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ENVIRONMENTAL PROTECTION AGENCY

[EPA-HQ-SFUND-2010-1086; FRL – ] 

Potential Addition of Vapor Intrusion Component to the Hazard Ranking System

AGENCY: Environmental Protection Agency (EPA) 

ACTION: Notice of Opportunity for Public Input 

SUMMARY: The Environmental Protection Agency (“EPA”) is soliciting stakeholder input on whether 

to include a vapor intrusion component to the Hazard Ranking System (“HRS”). The HRS is the principal 

mechanism EPA uses to place sites on the Comprehensive Environmental Response, Compensation, and 

Liability Act (CERCLA) National Priorities List (NPL). This potential addition would allow the HRS to

directly consider the human exposure to contaminants that enter building structures through the 

subsurface environment and thus, enabling sites with vapor intrusion contamination to be evaluated for 

placement on the NPL. EPA is accepting public feedback on specific topics related to the potential HRS 

revision (see SUPPLEMENTARY INFORMATION section of this Notice), and will consider

information gathered during this comment period, as well as input from three public listening sessions 

before making a decision on whether to issue a proposed rulemaking to add a vapor intrusion component 

to the HRS. The Agency is requesting comments only regarding this potential addition to the HRS. The 

Agency is not considering changes to the remainder of the HRS. 

DATES: Comments on the topics identified in the SUPPLEMENTARY INFORMATION section of 

this notice must be submitted (postmarked) on or before [INSERT DATE 75 DAYS FROM 

PUBLICATION IN THE FEDERAL REGISTER]. 

ADDRESSES: Submit comments on the topics identified in the SUPPLEMENTARY 

INFORMATION section of this notice, identified by Docket ID No. EPA-HQ-SFUND-2010-1086, by 

one of the following methods: 

• http://www.regulations.gov: Follow the on-line instructions for submitting comments.
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• E-mail: superfund.docket@epa.gov 

• Fax: (202) 566–9744

• Mail: U.S. Environmental Protection Agency; EPA Docket Center, Superfund Docket, Mail Code 

28221T; 1200 Pennsylvania Avenue, NW., Washington, DC 20460

• Hand Delivery: EPA Docket Center—Public Reading Room; EPA West Building, Room 3334; 

1301Constitution Avenue, NW, Washington, DC 20004. Such deliveries are only accepted during 

the Docket’s normal hours of operation, and special arrangements should be made for deliveries 

of boxed information. 

• Listening Session: Oral and written comments on the topics in the SUPPLEMENTARY 

INFORMATION section of this Notice will be accepted at each of the three listening sessions. 

Follow the instructions provided on the listening session website at 

http://www.epa.gov/superfund/sites/npl/hrsaddition.htm for preparing written comments to be 

submitted at one of the listening sessions.

Instructions: Direct comments on the topics identified in the SUPPLEMENTARY INFORMATION

section of this notice to Docket ID No. EPA–HQ–SFUND–2010-1086. EPA’s policy is that all 

comments received will be included in the public docket without change and may be made available 

online at http:// www.regulations.gov, including any personal information provided, unless the comment 

includes information claimed to be Confidential Business Information (CBI) or other information whose 

disclosure is restricted by statute. Do not submit information that you consider to be CBI or otherwise 

protected through http://www.regulations.gov or superfund.docket@epa.gov. Note that the 

http://www.regulations.gov website is an ‘‘anonymous access’’ system, which means EPA will not know 

your identity or contact information unless you provide it in the body of your comment.

If you send an e-mail comment directly to EPA without going through 

http://www.regulations.gov, your e-mail address will be automatically captured and included as part of the 

comment that is placed in the public docket and made available on the Internet. If you submit an 

electronic comment, EPA recommends that you include your name and other contact information in the 
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body of your comment and along with any disk or CD–ROM submitted. If EPA cannot read your 

comment due to technical difficulties and cannot contact you for clarification, EPA may not be able to 

consider your comment.

