Proposed Rule: Addition of a Subsurface Intrusion 

Component to the Hazard Ranking System; 40 

CFR Part 300; EPA-HQ-SFUND-2010-1086; 

FRL_XXXX-X (review draft)

External Peer Review Record (modified)

November 21, 2011 – February 20, 2012 

Contents

Peer Review Charge Questions

Summary Matrix of Peer Review Comments on Preamble

Summary Matrix of Peer Review Comments on Charge Questions and Proposed Rule

Peer Reviews 

• Tonia Burk

o Charge Question Comments

o CV

o COI Certification

• Blayne Hartman

o Charge Question Comments

o CV

o COI Certification

• Paul Johnson

o Charge Question Comments

o CV

o COI Certification

1
• Kimi Klein/Dot Lofstrom (Joint Review)

o Charge Question Comments

o CVs

o COI Certifications

• Henning Larsen

o Charge Question Comments

o CV

o COI Certification

2
Peer Review Charge

Questions

3
Peer Review Charge for:

U.S. Environmental Protection Agency (EPA). Proposed Rule: Addition of a Subsurface Intrusion 

Component to the Hazard Ranking System; 40 CFR Part 300; EPA-HQ-SFUND-2010-1086; FRL_XXXX-X

(review draft). 

Background

The U.S. Environmental Protection Agency (EPA) is proposing to include a subsurface intrusion (SsI) 

component to the Hazard Ranking System (HRS). Subsurface intrusion is the migration of hazardous 

substances from the unsaturated zone and/or the surficial ground water into overlying structures. The HRS is 

the principal mechanism the EPA uses to evaluate sites for placement on the National Priorities List (NPL). 

The subsurface intrusion component addition (this addition) would primarily 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 and the environment from releases of hazardous substances. 

This addition will allow the HRS evaluation to directly consider human exposure to hazardous substances 

that enter building structures through subsurface intrusion, and thus enable sites with subsurface intrusion 

contamination to be evaluated for placement on the NPL. This addition will make the HRS more accurate in 

assessing a site’s relative potential risk. The Agency is not considering changes to the remainder of the HRS 

except for minor updates reflecting changes in terminology related to revised toxicological parameters. This 

proposed regulatory change does not affect the status of sites currently on or proposed to the NPL. 

Expertise Required

The peer review panel for U.S. EPA’s Proposed Rule: Addition of a Subsurface Intrusion Component to the 

Hazard Ranking System should include expertise in: 

Federal Agency Panelist: Panelist must have a strong working knowledge of policy and technical issues 

related to topic of vapor intrusion. Knowledge of recent developments in vapor intrusion technologies and 

research is required, in addition to working knowledge of federal vapor intrusion response programs. 

Expertise in hydrogeology, chemistry, knowledge of public health risks associated with indoor air threats, 

and the subsurface migration of volatile hazardous substances is necessary. Field experience conducting 

vapor intrusion investigations, while not required, is highly desirable. Experience conducting field 

investigations for the purpose of listing sites on the NPL and/or experience working with the HRS to 

evaluate sites for inclusion on the NPL is highly recommended, but not necessary. 

State Environmental Program Panelist: Panelist must have strong technical experience and working 

knowledge of policy and technical issues (e.g., mitigation and remediation) related to the topic of vapor 

intrusion. Expertise in hydrogeology, chemistry, knowledge of public health risks associated with indoor air 

threats, and the subsurface migration of volatile hazardous substances is necessary. Knowledge of recent 

developments in vapor intrusion technologies and research is required, in addition to working knowledge of 

state vapor intrusion response programs. Field experience conducting vapor intrusion investigations, while 

not required, is highly desirable. Experience related to conducting field investigations for the purpose of 

listing sites on the NPL and/or experience working with the HRS to evaluate sites for inclusion on the NPL is 

highly recommended, but not necessary. 

Academia: Panelist must have experience working, researching, and developing opinions on the topic of 

vapor intrusion. Expertise in the history and recent developments of vapor intrusion research and 

development, remediation, and mitigation technologies is required. Expertise in hydrogeology, chemistry, 

knowledge of public health risks associated with indoor air threats, and the subsurface migration of volatile 

hazardous substances is necessary. Experience working on Superfund issues is highly recommended, but not 

necessary. 

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Panelist from non-specified sector: Panelist must have a strong working knowledge of policy and technical 

issues related to the topic of vapor intrusion. Knowledge of recent developments in vapor intrusion 

technologies and research is required, in addition to working knowledge of federal vapor intrusion response 

programs. Expertise in hydrogeology, chemistry, knowledge of public health risks associated with indoor air 

threats, and the subsurface migration of volatile hazardous substances is necessary. Field experience 

conducting vapor intrusion investigations, while not required, is highly desirable. Experience conducting 

field investigations for the purpose of listing sites on the NPL and/or experience working with the HRS to 

evaluate sites for inclusion on the NPL is highly recommended, but not necessary. 

Peer Review Charge Questions

1. Potential for subsurface exposure (intrusion) into occupied structures

Background: The current HRS evaluates the likelihood of a release of a hazardous substance when an actual 

release has occurred through either chemical analysis or direct observation. The current HRS also evaluates 

the potential for a release to occur within the ground water, surface water and air pathways (see section 2.3 

of the current HRS). The potential for a release is determined by the consideration of pathway specific 

factors that aid the site evaluator in predicting whether a release to the pathway is likely to occur. These 

factors are based on containment features of the source of contamination (whether or not hazardous 

substance can get out), route characteristics specific to each pathway (how far hazardous substances could 

migrate based on knowledge of site conditions) and include physical/chemical properties of the hazardous 

substances being evaluated (how the hazardous substances act in the environment). 

Proposed Approach: EPA is proposing a parallel approach for evaluating potential and actual exposure of 

intruded hazardous substances for the subsurface intrusion addition to the HRS. In determining which route 

characteristics are appropriate for evaluating potential exposure to subsurface contaminants, EPA examined 

present modeling methods such as the Johnson-Ettinger model and also considered multiple lines of evidence 

approaches which estimate the levels of contaminant exposure based on numerous route characteristics. In 

addition, EPA examined the relationship between these factors to determine which have the greatest 

influence on the likelihood that an exposure would occur, and then incorporated these factors within its 

proposed approach. EPA also gave careful consideration to ensure that the data necessary to obtain route 

characteristic factors could be measured or calculated on a site-specific basis and in a manner consistent with 

current HRS evaluations. Based on the Agency’s analysis, the following three factors for which sufficient 

site-specific information could be collected during a site inspection represented the greatest impact on the 

potential for exposure: (1) depth to contamination; (2) vertical migration; and (3) vapor migration potential 

(see Figure 1). 

5
Figure 1 

Charge Question #1 : Is EPA’ s p roposed approa ch scientifically reasona ble for evaluating and assigning 

proportional weightings for the following whe n evaluating potential for exposure ? If no, what al ternative 

approach would you recommend? 

a. Consideration of the construction/structure type for which sufficient site-specific information

could be collected during a site inspection for the occupied structure;

b. Distance between occupied structure and depth of contamination; and

c. Evaluation of the vertical migration factor based on the thickness and porosity/permeability of

geologic materials in the interval between the lowest point of an occupied structure and the highest

known point of hazardous substances in the subsurface.

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2. Hazardous Waste Quantity

Background: In the current HRS, the hazardous waste quantity factor reflects the risk consideration related 

to the magnitude and duration of either the release for ground water, surface water, and air pathways, or the 

exposure for the soil exposure pathway (see section 2.4.2 of the current HRS). Hazardous waste quantity is 

evaluated for all four pathways. At each site evaluated, EPA uses a four-tiered hierarchy for calculating the 

hazardous waste quantity that is based on (1) constituent quantity; (2) waste stream; (3) volume; and (4) area 

of the sources of hazardous waste at the site. EPA uses minimum waste quantity factors when there is 

insufficient information to estimate hazardous waste quantity. In the ground water, surface water, and air 

pathways, the HRS evaluates the total quantity of hazardous substances available to migrate from the original 

sources (how much has migrated and how much can be released in the future). In the soil exposure pathway, 

the hazardous waste quantity does not include the total amount of hazardous substances in all site sources, 

but rather is based on the amount of hazardous substances to which a receptor can be exposed where actual 

contamination has been documented. In other words, for the soil exposure pathway, the risk posed by a 

release of hazardous substances is directly related to the amount of hazardous substances that receptors are 

exposed to, as opposed to how much of the hazardous substances from the original sources may migrate to 

the receptors. 

