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Page 1 of 162 6560
- 50
- P ENVIRONMENTAL PROTECTION AGENCY 40 CFR Part 300 EPA
- HQ
- SFUND
- 2010
- 1086 ; FRL_XXXX - X RIN 2050
- AG67 Addition of a Subsurface Intrusion Component to the Hazard Ranking System AGENCY: Environmental Protection Agency (EPA)

. ACTION: Proposed Rule

.

______________________________________________________________________ SUMMARY : The U.S. Environmental Protection Agency (EPA) is proposing to add a subsurface intrusion (SsI) component to the Hazard Ranking System (HRS) which is the principal mechanism that EPA uses to evaluate sites for placement on the National Priorities List (NPL ). The subsurface intrusion component (this addition) would expand the number of available options for EPA and state and tribal organizations performing work on behalf of EPA to evaluate potential threats to public health from releases of hazardous substan ces, pollutants, or contaminants. This addition will allow an HRS evaluation to directly consider human exposure to hazardous substances, pollutants, or contaminants that enter regularly occupied structures through subsurface intrusion in assessing a site’ s relative risk, and thus, enable sites with subsurface intrusion contamination to be evaluated for placement on the NPL. The agency is not considering changes to the remainder of the HRS except for minor updates reflecting changes in terminology. 

### DATES: Comments shall be submitted (postmarked) on or before [INSERT DATE 60 DAYS FROM PUBLICATION IN THE FEDERAL REGISTER]

. ADDRESSES : Submit your comments, identified by Docket ID No. EPA

- HQ

- SFUND

- 2010

- 1086 , to the Federal eRulemaking Portal: http:// www.regulations.gov . Follow the online instructions for submitting comments. Comments may not be edited once submitted, and may publish in the docket***E.O. 12866 Review

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Page 2 of 162 without changes by the EPA. Do not submit electronically any info rmation you consider to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. If you need to include CBI as part of your comment, please visit htt p://www.epa.gov/dockets/comments.html for instructions. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to mak e. For additional submission methods, the full EPA public comment policy, and general guidance on making effective comments, please visit http://www.epa.gov/dockets/comments.html

. F OR FURTHER INFORMATION CONTACT: Terry Jeng, phone: (703) 603

- 8852, email: jeng.terry@epa.gov , Site Assessment and Remedy Decisions Branch, Assessment and Remediation Division, Office of Superfund Remediation and Technology Innovation (Mail Code 5204P), U. S. Environmental Protection Agency, 1200 Pennsylvania Avenue, NW, Washington, DC 20460; or the Superfund Hotline, phone (800) 424

- 9346 or (703) 412

- 9810 in the Washington, DC metropolitan area. S UPPLEMENTARY INFORMATION : Table of Contents
I. General Informati on A. What is EPA Seeking Comment On?
B. How Does this Action Apply to Me?
II. Statutory Authority
III. Background A. Why is EPA Proposing an Addition to the Hazard Ranking System?
B. What is the History of the Hazard Ranking System? C. What is the Impact of this Proposed Rule? 1. Impact on Current Cleanup Programs 2. Impact on Resources and Costs 3. Children’s Environmental Health***E.O. 12866 Review

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Page 3 of 162 4. Environmental Justice
IV. Hazard Ranking System A. Purpose
B. Structure
V. Approach to HRS Addition A. General Approach 1. What is the Need for Regulatory Action on the HRS? 2. What Alternative Regulatory Options to this Action Were Considered by EPA ? 3. What Public Outreach Activities Did EPA Conduct? 4. What Peer Review Process Did EPA Use? 5. How Did EPA Select the Approach for Including the Addition in the HRS?
B. Technical Consideration s to Maintaining the Current HRS Structure and Algorithm 1. Maintaining the Current Ground Water, Surface Water, and Air Migration Pathways 2. Addition of the New Component to Restructure and Rename the Soil Exposure Pathway 

### C. Supporting Materials
VI. Discussion of the Proposed Subsurface Intrusion Addition to the HRS A. Addition Within a Restructured Soil Exposure and Subsurface Intrusion Pathway
B. Subsurface Intrusion Component Addition 1. New Definitions 2. Delineation of Areas of Subsurface Intrusion

a. Area of Observed Exposure (AOE) b. Area of Subsurface Contamination (ASC)

c. Other Areas of Subsurface Intrusion Considered: Potential Migration Zone 3. Likelihood of Exposure

a. Observed Exposure b. Potential for Exposure***E.O. 12866 Review

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Page 4 of 162 c. Calculation of the Likelihood of Exposure Factor Category Value 4. Waste Characteristics

a. Toxicity/Biodegradation b. Hazardous Waste Quantity

c. Calculation of the Waste Characteristics Factor Category Value 5. Targets

a. Identification of Eligible Targets b. Exposed Individual and Levels of Exposure

c. Population d. Workers

e. Resources f. Calcul ation of the Targets Factor Category Value
6. Calculation and Incorporation of the Subsurface Intrusion Component Score into the HRS Site Score

a. Calculation of the Subsurface Intrusion Component Score b. Incorporation of the Subsurface Intrusion Component Score i nto the Soil Exposure and Subsurface Intrusion Pathway Score

c. Incorporation of the Soil Exposure and Subsurface Intrusion Pathway Score into a Site Score
7. Example Site Scoring Scenarios
VII. Terminology Updates Affecting Specific Sections of HRS (Sections 2 & 5)
VIII. Statutory and Executive Order Reviews A. Executive Order 12866: Regulatory Planning and Review and Executive Order 13563: Improving Regulation and Regulatory Review
B. Paperwork Reduction Act C. Regulatory Flexibility Act***E.O. 12866 Review

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Page 5 of 162 D. Unfunded Mandates Reform Act
E. Executi ve Order 13132: Federalism
F. Executive Order 13175: Consultation and Coordination with Indian Tribal Governments G. Executive Order 13045: Protection of Children from Environmental Health Risks and Safety Risks
H. Executive Order 13211: Actions that Significantly Affect Energy Supply, Distribution, or Usage
I. National Technology Transfer and Advancement Act
J. Executive Order 12898: Federal Actions to Address Environmental Justice in Minority Populations and Low Income Populations
K. Executive Order 12580: Superfund Implem entation

I. General Information A. What is EPA Seeking Comment On?
EPA is proposing an addition of one new component to one part of the current HRS. No major structural changes to other parts of the HRS are proposed. Therefore, comments are only being solicited on the addition of the subsurface intrusion component to the HRS . Comments on unmodified parts of the HRS are not being requested and will not be considered if submitted.

B. How Does this Action Apply to Me? This action proposes an addition to the HRS. The HRS is used for evaluating the relative potential risk posed by the uncontrolled release, or potential release, of hazardous substances to human health or the environment. This addition will enable EPA to identify risks posed by subsurface intrusion of hazardous substances into regularly occupied structures for all pop ulations who live and work in areas where the subsurface environment may create exposures. The agency considers that including the evaluation of subsurface intrusion in the HRS serves the public interest by widening EPA ’s ability to evaluate these threats.***E.O. 12866 Review

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Page 6 of 162 This proposed regulatory change expands the available options for EPA and organizations performing work on behalf of EPA (state and tribal partners) to evaluate potential threats to public health and the environment from hazardous waste sites. State and tribal partners may receive financial assistance from
EPA to evaluate sites through a Cooperative Agreement. EPA and states or tribes collaborate closely throughout the Cooperative Agreement process, particularly when identifying sites to be evaluated and establishing priorities for performing evaluations. As necessary, sites where subsurface intrusion threats exist may be evaluated using the HRS and, if warranted, proposed for placement on the NPL. EPA does not expect that this proposed change will result in additional site assessments being conducted per year. However, because subsurface intrusion sites have the potential to pose a higher level of risk than other exposure routes based on site

- specific factors such as exposure duration, EPA expects that the re will be a realignment and reprioritization of its internal resources and Cooperative Agreement funding toward subsurface intrusion evaluations. No authority consistently and comprehensively addresses subsurface intrusion contamination across all potent ial sites, particularly when subsurface intrusion is the key exposure pathway. While most states have identified subsurface intrusion sites as an issue, not all states have subsurface intrusion programs, and states with subsurface intrusion remediation pro grams vary in their authority, resources, and remediation criteria. A redirection of resources available through Cooperative Agreement funding is expected to provide for greater national consistency in the identification and evaluation of subsurface intrus ion sites. Furthermore, EPA is planning on issuing a final guidance document for evaluating the vapor intrusion threat after all public comments have been addressed. (The most common form of the intrusion of contaminants from the subsurface into an overly ing structure is vapor intrusion.) This document, OSWER Final Guidance for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Sources to Indoor Air , is an update of the agency’s 2002 draft guidance, OSWER Draft Guidance for Evaluating the Vapor Intrusion into Indoor Air Pathway from Ground Water and Soils

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Page 7 of 162 This proposed regulatory change does not affect the status of sites currently on or proposed to be added to the NPL.

II. Statutory Authority The authority for these proposed technical mod ifications to the HRS (40 CFR 300, Appendix A) is in section 105(a)(8)(A) of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) enacted in 1980. Under this law, the National Oil and Hazardous Substances Pollution Contingency Plan (NCP)(40 CFR 300) must include criteria for determining priorities among releases or threatened releases for the purpose of taking remedial or removal actions. In 1986, Congress passed the Superfund Amendments and Reauthorization Act (SARA) (Pub. L. 99

- 499), which added section 105(c)(1) to CERCLA, requiring EPA to amend the HRS to assure "to the maximum extent feasible, that the hazard ranking system accurately assesses the relative degree of risk to human health and the environment posed by sites an d facilities subject to review." Furthermore, CERCLA section 115 authorizes EPA to promulgate any regulations necessary to carry out the provisions of CERCLA.

III. Background A. Why is EPA Proposing an Addition to the Hazard Ranking System? Contaminant subsurface intrusion 1 is defined as the migration of hazardous substances, pollutants, or contaminants 2 from the subsurface environment, or more specifically, the unsaturated zone and/or the surficial ground water into overlying structures. Subsurface intrusion can result in people being exposed to harmful levels of hazardous substances and cause negative h ealth effects. While subsurface intrusion can take multiple forms, the most common form of subsurface intrusion is vapor intrusion. There are several reasons why EPA is proposing today’s addition to the HRS.

1 Subsurface intrusion, for the purposes of this preamble, refers to the intrusion of hazardous substances from the subsurface into a structure. 2 For the purpose of this preamble, the term “hazardous substances, pollutants or contaminants” will be referred to simply as “hazardous substances.” See section 1.1, of the current HRS for the definition of a hazardous substance.***E.O. 12866 Review

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Page 8 of 162 First, the current HRS (40 CFR 300, Appendix A), promulgated December 14, 1990 (hereafter referred to as the current HRS), discussed in more detail in section IV of this preamble, does not consider the threat posed by subsurface intrusion in its evaluation of relative risk posed by a site; therefore, it does not provide a complete assessment of the relative risk that a site may pose to the public (see section III.B of this preamble). For example, the ground water migration pathway evaluates the threat posed by contaminated ground water if there is an ind ication that ground water is being consumed. Similarly, the soil exposure pathway evaluates the threat posed by contaminated surfaces (e.g., surface soils) if there is an indication of human exposure. The air migration pathway considers the threat posed by hazardous substances released to atmospheric air (ambient air), but does not address indoor air, and has no subsurface component. The surface water migration pathway does not cover subsurface intrusion as it only considers the threat posed by contaminated surface water bodies. As such, none of the existing pathways address the threat posed by hazardous substances entering a regularly occupied structure from the subsurface. In fact, in a May 2010 report, 3 the Government Accountability Office (GAO) concluded that if vapor intrusion sites “are not assessed and, if needed, listed on the NPL, some seriously contaminated hazardous waste sites with unacceptable human exposure may not otherwise be cleaned up.” The GAO recommended that EPA consider vapor intrusion a s part of the NPL process; EPA agreed with the GAO recommendation. With the addition of a subsurface intrusion component, a site with vapor intrusion may qualify for the NPL, whereas presently the site may not have qualified using the threats evaluated in the current HRS. Therefore, without this addition, EPA may not be identifying the highest priority sites, that is, the sites posing the greatest risk to human health and the environment. Second, EPA is offering today’s proposal because of the substantial p ublic support for this action.
EPA conducted outreach activities to determine the level of interest and support from the public. This included a Notice of Opportunity for Public Input (76 FR 5370, January 31, 2011) and four public

3 EPA’s Estimated Costs to Remediate Existing Sites Exceed Current Funding Levels, and More Sites are Expected to Be Added to the National Priorities List, GAO Report to Congressional Requesters, GAO

- 10

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Page 9 of 162 listening sessions held a cross the country. More than 40 written comments, from a diverse group of private citizens, businesses, states, Native American tribes, environmental action groups, and other governmental agencies, were received during the public comment period. Of the pub lic who attended the listening sessions and provided comments, the majority were supportive of the addition of a subsurface intrusion component to the HRS. In addition, five states and two tribes submitted comments

— all in support of the addition. The Assoc iation of State and Territorial Solid Waste Management Officials (ASTSWMO) compiled and presented input from 14 states

— all but one favoring the addition of subsurface intrusion to the HRS. The comments opposing the HRS addition were, in general, from indus try representatives. Third, to support development of this proposal, EPA evaluated the need for this proposed addition to the current HRS by identifying the scope of the subsurface intrusion contamination problem. These efforts to identify and classify si tes that may pose a subsurface intrusion threat have resulted in the identification of 1,073 sites that may or may not qualify for the NPL but are suspected of having vapor intrusion issues. Many of the sites in this inventory are currently listed in the S uperfund Enterprise Management System (SEMS ). Of the 1,073 identified sites:

• 328 sites are identified as having a suspected subsurface intrusion threat based on SEMS and Agency for Toxic Substances and Disease Registry (ATSDR) key word searches, as well a s EPA or state self

- identification, but for which no sampling data were obtained

• 532 sites are identified as having characteristics or evidence that indicate subsurface intrusion (e.g., volatile hazardous substance in ground water) may have occurred or wil l occur.

• 202 sites are identified as having a subsurface intrusion threat documented by subslab, crawl space, or indoor air samples but insufficient HRS

- required evaluation factors to qualify for the
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Page 10 of 162 • 11 sites are identified as having a subsurface int rusion threat with documented actual exposure of a sufficient number of targets and sufficient other HRS

- required evaluation factors to suggest the site would qualify for the NPL.

As stated previously, EPA is also considering sites with another form of su bsurface intrusion, namely, intrusion of contaminated ground water into regularly occupied structures, which appears to be an emerging issue. Recently, a site was discovered where shallow (surficial) ground water had intruded into residential basements. Af ter the water receded or evaporated, a precipitate of chromium remained as a residue in the basements. Although EPA considers the presence of this residue as posing a significant threat to public health, the current HRS does not include a mechanism to eval uate human exposure resulting from subsurface intrusion. A determination by the ATSDR that such exposure posed a significant threat was relied upon to place this site on the NPL. The decision to include sites on the NPL based on a determination by the ATSD R is made infrequently, as the HRS is the primary mechanism for placing a site on the NPL and therefore needs to comprehensively assess site threat. EPA regional site assessment programs have identified 8 additional sites where intrusion of contaminated gr ound water is a potential issue and the related threat cannot be evaluated using the current HRS. By including ground water intrusion as part of a subsurface intrusion component to the HRS, it will be possible for EPA to accurately evaluate sites where con taminated ground water has impacted regularly occupied structures. Under the proposed SsI addition, ground water intrusion would be evaluated using current conditions, which may involve situations where metals have precipitated from water or where volatile substances have entered a structure via infiltrating ground water. As EPA further explores this emerging issue, the agency considers it likely that other ground water intrusion sites requiring evaluation will be identified.
EPA ’s identification of sites w ith a possible threat from contaminated vapor or ground water intruding into overlying regularly occupied structures does not represent a comprehensive assessment of the potential scope of the subsurface intrusion threat. EPA identified these sites based o n currently available information to serve as the basis for initially assessing the subsurface intrusion problem in***E.O. 12866 Review

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Page 11 of 162 general. In the case of vapor intrusion, certain states undertook comprehensive efforts to identify and evaluate subsurface intrusion threat s, which resulted in the identification of a proportionately higher number of sites with potential vapor intrusion problems in those states. In the case of ground water intrusion, the issue is still emerging. For these reasons, EPA recognizes that there exists a degree of inherent uncertainty associated with compiling an inventory of sites with potential subsurface intrusion problems and that additional analysis is necessary, especially in cases where little information exists. See Appendix A of the Technical Support Document for this proposed addition (Proposal TSD) for the inventory of subsurface intrusion sites. As additional information is gathered and new sites are added to SEMS and undergo the site assessment process, the numbe r of sites with subsurface intrusion threats is likely to change. Nevertheless, the aforementioned illustrates that there currently exists at least 1,073 sites that have significant actual or potential human exposure due to subsurface intrusion, but becaus e of the shortcomings of the current HRS, cannot be identified as high priority releases and, as necessary, included on the NPL. It is also important to emphasize that the inventory of sites compiled where subsurface intrusion has been identified as a pos sible issue does not represent a list of sites that will be placed on the NPL. EPA recognizes that, in many instances, additional information is needed to verify the presence, and to determine the nature/extent, of a subsurface intrusion problem. As such, the inventory should not be considered as a list of NPL candidate sites. EPA notes that less than 5% of all sites evaluated through the site assessment process are actually added to the NPL. This percentage is not expected to change significantly with this addition to the HRS. Finally, in addition to the significant number of sites with possible subsurface intrusion issues, the public support for this addition, and the limitation in the HRS to address subsurface intrusion issues, EPA has concluded that for non - federal facilities no other national program is able to consistently and comprehensively evaluate and, if warranted, address subsurface intrusion contamination. This topic is further discussed in section V.A.2 of this preamble.***E.O. 12866 Review

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Page 12 of 162 B. What is the History of the Hazard Ranking System? In 1980, Congress enacted CERCLA (42 U.S.C. 9601 et seq. ), commonly called Superfund, in
response to the dangers posed by uncontrolled releases of hazardous substances into the environment. To implement section 105 (a)(8)(A) of C ERCLA and Executive Order 12316 (46 FR 42237, August 20, 1981), EPA revised the NCP on several occasions, with the most recent comprehensive revision occurring on March 8, 1990 (55 FR 8666). The NCP sets forth the guidelines and procedures needed for respo nding to releases or potential releases of hazardous substances. Section 105(a)(8)(A) of CERCLA required EPA to establish: ...criteria for determining priorities among releases or threatened releases [of hazardous substances] throughout the United States fo r the purpose of taking remedial action and, to the extent practicable, taking into account the potential urgency of such action, for the purpose of taking removal action. Criteria and priorities...shall be based upon relative risk or danger to public heal th or welfare or the environment...taking into account to the extent possible the population at risk, the hazard potential of hazardous substances at such facilities, the potential for contamination of drinking water supplies, the potential for direct human contact [and] the potential for destruction of sensitive ecosystems....

To meet this requirement and provide criteria to set priorities, EPA adopted the HRS as Appendix A to the NCP (47 FR 31180, July 16, 1982). The HRS was last revised on December 14, 19 90 (55 FR 51532). The HRS is a scoring system used to assess the relative threat associated with actual or potential releases of hazardous substances from a site based on the information that can be collected in a limited one to two day site inspection (SI ). The HRS is designed to be applied uniformly to each site, enabling sites to be ranked relative to each other with respect to actual or potential hazards. As EPA explained when it originally adopted the HRS, "the HRS is a means for applying uniform technical judgment regarding the potential hazards presented by a facility relative to other facilities. It does not address the feasibility, desirability, or degree of cleanup required" (47 FR 31220, July 16, 1982). Although the HRS***E.O. 12866 Review

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Page 13 of 162 is designed to assess the relative risk of a site compared to other sites, it is not designed to be used as a site

- specific quantitative risk assessment. Such an assessment is conducted late r in the Superfund process,
as necessary. Section 105(a)(8)(B) of CERCLA requires that the statutory criteria described in section 105(a)(8)(A) be used to prepare a list of national priorities among the known releases, or threatened releases throughout the United States. The list, which is Appe ndix B of the NCP, is the NPL. The HRS is a crucial part of the agency’s program to address the identification and cleanup of actual and potential releases of hazardous substances because the HRS score is the primary criterion for determining whether a site is to be included on the NPL. The NPL (Appendix B to 40 CFR 300) includes those sites that appear to pose the most serious threats to public health and the environment and that may warrant remedial investigation and possible cleanup under CERCLA. Only sites on the NPL are eligible for Superfund

- financed remedial actions. Emergency removal and enforcement actions can be conducted at any site, whether or not it is on the NPL.

In 1986, Congress passed the Superfund Ame ndments and Reauthorization Act (SARA) (Pub. L. 99

- 499), which added section 105(c)(1) to CERCLA, requiring EPA to amend the HRS to assure "to the maximum extent feasible, that the hazard ranking system accurately assesses the relative degree of risk to hu man health and the environment posed by sites and facilities subject to review." The HRS was previously amended in 1990. This proposed action will amend the HRS to add a subsurface intrusion component to the evaluation.

C. What is the Impact of this Propos ed Rule? 1. Impact on Current Cleanup Programs When hazardous substances are released and enter the subsurface environment, they can move within the subsurface into buildings as a gas, vapor, or liquid. The addition of a subsurface intrusion component to the HRS would enable EPA to directly consider at sites the relative degree of risk posed by human***E.O. 12866 Review

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Page 14 of 162 exposure to hazardous substances that enter regularly occupied structures through the subsurface environment. The current HRS considers releases to the ground water, surface water, air, and soil in identify ing the highest priority releases. If promulgated, this proposed rule will not impact the way the current HRS addresses these releases. However, in the course of present HRS assessments, sometimes subsurface intrusion issues are coincident with a ground wa ter or soil contamination problem. The HRS presently does not consider the threat posed by sites with subsurface intrusion problems and direct human exposure, when ground water is not being used as a drinking water source or surficial soils are not contami nated. If promulgated, this proposed rule will for the first time allow the EPA site assessment program to address sites with only subsurface intrusion issues and no coincidental exposure. This proposed regulatory change would expand available options fo r EPA and organizations performing work on behalf of EPA (state and tribal partners) to evaluate potential threats to public health and the environment from hazardous waste sites. This modification to the HRS, by itself, only augments the criteria for appl ying the HRS. EPA also does not expect this proposed rulemaking to affect the status of sites currently on or proposed to the NPL. Sites that are currently on or proposed to the NPL have already been evaluated under another pathway (i.e., ground water migr ation, air migration, surface water migration, or soil exposure) and, in accordance with section 105(c)(3) of CERCLA, as amended, would not be re

- evaluated. To the extent practicable, EPA attempts to score all pathways that pose significant threats. If the contribution of a pathway is minimal to the overall score, in general, that pathway will not be scored. In these cases, the HRS documentation record may include a brief qualitative discussion to present a more complete picture of the conditions and hazard s at the site. As a matter of policy, EPA does not delay listing a site to incorporate new data or score new pathways if the listing decision would not be affected by such action. EPA must balance the need to fully characterize a site and to perform the a nalysis with the limited resources available to collect and analyze site data. For this reason, EPA generally will not score additional pathways upon receiving new data as long as the site still meets the HRS cutoff score. However, any additional data char acterizing site conditions collected during the HRS evaluation process could provide useful information during the***E.O. 12866 Review

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Page 15 of 162 Remedial Investigation( RI). It is important to note that the HRS is intended to be a “rough list” of prioritized hazardous sites; a “first s tep in a process

-- nothing more, nothing less” Eagle Picher Indus. v.
EPA , 759 F.2d 922, 932 (D.C. Cir. 1985) (Eagle Picher II). EPA would like to investigate each possible site completely and thoroughly prior to evaluating the site for proposal to the NPL, but must reconcile the need for certainty before action with the need for procedures that are expeditious and limited in scope to identify potentially hazardous sites. The D.C. Circuit Court of Appeals has found EPA 's approach to solving this conundrum to be “reasonable and fully in accord with Congressional intent.” Eagle Picher Industries, Inc. v. EPA , (759 F.2d 905 (D.C. Cir. 1985) (Eagle Picher I)).
EPA ’s site assessment program is operated strictly by the public sector. EPA uses funds that are appropriated annually and reside in the Superfund Trust Fund, while other federal agencies that conduct CERCLA site assessments use funds appropriated annually to them for the purposes of implementing CERCLA at their proper ties. Because subsurface intrusion sites have the potential to pose a high level of risk to residents and occupants of structures, EPA expects that there will be a realignment and reprioritization of its internal resources and in Cooperative Agreement fund ing to address sites with subsurface intrusion as a priority. Therefore the proposed rule is likely to result in less effort in some site assessment areas to free resources that can be used for subsurface intrusion evaluations. For this reason,
EPA conside rs that this proposed rule is not expected to result in either an increase in the number of site assessments per year or in the placement of more sites on the NPL per year. Because federal agencies already have the authority to address subsurface intrusio n issues as part of their environmental programs, this proposed rule is anticipated to have minimal impacts on federal facility cleanup programs. Executive Order 12580 delegates broad CERCLA authority to federal agencies for responding to actual and potent ial releases of hazardous substances where a release is either on, or the sole source of the release is from, any facility or vessel under the jurisdiction, custody, or control of the federal agency. Federal agencies are required to exercise this authority consistent with the requirements of CERCLA section 120, as amended, and implement regulations under the NCP, for both NPL and non

NPL sites. Therefore, federal agencies are in a position to proactively identify and respond to risks posed***E.O. 12866 Review

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Page 16 of 162 by subsurface int rusion of hazardous substances into regularly occupied structures for all populations who live and work in areas where the subsurface environment may create exposures. If it is determined that releases of hazardous substances pose immediate threats to publ ic health and the environment, EPA fully expects that the appropriate federal agency will continue to undertake response actions to address such threats. In fact, some federal agencies, including EPA , have developed or are developing new or updated
agency - specific policy and guidance documents to address subsurface intrusion threats.

2. Impact on Resources and Costs No present program consistently and comprehensively addresses subsurface intrusion contamination

across non - federal possible sites, particularly when subsurface intrusion is the primary threat. While most states have identified subsurface intrusion sites as an issue, not all states have subsurface intrusion programs, and states with programs vary in their authority, resources, and remediation crit eria. A redirection of resources available through EPA’s Cooperative Agreement funding is expected to provide for greater national consistency in the identification and evaluation of sites with subsurface intrusion contamination. Additionally, EPA is plann ing to issue new vapor intrusion guidance in the near future. Together with this proposed rule, EPA will provide a comprehensive framework to guide evaluation of subsurface intrusion sites across the country. Conducting an HRS evaluation imposes no direct costs on any private entity. After EPA or a state/tribe conducts a site assessment and EPA determines that a site is eligible for the NPL, additional regulatory actions must be taken before any costs or other impacts would occur. Placement of a site on the NPL does not ascribe liability or in any way impose requirements on private parties. Later decisions that consider information collected under the proposed addition could separately have specific economic co sts and benefits (e.g., remediation costs and reduced risk), but these impacts are contingent upon a series of separate and sequential actions after listing a site on the NPL. The addition of subsurface intrusion to the HRS is several regulatory steps remo ved from imposing costs on private entities.***E.O. 12866 Review

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Page 17 of 162 3. Children’s Environmental Health EPA interprets Executive Order 13045, Protection of Children from Environmental Health Risks and Safety Risks, as applying only to those regulatory actions that concern environme ntal health or safety risks that EPA believes may disproportionately affect children. This rulemaking is expected to have only moderate costs and no direct impact on human health risk. In addition, any impacts resulting from future actions to remediate sit es with SsI contamination would reduce the human health risk at these sites. Therefore, EPA concludes that this rule will have no significant impacts on children’s health.

4. Environmental Justice This rulemaking is expected to have only moderate costs and n o impact on human health risk. Therefore, the rule has no impacts on communities considered under Executive Order 12898, Federal Actions to Address Environmental Justice in Minority Populations and Low

- Income Populations

. Therefore, EPA did not conduct a c omplete environmental justice analysis. However, EPA did consider whether the proposed action might have contingent impacts on minority or low

- income populations located near potential SsI sites if future actions affect remediation of these sites. This ana lysis concluded that potentially affected sites are located in areas that have slightly higher concentrations of minority populations and populations below the poverty line than surrounding areas. Therefore, any future actions addressing risks in these com munities would not contribute to disproportionate adverse impacts on human health. A regulatory impact analysis (RIA) of the three regulatory options considered in the development of this rulemaking was also conducted. The option selected as the preferred option was chosen as it is consistent with the 1990 HRS, serves as an effective screening tool that would both minimize unnecessary resource expenditures and the erroneous inclusion or exclusion of sites from possible placement on the NPL, and is based on proven science. The RIA for this rulemaking can be found in the official Docket for this action.***E.O. 12866 Review

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Page 18 of 162 Before making the decision to proceed with this action, EPA also conducted outreach activities to determine interest and support from the public. On January 3 1, 2011, EPA published a “Notice of Opportunity for Public Input (76 FR 5370, January 31, 2011) soliciting public input on whether to include a subsurface intrusion component in the HRS. EPA also sent letters to all federally recognized tribes asking for t heir comments on the FR notice. Four public listening sessions were also held throughout the country (Arlington, VA; San Francisco, CA; Albuquerque, NM; and Edison, NJ).

