ State Parks, Forests Wildlife Preserves and Residential Areas Distance (miles) to Agricultural Lands: Ag Land Prime Ag Land Distance to Historic/ Landmark Sites 0 5+ 10+ 5+ 10+ 1-5 1/2-1 5-10 2-5 1-5 5-10 1/2 - 1 2-5 0 - 1/2 0-2 0 - 1/2 0-2 3, if within view of site or if site is subject to significant impacts. 176 ------- TABLE B-8 ALTERNATE VALUES FOR LAND USE (Variation 2) ASSIGNED VALUE - Distance (miles) to Commercial/Industrial Distance (miles) to Nat./ State Parks, Forests Wildlife Preserves . and Residential Areas Distance (miles) to Agricultural Lands: Ag Land Prime Ag Land Distance to Historic/ Landmark Sites 0 5+ 15+ 5+ 15+ 1-5 1/2-1 10-15 5-10 0 - 1/2 0-5 1-5 10 - 15 1/2 - 1 5-10 0 - 1/2 0-5 3, if within view of site or if site is subject to significant impacts. 177 ------- TABLE B-9 ALTERNATE VALUES FOR SENSITIVE ENVIRONMENT (Variation 1) ASSIGNED VALUE - STANCE (MILES) TO TLANDS Coastal Fresh Water STANCE (MILES) TO 5+ 2+ 2+ 2 - 1/2 - 1 - 5 2 2 1 - 1/4 - 1/2 - 2 1/2 1 0 - 0 - 0 - 1 1/4 1/2 CRITICAL HABITAT TABLE B-10 ALTERNATE VALUES FOR SENSITIVE ENVIRONMENT (Variation 2) ASSIGNED VALUE - STANCE (MILES) TO TLANDS Coastal Fresh Water STANCE (MILES) TO 1+ 1/4+ 1/2+ 1/2 - 1 100 ft - 1/4 1/4 - 1/2 0 - 0 - 0 - 1/2 100 ft 1/4 CRITICAL HABITAT 178 ------- TABLE B-ll ALTERNATE VALUES FOR SENSITIVE ENVIRONMENT (Variation 3) ASSIGNED VALUE - 1 2 3 DISTANCE (MILES) TO WETLANDS Coastal 2+ 1-2 0-1 Fresh Water 1/2+ 1/4 - 1/2 0 - 1/4 DISTANCE (MILES) TO 1+ 1/2-1 0 - 1/2 CRITICAL HABITAT 179 ------- TABLE B-12 OVERVIEW OF IMPORTANT FEATURES OF REJECTED AIR PATHWAY OPTIONS Release Category 00 o Waste Characteristics Targets Option 3 Seven-level observed release 5 descriptors Size not included Mobility* factor (3 measures) (5 contaminants) Simplified gas containment Probabilistic combinatorics Combined toxicity- mobility factor Waste quantity Population Sensitive environment Land use Based on a to-be- determined distance limit Option A Five-level observed release 5 descriptors Size not included Mobility* factor (3 measures) (5 contaminants) Simplified gas containment Probabilistic combinatorics Combined tozicity- mobility factor Waste quantity Population Sensitive environment Land use Based on a to-be- determined distance limit Option 5 Five-level observed release 5 descriptors Size not included Mobility factor not included Simplified gas containment Probabilistic combinatorics Combined toxicity- mobility factor Waste quantity Population Sensitive environment Land use Based on a to-be- determined distance limit Option 6 Five-level observed release with a nonzero minimum value for potential to release Combined toxicity- mobllity factor Waste quantity Population Sensitive environment Land use Based on a to-be- determined distance limit •Applicable to gases only. under investigation. Particulates are assumed to be mobile. Particulate mobility is currently ------- APPENDIX C STEP-BY-STEP INSTRUCTIONS AND EXAMPLES This appendix provides step-by-step instructions for using Option 1, including worksheets to facilitate calculations. Substantially the same instructions are used for all of the options. The differences lie primarily in the tables and worksheets used. Many of the required tables can be found in Sections 4 and 5, as applicable. Additional tables can be found in Appendix D. This appendix also included two examples illustrating the application of Options 1 and 2 to a hypothetical wastes site. C.I Step-By-Step Instructions This section provides step-by-step instructions for evaluating a site using Option 1. Step 1; For each CERCLA contaminant detected in the ambient atmosphere, calculate the ratio between the concentration detected in the site samples and the concentration detected in the background samples.* If the background samples are below the detection limit, then the detection limit should be substituted for the background concentration. Select the CERCLA contaminant with the greatest *These instructions are based on the use of the ratio of background to site sample concentrations. As stated in Section 4, a similar approach can be developed using the difference between the concentrations. A discussion of the use of differences in determining an observed release can be found in Brown, 1986. 181 ------- ratio ^s the reference conta-nlaan'- and record its Chemical Abstracts Service (CAS) code, the concentrations detected, and the detection limit on Worksheet 1: Observed Release Worksheet (Table C-l). If the ratio of the site sample concentration to the background sample concentration is above 10.J, assign an observed release value of 45.* If the ratio is above 1.5 and suppressive conditions prevailed during sampling, assign an observed release value of 45. Assign a potential to release value of 0. Record the release values on Worksheet 1 and go to Step 9. Otherwise, record an observed release value of 0 on Worksheet 1 and go to Step 2. Step 2; Select up to three emission source descriptors from the list of emission source descriptors (Table 9) that apply to the site and record the codes for the descriptors selected on Worksheet 2: Potential to Release Worksheet (Table C-2). If more than three apply, select the three that best describe the site. Calculate the size of the areas described by the selected descriptors, including only those applicable areas which contain waste materials. In general, the areas covered by the descriptors selected must be larger than the minimum size in the "Small" size category. If this constraint cannot be met, then select only the descriptor whose size is greatest relative to the minimum size in its "Small" category. Emission source descriptor definitions are *The reader is reminded that tne values of 10 and 1.5 used in Step 1 are provided for illustrative purposes only. 132 ------- TABLE C-l WORKSHEET 1: OBSERVED RELEASE WORKSHEET Units REFERENCE CONTAMINANT CAS NUMBER MLMIMUM DETECTION LEVEL BACKGROUND CONCENTRATION SITE SAMPLE CONCENTRATION RATIO VALUE (0 or 45) 183 ------- TABLE C-2 WORKSHEET 2: POTENTIAL TO RELEASE WORKSHEET Mobility Descriptor Value Value Sum Containment Product Code Size (A) (B) (A+B) Value (C) t(A+B)zC] (1) (2) (3) (4) (1)+ (2)+ (3) (5) (1) x (2) / 45 (6) (1) x (3) / 45 (7) (2) x (3) / 45 (8) (1) x (2) x (3) /2025 (9) (4) - (5) - (6) - (7) + (a) (10) Potential to Release Value* *Round-off to nearest whole number. Descriptor Code: From Table 9. Size: From Table 11. Des. Value: From Table 13. Mooility Value: From Worksheet 5. Containment Value: From Worksheet 6. 164 ------- provided in Appendix D (Table D-l). Using the table of size ranges (Table 11), record the sizes selected on Worksheet 2. Determine the emission source descriptor values from the emission source descriptor table (Table 13) and record the values on Worksheet 2. Step 3; Calculate the gas mobility as follows. For each emission source descriptor, determine up to five contaminants identified at the applicable portion of the site from the list of CERCLA contaminants. Contaminants whose locations on the site were not determined cannot be used to evaluate mobility for any descriptor. Record the CAS codes for the identified contaminants on Worksheet 3: Gas Mobility Worksheet (Table C-3). Using the information provided in the gas mobility tables (Table 15), assess the mobility of each contaminant and record the results on Worksheet 3. For R.CRA wastes and contaminants, the information required can be found in Versar, 1984. Standard references such as Weast, 1977 contain information on vapor pressure and Henry's constants for other contaminants. Versar, 1984 describes the derivation of the dry relative soil volatility index. Supplemental information on PCBs can be found in Burkhard, Andren and Armstrong; 1985a, 1985b. Step 4; Calculate the particulate mobility value as follows. Estimate the threshold wind speed for the site as indicated in Cowherd et al., 1985, or use the default value of 12.5 meters per second. Record the appropriate value as indicated on Worksheet 4: Particulate Mobility Worksheet (Table C-4). Identify the airport 185 ------- TABLE C-3 WORKSHEET 3: GAS MOBILITY WORKSHEET First Emission Source Descriptor Code CAS Number VP Value AQ Value RS Value Sum (1) (2) (3) (4) (5) (6) Average of positive values in lines 1 through 5 (7) Gas Mobility Value for First Emission Source Descriptor (see table below) Second Emission Source Descriptor Code CAS Number VP Value AQ Value RS Value Sum (1) (2) (3) (4) (5) (6) Average of positive values in lines 1 through 5 ('/) Gas Mobility Value for Second Emission Source Descriptor (see table below) VP Value:From Table 15. AQ Value: From Table 15. RS Value: From Table i5. 186 ------- (1) (2) (3) (4) (5) TABLE C-3 (Concluded) Third Emission Source Descriptor Code CAS Number VP Value AQ Value RS Value (6) Average of positive values in lines 1 through 5 (7) Gas Mobility Value for Third Emission Source Descriptor (see table below) Sum GAS MOBILITY FACTOR TABLE Range of Average Value Greater than or equal to Less than 0 3 5 7 3 5 7 10 Value 0 1 2 3 VP Value: From Table 15. AQ Value: From Table 15. RS Value: From Table 15. 