Proposed Approach: EPA is proposing a parallel approach to the soil exposure pathway to calculate 

hazardous waste quantity for the subsurface intrusion addition to the HRS. Since the subsurface intrusion 

component also focuses on exposure, the waste quantity factor value for this component should also reflect 

only the amount of hazardous substances that people actually are exposed to (the amount present in occupied 

structures). EPA is proposing to use a similar four-tiered hierarchical approach to calculate hazardous waste 

quantity within occupied structures with contamination. In cases where no home is subject to actual 

contamination, EPA is proposing to use minimum waste quantity factors. In situations where there is an 

observed release within a structure above benchmarks (Level I), a default value of 100 is proposed for the 

hazardous waste quantity factor value. This value is not used in the current soil exposure pathway, but is 

consistent with the ground water, surface water, and air pathways and reflects the increased exposure risk of 

a release within an occupied structure. 

Charge Question #2: Is EPA’s approach of basing the hazardous waste quantity on the amount of 

contaminants that could be found in the intruded structures appropriate? If no, what alternative approach 

would you recommend? 

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3. Population score

Background: Within the current HRS, receptors are evaluated in two main categories: whether they are 

exposed to 1) actual contamination; or 2) potential contamination (see section 2.5 of the current HRS). If 

receptors are exposed to contaminant levels meeting observed release criteria, they are identified as actually 

contaminated; however, if the receptors are not exposed to contaminants that meet the observed release 

criteria but are within the target area being evaluated, they are considered potentially contaminated. Actual 

contamination is further divided into two sub-categories based on whether the hazardous substance is present 

at or above a health-based benchmark. If the concentration of the hazardous substance released at the 

receptor is greater than a health-based benchmark, the receptors are identified as Level I receptors and are 

weighted (multiplied by a factor of 10) in scoring. If the release concentrations are less than a health-based 

benchmark, the receptors are identified as Level II receptors and are not weighted (multiplied by a factor of 

1). Potential receptors are distance/dilution weighted; in other words, the farther away a receptor is located 

from a source, the less the population contributes to the site score. 

Proposed Approach: EPA is proposing to generally use the same receptor weighting structure in the 

subsurface intrusion component as the one used in the current HRS. Those receptors in the area(s) of 

observed exposure (AOE) are considered actually contaminated, and those in the area(s) of subsurface 

contamination (ASC) are considered potentially contaminated (See Figure 2). The receptors in an AOE are 

further differentiated based on whether the contaminant concentrations are at levels above identified 

benchmarks (Level I) or are at levels establishing a release but below identified benchmarks (Level II). The 

benchmarks that EPA is proposing to use for the subsurface intrusion component are: 

• Screening concentration for cancer effects; and

• Screening concentration for non-cancer effects (systemic toxicants).

Consistent with the weighting of populations throughout the HRS, the proposed subsurface intrusion 

component will weight targets within the AOE subject to Level I contaminant concentrations by a factor of 

10 and weight targets subject to Level II contaminant concentrations by a factor of 1. 

EPA is proposing to evaluate the weighting of targets within the ASC based on sub-slab, soil gas, and/or 

ground water samples. Potential receptors within the ASC receive less weight (population multiplied by a 

factor of 0.1), except in cases where a sub-slab sample indicates contaminant levels are at least 10 times 

higher than a health-based benchmark (population is multiplied by a factor 0.75). The value of 0.75 was 

determined based on an evaluation of paired data when both a sub-slab and indoor air sample were collected. 

The 0.75 weighting reflects the observation that for approximately 80 percent of the sampling events where 

contamination was detected in the sub-slab, contamination was also detected in the indoor air sample. The 

order of magnitude adjustment applied to the health-based benchmark reflects EPA’s finding that, in such 

paired sampling events, the indoor air sample concentration is, on average, 10 times lower than the sub-slab 

sample concentration. 

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Figure 2 

Charge Question #3: Is it appropriate to consider individuals/populations located within the area of 

subsurface contamination (ASC) to be at a higher relative risk in situations when sub-slab contaminant 

concentrations are at least ten times greater than a health-based benchmark? If no, please explain. 

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4. Multi-story and multi-tenant structures

Background: In the current HRS, multi-story and multi-tenant buildings are evaluated based on population 

associated with an actually or potentially impacted target. In the ground water pathway, all residents who are 

served by a well are considered subject to the actual or potential contamination of the well. In the air 

pathway, all residents who have an opportunity to breathe ambient air are considered subject to the actual or 

potential contamination of the ambient environment within a distance category. All receptors within a 

contaminated surface water stretch are subject to the level of contamination associated with that surface 

water stretch. In the soil exposure pathway, receptors must be able to come in contact with areas of 

contamination. In determining the likelihood a person will come in contact with areas of contamination, the 

HRS uses a 200 foot rule (see section 5.1.3 of the current HRS) because it is reasonable to assume that that a 

person will walk/use areas within a 200 foot areal extent of their residence/property. The 200 foot rule is 

used regardless of whether a building is multi-tenant or multi-story (the assumption being that is reasonable 

for people to use the outside of their properties). 

Proposed Approach: EPA is proposing to evaluate multi-story/multi-tenant buildings utilizing a similar 

approach as soil exposure, limiting the receptors to those individuals that reasonably can be exposed to 

subsurface intrusion within an occupied multi-tenant/multi-story building. EPA is proposing to consider all 

receptors exposed to actual contamination as the population inhabiting the floor of the intruded space and the 

population inhabiting the floor above and the floor below the intruded space when calculating waste quantity 

and population. EPA considers that this approach will more accurately reflect risk to both actual and 

potential receptors, while also minimizing the potential for over counting (Figure 3). 

Figure 3 

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Charge Question #4: When calculating waste quantity and population, is it scientifically reasonable for 

populations in multi-story or multi-tenant structures to be evaluated based on using only the population 

inhabiting the intruded space and the population on the floor above and below the intruded space (For 

example, if contamination is found on the first floor, population from the basement and second floor would 

be used in the calculation. If contamination is found on the fifth floor, population from the fourth floor and 

sixth floor would be used in the calculation – for further explanation, see detailed discussion in above 

paragraph “Proposed Approach”)? If no, what alternative approach would you recommend? 

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5. Factor Value for Workers

Background: In the current HRS, 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 of observed 

contamination. These factor values range from 0 to15, depending on the number of workers exposed to 

outdoor contamination (see section 5.1.3.3 of the current HRS). 

Proposed Approach: EPA is proposing to mirror the procedures for the resident population threat in the soil 

exposure component when 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 and 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., factor values ranging from 0 to 45).

Charge Question #5: Because of longer exposure times indoors, is it reasonable to assume that the relative 

risk is three times greater for workers exposed to subsurface intrusion within the workplace than it is for 

workers exposed to outdoor surface contamination at the workplace? If no, please explain. 

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Summary Matrix of

Peer Review

Comments on

Preamble

13
Commenter Guidance 

Section

Line 

Number

Comment 

Burk VI.B.2.b. 824 Parenthetical Comment: Reference Section 5.2.1.3.2.3 for weightingBurk VI.B.3. 842 Consider replacing “this” with “observed exposure (section 5.2.1.1.1.)”Burk VI.B.3.a.ii 887-888 Comment: Consider using reference values as a first line of comparison, instead of nearby sampling data

area of release, what would the source(s) be? Many are totally dependent on individual occupants’ lifesty

house to the next: use of household products (hobbies, cleaning, home/auto/garden maintenance), use obusinesses, attached garages, and worker take-home exposures. Background sources that may come fr

volatilization from household water use from a similar water source, outdoor air, or subsurface sources fr

generators. However, most of these regional sources could be accounted for independently. Literature da

significant sources from individual occupant sources than select samples in the region of the site under in

Preamble or the HRS Rule documents are whether background implies the average concentration, UCL Reference to guidance on selecting background values could be provided (http://www.epa.gov/oswer/va

background-Report-062411.pdf), if explicit discussion is not. This reference includes data from thousands represent the wide range of behaviors and contributors to background indoor air contamination.

Burk VI B 3 a ii VI.B.3.a.ii 894 Consider adding: Consider adding: “Furthermore the background of some contaminants is expected to be negligible Furthermore, the background of some contaminants is expected to be negligible.”

Burk VI.B.3.a.ii 898 Consider adding “(or the similarity)” [...that the difference or the similarity is not simply...] 

Burk VI.B.3.a.ii 898-900 Extreme temporal and spatial variability is also a hallmark of the vapor migration pathway due to barome

complex factors, such as HVAC operation, opening a window, varying soil moisture content, snow/ice caeffects, to name only a few examples. Note should be made within the document that such untraditional hourly, daily and monthly basis and should be noted in site assessment for NPL listing. Perhaps this can 

Burk VI.B.3.a.ii 906 Consider inserting “a pre-determined” after "below" [...background level is below a pre-determined detecBurk VI.B.3.a.ii 906 Consider inserting “limit” after "detection" [...detection limit, any level...]

Burk VI.B.3.a.ii 929-931 This situation can get complex and may warrant further discussion in the technical document. While it is 

significantly higher than background, should the background be elevated with regard to health or quality should be deemed “elevated.” Also, let’s not forget about false negatives. If a GW plume has VOCs and those VOCs , and the indoor air is above a benchmark, then we should consider the exposure from the Chousehold sources are removed and levels found to be below levels of concern.