Electronic files should avoid the use of special characters, any form of encryption, and be free of 

any defects or viruses. For additional information about EPA’s public docket, visit the EPA Docket 

Center homepage at http://www.epa.gov/epahome/dockets.htm.

Docket: All documents in the docket are listed in the http:// www.regulations.gov index. Although listed 

in the index, some information is not publicly available, e.g., CBI or other information whose disclosure 

is restricted by statute. Certain other material, such as copyrighted material, will be publicly available 

only in hard copy. Publicly available docket materials are available either electronically in 

http://www.regulations.gov or in hard copy at the EPA Docket Center—Public Reading Room, EPA/DC, 

EPA West, Room 3334; 1301 Constitution Ave., NW., Washington, DC. The Public Reading Room is 

open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone 

number for the Public Reading Room is (202) 566–1744, and the telephone number for the Superfund 

docket is (202) 566–0276.

FOR 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.

SUPPLEMENTARY INFORMATION: 

EPA is considering adding a vapor intrusion component as a new mechanism to the HRS that

would enable vapor intrusion contamination to be included in an HRS evaluation. Presented below is 

background information on the HRS, its statutory basis, and further detail regarding this potential addition 

and related topics on which EPA is requesting public comment. 
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The Agency will conduct public outreach activities, including facilitating public listening 

sessions, providing public information documents, and establishing a website with more information 

regarding this potential addition to the HRS. The Agency will consider the information gathered from 

this Notice, listening sessions, and other sources before making a decision on whether to issue a proposed 

rulemaking to add subsurface contaminant intrusion to the HRS. The Agency is therefore requesting 

comments only regarding this potential addition to the HRS, and is not considering changes to the 

remainder of the HRS.

EPA is currently scheduled to hold three listening sessions following publication of this Notice 

to allow interested parties to present feedback on the potential HRS addition. EPA welcomes the input 

that will be provided to the Agency by listening session participants. This input will be considered by the 

Agency as it determines the need for and nature of the addition to the HRS.

For those stakeholders who cannot attend one of the listening sessions, comments on the topics 

described below in the Potential Addition of Vapor Intrusion Component to the HRS subsection of this 

Notice should be submitted in accordance with the instructions in the DATES and ADDRESSES

sections of this Notice. Written comments will also be accepted at the listening sessions. Follow the 

instructions provided on the listening session website at 

http://www.epa.gov/superfund/sites/npl/hrsaddition.htm for preparing written comments to be submitted 

at one of the listening sessions; see also the ADDRESSES section of this Notice.

In a separate effort, EPA is also preparing a final guidance document on vapor intrusion that will 

replace the 2002 Office of Solid Waste and Emergency Response (OSWER) Draft Guidance for 

Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (Subsurface Vapor 

Intrusion Guidance). The guidance document is not directly related to the potential addition of a vapor 

intrusion component to the HRS and more information about this effort will be provided in a future

Federal Register Notice. More information can be found on EPA’s vapor intrusion website at 

http://www.epa.gov/oswer/vaporintrusion/.
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Background

Vapor Intrusion

When hazardous substances, pollutants or contaminants are spilled on the ground or otherwise 

migrate to the subsurface, they can move in the subsurface environment and eventually enter buildings as 

a gas or vapor, or even as a liquid in some cases. Dry cleaning solvents and industrial de-greasers are 

products that contain hazardous substances that when released to the environment, can migrate into the 

soil and subsurface environment, enter buildings by seeping through cracks in basements, foundations, 

sewer lines and other openings and ultimately result in human exposures. Vapor intrusion is of particular 

concern because concentrations of vapors can rise to a point where the health of residents or workers in 

those buildings could be at risk. Intrusion of contaminants in a non-vapor state may also be a pathway of 

concern because of the potential for human exposure to the liquids, the resulting precipitates, or 

associated vapors.