IV. Hazard Ranking System

A. Purpose The current HRS serves as a screening tool to evaluate the potential for uncontrolled hazardous substances to cause human health problems or environmental damage at one site relative to other sites evaluated. The pre

- remedial portion of the Superfund progr am

— the portion prior to placing sites on the
NPL

— is intended to identify those sites that present the highest priority for further investigation and possible cleanup under CERCLA. (See Figure 1 for a general depiction of the Superfund Site Assessment
proce ss.) During site discovery, which is the first step of the pre

- remedial process, possible releases of hazardous substances are listed in EPA’s SEMS. If based on the results of a preliminary assessment (an assessment made using existing data to determine if there is evidence of a potential threat), EPA determines that a site warrants further investigation, the agency initiates a site inspection as specified in the NCP (40 CFR 300.420). The site inspection usually includes the collection of samples for chemic al analysis. Such samples aid in ascertaining what substances are present at the site and whether they are being released. The purpose of the site inspection is to determine if there is an actual or potential threat to human health or the environment, to d etermine if there is an immediate threat to people or the environment in the area, and to collect sufficient data to enable the site to be scored using the HRS.***E.O. 12866 Review

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Page 19 of 162 Figure 1. Superfund Site Assessment Process

EPA has designed the Superfund program to focu s its resources on the highest priority sites. Consequently, the initial studies, the preliminary assessment and site inspection, which are performed on a large number of sites, are relatively modest in scope and cost compared to the remedial investigation s and feasibility studies subsequently performed on NPL sites. Because of the need to carry out the initial studies expeditiously, EPA elected to place certain constraints on the data requirement for an HRS evaluation. The required HRS data should be infor mation that, for most sites, can be collected during a screening level site inspection or that are already available. Thus, the HRS does not rely on data that require extensive sampling or repeated sampling over a long period of time. The HRS has also been designed so that it can be applied consistently to a wide variety of sites. The HRS is not a tool for***E.O. 12866 Review

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Page 20 of 162 conducting quantitative risk assessment and was designed to be a measure of relative risk among sites rather than absolute risk at an individual site. The narrow technical modifications being proposed reflect the agency’s actions to encompass additional risks posed by releases of hazardous substances and to address the SARA statutory requirement that EPA amend the HRS to assure “to the maximum extent fea sible, that the HRS accurately assesses the relative degree of risk to human health and the environment posed by sites subject to review.” Thus, the fundamental purpose and structure of the HRS approach will not be changed when the HRS is amended to includ e consideration of subsurface intrusion.

B. Structure The current HRS (40 CFR 300, Appendix A) evaluates four pathways in projecting the relative threat a site poses:

• The ground water migration pathway evaluates the likelihood that hazardous substances will migrate to ground water and contaminate aquifers and drinking water wells that draw on those aquifers.

• The surface water migration pathway evaluates the likelihood that hazardous substances can enter surface water and affect people or the environment. Threats to human health and the environment included in this pathway include drinking water (DW), the human food chain (HFC) (i.e., hazardous substances accumulate in t he aquatic organisms that humans in turn consume), and sensitive environments (ENV). The surface water migration pathway is also divided into two “components” reflecting different mechanisms for contaminant transport within each component (i.e., overland/f lood migration to surface water component and ground water to surface water migration component).

• The air migration pathway evaluates the likelihood of release of hazardous substances into the atmosphere and the number of people and sensitive environments actually or potentially exposed***E.O. 12866 Review

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Page 21 of 162 to hazardous substances carried in the ambient (outdoor) air, including gases and particulates. The air migration pathway does not evaluate releases to indoor air originating from the subsurface.

• The soil exposure pathway ev aluates the potential threats to humans and terrestrial environments posed by direct, physical contact with, and subsequent ingestion of, hazardous substances. This pathway includes threats to people living on property where hazardous substances are presen t in the surface/subsurface, including contaminated soils (resident population threat), and to people living nearby with access to the contaminated area (nearby population threat).

Figure 2 illustrates the general structure of the current HRS.

Figure 2. Structure of the Current HRS

Ground Water Migration Pathway Score (S GW ) Surface Water Migration Pathway Score (S SW ) Soil Exposure Pathway Score (S SE ) Air Migration Pathway Score (S A )***E.O. 12866 Review

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Page 22 of 162 The scoring system for each pathway is based on a number of individual factors associated with risk

related conditions at the site. These factors are grouped into three factor categories as discussed below. These categories include factors that are used to characterize the relative risk at the site. 1. Likelihood of release/exposure (i.e., likelihood that hazardous substances have been released or potentially could be released from a source into the environment, or that people or sensitive environments could come into contact with hazardous substances). 2. Waste characteristics (i.e., toxicity, mobility, and/or persistence of the substances in the environment and the quantity of the hazardous substances that have or could be released). 3. Targets (i.e., people or sensitive environments actually or potentially exposed to the release).

An HRS score is determined for a site by summing the score for the four pathways. Specifically, the score for each pathway is obtained by evaluating a set of factors that characteriz e the potential of the release to cause harm via that pathway. The factors, which represent toxicity of the hazardous substance(s) at a site, waste quantity, and population are multiplied by a weighting factor, yielding the factor value; the factor values are used to assign factor category values. The factor category values are then multiplied together to develop a score for the pathway being evaluated. Finally, the pathway scores are combined according to the root

- mean - square equation presented below to de termine the HRS score for the site. See also Table 2

- 1 of the proposed addition (section 2.1.2) for additional discussion regarding the method for calculating an HRS site score.***E.O. 12866 Review

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Page 23 of 162 SS = � SS

gggg 2 + SS ss 2 + SS ssss 2 + SS aa 2 4 

### S = site score Sgw = ground water migration pathway score Ssw = surface water migration pathway score Sse = soil exposure pathway score Sa = air migration pathway score

By using this formula to assign a site score, the HRS score will be low if all pathway scores are low. However, the final score c an be relatively high if one pathway score is high. This approach was chosen to ensure that the site scores do not deemphasize single

- pathway problems, underestimating their importance. EPA considers this an important requirement for the HRS scoring method ology because some extremely dangerous sites pose threats through only one pathway. For example, leaking drums of hazardous substances can contaminate drinking water wells, but if the drums are buried deeply enough and the hazardous substances are not very volatile, they may not release any hazardous substances to the air or to surface water. It should be emphasized that the existing pathways can address subsurface contamination if it enters into ground water (in the ground water migration pathway), if it e nters into surface water (in the surface water migration pathway), if it enters into ambient air (in the air migration pathway) from the soil surface or if it leads to surface soil contamination (in the soil exposure pathway). However, none of these

scenar ios address intrusion from the subsurface into regularly occupied structures. Finally, it should also be emphasized that the HRS score does not represent a specific level of risk at a site. Rather, the score serves as a screening

- level indicator of the relative risk among sites reflecting the hazardous substance releases or potentia l releases at sites based on the criteria identified in CERCLA.***E.O. 12866 Review

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Page 24 of 162 V. Approach to HRS Addition The following sections detail EPA ’s comprehensive approach to the consideration of exposures to hazardous substances due to subsurface intrusion and the relevant sci entific and technical considerations in developing this proposed rule.

A. General Approach 1. What Is the Need for Regulatory Action on the HRS? Without an evaluation of threats posed by subsurface intrusion contamination, the HRS is not a complete assessment and omits a known pathway of human exposure to contamination. EPA considers the addition of subsurface intrusion to the HRS to be consistent with CERCLA section 105 because it will improve the agency’s ability to identify sites of the highest priority for further investigation and will enhance EPA ’s ability, in dialogue with other federal agencies and the states and tribes, to determine the most appropriate state or federal authority to address sites. As is currently the case, EPA often defers to other sta te and federal cleanup authorities based on the site assessments and HRS evaluations. While some states/tribes have programs to address subsurface intrusion contamination, they often have limited authority and resources, and variable remediation criteria. The availability of the federal remedial authority and the more comprehensive site assessment program should complement and strengthen these
programs. Other EPA programs such as the Resource Conservation and Recovery Act (RCRA) and the Brownfields program have limited authority and ability to address all subsurface intrusion threats. The RCRA Corrective Action/Enforcement is only applicable at sites subject to RCRA permitting or sites reachable by RCRA's enforcement activities. However, because RCRA is a s tate delegated program and not all states recognize subsurface intrusion as a significant issue; those that do may have variable remediation criteria. RCRA sites with subsurface intrusion issues may not be addressed in all states. Also, governmental entiti es with site

- specific Brownfields assessment and/or revolving loan fund cleanup may only use grant funds on the selected eligible property. While subsurface intrusion sites may be eligible for***E.O. 12866 Review

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Page 25 of 162 Brownfields cleanup grants, site or property

- specific limitatio ns may not allow for permanent remediation where multiple properties may be involved or where Brownfields grant funds, as limited by statute, may not be adequate to fund long

- term cleanups 4

. While EPA ’s removal program can provide a response to an emergi ng subsurface intrusion issue, it may not be appropriate in all cases, such as when actions are needed at a complex site to provide more comprehensive protection of human health and the environment. EPA ’s removal program may only address subsurface intrusi on when contaminant levels cause an imminent threat as opposed to a long

- term threat. Also, the removal program may only be preventing the exposure to subsurface contamination via intrusion, and not addressing the underlying cause of the contamination. Under the Superfund remedial program for NPL sites, subsurface intrusion is only addressed at sites placed on the NPL based on threats from other pathways. That is, subsurface intrusion issues are addressed later in the remedial process after placement on the NPL. For example, this may be done as part of EPA ’s five

- year review process. S ites with only subsurface intrusion issues are not being included on the NPL due to the lack of a subsurface intrusion component in the HRS. Therefore, many sites, especiall y those not evaluated under another HRS pathway or those not scoring high enough under another HRS pathway, may not be addressed for threats due to subsurface intrusion because they may not qualify for placement on the NPL. As GAO states in its May 2010 re port: ...EPA may not be listing some sites that pose health risks that are serious enough that the sites should be considered for inclusion on the NPL. While EPA is assessing vapor intrusion contamination at listed NPL sites, EPA does not assess the relative risks posed by vapor intrusion when deciding which sites to include on the NPL. By not including these risks, states may be left to remediate those sites without federal assistance, and given states’ constrained budgets, some states may not have t he ability to clean up these

4 EPA’s Estimated Costs to Remediate Existing Sites Exceed Curre nt Funding Levels, and More Sites are Expected to Be Added to the National Priorities List, GAO Report to Congressional Requesters, GAO

- 10

- 380, May 2010.***E.O. 12866 Review

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Page 26 of 162 sites on their own...However, if these sites are not assessed and, if needed, listed on the NPL, some seriously contaminated hazardous waste sites with unacceptable human exposure may not otherwise be cleaned up.

2. What Alternat ive Regulatory Options to this Action Were Considered by EPA ?
EPA considered alternatives to this proposed regulatory action for addressing the need to evaluate subsurface intrus ion threats as discussed below. Specifically, EPA considered whether existing programs adequately address the risks associated with subsurface intrusion at contaminated sites, as discussed in the previous section. If one or more programs were in place to adequately address concerns from subsurface intrusion, this could obviate the n eed for EPA action. However, no other authority consistently and comprehensively addresses subsurface intrusion across all potential non

- federal sites, particularly when subsurface intrusion is the key exposure route. In particular, state programs vary sig nificantly in addressing subsurface intrusion. In fact, not all states have subsurface intrusion programs, and states with programs vary in their authority, resources, and remediation criteria. The 2004 Interstate Technology and Regulatory Council’s (ITRC) Vapor Intrusion Team developed and conducted an on

- line survey of state, federal, and tribal agencies regarding vapor intrusion regulations, policy, and guidance. Ninety

- six percent (96%) of survey respondents consider vapor intrusion a concern; however, only 11% have a procedure for evaluating vapor intrusion codified into law, while a larger number of states have developed or are developing guidance for addressing vapor intrusion issues. A majority of the states that responded to the survey expressed tha t their processes for addressing vapor intrusion were only informally adopted by their agencies, and most defer to EPA . The 2009 Vapor Intrusion Pathway: A Guide for State and Territorial Federal Facilities Managers study also surveyed state and territoria l subsurface intrusion programs. According to this study, there were no states with a statute directly addressing vapor intrusion or identifying requirements for assessing the risk. Nine states had regulations that address vapor intrusion specifically; thr ee states had regulations under development. Thirty

- four states either have guidance for addressing vapor intrusion or are in the process***E.O. 12866 Review

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Page 27 of 162 of developing guidance. In addition, the ASTSWMO has expressed support for the proposed rule and has requested that EP A take leadership on this issue. Since vapor intrusion is projected to be the most significant component of subsurface intrusion, these responses would apply to subsurface intrusion as well. As previously discussed in section V.A.1 of this preamble, other federal programs were reviewed; while some programs could address subsurface intrusion at some sites, they cannot comprehensively address all sites (federal and non

- federal). Two other mechanisms currently exist to place sites on the NPL. First, each state can designate a single site to the NPL as a state top priority site regardless of its HRS score; this can be done only once. (See NCP, 400 CFR 300.425(c)(2).) This state

- designated sites option has been implemented for 43 states/territories, and the remai ning state options would not be sufficient to address the subsurface intrusion issue nationally and comprehensively, given the projected number of sites with subsurface intrusion problems. Second, sites may be added in response to a health advisory from th e ATSDR. (See NCP, 40 CFR 300.425(c)(3).) However, the ATSDR mechanism was designed to be used only when the ATSDR designated the threat found to warrant immediate dissociation from the release and other criteria are met. This is not a mechanism that can b e used uniformly and consistently. It is highly resource intensive and may not comprehensive ly address all chronic threats. Furthermore, CERCLA section 105 clearly mandates that EPA implement the HRS to take into account “...to the extent possible the popula tion at risk, the hazard potential of hazardous substances..., the potential for contamination of drinking water supplies and the potential for direct human contact.” When the HRS was last revised in 1990, the technology to detect and evaluate subsurface int rusion threats was not sufficiently developed. For example, there were no health

- based benchmark concentration values for residences or standardized technologies for sampling indoor air, precision of analytical equipment prior to computerization was limite d, and associations between contaminated ground water and soil vapors were not well understood. However, it is now possible for subsurface intrusion threats to be evaluated comprehensively. Therefore, it is now appropriate, given the potential that subsurf ace intrusion***E.O. 12866 Review

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Page 28 of 162 presents for direct human contact, to add to the HRS the consideration of threats due to subsurface intrusion.

3. What Public Outreach Activities Did EPA Conduct? Before making the decision to issue this proposed rulemaking, EPA conducted outreach activities to determine interest and support from the public. Thus, on January 31, 2011, EPA published a “Notice of Opportunity for Public Input” (76 FR 5370, January 31, 2011) soliciting stakeholder comment on whether to include a subs urface intrusion component in the HRS. Additionally, EPA sent letters to all federally recognized tribes, asking for their comments on the FR notice. During the 75

- day public comment period on this notice, four listening sessions were held throughout the c ountry (Arlington, VA; San Francisco, CA; Albuquerque, NM; and Edison, NJ). The comments by a majority of speakers, including members of the public, at the listening sessions were supportive of the potential addition of a subsurface intrusion component int o the HRS. Of the 43 written comments received during the public comment period, 35 were in support of adding a vapor intrusion component to the HRS, 6 comments (generally from industry representatives) were opposed to this addition, and 2 comments were ne utral. The comments received during the public listening sessions and in response to the “Notice of Opportunity for Public Input” have been reviewed and considered in the development of this proposed rulemaking. EPA has also established a public website, http://www.epa.gov/superfund/sites/npl/hrsaddition.htm , providing background information on why this addition to the HRS is being considered.

4. What Peer Review Process Did EPA Use? This proposed rule consists of narrow technical modifications and is an expansion of the current HRS, which was peer reviewed by the agency’s Science Advisory Board (SAB). The 1988 SAB review was comprehensive and addressed the basic structure and concepts of the HRS. This proposed addition adheres to the basic structure and concepts of the current HRS, and thus, is consistent with the recommendations of the SAB. The 1988 SAB report focused on the following issues:***E.O. 12866 Review

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Page 29 of 162 • The overall algorithm for the HRS;

• The i nclusion of exposure in the HRS;

• How the HRS could be evaluated in the future;

• Work that could be done to provide better documentation for the next revision of the HRS;

• The types of toxicity the HRS should address and how it should do so;

• Distances fro m an uncontrolled hazardous waste site that are relevant when considering air pollutants from sites; and

• The feasibility of including waste concentration in the HRS and whether large volume waste sites had been treated differently than others in the HRS. The 1988 SAB report is available in the public docket for this proposed rulemaking. During development of this proposed HRS update, EPA determined that several subsurface intrusion

specific issues warranted external independent scientific peer review. As a result, EPA has identified elements that have undergone peer review including:

• Consideration of potential for subsurface exposure (intrusion) into regularly occupied structures;

• Determination of hazardous waste quantity for the subsurface intrusion compo nent;

• Population scoring;

• Evaluating populations in multi

- story and multi

- tenant structures; and

• Evaluation of target values for workers

The results of the 2011 peer review of the proposed addition are discussed in the Summary of Peer Review Comments and Suggested Responses on the Proposed Addition of a Subsurface Intrusion Component to the HRS, which is available in the public docket for t his proposed rulemaking. Additional information, such as the official charge questions and other documents provided to the 2011 peer reviewers and the original peer review comments received on this proposed addition to the HRS are also available in the pub lic docket for this proposed rulemaking. Comments and EPA responses associated***E.O. 12866 Review

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Page 30 of 162 with the five charge questions are discussed in Appendix E, Peer Review Responses, of the Proposal TSD. This proposed addition reflects modifications made as a result of EPA ’s p eer review process.

5. How did EPA Select the Approach for Including the Addition in the HRS? The following six concepts were used as the basis for evaluating possible approaches to the HRS addition and the selection of a preferred approach: 1. Limit the propos ed addition to the existing HRS structure to avoid confusion by minimizing the portions of the present HRS that would need to be revised. 2. Utilize the existing HRS basic structure and scoring algorithm, and maintain the relative weighting of the different p athways. 3. Base technical decisions on sound and proven science. 4. Ensure the HRS acts as an effective screening tool and minimizes unnecessary resource expenditures, while also minimizing the erroneous inclusion or exclusion of sites for possible NPL placeme nt. 5. Assemble and utilize conceptual site models, case studies, and sensitivity analyses to test the model.
6. Ensure that an HRS scoring evaluation of the soil exposure and subsurface intrusion pathway can be completed using the information and level of effo rt that are typical of a site inspection or expanded site inspection (ESI).

In the process of developing the proposed rule, EPA identified multiple options that are consistent with the above concepts. Based on literature reviews and agency experience, EPA projected the range of conditions at which the proposed addition might be applied. Using the basic structure of the current HRS,
EPA tested each option by simulating the scores for typical scenarios. Using the results of these studies,
EPA selected the op tion that best met the above criteria. To verify that the selected option would provide comparable results at actual sites, EPA tested the scoring algorithm using existing subsurface intrusion***E.O. 12866 Review

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Page 31 of 162 data from actual sites. The results of these studies demonstrat e that the proposed addition functioned as expected. See section 8.0 of the Proposal TSD for supplemental information regarding EPA ’s testing efforts.

B. Technical Considerations to Maintaining the Current HRS Structure and Algorithm 1. Maintaining the Current Ground Water, Surface Water, and Air Migration Pathways The current approach for scoring the ground water, surface water, and air migration pathways is not being altered by the proposed addition of a subsurface intrusion component. Therefore, EPA is not soliciting comments on these pathways and will not respond to comments that are submitted on these pathways.

2. Addition of the New Component to Restructure and Rename the Soil Exposure Pathway
EPA is proposing to add the subsurface intrusion threat to the present soil exposure pathway, which already considers di rect exposure to receptors. This pathway is proposed to be restructured and renamed the soil exposure and subsurface intrusion pathway. The restructured pathway will retain unchanged the existing two soil exposure threats (resident population and nearby po pulation) in the pathway as one component. The threat posed by subsurface intrusion is proposed to be added as a new component. The internal structure of the soil exposure component, including the two soil exposure threats within that component, remains u nchanged. Therefore, EPA is not soliciting comments on the soil exposure component of the proposed soil exposure and subsurface intrusion pathway, nor will it respond to comments that are submitted on the soil exposure component. The soil exposure pathway was selected for modification because its structure already focuses on populations actually coming into or potentially coming into direct contact with hazardous substances. The present soil exposure pathway addresses direct contact with contamination outsi de of structures. The new subsurface intrusion component also addresses direct contact with contamination that has already been demonstrated to have entered into regularly occupied structures or where the contamination is present***E.O. 12866 Review

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Page 32 of 162 beneath the regularly occu pied structures and is likely to enter into regularly occupied structures. See section VI.A of this preamble for further discussion.

C. Supporting Materials The proposed addition to the HRS is discussed in the following primary documents: (1) the proposed

ru le, (2) this preamble, (3) the Proposal TSD (including supporting materials), (4) the RIA, and (5) a summary document of peer review comments on the proposed addition and agency responses. The proposed rule identifies the proposed changes to the NCP and fo cuses on the specific mechanics of scoring sites with the new component. This preamble provides an overview of the proposed HRS addition, along with an explanation of any modifications and the supporting justification. The Proposal TSD contains a more deta iled explanation of the technical basis for the proposed additions to the HRS, along with descriptions of the options considered, analyses that were used to evaluate the performance of the new subsurface intrusion component, and technical literature that w as used in the development of the addition. The Proposal TSD is available to help guide the evaluation of subsurface intrusion sites. The Proposal TSD follows the same general outline as the preamble, with one section describing the necessary narrow techni cal modifications that affect multiple pathways, and the remaining sections describing the addition of the subsurface intrusion component to the current soil exposure pathway. The Proposal TSD contains a description of the current HRS, the options consider ed, and the technical justifications for the option chosen. In addition, the Proposal TSD references other supporting documents that provide an even greater level of detail on the proposed additions. These five documents are available to the public in the Docket for this rulemaking. To facilitate public review, EPA has prepared an index to the proposed rule, the preamble to the proposed rule, and the Proposal TSD with detailed cross referencing of issues. This index is available in the public Docket. See
t he ADDRESSES section of this preamble for further information.

VI. Discussion of the Proposed Subsurface Intrusion Addition to the HRS***E.O. 12866 Review

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Page 33 of 162 This section first discusses why the evaluation of the relative risk posed by subsurface intrusion has been added as a component to the same HRS pathway as for soil exposure. It then discusses how the evaluation will be performed using a structure consiste nt with the other threats, components, and pathways in the HRS, but taking into account the unique parameters impacting the probability of exposure to subsurface intrusion.

A. Addition Within a Restructured Soil Exposure and Subsurface Intrusion Pathway
EPA is proposing to add the evaluation of the relative risk posed by subsurface intrusion of hazardous substances into regularly occupied structures by restructuring the soil exposure pathway in the current HRS to include subsurface intrusion. As noted previo usly, no changes are being proposed for the other three pathways in the present HRS. The restructured soil exposure pathway is proposed to be renamed the soil exposure and subsurface intrusion pathway to reflect both components of the restructured pathway. See Figure 3 for a depiction of how the proposed addition fits into the HRS structure.***E.O. 12866 Review

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Page 34 of 162 Figure 3. HRS Structure with Proposed Addition

Ground Water Migration Pathway Score (S GW ) Surface Water Migration Pathway Score (S SW ) Soil Exposure and Subsurface In trusion Pathway Score (S SESSI ) Air Migration Pathway Score (S A ) The threat posed by subsurface intrusion is proposed to be added to the soil exposure pathway because both consider the relative risk posed by direct contact with existing contamination areas. As identified in the preamble to the 1988 Federal Register notice proposing the current HRS (53 FR 51997

- 52000, December 23, 1988), the soil exposure pathway, proposed in 1988 to be named the “onsite exposure” pathway, was added to the HRS to address the threat posed by direct contact with existing contamination and focused on ingestion of contaminated soil. This is in contrast with the other existing HRS pathways, which evaluate the relative risk posed by actual or potential migration of contamination fro m an original release location (called a “source” in HRS terminology) via ground water, surface water, or ambient air to other locations where exposure may occur. Given that the relative risk posed by subsurface intrusion is also due to direct contact with contamination already present in or likely to be intruding into regularly occupied structures, and no further migration away from the existing contamination areas need occur,***E.O. 12866 Review

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Page 35 of 162 EPA considers it appropriate to incorporate the subsurface intrusion threat in t he same direct exposure pathway that includes the soil exposure relative risk. See section 6.0 of the 1988 Revised HRS TSD for supplemental information (originally referred to as the onsite exposure pathway). The existing soil exposure pathway will be reta ined as one component of the restructured pathway, with the two threats within the present soil exposure pathway, resident and nearby populations, being retained as threats within the soil exposure component. The scoring of the soil exposure component will remain unaltered, but the score will be assigned as the soil exposure component score, not the pathway score. (See section 5.1 of the Proposed HRS Addition.) The proposed subsurface intrusion component will be added as a new component of the restructured soil exposure and subsurface intrusion pathway. As discussed in greater detail below, it will have the same basic structure, scoring, and weighting as other parts of the HRS. The score for the restructured pathway is based on a combination of the two com ponent scores

soil exposure and subsurface intrusion. The soil exposure component score is added to the subsurface intrusion component score to determine the pathway score. The two component scores are proposed to be additive because the populations may be subjected to exposures via both routes: the soil exposure component reflects exposures to people when outside a structure and focuses on ingestion and the subsurface intrusion component reflects exposures inside a structure and focuses on inhalation. Henc e, the addition of the two component scores reflects the potential cumulative risk of multiple exposure routes and is not doub le counting the relative risk. A maximum pathway score is not contingent on scoring both the soil exposure and subsurface intrusi on components. It is possible for a site to have only one component evaluated and still reach the maximum pathway score. Because the scoring of the soil exposure component is not being altered, this component would contribute the same score to the overall site score absent the addition of subsurface intrusion.

B. Subsurface Intrusion Component Addition***E.O. 12866 Review

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Page 36 of 162 The structure of the current HRS is basically the same for all individual pathways, components, and/or threats. This structure was first used in the original HRS (47 FR 31220, 1982), and was only slightly altered when the HRS was revised in 1990 (55 FR 51532, December 14, 1990) to fit pathway

specific parameters and to address comments on the proposed rule. See also section 2.2 of the 1988 Revised HRS TSD for supplemental information. The design of the HRS reflects a conceptual understanding of how hazardous substance releases from CERCLA sites can result in risks to public health and welfare and the environment. The risk scenario at these sites is a function o f:

• The probability of exposure to (or releases to a medium in a migration pathway of) hazardous substances,

• The expected magnitude and duration of the releases or exposures,

• The toxicity or other potential adverse effects to a receptor (target) from the re leases,

• The probability that the release will reach a receptor(s) and the expected change in the concentration of hazardous substances during the movement from the location of the contamination to the receptors,

• The expected dose to the receptor, and

• The expected number and character of the receptors. The above considerations are addressed in three factor categories: likelihood of exposure (or release),
waste characteristics, and targets. The following discussion describes the structure of the proposed subsurface intrusion component and how this structure is consistent conceptually with the existing structure of the other HRS pathways and components in subsections: 1) new definitions, 2) delineation of areas of subsurface intrusion, 3) likelihood of exp osure, 4) waste characteristics, 5) targets, and 6) calculating and incorporating the subsurface intrusion component score into the HRS site score. For background on why this structure was selected by EPA and peer reviewed by the SAB, see section 2.0 of th e 1988 Revised HRS TSD.***E.O. 12866 Review

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Page 37 of 162 1. New Definitions

– See section 1.1 of the Proposed HRS Addition 5
EPA is proposing that 15 new definitions be added to the HRS, section 1.1, with additional modifications to existing definitions. EPA is adding these new definitions t o aid the site evaluator in establishing the environmental boundaries that are being evaluated in this component (e.g., contamination in or above the surficial aquifer), in identifying factors unique to the subsurface intrusion component (e.g., channelized flow through which soil gas transports with no resistance), and to ensure consistent application of the HRS.