Burk VI.B.3.b.v. 1033 Delete second "to be" [...projected to be to be the most...] 

Burk VI.B.4.b. 1089 Remove "s" from "pathways"Burk VI.B.4.b. 1100 Change "potions" to "portions"Burk VI.B.4.b. 1108 Change "adequate" to "adequately"Burk VI.B.4.b. 1121 Consider changing "occur" to “be detected” [subsurface intrusion would be detected if sampling...]

Burk VI.B.4.b. 1126 Consider changing "actual" to “indoor air” [...sampling would document indoor air contamination.] 

Burk VI.B.5.c.ii 1280-1281 1280 1281 What is the basis f 0 ?C or using 0.75? Consider using 0.80 instead o 0 80 f 0 .75. It is more conservative and it is the 

data is available, such as for a nearby AOE, perhaps consider that percentage.

Burk VI.B.5.c.ii 1284 Will additive effects for generic types of contaminant VOCs and sVOCs be taken into account?

Hartman I.B 170-171 [Response to statement: "The EPA does not expect that this proposed change will result in additional s

will

Hartman I.B 174-175 [Response to statement: "For these reasons, the EPA considers that this proposed rule is not expected t

during any particular time period."] It definitely will 

Hartman I.B 183-184 The proposed rule is not compliant with the current & updated EPA-OSWER & EPA-OUST vapor intrusio

create more confusion.

Hartman III.A 241-243 This is deceptive. Because vapor intrusion screening levels are so low, the benchmarks the rule propose

will possibly score high in the HRS. 

Hartman III.A 243-245 Only true for sites with only vapor releases, but not sites with soil & groundwater contamination. Your cu

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Commenter Guidance 

Section

Line 

Number

Comment 

Hartman III.A 251-252 [In response to statement: "Over 40 written comments were received during the public comment period."

country with millions of people that could be affected by this new rule.

Hartman III.A 252-253 Your first line says ”because of the substantial public support.” But here you admit that of 40 comments, 

is not the public. Just how many comments were actually from non-government agencies? This means Seems to me that the public doesn’t really care about this proposed new rule.

Hartman III.A 255-256 5 out of 50 states says to me that the 90% of the States are not interested in this new ruleHartman III.A 256-258 ASTSWMO is NOT supportive of this rule for petroleum hydrocarbons. Your rule makes no distinction foHartman III.A 261-263 But didn’t you say previously on lines #171 & #174 that this new rule would not result in additional site inv

sites won’t result in more investigations?

Hartman III.A 283-284 Lines #171 & #174 say that the new rule won’t lead to additional site assessments, but here you admit th

Hartman III.A 286-289 [Regarding public support]: This is debatable as commented on above.Hartman III.A 288 [Regarding national program consistency]: Don’t the State Environmental regulatory agencies oversee th

Hartman III.C 390-391 I disagree with this statement.Hartman III.C 404-405 But your new rule is inconsistent with the EPA vapor intrusion guidance in some areas. This will create m

Hartman Hartman III.C 415 416 - [Regarding imposing costs on private entities]: But is likely the inevitable end [Regarding imposing costs on private entities]: But is likely the inevitable end result. -result.Hartman IV.B.2 488-489 This is where the rule is really lacking. Petroleum hydrocarbon VOCs behave very differently than haloge

proposed rule. 

Hartman V.A.2 569-572 This ITRC survey is out of date. Between 35 to 40 States now have their own vapor intrusion guidanceHartman V.A.2 574-575 [Regarding ASTSWMO support]: Not for petroleum hydrocarbon sites.Hartman V.A.3 605-607 Tiny number of comments from a nation this large. I consider this to not indicate a large public connern 

Hartman V.A.4 628-629 [Regarding "placeholder for topics identified as needing peer review"]: Would be nice to know what these Hartman VI.B.3.b.v. 1029-1030 This is where the rule is lacking. For hydrocarbon VOCs, bioattenuation will greatly reduce the migration 

for that.

Hartman VI.B.4.b. 1120-1122 But again, this needs to be broken down into hydrocarbon VOCs and halogenated VOCs? This 80% sho

Hartman VI.B.5.b.i 1203 [Regarding "• Screening concentration for cancer"]: The problem here is your are proposing to use a ben

too low and will be easily exceeded. Some States regulate this pathway at 1 in 100,000 and some at 1 

benchmark at the 1 in 10,000 risk level to avoid listing too many sites with a low potential for VI problems

Hartman VI.B.5.b.i 1204 [Regarding "• Screening concentration for noncancer toxicological responses"] With new toxilogical data 

(HI=1) are very low. Again, you will be listing too many sites if you use this as a benchmark. It is advised 

Hartman VI.B.5.b.ii 1220-1221 [Regarding value of 20]: This value seems completely subjective to me. What is the basis? You have no Hartman VI.B.5.c.ii 1280-1282 No, this is the 95th percentile, in the EPA report not the average. The 10x criterion is too low and will res

In addition, this rule should not apply to hydrocarbon VOCs since the EPA report was based upon haloge

H t ar man VI B 5 d VI.B.5.d 1303 1304 1303-1304 B t th b h k h ld l b t t bli h d i l f i l/i d t i l t 

But the benchmark should also be set to published screening values for commercial/industrial receptors, 

Johnson 9 General 

Comment

I understand the need to generalize and provide flexibility to deal with any intrusion to buildings (gases or 

is specific to vapor intrusion and is not relevant to intrusion of liquids. This should probably be mentioned discussions of specifics should be stated up front. 

Johnson Summary 25-26 To be consistent with other USEPA documents, should this state “The NPL is a list of national priorities a

releases”?

Johnson Summary 30 I can understand this addition to the HRS not affecting the current placement of sites on the NPL, but cou

a “proposed” site is selected for the NPL?

Johnson I.B 163 “contaminant” is redundant, given the definition of “subsurface intrusion”given above.Johnson I.B 170-171 [Regarding "The EPA does not expect that this proposed change will result in additional site assessment

that many sites do not have the appropriate data to assess the pathway. For example, I work close to a than a decade and that has in the last year conducted a new off-site site assessment specific to this pathbelow.

15
Commenter Guidance 

Section

Line 

Number

Comment 

Johnson III.A 224-225 [Regarding "The most common form of subsurface intrusion is vapor intrusion."]: What other forms are a

Johnson III.A 230 Is “relative” necessary or appropriate here? If so, should you add “compared to other sites” as is done be

Johnson III.A 233 [Regarding "exposure"]: Should you say “contact or ingestion” here to be consistent with the sentence str

Johnson III.A 261 [Regarding "the subsurface"]: Should you insert “scope of”, “breadth of” or “scale of” here?

Johnson III.A 265-275 Bulleted Text Are any of these sites ones where it is something other than vapor intrusion? It would be useful to clarify 

Johnson III.A 280 [Regarding "...nor does the EPA have any specific subsurface intrusion sites for the NPL identified at this 

52nd Street site? They are devoting a lot of effort now to look at this pathway.

Johnson III.A 280-283 This seems to conflict with earlier statements about how addition of this pathway is unlikely to change the 

Johnson III.C 350 [Regarding "gas, vapor"]: Are “gas” and “vapor” different things to the authors? They mean the same to m

Johnson III.C 383 [Regarding "is operated strictly by the public sector"]: Is this a true statement? There are DoD (non-publi

assessments are reviewed and commented on by EPA and its contractors.

Johnson III.C 389-391 The reasoning here is a little strange – basically it’s saying that the number of sites on the NPL is constra

risks posed by the sites. It is not clear why this concept is needed in this preamble or why it is repeated oor not evaluation of this pathway will lead to more cleanup or the identification of more sites requiring furt

sites on the NPL grow)? The GAO reported seemed to anticipate the potential growth in the number of s

pathway.

Johnson III.C 392-394 What evidence do you have to back this up? There are a few well-known sites with exemplary programs 

have not yet even looked at the pathway.

Johnson III.C 400 [Regarding "most states"]: Is “most” a true statement at this point in time? I can think of “a few” or “some

569 – 577 below as contradictory statements.

Johnson V.A.2 565 [Regarding "non-federal"]: Is it assumed here that there is a comprehensive program for evaluation SsI a

Johnson VI.B.2.b. 820 Lines 817-819 indicate that that the ASC is based on known subsurface contamination, so why include th

documented that subsurface contamination has occurred..”?