Statutory Basis

In 1980, Congress enacted the Comprehensive Environmental Response, Compensation, and 

Liability Act, 42 U.S.C. 9601, et seq. ("CERCLA or "the Act") in response to the dangers posed by

uncontrolled releases of hazardous substances, pollutants, or contaminants. Section 105(a)(8)(A) of 

CERCLA required that the National Oil and Hazardous Substances Pollution Contingency Plan (NCP) 

include criteria for determining priorities among releases or threatened releases for the purpose of taking 

remedial or removal action. Criteria were to be based upon relative risk or danger, taking into account the 

population at risk, the hazardous potential of the substances at a facility, the potential for contamination of

drinking water supplies, direct human contact, destruction of sensitive ecosystems, and other appropriate 

factors. 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, and that at least 400 sites be designated for priority. The list, which 

is Appendix B of the NCP, is the National Priorities List (NPL).
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To implement CERCLA, EPA promulgated the revised NCP, 40 CFR Part 300, on July 16, 1982

(47 FR 31180) pursuant to section 105 of CERCLA and Executive Order 12316 (48 FR 42237 August 20, 

1981). The NCP, further revised by EPA on September 16, 1985 (50 FR 37624) and November 20, 1985 

(50 FR 47912), sets forth the guidelines and procedures needed to respond to releases and threatened 

releases of hazardous substances, pollutants, or contaminants under CERCLA. The Agency developed 

the Hazard Ranking System ("HRS") to implement Section 105(a)(8)(A). The HRS was codified as 

Appendix A of the NCP. The HRS is the primary mechanism EPA uses to evaluate a site for placement 

on the NPL. 

CERCLA was amended by the Superfund Amendments and Reauthorization Act (SARA) in 

1986. This amendment required the HRS to be revised to more accurately assess the relative degree of 

risk to human health and the environment posed by sites and facilities subject to review. Revisions to the 

HRS were proposed in 1988 (53 FR 51962) and promulgated in 1990 (55 FR 51532). The revisions 

changed the way EPA evaluates potential threats to human health and the environment from hazardous 

waste sites, as well as made the HRS more accurate in assessing relative risk. The revisions included the 

addition of the human food chain and recreation threats to the surface water pathway and the addition of a 

new exposure pathway (i.e., soil exposure pathway). CERCLA called for the establishment of both the 

NPL and the HRS.

National Priorities List

CERCLA established in Appendix B of the NCP, the NPL, which is also commonly known as the 

Superfund List. The NPL is a list of contaminated sites identified to have known releases or threatened 

releases of hazardous substances, pollutants, or contaminants throughout the United States and its 

territories. The NPL is intended primarily to guide EPA in determining which sites warrant further 

investigation. A site can be placed on the NPL via three methods (see 40 CFR 300.425(c) of the NCP for 

further information):

• Achieving a score of 28.50 or greater under the HRS;
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• Designating by a State or Territory as its top priority for listing on the NPL (regardless of its HRS 

score); or

• Using the Agency for Toxic Substances and Disease Registry (ATSDR) listing mechanism (see 

40 CFR.300.66(b)(4) of the NCP for further information).

Rationale for Adding Vapor Intrusion to the Hazard Ranking System

In a May 2010 report (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-10-380, May 2010), the Government Accountability Office (GAO) 

concluded that if vapor intrusion sites are not assessed and, if needed, listed on the NPL, there is the 

potential that contaminated sites with unacceptable human exposure will not be acted upon. GAO 

recommended that the EPA Administrator determine the extent to which EPA will consider vapor 

intrusion in listing NPL sites and how this will affect the number of NPL sites listed in the future. 

Many sites on the NPL that have subsurface contaminant intrusion problems were placed on the 

NPL by evaluation of pathways other than a contaminant intrusion pathway. There are other 

contaminated sites, however, that did not qualify for placement on the NPL under the current HRS. 

However, these sites may qualify for placement on the NPL if the threat from vapor intrusion was 

included in the HRS. A new HRS mechanism would enable EPA to identify situations in which 

individuals are exposed or potentially exposed to vapor or other contaminant intrusion in dwellings, work 

places, or other structures or enclosures. 