2. Delineation of Areas of Subsurface Intrusion

– See section 5.2.0 of the Proposed HRS Addition
EPA is proposing to include in the subsurface intrusion component evaluation, two areas in which exposure due to subsurface intrusion contamination exists or is likely to exist: 1) areas of observed exposure: areas in which contaminant intrusion into regularl y occupied structures has been documented, and 2) areas of subsurface contamination: areas in which subsurface contamination underlying regularly occupied structures (such as in surficial ground water or soil vapor) has been documented, but at which either sampling of indoor air has not documented that subsurface contamination has entered a regularly occupied structure or no sampling of indoor air has been undertaken. See Figure 4 for an illustration of the two areas. Additionally, special considerations ar e given to buildings with multiple tenant spaces with multiple stories (e.g., apartment buildings) when establishing areas of subsurface intrusion. For a more detailed discussion on the selection of these areas, see section 6.0 of the Proposal TSD.

a. Area o f Observed Exposure (AOE)

– See section 5.2.0 of the Proposed HRS Addition
EPA is proposing to identify an area (or areas) of observed exposure at a site based on the location of regularly occupied structures with documented contamination resulting from su bsurface intrusion attributable to the site being evaluated. The area encompassed by such structures constitutes the area of

5 For reference s to a specific section of the P roposed HRS A ddition, please refer to the regulatory t ext of the proposed rulemaking.***E.O. 12866 Review

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Page 38 of 162 observed exposure (AOE). Other regularly occupied structures within this encompassed area (or areas) will also be considered in the AOE unless available information indicates otherwise. Populations occupying structures within the AOE are considered exposed to subsurface contamination for HRS scoring purposes, and thus, are included in the HRS evaluation. See section 6.0 of the Proposa l TSD for further discussion on the delineation of an AOE and the rationale for the inclusion of this area in an HRS evaluation.

b. Area of Subsurface Contamination (ASC)

– See section 5.2.0 of the Proposed HRS Addition
EPA is proposing to also identify an area (or areas) of subsurface contamination as an area outside that of the AOE, but for which subsurface contamination has been documented at levels meeting observed release criteria (contamination at levels significantly above background and the significa nt increase can be attributed at least in part to the site). The contamination would be present either in surficial ground water samples, in subslab or semi

- enclosed or enclosed crawl space samples, in subsurface soil samples, or in soil gas samples in the unsaturated zone. An ASC may also include regularly occupied structures where indoor air sampling has not documented that an observed exposure has occurred. (See current HRS section 2.3 for observed release criteria.) In addition, EPA is proposing to limi t the delineation of an ASC based on the location of subsurface volatile hazardous substances. However, non

- volatile hazardous substances may be used to establish an ASC if they have also been documented in an observed exposure. Populations in regularly o ccupied structures within an ASC are considered potentially contaminated, but are weighted less in the HRS evaluation than those populations in an AOE. The populations in an ASC are assigned a weighting value ranging from 0.1 to 0.9 depending on such fact ors as the distance of subsurface contamination to a regularly occupied structure’s foundation and the sample media (see section 5.2.1.3.2.3 of the Proposed HRS Addition). The ASC is included in the HRS evaluation because there is currently contamination b elow regularly occupied structures in the ASC, and although a sampling event has not documented intrusion into these structures, based on previous studies, it is likely that intrusion has occurred or could occur when suitable climatic and lifestyle conditi ons were or are present.***E.O. 12866 Review

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Page 39 of 162 The populations in the ASC are weighted less to reflect the relatively lower demonstrated risk in the ASC in comparison to the AOE. See section 6.0 of the Proposal TSD for further discussion on the delineation of an ASC and the rat ionale for inclusion of this area in an HRS evaluation.

Figure 4. Areas of Observed Exposure or Subsurface Contamination

c. Other Area of Subsurface Intrusion Considered: Potential Migration Zone In the three current HRS migration pathways (ground water, surface water, and air migration pathways), a projected present and future migration distance called the target distance limit is assigned based on studies performed when the HRS was revised in 198 8. Targets (receptors) within that distance are considered either actually or potentially exposed and the values assigned to these receptors are***E.O. 12866 Review

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Page 40 of 162 weighted based on the level of contamination, the distance from a source, and the possible amount of hazardous substance dilution. As a result, EPA considered including within the subsurface intrusion component an approach for incorporating populations subject to future migration (outside the ASC) similar to that used for the ground water migration pathway. The approach included a standard 4

- mile dis tance (modified if site

- specific geologic information indicates otherwise) radiating either in all directions or only in the probable downgradient direction from each source at a site to establish this future migration zone. This approach could account for the possibility of future horizontal migration of either volatile substances in contaminated ground water or as a soil gas beyond the demonstrated boundaries of the subsurface contamination and subsequently into regularly occupied structures (i.e., a pote ntial future migration zone). This might happen, for example, if hazardous substance plumes expand or migrate due to the additional release of hazardous substances, shift side

- to

- side due to ground water gradient changes resulting from seasonal variations or tidal influences, or change direction due to the sequencing of dry and wet years or pumping at municipal water supply or other well fields. Additionally, natural and anthropogenic influences, such as utility corridors, fracture patterns, karst features, or buried stream channels or other geologic heterogeneity may alter or enhance hazardous substance migration. However, EPA ’s confidence in the present science to accurately project hazardous substance migration through both the ground water and the unsat urated zone is limited. Several fate and transport models, many based on the Johnson and Ettinger Model, currently exist and are used to project vapor migration and predict contaminant vapor intrusion into a structure. The ability of a site assessor to

acc urately evaluate the potential future migration of subsurface hazardous substances would rely heavily on the ability to gather site

- specific data in all areas of future migration in the relatively short time period and with minimal resources available when data collection for an HRS evaluation is performed (i.e., during the site inspection). EPA ’s review of existing models indicated that in most instances, to obtain acceptable projections, extensive site

- specific data collection efforts and often multiple r ounds of site investigations are required to develop an accurate model for projecting the future extent of vapor***E.O. 12866 Review

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Page 41 of 162 migration, especially in the unsaturated zone. As discussed in section 2.5 of the 1988 TSD, the “...misapplication of a model or the use of incom plete data would, of course, result in less accuracy... [and] a very conservative model may also increase the frequency with which sites that do not pose significant risks are placed on the NPL.” Therefore, after thorough review of this option, the agency h as chosen not to include the consideration of future subsurface contaminant migration in the proposed subsurface intrusion component. The possibility of placing sites on the NPL based on speculative projections with no demonstrated risk of actual exposure is too significant. The exclusion of this option in the proposed HRS addition does not directly prevent a site from being considered for listing on the NPL based on demonstrated intrusion, nor does it restrict future investigations from expanding the site boundaries or re

evaluating a site if further studies indicate that the extent of contamination at a site may have increased due to future migration. Please refer to section 6.0 of the Proposal TSD for supplemental information regarding consideration of a potential migration zone.

3. Likelihood of Exposure

– See section 5.2.1.1 of the Proposed HRS Addition A key factor considered in the HRS relative risk ranking is whether any exposure has occurred and if not, whether there is a probability that exposure coul d occur. This is termed the likelihood of exposure for the subsurface intrusion component. For purposes of an exposure assessment, not only must subsurface intrusion have occurred, but the structure must be regularly occupied. Consistent with other HRS pat hways and components, likelihood of exposure is evaluated in two ways within the proposed subsurface intrusion component. The first step is to determine whether contamination has entered a regularly occupied structure; if this has occurred, “observed expos ure” is established. If an observed exposure can be demonstrated in at least one structure, the likelihood of exposure category value is assigned the highest possible score. If observed exposure has not been documented, the second step is to evaluate the “ potential for exposure.” The potential for exposure factor is assigned a score lower than that given when an observed exposure has been documented. How to evaluate the likelihood of exposure is***E.O. 12866 Review

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Page 42 of 162 discussed below. See section 4.0 of the Proposal TSD for suppl emental information regarding likelihood of exposure.

a. Observed Exposure

– See section 5.2.1.1.1 of the Proposed HRS Addition For HRS purposes, an observed exposure is established if it can be documented that a hazardous substance from the site being evalu ated has moved through the subsurface and has entered at least one regularly occupied structure. When it can be documented that subsurface intrusion has occurred, the likelihood of exposure is assigned its maximum value. The HRS identifies for all the path ways a consistent approach for establishing observed exposure (or observed release in migration pathways) and is discussed in section 2.3 of the current HRS. Also, the requirements for establishing observed exposure (or observed releases) are equivalent to those used to establish releases throughout the HRS. See section 2.6 of the 1988 Revised HRS TSD for supplemental information. Consistent with the current HRS structure,
EPA is proposing to establish observed exposure in the subsurface intrusion component by one of the following methods:

i. Observed Exposure by Direct Observation

– See section 5.2.1.1.1 of the Proposed HRS Addition

The identification of an observed exposure by direct observation can be based on a solid, liquid, or gaseous hazardous substanc e attributable to the site being observed or known to have entered a regularly occupied structure from the subsurface . This finding will in general require the observation that a solid, liquid, or gas is entering the structure, and can be documented from a sample of the material that shows the hazardous substance is present due to the release(s) from the site being evaluated. For example, this type of direct exposure could be documented if: 1) contaminated vapors are found in a sample from a sump open to th e regularly occupied structure, and 2) the same hazardous substances are found in subsurface samples collected beneath the regularly occupied structure or otherwise can be demonstrated as having been emanated from known contamination underlying the structu re. Another example would be if chromium precipitate is found in basements subject to ground water flooding and it is known that a***E.O. 12866 Review

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Page 43 of 162 chromium contaminant plume is present, and its presence is not from indoor sources. (In neither example would a significant i ncrease above a background contaminant level be required.) For exposures to intruded ground water, EPA is proposing documented observed exposure by direct observation as the only method for establishing likelihood of exposure. Figure 5 below depicts an add itional example of documenting observed exposure by direct observation through collection of a contaminated water sample taken from the sump of an occupied structure that is known to be subject to flooding. Other methods may also be used for establishing d irect observation depending on site

- specific conditions. See section 4.0 of the Proposal TSD for further information.

Figure 5. Observed Exposure by Direct Observation Example: Intrusion of Contaminated Ground Water

ii. Observed Exposure by Chemical Analysis

– See section 5.2.1.1.1 of the Proposed HRS Addition

Observed exposure by “chemical analysis” is established by comparing hazardous substance concentrations in background and release samples that have been chemically analyzed. The concentration***E.O. 12866 Review

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Page 44 of 162 of one or more hazardous substance(s) in one or more indoor air sample(s) taken from a regularly occupied structure (termed the “release sample”) is compared to the concentration(s) at appropriate background locations and under appropriate background conditi ons. If the chemical analyses document a significant increase over background levels and if at least part of the significant increase can be shown to be attributable to a release(s) from the site being evaluated, then observed exposure by chemical analysis has been documented. (This option for establishing observed exposure differs from observed exposure by direct observation in that comparison of the hazardous substance concentration in a release sample to a background level is required.) This method for e stablishing observed exposure by chemical analysis is outlined in detail below. Background levels for this situation, in some cases, may be determined by chemical analysis of samples from similar environments collected from outside the area impacted by the release(s) from the site being evaluated. While the appropriate sample locations to be used to establish this background level will vary based on site

- specific conditions, an appropriate background level needs to account for both outdoor air concentration s and indoor air concentrations in structures of similar construction type (e.g., basement, slab

- on - grade) within the vicinity. This is to ensure that the background level represents the concentration of a hazardous substance in the absence of the subsurfa ce intrusion. In some cases it may be possible to use published studies on typical background concentrations in establishing an appropriate background level. See section 4.0 of the Proposal TSD for further d iscussion on background levels. The first step in determining if observed exposure by chemical analysis has occurred is documenting that the magnitude of the difference between the background level concentration and the release sample concentration is sufficient to rule out the possibility that neither t he difference nor the similarity is simply due to variation in site conditions and in the replicability and precision of the sampling and analytical procedures. The magnitude of this “significant increase” was established for all HRS pathways based on stud ies peer reviewed by the Science Advisory Board when the HRS was last revised in 1990. See section 2.6 of the 1988 Revised HRS TSD for supplemental information.***E.O. 12866 Review

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Page 45 of 162 A significant increase is generally identified to have occurred if the release sample hazardou s substance concentration is at least three times the background level, provided the background sample concentrations for the hazardous substance are found at or above appropriate detection limits. If the hazardous substance background level is below the d etection limit, any level of the hazardous substance detected in the targeted structure is considered to have a concentration significantly above background. The second step in determining if observed exposure by chemical analysis has occurred is that at l east part of the significant increase must be attributed to a release from the site being evaluated. This step is required for establishing observed releases or observed exposures in all HRS pathways. See section 2.3 of the current HRS and section 2.6 of t he 1988 Revised HRS TSD for supplemental information. This step is to ensure that the increase is due to the release being evaluated and not from other contaminant sources in the vicinity. (See section 4.0 of the Proposal TSD for further discussion.) For t he proposed subsurface intrusion component, establishing significant increase over background is particularly critical because many of the projected intrusion contaminants are solvents and, in particular, chlorinated solvents. Chlorinated solvents are comm only found in multiple household and commercial cleaning products and in various consumer goods found in regularly occupied structures. These products present a substantial challenge for discerning the contribution from the environmental release that is be ing evaluated. Therefore, it is critical that a significant increase in these hazardous substances be documented as coming from the subsurface and not simply emanating from these products. It is suggested that the evidence to support this determination in clude multiple lines of evidence, including determining outdoor air hazardous substance concentrations; finding the hazardous substance at the source facility, site, or release being investigated; and finding the hazardous substance in subsurface samples. (See section 4.0 of the Proposal TSD regarding lines of evidence.) In addition, actions should be taken to ensure that sources of the hazardous substances inside a structure (e.g., household chemicals) have been removed from the structure prior to sampling . Establishing attribution to the site in some situations, however, may be straightforward to document, such as when the hazardous substance is manmade, unique, and not used in consumer products and thus, there would be no need to follow all the***E.O. 12866 Review

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Page 46 of 162 steps iden tified above to establish attribution. EPA expects that future advancement in methods for establishing the source of indoor contamination will be helpful for dr awing attribution conclusions. In summary, if it is demonstrated that there is a significant in crease in hazardous substance levels in a regularly occupied structure and it is demonstrated that the significant increase in the contamination is in part due to the release from subsurface intrusion being evaluated, then an observed release by chemical

a nalysis has been established.

b. Potential for Exposure

– See section 5.2.1.1.2 of the Proposed HRS Addition When an observed exposure has not been established, EPA is proposing to evaluate the potential for exposure within structures located in the ASC usi ng the subsurface intrusion component. Given that within an ASC, contamination has been demonstrated to be below or in the subsurface encompassing regularly occupied structures, it is probable that exposure to the intruding hazardous substance(s) has

occur red but that sampling has not been performed at the time the exposure took place. As explained in section 4.0 of the Proposal TSD, the factors affecting when intrusion will occur and the rate of subsurface intrusion are extremely time

- , site

- , and climate

- specific. Sampling may not have been performed in these structures for a number of reasons, or, even if performed during the limited time period of a site inspection, the sampling may have been conducted during conditions that the subsurface intrusion was not occurring or occurring at levels not detectable or differentiable from that in background sources of the hazardous substance. (Due to resource limitations, site inspections are conducted over a limited period of time, usually 1 to 2 days.) Therefore, i t is important that the potential for exposure be included as a consideration when evaluating subsurface intrusion threats, especially when volatile substances are documented in the subsurface below regularly occupied structures. As also explained in sect ion 4.0 of the Proposal TSD, EPA is proposing to evaluate the potential for exposure for the subsurface intrusion component using the same concept and framework used to estimate the potential to release in other pathways. (See section 2.3 of current HRS.) As depicted in Figure 6 below, this involves predicting the probability of exposure in area(s) of subsurface contamination based***E.O. 12866 Review

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Page 47 of 162 on structural containment features of the regularly occupied structure and the route characteristics in the subsurface, includi ng hazardous substance physical and chemical properties and physical subsurface properties that influence the probability that intrusion is occurring.

Figure 6. Potential for Exposure

i. Structure Containment

– See section 5.2.1.1.2.1 of the Proposed HRS Addition

Containment within the current HRS is used to consider the barriers that are present that restrict the movement of hazardous substances. See the preamble to the 1988 Revised HRS (53 FR 51985, December 23, 1988) for supplemental information. For th e proposed subsurface intrusion component, the containment features considered represent structural features that block the movement of hazardous substances so as to minimize or prevent indoor exposures resulting from subsurface intrusion into a regularly occupied structure. As is consistent with the current HRS, EPA is proposing containment factor***E.O. 12866 Review

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Page 48 of 162 values that range from zero to ten where a low containment factor value indicates a low chance for exposure. For example, in Table 5

- 12 of the proposed HRS addition, a structure with no visible open preferential pathways fr om the subsurface has a lower containment value than a structure with documented open preferential pathways because open preferential pathways (e.g., sumps, foundation cracks) represent a situation in which a greater probability for subsurface intrusion t o occur is present. Supplemental information regarding containment and the factor values specified in Table 5

- 12 is provided in section 4.0 of the Proposal TSD.

ii. Route Characteristics

– See section 5.2.1.1.2 of the Proposed HRS Addition

The HRS uses “route characteristics” to index the relative degree to which hazardous substances move into or have already moved into specific areas, such as from a source into ground water, or for the subsurface intrusion component into a regularly occupied structure (see th e 1988 TSD and section 4.0 of the Proposal TSD for supplemental information). These characteristics represent the physical and chemical properties of the specific hazardous substances and the media in which they must have moved through or could move throug h. To determine which route characteristics are appropriate for evaluating potential exposure to subsurface hazardous substances, EPA examined the literature to identify the modeling methods that are currently used to estimate the levels of hazardous subst ance exposure. Numerous route characteristics and the relationship of these and site

- specific input requirements were identified. EPA also gave careful consideration to ensure that route characteristic factors may be measured or calculated on a site

- specif ic basis in a manner appropriate with current HRS evaluations. See section 4.0 of the Proposal TSD for supplemental information evaluated as part of this process.
EPA reviewed existing sensitivity analyses and performed further analyses to evaluate the in trinsic relationships among the examined route characteristics to identify those that have the greatest impact on potential for exposure. Based on the agency’s analysis, three factors represented the greatest impact on potential for exposure and for which sufficient site

- specific information could be collected during a site***E.O. 12866 Review

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Page 49 of 162 inspection: 1) depth to contamination, 2) vertical migration, and 3) vapor migration potential. These three factors are described in the following sections.

a. Depth to Contamination

– See section 5.2.1.1.2.2 of the Proposed HRS Addition The depth to contamination factor represents the vertical distance between contamination (either in soil, soil gas, or surficial ground water) and the lowest horizontal point of an overlying regularly
occup ied structure (e.g., a basement floor). This distance represents how far a hazardous substance would have had to travel through the subsurface to intrude into that structure. Based on available data, the probability of exposure decreases as the depth to co ntamination increases. In addition, as part of EPA ’s sensitivity analysis in developing route characteristics, at depths greater than 150 feet it became increasingly unlikely that exposure would occur and this fact is reflected in Table 5

- 13 (section 5.2.1 .1.2.2 of the Proposed HRS Addition). EPA is proposing depth to contamination factor values ranging from zero to ten, where increasing depth results in a lower factor value.
EPA is also proposing to give special consideration in two situations in which it is likely that exposure has occurred. One situation is when subsurface profiles may be impacted by channelized flow features, such as fractured bedrock or karst. The other situation is at locations where the contamination is measured directly below the st ructure (e.g., in subslab or enclosed/semi

- enclosed crawl space samples). These features reflect a situation with a high probability of exposure to intruded hazardous substances because of limited resistance to migration of the substances into the structur e. See section 4.0 of the Proposal TSD for supplemental information on how the depths to contamination were weighted when assigning the factor values to different distances.

b. Vertical Migration

– See section 5.2.1.1.2.3 of the Proposed HRS Addition The ver tical migration factor considers the geologic makeup of materials between a regularly occupied structure and the hazardous substance plume and the rate at which substances are likely to have moved through the materials. EPA is proposing to index vertical m igration based on two factors: effective***E.O. 12866 Review

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Page 50 of 162 porosity (or equivalently, the permeability) of geologic materials and the thickness of the lowest porosity layer. Factor values for effective porosity (as it relates to permeability) of geologic materials range fro m one to four and are based solely on the typical range of porosity of subsurface materials (e.g., gravel, sand, silt and clay). These factor values are used in conjunction with the thickness of the lowest porosity layer (greater than 1 foot thickness) to establish a vertical migration factor value , ranging from one to fifteen. As part of the vertical migration factor, EPA identified soil moisture content to potentially be a significant route characteristic variable. Thus, to incorporate soil moisture in E PA ’s assessment of potential for exposure, the agency used published “average soil moisture content” values for specific soil types. These averages were used to develop effective porosity/permeability factor values. See section 4.0 of the Proposal TSD for supplemental information.

c. Vapor Migration Potential

– See section 5.2.1.1.2.4 of the Proposed HRS Addition The vapor migration potential factor is based on hazardous substance

- specific chemical properties, including both the vapor pressure and Henry’s con stant values for hazardous substances associated with the site. This factor evaluates the volatile nature of these hazardous substances and is projected to be the most influential route characteristic factor on calculating potential for exposure based on a sensitivity analysis using subsurface migration modeling. When calculating the vapor migration potential, a factor value is determined only for the most volatile hazardous substance based on vapor pressure and Henry’s constant values. Those values are use d to establish the vapor migration potential factor value. See section 4.0 of the Proposal TSD for supplemental information on this topic.

iii. Calculation of the Potential for Exposure Factor Value

– See section 5.2.1.1.2.5 of the Proposed HRS Addition***E.O. 12866 Review

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Page 51 of 162 Consis tent with potential to release determinations in the HRS, the potential for exposure for this component is calculated by summing all route characteristic factor values and multiplying the sum by the containment factor value to determine a potential for exp osure factor value.

c. Calculation of the Likelihood of Exposure Factor Category Value

– See section 5.2.1.1.3 of the Proposed HRS Addition As in all HRS pathways and components, the likelihood of exposure factor category value is assigned based on the higher of the observed exposure (or release) value or the potential for exposure (or release) value. The maximum value assigned for the likelihood of exposure factor category is 550 and is assigned if observed exposure is documented. If observed exposure i s not documented, the value assigned when evaluating potential for exposure ranges between 0 and 500. This approach is consistent with the current HRS structure. See sections 2.2 of the 1988 Revised HRS TSD for supplemental information regarding this appro ach.

4. Waste Characteristics

– See section 5.2.1.2 of the Proposed HRS Addition The waste characteristics factor category is based on factors that are related to the relative risk considerations included in the basic HRS structure: 1) the toxicity or other potential adverse effects to a receptor from the releases, 2) the potential to biodegrade in the subsurface prior to intruding into a regularly occupied structure, and 3) the expected magnitude and duration of the exposure. The factors considered in determ ining the waste characteristics factor category value are the toxicity of the hazardous substances, the biodegradability of the hazardous substance, and an estimate of the quantity of the hazardous substances to which occupants could be exposed. Consistent with the soil exposure component, the assigned factor values are multiplied together to determine this category value for the subsurface intrusion component. (See sections 2.2 and 2.4 of the 1988 Revised HRS TSD for further discussion on the structure of this factor category and how it fits within the overall HRS structure.) How and why these factors are proposed to be included in this factor category is discussed below.***E.O. 12866 Review

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Page 52 of 162 a. Toxicity/Biodegradation

– See section 5.2.1.2.1 of the Proposed HRS Addition The comb ined toxicity/biodegradation factor includes consideration of both the toxicity and the possibility for biodegradation of hazardous substances being evaluated for HRS purposes. The toxicity factor in the overall HRS structure reflects the toxicity of a haz ardous substance associated with a release or exposure, and is assigned the same factor value for all the pathways and components in the current HRS. As in all HRS pathways and components, it is proposed to be assigned the same corresponding factor value a s for other parts of the HRS. The rationale for the assignment of the factor value is discussed in the section 2.3 of the 1988 Revised HRS TSD. This toxicity factor is based on the toxicity of the substances present at a site. In the HRS addition, a differ ent factor value is proposed to be assigned to each hazardous substance that an occupant has been or is potentially exposed to. The factor value is driven by the magnitude of each hazardous substance’s acute and chronic toxicity to humans. The toxicity fac tor value is directly related to the concentration at which the hazardous substance is known to have a health effect: the more toxic the chemical, the higher the toxicity value. Any hazardous substance identified in an observed exposure within the AOE or m eeting the observed release criteria in either the AOE or ASC will be assigned a toxicity factor value. The method for assigning this value is contained in section 2.4.1.1 of the current HRS (40 CFR 300, Appendix A) and is discussed in section 2. 3 of the 1 988 Revised HRS TSD. The biodegradation factor represents the possibility for a substance to biodegrade in the subsurface prior to intruding into a regularly occupied structure. The potential of a substance to biodegrade has been identified as a significant factor in numerous studies evaluating the potential for intrusion by a vapor. The possibility that a substance may biodegrade is both a substance

- and location

- specific evaluation that is influenced by factors such as molecular structure, makeup of the immediate subsurface g eology, and the presence or absence of oxygen within intervening unsaturated soils. Because many of the site

- specific characteristics impacting the rate of biodegradation are considered beyond the scope of a typical site investigation, EPA is proposing to evaluate biodegradation based on the***E.O. 12866 Review

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Page 53 of 162 substance being evaluated and if appropriate environmental conditions are present to ensure that sufficient biodegradation will occur to diminish the threat. Based on EPA ’s review of the current literature and

researc h on this topic, the assigned biodegradation factor is limited to only two possible factor values, one for substances that are readily biodegradable and the appropriate environmental factors are present, and one for when either of the se parameters are not present. It is EPA ’s determination that substances with relatively low structural complexity, such as petroleum and petroleum

- like substances (having straight carbon chain or simple ring structures), have the greatest potential to biodegrade in the subsur face while halogenated and poly

- aromatic ringed substances (e.g., tetrachloroethylene, PCBs) are less likely to significantly degrade as result of subsurface microbial activity. Therefore, if a substance is likely to biodegrade based on its structure and if there are appropriate environmental conditions present, the biodegradation factor value will be less than if the substances are not biodegradable or if environmental conditions are not conducive to biode gradation. In addition, if it has been documented that a hazardous substance has been found to have entered a regularly occupied structure, regardless of the substance or the site conditions, the biodegradation value is adjusted accordingly. See also section 5.0 of the Proposal TSD for additional discussi on regarding the inclus ion of a biodegradation factor. The toxicity and biodegradation factors are multiplied together to assign a combined factor value. If multiple substances are present, the highest combined factor value is selected for use in determini ng the waste characteristics factor category value, as discussed below.

b. Hazardous Waste Quantity

– See section 5.2.1.2.2 of the Proposed HRS Addition In the basic HRS structure used in all pathways and components, the hazardous waste quantity factor refle cts the risk consideration related to the magnitude and duration of either the release for a migration pathway or the exposure for an exposure pathway. In other words, for an exposure pathway, the risk posed by a release of hazardous substances is directly related to the amount of hazardous substances to which receptors (targets) are exposed and the length of the exposure.***E.O. 12866 Review

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Page 54 of 162 As explained in the preamble to the 1990 HRS and in the 1988 Revised HRS TSD, an estimate of the waste quantity associated with a site was the best surrogate for the amount of hazardous substances that receptors were exposed to and that the duration of the exposure was probably correlated to the magnitude of the exposure. In the current three migration pathways (ground water, surface wat er, air), the hazardous waste quantity factor reflects the total amount of hazardous substances in sources at the site to take into account not only where contamination has already migrated to, but also future migration of contamination to other locations. For the soil exposure pathway, however, the estimate does not include the total amount in or released from the site sources, but only the amount of hazardous substance in the top 2 feet of contaminated soils sources and in the surface portions of other so urce types in an area of observed contamination. (See sec tion 5.0.1 of the current HRS.)
EPA is proposing that since the subsurface intrusion component also focuses on exposure and not the amount of hazardous substances that might migrate to targets in the future, the waste quantity factor value for this component should also reflect only the amount of hazardous substances that people currently are exposed to, that is, the amount in regularly occupied structures. EPA is proposing a four

tiered hierarchical approach consistent with the current HRS (see section III.C of the preamble of the current HRS (55 FR 51542, December 14, 1990)) as well as minimum waste quantity factors (see section 2.4.2 of the current HRS). The minimum waste quantity factors are includ ed because of insufficient information at many sites to adequately estimate waste quantity with confidence, as discussed in section I of the preamble to the current HRS (55 FR 51533, December 14, 1990). The current HRS establishes a minimum waste quantity factor value of 10 for each pathway or component at sites with no actually contaminated targets and a waste quantity factor value of 100 for the migration pathways if observed exposure has been documented. (See sec tion 2.4.2 of the current HRS.) It is prop osed for the estimation of waste quantity for the subsurface intrusion component, that regularly occupied structures within the AOE and ASC be considered. For sites at which the component waste quantity (the sum waste quantities for all occupied structures in the AOE and ASC) is below 10, it***E.O. 12866 Review

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Page 55 of 162 is proposed that a minimum factor of 10 should apply the same as in other pathways and components. This minimum factor reflects that in a limited site inspection, it is likely that information on the actual waste quanti ty at a site may not be available and a lower value would likely underestimate the actual conditions. Furthermore, if any target is subject Level I or II contaminant concentrations a minimum hazardous waste quantity factor value of 100 could be assigned.
T he component waste quantity is the sum of all the waste quantities for all the regularly occupied structures found in both the AOE(s) and ASC(s). The component waste quantity factor value assigned is then based on the magnitude of this sum, subject to mini mum values. See section 5.0 of the Proposal TSD for supplemental information regarding this topic.

c. Calculation of the Waste Characteristics Factor Category Value

– See section 5.2.1.2.3 of the Proposed HRS Addition As in all HRS pathways and components, t he waste characteristics category value is the product of the toxicity/biodegradation factor value (or the functional equivalent) and the hazardous waste quantity factor value, scaled so as to be weighted consistently in all pathways. Similar to the likeli hood of exposure factor category, the waste characteristics factor category is subject to a maximum value to maintain the balance between factor categories. This approach is consistent with the current HRS structure. See sections 2.2 and 2.4 of the 1988 Re vised HRS TSD for supplemental information regarding this approach.