Johnson VI.B.3.a.ii 887-894 How will you deal with the situation where health levels of concern are at or below background levels for 

Johnson VI.B.3.a.ii 904-905 [Regarding "three times the background level"]: Why 3X? If I measure background at about 0.2 ug/m3 a

are 0.2 ug/m3 , is this the right conclusion? These issues will be important for this pathway (more so tha

measured values, background levels, and levels of concern are likely to fall in the 1X – 10X real detection

Johnson VI.B.3.a.ii 906-907 Even if 10% above detection levels?Johnson VI.B.3.a.ii 919-923 Note that our research has shown that indoor air sources can themselves cause subsurface contaminatio

So simply looking for the presence indoors and in the subsurface does not conclusively prove that indoor 

Johnson VI.B.3.a.ii 929-931 This section’s discussion is predicated on the assumption that not seeing a chemical in typical indoor air 

occurring. Our detailed field study data from Utah has shown that to not be true. Probably need to ment

lines 934 – 937.

Johnson VI.B.3.b 940 This “samp g lin ” seems to assume that all sampg p lin is of the point-in-time and p p yp ( g point-in-space type (e.g. Su

that may prove to be more reliable in the next few years. The language should allow for the developmenspecific to say that it is considering conventional sampling approaches as the current norm.

Johnson VI.B.3.b 944-945 Good point and this paragraph is pretty well written and important.Johnson VI.B.3.b 949 Note that this figure [5] only shows vapor intrusion and not any other anticipated “subsurface intrusion” ro

Johnson VI.B.3.b.ii 991-992 [Regarding "depth to contamination"]: This one should probably be replaced with chemical type. Whethe

biodegradable is a much more significant factor than depth (see comment below) and modeling and emp

Johnson VI.B.3.b.iii 996-1003 I have concerns about this factor. In theory, for non-biodegradable chemicals, depth can at most affect t

source 200 ft deep would only be 10X less than one from 20 ft deep, and there would be even less differdiffusion resistance (i.e., if the capillary fringe or the building structure were instead the controlling factors

show a strong dependence on depth, if I remember correctly.

16
Commenter Guidance 

Section

Line 

Number

Comment 

Johnson VI.B.3.b.iv 1019-1022 I would like to see the back-up for this. As shown in EPA guidance document modeling and other work t

does not have a significant effect on effective diffusion coefficients. 10000X differences in permeability m

differences in diffusion coefficients. The one thing (perhaps the only thing) that will make a significant di

between the vapor source and building or the presence of a highly water saturated soil layer. The EPA esignificant effect of soil type.

Johnson VI.B.3.b.v 1034-1037 This should focus more on some combination of vapor pressure, Henry’s Law constant, site concentratio

always the most volatile chemical that poses the greatest health threat.

Johnson VI.B.4.b 1119 [Regarding "waste quantity"]: Wouldn’t it make more sense to have this factor related to either groundwa

Johnson VI.B.4.b 1123-1124 See comment above concerning the connection between indoor air sources and subsurface vapor clouds

of causing the latter.

Johnson VI.B.5.a 1167-1169 This makes sense.Johnson VI.B.5.b.i 1189 [Regarding "outdoor"]: Do you mean “outdoor” or “exterior” sampling. The former implies above-ground s

terminology for sub-slab, subsurface, and groundwater sampling around and beneath a building.

Johnson VI.B.5.c.i 1251-1253 This seems reasonable for this pathway, although I’d expect some people to object.Johnson VI.B.5.c.ii 1279-1282 Note comments above concerning indoor air sources and subslab vapor concentrations – this high corre

as well as for subsurface sources, so the relationship is not unique nor proof that subslab detections are 

pathway.

Lofstrum/Klein 13 General 

Comment

It should be made clear from the outset that the ‘hazardous substances’ referred to in the proposed subssubstances that can volatilize and migrate through the subsurface to inhabited structures. This is not ma

Lofstrum/Klein III.A 225 There are several places where the term ‘EPA’ is used instead of ‘the EPA’. It should be ‘the EPA’Lofstrum/Klein III.A 235-236 How would contaminants from surface water bodies enter indoor air spaces?Lofstrum/Klein III.A 247 Replace with ‘Second, the” and delete ‘is’ before 'because' to be consistent with the first paragraph on th

EPA is offering today’s proposal because of the substantial..."] 

Lofstrum/Klein III.A 260 Replace with ‘Third,”. [Sentence should read: "Third, the EPA has..."]

Lofstrum/Klein III.A 260 Replace with ‘evaluated’ [Sentence should read "...the EPA has evaluated..."]

Lofstrum/Klein III.A 261 Replace with ‘by identifying the magnitude of”. [Sentence should read "...to the current HRS by identifyi

Lofstrum/Klein III.C 349 I think it would be clarifying to add ‘volatile’ before ‘hazardous substances’. Or say ‘hazardous substanceLofstrum/Klein III.C 350 What is the difference between a gas and a vapor?

Lofstrum/Klein IV.B 474 Figure 2 Define the abbreviations/symbols across the bottom of this figure.Lofstrum/Klein V.A.1 524 Replace with ‘the EPA’.Lofstrum/Klein V.A.1 526 Replace with ‘the EPA’.Lofstrum/Klein V.A.1 532 Add ‘the’ before ‘Resource’.Lofstrum/Klein V.A.1 547 Replace with ‘are’. ['...intrusion issues are evaluated..."]

Lofstrum/Klein V.A.2 575 Define. [ASTSWMO]Lofstrum/Klein V.A.2 579 Delete. ['In addition']Lofstrum/Klein V.A.2 581 Define. [ ] ATSDR

Lofstrum/Klein V.A.2 584 Add ‘the’ before ‘ATSDR’.Lofstrum/Klein V.A.2 586 Make this a period. Start a new sentence. [Sentences should read: "...uniformly and consistently. It is hig

Lofstrum/Klein V.A.4 628 Replace [agency] with ‘EPA’.Lofstrum/Klein V.A.4 629 Replace [agency] with ‘EPA’.Lofstrum/Klein V.A.5.5 645 This sentence should be changed to match the style of the other points. Like ‘Assemble and rely upon e

Lofstrum/Klein VI.A 723 This paragraph should include a discussion of ground water and how the proposal will not overlook groun

with the capability of intruding into indoor air spaces.

Lofstrum/Klein VI.A 724 Replace ['are consideration of'] with ‘consider’.

Lofstrum/Klein VI.B.2.b. 814 The approach for evaluating the area of subsurface contamination should be revised to include the ability 

contamination but without current structures.

Lofstrum/Klein VI.B.3 836 Delete the comma. [After 'HRS']

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Lofstrum/Klein VI.B.3.a 850 The terms contaminant and hazardous substance are used interchangeably throughout this preamble. W

replaced with’ hazardous substance’, because this term is what is used in the proposed regulations, and like ‘containment’ to the tired reader. 

Lofstrum/Klein VI.B.3.a.i 862 Why call out solid and liquid when only gas is addressed in the proposed revision to the HRS regulations

Lofstrum/Klein VI.B.3.a.i 865 Same comment as previous [Why call out solid and liquid when only gas is addressed in the proposed re

it should be clarified that the solid or liquid would contain a volatile hazardous substance(s).

Lofstrum/Klein VI.B.3.a.ii 904 Replace ['considered'] with ‘assumed’.Lofstrum/Klein VI.B.3.a.ii 919 Delete this phrase ['It is suggested that'] and add ‘should’ before ‘include’. ["The evidence to support this 

Lofstrum/Klein VI.B.3.a.ii 923 Delete. ['In addition,']Lofstrum/Klein VI.B.3.b 955 Figure 5 It would be clarifying to add the term ‘Chemical-specific’ to ‘Vertical Migration Factor’.Lofstrum/Klein VI.B.3.b.i 969 Change ['of'] to ‘to’. [...'minimize exposure to hazardous substances..."]Lofstrum/Klein VI.B.4.b. 1096 Delete. ['ever']Lofstrum/Klein VI.B.4.b. 1108 Replace ['insignificant'] with ‘insufficient’.Lofstrum/Klein VI.B.4.b. 1108 Replace ['adequate'] with ‘adequately’.Lofstrum/Klein VI.B.5.a 1164-1165 This ["Given that the subsurface...intrusion pathway."] is not a complete sentence.

Lofstrum/Klein VI B 5 c ii VI.B.5.c.ii 1261 The approach to weighting targets should be revised to include evaluating areas of subsurface contamin

The approach to weighting targets should be revised to include evaluating areas of subsurface contamin

Lofstrum/Klein VI.B.6 1351-1352 [Regarding: "...incorporation of the pathway score into a site score."]: Does this mean to say ‘how the intr

site score’? If so, this sentence should be rewritten for clarity.

Lofstrum/Klein VI.B.6.a 1361 Change ['reflect'] to another word to avoid redundancy in the same sentence. Change to ‘expresses’.Lofstrum/Klein VI.B.6.a 1362 Change ["each of the"] to ‘of each of the’. ["...the magnitude of each of the factor..."] Lofstrum/Klein VI.B.6.a 1363 Change ['probably'] to ‘probability’.

Lofstrum/Klein VI.B.6.a 1365 Change ['probably'] to ‘probable’.Lofstrum/Klein VI.B.6.b 1374 Delete. ["proposed to be"]Lofstrum/Klein VI.B.6.b 1381 Move this phrase ["using this approach to assigning the pathway score"] to the end of the sentence for cl

score’.