187 ------- TABLE C-4 WORKSHEET 4: PARTICULATE MOBILITY WORKSHEET Weather Station: Threshold wind speed8: meters per second (ut) Fastest Precip. Temp.b Month Mile (F) (P) (T) (T-10) P/(T-lO) [P/(T-lO)]10/9 Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Sum = Sum divide by 12 x 115 u D PE Index - 188 ------- TABLE C-4 (Concluded) Mobility Index (I) = (u+ - ut)/PE2 Particulate Mobility Value (4 - log-,0I)c aDefault value of 12.5 may be used. ^Methodology is valid in the temperature range 28.5 to 90.0 degrees Fahrenheit. If average monthly temperature is below 28.5 degrees, set T-10 equal to 18.5. If average monthly temperature is above 90.0 degrees, set T-10 equal to 80.0. cRound off to nearest whole number. If logio1 exceeds 4, value = 0. If log10I is less than 0.5, value = 3. The following table provides alternate, equivalent way to determine the particulate mobility value. ALTERNATE PARTICULATE MOBILITY VALUE TABLE Range of Values for I Value Less than 3.16 x 10~4 0 3.17 x 10~4 - 3.16 x 10~3 1 3.17 x 10~3 - 3.16 x 10~2 2 _2 Greater than 3.16 x 10 3 189 ------- closest to the site and listed in the Local Climatological Data Summary. Calculate the average of the monthly fastest miles recorded at that airport as indicated on the worksheet. Calculate the PE Index as indicated on the worksheet or as estimated from Figure 2. Record the PE Index as indicated. Combine these three estimates as indicated and record the particulate mobility value. Step 5; Record the gas mobility values for each emission source descriptor as indicated on Worksheet 5: Combined Mobility Worksheet (Table C-5). Record the particulate mobility value (assumed to be the same for each descriptor) as indicated on the worksheet. Calculate the combined mobility values for each descriptor using the table on the worksheet and record the values as indicated and on Worksheet 2. Step 6: Evaluate the gas and particulate containment aspects of the site corresponding to the selected emission source descriptors using the lists of gas and particulate containment factors (Tables D-3 and D-4). If more than one containment descriptor corresponds to the selected emission source descriptor, select the one that best applies. Record the containment values for each descriptor on Worksheet 6: Containment Worksheet (Table C-6). Step 7; Combine the site containment values using the combined containment factor matrix (Table 20) and record the results on Worksheet 6 and Worksheet 2. 190 ------- TABLE C-5 WORKSHEET 5: COMBINED MOBILITY WORKSHEET Descriptor Code Gas Mobility Value* Particulate Mobility Combined Value** Value (1) (2) (3) COMBINED MOBILITY FACTOR MATRIX Gas Mobility Value 0123 0: 0 1 23 1: 1 2 34 2: 2 3 45 Particulate Mobility Value 3: *From Worksheet 3. **From Worksheet 4. 191 ------- TABLE C-6 WORKSHEET 6: CONTAINMENT WORKSHEET First Descriptor Code Particulate Containment Code Gas Containment Code Second Descriptor Code Particulate Containment Code Gas Containment Code Third Descriptor Code Particulate Containment Code Gas Containment Code Descriptor Particulate Containment Gas Containment Combined Code Value Value Value (1) (2) (3) Descriptor Code: From Table 9. Particulate Containment Code: From Table D-3. Gas Containment Code: From Table D-4. Combined Value: From Table 20. 192 ------- Step 8; Combine the values calculated previously as indicated on Worksheet 2. This step concludes the calculation of the potential to release value. Step 9; Select up to five contaminants identified at the site and calculate the toxicity value as indicated in the Tables 4, 6, and 7 of the HRS User's Manual (47 FR 31219-31243). Record these values on Worksheet 7: Toxicity-Mobility Worksheet (Table C-7). Evaluate the mobility of the contaminants as follows. If the contaminant has been identified as being emitted from the site in an observed release, its mobility value is set equal to 3. If the contaminant has not been identified as part of an observed release, then its mobility value is assessed differently. Mobility values for particulate contaminants that have not been identified as being emitted from the site are evaluated using the particulate mobility factor discussed previously. The mobility value for a nonemitted gaseous contaminant is calculated as the average of its vapor pressure, Henry's constant and dry relative soil volatility values according to Table 15. The mobility value for a contaminant present as both a gas and a particle is the greater of the applicable gas and particle mobility values. Combine the toxicity and mobility values as indicated on the combined toxicity-mobility factor matrix (Table 22). Record the highest contaminant toxicity-mobility value as indicated. 193 ------- TABLE C-7 WORKSHEET 7: TOXICITY-MOBILITY WORKSHEET Toxicity Mobility CAS Number Value Value Combined Value (1) (2) (3) (4) (5) (6) Maximum Combined Value Level of Toxicity COMBINED FACTOR MATRIX Level of Mobility 0 1 _2 _3 0: 0 0 00 1: 0 2 46 4 8 12 2: 3: 12 18 VP Value: From Table 15. AQ Value: From Table 15. RS Value: From Table 15. Toxicity Value: From MRS User's Manual. 194 ------- Step 10; Record the Observed Release Value (Worksheet 1), Potential to Release Value (Worksheet 2) and Toxicity-Mobility Value (Worksheet 7) as indicated on Worksheet 8: Summary Air Route Score (Table C-8). Step 11; Evaluate the hazardous waste quantity as indicated in the HRS User's Manual (47 FR 31219-31243) and record the result on Worksheet 8. Step 12; Add lines 3 and 4 on Worksheet 8 as indicated to determine the waste characteristics value. Step 13; Evaluate the targets, as indicated in the HRS User's Manual (47 FR 31219-31243) employing the effective source radius, as applicable. Add lines 7, 8, and 9 as indicated. Step 14; Calculate the air migration route score as indicated on Worksheet 8, lines 11 and 12. C.2 Hypothetical Examples; The Clean River Site This section presents a hypothetical example of the application of Options 1 and 2. It is adapted from the Clean River problem currently used in HRS training. It is intended to be realistic but the data do not represent a known hazardous wastes site. C.2.1 Description of the Site The site is a closed chemical manufacturing facility that was in operation between 1945 and 1968. It was engaged in the manufacture of a wide variety of organic and inorganic chemicals. The facility is located on 20 acres of mostly low-lying land with a 195 ------- TABLE C-8 WORKSHEET 8: SUMMARY AIR ROUTE SCORE 1. OBSERVED RELEASE VALUE8 2. POTENTIAL TO RELEASE VALUEb 3. TOXICITY-MOBILITYC 4. HAZARDOUS WASTE QUANTITY*1 5. WASTE CHARACTERISTICS VALUE (Lines 3 + 4) 6. TARGETS 7. Population 8. Land Used 9. Sensitive Environment 10. TARGETS VALUE (Lines 7+8+9) 11. If line 1 is not equal to 0.0, multiply lines 1 x 5 x 10 If line 2 is not equal to 0.0, multiply lines 2 x 5 x 10 12. Divide line 11 by 351 S aFrom Worksheet 1. bFrom Worksheet 2. cFrom Worksheet 7. dFrom HRS User's Manual. a 196 ------- few hills of low elevation along the Clean River, as depicted in Figure C-l. The Clean River flows through the southwest section of Charles County, and into Union Lake, before reaching the Major River. Charles County is approximately 50 square miles in area and includes the incorporated cities of Catsville and Maryville. A large portion of the area in Charles County is undeveloped land. This undeveloped land consists mainly of agricultural and marsh land (more than 5 acres) along the Clean River, and also includes some wooded areas. The agricultural land and marsh land are within 1,000 feet of the site fence, but the wooded areas are at least 5 miles away from the site. The developed land is divided among residential and industrial use. Both residential and industrial areas are concentrated in Catsville (population 2,957) and Maryville (population 5,258). Near the site there are many privately owned farms which cultivate vegetable crops with the nearest farm house located approximately 1,000 feet from the site fence (Figure C-2). A new subdivision of 50 houses, called River View Estates, was built in 1980 approximately one mile from the site fence along Suburban Road (Figure C-2). Construction of 100 additional houses is planned over the next three years. The chemical manufacturing facility has recently been purchased by a housing developer and the old plant is slated for demolition. 