5. Targets

– See section 5.2.1.3 of the Proposed HRS Addition The targets factor is based upon estimates of the expected dose to each receptor and the number and type of receptors present. I n a human health risk assessment, it is critical to understand the nature and extent of exposure to individuals, populations, and resources. The relative risk assessment embodied within the HRS uses the targets factor as an index of the nature and extent o f exposure to individuals, populations, resources, and sensitive environments.***E.O. 12866 Review

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Page 56 of 162 a. Identification of Eligible Targets

– See section 5.2.1.3 of the Proposed HRS Addition. The target factors evaluated by all pathways under the current HRS include the followin g:

• The most exposed individual (i.e., nearest well for ground water migration, nearest intake for drinking water threat, food chain individual for human food chain threat, resident individual for resident population threat, and nearest individual for near by population threat and air migration),

• Populations (including residents, workers, students, and those in daycare),

• Resources (including economic and cultural uses of contaminated resources),

• Sensitive environments (except for the ground water migration pathway). (Examples of sensitive environments include government designated protected areas (e.g., national wildlife refuge), wetlands and critical habitat known to be used by a State or Federally

- designated threatened or endangered species.) See sections 2.5 and 5.1.3 of the current HRS for supplemental information on how e ligible targets are identified. Given that the subsurface intrusion component is proposed to be included as an exposure component within the modified soil exposure and subsurface intrusi on pathway, the agency is proposing to use the same target categories used in the current soil exposure pathway, including exposed individual, resident populations, workers, and resources. However, unlike the current soil exposure pathway, sensitive enviro nments are not being considered as eligible targets because exposures related to subsurface intrusion are limited to indoor areas and it is unlikely that sensitive environments would be exposed. See section 5.2.1.3 of the proposed HRS addition.

b. Exposed In dividual and Levels of Exposure

– See section 5.2.1.3.1 of the Proposed HRS Addition This section introduces the methods used to identify and establish the levels of contamination and benchmarks proposed to be used within the subsurface intrusion componen t. Additionally, the exposed***E.O. 12866 Review

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Page 57 of 162 individual factor is discussed, as well as how to apply a factor value based on the benchmarks and the resulting levels of exposure.

i. Identifying Levels of Exposure and Benchmarks for Subsurface Intrusion

– See section 5.2.1.3. 1 of the Proposed HRS Addition For all current HRS pathways, the magnitude of the values assigned to the individual and population factors depend on the concentration of the contamination to which the receptors (targets) are exposed. If receptors are expos ed to hazardous substance levels that meet observed release criteria, they are identified as actually contaminated; however, if the receptors are not exposed to hazardous substances that meet the observed release criteria but are within the target area bei ng evaluated, they may be considered potentially contaminated. Potential targets are evaluated because a typical site inspection may not identify the extent of contamination. A site inspection typically includes 1 to 3 days of sampling and investigation ac tivities. These limited investigations may not adequately characterize the annual or longer term indoor exposure levels (see page 4 of the 1988 SAB report and section 6.0 of the Proposal TSD), especially in the case of subsurface intrusion where seasonal a nd temporal fluctuations can significantly impact the rate of subsurface intrusion. Actually contaminated targets are further divided into two categories based on whether the hazardous substance concentrations are above standard health

- based benchmarks (o r for environmental receptors, ambient water quality criteria). If so, they are identified as Level I; if they are not, they are identified as Level II. See section 2.5.2 of the current HRS for a discus sion of applicable benchmarks.
EPA is proposing to use a similar target weighting structure in the subsurface intrusion component. (See sections 5.2.1.3.1 and 5.2.1.3.2 of the proposed HRS addition.) Those targets in the AOE are considered actually contaminated, whereas, those in the ASC a re considered potentially contaminated. The targets in an AOE are further divided into Level I and II, based on whether the hazardous substance concentrations are at or above identified health

- based benchmarks. EPA is proposing to use the following benchma rks for the subsurface intrusion component:***E.O. 12866 Review

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Page 58 of 162 • Screening concentrations for cancer

• Screening concentrations for noncancer toxicological responses Because targets associated with an observed exposure by direct observation are only considered subject to Level II contamination in all parts of the HRS and intrusion by contaminated ground water is documented by direct observation only, targets residing within a structure subject to intrusion by contaminated ground water are evaluated as Level II (see section 2.5 of the proposed HRS addition). The targets within an ASC are also further divided based on the type of sample (e.g., gas, soil, water) and the distance of the sample from the targets (e.g., the depth of the sample below the structure). Weighting factors ranging from 0.1 to 0.9 are then assigned accordingly as discussed below in section 5.c.ii. See also section III.H. of the preamble to the current HRS (55 FR 51547, December 14, 1990) for supplemental information.

ii. Exposed Individual

– See section 5.2.1.3. 1 of the Proposed HRS Addition

The standard HRS approach for scoring targets is to include a measure reflecting the maximum level of exposure to individuals. The reasonably maximally exposed individuals are those individuals in the eligible target populati on that are expected to be exposed to the highest concentration of the hazardous substance in question for a significant time. See section V.C.9 of the preamble to the proposed 1988 HRS (53 FR 51978, December 28, 1988) for supplemental information.
EPA is proposing to retain the basic scoring approach used throughout the current HRS for evaluating the exposed individual factor. As is consistent with all pathways, a value of 50 points is assigned if there is any individual exposed to Level I concentrations o r 45 points if there is any individual exposed to Level II concentrations. If there are no individuals exposed to Level I or Level II concentrations, but at least one individual is living or attending school or day care in a regularly occupied structure wi thin an ASC, EPA proposes to assign a value of 20. See section 2.5 of the current HRS for supplemental information as to how EPA addresses exposed individuals within the HRS structure.***E.O. 12866 Review

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Page 59 of 162 c. Population

– See section 5.2.1.3.2 of the Proposed HRS Addition The po pulation factor is evaluated using media

- specific, health

- based benchmarks as discussed above, and does not include workers. EPA is proposing to retain the current scoring methodology for weighting populations used throughout the HRS, with actual exposure more heavily weighted than those potentially exposed. The proposed subsurface intrusion component will evaluate populations based on the number of individuals located within an identified AOE (i.e., those populations exposed to Level I and Level II
concent rations) and the number of individuals located within an ASC (i.e., potential contamination as determined based on subsurface sampling), which is further subdivided as described in subsection ii below.

i. Weighting of Targets in the Area of Observed Exposure (AOE)

– See sections 5.2.1.3.2.1 and 5.2.1.3.2.2 of the Proposed HRS Addition
EPA is proposing to establish an AOE based on documented contamination meeting observed exposure criteria (either by direct observation or chemical analysis). Consistent with th e weighting of populations throughout the HRS (see section 2.5 of the current HRS), the proposed subsurface intrusion component will weight targets subject to Level I contaminant concentrations by a factor of 10 and weight targets subject to Level II conta minant concentrations by a factor of 1. For example, if a single residence occupied by a family of four was observed to be exposed to hazardous substance concentrations above a media

- specific, health

- based benchmark, the number of residents would be multi plied by 10 for a factor value of 40. However, if that same family was exposed to a hazardous substance and the hazardous substance concentration was below the applicable benchmark but met the criteria for observed exposure, the number of residents would b e multiplied by 1 for a factor value of 4. To ensure the entire population within an AOE is included in the HRS evaluation, both Level I and Level II factor values ar e counted and summed together. Within the AOE, EPA is proposing to consider as actually c ontaminated those populations in regularly occupied structures for which an observed exposures has not been established but the structures***E.O. 12866 Review

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Page 60 of 162 are surrounded by regularly occupied structures in which observed exposures have been identified, unless evidence ind icates otherwise. This action is proposed because it is considered likely that if sampled during the correct conditions, observed exposure would be identified in these structures at levels similar to those in surrounding structures. Targets inferred to be exposed to this contamination will be weighted as Level II as there are no actual sample results to compare against benchmarks. However, EPA has included the requirement of “unless available information indicates otherwise” to allow for situations where si te

- specific conditions clearly document that there could be no observed exposures in these structures. This concept of inferred exposure is also included in the existing soil exposure pathway and in the a ir migration pathway. In the case of multi

- story/mu lti

- tenant structures, all regularly occupied tenant spaces on a level with an observed exposure and all levels below are considered to be within an AOE, unless available information indicates otherwise. For multi

- story/multi

- tenant structures located with in an AOE, but where an observed exposure has not been documented, only those regularly occupied tenant spaces on the lowest level are considered to be within an AOE, unless available information indicates otherwise. (See sections 5.0.1 and 6.3 of the curr ent HRS.)

ii. Weighting of Targets in the Area of Subsurface Contamination (ASC)

– See section 5.2.1.3.2.3 of the Proposed HRS Addition
EPA is proposing to establish an ASC as defined by documented ground water, subslab, soil, semi

enclosed or enclosed crawl space, or soil gas contamination meeting observed release criteria. These areas are included in the subsurface intrusion component due to the potential that limited sampling conducted during a site inspection may not identify that subsurface intrusion is o ccurring because of the high temporal and spatial variability associated with detecting subsurface intrusion. Temporal and spatial differences can significantly impact the rate at which volatile hazardous substances enter a structure. However, when an ASC has been defined, that area represents a location where subsurface hazardous substances have the potential to intrude into a structure. EPA is limited in its extent of preliminary***E.O. 12866 Review

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Page 61 of 162 screening activities, and a single indoor air sampling event is unlikely to identify the full threat posed by subsurface intrusion. As is consistent with the 1990 HRS, EPA is proposing to weight these potentially exposed targets at a value less than those targets that have been identified to be actually exposed. Due to the variabi lity in subsurface intrusion rates, the potential weighting factor values for targets within an ASC range from 0.1 to 0.9 and depend on where the subsurface contamination has been found. Using EPA ’s vapor intrusion attenuation factors published in 2012 and basic subsurface contaminant transport concepts, EPA developed a relatively proportional weighting for potential targets based on the sampling media being considered. This range of weighting factors represents the proportional probability of a target to b e exposed as a result of contaminant intrusion from the subsurface in a variety of likely sampling scenarios. The potential target weighting factors presented in the proposed addition do not directly correspond to attenuation factors in themselves. Instead , the relative weighting between these values is based on the published attenuation factors. These weighting factors are presented in this manner to project that contaminants found in a crawl space sample, for example, are more likely to attenuate less bef ore entering into an overlying structure, and thus more likely to pose a threat, as opposed to those found in a shallow ground water sample.
EPA is proposing that the weighting of potential targets also reflect the distance to or the depth at which contamination is found. For any contamination found at a horizontal or vertical distance of five feet or less from a regularly occupied structure’s fou ndation, EPA is proposing to assign a minimum weighting factor of 0.4 regardless of the sample medium. Similarly, EPA is proposing to assign a weighing factor of 0.1 to any contamination found or inferred at depths greater than 30 feet regardless of sampli ng medium. These minimum weighting values are in response to an analysis of the data used in deriving published attenuation values. The attenuation values were published based on real

- world sampling data collected from numerous sites across the United Stat es. The majority of sampling data collected as part of this effort came from sites where contamination was generally found at depths less than 30 feet. Therefore, EPA considers the attenuation factors and relative weightings between them to***E.O. 12866 Review

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Page 62 of 162 only be appropr iate for shallower depths. The minimum value for the upper five feet allows consideration of sites where contamination is found at extremely shallow depths and therefore has a minimal vertical distance to travel before intruding into a regularly occupied s tructure. In the case of multi

- story/multi

- tenant structures, all regularly occupied tenant spaces on a level above one where an observed exposure has been documented or inferred, or where a gaseous indoor air sample meeting observed release criteria is p resent, are considered to be located within an ASC, unless available information indicates otherwise. For multi

- story/multi

- tenant structures located only within an ASC, only those regularly occupied tenant spaces within the lowest level are co nsidered in an HRS evaluation. The proposed weighting factors for targets within an ASC include:

• 0.9

- Population residing in a structure with levels of contamination in a semi

- enclosed or enclosed crawl space sample meeting observed release criteria.

• 0.9

- Populatio n residing in a tenant space of a multi

- story structure within an area of subsurface contamination located directly above a story with an observed exposure or a gaseous indoor air sample meeting observed release criteria.

• 0.4

- Population residing in a str ucture where levels of contaminants meeting observed release criteria are found in any sampling media at or within 5 feet horizontally or vertically of the structure foundation.

• 0.2

- Population residing in a structure where levels of contaminants meeting observed release criteria are found or inferred based on any underlying non

- ground water subsurface sample at a depth less than or equal to 30 feet

• 0.2

- Population residing in a structure within an area of subsurface contamination where levels of contamin ants meeting observed release criteria are inferred based on semi

- enclosed or enclosed crawl space samples in surrounding structures***E.O. 12866 Review

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Page 63 of 162 • 0.1

- Population residing in a structure where levels of contaminants meeting observed release criteria are found or inferr ed based on underlying ground water samples greater than 5 feet from the structure foundation.

• 0.1

- Population residing in a structure where levels of contaminants meeting observed release criteria are found or inferred based on any underlying sample at d epths greater than 30 feet. Additional information regarding this analysis is presented in section 6.0 of the Proposal TSD.

d. Workers

– See section 5.2.1.3.3 of the Proposed HRS Addition
EPA is proposing to include a worker factor in the subsurface intrusio n component. Such a consideration is included in all of the existing HRS pathways. This factor reflects the possibility that indoor workers can be exposed in a workplace to contamination from the subsurface. This worker factor evaluation is proposed to be structured the same as in the current soil exposure pathway. Currently, for the resident population threat of the soil exposure pathway, a factor value for workers is assigned based on the total number of workers present within the area established by obse rved contamination criteria. These factor values range from 0 to 15, depending on the number of workers exposed to outdoor contamination. (See section 5.1.3.3 of the current HRS.)
EPA is proposing to mirror the procedures in the resident population threat in the soil exposure component for assigning a worker factor value in the subsurface intrusion component. (See Table 5

- 4 in section 5.1.3.3 of the current HRS.) However, since it is anticipated that workers spend a larger percentage of their time indoors a nd therefore, may be more exposed to contamination resulting from subsurface intrusion than to outdoor soil (or other surface) contamination, EPA is proposing to assign workers exposed to subsurface intrusion a higher weighting (i.e., ranging from 0 to 45) . See section 6.0 of the Proposal TSD for supplemental information regarding EPA ’s decision to include workers within the subsurface intrusion component, as well as the basis for the weightings. It should also be noted that, in developing the current HRS , EPA investigated statutory, regulatory, and policy conditions that might restrict the inclusion of workers in target populations. This analysis***E.O. 12866 Review

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Page 64 of 162 found no broad statutory or regulatory authority for excluding workers covered by the Occupational Safety and Health Administration (OSHA) regulations from consideration as targets in the HRS when they are exposed to a CERCLA release. Although the definition of a release under CERCLA section 101(22) excludes “any release which results in exposure to persons solely within a workplace,” it only does so for purposes of claims by workers who are covered by state worker compensation laws. The legislative history of section 101(22) specifically anticipated that authority under CERCLA might, in appropriate cases, be used to respond to releases that migrate into a workplace. Thus, EPA concluded that there are no broad statutory or regulatory restrictions against evaluating CERCLA releases at OSHA

regulated facilities. Therefore, EPA has determined that the evaluation of the potential threat to workers posed by subsurface intrusion is not restricted at OSHA

- regulated facilities. EPA will use the HRS to evaluate releases and threats of a release to the environment, including situations where those releases may have entered a w orkplace; however EPA will generally not use the HRS to evaluate occupational sources of contamination that have not been released or threatened to release to the environment.

e. Resources

– See section 5.2.1.3.4 of the Proposed HRS Addition The resources target factor is evaluated in all pathways under the current HRS. A factor value of five is assigned if at least one resource is present and a factor value of zero if no resource is present. Eligible resources are pathway

- , component

- , or threat

- specific. These resources represent uses of a contaminated medium or area where exposures occur and are not covered by the other identified targets. For example, resources within the air migration pathway include commercial agriculture or silviculture and major/des ignated recreation areas. The resident population threat also includes commercial livestock production or grazing. See section III.I of the preamble to the current HRS (55 FR 51549, December 14, 1990) for supplemental information. Because subsurface intrus ion is limited to indoor spaces, EPA is proposing to include regularly occupied structures that are located within a defined AOE or ASC (as previously discussed in section***E.O. 12866 Review

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Page 65 of 162 VI.B.2 of this preamble) and in which populations may be exposed to contamination due to subsurface intrusion. For example, libraries, churches, and tribal facilities may qualify as eligible resources.

f. Calculation of the Targets Factor Category Value

– See section 5.2.1.3.5 of the Proposed HRS Addition As is done throughout the HRS, EPA is proposing to sum all of the target factor values together to establish a target factor category value in calculating the proposed subsurface intrusion component score. Unlike the likelihood of exposure and waste characteristics factor category value s in all HRS pathways, which are subject to maximum values, the target factor category is not limited in the current HRS. This is to ensure that all individuals, populations, resources, and sensitive environments are included; thereby, representing the ful l relative risk associated with the identified threat. It is also consistent with the direction of CERCLA section 105 to amend the HRS “to the maximum extent feasible” to address “the relative degree of risk to human health and the environment” by putting the emphasis on the number of receptors exposed to contamination.

6. Calculation and Incorporation of the Subsurface Intrusion Component Score into the HRS Site Score The following subsections summarize the calculation of the subsurface intrusion component score, how the component score is then used in the calculation of the soil exposure and subsurface intrusion pathway score, and how, in turn, the pathway score is subsequently incorporated into the HRS site score.

a. Calculation of the Subsurface Intrusion Component Score

– See section 5.2.2 of the Proposed HRS Addition
EPA is proposing to calculate the subsurface intrusion component score using the same algorithm as in other components and pathways of the HRS. (See section 2.2 of the 1988 Revised HRS TSD. ) This involves multiplying the likelihood of exposure factor category value times the waste characteristics factor category value times the targets factor category value and dividing that value by a weighting factor***E.O. 12866 Review

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Page 66 of 162 so that it has equal magnitude to other component scores (subject to a maximum value). The values are multiplied to reflect that it is the product of these values that represents a relative risk level. In a relative risk (or in a site

- specific risk) assessment, the use of the product of the fa ctor category values is considered appropriate because the magnitude of each of the factor category values reflects the probability of exposure occurring: likelihood of releases reflects the probability of exposure actually occurring, waste characteristics reflects the probable quantity and duration of the exposure, and targets reflect the probable number of receptors at risk. Thus, since each factor category value reflects a probability in a series of events, the overall probability associated with the ser ies is the product of the individual probabilities. For example, if any factor category value is zero, such as when there are no targets exposed or potentially exposed to subsurface intrusion, the component score is zero, consistent with there being no ris k due to subsurface intrusion.

b. Incorporation of the Subsurface Intrusion Component Score into the Soil Exposure and Subsurface Intrusion Pathway Score

– See section 5.3 of the Proposed HRS Addition The score for this restructured pathway is proposed to be a combination of two component scores. The subsurface intrusion component score is added to the soil exposure component score (subject to a maximum value) to determine the pathway score. The two component scores are proposed to be additive because the p opulations may be subjected to exposures separately via both routes: the soil exposure component reflects exposures to people when outside a structure and focuses on ingestion, while the subsurface intrusion component reflects exposures to people when insi de a structure and focuses on inhalation. Hence, the addition of the two component scores reflects the cumulative potential risk and is not double counting the relative risk. In addition, a pathway score can be assigned without scoring both the soil expos ure and subsurface intrusion components using this approach. It is possible for a site to have only one component evaluated and still reach the same pathway score as under the current HRS. It should be observed that because the scoring of the soil exposure component is not being altered, the soil exposure component would***E.O. 12866 Review

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Page 67 of 162 contribute the same score to the overall site score as it would if the subsurface intrusion component is not added.

c. Incorporation of the Soil Exposure and Subsurface Intrusion Pathway Scor e into a Site Score

– See section 2.1.1 of the Proposed HRS Addition
EPA is not proposing any changes to the methodology used to assign an overall site score due to the addition of the subsurface intrusion component to the soil exposure pathway and renamin g that pathway the soil exposure and subsurface intrusion pathway. The overall site score remains a function of four pathway scores and the same weighting is given to each pathway score as in the current HRS. See section 2.2 of the 1988 Revised HRS TSD for supplemental information on why the existing methodology was chosen.

7. Example Site Scoring Scenarios To evaluate the proposed subsurface intrusion component and factor category weighting, EPA developed three conceptual site scenarios: one that would not qualify for the NPL (score below 28.50); one that would qualify marginally for the NPL (score of about 28.50); and one that should clearly qualify for the NPL (site score considerably above 28. 50). The first scenario consists of a ground water plume contaminated with a hazardous substance with moderate toxicity that underlies approximately 3 acres of a residential neighborhood comprised of single

family detached homes. Indoor air samples have be en collected from inside two homes and have reported hazardous substance concentrations above background, but below the applicable benchmarks. Additionally, several other occupied structures were sampled for indoor air and subslab contaminant concentration s; however, no other detections of hazardous substances were observed. This site would not qualify for the NPL based on available informa tion (i.e., score below 28.50). The second scenario also consists of a ground water plume contaminated with a hazardous substance with moderate toxicity as in the first scenario, but it has a considerably larger plume and more targets.***E.O. 12866 Review

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Page 68 of 162 The ground water plume underlies approximately 20 acres of a residential neighborhood comprised of single

- family detached homes. Indoor air samples collected inside 14 homes have hazardous substance concentrations above the applicable benchmark. Indoor air samples in 5 homes and one daycare facility with approximately 25 children enrolled have hazardous substance concentrations above backgrou nd, but below the applicable benchmark. The homes and daycare facility were checked for indoor sources of hazardous substances prior to sampling and such sources were removed if found. This site would likely qualify for the NPL based on available informati o n (i.e., score of about 28.50). The third scenario consists of a ground water plume contaminated with a highly toxic hazardous substance and a larger number of targets than the second scenario. The plume underlies approximately 25 acres of a residential n eighborhood and hazardous substance concentrations above a benchmark were detected in indoor air samples from 25 homes and one daycare with approximately 25 children enrolled. Hazardous substance concentrations above background but below benchmarks were de tected within 15 homes. The homes and daycare facility were checked for indoor sources of hazardous substances prior to sampling and such sources were removed if found. Based on available information, this site would qualify for the NPL and would likely ac hieve the maximum HRS score for a single compo nent and pathway (i.e., 50.00). Further evaluation of the varying factor values and resulting HRS site scores, along with further discussion of these three scenarios is presented in section 8.1.c of the Proposa l TSD.

VII. Terminology Updates Affecting Specific Sections of the HRS (Sections 2 & 5) During the development of this proposed addition to the HRS, the agency determined that the following terms should be updated to reflect current terminology and procedures used by EPA in performing risk assessments. A. Ambient Water Quality Criteria: Ambient Water Quality Criteria (AWQC) are now identified also as National Recommended Water Quality Criteria (NRWQC). In addition, the acute AWQC are now identified as the Criterion Maximum Concentration (CMC) and the chronic criteria are referred to as***E.O. 12866 Review

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Page 69 of 162 the Criterion Continuous Concentration (CCC). (See section 1.1 of the proposed HRS addition.) These criteria are used to determine the level of threat to environmental target s. B. Reference Concentrations: For inhalation exposures, EPA is adopting the use of Reference Concentrations (RfCs) instead of Reference Doses (RfDs) when determining non

- cancer related risk levels. RfCs are used in determining the level of threat to human t argets due to possible inhalation and when determining the toxicity of the substances. C. Cancer Unit Risk: For inhalation exposures, EPA is adopting the use of Inhalation Unit Risk (IUR) instead of cancer slope factors in determining cancer

- related risk leve ls. IURs are used in determining the level of threat to human targets due to possible inhalation and when determining the toxicity of the substances.
D. Weight

- of

- Evidence Groupings: The 2005 EPA weight

- of

- evidence groupings supporting the designation of a su bstance as a human carcinogen have been incorporated into the HRS algorithm for determining the toxicity factor value. (The former EPA weight

- of

- evidence categories included as part of the 1990 HRS have been retained as EPA has not yet completed assigning all substances to the revised categories and are doing so at the time the EPA substance literature reviews are updated.) These terminology updates are reflected in the HRS addition and do not represent any substantive change in the application of the HRS.

VIII. Statutory and Executive Order Reviews Additional information about these statutes and Executive Orders can be found at http://www2.epa.gov/laws

- regulations/laws

- and

- executive

- orders

. A. Executive Order 12866: Regulatory Planning and Review and Executive Order 13563: Improving Regulation and Regulatory Review This action is a significant regulatory action that was submitted to the Office of Management and Budget (OMB) for review. This action may raise novel legal or policy issues arising out of legal mandates, the President’s priorities, or the principles set forth in the EO. Any changes made in response***E.O. 12866 Review

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Page 70 of 162 to OMB reco mmendations have been documented in the docket.
EPA prepared an analysis of the potential costs and benefits associated with this action. This analysis, Addition of a Subsurface Intrusion (SsI) Component to the Hazard Ranking System (HRS): Regulatory Im pact Analysis is available in the docket for this action.

B. Paperwork Reduction Act (PRA ) This action does not impose any new information collection burden under the PRA. OMB has previously approved the information collection activities contained in th e existing regulations and has assigned OMB control number 2050

- 0179 (formerly 2050

- 0095 prior to consolidation)

. This proposed regulatory change will only affect how EPA and organizations performing work on behalf of EPA (state or tribal partners) conduct site assessments and HRS scoring at sites where certain environmental conditions exist. This proposed regulatory change will result in data collection at these types of sites to allow evaluation under the HRS. EPA expect s that the total number of site assessments performed and the number of sites added to the NPL per year will not change , but rather expects that there will be a realignment and reprioritization of its internal resources and state cooperative agreement fund ing.

C. Regulatory Flexibility Act (RFA) I certify that this action will not have a significant economic impact on a substantial number of small entities under the RFA. This action will not impose any requirements on small entities. This proposed regulatory change enables the HRS evaluation to directly consider human exposure to hazardous substances that enter building structures through subsurface intrusion. This addition to the HRS would not impose direct impacts on any other entiti es. For additional discussion on this subject see section 4.9 of the Regulatory Impact Analysis (see the docket for this action.

D. Unfunded Mandates Reform Act (UMRA)***E.O. 12866 Review

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Page 71 of 162 This action does not contain any unfunded mandate as described in UMRA, 2 U.S.C. 153 1

- 1538, and does not significantly or uniquely affect small governments. The action imposes no enforceable duty on any state, local, or tribal governments or the private sector.