Hazard Ranking System

The HRS is a screening tool used by EPA to assess the relative threat that sites with actual or 

potential contaminant releases pose to human health or the environment. The HRS is the primary 

mechanism EPA uses to place a site on the NPL. (As noted earlier, there are two other mechanisms that 

can be used to place sites on the NPL.) The sites on the NPL are then further investigated to determine the 

extent of the threat and whether cleanup of the site under EPA’s Superfund Remedial program is 
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warranted. The HRS is a numerically based screening system that uses information from initial, limited 

investigations that can be collected relatively quickly and inexpensively, thus allowing most Superfund 

resources to be directed to remedial actions at sites on the NPL. The HRS does not provide a risk 

assessment of a specific site, but serves as a screening level indicator of the highest priority hazardous 

releases or potential releases.

The HRS score is currently based on an evaluation of up to four separate pathways: ground water 

migration, soil exposure, surface water migration, and air migration. Pathways are routes by which 

exposure to contaminant releases by human or sensitive environments can occur.

1. The ground water migration pathway evaluates the likelihood that hazardous substances will 

travel through the ground below and contaminate aquifers and drinking water wells that draw on 

those aquifers. The groundwater pathway does not consider the potential risk of exposure to 

vapor intrusion from contaminated aquifers. 

2. The surface water migration pathway evaluates the likelihood that hazardous substances can enter 

surface water and affect people or the environment. Threats to humans from this pathway include 

drinking water, the human food chain (i.e., contaminants build up in the aquatic organisms that 

humans in turn consume), and sensitive environments. 

3. The soil exposure pathway evaluates the potential threats to humans and terrestrial environments 

posed by direct, physical contact with hazardous substances or contaminated soil. This pathway 

includes threats to those living on property with hazardous substances or soils contaminated 

with hazardous substances, and those living nearby with access to the property. 

4. Finally, the air migration pathway evaluates the likelihood of release of hazardous substances into 

the atmosphere and how many people and sensitive environments could be exposed to hazardous 

substances carried in the air, including gases and particulates. The air migration pathway does 

not consider indoor air contamination. 

The scoring system for each pathway is based on a number of individual factors associated with riskrelated conditions at the site. These factors are grouped into three categories: 
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1. Likelihood of exposure (i.e., likelihood that a site has released or has the potential to release 

hazardous substances into the environment) 

2. Waste characteristics (i.e., inherent toxicity, mobility of the substances and the quantity of the 

hazardous substances that has been released) 

3. Targets (i.e., people or sensitive environments actually or potentially exposed to the release) 

The HRS site score, which ranges from 0 to 100, is obtained by combining the pathway scores. A site 

may be scored for one or more of the pathways depending on the nature of the release. Any site scoring 

28.50 or greater is eligible for placement on the NPL. As noted previously, the HRS score does not 

represent a specified level of risk, but is a cutoff point that serves as a screening-level indicator of the 

highest priority hazardous releases or potential releases based on the criteria identified in SARA. 

Potential Addition of Vapor Intrusion Component to the HRS

Consistent with CERCLA Section 105 and SARA, the Agency regards it appropriate to consider 

amending or adding to the HRS when such amendments would identify sites of the highest priority for 

evaluation. EPA is considering the potential enhancement of the HRS by including a vapor intrusion 

component that address issues related to the intrusion of hazardous substances, pollutants, and 

contaminants into structures (e.g., homes, offices, schools, manufacturing facilities). To comprehensively 

explore, and if determined appropriate, identify approaches for adding the threat posed by contaminant 

vapor intrusion into occupied structures to the HRS, EPA is beginning the process of soliciting 

stakeholder input. To determine whether to move forward with this addition, and if so, to determine a 

range of potential approaches, EPA is soliciting input on the topics described below.

1. The level and extent of vapor intrusion contamination that would warrant evaluation for 

placement on the NPL, as well as the identification of screening level information sufficient to 

perform this evaluation.

2. Methods for incorporating vapor intrusion into the HRS while, to the extent possible, maintaining 

the structure of the other pathways in the current HRS and retaining that same structure 
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throughout the new mechanism for vapor intrusion (i.e., likelihood of release, waste 

characteristics, and targets). These methods could include the addition of vapor intrusion as a 

migration pathway (e.g., groundwater), or part of an exposure pathway (e.g., threat within a direct 

exposure pathway along with soil).