197 ------- Key: D Sediment Sampling Location • Surface Water Intake Catsvllle n t \ r Scale 2 Miles Irrigation Pond Charles County FIGURE C-1 CLEAN RIVER SITE LOCATION 198 ------- Key: A Monitoring Well IN t Scale 1/8 1/4 Miles Farm House Farm House River View Estimates <50 Houses) FIGURE C-2 CLEAN RIVER SITE PLAN 199 ------- The site investigation team found several disposal areas on the site. A discussion with the previous owners of the facility revealed that processing wastes were disposed of on the site. In particular, the off-specification products and undesirable by-products of the processes were disposed of in an abovegrade landfill (30 percent slope) along the Clean River (Figure C-2). The landfill has not been maintained and signs of erosion are everywhere. When a storm came through the area in late 1979, the Clean River flooded and a section of the landfill was eroded away, leaving a portion of the waste in the landfill exposed. The land was purchased by the housing developer in 1980, but the present owner did not take any measures to secure the landfill from further erosion. An examination of the site map reveals that the landfill measures about 245 x 245 feet or about 60,000 square feet. In addition, wastes of an unspecified origin were disposed of In two settling ponds. The ponds are approximately 125 feet in diameter and 2-1/2 feet deep. The site investigation team also located an underground tank (between Buildings B & C), and a drum storage area located near the landfill. The underground tank has a capacity of 50,000 gallons and was half full at the time of the investigation. The drums were allegedly removed in 1975 by the former owners. The site Investigation team also found 67 drums in various degrees of decay inside Building B, with liquid oozing from some of 200 ------- the drums and contaminating the grassy area behind the building, but the team did not locate any liner or containment structure in the grassy area upon searching. A summary of the sampling results from the site investigation is provided in Table C-9. Samples taken around the top perimeter of the landfill showed concentrations of arsenic and cadmium, while leachate from the south toe showed high concentrations of arsenic, phenol, toluene and benzene. Wet sludge samples (50 percent water) from the ponds showed concentrations of heavy metals including arsenic and cadmium as well as benzene. A sampling of the contents of the tank revealed toluene and phenol as its contents. A sample of the liquid found leaking from the drums inside Building B indicated the presence of phenol and toluene. The various detection limits were all less than one part per million. C.2.2 Step-by-Step Application of the Option 1 Methodology This section illustrates the step-by-step application of the Option 1 air pathway evaluation method to the hypothetical Clean River site. The step numbers corresponds directly to the steps in Section C.I. Step 1 (Observed Release Value); No air monitoring was conducted on the site, hence an observed release value of 0 is assigned (see Table C-10). Step 2 (Emission Source Descriptor Values); The following Option 1 emission source descriptors can potentially be used in scoring this site: 201 ------- TA3LE C-9 SUMMARY OF SAMPLING RESULTS. CLEAN RIVER SITE (ppm) Location Landfill Cover Soil Background Soil Leachate Sludge Drum Liquid Arsenic 41 15 120 200 ND Cadmium 19 ND ND 150 ND Phenol ND NA 250 ND 750 Toluene ND NA 350 ND 1550 Benzene ND NA 990 0.1 ND NA: Not available. ND: Not detected. 202 ------- TABLE C-10 CLEAN RIVER EXAMPLE WORKSHEET 1: OBSERVED RELEASE WORKSHEET Units REFERENCE CONTAMINANT CAS NUMBER MINIMUM DETECTION LEVEL BACKGROUND CONCENTRATION SITE SAMPLE CONCENTRATION RATIO VALUE (0 or 45) 0 203 ------- • flelowground Tanks—5 • Contaminated Surface Soil: Background below analytical detection limit; contamination level above analytical detection limit—10 • Exposed Drums: Drums broken—11 • Landfill: All other situations—20 • Surface Impoundment: Wet; evidence of waste contamination near surface—26 The principal consideration in selecting a descriptor is whether there is evidence that hazardous materials have been placed in the area covered by the selected descriptor. The sampling data and site investigation Indicated that hazardous materials have been found, or were known to be disposed of, in the tanks, drums, landfill and ponds. The materials have either been disposed of on the surface or have migrated to the surface. The acceptability of the belowground tanks and exposed broken drums is straightforward. The contaminated surface soil is acceptable given the increased cadmium soil level in the cover soil of the landfill. The fact that cadmium was found in the soil on the landfill and not in the landfill would indicate that the cover soil is contaminated with a material other than that disposed of in the landfill. Hence, it can be considered a separate source, distinct from the landfill. No information is provided on the presence of biodegradable material in the landfill, hence the selection of that descriptor. 204 ------- The wet surface impoundment descriptor was selected for the ponds reflecting the water content of the sludge samples and the presence of contaminants in the sludge. The sizes of the areas covered by each descriptor also meet the minimum size requirements: • Belowground Tanks: 50,000 gallons or about 7,000 cubic feet • Contaminated Surface Soil: About 245 x 245 feet or about 60,000 square feet • Exposed Drums: 67 drums • Landfill: About 245 x 245 feet or about 60,000 square feet • Surface Impoundment: 125 in diameter x 2.5 feet in-depth each or about 61,000 cubic feet in total Of the applicable descriptors, the following three descriptors best describe the site: • Contaminated Surface Soil: Background below analytical detection limit; contamination level above analytical detection limit—10 • Landfill: All other situations—20 • Surface Impoundment: Wet; all other situations—26 The use of the exposed, broken drum descriptor in place of any of these three would be acceptable. The use of the underground tank descriptor, while acceptable, would not be indicated since its containment value would be 0. The size data indicated that the landfill and ponds would be considered "medium" while the contaminated surface soil would be considered "small". The resulting values are listed on Table C-ll. 205 ------- TABLE C-ll CLEAN RIVER EXAMPLE WORKSHEET 2: POTENTIAL TO RELEASE WORKSHEET Des. Mobility Descriptor Value Value Sum Containment Code Size (A) (B) (A+B) Value (C) (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) 20 26 10 (1)H (1) (1) (2) (1) (4) M 3 4 7 3 M 7 4 11 3 S 6 1 7 3 H (2H (3) x (2) / 45 x (3) / 45 x (3) / 45 x (2) x (3) /2025 - (5) - (6) - (7) + (8) Potential to Release Value* Product [(A+B)rC] 21 33 21 75 15.4 9.8 15.4 7.19 41.59 42 *Round-off to nearest whole number. Descriptor Code: From Table 9. Size: From Table 11. Des. Value: From Table 13. Mobility Value: From Worksheet 5 (Table C-14). Containment Value: From Worksheet 6 (Table C-15). 206 ------- Step 3 (Gas Mobility Value); An examination of the site information shows that the landfill contains three potentially gaseous contaminants; phenol, toluene and benzene, while the surface impoundment contains only one; benzene. The area covered by the contaminated surface soil descriptor shows no gaseous contaminants. The gas mobility value for the contaminated surface soil, therefore, is 0. The following values for the three identified gaseous contaminants were calculated using Table 15 and Versar, 1984: • Phenol (CAS Number 00108-95-2); - VP value: 2 - AQ value: 1 - RS value: 2 • Toluene (CAS Number 00108-88-3); - VP value: 3 - AQ value: 3 - RS value: 3 • Benzene (CAS Number 00071-43-2); - VP value: 3 - AQ value: 3 - RS value: 3 Phenol, toluene and benzene can be used to evaluate the gas mobility factor for the landfill, while benzene can also be used in the evaluation for the surface impoundments. The gaseous mobility values for each descriptor are, therefore, as follows (see Table C-12): Landfill~3, Surface Impoundment—3, Contaminated Surface Soil—0. 207 ------- TABLE C-12 CLEAN RIVER EXAMPLE WORKSHEET 3: GAS MOBILITY WORKSHEET First Emission Source Descriptor Code 20 (1) (2) (3) (4) (5) (6) (7) (1) (2) (3) (4) (5) (6) (7) CAS Number VP Value AQ Value 00108952 2 1 00071432 3 3 00108883 3 3 Average of positive values in lines 1 Gas Mobility Value for First Emission Descriptor (see table below) Second Emission Source Descriptor CAS Number VP Value AQ Value 00071432 3 3 RS Value 2 3 3 through 5 Source Code 26 RS Value 3 Average of positive values in lines 1 through 5 Gas Mobility Value for Second Emission Source Descriptor (see table below) VP Value:From Table 15. AQ Value: From Table 15. RS Value: From Table 15. Sum 5 7.7 •(•BM^MMH 3 Sum 9 208 ------- TABLE C-12 (Concluded) Third Emission Source Descriptor Code 08 CAS Number VP Value AQ Value RS Value Sum (1) (2) (3) (4) (5) (6) Average of positive values in lines 1 through 5 (7) Gas Mobility Value for Third Emission Source 0 Descriptor (see table below) GAS MOBILITY TABLE Range of Average Value Greater than or equal to Less than Value 030 351 5 7 2 7 10 3 VP Value: From Table 15. AQ Value: From Table 15. RS Value: From Table 15. 