Lofstrum/Klein VII 1396 In Section 2.4.1.1 Toxicity Factor, carcinogenicity is divided into weight of evidence categories: A, B, and 

using these categories, so consideration should be given to updating that section as well.

18
Summary Matrix of

Peer Review

Comments on Charge

Questions and

Proposed Rule

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Burk 1.a No mention of the potential for intrusion from wet basements or factors affecting indoor air pre

structural integrity (“leakiness”) of building, was identified. Section 5.2.1.1.2.1 Structure Conta

place to add consideration of these topics.

Burk 1.b Agreed, reasonable.

Burk 1.c Consideration of the possibility for hydraulic pumping in areas prone to rapid rise of the gro

vapor intrusion events in Hartford, IL have been correlated with rise in the (http://www.atsdr.cdc.gov/HAC/pha/HartfordResidentialCommunity/HartfordResidentialComm

Burk 2 Agreed, appropriate.Burk 3 Agreed, however, the last bullet in section 5.2.1.2.2 of the HRS Rule document includes 

attenuation factor for crawl space intrusion to indoor air is 1, the crawl space criteria may be concentrations are greater than a benchmark (instead of 10 times a benchmark).

Burk 4 The charge question seems to be worded differently than the description in the HRS Rule doc

contaminated floor and one floor below and above the contaminated floor. Sections 5.2.1.3.2.within the story with Level I/II concentrations and those stories below that story. Section 5.2.1observed exposure, one story above and all stories below. I agree with either approach with a ventilation systems, may serve to transport hazardous vapors to distant floors. It may be prud

from floor to floor and not rule out floors that have not been sampled in such cases. Also, if a contamination in an isolated upper floor, all floors below seem at risk.

Burk 5 Agreed reasonable.

Burk 1.1 7 1 Phrases with the term “observed” are used frequently throughout the document but not ex

somewhere, such as adding Oserved Contamination: The presence of contamination determand differentiated from background by comparison with background concentrations.

Burk 2.4.2.2 23 36-37 Consider changing criteria for crawl space to: greater than its appropriate benchmark, since d

attenuation).

Burk 5.2.1.1.1 45 20 [Regarding background concentration]: More explanation of appropriate use of background or 

more detailed discussion is provided in the preamble. Consider inserting a reference to the co

more detailed section on this topic.

Burk 5.2.1.1.2.1 45 37 [Regarding structure containment]: Perhaps add a paragraph to this section explaining the po

structural integrity (leaky buildings) on structure containment. These topics are discussed in thhttp://www.itrcweb.org/Documents/VI-1.pdf

Burk 5.2.1.2.2 50 18-19 [Regarding enclosed crawl space]: Consider changing criteria for crawl space to: greater than 

factor for crawl spaces is 1 (no attenuation).

Burk 5.2.1.3 50 51 [Following "...with observed exporure."]: Consider adding: “, unless a preferential pathway exis

exists, such as an elevator shaft, count those targets in affected stories, unless information, sotherwise.

Burk 5.2.1.3.1 51 11 Consider moving the word “only” to follow the word “observation” [...if there is an only observe

Burk 5.2.1.3.2.3 52 4-5 Consider the possibility of preferential pathways, such as by elevator shaft, to different floors.

Burk 5.2.1.3.2.3 52 6-7 Consider changing criteria for crawl space to: greater than its appropriate benchmark, since d

attenuation).

Burk 5.2.1.3.2.3 52 11 Consider changing criteria for crawl space to: greater than its appropriate benchmark, since d

attenuation).

Burk 5.2.1.3.3 52 22-23 Consider the possibility of preferential pathways, such as by elevator shaft, to different floors.

Hartman 1 No, it is not scientifically reasonable using these 3 factors alone.

Hartman 1.c This is a better approach than the one written above. However, this approach is also flawed i

factor/potential. As now written, Section 5.2.1.1.2.3 & 4 & 5 have no allowance for bioattenua

that can bioattenuate such as vinyl chloride and petroleum VOCs.

Hartman 2 This approach is appropriate, but what is not appropriate is defining the level I & II benchmark

benchmarks at a 1 in 10,000 risk level.

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Hartman 3 EPA OSWER has released a paper evaluating attenuation factors, including sub-slab to indoo

above paragraph is not an average. It is a 95th percentile. If you are going to use an average higher. A paper released in 2011 says that a more reasonable subslab to indoor air attenuatioindividuals/populations located within the area of subsurface contamination (ASC) to be at a h

concentrations are high, the weighting factor of 0.75 should not apply until sub-slab values are 

10x higher.

Hartman 4 This protocol is okay so long as there are no elevators in the building or pipe/electrical chases 

Hartman 5 There’s no explanation as to where the factor of 3 came from. Hence, while it is reasonable to 

3 should be explained. 

Hartman General 

Comment

There needs to be a distinction in this rule between petroleum hydrocarbon VOCs which readcontaining halogens) that do not bioattenuate. I do not see any allowance for this under vapo

Hartman General 

Comment

One idea to distinguish between VOCs that bioattenuate versus those that don’t would be to c

be 0.1, 0.01, 0.001, and 0.0 using exclusion criteria that EPA-OUST is now considering.

Hartman General 

Comment

Setting benchmarks for cancer effects at 1e-6 risk level and for non-cancer at a HI=1 is going compounds are below ambient levels. Since your goal is to rank the highest priority sites, you 

cancer at HI 10 Thi ill li h th HRS l f ki th hi h t i it it b t 

HI=10. This will accomplish the HRS goal of ranking the highest priority sites but no

that are unlikely to have a vapor intrusion concern.

Hartman Table 5-13 46 13 General 

Comment

In some places (such as table 5-13 and section 5.2.1.3.2.3), the rule is inconsistent with curre

needs to be compliant with the two guidances coming out in March by EPA-OSWER & EPA-O

Hartman 5.2.1.3.2.3 52 3-16 General 

Comment

In some places (such as table 5-13 and section 5.2.1.3.2.3), the rule is inconsistent with curre

needs to be compliant with the two guidances coming out in March by EPA-OSWER & EPA-O

Hartman 5.2.1.1.1 45 21-23 If you set benchmark at 1 in 10,000 risk level for cancer and HI=10 for non-cnacer, the backgr

Hartman 5.2.1.1.2 45 32-36 You need to separate hydrocarbon VOCs from halogenated VOCs. Hydrocarbon VOCs bioatt

potential.

Hartman 5.2.1.1.2 46 13 Table 5-13, 

Row 6

EPA vapor intrusion guidance only goes out to 100 feet, so to be consistent, this value needs 

Hartman 5.2.1.1.2.3 46 22 This should not be applied to hydrocarbon VOCs to be consistent with EPA vapor intrusion guHartman 5.2.1.1.2.4 47 17 This approach is not valid for petroleum hydrocarbons as it does not account for bioattenuatio

bioattenuate.

Hartman 5.2.1.3.2 51 29 Table 5-20 10-6 risk is far too low a benchmark. A more appropriate one for the HRS would be 10-4.Hartman 5.2.1.3.2 51 29 Table 5-20 A HI of 1 is too low a benchmark. A HI of 10 would be more appropriate as a benchmark for tHartman 5.2.1.3.2.3 52 6-9 10 times is too low for subslab samples for this ranking. 50x is more appropriate. For crawlsp

This rule is inconsistent with EPA VI guidance.

Hartman 5.2.1.3.2.3 52 13 Thisfactor should be zero, not 0.1.

Johnson 1 Overall, the structure of this section seems to be based more on conventional wisdom (and co

understanding gained from theory/modeling and critically-reviewed empirical observations. 

For example field data and modeling show that the single most significant influence on vapor For example, field data and modeling show that the single-most significant influence on vapor 

biodegradable, and that is not considered here.In addition, for chemicals that do not significantly biodegrade during vapor transport (i.e., chloimpacts is primarily related to the quantity {(C Deff/L AB)/(QB Ctarget)}, where C is the source con

coefficient, L is the depth to the concentration C, AB and EB are the building footprint and exch

impacts. Of these quantities, the ones that might vary most from site to site and have the grearatios (C/Ctarget) and (Deff/L). The first is a measure of how strong the source is, while the seco

through the soil. The relative interplay between these quantities, the strength of the source, an

not reflected in the proposed approach.The proposed approach could be replaced by a simpler one based on only two primary factors

vs. depth table. There could also be a modifying factor for chemical degradability that would bconcentrations/oxygen content in air and depth).