3. Consideration of the importance of evaluating the potential threat to populations not demonstrated 

to be exposed to contaminant intrusion.

4. The identification of sampling procedures available and practical to detect the presence of 

contamination due to vapor intrusion.

5. The availability of screening sampling strategies that can adequately compensate for the 

variability in vapor intrusion rates under different climatic and seasonal conditions. 

6. Identification of analytical methods that are sufficiently precise and accurate to demonstrate a 

significant increase in contaminant levels from vapor intrusion.

7. The importance of the threat posed by exposure to contaminant vapor intrusion via inhalation, 

dermal contact with the vapors or condensate on surfaces, and ingestion.

8. The identification of what environmental factors (e.g., porosity of soil, presence of a 

contaminated aquifer, climate) and structural and lifestyle factors (e.g., houses with basements) 

should appropriately be considered in determining whether a site warrants sampling for 

contaminant vapor intrusion. 

9. In addition to residences, schools and other occupied structures, the identification of structures in 

which contaminant vapor intrusion could result in a significant threat to human health (e.g., 

community recreation centers, cultural centers, museums, athletic facilities).

10. The possible need to consider not only contaminant vapor intrusion, but also intrusion of 

contaminants in solid (i.e., particulates) and liquid forms. 
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In addition to these topics, EPA also solicits input on community outreach methods that would be 

most effective in gathering and disseminating information regarding this potential addition to the HRS. 

To further support this effort, EPA requests public input on the identification of possible vapor intrusion 

sites. This information will be used for informational purposes only.

EPA will consider all public input when evaluating whether changes to the HRS are appropriate, and 

whether to issue a proposed amendment to the HRS.

Listening Sessions

The first listening session will be held in Arlington, VA on February 24, 2011. Specific details of 

the listening sessions, including dates and locations for the other two sessions, and instructions for those 

wishing to present oral comments will be posted at: 

http://www.epa.gov/superfund/sites/npl/hrsaddition.htm. At this site, users will also be able to sign up for 

a mailing list that will be used to distribute logistical information on these listening sessions. Registration 

is not required to attend a listening session with the following exceptions.

Due to space limitations, parties interested in presenting oral comments at the Arlington, VA 

listening session only, must register for that session. Registration must be completed at least 3 calendar 

days prior to the session. Details for registration will be posted on the Web at 

http://www.epa.gov/superfund/sites/npl/hrsaddition.htm. If no speakers have registered by 2 calendar 

days prior to this listening session, it will be cancelled and EPA will notify those registered of the 

cancellation. The Agency will also post on its website that the listening session has been cancelled.

In addition to attending in person, participation in the Arlington, VA listening session will be 

available via a teleconference. Those wishing to attend via teleconference must register as described 

above. EPA will provide the teleconference information to registrants via email notification in advance of 

the session.

The Arlington, VA listening session will be held at EPA’s Potomac Yard office located at: 2777 

Crystal Drive, Arlington, VA 22202. The listening session will begin at 9:00 a.m. and end at 5:00 p.m. 

The Arlington, VA listening session may be webcast. Please refer to the Superfund “Addition of Vapor 
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Intrusion to HRS” Web Site, http://www.epa.gov/superfund/sites/npl/hrsaddition.htm for information on 

how to access the webcast. Please note that the webcast is a supplementary public process provided only 

for convenience. If difficulties arise resulting in webcasting outages, the meeting will continue as 

planned. 

In general, each oral comment at listening sessions should be limited to no more than 15 minutes 

in length. If, however, there are more individuals who wish to present comments than the allotted time 

for the listening session allows, an announcement will be made at the beginning of the listening session 

that the time limit has been adjusted to allow for the presentation of more comments. 

Dated: 

Mathy Stanislaus, 

Assistant Administrator,

Office of Solid Waste and Emergency Response. 

BILLING CODE: 6560-50-P