209 ------- Step 4 (Particulate Mobility Value); The Charles County Airport is the closest weather station to the site that is listed in the Local Climatological Data Annual Summaries (LCD). The applicable data for this airport taken from the LCD are given in Table C-13. The default threshold friction velocity of 12.5 was employed since the site investigation does not provide the data needed to calculate a site-specific value. The average of the monthly fastest miles is 40.25 miles per hour or 17.99 meters per second. The PE index for the site is 90. This results in a Particulate Mobility Index of -4 6.78 x 10 . Using the equation for the partlculate mobility value results in a value of 1 for the site (see Table C-13). This value also applies to any particulate contaminant in calculating the toxicity-mobility value for that contaminant. Step 5 (Combined Mobility Value): The gas and particulate mobility values are recorded on Worksheet 5 (Table C-14) and the combined mobility values for each descriptor calculated as indicated. Step 6 and Step 7 (Containment Values); The site description indicates that the landfill cover has been eroded and that waste material is exposed to the atmosphere. Also, the slope of the landfill is estimated to be 30 percent. Thus, the particulate containment descriptor LF05P: "Site substantially devoid of vegetation with a large percentage of exposed soil or waste-bearing liquids. No other cover. Facility slope greater than 10 degrees 210 ------- TABLE C-13 CLEAN RIVER EXAMPLE WORKSHEET 4: PARTICULATE MOBILITY WORKSHEET Weather Station: Charles County Airport Threshold wind speeda: Fastest Precip. Month Mile (F) (P) Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. 40 30 47 46 41 41 43 45 46 40 31 33 2.83 2.64 3.43 3.14 3.62 4.23 3.75 4.16 3.26 3.01 2.99 3.29 12 Temp.b (T) 31.4 33.6 42.4 43.3 62.4 70.7 75.5 74.3 67.4 55.3 44.8 35.1 .5 meters per secc (T-10) 21.4 23.6 32.4 33.3 52.4 60.7 65.5 64.3 57.4 45.3 34.8 25.1 P/CT-10) 0.1322 0.1119 0.1059 0.0725 0.0691 0.0697 0.0573 0.0647 0.0568 0.0664 0.0859 0.1311 jnd (ut) [P/(T-10)]10/9 0.1056 0.0877 0.0825 0.0542 0.0513 0.0518 0.0417 0.0477 0.0413 0.0491 0.0654 0.1046 Sum = 483 divide by 12 u+ - 40.25 17.99 meters per second Sum 0.7829 x 115 PE Index = 90 211 ------- TABLE C-13 (Concluded) Mobility Index (I) - (u+ - ut)/PE2 6.78 x 10 Particulate Mobility Value (4 - log10Dc 1 aDefault value of 12.5 may be used. Methodology is valid in the temperature range 28.5 to 90.0 degrees Fahrenheit. If average monthly temperature is below 28.5 degrees, set T-10 equal to 18.5. If average monthly temperature is above 90.0 degrees, set T-10 equal to 80.0. cRound off to nearest whole number. If logiQl exceeds 4, value " 0. If log^o1 is less than 0.5, value " 3. The following table provides alternate, equivalent way to determine the particulate mobility value. ALTERNATE PARTICULATE MOBILITY VALUE TABLE Range of Values for I Value -4 Less than 3.16 x 10 0 3.17 x 10~4 - 3.16 x 10~3 1 3.17 x 10~3 - 3.16 x 10"2 2 Greater than 3.16 x 10 3 212 ------- TABLE C-14 CLEAN RIVER EXAMPLE WORKSHEET 5: COMBINED MOBILITY WORKSHEET (1) (2) (3) Descriptor Code 20 26 08 Gas Mobility Value* 3 3 Particulate Mobility Value** Combined Value 4 4 1 COMBINED MOBILITY FACTOR MATRIX Particulate Mobility Value Gas Mobility Value 0 ill 0: 0 123 1:1 234 2: 2 345 3: 3 455 *From Worksheet 3. **From Worksheet 4. 213 ------- was selected as the best containment descriptor. The value for this descriptor is 3. Similarly, since the waste material is exposed, tne gas containment descriptor LF15G: "Waste uncovered or exposed" was selected as the best gas containment descriptor. The value for this descriptor is 3. Therefore, the combined containment descriptor value for the landfill is 3 (see Table C-15). There is little information provided on the state of the ponds. Since the impoundments do not contain liquids (only a wet sludge resting at the bottom), the depth of the impoundment can be taken as the freeboard. Therefore, the impoundment can be considered "enclosed". The information provided on the impoundment indicates that the descriptor WSI05P: "Enclosed impoundment; uncovered, surface completely open to atmosphere" is the best applicable descriptor. Its value is 3. The best gas containment descriptor for tne impoundment is WSI05G: "Wet enclosed impoundment; uncovered, surface completely open to atmosphere" with an associated value of 3. Therefore, the combined value for the surface impoundment is 3 (see Table C-15). The containment descriptors in Option 1 are the same for the contaminated surface soil descriptors as they are for the landfill descriptors. There is also little information provided for the surface of the landfill, the area of known soil contamination. Given the information provided, except that signs of erosion are everywhere, the best particulate containment descriptor is LF05P: 214 ------- TABLE C-15 CLEAN RIVER EXAMPLE WORKSHEET 6: CONTAINMENT WORKSHEET First Descriptor Code Particulate Containment Code Gas Containment Code 20 LF05P LF15G Second Descriptor Code Particulate Containment Code Gas Containment Code 26 WSI05P WSI05G Third Descriptor Code Particulate Containment Code Gas Containment Code 10 LF05P LF08G Descriptor Particulate Containment Gas Containment Combined (1) (2) (3) Code 20 26 08 Value 3 3 3 Value 1 3 _1 Value 3 3 3 Descriptor Code: From Table 9. Particulate Containment Code: From Table D-3. Gas Containment Code: From Table D-4. Combined Value: From Table 20. 215 ------- "Site substantially devoid of vegetation with a large percentage of exposed soil or waste-bearing liquids. No other cover. Facility slope greater than 10 degrees" with an associated value of 3. Similarly, since the soil type is unknown, the best gas containment descriptor is LF08G: "Uncontaminated soil cover less than six inches; cover soil type unknown" with an associated value of 1. Therefore, the combined containment value for the contaminated surface soil is 3 (see Table C-15)- Step 8 (Potential To Release Value); The preceding data are recorded on Table Oil. This table also illustrates the calculation of the potential to release value for the site. Thus, the overall site potential to release value is 42, based on the Option 1 methodology. Step 9 (Toxicity-Mobility Value): Since none of the contaminants have been detected in an observed release, the mobility value for each is calculated using the gas or particulate mobility value as applicable. Therefore, the mobility values for the gaseous contaminants are as follows: • Phenol (CAS Number 00108-95-2): 2 • Benzene (CAS Number 00071-43-2): 3 • Toluene (CAS Number 00108-88-3): 3 Arsenic (CAS Number 07440-37-1) and cadmium (CAS Number 07440-43-9) would appear as particulates and, therefore, their mobility values are set equal to the site particulate mobility value of 1. 216 ------- The HRS (47 FR 31219-31243) indicated the following air toxicity values for the contaminants: • Phenol: 3 • Toluene: 2 • Benzene: 3 • Cadmium: 3 • Arsenic: 3 These values and the combined toxicity-mobility values for each contaminant are indicated in Table C-16. These values indicate that benzene has the largest combined toxicity-mobility value and thus the site toxicity-mobility value is 18. Step 10; The Observed Release Value (Worksheet 1), Potential to Release Value (Worksheet 2), and Toxicity-Mobility Value (Worksheet 7) are recorded on Worksheet 8: Summary Air Route Score (Table C-17). Step 11 (Waste Quantity Value); The site description provides the following data pertinent to the calculation of hazardous waste quantity: • 67 drums in Building B • Volume of ponds is about 61,000 cubic feet • Belowground tank contains about 25,000 gallons of phenol and toluene • Contaminated surface area of the landfill is about 60,000 square feet • All of the above contained hazardous materials 217 ------- TABLE C-16 CLEAN RIVER EXAMPLE WORKSHEET 7: TOXICIIY-MOBILITY WORKSHEET (1) (2) (3) (4) (5) CAS Number 00108952 00108883 00071432 07440371 07440439 Toxicity Value 3 2 3 3 3 Mobility Value 2 3 3 1 1 Combined Value 12 12 18 6 6 (6) Maximum Combined Value 18 Level of Toxicity COMBINED FACTOR MATRIX Level of Mobility 0 1 _2 _3 0: 0 0 00 1:0 246 2: 2 4 8 12 3: 4 6 12 18 VP Value: From Table 15. AQ Value: From Table 15. RS Value: From Table 15. Toxicity Value: From HRS User's Manual. 218 ------- TABLE C-17 CLEAN RIVER EXAMPLE WORKSHEET 8: SUMMARY AIR ROUTE SCORE 1. OBSERVED RELEASE VALUE3 0_ 2. POTENTIAL TO RELEASE VALUEb 42 3. TOXICITY-MOBILITYC 18 4. HAZARDOUS WASTE QUANTITY*1 7 5. WASTE CHARACTERISTICS VALUE (Lines 3+4) 25 6. TARGETS 7. Population 18 8. Land Used 3_ 9. Sensitive Environment 3 10. TARGETS VALUE (Lines 7+8+9) 24 11. If line 1 is not equal to 0.0, multiply lines 1 x 5 x 10 If line 2 is not equal to 0.0, multiply lines 2 x 5 x 10 25200 12. Divide line 11 by 351 Sa = 71.79 aFrom Worksheet 1. bFrom Worksheet 2. cFrom Worksheet 7. HRS User's Manual. 