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Johnson 1.a With respect to Table 5-12 (structure containment), I am not aware of definitive studies or sign

Items 4, 5, or 7. USEPA’s empirical database does not show a clear dependence on foundati

validation studies of the performance of passive systems (Items 5 and 7). It is also not clear t

the reality that it is not feasible to identify all intrusion points to buildings. Item 1 should include non-hazardous contaminants). This table could probably be reduced to three items (current ItItem 9)

Johnson 1.b There are ambiguities and potential issues with application of Table 5-13 (depth to contamina

clear if the authors intended for contaminant concentrations to be below background or detect

simply the depth to the closest detection above background or detection levels? These are twuse in a scoring system like this.For example, if the authors intended contaminant concentrations to be below background or d

this depth, then Table 5-13 is likely overly conservative.On the other hand, if the depth to be used is the depth to the closest detection above backgrothere are non-detect/background-level samples until that point is encountered), then the table may only be groundwater data available, and so people will be using depth to groundwater witdepth to groundwater has not been shown through field data or modeling to be as significant a

most intrusion rates would be 10X less for a 200 ft depth than for a 20 ft depth for comparable most intrusion rates would be 10X less for a 200 ft depth than for a 20 ft depth for comparable 

show little dependence on depth for the range of depths represented in the empirical data setThe following revisions are suggested:1) Clarify the meaning of “depth to contamination”. 2) If contaminant concentrations are supposed to be below background or detection levels fo

with typical data used for ranking), then only two or three depth categories are justified and th

20 ft.3) If it is the depth to the closest detection above background or detection levels, then Depth t

significantly with depth as happens in Table 5-13. It is justified to have a high value for cases but depths to about 100 ft (most sites) should probably all have about the same value and depvalues that are within 50% of the <100 ft values. This is in part because there is a second imp

contaminant concentration. For example, a groundwater plume with a 20 ug/L concentration 

with a 200 ug/L concentration at a 100 ft depth and a groundwater plume with a 400 ug/L concand a non-biodegradable chemical).

Johnson 1.c The vertical migration factor should be presented as being related to “soil type” and not effect

the vapor intrusion pathway and only soil descriptions are used in Table 5-14 anyway.Categories 2 and 3 in Table 5-14 should be adjusted so that “silty loams; loesses; silty clays; spermeable till (fine-grained, unconsolidated till, or compact till with some fractures)” should be assessment guidance document (as well as other publications) and empirical data show little 

Depth creeps in as an overly-sensitive modifying factor in Table 5-15, compounding its use al

Johnson 2 It is suggested that this be eliminated as a factor in assessing the relative risk of vapor intrusio

intrusion impacts, except to the extent that it might impact the longevity of the contaminant va

The proposed approach makes little sense and is not technically defensible. The mass of con

instead it is the duration of time that the vapor source will produce vapor concentrations of sig

to source zone longevity (under natural or remediation conditions) and groundwater migration very long time – probably decades for most sites evaluated by this process, unless source rem

less than a decade.Source concentrations should be included somewhere in the analysis as discussed above.

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Johnson 3 It should be recognized that this approach is predicated on two assumptions, both of which ha

1) It is assumed that areas of subsurface contamination have a 10X lower relative potential fo2) Sub-slab soil gas samples are reliable indicators of vapor intrusion.With respect to (1), the preamble document contains the paragraph:

“When an observed exposure has not been established, the EPA is proposing to evaluate the within the subsurface intrusion component. Given that contamination within an ASC is docum

that intrusion and exposure to the intrusion has occurred but that sampling has not been perfoexplained in section XXXX of the Proposal TSD, the factors affecting when intrusion will occur site- and climatic-specific. Sampling may not have been performed in these structures, or, eve

inspection, the sampling may have been during conditions that the intrusion was not occurring 

background sources of the contaminant. Site inspections are conducted over a limited period potential for exposure be included as a consideration when evaluating subsurface intrusion thThis paragraph reasonably captures the current state of the practice – namely that conventioncanisters) has been shown to be inadequate for confidently assessing the presence or absenc

unacceptable and highly variable indoor air impacts at chlorinated solvent sites with groundwadependence on groundwater concentration, soil type, or depth. Thus, the reality is that we are 

expected to be impacted, and which homes are likely to be the most impacted above a dissolvThis proposed approach seems to ignore this. There is no basis for assigning lower risks to a

conditions as nearby areas of observed impacts simply because impacts have not been obse

potential for exposure is the same in all areas having similar conditions, unless there has beefactors discussed above already reflect differences in potential for impacts based on soil type 

Johnson 3 (con't) USEPA’s database (raw data – not the alpha factor analysis) should be reviewed carefully in d

exposure vs. areas of subsurface contamination. For example, the figure below is from this dJohnson (2011, presentations) to point out that indoor air concentrations of concern have bee

chlorinated solvent sites:[See graph included in pdf version of response to charge questions ]

With respect to (2), the approach ignores the debate and recent technical advances regarding assessment. It has been shown at a field study site in Utah that indoor air sources can cause 

correlation between indoor air and sub-slab soil gas detections is not validation that sub-slab above ( ) as 1:1 correlation would occur with indoor sources as well). 

There are also field study results showing temporal and spatial variability in sub-slab soil gas 

even have been done for pathway assessment by the time that HRS calculations are being do

Johnson 4 It is not clear why possible exposures in the lowest floors (closest to the vapor source) would 

approach as I have little experience with impacts in multi-story buildings to draw from at this pthis issue will be a determining factor in HRS calculations.

Johnson 5 This seems to be a comparison of apples and oranges (indoor vapor inhalation vs. outdoor so

the two would be inappropriate.  It might be reasonable to assume that worker inhalation risks would be less than those of resin exposure durations. The type of work might affect both the building ventilation and worker and inhalation higher in more industrial settings vs. office and residential settings. 

23
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Johnson 1.1 4 37 Need to add a manmade example to the list – perhaps “utility conduit”?

Johnson 1.1 4 37-38

How is this different from “preferential subsurface intrusion pathways” given below?

Johnson 2.1 10 8 [Referring to "Soil Exposure and Subsurface Intrusion"]: Might be better to make this the fourt

sequentially.

Johnson 2.1 10 17 It’s not clear that this is true if you define the subsurface intrusion pathway to include both vap

inhalation while the threat from the latter might include direct contact as well as inhalation. Su

Johnson 2.1.3 10 40 [Referring to "...or observed exposure..."]: Should be either “and any verified areas of exposur

appropriate here as you will always have areas of observed contamination.

Areas of observed contamination are defined in §2.3, the terminology in §5.2 is “area of subsu

Johnson 2.1.3 12 16 As “migration pathways” is used as terminology throughout the document, it is suggested that 

Johnson 2.2 12 32 [Referring to "...areas of observed contamination or observed exposure..."]: Should be “subs

intrusion pathway?

Johnson Johnson 2 2. 12 32 [Referring to [Referring to ... " areas of observed contamination areas of observed contamination or observed exposure observed exposure..."]: Should be ]: Should be “and a

and a

Johnson 2.2 12 33 [Referring to "...areas of observed contamination or observed exposure..."]: Should be “subs

intrusion pathway?

Johnson 2.2 12 33 “areas of observed contamination” not a term defined in Definitions – “areas of subsurface co

Johnson 2.2 12 33 [Referring to "...areas of observed contamination or observed exposure..."]:Should be “and ar

Johnson 2.2.1 12 39 I suspect that people will get confused by “migration pathway” terminology – so you might con

include additional headings that clearly group air, groundwater, and surface water together as 

pathway.

Johnson 2.2.1 12 41 [Referring to "...areas of observed contamination or observed exposure..."]: Should be “areas 

terminology for the subsurface intrusion pathway?

Johnson 2.2.1 12 45 Table 2-2 Should this also include area of observed exposure? Also, it’s not clear what should be enter

Johnson 2.2.2 13 12 [Regarding "area of observed contamination"]: Needs to be defined in Definitions.

Johnson 2.2.2 13 18 [Regarding "observed contamination"]: See comment above concerning “observed contamina

Johnson 2.2.3 14 31 [Regarding "observed contamination"]: This terminology is not used in §5.2

Johnson 2.3 15 1 Table 2-3 Should be “Observed Release and Observed Contamination Criteria”? to be consistent with li

Johnson 2.3 15 1 Table 2-3 

[bulleted text]

I’m not sure if these criteria are useful for the vapor intrusion pathway. First, it is not clear wha

groundwater?) and second it does not include consideration of indoor air sources. Finally, for level, target acceptable breathing concentrations, and indoor air concentrations are often with You might consider limiting the analysis to only groundwater and soil gas data (and not indoo

some of my concerns.

What do you do when you have conflicting lines of evidence (e.g., indications of groundwater 

Johnson 2.4.1.1 15 30 [Referring to "a inhalation risk"]: [Should "a" be changed to]: “an”?

Johnson 2.4.1.2 18 34 [Referring to the word "or"]: “and” more appropriate here?Johnson 2.4.1.2 18 34 [Referring to "underlying"]: “from substances underlying”?

Johnson 2.4.2 18 38 [Referring to "...area of observed contamination or observed exposure..."]: Should be “area of 

observed exposure”?