E. Executive Order 13132: Federalism This action does not have federalism implications. It will not have substantial direct effects on the states, on the relationship between the national government and the states, or on the distribution of power and responsibilities among the various levels of government

.

F. Executive Order 13175: Consultation and Coordination with Indian Tribal Governments This action does not have tribal implications, as specified in Executive Order 13175. EPA ’s evaluation of a site using the HRS does not impose any costs on a tribe (except those already in a cooperative agreement relationship with EPA ). Thus, Executive Order 13175 does not apply to this action. Although Executive Order 13175 does not apply to this action, EPA consulted with tribal officials through meetings and correspondence, including a letter sent to all federally recognized tribes asking for comment on the “Notice of Opportunity for Public In put” that was published in the Federal Register on January 31, 2011 (76 FR 5370), and public listening sessions regarding the decision to proceed with the development of this action. All tribal comments indicated support for this action.
EPA specificall y solicits additional comment on this proposed action from tribal officials.

G. Executive Order 13045: Protection of Children from Environmental Health and Safety Risks
EPA interprets Executive Order 13045 as applying only to those regulatory actions that concern environmental health or safety risks that EPA has reason to believe may disproportionately affect children, per the definition of “covered regulatory action” in section 2

- 202 of the Executive Order. This action is not subject to Executive Or der 13045 because it does not concern an environmental health risk***E.O. 12866 Review

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Page 72 of 162 or safety risk.

H. Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution or Use This action is not a “significant energy action” b ecause it is not likely to have a significant adverse effect on the supply, distribution, or use of energy. The site assessment activities affected by this rule are limited in scope and number and rely on existing energy distribution systems. Further, we h ave concluded that this proposed rule would not significantly expand the energy demand for site assessments, and would not require an entity to conduct any action that would require significant energy use, that would significantly affect energy supply, dis tribution, or usage. Thus, Executive Order 13211 does not apply to this action.

I. National Technology Transfer and Advancement Act This rulemaking does not involve technical standards.

J. Executive Order 12898: Federal Actions to Address Environmental Justice in Minority Populations and Low

- Income Populations
EPA believes the human health or environmental risk addressed by this action will not have potential disproportionately high and adverse human health or environmental effects on minority, low

- income or indigenous populations. The results of this evaluation are contained in section III.C.4 of this preamble and section 4.3 (and all subsectio ns) and Appendix C of the Regulatory Impact Analysis for this proposed rulemaking. A copy of the Addition of a Subsurface Intrusion (SsI) Component to the Hazard Ranking System (HRS): Regulatory Impact Analysis is available in the docket for this action.

K. Executive Order 12580

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Page 73 of 162 Executive Order 12580, section 1(d), states that revisions to the NCP shall be made in consultation with members of the National Response Team (NRT) prior to publication for notice and comment. Revisio ns shall also be made in consultation with the Director of the Federal Emergency Management Agency (FEMA) and the Nuclear Regulatory Commission (NRC) to avoid inconsistent or duplicative requirements in the emergency planning responsibilities of those agen cies. Executive Order 12580 delegates responsibility for revision of the NCP to EPA

. The agency has complied with Executive Order 12580 to the extent that it is related to the addition of a new component to the HRS, through consultation with members of the NRT.

List of Subjects in 40 CFR Part 300 Environmental protection, Air pollution control, Chemicals, Hazardous substances, Hazardous waste, Intergovernmental relations, Natural resources, Oil pollution, Penalties, Reporting and recordkeeping requirements , Superfund, Water pollution control, Water supply.

Dated:

Gina McCarthy, Administrator.

For the reasons set out in the preamble, Title 40, Chapter 1 of the Code of Federal Regulations is proposed to be amended as follows:
Appendix A of Part 300
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Page 74 of 162 1. The authority citation for Appendix A of Part 300 continues to read as follows:

Authority: 42 U.S.C. 9601

- 9657; 33 U.S.C. 1321(d); E.O. 11735, 38 FR 21243; E.O. 12580, 52 FR 2923; E.O. 12777, 56 FR 54757

2. Section 1.0 of Appendix A is amended by revising the text of subsection 1.1 as follows:

a. In the definition of “Ambient Water Quality Criteria (AWQC),” replace “Ambient Water Quality Criteria (AWQC)” with “Ambient Water Quality Criteria (AWQC)/Nati onal Recommended Water Quality Criteria”; in the text of this definition, replace “maximum acute or chronic toxicity” with “maximum acute (Criteria Maximum Concentration or CMC) or chronic (Criterion Continuous Concentration or CCC) toxicity.”

b. Following t he definition of “CERCLA,” add a definition for “Channelized flow.”

c. In the text of the definition for Chronic toxicity, replace the words “Reference Dose (RfD) values” with the words “Reference Dose (RfD) and Reference Concentration (RfC) values.”

d. Following the definition of “Contract

- Required Detection Limit (CRDL),” add a definition for “Crawl space.”

e. Re vise the text of the definition of “Distance weight

. ” f. In the text of the definition for “HRS ‘pathway’,” re place the words “soil exposure” with the words “soil exposure and subsurface intrusion.”

g . Following the definition of “Hydrolysis,” add definitions for “Indoor air” and “Inhalation Unit Risk (IUR) .”***E.O. 12866 Review

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Page 75 of 162 h

. Following the definition of “Mixed radioactive and other hazardous substances,” a dd a definition for “Multi

- tenant structures.”

i

. Following the definition of “National Emission Standards for Hazardous Air Pollutants (NESHAPs),” add a definition for “Occupied structures.”
j

. Following the definition of “Photolysis,” add a definition fo r “Preferential subsurface intrusion pathways.”

k

. Following the definition of “Radionuclide/radioisotope,” add a definition for “Reference concentration (RfC).”

l. Revise the text of the definition of “Reference dose (RfD).”

m . Revise the definition of “S creening concentration.”

n . Revise the definition of “Slope factor (also referred to as cancer potency factor) .”

o . Following the definition of “Slope factor (also referred to as cancer potency factor),” add definitions for “Soil gas” and “Soil porosity.”

p . Following the definition of “Source,” add definitions for “Subslab,” “Subsurface Intrusion” and “Surficial ground water

. ”

q . Following the definition of “Target Distance Limit,” add definitions for “Unit Risk” and “Unsaturated Zone.”

r . Revis e the definition of “Weight

- of

- evidence.”

1.1 Definitions

* * * * ****E.O. 12866 Review

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Page 76 of 162 Ambient Water Quality Criteria (AWQC)/National Recommended Water Quality Criteria: EPA's maximum acute (Criteria Maximum Concentration or CMC) or chronic (Criterion Contin uous Concentration or CCC) toxicity concentrations for protection of aquatic life and its uses as established under section 304(a)(1) of the Clean Water Act, as amended.

* * * * *
Channelized flow: Natural geological or manmade features such as karst, fractures, lava tubes , and utility conduits (e.g., sewer lines), which allow ground water and/or soil gas to move through the subsurface environment more easily

. Chronic toxicity : * * * HRS measures of chronic toxicity include Reference Dose (RfD) and Reference Concentration (RfC) values.

* * * * *
Crawl space: The enclosed or semi

- enclosed area between a regularly occupied structure’s foundation (e.g., pier and beam construction) an d the ground surface. Crawl space samples are collected to determine the concentration of hazardous substances in the air beneath a regularly occupied structure.

* * * * *
Distance weight: Parameter in the HRS air migration pathway , ground water migrat ion pathway , and the soil exposure component of the soil exposure and subsurface intrusion pathway that reduces the point value assigned to targets as their distance increases from the site. [unitless].

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Page 77 of 162 HRS "pathway": Set of HRS factor categ ories combined to produce a score to measure relative risks posed by a site in one of four environmental pathways (that is, ground water, surface water, soil exposure and subsurface intrusion, and air).

* * * * *

Indoor air: The air present within a s tructure.
Inhalation Unit Risk (IUR): The upper

- bound excess lifetime cancer risk estimated to result from continuous exposure to an agent (i.e., hazardous substance) at a concentration of 1μg/m 3 in air.

* * * * *

Multi

- tenant structures: Structures t hat contain more than one commercial, residential, or industrial tenant space (e.g., apartment buildings, shopping centers, day care centers). They may or may not have multiple stories, and the tenant space may be on more than one floor.

* * * * *

Occu pied structures: Structures with enclosed air space, either where people are present on a regular basis or that were previously occupied but vacated due to a site

- related hazardous substance(s).

* * * * *
Preferential subsurface intrusion pathways: Sub surface features such as animal burrows, cracks in walls, spaces around utility lines or drains through which a hazardous substance moves more easily into a regularly occupied structure

.
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Page 78 of 162 Reference concentration (RfC): An estimate of a contin uous inhalation exposure to the human population that is likely to be without an appreciable risk of deleterious effects during a lifetime

. Reference dose (RfD) : An estimate of a daily oral exposure to the human population that is likely to be without an appreciable risk of deleterious effects during a lifetime.

* * * * *
Screening concentration: * * * The screening concentration for a specific hazardous substance corresponds to its reference concentration for inhalation exposures or reference dose for oral exposures, as appropriate, and, if the substance is a human carcinogen with either a weight

- of

- evidence classification of A, B, or C, or a weight

- of

- evidence classification of carcinogenic to humans, likely to be carcinogenic to humans or suggesti ve evidence of carcinogenic potential, to that concentration that corresponds to its 10 − 6 individual lifetime excess cancer risk for inhalation exposures or for oral exposures, as appropriate.

* * * * *
Slope factor (also referred to as cancer potency factor): * * * The slope factor is typically used to estimate upper

- bound probability of an individual developing cancer as a result of exposure to a particular level of a human carcinogen with either a weight

- of

- evidence classification of A, B, or C, o r a weight

- of

evidence classification of carcinogenic to humans, likely to be carcinogenic to humans or having suggestive evidence of carcinogenic potential. [(mg/kg

- day)
− 1 for non

- radioactive substances and (pCi)
− 1 for radioactive substances].
Soil gas: T he gaseous elements and compounds in the small spaces between particles of soil.
Soil porosity: The degree to which the total volume of soil is permeated with pores or cavities through which fluids (including air or gas) can move. It is typically calculate d as the ratio of the pore spaces within the soil to the overall volume of the soil.***E.O. 12866 Review

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Page 79 of 162 * * * * *

Subslab: The area immediately beneath a regularly occupied structure with a basement foundation or a slab

- on - grade foundation. Subslab samples are collected to determine the concentration of hazardous substances in the soil gas beneath a home or building.
Subsurface Intrusion: The migration of hazardous substances from th e unsaturated zone and/or the surficial ground water into overlying structures.
Surficial ground water: The uppermost saturated zone, typically unconfined .

* * * * *

Unit Risk: The upper

- bound excess lifetime cancer risk estimated to result from cont inuous exposure to an agent (i.e., hazardous substance) at a concentration of 1 μg/L in water, or 1 μg/m 3 in air.

Unsaturated Zone: The portion of subsurface between the land surface and the zone of saturation. It extends from the ground surface to the surficial water table (excluding localized or perched water).

* * * * *
Weight

- of

- evidence: * * * T he EPA weight

- of

- evidence groupings , depending on the date EPA updated the profile , include either:

* * * * *

or:

• Carcinogenic to humans.

• Lik ely to be carcinogenic to humans.

• Suggestive evidence of carcinogenic potential.***E.O. 12866 Review

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Page 80 of 162 • Inadequate information to assess carcinogenic potential.

• Not likely to be carcinogenic to humans.

3. Section 2.0 of Appendix A is amended as follows:
a. By revising subsecti on 2.1 and subordinate subsections 2.1.1, 2.1.2 and 2.1.3.
b. By revising subsection 2.2 and subordinate subsections 2.2.1, 2.2.2 and 2.2.3.
c. By revising subsection 2.3.
d. By revising subsection 2.4 and subordinate subsection s 2.4.1, 2.4.1.1, 2.4.1.2 , 2.4.2, 2.4.2.1, 2.4.2.1.1, 2.4.2.1.2, 2.4.2.1.3, 2.4.2.1.4, 2.4.2.1.5, 2.4.2.2 , and 2.4.3.1.
e. By revising Table 2

- 4 to add RfC and IUR assigned values.
f. By revising subsection 2.5 and subordinate subsections 2.5.1 and 2.5.2.

2.0 Eval uations Common to Multiple Pathways

2.1 Overview

* * * * *

• Soil Exposure and Subsurface Intrusion (S sessi).

* * * * *
The ground water and air migration pathways use single threat evaluations, while the surface water migration and soil exposure and subsurface intrusion pathways use multiple threat evaluations. * * * Two components are evaluated for the soil exposure and subsurface intrusion pathway: soil exposure and***E.O. 12866 Review

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Page 81 of 162 subsurface intrusion. The soil exposure component evaluates two threa ts: resident population and nearby population, and the subsurface intrusion component is a single threat evaluation.
The HRS is structured to provide a parallel evaluation for each of these pathways, components and threats. This section focuses on these pa rallel evaluations, starting with the calculation of the HRS site score and the individual pathway scores.

**2.1.1 Calculation of HRS site score.**  * * *



### SS = � SS

gggg 2 

### + SS ss 2 

### + SS ssssssssss 2 

### + SS aa 2 

### 4

2.1.2 Calculation of pathway score

. * * * As Table 2

- 1 shows, each pathway (component or threat) score is the product of three "factor categories": likelihood of release, waste characteristics, and targets. (The soil exposure and subsurface intrusion pathway uses likelihood of exposure rather than likelihood of release.) * * *

2.1.3 Common evaluations

. * * *

* * * * *

– Identifying sources (and, for the soil exposure and subsurface intrusion pathway, areas of observed contamination , areas of observed exposure , and/or areas of subsurface contamination [see sections 5.1.0 and 5.2.0]). Identifying hazardous substances associated with each source (or area of observed contamination or observed exposure).

* * * * *

– Scoring observed release (or observed exposure or observed contamination)

. * * ****E.O. 12866 Review

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Page 82 of 162  Combining toxicity with mobility, persistence, biodegradation , and/or bioaccumulation (or ecosystem bioaccumulation) potential, as appropriate to the pathway (component or threat).

* * * * *
* * * However, the evaluations differ in certain respects for the soil exposure and subsurface intrusion pathway. * * *
Section 2 focuses on evaluations common at the pathway, component and threat levels. * * *

2.2 Characterize sources

. * * *

• Sources (and areas of observed contamination , areas of observed exposure , or areas of subsurface contamination ) at the site.

• Hazardous substances associated with these sources (or areas of observed contamination , areas of observed exposure , or areas of subsurface contamination ).

* * * * *

2.2.1 Identify sources

. * * * For the soil exposure and subsurface intrusion pathway, identify areas of observed contamination , areas of observed exposure , and/or areas of subsurface contamination at the site (see sections 5.1.0 and 5.2.0).***E.O. 12866 Review

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Page 83 of 162 T ABLE 2 - 2. S AMPLE S OURCE C HARACTERIZATION W ORKSHEET

Source: __________________ A. Source dimensions and hazardous waste quantity.

Hazardous constituent quantity: ___ Hazardous wastestream quantity: ___ Volume: ___ Area: ___ Area of observed contamination: ___ Area of observed exposure : ___ Area of subsurface contamination : ___

B. Hazardous substances associated with the source.

Hazardous Substance Available to Pathway

Air Ground
water (GW) Surface Water (SW) Soil Exposure/Subsurface Intrusion (SES S I)
Soil Exposure Subsurface Intrusion

Gas Particulate Overland/ flood GW
to SW Resident Nearby Area of Observed Exposure Area of Subsurface Contamination

..... ..... ..... ..... ..... ..... ..... ..... ..... .....

..... ..... ..... ..... ..... ..... ..... ..... ..... .....

..... ..... ..... ..... ..... ..... ..... ..... ..... .....

..... ..... ..... ..... ..... ..... ..... ..... ..... .....

..... ..... ..... ..... ..... ..... ..... ..... ..... .....

2.2.2 Identify hazardous substances associated with a source

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Page 84 of 162 For an area of observed contamination in the soil exposure component of the soil exposure and subsurface intrusion pathway, consider only those hazardous substances that meet the criteria for observed contamination for that area (see section 5.1.0) to be associated with that area when evaluating the pathway.
For an area of observed exposure or area of subsurface contamination in the subsurface intrusion component of the soil exposu re and subsurface intrusion pathway, consider only those hazardous substances that meet the criteria for observed exposure or observed release associated with that area when evaluating the pathway (see section 5.2.0). Furthermore, evaluate an area of subsu rface contamination based only on the presence of hazardous substances with a vapor pressure greater than or equal to 10

- 9

torr . Consider those hazardous substances with in an area of subsurface contamination with a vapor pressure less than 10
- 5 , only if th ey have also been documente d to be in an observed exposure (see section 5.2.0 ).

2.2.3 Identify hazardous substances available to a pathway

. * * *

* * * * *
In evaluating the soil exposure and subsurface intrusion pathway, consider the following hazardous substances available to the pathway:

• Soil exposure component

— resident population threat.

− All hazardous substances that meet the criteria for observed contam ination at the site (see section 5.1.0).

• Soil exposure component

— nearby population threat.

− All hazardous substances that meet the criteria for observed contamination at areas with an attractiveness/accessibility factor value greater than 0 (see section 5. 1.2.1.1).***E.O. 12866 Review

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Page 8 5 of 162 • Subsurface intrusion component.

− All hazardous substances that meet the criteria for observed exposure at the site (see section 5.2.0).

− All hazardous substances with a vapor pressure less than 10
- 5 torr that meet the criteria for an observed relea se in the area of subsurface contamination at the site (see section 5.2.0).

− All hazardous substances with a vapor pressure less than 10
- 5 torr but greater than or equal to 10
- 9 torr that meet the criteria for observed release in an area of subsurface conta mination, and that have also been documented to be in an observed exposure at the site (see section 5.2.0)

.

2.3 Likelihood of release

. * * *

* * * (The criteria in Table 2

- 3 are also used in establishing observed contamination for the soil exposure component and for establishing areas of observed exposure and areas of subsurface contamination in the subsurface intrusion component of the soil exposure and subsurface intrusion pathway, see section 5.1.0 and section 5.2.0.) 

### * * *

2. 4 Waste characteristics



### . The waste characteristics factor category includes the following factors: hazardous waste quantity, toxicity, and as appropriate to the pathway or threat being evaluated, mobility, persistence, biodegradation, and/or bioaccumulation (or ecosystem bioaccumulation) potential.

2.4.1 Selection of substance potentially posing greatest hazard

. For all pathways (components and threats), select the hazardous substance potentially posing the greatest hazard for the pathway (component or threat) and use that substance in evaluating the waste characteristics category of the pathway (component or threat). For the three migration pathways (and threats), b ase the selection of this hazardous substance on the toxicity factor value for the substance, combined with its mobility, persistence, and/or bioaccumulation (or ecosystem bioaccumulation) potential factor values, as applicable***E.O. 12866 Review

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Page 86 of 162 to the migration pathway (or threat). For the soil exposure component of the soil exposure and subsurface intrusion pathway, base the selection on the toxicity factor alone . F or the sub surface intrusion component of the soil exposure and subsurface intrusion pathway, base the selecti on on the toxicity factor value for the substance , combined with its biodegradation factor value . Evaluation of the toxicity factor is specified in section 2.4.1.1. Use and evaluation of the mobility, persistence, biodegradation , and/or bioaccumulation (or ecosystem bioaccumulation) potential factors vary by pathway (component or threat) and are specified under the appropriate pathway (component or threat) section. Section 2.4.1.2 identifies the specific factors that are combined with toxicity in evaluating each pathway (component or threat).

**2.4.1.1 Toxicity factor** 

. * * *

* * * * *

• Cancer

— Use slope factors (also referred to as cancer potency factors) combined with weight

- of

evidence ratings for carcinogenicity for all exposure routes except inhalation. * * * If an inhalation unit risk or a slope factor is not available for a substance, use its ED 10 value to estimate a slope factor as follows:

* * * * *

• Noncancer toxicological responses of chronic exposure

— use reference dose (RfD) or reference concentration (RfC) values as applicable

.
* * * * *

• If RfD/RfC and slope factor/ inhalation unit risk values are available for the hazardous substance, assign the substance a value from Table 2

- 4 for each. Select the higher of the two value s assigned and use it as the overall toxicity factor value for the hazardous substance.***E.O. 12866 Review

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Page 87 of 162 • If either an RfD/RfC or slope factor/ inhalation unit risk value is available, but not both, assign the hazardous substance an overall toxicity factor value from Table 2

- 4 based solely on the available value (RfD/RfC or slope factor/ inhalation unit risk ).

• If neither an RfD/RfC nor slope factor/ inhalation unit risk value is available, assign the hazardous substance an overall toxicity factor value from Table 2

- 4 based so lely on acute toxicity. That is, consider acute toxicity in Table 2

- 4 only when both RfD/RfC and slope factor/ IUR values are not available.

• If neither an RfD/RfC, nor slope factor/ inhalation unit risk , nor acute toxicity value is available, assign the haz ardous substance an overall toxicity factor value of 0 and use other hazardous substances for which information is available in evaluating the pathway.***E.O. 12866 Review

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Page 88 of 162 T ABLE 2 - 4. T OXICITY F ACTOR E VALUATION***E.O. 12866 Review

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Page 89 of 162 Chronic Toxicity (Human)

Reference dose (RfD) (mg/kg - day) Assigned Value

RfD < 0.0005 10,000

0.0005 ≤ RfD < 0.005 1,000

0.005 ≤ RfD < 0.05 100

0.05 ≤ RfD < 0.5 10

0.5 ≤ RfD 1

RfD not available 0

Reference concentration (RfC) (mg/m 3) Assigned value RfC < 0.0001 10,000 0.0001 ≤ RfC < 0.006 1,000 0.006 ≤ RfC < 0.2 100 0.2 ≤ RfC < 2.0 10 2.0 ≤ RfC 1 RfC not available 0 Carcinogenicity (Human)
Weight - of - evidence a /Slope factor (mg/kg - day) - 1 Assigned value A or Carcinogenic to humans B or Likely to be carcinogenic to humans C or Suggestive evidence of carcinogenic potential

0.5 ≤ SF b 5 ≤ SF 50 ≤ SF 10,000

0.05 ≤ SF < 0.5 0.5 ≤ SF < 5 5 ≤ SF < 50 1,000***E.O. 12866 Review

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Page 90 of 162 SF < 0.05 0.05 ≤ SF < 0.5 0.5 ≤ SF < 5 100

_ _ _ SF < 0.05 SF < 0.5 10
Slope factor not available. Slope factor not available. Slope factor not available. 0 Weight - of - evidence a /Inhalation unit risk (μg/m 3)
A or Carcinogenic to humans B or Likely to be carcinogenic to humans C or Suggestive evidence of carcinogenic potential Assigned value

0.00004 ≤ IUR c 0.0004 ≤ IUR 0.004 ≤ IUR 10,000 0.00001 ≤ IUR < 0.00004 0.0001 ≤ IUR < 0.0004 0.001 ≤ IUR < 0.004 1,000 IUR < 0.00001 0.00001 ≤ IUR < 0.0001 0.0001 ≤ IUR < 0.001 100

_ _ _ < 0.00001 IUR < 0.0001 10 Inhalation unit risk not available. Inhalation unit risk not available. Inhalation unit risk not available. 0

a A, B, and C, as well as Carcinogenic to humans, Likely to be carcinogenic to humans, and Suggestive evidence of carcinogenic potential refer to weight

- of

- evidence categories. Assign substances with a weight

- of

- evidence category of D (inadequate evidence of carcinogenicity) or E (evidence of lack of carcinogenicity) , as well as inadequate information to assess carcinogenic potential and not likely to be carcinogenic to humans a value o f 0 for carcinogenicity.
* * * * *

c IUR = Inhalation Unit Risk.

* * * * *

**2.4.1.2 Hazardous substance selection** 

. * * *

* * * * *
For the soil exposure and subsurface intrusion pathway, determine toxicity and toxicity/biodegradation factor values as follows:

• S oil exposure and subsurface intrusion

— soil exposure component

.***E.O. 12866 Review

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Page 91 of 162 – S elect the hazardous substance with the highest human toxicity factor value from among the substances that meet the criteria for observed contamination for the threat evaluated and use that substance in evaluating the waste characteristics factor category (see section 5.1.1.2.1)

.

• Soil exposure and subsurface intrusion

— subsurface intrusion component

. Determine a combined human toxicity/biod egradation factor value for each hazardous substance being evaluated that meets the criteria for observed exposure or meets the criteria for observed release and has a vapor pressure greater than or equal to 10
- 9 torr within an area of subsurface contamina tion . Those hazardous substances with a vapor pressure less than 10
- 5 torr but greater than or equal to 10
- 9 torr that meet the criteria for observed release in an area of subsurface contamination must also have been documented to be in an observed exposur e at the site. S elect the hazardous substance with the highest combined factor value and use that substance in evaluating the waste characteristics factor category (see section 5.2.1.2.1).

2.4.2 Hazardous waste quantity

. Evaluate the hazardous waste quantity factor by first assigning each source (or area of observed contamination , area of observed exposure , or area of subsurface contamination ) a source hazardous waste quantity value as specified below. Sum these values to obtain the hazardous waste qu antity factor value for the pathway being evaluated.

* * * * *
In evaluating the hazardous waste quanti ty factor for the soil exposure component of the soil exposure and subsurface intrusion pathway, allocate to each area of observed contamination only those hazardous substances that meet the criteria for observed contamination for that area of observed contamination and only those hazardous wastestreams that contain hazardous substances that meet the criteria for observed contamination for that ar ea of observed contamination. Do not consider other hazardous substances or hazardous wastestreams at the site in evaluating this factor for the soil exposure component of the soil
exposure and subsurface intrusion pathway.***E.O. 12866 Review

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Page 92 of 162 In evaluating the hazardous was te quantity factor for the subsurface intrusion component of the soil exposure and subsurface intrusion pathway, allocate to each area of observed exposure or area of subsurface contamination only those hazardous substances that meet the criteria for obser ved exposure or observed release for that area of observed exposure or area of subsurface contamination and only those hazardous wastestreams that contain hazardous substances that meet the criteria for observed exposure or observed release for that area o f observed exposure or area of subsurface contamination. Furthermore, include only those hazardous substances in an area of subsurface contamination with a vapor pressure greater than or equal to 10

- 9 torr. Do not consider other hazardous substances or haz ardous wastestreams at the site in evaluating this factor for the subsurface intrusion component of the soil exposure and subsurface intrusion pathway. When determining the hazardous waste quantity for multi

- tenant structures, use the procedures identified in section 5.2.1.2.2.

**2.4.2.1 Source hazardous waste quantity** 

. * * *
For the soil exposure component of the soil exposure and subsurface intrusion pathway, assign a source hazardous waste quantity value to each area of observed contamination, a s applicable to the threat being evaluated.
For the subsurface intrusion component of the soil exposure and subsurface intrusion pathway, assign a source hazardous waste quantity value to each regularly occupied structure within an area of observed
exposure or an area of subsurface contamination that has a structure containment factor value greater than 0

. For determining all hazardous waste quantity calculations except for an unallocated source or an area of subsurface contamination , evaluate using the following four measures in the following hierarchy:

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Page 93 of 162 * * * For an area of subsurface contamination, evaluate non

- radioactive hazardous substances using only the last two measures and evaluate radioactive hazardous substa nces using hazardous wastestream quantity only. See also section 7.0 regarding the evaluation of radioactive substances.

* * * * *

2.4.2.1.1 Hazardous constituent quantity

. * * *

* * * * *

• For the soil exposure and subsurface intru sion pathway

— soil exposure component, assign the area of observed contamination a value using the Tier A equation of Table 5

- 2 (section 5.1.1.2.2).

• For the soil exposure and subsurface intrusion pathway

— subsurface intrusion component, assign the area of observed exposure a value using the Tier A equation of Table 5

- 1 8 (section 5.2.1.2.2).
If the hazardous constituent quantity for the source (or area of observed contamination or area of observed exposure) is adequately determined (that is, the total mass of all CERCLA hazardous substances in the source and releases from the source [or in the area of observed contamination or area of observed exposure] is known or is estimated with reasona ble confidence), do not evaluate the other three measures discussed below. Instead assign these other three measures a value of 0 for the source (or area of observed contamination or area of observed exposure) and proceed to section 2.4.2.1.5.

If the haza rdous constituent quantity is not adequately determined, assign the source (or area of observed contamination or area of observed exposure) a value for hazardous constituent quantity based on the available data and proceed to section 2.4.2.1.2.