219 ------- Current practice in the HRS allows the inclusion of the 67 drums and the once-filled volume of the ponds in computing hazardous waste quantity. No information is given in the site description that would allow the analyst to determine if the material in the tank is available for migration. Thus, current HRS practice would not allow the inclusion of the 25,000 gallons in the tank. Additionally, no information is provided about the volume of the landfill or the fraction of the volume that is hazardous. Similarly, data are lacking on the depth (and hence, volume) of the contaminated soil on the surface of the landfill (although concentration data are available in this case). Therefore, no hazardous waste quantity can be associated with either the landfill or the contaminated surface soil. Based on these considerations, the total hazardous waste quantity is 67 drums plus 9,090 drums (the equivalent volume of the ponds) for a total of 9,157 drums. This yields a waste quantity value of 7. Step 12 (Waste Characteristics Value): Add lines 3 and 4 on Worksheet 8 as indicated to form the waste characteristics value. Step 13 (Targets Value); Building il and the landfill are the two identifiable potential sources of air releases that are the furthest apart (see Figure C-2). The distance between then is 220 ------- 1/4 mile, according to the site map. Thus, the effective source radius is 1/8 mile or 660 feet. The map of the site (Figure C-2) indicates that one farmhouse is located within 3/8 (1/4 + 1/8) miles of the site. No additional houses lie within 5/8 (1/2 + 1/8) miles of the site. All of Riverview Estates (50 houses) lies within 1-1/8 (1 + 1/8) miles of the site, as do the three identified farm houses. The town of Catsville lies within 4-1/8 miles of the site as does a small portion of the town of Maryville. The value for the population residing within 3/8 miles of the site is 18. The number of people residing within 1-1/8 miles of the site cannot be determined from the data presented but can be seen to be undoubtedly less than the 3,001 persons needed to achieve a value greater than 18. The population of Catsville and the small portion of Maryville located within 4-1/8 miles of the site is less than the 10,000 persons required to achieve a value greater than 18, as well. Therefore, the population targets value for this site is 18. The distance to the nearest wetland is less than 1,000 feet but may be more than 100 feet (the information provided is not specific). The wetland lies along the Glean River and is a fresh water wetland. No critical habitats of Federal endangered species have been identified near the site. Therefore, the sensitive environment value is 2. 221 ------- No national or state parks, forests, or wildlife preserves have been identified within two miles of the site. No historic or landmark sites have been identified as being within view of the site, either. The nearest residential area is the River View estates, one mile from the site. Agricultural land has been found within 1,000 feet of the site but it is unknown whether this land is prime or not. The distance to the nearest industrial/commercial area is also unknown. Based on the distance to the nearest agricultural land, the land use value is 3. These values are recorded on Table C-17- Step 14 (Overall Air Pathway Value); Table C-17 illustrates the calculation of the overall air pathway score of 71.19 for the Clean River site. C.2.3 Application of the Option 2 Methodology The steps taken in evaluating the site using the Option 2 methodology are very similar to those taken in the Option 1 methodology. The principal differences are in the tables of factors used and the worksheets. Step 1 (Observed Release Value); No air monitoring was conducted on the site, hence an observed release value of 0 is assigned (see Table C-10). Step 2 (Emission Source Descriptor Values); The following Option 2 emission source descriptors can potentially be used in scoring this site: 222 ------- • Containers—1 • Contaminated Soil—2 • Landfill—4 • Surface Impoundment—5 The justifications for employing these descriptors has been discussed previously (see Section C.2.2). Note, the descriptor "containers" can refer to either the underground tanks and the exposed drums. However, the sources are not similar in containment. Hence, they must be evaluated separately. The sizes of the areas covered by each descriptor are as follows: • Containers (underground tanks): 50,000 gallons or about 7,000 cubic feet. • Contaminated Soil: About 245 x 245 feet or about 60,000 square feet. • Containers (drums): 67 drums. • Landfill: About 245 x 245 feet or about 60,000 square feet. • Surface Impoundment: 125 in diameter x 2.5 feet in depth each or about 61,000 cubic feet in total. All of the area meet the minimum size requirement and thus can be used in evaluating the site's potential to release. The values for the remaining emission source descriptors are indicated on Worksheet 1: Potential to Release Worksheet (Table C-18). Step 3 (Gas Mobility Value); The gas mobility values for each descriptor have been discussed previously and are as follows: 223 ------- TABLE C-18 WORKSHEET 1: POTENTIAL TO RELEASE WORKSHEET (1) (2) (3) (4) (5) (6) (7) (8) (9) Descriptor Code 01* 02 04 05 01** Potential Des. Value (A) 4 7 6 8 4 Mobility Value (B) 4 1 4 4 4 Sum (A+B) 8 8 10 12 8 Containment Value (C) 3 3 3 3 1 to Release Value Product [(A+B)xC] 24 24 30 36 8 36 *Drums. **Underground tanks. 224 ------- • Containers—3 • Contaminated Soil—0 • Landfill—3 • Surface Impoundment—3 Step 4 (Particulate Mobility Value); The evaluation discussed previously indicated that the PE index for the site is 90. Thus, the particulate mobility value for all descriptors is 1. Step 5 (Combined Mobility Value); The gas and particulate mobility values are summed from the applicable mobility factors for each descriptor, yielding the following results: • Containers (both types)—4 • Contaminated Soil—1 • Land fin—4 • Surface Impoundment—4 These values are recorded on Worksheet 1 (Table C-18). Step 6 and Step 7 (Containment Values); Based on the site investigation and the previous discussion, the containment descriptors indicated on Worksheet 2; Containment Worksheet (Table C-19) were selected. The combined containment values were determined using Table 20 and the results recorded on Worksheet 1 (Table C-18). Step 8 (Potential To Release Value); The preceding information is used to determine the potential to release values for each descriptor. The potential to release value for the site, as a whole, 225 ------- TABLE C-19 WORKSHEET 2: CONTAINMENT WORKSHEET First Descriptor Code Participate Containment Code Gas Containment Code Second Descriptor Code Particulate Containment Code Gas Containment Code Third Descriptor Code Particulate Containment Code Gas Containment Code Fourth Descriptor Code Particulate Containment Code Gas Containment Code Fifth Descriptor Code Particulate Containment Code Gas Containment Code Sixth Descriptor Code Particulate Containment Code Gas Containment Code Seventh Descriptor Code Particulate Containment Code Gas Containment Code Eighth Descriptor Code Particulate Containment Code Gas Containment Code C007P COTF7G LD04P LD15G LD04P LD15G SI05P SI06G LD11P LD08G 01 02 04 05 01 226 ------- TABLE C-19 (Concluded) Particulate Gas Descriptor Containment Containment Combined Code Value Value Value (1) 01 3 3 3 (2) 02 3 1 3 (3) 04 3 3 3 (4) 05 3 3 3 (5) 01 1 1 1 (6) (7) (8) 227 ------- is the largest of the calculated values. Thus, using the Option 2 methodology, the site potential to release value is 36. 228 ------- APPENDIX D ADDITIONAL TABLES This appendix presents the additional tables needed to implement the proposed revision options. The tables include the fundamental definitions of the emission source descriptors (Table D-l), as well as the particulate and gas containment factor definitions and values for both Options 1 and 1A. 229 ------- TABLE D-l EMISSION SOURCE DESCRIPTOR DEFINITIONS Active Fire; A wastes site that is presently burning or smoldering and, without remedial action, will continue to do so for an extended period of time. Belowground Injection; Belowground injection is a liquid waste disposal method in which the wastes are emplaced belowground using a bored, drilled, driven, or dug well to a depth significantly below the surface. The well rigs may or may not be present on the site. If they are missing evidence of the injection, holes should still be present. If the disposal method is a dug well, then its depth must exceed its width, otherwise it is considered to be a surface impoundment. Belowground Tank; A tank is any stationary device, designed to contain an accumulation of waste, which is constructed primarily of nonearthen materials (such as wood, concrete, steel, or plastic) which provide structural support. A belowground tank is a tank the entire surface area of which is situated completely below the plane of ground level. Belowground tanks are not externally viewable. The descriptors "Inground or Aboveground Tanks" should be used whenever the tanks are at least partially exposed. Contaminated Surface Soil; Contaminated surface soil is soil taken from the surface of a site that contains detectable concentrations of a hazardous substance. Evidence that the substance detected is related to the site must be provided to substantiate use of this descriptor. Emission Sources Not Elsewhere Specified; This descriptor refers to situations not adequately handled by the other descriptors. A complete, written description of the site must be provided as support for the decision to use this descriptor. Exposed Drum Site; A drum is any portable device in which waste is stored or otherwise handled. An exposed drum site is a site in which drums are placed or stacked on the surface of the land without a soil cover. It also covers the situation in which drums are buried but partially exposed. The individual drums may be broken or intact. Sites with completely buried drums are considered landfills. 