Johnson 2.4.2 18 51 [Referring to "observed contamination"]: Should be “subsurface contamination” here?

Johnson 2.4.2 18 51 [Referring to "...observed contamination or observed exposure..."]: Should be “area of observ

exposure”?

Johnson 2.4.2 18 52 Do we have a criterion for “observed exposure”?

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Johnson 2.4.2 18-19 50-53, 1 This sentence makes my head hurt real bad [smiley face] Might be best to break it up into bu

terminology is being used correctly. As they are introduced originally in the text, “Observed contamination” seems to refer to a detlevels of significance, while areas of subsurface contamination and exposure are delineated acontamination” confuses me...

Johnson 2.4.2.1 19 13-14 What do you do in the situation where many homes overlie a single large dissolved chlorinate

Johnson 2.4.2.1.1 20 3-4 Why only the area of observed exposure, given the caveats concerning the difficulty in identify

Johnson 2.4.2.1.1 20 6 [Regarding "or area of observed contamination or observed exposure"]: Should be “area of ob

observed exposure”?

Johnson 2.4.2.1.1 20 8 [Regarding "area of observed contamination or observed exposure"]: Should be “area of obse

exposure”?

Johnson 2.4.2.1.1 20 10 [Regarding "area of observed contamination or observed exposure"]: Should be “area of obse

exposure”?

Johnson 2.4.2.1.2 21 1-2 [Regarding "area of observed contamination or observed exposure"]: Should be “area of obse

exposure”?

Johnson Johnson 24212 . . .1.2 21 4 [Regarding [Regarding "area of observed contaminat area of observed contamination or observed exposure or observed exposure ]: " Should be Should be “area of obse

area of obse

exposure”?

Johnson 2.4.2.1.2 21 15-16 Why only the area of observed exposure, given the caveats concerning the difficulty in identify

Johnson 2.4.2.1.3 21 33 [Regarding "area of observed contamination or observed exposure"]: Should be “area of obse

exposure”?

Johnson 2.4.2.1.3 21 43 Why only the area of observed exposure, given the caveats concerning the difficulty in identifyJohnson 2.4.2.1.3 21 45 [Regarding "area of observed contamination or observed exposure"]: Should be “area of obse

exposure”?

Johnson 2.4.2.1.3 21 48 [Regarding "area of observed contamination or observed exposure"]: Should be “area of obse

exposure”?

Johnson 2.4.2.1.4 22 1-2 [Regarding "area of observed contamination or observed exposure"]: Should be “area of obse

exposure”?

Johnson 2.4.2.1.4 22 11 Why only the area of observed exposure, given the caveats concerning the difficulty in identifyJohnson 2.4.2.1.5 22 15 [Regarding "area of observed contamination or observed exposure"]: Should be “area of obse

exposure”?

Johnson 2.4.2.2 23 12 [Regarding "observed contamination"]: “observed” or “subsurface” contamination?

Johnson 2.4.2.2 23 14 [Regarding "observed contamination"]: “observed” or “subsurface” contamination?

Johnson 2.4.2.2 23 18 Why only the area of observed exposure, given the caveats concerning the difficulty in identify

Johnson 2.4.2.2 23 20 Why only the area of observed exposure, given the caveats concerning the difficulty in identify

Johnson 2.4.2.2 23 36-38 This assumes that sub-slab samples are reliable indicators of vapor intrusion potential, and th

influenced by indoor air sources and the potential for significant spatial heterogeneity.

Johnson 5.2.0 44 31-37 What do you do if you have conflicting lines of evidence (e.g., groundwater impact but no soil 

condition for vapor intrusion assessments.

Johnson 5.2.0 44 39-40 You should probably also mention that unacceptable indoor air impacts have been observed a

in the 10’s of ug/L range to help put this issue in perspective.

Johnson 5.2.1.1 45 1 Empirical and modeling data for indoor concentrations at chlorinated solvent sites do not show 

soil type, or groundwater concentration, etc.. (the factors considered here). They most signific

contradictory to the implicit underlying assumptions that this section is based on.

Johnson 5.2.1.1.1 45 21-23 Not clear why this is a bullet item under a statement specific to indoor air samples?Johnson 5.2.1.1.2 45 32-33 Need some statement here explaining that the vapor intrusion pathway is difficult to observe u

potential must be looked at closely and weighted higher than for a pathway where it is easier ttext in the Preamble on this topic.

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Johnson 5.2.1.1.2.1 45 37-39 I’m not familiar with any studies showing the effectiveness of passive systems, and am therefo

potential for exposure (Item 5)Also EPA’s empirical database does not show any significant impact of foundation type on ind

Johnson 5.2.1.1.2.2 46 2-3 What if you only have groundwater data and no soil gas data? This would lead to deeper dep

Johnson 5.2.1.1.2.2 46 13 Table 5-13 This table assumes a significant reduction in exposure potential in moving to >20 ft BGS. For 

and so people will be using depth to groundwater with Table 5-13. The vapor intrusion impac

to be as significant as suggested by this table in either empirical data or modeling. Depth profactor for this pathway, unless it is required that both groundwater and soil gas data be collectSuggest changing to the following:- structures with intrusion of contaminated liquids probably should be prioritized above others 

- Depths to at least about 50 ft should probably all be assigned the same value 

Johnson 5.2.1.1.2.3 46 26 [Regarding "effective porosity/permeability"]: Suggest removing this terminology and just refer 

effective porosity or permeability when discussing vapor intrusion, as these are irrelevant qua

Johnson Johnson 521123 . .1.1.2.3 47 4 Table 5 Table 5 14 - See comment above [[Regarding See comment above [[Regarding "effective porosity/permeability effective porosity/permeability ]: " Suggest removing this term

Suggest removing this term

no need to mention effective porosity or permeability when discussing vapor intrusion, as thes

Johnson 5.2.1.1.2.3 47 4 Table 5-14 [Regarding "Assigned Porosity/Permeability Value"]: See comment above. Just call this “soil t

Johnson 5.2.1.1.2.3 47 4 Table 5-14 [Regarding "...silty loams; loesses; silty clays; sediments that are predominantly silts; moderat

compact till with some fractures)..."]: These materials should be in the second category – the 

difference in vapor intrusion impacts for these materials in comparison with sandy silts, etc.

Johnson 5.2.1.1.2.3 47 6 Table 5-15 [Regarding "Lowest Porosity"]: Need to change...Johnson 5.2.1.1.2.4 48 9 Table 5-16 This approach assumes that there are no combinations of low volatility and high toxicity of conJohnson 5.2.1.1.2.4 48 14 Table 5-18 [Regarding "Average of Vapor Migration Potential Values for Three Hazardous Substances"]: 

Johnson 5.2.1.1.2.5 48 18-19 [Regarding "factor value for containment"]: What is this? Is it the structure containment value

Johnson 5.2.1.2.2 49 10 [Regarding "Hazardous waste quantity"]: It is not clear that this quantity has any relevance to a

Why is it even considered?

Johnson 5.2.1.2.2 49 37 Why only areas of observed exposure?

Johnson 5.2.1.2.2 50 18-20 See comments above concerning the use of sub-slab samples.

Johnson 5.2.1.3.2.3 52 6-7 See comments above concerning sub-slab and crawlspace samples.

Johnson 5.2.1.3.2.3 52 10-13 This assumes a higher confidence in sub-slab samples than in groundwater samples.

Larsen 1.a Potential for Exposure Equation

I agree generally with the mathematical set up of the equation (2a*(2b+2c+2d) and the decisio

mathematical sense) of a building’s characteristics and the subsurface conditions that lay ben

professionals and researchers conceptualize t professionals and researchers conceptualize the vapor intrusion pathway to be Furthermore 

vapor intrusion pathway to be. Furthermore

pathway by assigning a value of 0 to structures that employ demonstrated effective vapor conOverall, the term for the structure (a) ranges from 0-10 while the subsurface term (the sum of 

range as low as zero to reflect the absence of vapor intrusion risks associated with high moleand most pesticides. Thus, either term could have a zero value and the exposure pathway woconditions: 1) in cases where a demonstrated effective vapor control technology is used, and Mathematically, this could be accomplished by multiplying the Depth to Contamination (b) and Potential (d) term. Thus a zero Vapor Migration Potential value would yield a zero for the enti

in this way, the range in values for the Depth to Contamination and Vertical Migration terms w

results fall into the intended range of values (0-500). 