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Page 94 of 162 2.4.2.1.2 Hazardous wastestream quantity



### . Evaluate hazardous wastestream quantity for the source (or area of observed contamination or area of observed exposure) based on the mass of hazardous wastestreams plus the mass of any additional CERCLA po llutants and contaminants (as defined in CERCLA section 101[33], as amended) that are allocated to the source (or area of observed contamination or area of observed exposure). For a wastestream that consists solely of a hazardous waste listed pursuant to s ection 3001 of RCRA, as amended or that consists solely of a RCRA hazardous waste that exhibits the characteristics identified under section 3001 of RCRA, as amended, include the mass of that entire hazardous waste in the evaluation of this measure.

* * * * *

• For the soil exposure and subsurface intrusion pathway

— soil exposure component, assign the area of observed contamination a value using the Tier B equation of Table 5

- 2 (section 5.1.1.2.2).

• For the soil exposure and subsurface intrusion pathway

— subsurface intrusion component, assign the area of observed exposure a value using the Tier B equation of Table 5

- 1 8 (section 5.2.1.2.2).

* * * * *

2.4.2.1.3 Volume



### . Evaluate the volume measure using the volume of the source (or the volume of
the area of observed contamination , a r ea of observed exposure , or area of subsurface contamination ). For the soil exposure and subsurface intrusion pathway, restrict the use of the volume measure to those areas of observed contamination , a r eas of observed exp osure , or areas of subsurface contamination as specified in sections 5.1.1.2.2 and 5.2.1.2.2.

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Page 95 of 162 • For 

### the soil exposure and subsurface intrusion pathway

— soil exposure component, assign the
area of observed contamination a value for volume using the appropriate Tier C equation of Table 5

- 2 (section 5.1.1.2.2).

• For the soil exposure and subsurface intrusion pathway

— subsurface intrusion component, assign the value based on the volume of the regularly occupied structures within the area of obse rved exposure or area of subsurface contamination using the Tier C equation of Table 5

- 1 8 (section 5.2.1.2.2).
If the volume of the source (or volume of the area of observed contamination , a r ea of observed
exposure, or area of subsurface contamination, if applicable) can be determined, do not evaluate the area measure. Instead, assign the area measure a value of 0 and proceed to section 2.4.2.1.5. If the volume cannot be determined (or is not applicable for the soil exposure and subsurface intrusion pathway ), assign the source (or area of observed contamination , area of observed exposure , or area of subsurface contamination ) a value of 0 for the volume measure and proceed to section 2.4.2.1.4.

2.4.2.1.4 Area
. Evaluate the area measure using the area of the source (or the area of the area of observed contamination , a rea of observed exposure , or area of subsurface contamination ). * * *

* * * * *



### • For 

### the soil exposure and subsurface intrusion pathway

— soil exposure component, assign the
area of observed contamination a value for area using the appropriate Tier D equation of Table 5

- 2 (section 5.1.1.2.2).

• For the soil exposure and subsurface intrusion pathway

— subsurface intrusion component, assign a value based on the area of regularly occupied st ructures within the area of observed exposure or area of subsurface contamination using the Tier D equation of Table 5

- 19 (section 5.2.1.2.2).***E.O. 12866 Review

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Page 96 of 162 2.4.2.1.5 Calculation of source hazardous waste quantity value



### . Select the highest of the values assigned to the source (or area of observed contamination , a r ea of observed exposure , or area of subsurface contamination ) for the hazardous constituent quantity, hazardous wastestream quantity, volume, and area measures. * * *

2.4.2.2 Calculation of hazardous waste quantity factor value

. Sum the source hazardous waste quantity values assigned to all sources (including the unallocated source) or areas of observed contamination , a r ea of observed exposure , or area of subsurface contamination ) for the pathway bein g evaluated and round this sum to the nearest integer, except: if the sum is greater than 0, but less than 1, round it to 1. * * *

* * * * *
For the soil exposure component of the soil exposure and subsurface intrusion pathway, if the hazardous c onstituent quantity is adequately determined for all areas of observed contamination, assign the value from Table 2

- 6 as the hazardous waste quantity factor value. * * *
For the subsurface intrusion component of the soil exposure and subsurface intrusion pathway, if the hazardous constituent quantity is adequately determined for all areas of observed exposure, assign the value from Table 2

- 6 as the hazardous waste quantity factor value. If the hazardous constituent quantity is not adequately determined fo r one or more areas of observed exposure, assign either the value from Table
2

- 6 or assign a factor value as follows:

• If any target for the subsurface intrusion component is subject to Level I or Level II concentrations (see section 2.5), assign either the value from Table 2

- 6 or a value of 100, whichever is greater, as the hazardous waste quantity factor value for this c omponent.

• If none of the targets for the subsurface intrusion component is subject to Level I or Level II concentrations and if there has been a removal action, assign a factor value as follows:***E.O. 12866 Review

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Page 97 of 162 − Determine the values from Table 2

- 6 with and without consideration of the removal action.

− If the value that would be assigned from Table 2

- 6 without consideration of the removal action would be 100 o r greater, assign either the value from Table 2

- 6 with consideration of the removal action or a value of 100, whichever is greater, as the hazardous waste quantity factor value for the component.

− If the value that would be assigned from Table 2

- 6 without c onsideration of the removal action would be less than 100, assign a value of 10 as the hazardous waste quantity factor value for the component.

• Otherwise, i f none of the targets for the subsurface intrusion component is subject to Level I or Level II conce ntrations and there has not been a removal action, assign a value from Table 2

- 6 or a value of 10, whichever is greater

* * * * *

2.4.3.1 Factor category value

. For the pathway (component or threat) being evaluated, multiply the toxicity or combined factor value, as appropriate, from section 2.4.1.2 and the hazardous waste quantity factor value from section 2.4.2.2, subject to a maximum product of 1x10 8 . Based on this waste characteristics product, assign a waste characteristics factor catego ry value to the pathway (component or threat) from Table 2

- 7.

* * * * *

2.5 Targets. * * *

• Individual (factor name varies by pathway , component, and threat).

* * * * ****E.O. 12866 Review

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Page 98 of 162 • Resources (these vary by pathway , component, and threat).

• Sensitive environments (included for the surface water migration pathway, air migration pathway, and soil exposure component of the soil exposure and subsurface intrusion pathway).

* * * * *

• Actual contamination: Target is associated either with a s ampling location that meets the criteria for an observed release (or observed contamination or observed exposure) for the pathway or with an observed release based on direct observation for the pathway (additional criteria apply for establishing actual con tamination for the human food chain threat in the surface water migration pathway, see sections 4.1.3.3 and 4.2.3.3). * * *

– Level I:

 Media

- specific concentrations for the target meet the criteria for an observed release (or observed contamination or o bserved exposure ) for the pathway and are at or above media

- specific benchmark values. * * *
* * * * *

− Level II:

 Media

- specific concentrations for the target meet the criteria for an observed release (or observed contamination or observed exposure) for the pathway, but are less than media

- specific benchmarks. * * *

 For observed releases or observed exposures based on direct observation, assign Level II to targets as specified in sections 3, 4, 5, and 6, or
* * * * ****E.O. 12866 Review

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Page 99 of 162 • * * * The value assigned is 20 unless reduced by a distance or dilution weight appropriate to the pathway.

* * * * *

• * * * (Level I is not used for sensitive environments in the soil exposure component of the soil exposure and subsurface intrusion and air migration pathways.)

• * * * Multiply potential targets in all but the soil exposure and subsurface intrusion pathway by distance or dilution weights appropriate to the pathway, sum, and divide by 10. * * * For targets within

an area of subsurface contamination in the subsurface intrusion component of the soil exposure and subsurface intrusion pathway, multiply by a weight ing factor as directed in section 5.2.1.3.2.3.

* * * * *

2.5.1 Determination of level of actual contamination at a sampling location



### . * * *

• Select the benchmarks applicable to the pathway (component or threat) being evaluated.

• Compare the concentrations of hazardous substances in the sample (or comparable samples) to their benchmark concentrations for the pathway (component or threat), as specified in section 2.5.2.

* * * * ****E.O. 12866 Review

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Page 100 of 162 • If none of the hazardous substances eligible to be evaluated for the sampling location has an applicable benchmark, assign Level II to the actual contamination at that sampling location for the pathway (component or threat).

In making the comparison, consider only those samples, and only those hazar dous substances in the sample, that meet the criteria for an observed release (or observed contamination or observed exposure) for the pathway, except: tissue samples from aquatic human food chain organisms may also be used as specified in sections 4.1.3.3 and 4.2.3.3 of the surface water

- human food chain threat. * * *

* * * * *

2.5.2 Comparison to benchmarks

. * * *

* * * * *

• EPA Ambient Water Quality Criteria (AWQC/National Recommended Water Quality Criteria) for protection of aquatic life

— environmental threat in surface water migration pathway.

* * * * *

• Screening concentration for cancer corresponding to that concentr ation that corresponds to the 10 − 6 individual cancer risk for inhalation exposures (air migration pathway or subsurface intrusion component of the soil exposure and subsurface intrusion pathway) or for oral exposures (ground water migration pathway; drinki ng water and human food chain threats in surface water migration pathway; and soil exposure and subsurface intrusion pathway).***E.O. 12866 Review

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Page 101 of 162 • Screening concentration for noncancer toxicological responses corresponding to the RfC for inhalation exposures (air migration pathway and subsurface intrusion component of the soil exposure and subsurface intrusion pathway) or RfD for oral exposures (ground water migration pathway; drinking water and human food chain threats in surface water migration pathway; and soil exposure a nd subsurface intrusion pathway).
Select the benchmark(s) applicable to the pathway (component or threat) being evaluated as specified in sections 3 through 6. Compare the concentration of each hazardous substance from the sampling location to its benchma rk concentration(s) for that pathway (component or threat). Use only those samples and only those hazardous substances in the sample that meet the criteria for an observed release (or observed contamination or observed exposure ) for the pathway, except: tissue samples from aquatic human food chain organisms may be used as specified in sections 4.1.3.3 and 4.2.3.3

. * * *

If no hazardous substance individually equals or exceeds its benchmark concentration, but more than one haza rdous substance either meets the criteria for an observed release (or observed contamination or observed exposure ) for the sample (or comparable samples) or is eligible to be evaluated for a tissue sample (see sections 4.1.3.3 and 4.2.3.3 ), calculate the i ndices I and J specified below based on these hazardous substances.

For those hazardous substances that are carcinogens (that is, those having either a carcinogen weight

of

- evidence classification of A, B, or C or a weight of evidence classification of ca rcinogenic to humans, likely to be carcinogenic to humans , or suggestive evidence of carcinogenic potential), calculate an index I for the sample location as follows:

* * * * ****E.O. 12866 Review

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Page 102 of 162 For those hazardous substances for which an RfD or RfC is available, calculate an index J for the sample location as follows:

* * * * *

CR j =Screening concentration for noncancer toxicological responses corresponding to RfD or RfC for applicable exposure (inhalation or oral) for hazardous substance j.

* * * * *

If either I or J equals or exceeds 1, consider the sampling location to be subject to Level I concentrations for that pathway ( component or threat). If both I and J are less than 1, consider the sampling location to be subject to Level II concentrations f or that pathway ( component or threat). * * *

* * * * ****E.O. 12866 Review

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Page 103 of 162 4. Section 5.0 of Appendix A is amended as follows:
a. By revising the designation of subsections as follows:

Section or Subsection Remove Add

5.0 n/a 5.0.1 and 5.1
5.0.1 5.0.1 5.1.0
5.1 5.1 5.1.1
5.1.1 5.1.1 5.1.1.1
5.1.2 5.1.2 5.1.1.2
5.1.2.1 5.1.2.1 5.1.1.2.1
5.1.2.2 5.1.2.2 5.1.1.2.2
5.1.2.3 5.1.2.3 5.1.1.2.3
5.1.3 5.1.3 5.1.1.3
5.1.3.1 5.1.3.1 5.1.1.3.1
5.1.3.2 5.1.3.2 5.1.1.3.2
5.1.3.2.1 5.1.3.2.1 5.1.1.3.2.1
5.1.3.2.2 5.1.3.2.2 5.1.1.3.2.2
5.1.3.2.3 5.1.3.2.3 5.1.1.3.2.3
5.1.3.3 5.1.3.3 5.1.1.3.3
5.1.3.4 5.1.3.4 5.1.1.3.4
5.1.3.5 5.1.3.5 5.1.1.3.5
5.1.3.6 5.1.3.6 5.1.1.3.6***E.O. 12866 Review

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Page 104 of 162 Section or Subsection Remove Add

5.1.4 5.1.4 5.1.1.4
5.2 5.2 5.1.2
5.2.1 5.2.1 5.1.2.1
5.2.1.1 5.2.1.1 5.1.2.1.1
5.2.1.2 5.2.1.2 5.1.2.1.2
5.2.1.3 5.2.1.3 5.1.2.1.3
5.2.2 5.2.2 5.1.2.2
5.2.2.1 5.2.2.1 5.1.2.2.1
5.2.2.2 5.2.2.2 5.1.2.2.2
5.2.2.3 5.2.2.3 5.1.2.2.3
5.2.3 5.2.3 5.1.2.3
5.2.3.1 5.2.3.1 5.1.2.3.1
5.2.3.2 5.2.3.2 5.1.2.3.2
5.2.3.3 5.2.3.3 5.1.2.3.3
5.2.4 5.2.4 5.1.2.4
5.3 5.3 5.1.3

b. By revising Section 5.0 to divide the introductory text into two numbered subsections (5.0.1 and 5.1) as indicated above, and revis ing text.
c. By redesignating subsection 5.0.1 as subsection 5.1.0 as indicated above, and revising text.***E.O. 12866 Review

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Page 105 of 162 d. By revising the title of Figure 5

- 1 from “Overview of Soil Exposure Pathway” to “Overview of the Soil Exposure and Subsurface Intrusion Pathway” and adding a subsurface intrusion component to the Figure.
e. By revising the title of Table 5

- 1 from “Soil Exposure Pathway Scoresheet” to “Soil Exposure Component Scoresheet,” reformatting the table, and revising the last two rows of the table to change “Soil Exposure Pathway” to “Soil Exposure Component” and “S s ” to “S se .”
f. By redesignating s ubsection 5.1 as subsection 5.1.1, redesignating subsection 5.1.1 as subsection 5.1.1.1, redesignating subsection 5.1.2 as subsection 5.1.1.2, as indicated above, and revising references contained in these subsections to reflect changed subsection designat ions.
g. By redesignating subsection 5.1.2.1 as subsection 5.1.1.2.1, redesignating subsection 5.1.2.2 as subsection 5.1.1.2.2, and redesignating subsection 5.1.2.3 as subsection 5.1.1.2.3, as indicated above.
h. By revising the title of Table 5

- 2 to remo ve “Pathway” and add in its place “Component.”
i. By redesignating subsection 5.1.3 as 5.1.1.3, redesignating subsection 5.1.3.1 as subsection 5.1.1.3.1, redesignating subsection 5.1.3.2 as subsection 5.1.1.3.2, redesignating subsection 5.1.3.2.1 as subsec tion 5.1.1.3.2.1, redesignating subsection 5.1.3.2.2 as 5.1.1.3.2.2, redesignating subsection 5.1.3.2.3 as subsection 5.1.1.3.2.3, redesignating subsection 5.1.3.3 as subsection 5.1.1.3.3, redesignating subsection 5.1.3.4 as subsection 5.1.1.3.4, redesigna ting subsection 5.1.3.5 as subsection 5.1.1.3.5, redesignating subsection 5.1.3.6 as subsection 5.1.1.3.6, and redesignating subsection 5.1.4 as subsection 5.1.1.4, as indicated above, and revising references contained in these subsections to reflect chan ged subsection designations.
j. By redesignating subsection 5.2 as subsection 5.1.2, redesignating subsection 5.2.1 as subsection 5.1.2.1, redesignating subsection 5.2.1.1 as subsection 5.1.2.1.1, redesignating subsection 5.2.1.2 as subsection 5.1.2.1.2, redesignating subsection 5.2.1.3 as subsection 5.1.2.1.3, redesignating subsection***E.O. 12866 Review

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Page 106 of 162 5.2.2 as subsection 5.1.2.2, redesignating subsection 5.2.2.1 as subsection 5.1.2.2.1, redesignating subsection 5.2.2.2 as subsection 5.1.2.2.2, redesignating subsection 5.2 .2.3 as subsection 5.1.2.2.3, redesignating subsection 5.2.3 as subsection 5.1.2.3, redesignating subsection 5.2.3.1 as subsection 5.1.2.3.1, redesignating subsection 5.2.3.2 as subsection 5.1.2.3.2, redesignating subsection 5.2.3.3 as subsection 5.1.2.3.3 , and redesignating subsection 5.2.4 as subsection 5.1.2.4, as indicated above, and revising references contained in these subsections to reflect changed subsection designations.
k. By redesignating subsection 5.3 as subsection 5.1.3 as indicated above, a nd revising text.
l. By adding subsection 5.2 and subordinate subsections 5.2.0, 5.2.1, 5.2.1.1, 5.2.1.1.1, 5.2.1.1.2, 5.2.1.1.2.1, 5.2.1.1.2.2, 5.2.1.1.2.3, 5.2.1.1.2.4, 5.2.1.1.2.5, 5.2.1.1.3, 5.2.1.2, 5.2.1.2.1, 5.2.1.2.1.1, 5.2.1.2.1.2, 5.2.1.2.1.3, 5. 2.1.2.2, 5.2.1.2.3, 5.2.1.3, 5.2.1.3.1, 5.2.1.3.2, 5.2.1.3.2.1, 5.2.1.3.2.2, 5.2.1.3.2.3, 5.2.1.3.2.4, 5.2.1.3.3, 5.2.1.3.4, 5.2.1.3.5 and 5.2.2.
m. By adding Tables 5

- 11, 5

- 12, 5

- 13, 5

- 14, 5

- 15, 5

- 16, 5

- 17, 5

- 18, 5

- 19, 5

- 20 and 5

- 21.
n. By adding subsect ion 5.3.

5.0 Soil Exposure and Subsurface Intrusion Pathway

5.0.1 Exposure c omponents
**.** Evaluate the soil exposure and subsurface intrusion pathway based on two exposure components:

• Soil exposure component (see section 5.1).

• Subsurface intrus ion component (see section 5.2)

Score one or both components considering their relative importance. If only one component is scored, assign its score as the soil exposure and subsurface intrusion pathway score. If both components are***E.O. 12866 Review

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Page 107 of 162 scored, sum the two s cores and assign it as the soil exposure and subsurface intrusion pathway score, subject to a maximum of 100.

5.1 Soil exposure component
**.** Evaluate the soil exposure component based on two threats: Resident population threat and nearby population th reat. * * *

Determine the soil exposure component score (S se ) in terms of the factor category values as follows:


## S se 

## = ∑ ( LE i 

## ) ( WC i 

## ) ( T i 

## ) 2 i = 1 

## SF

* * * * ****E.O. 12866 Review

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Page 108 of 162 Observed Contamination

Area with Resident Targets

Attractiveness / Accessibility Area of Contamination

Observed Exposure Potential for Exposure
• Structure Containment
• Depth to Contamination
• Vertical Migration
• Vapor Migration Potential Toxicity
• Chronic
• Carcinogenic
• Acute Hazardous Waste Quantity
• Hazardous Constituent Quantity
• Hazardous Wastestream Quantity
• Volume
• Area

Toxicity
• Chronic
• Carcinogenic
• Acute Biodegradation Hazardous Waste Quantity
• Hazardous Constituent Quantity
• Hazardous Wastestream Quantity
• Volume
• Area Resident Individual Resident Population
• Level I Concentrations
• Level II Concentrations Workers Resources Terrestrial Sensitive Environments

Nearby Individual Population Within One Mile

Exposed Individual Population
• Level I Concentrations
• Level II Concentrations
• Population on ASC Workers Resources Resident Population

Nearby Population

Subsurface Intrusion Component Toxicity
• Chronic
• Carcinogenic
• Acute Hazardous Waste Quantity
• Hazardous Constituent Quantity
• Hazardous Wastestream Quantity
• Volume
• Area Likelihood of Exposure ( LE ) Waste Characteristics ( WC ) Targets ( T )

Likelihood of Exposure ( LE ) Waste Characteristics ( WC ) Targets ( T ) 

# +

+ Likelihood of Exposure ( LE ) Waste Characteristics ( WC ) Targets ( T ) 

## X X

X X

X X Figure 5 - 1 Overview of the Soil Exposure and Subsurface Intrusion Pathway

Soil Exposure ComponentPage 109 of 162 T ABLE 5 - 1. S OIL E XPOSURE C OMPONENT S CORESHEET
Factor categories and factors Maximum value Value assigned
Resident Population Threat
Likelihood of Exposure

1. Likelihood of Exposure 550

Waste Characteristics
2. Toxicity (a)
3. Hazardous Waste Quantity (a)

4. Waste Characteristics 100
Targets

5. Resident Individual 50
6. Resident Population:

6a. Level I Concentrations (b)

6b. Level II Concentrations (b)

6c. Resident Population (lines 6a + 6b) (b)

7. Workers 15

8. Resources 5

9. Terrestrial Sensitive Environments (c)
10. Targets (lines 5 + 6c + 7 + 8 + 9) (b)
Resident Population Threat Score
11. Resident Population Threat (lines 1x4x10) (b)Page 110 of 162 Factor categories and factors Maximum value Value assigned
Nearby Population Threat
Likelihood of Exposure
12. Attractiveness/Accessibility 100

13. Area of Contamination 100
14. Likelihood of Exposure 500

Waste Characteristics
15. Toxicity (a)
16. Hazardous Waste Quantity (a)

17. Waste Characteristics 100
Targets
18. Nearby Individual 1
19. Population Within 1 Mile (b)
20. Targets (lines 18 + 19) (b)
Nearby Population Threat Score
21. Nearby Population Threat (lines 14x17x20) (b)
Soil Exposure Component Score
22. Soil Exposure Component Score d (S se ), (lines [11+21] /82,500, subject to a maximum of 100) 100

a Maximum value applies to waste characteristics category.

b Maximum value not applicable.

c No specific maximum value applies to factor. However, pathway score based solely on terrestrial sensitivePage 111 of 162 environments is limited to maximum of 60.

d Do not round to nearest integer.
5.1.0 General considerations

. Evaluate the soil exposure component based on areas of observed contamination:

* * * * *

• If an area of observed contamination (or portion of such an area) is covered by a permanent, or otherwise maintained, essentially impenetrable material (for example, asphalt) that is not more than 2 feet thick, exclude that area (or portion of the area) in evaluating the soil exposure component.

• For an area of observed contamination, consider only those hazardous substances that meet the criteria for observed contamination for that area to be associa ted with that area in evaluating the soil exposure component (see section 2.2.2).
If there is observed contamination, assign scores for the resident population threat and the nearby population threat, as specified in sections 5.1.1 and 5.1.2. If there is no observed contamination, assign the soil exposure component of the soil exposure and subsurface intrusion pathway a score of 0.

5.1.1 Resident population threat

. * * *

* * * * *

• Within the boundaries of a resource specified in section 5.1.1.3.4, or

• Within the boundaries of a terrestrial sensitive environment specified in section 5.1.1.3.5.Page 112 of 162 If not, assign the resident population threat a value of 0, enter this value in Table 5

- 1, and proceed to the nearby population threat (section 5.1.2).

5.1.1.1 Likelihood of exposure

. Assign a value of 550 to the likelihood of exposure factor category for the resident population threat if there is an area of observed contamination in one or more locations listed in section 5.1.1. * * *

5.1.1.2 Waste c haracteristics

. * * * Evaluate only those hazardous substances that meet the criteria for observed contamination at the site (see section 5.1.0).

5.1.1.2.1 Toxicity



### . * * *

5.1.1.2.2 Hazardous waste quantity



### . * * *

* * * * *

T ABLE 5 - 2. H AZARDOUS W ASTE Q UANTITY E VALUATION E QUATIONS FOR S OIL E XPOSURE C OMPONENT

* * * * *

5.1.1.2.3 Calculation of waste characteristics factor category value



### . * * *

* * * * *

5.1.1.3 Targets * * *

* * * * *

• Resources located on an area of observed contamination, as specified in section 5.1.1.

• Terrestrial sensitive environments located on an area of observed contamination, as specified in section 5.1.1.Page 113 of 162 5.1.1.3.1 Resident individual



### . Evaluate this factor based on whether the re is a resident individual, as specified in section 5.1.1.3, who is subject to Level I or Level II concentrations.

* * * * *

5.1.1.3.2 Resident population



### . * * * Evaluate populations subject to Level I concentrations as specified in section 5.1.1.3.2.1 and populations subject to Level II concentrations as specified in section 5.1.1.3.2.2.

* * * * *
Count only those persons meeting the criteria for resident ind ividual as specified in section 5.1.1.3. * * *

5.1.1.3.2.1 Level I concentrations



### . * * *

5.1.1.3.2.2 Level II concentrations



### . * * *

5.1.1.3.2.3 Calculation of resident population factor value



### . * * *

5.1.1.3.3 Workers



### . Evaluate this factor based on the number of workers that meet the
section 5.1.1.3 criteria. * * *

* * * * *

5.1.1.3.4 Resources



### . * * *

* * * * *

5.1.1.3.5 Terrestrial sensitive environments



### . Assign value(s) from Table 5

- 5 to each terrestrial sensitive environment that meets the eligibility criteria of section 5.1.1.3.Page 114 of 162 * * * * *
n=Number of terrestrial sensitive environments meeting section 5.1.1.3 criteria.

* * * * *

5.1.1.3.6 C alculation of resident population targets factor category value



### . * * *

5.1.1.4 Calculation of resident population threat score

. * * *

**5.1.2 Nearby population threat** 

. Include in the nearby population only those individuals who live or attend school within a 1

- mile travel distance of an area of observed contamination at the site and who do not meet the criteria for resident individual as specified in section 5.1.1.3.

Do not consider areas of observed contamination that have an attractiveness/ac cessibility factor value of 0 (see section 5.1.2.1.1) in evaluating the nearby population threat.

5.1.2.1 Likelihood of exposure

. * * *

5.1.2.1.1 Attractiveness/accessibility



### . * * *

5.1.2.1.2 Area of contamination



### . * * * Count only th e area(s) that meet the criteria in section 5.1.0 and that receive an attractiveness/accessibility value greater than 0. * * *

5.1.2.1.3 Likelihood of exposure factor category value



### . * * *

* * * * *

5.1.2.2 Waste characteristics

. * * * Evaluate only those hazardous substances that meet the criteria for observed contamination (see section 5.1.0) at areas that can be assigned an attractiveness/accessibility factor value greater than 0.Page 115 of 162 5.1.2.2.1 Toxicity



### . Assign a toxicity factor value as specified in section 2.4.1.1 to each hazardous substance meeting the criteria in section 5.1.2.2. * * *

5.1.2.2.2 Hazardous waste quantity



### . Assign a value to the hazardous waste quantity factor as specified in secti on 5.1.1.2.2, except: consider only those areas of observed contamination that can be assigned an attractiveness/accessibility factor value greater than 0. * * *

5.1.2.2.3 Calculation of waste characteristics factor category value



### . * * *

5.1.2.3 Targets

. * * *

5.1.2.3.1 Nearby individual



### . If one or more persons meet the section 5.1.1.3 criteria for a resident individual, assign this factor a value of 0. * * *

* * * * *

T ABLE 5 - 9
. N EARBY I NDIVIDUAL F ACTOR V ALUES

* * * * *

a Assign a value of 0 if one or more persons meet the section 5.1.1.3 criteria for resident individual.

5.1.2.3.2 Population within 1 mile



### . * * * Determine travel distances as specified in
section 5.1.2.3.1.

* * * * *

5.1.2.3.3 Calculation of nearby population targets factor category value

. * * *

5.1.2.4 Calculation of nearby population threat score

. * * *Page 116 of 162 **5.1.3 Calculation of soil exposure component score** 

. * * * Assign the resulting value, subject to a maximum of 100, as the soil exposure component score (S se ). 

### * * *

5.2 Subsurface intrusion component
**.** Evaluate the subsurface intrusion component based on three factor categories: likelihood of exposure, waste characteristics, and targets. Figure 5

- 1 indicates the factors included within each factor category for the subsurface intrusion component.

Determ ine the component score (S ssi ) in terms of the factor category values as follows:



## S ssi 

## = ( LE ) ( WC ) ( T ) SF

where:
LE=Likelihood of exposure factor category value. WC=Waste characteristics factor category value. T=Targets factor category value. SF=Scaling factor.