230 ------- TABLE D-l (Continued) Inactive Aboveground Fire; A wastes site that is located aboveground and was at one time significantly inflamed but is not presently burning. Inground or Aboveground Tanks; A tank is any stationary device, designed to contain an accumulation of waste, which is constructed primarily of nonearthen materials (such as wood, concrete, steel, or plastic) which provide structural support. Any tank situated in such a manner that the bottom of the tank is at or above the plane of ground level is considered to be aboveground. A tank is considered to be inground if its base is to any degree situated below the plane of ground level and is in direct contact with the ground (ignoring liners) such that a portion of the tank wall of tank top is above the ground and a portion of the tank wall is belowground (not externally viewable). Landfarm/Landtreatment; Landfarming or landtreatment is a method of waste disposal in which liquid wastes or sludges are spread over land and tilled, generally to a depth of about six inches. It also applies to the shallow (i.e., of insufficient depth) injection of liquids if the depth of injection exceeded six inches but did not qualify as belowground injection. The wastes are reduced or detoxified through a combination of evaporation, volatilization and microbiological activity. Landfarm/landtreatment areas are frequently revegetated after the wastes have decomposed. The distinguishing characteristic of landfarms and landtreatment facilities is the shallow injection or tilling of the soil. In those cases where tilling was not performed or when the depth of injection was less than six inches, the site should be considered a spill site. Landfill; A landfill is a manmade or natural hole in the ground, containing wastes, that has been backfilled with soil either after or contemporary with the waste disposal, covering the wastes from view. The landfill may have been formed either by excavating the hole or by forming earthen walls around a cleared area. The characteristics of a landfill that distinguish it from an open pit or a pile are that the wastes must be co-mingled with soil and that the wastes must be, or have been, covered with soil. Due to weathering, erosion and similar phenomena, however, once-buried wastes in a landfill may become exposed, e.g., partially buried drums. The contents of a landfill may include nearly any or all types of wastes including buried drums. 231 ------- TABLE D-l (Continued) Open Pit; An open pit has many of the characteristics of a landfill, the critical differences being that the wastes are not necessarily belowground level, soil is not intentionally co-mingled with the wastes and the wastes are not intentionally covered with soil. As a result, the wastes are exposed to the elements, vectors and scavengers. As in the case of landfills, the contents of an open pit may include nearly any or all types of wastes. However, for purposes of scoring, disposed or stored drums are considered separately (see exposed drum site definition). Spill Site; A spill site is a site at which a significant amount (i.e., at least a "reportable quantity") of liquid wastes or sludges has been intentionally or unintentionally deposited over the ground and left otherwise untouched. This descriptor also applies to landfarms/landtreatment facilities where either tilling was not performed or the wastes were tilled to a depth less than six Inches. Similarly, this descriptor applies to sites where shallow injection of wastes to a depth less than six Inches was performed. Surface Impoundment; A natural topographic depression, manmade excavation or diked area, primarily formed from earthen materials (lined or unlined) which was designed to hold an accumulation of liquid wastes, wastes containing free liquids, or sludges that were not backfilled or otherwise covered. If the impoundment has been backfilled, it is considered a landfill. The intention of a surface impoundment is to provide temporary storage or to allow the deposited liquid to be treated and rendered harmless in the future or volatilize and/or evaporate eventually leaving a "dry" residue to be covered as in a landfill. The distinguishing characteristics of a surface impoundment are the emphasis on liquid waste and the general lack of a cover. Two types of surface impoundments are distinguished in the air pathway: those with exposed liquid (wet) or those at which the deposited liquid has evaporated, volatilized or leached (dry). Synonymous terms include lagoon, pond, aeration pit, settling pond, and tailings pond. Surface Water Body or Outfall; A surface water body is an open expanse of water restricted only by natural topography, e.g., rivers, lakes, streams, etc. A surface water outfall is the area of interface between a waste discharge stream and a surface water body. This descriptor is for use in those situations where water sampling indicates the presence of volatile compounds in the water. Waste Pile; Any noncontalnerlzed accumulation of solid, nonflowing wastes. Waste piles include tailings piles but exclude tailings ponds. 232 ------- TABLE D-2 RELATIONSHIP BETWEEN OPTION 1 AND 1A EMISSION SOURCE DESCRIPTORS Option 2 Emission Source Descriptor Active Fire Site Belowground/Buried Containers Contaminated Soil Option 1 Emission Source Descriptor Dry Surface Impoundment Inactive Fire Site Intact Exposed/Aboveground Containers Active Fire Site Belowground Tanks Contaminated Surface Soil: • Background at or above analytical detection limit - Contamination level at or below background - Contamination level above background but not significantly above background - Contamination level significantly above background • Background below analytical detection limit - Contamination level below analytical detection limit - Contamination level above analytical detection limit Surface Impoundment: • Dry; evidence of waste contamination near surface • Dry; all other situations • Spill Site: spill dry Inactive Aboveground Fire Site: • Re-ignition expected • Re-ignition not expected Inactive Below Ground Fire Site • Re-ignition expected • Re-ignition not expected Exposed Drums: Drums intact Aboveground or Inground Tanks: Tanks intact 233 ------- TABLE D-2 (Continued) Option 2 Emission Option 1 Emission Source Descriptor Source Descriptor Landfarm Landfarm/Landtreatment Belowground Injection Landfill Landfill: • With both biodegradable material and exposed drums • With biodegradable material but without exposed drums • All other situations Open Pit Belowground Tanks Nonintact Exposed/ Exposed Drums: Drums broken Aboveground Containers: Aboveground or Inground Tanks: Tanks broken Wet Surface Impoundment Surface Impoundment: • Wet; evidence of waste contamination near surface • Wet; all other situations Spill Site: spill wet Emission Sources Not Surface Water Body or Outfall Elsewhere Specified Emission Sources Not Elsewhere Specified 234 ------- TABLE D-3 OPTION 1 PARTICULATE CONTAINMENT FACTORS (CHOOSE CHARACTERISTIC THAT BEST APPLIES) ACTIVE FIRE SITE (AFS01) 3_ BELOWGROUND INJECTION (BGI01) 0_ BELOWGROUND TANKS (see Landfill) CONTAINERS (Aboveground or Inground Tanks and Exposed Drums) C001P Intact, sealed containers protected from the 0_ weather by a maintained cover C002P Intact, sealed containers not protected from 1_ the weather by a maintained cover C003P Open, unsealed, or nonintact containers; waste 0_ totally covered with an essentially impermeable, maintained cover C004P Open, unsealed, or nonintact containers; waste 1_ partially covered with an essentially impermeable, maintained cover C005P Open, unsealed, or nonintact containers; 2_ wastetotally covered with an essentially impermeable, unmaintained cover C006P Open, unsealed, or nonintact containers; waste 3_ waste otherwise covered or uncovered C007P Other 1_ CONTAMINATED SURFACE SOIL (see Landfill) DRY SURFACE IMPOUNDMENT (see Landfill) EMISSION SOURCES NOT ELSEWHERE SPECIFIED NES01P Totally covered with a maintained covered NES02P Partially covered with a maintained covered NES03P Totally covered with an unmaintained covered NES04P Partially covered with an unmaintained covered NES05P Uncovered NES06P Other INACTIVE ABOVEGROUND FIRE SITE (see Landfill) 235 ------- TABLE D-3 (Continued) INACTIVE BELOW GROUND FIRE SITE (see Landfill) LANDFARM/LANUTREAIMENT (see Landfill) LANDFILL LF01P Site covered with an essentially impermeable and maintained cover or heavily vegetated with no exposed soil or waste-bearing liquids (e.g., paved-over) LF02P Site substantially vegetated or totally covered with a maintained nonwater-based dust- suppressing fluid. Little exposed soil or waste-bearing liquids LF03P Site lightly vegetated or partially covered with a maintained nonwater-based dust- suppressing fluid. Much exposed soil or waste-bearing liquids LF04P Site substantially devoid of vegetation with a large percentage of exposed soil or waste-bearing liquids. No other cover. Facility slope less than 10 degrees or unknown LF05P Site substantially devoid of vegetation with a large percentage of exposed soil or waste-bearing liquids. No other cover. Facility slope greater than 10 degrees LF06P Totally enclosed in a structurally intact building LF07P Partially enclosed in a structurally intact building LF08P Totally enclosed in an nonintact building LF09P Partially enclosed in an nonintact building LF10P Substantially surrounded with windbreak (e.g., mesh or other fence, trees, etc.) LF11P Active fire site LF12P Other OPEN PIT (see Landfill) SPILL SITE Spill dry (see Landfill) Spill wet (see Wet Surface Impoundment) 236 ------- TABLE D-3 (Concluded) SURFACE WATER BODY OR OUTFALL (see Wet Surface Impoundments) WASTE PILE (see Landfill) WET SURFACE IMPOUNDMENTS WSI01P Enclosed* impoundment; impoundment totally covered with a maintained cover WSI02P Enclosed impoundment; impoundment totally covered with an unmaintained cover WSI03P Enclosed impoundment; impoundment partially covered with a maintained cover WSI04P Enclosed impoundment; impoundment partially covered with an unmaintained cover WSI05P Enclosed impoundment; uncovered, surface completely open to atmosphere WSI06P Nonenclosed impoundment; impoundment totally covered with a maintained cover WSI07P Nonenclosed impoundment; impoundment totally covered with an unmaintained cover WSI08P Nonenclosed impoundment; impoundment partially covered with a maintained cover WSI09P Nonenclosed impoundment; impoundment partially covered with an unmaintained cover WSI10P Nonenclosed impoundment; uncovered, surface completely open to atmosphere WSI11P Other *An enclosed impoundment is one with a freeboard exceeding two feet in height or one that is substantially surrounded by a wall, fence, trees, or other adequate windbreak. 237 ------- TABLE D-4 OPTION 1 GAS CONTAINMENT FACTORS (CHOOSE CHARACTERISTIC THAT BEST APPLIES) ACTIVE FIRE SITE AFS01G Active aboveground fire site 3_ AFS02G Active belowground fire site: Uncontaminated* 1_ soil cover in excess of two feet AFS03G Active belowground fire site: Uncontaminated* 2_ soil cover less than two feet, soil resistant to gas migration** AFS04G Active belowground fire site: Uncontaminated* 3_ soil cover less than two feet, soil not resistant to gas migration** BELQWGROUND INJECTION (see Landfill) BELOWGROUND TANKS (see Landfill) CONTAINERS (Aboveground or Inground Tanks and Exposed Drums) C001G Intact, sealed containers protected from the 0_ weather by a maintained cover C002G Intact, sealed containers not protected from 1_ the weather by a maintained cover C003G Open, unsealed, or nonintact container; waste 0_ totally covered with an essentially impermeable, maintained cover C004G Open, unsealed, or nonintact container; 1_ waste partially covered with an essentially Impermeable, maintained cover C005G Open, unsealed, or nonintact container; 2_ waste totally covered with an essentially impermeable, unmaintained cover *Lacking contrary evidence, covering soils are assumed to be Uncontaminated. Soil cover contaminants must be attributable to the underlying waste materials and gaseous in origin. **USGS soil types GC, ML, CL and CH. Source: Adapted from Lutton, R. J., Evaluating Cover Systems for Solid and Hazardous Wastes, (EPA-530/SW-867c), U.S. Environmental Protection Agency, Washington, DC, September 1980. 238 ------- TABLE D-4 (Continued) CONTAINERS (Concluded) C006G Open, unsealed, or nonintact container; waste otherwise covered or uncovered C007G Aboveground containers; other CONTAMINATED SURFACE SOIL (see Landfill) DRY SURFACE IMPOUNDMENTS (see Landfill) EMISSION SOURCES NOT ELSEWHERE SPECIFIED NES01G Totally covered with a maintained covered NES02G Partially covered with a maintained covered NES03G Totally covered with an unmaintained covered NES04G Partially covered with an unmaintained covered NES05G Uncovered NES06G Other INACTIVE ABOVEGROUND FIRE SITE (see Landfill) INACTIVE BELOWGROUND FIRE SITE (see Landfill) LANDFARM/LANDTREATMENT (see Landfill) LANDFILL LF01G LF02G LF03G LF04G LF05G Functioning gas collection system Existing, nohfunctioning gas collection system Intact synthetic cover plus uncontaminated soil cover over 0.5 inches in depth* Totally covered with an intact synthetic cover; surface soil contaminated* Totally covered with a nonintact synthetic cover; surface soil contaminated* JL_ 2 *Lacking contrary evidence, covering soils are assumed to be uncontaminated. Soil cover contaminants must be attributable to the underlying waste materials and gaseous in origin. **USGS soil types GC, ML, CL and CH. Source: Adapted from Lutton, R. J., Evaluating Cover Systems for Solid and Hazardous Wastes, (EPA-530/SW-867c), U.S. Environmental Protection Agency, Washington, DC, September, 1980. 239 ------- TABLE D-4 (Continued) LANDFILL (Concluded) LF06G Uncontaminated soil cover* in excess of six inches LF07G Uncontaminated soil cover* greater than one inch and less than six inches; cover soil resistant to gas migration** LF08G Uncontaminated soil cover* less than six inches; cover soil type unknown LF09G Uncontaminated soil cover* greater than one inch and less than six inches; cover soil not resistant to gas migration** LF10G Uncontaminated soil cover* less than one inch; cover soil resistant to gas migration** LF11G Uncontaminated soil cover* less than one inch; cover soil not resistant to gas migration** LF12G Covering soil contaminated* with waste contaminants at surface and no synthetic cover between surface and bulk of waste materials LF13G Totally enclosed in a structurally intact building LF14G Totally enclosed in an nonintact building LF15G Waste uncovered or exposed LF16G Other OPEN PIT (OP01) SPILL SITE Spill Dry (see Landfill) Spill Wet (see Wet Surface Impoundment) SURFACE WATER BODY OR OUTFALL (see Wet Surface Impoundment) WASTE PILE (see Landfill) _1_ 3 *Lacking contrary evidence, covering soils are assumed to be Uncontaminated. Soil cover contaminants must be attributable to the underlying waste materials and gaseous in origin. **USGS soil types GC, ML, CL, and CH. Source: Adapted from Lutton, R. J., Evaluating Cover Systems for Solid and Hazardous Wastes, (EPA-530/SW-867c), U.S. Environmental Protection Agency, Washington, DC, September 1980. 240 ------- TABLE D-4 (Concluded) WET SURFACE IMPOUNDMENTS WSI01G Wet enclosed* impoundment; Impoundment totally 0_ covered with a maintained, essentially impermeable cover WSI02G Wet enclosed impoundment; impoundment totally 1_ covered with an unmaintained, essentially impermeable cover WSI03G Wet enclosed impoundment; impoundment partially 1_ covered with a maintained, essentially impermeable cover WSI04G Wet enclosed impoundment; impoundment partially 2_ covered with an unmaintained, essentially impermeable cover WSI05G Wet enclosed impoundment; uncovered, surface 3_ completely open to atmosphere WSI06G Wet nonenclosed impoundment; impoundment 0_ totally covered with a maintained, essentially impermeable cover WSI07G Wet nonenclosed impoundment; impoundment 1_ totally covered with an unmaintained, essentially impermeable cover WSI08G Wet nonenclosed impoundment; impoundment 2_ partially covered with a maintained, essentially impermeable cover WSI09G Wet nonenclosed impoundment; impoundment 3_ partially covered with an unmaintained, essentially impermeable cover WSI10G Wet nonenclosed impoundment; uncovered, surface 3_ completely open to atmosphere WSI11G Other 1 *An enclosed impoundment is one with a freeboard exceeding two feet in height or one that is substantially surrounded by a wall, fence, trees, or other adequate windbreak. 