Table 5

- 11 outlines the specific calculation procedure.Page 117 of 162 T ABLE 5 - 11. S UBSURFACE I NTRUSION C OMPONENT S CORESHEET
Factor Categories and Factors Maximum
Value Value Assigned Subsurface Intrusion Component Likelihood of Exposure:

1. Observed Exposure 550

2. Potential for Exposure
2a. Structure Containment 10 2b. Depth to contamination 10 2c. Vertical Migration 15 2d. Vapor Migration Potential 25
3. Potential for Exposure (lines 2a * (2b+2c+2d), subject to a maximum of 500) 500

4. Likelihood of Exposure (higher of lines 1 or 3 ) 550
Waste Characteristics:

5. Toxicity /Biodegradation (a)

6. Hazardous Waste Quantity (a)

7. Waste Characteristics (subject to a maximum of 100) 100 Targets:
8. Exposed Individual 50
9. Population:
9a. Level I Concentrations (b)
9b. Level II Concentrations (b)
9c. Population with in an A rea of S ubsurface C ontamination (b)Page 118 of 162 9 d . Total Population (lines 9a + 9b + 9c) (b)

10. Workers 45

11. Resources 5

12. Targets (lines 8 + 9 d + 10 + 11) (b) Subsurface Intrusion Component Score
13. Subsurface Intrusion Component (lines 4 x 7 x 12)/82,500 c (subject to a maximum of 100) 100

Soil Exposure and Subsurface Intrusion Pathway Score
14. Soil Exposure Component + Subsurface Intrusion Component (subject to a maximum of 100) 100

a Maximum value applies to waste characteristics category.

b Maximum value not applicable.

c Do not round to the nearest integer
.

**5.2.0 General considerations** 

. Th e subsurface intrusion component evaluates the threats from hazardous substances that have or could intrude into regularly occupied structures via surficial ground water or the unsaturated zone. Evaluate the subsurface intrusion component based on the actu al or potential intrusion of hazardous substances into a regularly occupied structure(s), or contaminants from the unsaturated zone or the surficial ground water below the regularly occupied structure(s).

In evaluating the subsurface intrusion component, consider the following:

• Area(s) of observed exposure: An area of observed exposure is delineated by regularly occupied structures with documented contamination meeting observed exposure criteria; an area of observed exposure includes regularly occupied structures which are either contaminated orPage 119 of 162 inferred to be contaminated (see section 5.2.1.1.1 Observed Exposure ). Establish areas of observed exposure as follows:

– Consider both the sampling location(s) with observed exposure from the site and the area ly ing between such locations to be an area of observed exposure, unless available information indicates otherwise.

– In multi

- tenant structures, consider both the tenant space(s) with observed exposure from the site and all other regularly occupied tenant spa ces on that level and all levels below, if any, to be within an area of observed exposure, unless available information indicates otherwise.

– In multi

- tenant structures that have multiple stories and have not documented an observed exposure, but are located in an area lying between locations where observed exposures have been documented, consider only those regularly occupied tenant spaces, if any, on the lowest level, to be within an area of observed exposure, unless available information indicates otherwis e.

• Area(s) of subsurface contamination: An area of subsurface contamination is delineated by sampling locations meeting observed release criteria for subsurface intrusion, excluding areas of observed exposure (see Table 2

- 3 in section 2.3). The area withi n an area of subsurface contamination includes potentially exposed populations

. If the significant increase in hazardous substance levels cannot be attributed at least in part to the site and cannot be attributed to other sites, attribution can be establis hed based on the presence of hazardous substances in the area of subsurface contamination. Establish areas of subsurface contamination based on sampling locations at which there is contamination as follows:

– Consider both the sampling location(s) with subsu rface contamination from the site and the area lying between such locations to be an area of subsurface contamination, unless available information indicates otherwise.Page 120 of 162 – Exclude those areas meeting the criteria defined as an area of observed exposure.

– Evalu ate an area of subsurface contamination based only on the presence of hazardous substances with a vapor pressure greater than or equal to 10
- 9 torr that also meet the criteria for an observed release for any location associated with an area of subsurface c ontamination (see section 2.2.2). Consider those hazardous substances with a vapor pressure less than 10
- 5 , only if they have also been documented to be in an observed exposure. See Section 7.0 for establishing an area of subsurface contamination based on the presence of radioactive hazardous substances.

– Evaluate multi

- tenant structures as follows:

 If an observed exposure has been documented based on a gaseous indoor air sample, consider all regularly occupied tenant spaces, if any, on the level immediately above the level where an observed exposure has been documented (or has been inferred to be within an area of observed exposure), to be within an area of subsurface contamination, unless available information indicates otherwise.

 If observed release criter ia have been met based on a gaseous indoor air sample collected from a level not regularly occupied, consider all regularly occupied tenant spaces, if any, on the level immediately above the level where the observed release criteria has been documented, to be within an area of subsurface contamination, unless available information indicates otherwise.

 If an observed exposure has been documented based on an intruded liquid or particulate sample, do not consider any regularly occupied tenant spaces above the level where an observed exposure has been documented to be within an area of subsurface contamination, unless available information indicates otherwise.

 If no observed exposure has been documented in any regularly occupied tenant space(s) of a multi

- tenant structure that is located within an area lying betweenPage 121 of 162 locations where subsurface contamination sampling meets the criteria for an observed release, consider only those regularly occupied tenant spaces, if any, on the low est level, to be within an area of subsurface contamination, unless available information indicates otherwise.

If there is no area of observed exposure and no area of subsurface contamination, assign a score of 0 for the subsurface intrusion component.

**5 .2.1**  **Subsurface intrusion component**

. Evaluate the component only if there is an area of observed exposure or area of subsurface contamination:

• Within or underlying a residence, school, or day care center, or

• Within or underlying a workplace, or

• Within or underlying a resource specified in section 5.2.1.3.4.

5.2.1.1 Likelihood of exposure

. Assign a value of 550 to the likelihood of exposure factor category for the subsurface intrusion component if there is an area of observed exposure in one or

m ore locations listed in section 5.2.1. Enter this value in Table 5

- 11.

5.2.1.1.1 Observed exposure

. Establish observed exposure in a regularly occupied structure by demonstrating that a hazardous substance has been released into a regularly occupied structure via the subsurface. Base this demonstration on either of the following criterion :

• Direct observation:Page 122 of 162 – A solid, liquid or gaseous material that contains one or more hazardous substances attributable to the site has been observed entering a regularly occupied structure through migration via the subsurface or is known to have entered a regularly occupied structure via the subsurface, or

– When evidence supports the inference of subsurface intrusion of a material that contains one or more hazardous substances associated with the site into a regularly occupied structure, demonstrated adverse effects associated with that release may be used to establish observed exposure.

• Chemical analysis:

– Analysis of indoor samples indicates that t he concentration of hazardous substance(s) has increased significantly above the background concentration for the site for that type of sample (see section 2.3 ).

– Some portion of the significant increase must be attributable to the site to establish the ob served exposure. Documentation of this attribution should account for possible concentrations of the hazardous substance (s) in outdoor air or from materials found in the regularly occupied structure , and should provide a rationale for the increase being fr om subsurface intrusion

.

If observed exposure can be established in a regularly occupied structure, assign an observed exposure factor value of 550, enter this value in Table 5

- 11, and proceed to section 5.2.1.1.3 . If no observed exposure can be established, assign an observed exposure factor value of 0, enter this value in Table 5

- 11, and proceed to section 5.2.1.1.2

.Page 123 of 162 5.2.1.1.2 Potential for exposure

. Evaluate potential for exposure only if an observed
exposure cannot be established , but an area of subsurface contamination has been delineated

. Evaluate potential for exposure based only on the presence of hazardous substances with a vapor pressure greater than or equal to 10
- 5 torr. Evaluate potential for exposure for each area of subsurface contamination based on four factors: structure containment (see section 5.2.1.1.2.1 ) , depth to contamination (see section 5.2.1.1.2.2), vertical migration (see section 5.2.1.1.2.3) and vapor migration potential (see section 5.2 .1.1.2.4). For each area of subsurface contamination, assign the highest value for each factor. If information is insufficient to calculate any single factor value used to calculate the potential for exposure factor values at an identified area of subsurfa ce contamination, information collected for another area of subsurface contamination at the site may be used when evaluating potential for exposure. Calculate the potential for exposure value for the site as specified in section 5.2.1.1.2.5.

5.2.1.1.2.1 Structure containment

. Calculate containment for eligible hazardous substances
within this component as directed in Table 5

- 12 and enter this value into Table 5

- 11. Assign each regularly occupied structure within an area of subsurface contamination the highest appropriate structure containment value from Table 5

- 12 and u se the regularly occupied structure at the site with the highest structure containment value in performing the potential for exposure calculation. Assign a structure containment factor va lue of 10 to any regularly occupied structure located within an area of observed exposure that is established based on documented surficial ground water intrusion, unless available information indicates otherwise.

T ABLE 5 - 12 S TRUCTURE C ONTAINMENTPage 124 of 162 No. Evid ence of Structure Containment Assigned value

1. Regularly occupied structure with evidence of subsurface intrusion, including documented observed exposure or sampling of bio or inert gases, such as methane and radon 10

2. Regularly occupied structure with open preferential pathways from the subsurface (e.g., sumps, foundation cracks, unsealed utility lines) 10

3

. Regularly occupied structure with an engineered vapor migration barrier system that does not address all preferential pathways 7

4

. Regular ly occupied structure with an engineered passive vapor mitigation system without documented institutional controls (e.g., deed restrictions) or evidence of regular maintenance and inspection 6

5

. Regularly occupied structure with no visible open preferential pathways from the subsurface (e.g., sumps, foundation cracks, unsealed utility lines) 4

6

. Regularly occupied structure with an engineered passive vapor mitigation system (e.g., passive venting) with documented institutional controls (e.g., d eed restrictions) or evidence of regular maintenance and inspection 3

7

. Regularly occupied structure with an engineered, active vapor mitigation system (e.g., active venting) without documented institutional controls (e.g., deed restrictions) and funding in place for on

- going operation, inspection and maintenance 2

8

. Regularly occupied structure with unknown containment features 2

9

. Regularly occupied structure with an engineered, active vapor mitigation system (e.g., active venting) with documented institutional controls (e.g., deed restrictions) and funding in place for on

- going operation, inspection and maintenance 0Page 125 of 162 No. Evid ence of Structure Containment Assigned value

10. Regularly occupied structure with a foundation raised greater than 6 feet (e.g., structure on stilts) 0

5.2.1.1.2.2 Depth to contamination

. Assign each area of subsurface contamination a depth to contamination based on the least depth to either contaminated crawl space or subsurface media underlying a regularly occupied structure. Measure this depth to contamination based on the distance between the lowest point of a regularly occupied structure to the highest known point of hazardous substances eligible to be evaluated. Use any regularly occupied structure withi n an area of subsurface contamination with a structure containment factor greater than zero. Subtract from the depth to contamination the thickness of any subsurface layer composed of features that would allow channelized flow (e.g., karst, lava tubes, ope n fractures).

Based on this calculated depth, assign a factor value from Table 5

- 13. If the necessary information is available at multiple locations, calculate the depth to contamination at each location. Use the location having the least depth to contami nation to assign the factor value. Enter this value in Table 5

- 11.

T ABLE 5 - 13 D EPTH TO C ONTAMINATION
Depth range 1, 2 Depth to Contamination Assigned Value 0 to 10 ft.( Including s ubslab and semi

- enclosed or enclosed crawl space contamination) 10

>10 to 20ft 8Page 126 of 162 >20 to 50ft 6 >50 to 100ft 4 >100 to 150ft 2 >150ft 0

1 If any part of the subsurface profile has channelized flow features, assign that portion of the subsurface profile a

depth of 0.

2 Measure elevation below any regularly occupied structure within an area of subsurface contamination at a site. Select

the regularly occupied structure with the least depth to contamination below a structure.

5.2.1.1.2.3 Vertical migration

. Evaluate the vertical migration factor for each area of
subsurface contamination based on the geologic materials in the interval between the lowest point of a regularly occupied structure and the highest known point of hazardous substances in the subsurface. Use any regularly occupied structure either within an area of subsurface contamination or overlying subsurface soil gas or ground water contamination. Assign a value to the vertical migration factor as follows:

• If the depth to contamination (see section 5.2.1.1.2.2 ) is 10 feet or less, assign a value of 15.

• Do not consider layers or portions of layers within the first 10 feet of the depth to contamination.

• If, for the interval identified above , all layers that underlie a portion of a regularly occupied structure at the sit e are karst or otherwise allow channelized flow, assign a value of 15.

• Otherwise:

– Select the lowest effective porosity/permeability layer(s) from within the above interval. Consider only layers at least 1 foot thick. (If site

- specific data is not availab le, use the layer with the highest value assigned in Table 5

- 14

. )

– Assign a value for individual layers from Table 5

- 14.

– If more than one layer has the same assigned porosity/permeability value, include allPage 127 of 162 such layers and sum their thicknesses. Assign a t hickness of 0 feet to a layer with channelized flow features found within any area of subsurface contamination at the site.

– Assign a value from Table 5

- 15 to the vertical migration factor, based on the thickness and assigned porosity/permeability value of the highest effective porosity/permeability layer(s).

Determine vertical migration only at locations within an area of subsurface contamination at the site. If the necessary subsurface geologic information is available at multiple locations, evaluate the vertical migration factor at each location. Use the location having the highest vertical migration factor value to assign the factor value. Enter this value in Table 5

- 11.

T ABLE 5 - 14 E FFECTIVE P OROSITY /P ERMEABILITY OF G EOLOGIC M ATERIALS

Type of Material Assigned Porosity/Permeability Value
Gravel; highly permeable fractured igneous and metamorphic rocks; permeable basalt; karst limestones and dolomites. 1

Sand; sandy clays; sandy loams; loamy sands; sandy silts; sediments that are predominantly sand; highly permeable till (coarse

- grained, unconsolidated or compact and highly fractured); peat; moderately permeable limestones and dolomites (no karst); moderately permeable sandstone; moderately permeable fractured igneous and metamorphic rocks. 2

Silt; l oams; silty loams; loesses; silty clays; sediments that are predominantly silts; moderately permeable till (fine

- grained, unconsolidated till, or compact till with some 3Page 128 of 162 fractures); low permeability limestones and dolomites (no karst); low permeability sand stone; low permeability fractured igneous and metamorphic rocks.
Clay; low permeability till (compact unfractured till); shale; unfractured metamorphic and igneous rocks. 4

T ABLE 5 - 15 V ERTICAL M IGRATION F ACTOR V ALUES a Assigned Porosity/ Permeability Value Thickness of Lowest Porosity Layer(s) b (feet)

0 to 5 Greater than 5 to 10 Greater than 10 to 20 Greater than 20 to 50 Greater than 50 to 100 Greater than 100 to 150

1 15 15 14 11 8 6

2 15 14 12 9 6 4

3 15 13 10 7 5 2

4 15 12 9 6 3 1

a If depth to contamination is 10 feet or less or if, for the interval being evaluated, all layers that underlie a portion of the structure at the site are karst or have other channelized flow features, assign a value of 15.

b Consider only layers at least 1 foot thick.

5.2.1.1.2.4 Vapor migration potential

. Evaluate this factor for each area of subsurface
contamination as follows:

• If the depth to contamination (see section 5.2.1.1.2.2 ) is 10 feet or less, assign a value of
2 5

.

• Assign a value for vapor migration potential to each of the gaseous hazardous substances associated with the area of subsurface contamination (see section 2.2.2 ) as follows:Page 12 9 of 162 – Assign values from Table 5

- 16 for both vapor pressure and Henry's constant to eac h hazardous substance. If Henry's constant cannot be determined for a hazardous substance, assign that hazardous substance a value of 2 for the Henry's constant component.

– Sum the two values assigned to each hazardous substance.

– Based on this sum, assign each hazardous substance a value from Table 5

- 17 for vapor migration potential.

• Assign a value for vapor migration potential to each area of subsurface contamination as follows:

– Select the hazardous substance associated with the area of subsurface contamination with the highest vapor migration potential value and assign this value as the vapor migration potential factor for the area of subsurface contamination.

Enter this value in Table 5

- 11

.

T ABLE 5 - 16 V ALUES FOR V APOR P RESSURE AND H ENRY ’ S C ONSTANT Vapor Pressure (Torr) Assigned Value

Greater than 10 3

Greater than 10 - 3 to 10 2

10 - 5 to 10 - 3 1

Less than 10 - 5 0
Henry’s Constant (atm - m 3 /mol ) Assigned Value

Greater than 10 - 3 3Page 130 of 162 Greater than 10 - 5 to 10 - 3 2

10 - 7 to 10 - 5 1

Less than 10 - 7 0

T ABLE 5 - 17 V APOR M IGRATION P OTENTIAL F ACTOR V ALUES FOR A H AZARDOUS S UBSTANCE Sum of Values for Vapor Pressure and Henry’s Constant Assigned Value

0 0 1 or 2 5 3 or 4 15 5 or 6 25

5.2.1.1.2.5 Calculation of potential for exposure factor value

. For each identified area of subsurface contamination, s um the factor values for depth to contamination, vertical migration and vapor migration potential, and multiply this sum by the factor value for structure containme nt. Select the highest product for any area of subsurface contamination and a ssign this value as the potential for exposure factor value for the component . Enter this value in Table 5

- 11.

5.2.1.1.3 Calculation of likelihood of exposure factor category value

. If observed exposure is established for the site, assign the observed exposure factor value of 550 as the likelihood of exposure factor category value for the site. Otherwise, assign the potential for exposure factor value for the component as the l ikelihood of exposure value. Enter the value assigned in Table 5

- 11.

5.2.1.2 Waste characteristics

. Evaluate waste characteristics based on two factors: toxicity/biodegradation and hazardous waste quantity.Page 131 of 162 5.2.1.2.1 Toxicity/biodegradation

. For each hazardous substance, assign a toxicity factor value, a biodegradation factor value and a combined toxicity/biodegradation factor value as specified in sections 2.2.3 and 5.2.1.2.1.1 through 5.2.1.2.1.3.

5.2.1.2.1.1 Toxicity . Assign a toxicity factor value to each hazardous substance as specified in section s 2.2.2 and 2.4.1.1

.

5.2.1.2.1.2 Biodegradation . Assign a biodegradation factor value to each hazardous substance as follows:

• For any hazardous substance that meets the criteria for an observed exposure assign a biodegradation factor value of 1.

For all hazardous substances not meeting observed exposure criteria:

• For any petroleum or petroleum

- like hazardous substance that is known to readily biodegrade in the subsurfac e ( e.g., non - halogenated straight chain and single ring hydrocarbons), assign a biodegradation factor value of 0.5 if depth to contamination is greater than 30 feet , unless available evidence suggests that 30 feet of biologically active soil is not present in the subsurface

. Otherwise, assign a biodegradation factor value of 1.

• For all other hazardous substances being evaluated, assign a biodegradation factor value of 1.

5.2.1.2.1.3 Calculation of toxicity/biodegradation factor value . Assign each substance a toxicit y/biodegradation value by multiplying the toxicity factor value by the biodegradation factorPage 132 of 162 value. Use the hazardous substance with the highest combined toxicity/biodegradation value to assign the factor value to the toxicity/ biodegrada tion factor for the subsurface intrusion threat. Enter this value in Table 5

- 11.

5.2.1.2.2 Hazardous waste quantity

. Assign a hazardous waste quantity factor value as specified in section 2.4.2 . Consider only those regularly occupied structures with a non

- zero structure containment value. In estimating the hazardous waste quantity, use Tables 2

- 5 and 5

- 18 and:

• For Tier A, hazardous constituent quantity, use the mass of constituents found in the regularly occupied structure(s) where the observed exposure has been identified.

– For multi

- tenant structures, when calculating Tier A, use the mass of constituents found in the regularly occupied tenant space(s) where the observed exposure has been identified.

• For Tier B, hazardous wastestream quantity, use the fl ow - through volume of the regularly occupied structures where the observed exposure has been identified.

– For multi

- tenant structures, when calculating Tier B, use the flow

- through volume of the regularly occupied tenant spaces where the observed exposure ha s been identified.

• For Tier C, volume, use the volume divisor listed in Tier C of Table 5

- 18. Volume is calculated for those regularly occupied structures located within areas of observed exposure with observed or inferred intrusion and within areas of su bsurface contamination.Page 133 of 162 – In evaluating the volume measure for these listed areas of observed exposure and areas of subsurface contamination based on a gaseous/vapor intrusion or the potential for gaseous/vapor intrusion, consider the following:

 Calculate t he volume of each regularly occupied structure based on actual data. If unknown, use a ceiling height of 8 feet.

 For multi

- tenant structures, when calculating Tier C, calculate volume for those tenant spaces with observed or inferred exposure and all other regularly occupied tenant spaces on that level, unless available information indicates otherwise. If the structure has multiple stories, also include the volume of all regularly occupied tenant spaces below the floor with an observed exposure and one story above, unless evidence indicates otherwise.

 For multi

- tenant structures within an area of subsurface contamination and no observed or inferred exposure, consider only the volume of the regularly occupied tenant spaces on the lowest story, unless ava ilable information indicates otherwise.

– In evaluating the volume measure for these listed areas of observed exposure and areas of subsurface contamination where intrusion of contaminated ground water has occurred, do not calculate the volume of each regula rly occupied structure. Instead, consider only the volume of contaminated ground water known to have intruded into

a regularly occupied structure.

• For Tier D, area, if volume is unknown , use the area divisor listed in Tier D of Table 5

- 1 8 for those regular ly occupied structures with in area s of observed exposure with observed or inferred intrusion and within areas of subsurface contamination. In evaluating the area measure for these listed areas of observed exposure and areas of subsurface contamination, cal culate the area of each regularly occupied structure (including multi

- tenant structures) based on actualPage 134 of 162 footprint area data. If the actual footprint area of the structure(s) is unknown, use an area of 1,740 square feet for each residential structure (or r esidential tenant space).

T ABLE 5 - 1 8 H AZARDOUS W ASTE Q UANTITY E VALUATION E QUATIONS FOR S UBSURFACE I NTRUSION C OMPONENT

Tier Measure Units Equation for assigning value a

A Hazardous Constituent Quantity (C) lb C

B b Hazardous Wastestream Quantity (W) lb W/5,000

C b ,c Volume (V)
Regularly o ccupied structure(s) in area s of observed exposure or subsurface contamination yd 3 V/2.5

D b ,d Area (A)
Regularly o ccupied structure(s) in area s of observed exposure or subsurface contamination ft 2 A/13

a Do not round to the nearest integer.

b Convert volume to mass when necessary: 1 ton=2,000 pounds=1 cubic yard=4 drums=200 gallons.

c Calculate volume of each regularly occupied structure or tenant space in area s of observed exposure and areas of subsurface contamination

– Assume 8

- foot ceiling height unless actual value is known.

d Calculate area of the footprint of each regularly occupied structure in area s of observed exposure and areas of subsurface contamination

. If the footprint area of a regularly occupied structure is unknown, use 1, 74 0 square feet as the footprint area of the structure or tenant space

.
For the subsurface intrusion component , if the hazardous constituent quantity is adequately determined for all areas of observed exposure, assign the value from Table 2

- 6 as the hazardous waste quantity factor value. If the hazardous constituent quantity is not adequately determined for

one or more areas of observed exposure or if one or more areas of subsurface contamination are present , assign either the value from Table 2

- 6 or assign a factor value as follows:Page 135 of 162 • If any target for the subsurface intrusion component is subject to Level I or Leve l II concentrations (see section 2.5 ), assign either the value from Table 2

- 6 or a value of 100, whichever is greater, as the hazardous waste quantity factor value for this component

.

• If none of the targets for the subsurface intrusion component is subject to Level I or Level II concentrations and if there has been a removal action, assign a factor value as follows:

– Determine the values from Table 2

- 6 with and without consideration of the removal action.

– If the value that would be assigned from Tabl e 2

- 6 without consideration of the removal action would be 100 or greater, assign either the value from Table 2

- 6 with consideration of the removal action or a value of 100, whichever is greater, as the hazardous waste quantity factor value for the compone nt.

– If the value that would be assigned from Table 2

- 6 without consideration of the removal action would be less than 100, assign a value of 10 as the hazardous waste quantity factor value for the component.

• Otherwise, if none of the targets for the subsu rface intrusion component is subject to Level I or Level II concentrations and there has not been a removal action, assign a minimum value of 10.

Enter the value assigned in Table 5

- 11.

5.2.1.2.3 Calculation of waste characteristics factor category valu e . Multiply the toxicity /biodegradation and hazardous waste quantity factor values, subject to a maximumPage 136 of 162 product of 1x10 8 . Based on this product, assign a value from Table 2

- 7 ( section 2.4.3.1 ) to the waste characteristics factor category. Enter this value in Table 5

- 11.

5.2.1.3 Targets

. Evaluate the targets factor category for the subsurface intrusion threat based on four factors: exposed individual, population, workers, and resources in regularly occupied
structures . Evaluate only those targets within ar ea s of observed exposure and area s of subsurface contamination ( s ee section 5.2.0).
In evaluating the targets factor category for the subsurface intrusion threat, count only the following as targets:

• Exposed individual

— a person living or attending school or day care in a structure with observed exposure, or living in a structure within an area of observed exposure or within an area of subsurface contamination.

• Population

— an exposed individual or a person living or attending school or day care in a
structure within an area of observed exposure or within an area of subsurface contamination.

• Worker

— a person working in a structure within an area of observed exposure or within an area of subsurface contamination

.

• Resources

— located with in an area of observed exposure or within an area of subsurface contamination as specified in section 5.2.1.3.4.

If a former structure that has been vacated due to subsurface intrusi on attributable to the site, count the initial targets as if they were still residing in the structure. In addition, if a removal action has occurred that has not completely removed the release, count the initial targets as if the removal action had not oc curred unless it has been demonstrated that no significant risk remains.Page 137 of 162 For populations residing in or working in a multi

- tenant structure with multiple stories in an area of observed exposure or area of subsurface contamination, count these targets as f ollows:

• If there is no observed exposure within the structure, include in the evaluation only those targets, if any, in the lowest occupied level, unless available information indicates otherwise.

• If there is an observed exposure in any level, include in the evaluation those targets in that level, the level above and all levels below, unless available information indicates otherwise. (The weighting of these targets is specified in Section 5.2.1.3.2.)

5.2.1.3.1 Exposed individual

. Evaluate this factor based on whether there is an exposed individual, as specified in section s 2.5.1, 2.5.2 and 5.2.1.3 , who is subject to Level I or Level II concentrations.
First, determine those areas of observed exposure subject to Level I concentrations and those subject to Level II concentrations as specified as follows:

• For contamination resulting from subsurface intrusion, compare the hazardous substance concentrations in any sample meeting the observed exposure by chemical analysis criteria to the appropriate benchmark. If the concentration equals or exceeds the appropriate benchmark, assume Level I concentrations. For those regularly occupied structures and regularly occupied tenant spaces in a multi

- tenant structure that are located within an area of observed exposure for which subsurface intrusion is inferred, or if there is an observed exposure by direct observation only, assume Level II concentrations.

Use the he alth

- based benchmarks from Table 5

- 19 in determining the level of contamination. Then assign a value to the exposed individual factor as follows:Page 138 of 162 • Assign a value of 50 if there is at least one exposed individual in one or more regularly occupied structure s subject to Level I concentrations.

• Assign a value of 45 if there are no such exposed individuals, but there is at least one exposed individual living in one or more regularly occupied structures subject to Level II concentrations.

• Assign a value of 20 if there is no Level I or Level II exposed individual but there is at least one individual living or attending school or day care in a structure within an area of subsurface contamination.

Enter the value assigned in Table 5

- 11.

5.2.1.3.2 Population . Evaluate population based on three factors: Level I concentrations, Level II concentrations, and population within an area of subsurface contamination. Determine which factors apply as specified in section 5.2.1.3.1, using the health

- based benchmarks fro m Table 5

- 19. Evaluate populations subject to Level I and Level II concentrations as specified in section 2.5

.

T ABLE 5 - 19 H EALTH - B ASED B ENCHMARKS FOR H AZARDOUS S UBSTANCES IN THE S UBSURFACE I NTRUSION C OMPONENT

Screening concentration for cancer correspondi ng to that concentration that corresponds to the 10 −6 individual cancer risk using the inhalation unit risk

. For oral exposures use the oral cancer slope factor.
Screening concentration for noncancer toxicological responses corresponding to the r eference d ose (RfD) for oral exposure and the reference concentration (RfC) for inhalation exposures.