241 ------- TABLE D-5 OPTION 1A PARTICULATE CONTAINMENT FACTORS (CHOOSE CHARACTERISTIC THAT BEST APPLIES) ACTIVE FIRE SITE (AFSOl) BELOWGROUND/BURIED CONTAINERS (see Landfill) CONTAINERS (Intact Exposed/Aboveground Containers and Nonlntact Exposed/Aboveground Containers) C001P Intact, sealed containers protected from the weather by a maintained cover C002P Intact, sealed containers not protected from the weather by a maintained cover C003P Open, unsealed, or nonlntact containers; waste totally covered with an essentially Impermeable, maintained cover C004P Open, unsealed, or nonlntact containers; waste partially covered with an essentially impermeable, maintained cover C005P Open, unsealed, or nonintact containers; waste totally covered with an essentially impermeable, unmalntained cover C006P Open, unsealed, or nonintact containers; waste otherwise covered or uncovered C007P Other CONTAMINATED SOIL (see Landfill) DRY SURFACE IMPOUNDMENT (see Landfill) EMISSION SOURCES NOT ELSEWHERE SPECIFIED NES01P Totally covered with a maintained covered NES02P Partially covered with a maintained covered NES03P Totally covered with an unmaintalned covered NES04P Partially covered with an unmaintained covered NES05P Uncovered NES06P Other INACTIVE FIRE SITE (see Landfill) LANDFARM (see Landfill) 242 ------- TABLE D-5 (Continued) LANDFILL LF01P Site covered with an essentially impermeable and maintained cover or heavily vegetated with no exposed soil or waste-bearing liquids (e.g., paved-over) LF02P Site substantially vegetated or totally covered with a maintained nonwater-based dust suppressing fluid. Little exposed soil or waste-bearing liquids. LF03P Site lightly vegetated or partially covered with a maintained nonwater-based dust suppressing fluid. Much exposed soil or waste-bearing liquids. LP04P Site substantially devoid of vegetation with a large percentage of exposed soil or waste-bearing liquids. No other cover. Facility slope less than 10 degrees or unknown LF05P Site substantially devoid of vegetation with a large percentage of exposed soil or waste-bearing liquids. No other cover. Facility slope greater than 10 degrees LF06P Totally enclosed in a structurally intact building LF07P Partially enclosed in a structurally intact building LF08P Totally enclosed in an nonintact building LF09P Partially enclosed in an nonintact building LF10P Substantially surrounded with windbreak (e.g., mesh or other fence, trees, etc.) LF11P Active fire site LF12P Other WASTE PILE (see Landfill) WET SURFACE IMPOUNDMENTS WSI01P Enclosed* impoundment; impoundment totally covered with a maintained cover WSI02P Enclosed impoundment; impoundment totally covered with an unmaintained cover JL_ 2 3 1 0 -^—-, 1 *An enclosed impoundment is one with a freeboard exceeding two feet in height or one that is substantially surrounded by a wall fence trees, or other adequate windbreak. ' 243 ------- TABLE D-5 (Concluded) WET SURFACE IMPOUNDMENTS (Concluded) WSI03P Enclosed Impoundment; Impoundment partially covered with a maintained cover WSI04P Enclosed Impoundment; Impoundment partially covered with an unmalntalned cover WSI05P Enclosed Impoundment; uncovered, surface completely open to atmosphere WSI06P Nonenclosed Impoundment; Impoundment totally covered with a maintained cover WSI07P Nonenclosed impoundment; Impoundment totally covered with an unmaintained cover WSI08P Nonenclosed impoundment; Impoundment partially covered with a maintained cover WSI09P Nonenclosed impoundment; impoundment partially covered with an unmaintained cover WSI10P Nonenclosed impoundment; uncovered, surface completely open to atmosphere WSI11P Other J 3 244 ------- TABLE D-6 OPTION 1A GAS CONTAINMENT FACTORS (CHOOSE CHARACTERISTIC THAT BEST APPLIES) ACTIVE FIRE SITE AFS01G Active aboveground fire site ; AFS02G Active belowground fire site: uncontaminated* J soil cover in excess of two feet AFS03G Active belowground fire site: uncontaminated* \ soil cover less than two feet, soil resistant to gas migration** AFS04G Active belowground fire site: uncontaminated* '. soil cover less than two feet, soil not resistant to gas migration** BELOWGROUND/BURIED CONTAINERS (see Landfill) CONTAINERS (Intact Exposed/Aboveground Containers and Nonintact Exposed/Aboveground Containers) C001G Intact, sealed containers protected from C the weather by a maintained cover C002G Intact, sealed containers not protected J from the weather by a maintained cover C003G Open, unsealed, or nonintact container; ( waste totally covered with an essentially impermeable, maintained cover C004G Open, unsealed, or nonintact container; J waste partially covered with an essentially impermeable, maintained cover C005G Open, unsealed, or nonintact container; / waste totally covered with an essentially impermeable, unmaintained covet C006G Open, unsealed, or nonintact container; ', waste otherwise covered or uncovered C007G Aboveground containers; other ; *Lacking contrary evidence, covering soils are assumed to be uncontaminated. Soil cover contaminants must be attributable to the underlying waste materials and gaseous in origin. **USGS soil types GC, ML, CL, and CH. Source: Adapted from Lutton, R. J., Evaluating Cover Systems for Solid and Hazardous Wastes, (EPA-530/SW-867c), U.S. Environmental Protection Agency, Washington, DC, September 1980. 245 ------- TABLE D-6 (Continued) CONTAMINATED SOIL (see Landfill) DRY SURFACE IMPOUNDMENTS (see Landfill) EMISSION SOURCES NOT ELSEWHERE SPECIFIED NES01G Totally covered with a maintained covered NES02G Partially covered with a maintained covered NES03G Totally covered with an unmaintained covered NES04G Partially covered with an unmaintained covered NES05G Uncovered NES06G Other INACTIVE FIRE SITE (see Landfill) LANDFARM (see Landfill) LANDFILL LF01G Functioning gas collection system LF02G Existing, nonfunctioning gas collection system LF03G Intact synthetic cover plus uncontaminated soil cover over 0.5 inches in depth* LF04G Totally covered with an intact synthetic cover; surface soil contaminated* LFO.DG Totally covered with a nonintact synthetic cover; surface soil contaminated* LF06G Uncontaminated soil cover* in excess of six inches LF07G Uncontaminated soil cover* greater than one inch and less than six inches; cover soil resistant to gas migration** LF08G Uncontaminated soil cover* less than six inches; cover soil type unknown LF09G Uncontaminated soil cover* greater than one inch and less than six inches; cover soil not resistant to gas migration** *Lack.ing contrary evidence, covering soils are assumed to be uncontaminated. Soil cover contaminants must be attributable to the underlying waste materials and gaseous in origin. **USGS soil types GC, ML, CL, and CH. Source: Adapted from Lutton, R. J., Evaluating Cover Systems for Solid and Hazardous Wastes, (EPA-530/SW-867c), U.S. Environmental Protection Agency, Washington, DC, September 1980. 246 ------- TABLE D-6 (Continued) LANDFILL (Concluded) LF10G Uncontaminated soil cover* less than one inch; cover soil resistant to gas migration** LF11G Uncontaminated soil cover* less than one inch; cover soil not resistant to gas migration** LF12G Covering soil contaminated* with waste contaminants at surface and no synthetic cover between surface and bulk of waste materials LF13G Totally enclosed in a structurally intact building LF14G Totally enclosed in an nonintact building LF15G Waste uncovered or exposed LF16G Other WASTE PILE (see Landfill) WET SURFACE IMPOUNDMENTS WSI01G Wet enclosed*** impoundment; impoundment totally covered with a maintained, essentially impermeable cover WSI02G Wet enclosed impoundment; impoundment totally covered with an unmaintained, essentially impermeable cover WSI03G Wet enclosed impoundment; impoundment partially covered with a maintained, essentially impermeable cover WSI04G Wet enclosed impoundment; impoundment partially covered with an unmaintained, essentially impermeable cover *Lacking contrary evidence, covering soils are assumed to be Uncontaminated. Soil cover contaminants must be attributable to the underlying waste materials and gaseous in origin. **USGS soil types GC, ML, CL, and CH. Source: Adapted from Lutton, R. J., Evaluating Cover Systems for Solid and Hazardous Wastes, (EPA-530/SW-S67c), U.S. Environmental Protection Agency, Washington, DC, September 1980. ***An enclosed impoundment is one with a freeboard exceeding two feet in height or one that is substantially surrounded by a wall, fence, trees, or o trier adequate windbreak. 247 ------- TABLE D-6 (Concluded) WET SURFACE IMPOUNDMENTS (Concluded) WSI05G Wet enclosed impoundment; uncovered, surface 3_ completely open to atmosphere WSI06G Wet nonenclosed impoundment; impoundment 0_ totally covered with a maintained, essentially impermeable cover WSI07G Wet nonenclosed impoundment; Impoundment 1_ totally covered with an unmalntained, essentially impermeable cover WSI08G Wet nonenclosed impoundment; impoundment 2_ partially covered with a maintained, essentially impermeable cover WSI09G Wet nonenclosed impoundment; impoundment 3 partially covered with an unmaintained, essentially impermeable cover WS110G Wet nonenclosed Impoundment; uncovered, 3_ surface completely open to atmosphere WSI11G Other 1 248 ------- |