Count only those persons meeting the criteria for population as specified in section 5.2.1.3 . In estimating the number of people living in structures i n an area of observed exposure or area ofPage 139 of 162 subsurface contamination, when the estimate is based on the number of residences, if actual number is not known, multiply each residence by the average number of persons per residence for the county in which the re sidence is located.

5.2.1.3.2.1 Level I concentrations

. Sum the number of exposed individuals subject to Level I
concentrations and multiply this sum by 10. Assign the resulting product as the value for this factor. Enter this value in line 9a of Table 5

- 11.

5.2.1.3.2.2 Level II concentrations

. Sum the number of exposed individuals subject to Level
II concentrations. Do not include those people already counted under the Level I concentrations factor. Also, i nclude those people who regularly occupy a structure with in area s of inferred exposure in an area of observed exposure . Assign this sum as the value for this factor. Enter this value in line 9b of Table 5

- 11.

5.2.1.3.2.3 Population within an area of subsurface contamination

. The population in an
area of subsurface contamination is determined as follows , unless available information indicates otherwise :

1. Identify the regularly occupied structures and the population associated with each category:

• For single tenant structures, count all residents and students residing in or attending school or daycare in those structures

.

• In multi

- tenant structures where an area of subsurface contamination includes only those regularly occupied tenant spaces on the lowest level, count the number of residents and stude nts residing in or attending school or daycare in those tenant spaces.Page 140 of 162 • In multi

- tenant structures with multiple stories where an area of subsurface contamination includes regularly occupied tenant spaces in the level directly above a level with an observed exposure, sum the number of residents and students residing or attending school or daycare in those tenant spaces.

• In multi

- tenant structures with multiple stories where an area of subsurface contamination includes regularly occupied tenant spaces in the level directly above a level with a gaseous indoor air sample meeting observed release criteria, sum the number of residents and students residing in or attending school or daycare in those tenant spaces.

2. Estimate the depth or distance to contamination at each regularly occupied structure within an area of subsurface contamination based on available sampling data, and categorize each eligible structure based on the depth or distance to contamination and sampling media as presented in Table 5

- 20. Weight the population in each structure using the appropriate weighting factors in Table 5

- 20. If samples from multiple media are available, use the sample that results in the highest weighting factor.

3. Sum the weighted population in the area(s) of subsurface contam ination and assign this sum as the value for this factor. Enter this value in line 9c of Table 5

- 11.

T ABLE 5 - 2 0 W EIGHTING F ACTOR V ALUES F OR P OPULATIONS WITHIN AN A REA OF S UBSURFACE C ONTAMINATION

Eligible Populations a in Structures b within an Area of Subsurface Contamination Population Weighting

Factor Population residing in a structure with levels of contamination in a semi

- enclosed or enclosed crawl space sample meeting observed release criteria

o r 0.9Page 141 of 162 Eligible Populations a in Structures b within an Area of Subsurface Contamination Population Weighting

Factor Population residing in a tenant space of a multi

- story structure within an area of subsurface contamination located directly above a story with an observed exposure or a gaseous indoor air sample meeting observed release criteria Population residing in a structure where levels of contaminants meeting observed release criteria are found in any sampling media at or within five feet horizontally or vertically of the structure foundation 0.4

Population residing in a structure where levels of contaminants meeting observed release criteria are found or inferred based on any underlying non

- ground water subsurface sample at a depth less than or equal to 30 feet

o r Population residing in a structure within an area of subsurface contamina tion where levels of contaminants meeting observed release criteria are inferred based on semi

- enclosed or enclosed crawl space samples in surrounding structures 0.2

Population residing in a structure where levels of contaminants meeting observed release criteria are found or inferred based on underlying ground water samples greater than five feet from the structure foundation

o r Population residing in a structure where levels of contaminants meeting observed release criteria are found or inferred based on any underlying sample at depths greater than 30 feet 0.1

a Eligible populations include residents and students attending school or daycare (see HRS Section 5.2.1.3.2.3). Workers are ex cluded from this evaluation (see HRS Sections 5.2.1.3 and 5.2.1.3.3).

b Eligible structures may include single

- or multi

- tenant structures where eligible populations reside or attend school or daycare. They
may also be mixed use structures

.

5.2.1.3.2.4 Calculation of population factor value

. Sum the factor values for Level I concentrations, Level II concentrations, and population in the area (s) of subsurfacePage 142 of 162 contamination. Assign this sum as the population factor value. Enter this value in line 9d of Table 5

- 11.

5.2.1.3.3 Workers

. Evaluate this factor based on the number of workers that meet the
section 5.2.1.3 criteria. Assign a value for these workers using Table 5

- 21 . Enter this value in Table 5

- 11.

T ABLE 5 - 2 1 W ORKER F ACTOR V ALUES Number of Workers Assigned Value

0 0

1

- 100 15
Greater than 100

- 1000 30
Greater than 1000 45

5.2.1.3.4 Resources

. Evaluate the resources factor as follows:

• Assign a value of 5 if a resource structure (e.g., library, church, tribal facility) is present and regularly occupied within either an area of observed exposure or area of subsurface contamination.

• Assign a value of 0 if there is no resource structure within an area of observed exposure or area of subsurface contamination.

Enter the value assigned in Table 5

- 11.Page 143 of 162 5.2.1.3.5 Calculation of targets factor category value

. Sum the values for the exposed individual, population, workers, and resources factors. Do not round to the nearest integer. Assign this sum as the targets factor category value for the subsurface intrusion comp onent . Enter this value in Table 5

- 11.

**5.2.2 Calculation of subsurface intrusion component score** 



### . Multiply the factor category values for likelihood of exposure, waste characteristics and targets and round the product to the nearest integer. Divide the pr oduct by 82,500. Assign the resulting value, subject to a maximum of 100, as the s ubsurface i ntrusion c omponent score and enter this score in Table 5

- 11.

5.3 Calculation of the soil exposure and subsurface intrusion pathway score : Sum the soil exposure component score and subsurface intrusion component

. A ssign the resulting value, subject to a maximum of 100, as the soil exposure and subsurface intrusion pathway score (S sessi ). Enter this score in Table 5

- 11.

5. Section 6.0 of Appendix A is amended as fo llows:

6.0 Air Migration Pathway

* * * * *

Table 6

- 14. * * *

* * * * *

• Screening concentration for noncancer toxicological responses corresponding to the Reference Concentration (RfC) for inhalation exposures.

* * * * *Page 144 of 162 6 . Section 7.0 of Appendix A is amended as follows:
a. By revising Table 7

- 1.
b. By revising section 7.0.
c. By revising subsections 7.1, 7.1.1 , and 7.1.2.

d . By revising subsection 7.2.4.

e . By revising subsections 7.2.5.1, 7.2.5.1.1, 7.2.5.1.2, 7.2.5.1.3, 7.2.5.2, and 7.2.5.3.

f . By revising subsections 7.3, 7.3.1 , and 7.3.2.
g. By adding subsection 7.3.3.

7.0 Sites Containing Radioactive Substances

* * * * *Page 145 of 162 T ABLE 7 - 1. HRS F ACTORS E VALUATED D IFFERENTLY FOR R ADIONUCLIDES

Ground Water Pathway Status a Surface Water Pathway Status

a Soil Exposure Component of SESSI Pathway Status a Subsurface Intrusion Component of SESSI Pathway Status a Air Pathway Status a

**Likelihood of Release**  **Likelihood of Release**  **Likelihood of Exposure**  **Likelihood of Exposure**  **Likelihood of Release** 
Observed Release Yes Observed Release Yes Observed Contamination Yes Observed Exposure Yes Observed Release Yes

Potential to Release No Potential to Release No Attractiveness/ Accessibility to Nearby Residents No Potential for Exposure Yes Gas Potential to Release No

Containment No Overland Flow Containment No Area of Contamination No Structure Containment No Gas Containment No

Net Precipitation No Runoff No Depth to Contamination Yes Gas Source Type No

Depth to Aquifer No Distance to Surface water No Vertical migration No Gas Migration Potential No

Travel Time No Flood Frequency No Vapor Migration Potential No Particulate Potential to Release NoPage 146 of 162 T ABLE 7 - 1. HRS F ACTORS E VALUATED D IFFERENTLY FOR R ADIONUCLIDES

Ground Water Pathway Status a Surface Water Pathway Status

a Soil Exposure Component of SESSI Pathway Status a Subsurface Intrusion Component of SESSI Pathway Status a Air Pathway Status a

Flood Containment No Particulate Containment No

Particulate Source Type No

Particulate Migration Potential No

**Waste Characteristics**  **Waste Characteristics**  **Waste Characteristics**  **Waste Characteristics**  **Waste Characteristics**  Toxicity Yes Toxicity/ Ecotoxicity Yes/Y

es Toxicity Yes Toxicity/ Biodegradation Yes Toxicity Yes

Mobility No Persistence/ Mobility Yes/N

o Hazardous Waste Quantity Yes Hazardous Waste Quantity Yes Mobility No

Hazardous Waste Quantity Yes Bioaccumu

lation Potential No Hazardous Waste Quantity YesPage 147 of 162 T ABLE 7 - 1. HRS F ACTORS E VALUATED D IFFERENTLY FOR R ADIONUCLIDES

Ground Water Pathway Status a Surface Water Pathway Status

a Soil Exposure Component of SESSI Pathway Status a Subsurface Intrusion Component of SESSI Pathway Status a Air Pathway Status a

Hazardous Waste Quantity Yes

**Targets Targets**  **Targets Targets**  **Targets**
Nearest Well Yes b Nearest Intake Yes b Resident Individual Yes b Exposed Individual Yes b Nearest Individual Yes b

Population Yes b Drinking Water Population Yes b Resident Population Yes b Population Yes b Population Yes b

Resources No Resources No Workers No Workers No Resources No
Wellhead Protection Area No Sensitive Environments Yes b Resources No Resources No Sensitive Environments No

Human Food Chain Individual Yes b Terrestrial Sensitive Environments No

Human Food Chain Population Yes b Nearby Individual NoPage 148 of 162 T ABLE 7 - 1. HRS F ACTORS E VALUATED D IFFERENTLY FOR R ADIONUCLIDES

Ground Water Pathway Status a Surface Water Pathway Status

a Soil Exposure Component of SESSI Pathway Status a Subsurface Intrusion Component of SESSI Pathway Status a Air Pathway Status a

Population Within 1 Mile No

a Factors evaluated differently are denoted by “yes”; factors not evaluated differently are denoted by “no”.

b Difference is in the determination of Level I and Level II concentrations.Page 149 of 162 * * * * *

* * * These differences apply largely to the soil exposure and subsur face intrusion pathway and to sites containing mixed radioactive and other hazardous substances . * * *

7.1 Likelihood of release/likelihood of exposure

. Evaluate likelihood of release for the three migration pathways and likelihood of exposure for the soil exposure and subsurface intrusion pathway as specified in sections 2 through 6, except: establish an observed release , observed contamination , and/ or observed exposure as specified in section 7.1.1. When an observed rel ease or exposure cannot be established for a migration pathway or the subsurface intrusion component of the soil exposure and subsurface intrusion pathway, evaluate potential to release as specified in section 7.1.2. When observed contamination cannot be e stablished, do not evaluate the soil exposure component of the soil exposure and subsurface intrusion pathway

.
**7.1.1 Observed release/observed contamination**  **/observed exposure**

. For radioactive substances, establish an observed release for each migratio n pathway by demonstrating that the site has released a radioactive substance to the pathway (or watershed or aquifer, as appropriate); establish observed contamination or observed exposure for the soil exposure and subsurface intrusion pathway as indicate d below. * * *

* * * * *

– For the subsurface intrusion component of the soil exposure and subsurface intrusion pathway, a material that contains one or more radionuclides has been observed entering a regularly occupied structure via the subsurface or is known to have entered

a regularly occupied structure via the subsurface. Also, when evidence supports the inference of subsurface intrusion of a material that contains one or morePage 150 of 162 radionuclides by the site into a regularly occupied structure, demonstra ted adverse effects associated with that release may also be used to establish observed exposure by direct observation.

• Analysis of radionuclide concentrations in samples appropriate to the pathway (that is, ground water, soil, air, indoor air, surface wa ter, benthic, or sediment samples):

* * * * *

 Some portion of the increase must be attributable to the site to establish the observed release (or observed contamination or observed exposure), and

 For the soil exposure component of the soil exposure and subsurface intrusion pathway only, the radionuclide must also be present at the surface or covered by 2 feet or less of cover material (for example, soil) to establish observed contamination.

* * * * *

 If the sample quantitation limit cannot be es tablished:

° If the sample analysis was performed under the EPA Contract Laboratory Program, use the EPA contract

- required quantitation limit (CRQL) in place of the sample quantitation limit in establishing an observed release (or observed contamination or observed exposure).

* * * * *

 For the soil exposure component of the soil exposure and subsurface intrusion pathway only, the radionuclide must also be present at the surface or covered byPage 151 of 162 2 feet or less of cover material (for example, soil) to establ ish observed contamination.

• Gamma radiation measurements (applies only to observed contamination or observed exposure in the soil exposure and subsurface intrusion pathway):

– The gamma radiation exposure rate, as measured in microroentgens per hour (μR/ hr) using a survey instrument held 1 meter above the ground surface or floor or walls of a structure (or 1 meter away from an aboveground source for the soil exposure component), equals or exceeds 2 times the site

- specific background gamma radiation
exposu re rate.

* * * * *

For the three migration pathways and for the subsurface intrusion component of the soil exposure and subsurface intrusion pathway , if an observed release or observed exposure can be established for the pathway (or threat, aquifer , or watershed, as appropriate), assign the pathway (or threat, aquifer , or watershed) an observed release or observed exposure factor value of 550 and proceed to section 7.2. If an observed release or observed exposure cannot be established, assign an obse rved release or observed exposure factor value of 0 and proceed to section 7.1.2

.

For the soil exposure component of the soil exposure and subsurface intrusion pathway , if observed contamination can be established, assign the likelihood of exposure facto r for resident population a value of 550 if there is an area of observed contamination in one or more locations listed in section 5.1.1; evaluate the likelihood of exposure factor for nearby population as specified in section 5.1.2.1; and proceed to sectio n 7.2. If observed contamination cannot bePage 152 of 162 established, do not evaluate the soil exposure component of the soil exposure and subsurface intrusion pathway

. At sites containing mixed radioactive and other hazardous substances, evaluate observed release (or o bserved contamination or observed exposure) separately for radionuclides as described in this section and for other hazardous substances as described in sections 2 through 6.
For the three migration pathways and the subsurface intrusion component of the s oil exposure and subsurface intrusion pathway , if an observed release or observed exposure can be established based on either radionuclides or other hazardous substances, or both, assign the pathway (or threat, aquifer , or watershed) an observed release or observed exposure factor value of 550 and proceed to section 7.2. If an observed release or observed exposure cannot be established based on either radionuclides or other hazardous substances, assign an observed release or observed exposure factor value o f 0 and proceed to section 7.1.2.
For the soil exposure component of the soil exposure and subsurface intrusion pathway , if observed contamination can be established based on either radionuclides or other hazardous substances, or both, assign the likeliho od of exposure factor for resident population a value of 550 if there is an area of observed contamination in one or more locations listed in section 5.1.1; evaluate the likelihood of exposure factor for nearby population as specified in section 5.1.2.1;

a nd proceed to section 7.2. If observed contamination cannot be established based on either radionuclides or other hazardous substances, do not evaluate the soil exposure component of the soil exposure and subsurface intrusion pathway

.
**7.1.2 Potential**  **to release/potential for exposure**

. For the three migration pathways and the subsurface intrusion component of the soil exposure and subsurface intrusion pathway, evaluate potential to release or potential for exposure for sites containing radionuclides in the same manner as specified for sites containing other hazardous substances. * * * For thePage 153 of 162 subsurface intrusion component of the soil exposure and subsurface intrusion pathway, if the potential for exposure is based on the presence of gamma emitting rad ioactive substances, assign a potential for exposure factor value of 500 only if the contamination is found within 2 feet beneath a regularly occupied structure, otherwise assign a potential for exposure factor value of 0.
For sites containing mixed radioa ctive and other hazardous substances, evaluate potential to release or potential for exposure considering radionuclides and other hazardous substances together. Evaluate potential to release for each migration pathway and the potential for exposure for the subsurface intrusion component of the soil exposure and subsurface intrusion pathway as specified in sections 3 through 6, as appropriate.

* * * * *

**7.2.4 Selection of substance potentially posing greatest hazard** 

. For the subsurface intrusion component of the soil exposure and subsurface intrusion pathway and each migration pathway ( or threat, aquifer, or watershed, as appropriate), select the radioactive substance or nonradioactive hazardous substance that potentially poses the greatest hazard based on its toxicity factor value, combined with the applicable mobility, persistence, biodegradation and/or bioaccumulation (or ecosystem bioaccumulation) potential factor values. Combine these factor values as specified in sections 2 through 6 . For the soil exposure component of the soil exposure and subsurface intrusion pathway, base the selection on the toxicity factor alone (see sections 2 and 5 ).

* * * * *Page 154 of 162 7.2.5.1 Source hazardous waste quantity for radionuclides

. * * * For the soil exposure component of the soil exposure and subsurface intrusion pathway, assign a source hazardous waste quantity value to each area of observed contamination, as applicable to the threat being evaluated. For the subsurface intrusion componen t , assign a source hazardous waste quantity value to each regularly occupied structure located within areas of observed exposure or areas of subsurface contamination . Allocate hazardous substances and hazardous wastestreams to specific sources (or areas of observed contamination , area of observed exposure or area of subsurface contamination ) as specified in section s 2.4.2 and 5.2.0

.

7.2.5.1.1 Radionuclide constituent quantity (Tier A)

. Evaluate radionuclide constituent quantity for each source (or area of observed contamination or area of observed exposure) based on the activity content of the radionuclides allocated to the source (or area of observed contamination or area of observed ex posure) as follows:

• Estimate the net activity content (in curies) for the source (or area of observed contamination or area of observed exposure) based on:

* * * * *

where:

N=Estimated net activity content (in curies) for the source (or area of observed contamination

or area of observed exposure). V=Total volume of material (in cubic yards) in a source (or area of observed contamination

or area of observed exposure) containi ng radionuclides.Page 155 of 162 ACi=Activity concentration above the respective background concentration (in pCi/g) for each radionuclide i allocated to the source (or area of observed contamination or area of observed exposure). n=Number of radionuclides allocated to the source (or area of observed contamination or area of observed exposure) above the respective background concentrations. or,

* * * * *

where:

N=Estimated net activity content (in curies) for the source (or area of observed contamination

or area of observed exposure). V=Total volume of material (in gallons) in a source (or area of observed contamination or area of observed exposure) containing radionuclides. AC i =Activity concentration above the respective background concentration (in pCi/1) for each radionuclide i allocated to the source (or area of observed contamination or area of observed exposure). n=Number of radionuclides allocated to the source (or area of observed contamination or area of observed exposure) above the respective backgrou nd concentrations.

• Estimate volume for the source (or volume for the area of observed contamination or area of observed exposure) based on records or measurements.

• For the soil exposure component, in estimating the volume for areas of observed contamination, do not include more than the first 2 feet of depth, except: for those types of areas of observed contamination listed in Tier C of Table 5

- 2 (section 5.1.1.2.2) * * *

.Page 156 of 162 • For the subsurface intrusion component, in estimating the volume for areas of observed exposure, only use the volume of air in the regularly occupied structures where observed exposure has been documented.

• Convert from curies of radionuclides to equivalent pounds of nonradioactive hazardous substances by multiplying the activity estimate for the source (or area of observed contamination

or area of observed exposure) by 1,000.

• Assign this resulting product as the radionuclide constituent quantity value for the source (or area of observed contamination or area of observed exposure).

If the radionuclide constituent quantity for the source (or area of observed contamination or area of observed exposure) is ade quately determined (that is, the total activity of all radionuclides in the source and releases from the source [or in the area of observed contamination or area of observed exposure] is known or is estimated with reasonable confidence), do not evaluate th e radionuclide wastestream quantity measure in section 7.2.5.1.2. * * * If the radionuclide constituent quantity is not adequately determined, assign the source (or area of observed contamination or area of observed exposure) a value for radionuclide con stituent quantity based on the available data and proceed to section 7.2.5.1.2.

7.2.5.1.2 Radionuclide wastestream quantity (Tier B)

. Evaluate radionuclide wastestream quantity for the source (or area of observed contamination , a r ea of observed expos ure , or area of subsurface contamination ) based on the activity content of radionuclide wastestreams allocated to the source ( or area of observed contamination , a r ea of observed exposure , or area of subsurface contamination ) as follows:Page 157 of 162 • Estimate the total volume (in cubic yards or in gallons) of wastestreams containing radionuclides allocated to the source ( or area of observed contamination , a r ea of observed
exposure , or area of subsurface contamination ).

* * * * *

• Assign the resulting value as the radionuclide wastestream quantity value for the source (or area of observed contamination , a r ea of observed exposure , or area of subsurface contamination )

.

• For the subsurface intrusion component of the soil exposure and subsurface intrusion pathway, esti mate the total wastestream volume for all regularly occupied structures located within areas of observed exposure with observed or inferred intrusion and within areas of subsurface contamination. C alculate the volume of each regularly occupied structure based on actual data. If unknown, use a ceiling height of 8 feet

.

7.2.5.1.3 Calculation of source hazardous waste quantity value for radionuclides

. Select the higher of the values assigned to the source ( or area of observed contamination , a r ea of ob served exposure , and/ or area of subsurface contamination ) for radionuclide constituent quantity and radionuclide wastestream quantity. Assign this value as the source hazardous waste quantity value for the source ( or area of observed contamination , a r ea of observed exposure , or area of subsurface contamination ). * * *

7.2.5.2 Calculation of hazardous waste quantity factor value for radionuclides

. Sum the source hazardous waste quantity values assigned to all sources ( or area of observedPage 158 of 162 contamination , a r ea of observed exposure , or area of subsurface contamination ) for the pathway being evaluated and round this sum to the nearest integer, except: if the sum is greater than 0, but less than 1, round it to 1. * * *

* * * * *

For the soil exposure component of the soil exposure and subsurface intrusion pathway, if the radionuclide constituent quantity is adequately determined for all areas of observed contamination, assign the value from Table 2

- 6 as the hazardous waste quantit y factor value. * *
* For the subsurface intrusion component of the soil exposure and subsurface intrusion pathway , if the radionuclide constituent quantity is adequately determined for all areas of observed exposure, assign the value from Table 2

- 6 as the hazardous waste quantity factor value. If the radionuclide constituent quantity is not adequately determined for one or more areas of observed exposure, assign either the value from Table 2

- 6 or a value of 10, whichever is greater, as the hazardous wa ste quantity factor value.

7.2.5.3 Calculation of hazardous waste quantity factor value for sites containing mixed radioactive and other hazardous substances

. For each source ( or area of observed contamination ,
a r ea of observed exposure , or area of subsurface contamination ) containing mixed radioactive and other hazardous substances, calculate two source hazardous waste quantity values

— one based on radionuclides as specified in sections 7.2.5.1 through 7.2.5.1.3 and the other based on the nonradioa ctive hazardous substances as specified in sections 2.4.2.1 through 2.4.2.1.5, and sections 5.1.1.2.2, 5.1.2.2.2 and 5.2.1.2.2 (that is, determine each value as if the other type of substance was not present). Sum the two values to determine a combined sou rce hazardous wastePage 159 of 162 quantity value for the source ( or area of observed contamination , a r ea of observed exposure , or area of subsurface contamination ). * * *

Use this combined source hazardous waste quantity value to calculate the hazardous waste quanti ty factor value for the pathway as specified in section 2.4.2.2, except: if either the hazardous constituent quantity or the radionuclide constituent quantity, or both, are not adequately determined for one or more sources (or one or more portions of sourc es or releases remaining after a removal action) or for one or more areas of observed contamination , areas of observed exposure, or areas of subsurface contamination, as applicable, assign the value from Table 2

- 6 or the default value applicable for the pathway, whichever is greater, as the hazardous waste quantity factor value for the pathway.

7.3 Targets

. For radioactive substances, evaluate the targets factor category as specified in section 2.5 and sections 3 through 6 , except: establish Level I and Level II concentrations at sampling locations as specified in sections 7.3.1 and 7.3.2 and establish weighting factors for populations associated with an area of s ubsurface contamination in the subsurface intrusion component of the soil exposure and subsurface intrusion pathway as specified in section 7.3.3

.

For all pathways (components and threats), use the same target distance limits for sites containing radioact ive substances as is specified in sections 3 through 6 for sites containing nonradioactive hazardous substances. At sites containing mixed radioactive and other hazardous substances, include all sources ( or area s of observed contamination , a r ea s of observ ed exposure ,
or area s of subsurface contamination ) at the site in identifying the applicable targets for the pathway.

**7.3.1 Level of contamination at a sampling location** 

. * * *Page 160 of 162 • Select the benchmarks from section 7.3.2 applicable to the pathway (or component or threat) being evaluated.

• Compare the concentrations of radionuclides in the sample (or comparable samples) to their benchmark concentrations for the pathway (or component or threat) as specified in section 7.3. 2 . Treat comparable samples as specified in section 2.5.1

.

* * * * *

• If none of the radionuclides eligible to be evaluated for the sampling location have an applicable benchmark, assign Level II to the actual contamination at that sampling location for the pathway (or component or threat).

• In making the comparison, consid er only those samples, and only those radionuclides in the sample, that meet the criteria for an observed release (or observed contamination or observed exposure) for the pathway, except: tissue samples from aquatic human food chain organisms may also be u sed for the human food chain threat of the surface water pathway as specified in s ections 4.1.3.3 and 4.2.3.3

.

**7.3.2 Comparison to benchmarks** 

. * * *

* * * * *

• Uranium Mill Tailings Radiation Control Act (UMTRCA) standards

— soil exposure component of the soil exposure and subsurface intrusion pathway only.Page 161 of 162 • Screening concentration for cancer corresponding to that concentration that corresponds to the 10
- 6 individ ual cancer risk for inhalation exposures (air migration pathway and subsurface intrusion component of the soil exposure and subsurface intrusion pathway ) or for oral exposures (ground water migration pathway; drinking water or human food chain threats in s urface water migration pathway; and soil exposure and subsurface intrusion pathway).

– For the soil exposure and subsurface intrusion pathway, include two screening concentrations for cancer

— one for ingestion of surface materials and one for external radiation exposures from gamma

- emitting radionuclides in surface materials.

Select the b enchmark(s) applicable to the pathway (component or threat) being evaluated. Compare the concentration of each radionuclide from the sampling location to its benchmark concentration(s) for that pathway (component or threat). Use only those samples and only those radionuclides in the sample that meet the criteria for an observed release (or observed contamination or observed exposure) for the pathway, except: tissue samples from aquatic human food chain organisms may be used as specified in sections 4.1.3.3 and 4.2.3.3. If the concentration of any applicable radionuclide from any sample equals or exceeds its benchmark concentration, consider the sampling location to be subject to Level I concentrations for that pathway (component or threat). If more than one benchmark applies to the radionuclide, assign Level I if the radionuclide concentration equals or exceeds the lowest applicable benchmark concentration. In addition, for the soil exposure and subsurface intrusion pathway, assign Level I concentrations at t he sampling location if measured gamma radiation exposure rates equal or exceed 2 times the background level (see section 7.1.1).

If no radionuclide individually equals or exceeds its benchmark concentration, but more than one radionuclide either meets t he criteria for an observed release (or observed contamination orPage 162 of 162 observed exposure) for the sample or is eligible to be evaluated for a tissue sample (see sections 4.1.3.3 and 4.2.3.3), calculate a value for index I for these radionuclides as specified in section 2.5.2. * * *

* * * Use only those samples and only those substances in the sample that meet the criteria for an observed release (or observed contamination or observed exposure) for the pathway except: tissue samples from aquatic human foo d chain organisms may be used as specified in sections 4.1.3.3 and 4.2.3.3. * * *

If no radionuclide or other hazardous substance individually exceed a benchmark concentration, but more than one radionuclide or other hazardous substance either meets th e criteria for an observed release (or observed contamination or observed exposure) for the sample or is eligible to be evaluated for a tissue sample, calculate an index I for both types of substances as specified in section 2.5.2. * * *

**7.3.3 Weighting of targets within an area of subsurface contamination** 

. For the subsurface intrusion component of the soil exposure and subsurface intrusion pathway, assign a weighting factor as specified in section 5.2.1.3.2.3 except when an area of s ubsurface contamination is bound by gamma radiation exposure rates meeting observed release criteria with a depth to contamination of 2 feet or less. For those populations residing in or attending school or daycare in a structure, assign a weighting factor of 0.9.