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Commenter Charge 

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Larsen 1.a Table 5-12 Table 5-12 Structure Containment

I suggest revisions to Table 5-12 with respect to the number of building types distinguished, th

• There does not appear to be a category that describes maybe the commonly encountered ty

apparent open preferential pathways or vapor migration barrier system. This is a significant omstructures. On the scale of 1-10 that is used for this factor I would assign this category of buil

not the most vulnerable of residential structures.• Homes that are underlain by a combination of basement and crawl space, and which do not 

described as such and placed in Category 2. This is a common type of residential constructioWith this type of building there usually is a 4-5 ft high stem wall that separates the crawl space poor seal between the crawl space and basement areas. This allows vapors to freely migrate 

some of the most sensitive and vulnerable with respect to vapor intrusion. This type of struct

• In my experience, residences that are completely underlain by vented crawl spaces generallto vapor intrusion is considerably less than other building types. This was observed at a chlo

Eugene, Oregon. At this site, crawl space concentration showed a broad range of attenuation 

appeared crawl space concentrations were most influenced by background and insignificantly 

Based on my experience I would assign a value of 6 rather than 8 to this type of construction. regional/climatic differences that affect the degree of communication between the crawl space • Evidence of biogas, inert gases. Is this referring to methane and radon? Typically this type o

Larsen 1.b At the depths beyond the 0-10 ft range presented in Table 5-13 chemical diffusion is generally 

Diffusion and diffusive flux is typically described using Fick’s Law J= -D(dc/dz). Using Fick’s L

indoor air, concentration gradients as a function of depth are plotted below. [See Graph in PDF of Henning's Response to Charge Questions]Using this approach and assuming a Depth to Contamination value of 10 for a source 10 ft bea value of 5, 50 feet would have a value of 2, 100 ft a value of 1 and 150 ft of 0.66. Since this 

subsurface and not attempting to consider geologic heterogeneity, the values should be basedemonstrated to be accurate in numerous column tests of porous media; this is unless there i

assignments in Table 5-13. Considering Depth to Groundwater Contamination and Depth to Soil Vapor Contaminat

An important concern in the assignment of Depth to Contamination values under section 5.2.1equivalent media and at any given site there depths are presumably comparable. However, it of contamination at the water table, there will be corresponding soil gas contamination above the groundwater contamination. Depending on where the soil gas measurement is taken it co

groundwater contamination is measured at. Thus, the depth to contamination that is entered 

media was sampled and not the actual site conditions. I ran one of our bigger vapor intrusion sites (Tarr Oil, Portland, OR) through the Potential for Egroundwater data, and a 500 based on soil gas data. The location of the measurement also aThe depth of measurement and choice of media to sample potentially introduces a bias that s

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Larsen 1.c Assignment of Vertical Migration Factor Values 

Vertical migration values for soils assigned a porosity/permeability value of 4 (clays, low perm

excessively high when compared to the values of other soils and thicknesses in Table 5-15 anfactor. True clays and unfractured igneous rocks have extremely low effective porosities and virtually complete barrier to vapor transport. The only exception would be if the clays were or 

It is difficult to say the 0-5 ft thickness value of 15 for soils assigned a porosity/permeability vadown to zero. However, I suggest revising the value for the 5-10 ft thickness to 8 rather 12, a50 ft range to 3 rather than 6 and the 50-100 ft and 100-150 ft ranges both should be 1. I can

50-100 ft of true clay.The values in Table 5-15 applied to soils assigned a permeability/porosity value of 1-3 appear Although not discussed, effective porosity for gas transport (diffusion rates through water-filled through air-filled) is highly sensitive to moisture content in the soil and I assume this considera

soils typically retain a higher moisture content that further reduces effective porosity. This degannual precipitation rates and their seasonal distribution. Therefore, for identical soils it’s antic

vertical migration factor. Ideally the moisture content factor would be considered in the scorin

confidently develop values. 

Larsen 2 I disagree with the proposed approach to calculating hazardous waste quantities for the subsu

is a much less dense medium and as a consequence, for equivalent risk levels between varioEssentially airborne contaminants can generate equivalent human health risks to those resultmass. For example, the State of Oregon assumes benzo(k)anthene has an oral slope factor oof 6.2 mg/kg (equating to 1x10-6 risk). Assuming a 5000 ft2 property that is 70% land 30% im

to the screening level would contain approximately 1,190 grams of benzo(k)fluoranthene. In c

(inhalation slope factor of 0.031) contamination at a concentration 0.14 ug/m3 (equivalent to 1

time. Assuming an air exchange rate of 6 exchanges/day, approximately 3.1 grams would hav

Assuming an identical toxicity and slope factor to that of benzo(k)fluoranthene, the mass of vfor the equivalent risk. Humans contact and take up air contaminants much more efficiently tless mass for equivalent risk.Using Table 2-6 (pg. 22) and the methods outlined in 5.2.1.2.2 to assign a Hazardous Waste 

would get a quantity of 1 unless an exposure is documented then it defaults to 100. It appear

factor larger than 100. This results in relatively low Waste Characteristic Factor values compa

In this respect it appears to underestimate the risk of the subsurface intrusion pathway relative Suggested Alternative Proposed HRS Method of Estimating Hazardous Waste Quantity 

Quantify and include contaminant sources in the subsurface in addition to the contamination f

the contamination within the buildings and so could be legitimately included in the inventory o

would make the magnitude/mass of sources of vapor intrus would make the magnitude/mass of sources of vapor intrusion more comparable to those con

more comparable to those con

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Larsen 3 An obvious answer to the Charge Question #3 is: yes, in general occupants of buildings where 

benchmark are at higher risk relative to occupants ofbuildings with sub-slab concentrations that are less than this value. However, the scheme for 

does not appear consistent with the results of EPA’s compilation of paired sub-slab and indooAs described in sections xxxx of the draft HRS rule revisions, for targets/receptors occupying concentrations exceed 10x the benchmark screening level should assigned a weighting of 0.7

paired data indicate 80% of the time a subslab concentration exceeds 10x its respective heal

air. • Why wasn’t a value of 0.8 used instead 0.75 since the correlation described above was obse• 0.75 is used in all where a subslab VOC concentration greater than 10x its corresponding he

However, subslab VOC concentrations at many sites are routinely observed at levels from 100proposed HRS scheme for weighting targets, irrespective of the concentration observed, any Using a single value (such as 0.75) may be reasonable for weighting receptors when subslab values, and indoor concentrations are likely detectable but below benchmark values. Howeve

concentration threshold is crossed where the results of EPA data compilation indicate the pro

high. For these cases assigning a weighting factor that is closer to10 is more appropriate.

Larsen 3 (con't) The proposed target weighting approach may introduce a low bias to population risks, particu

and not indoor air. soil gas and not • It is not clear from the rule revision whether the appropriate weighting for targets within the A

concentration or whether some form of average value is considered (i.e. arithmetic mean, UC

process, would be to use the maximum subslab concentration observed, and that this expecta

• The EPA database on paired subslab and indoor air data has been reviewed by many states 

performed on both filtered and unfiltered data. The filtering was done in an effort to eliminate 

calculated attenuation factors. EPA has recognized the need to perform the data filtering to reused in an attempt to separate out background influences was to only consider data from siteconcentrations greater than 1000 ug/m3.The results of the data analysis indicate unfiltered paired subslab-indoor air data had an averaapproximately 0.002. An analysis of highly filtered similar to data by ODEQ produced an aver0.0002. Thus the statement that approximately half of the vapor intrusion sites had an averag

analysis of VI data.[See pdf of charge questions response for three graphs ]

Larsen 3 (con't) Recommendation

Based on: statistical analyses of the EPA Database and the recognition t Based on: statistical analyses of the EPA Database, and the recognition that it does not neces

it does not neces

recommend that within defined ASCs assign a target weight factor of:• 0.1 to occupants of buildings with subslab contaminant concentrations less than 50x the hea• 1 to occupants of buildings with subslab contaminant concentrations between 50x-500x the 

• 10 to occupants of buildings with subslab contaminant concentrations greater than 500x the 

Larsen 4 Figue 3 [Referring to graphic of second building from left]: In this contaminant distribution, I would ass

uncertainty from temporal variability of indoor air quality

Larsen 4 Figure 3 [Referring to graphic of third building from left]: In the above scenario, if level I and level II exp

values to the basement dwellings also. They are overwhelming the most sensitive locations a

higher concentrations overlie lower concentrations would be very unusual for a VI site. A morwould be simply being temporal variability in indoor air levels. 

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Larsen 4 Figure 3 [Referring to graphic of far right building]: I would weight the occupants of the first floor based 

residences and their occupants may be under weighted just because of the absence of direct 

make educated inferences of exposure levels

Larsen 4 Regarding the Calculation of Waste Quantity

See comments and responses to Charge Question #2 Regarding Assumptions and Weighting of Occupants/Targets in Multi-Family ResidenceSome comments are made directly on the Figure 3 – see boxed text. Aside from those sugge

Regarding the Weighting of Population Targets in AOE

In my opinion the weighting is disproportionately influenced by data type – specifically the diffeto inferred impacts based on subslab sampling. Whereas an individual or population directly levels above the health-based benchmark is indoor exposure directly observed to be over a bThe weighting of targets/receptors exposed to Level 1 contamination 10x higher than those exwith the recognized temporal variability in indoor air concentrations (See Paul Johnson’s recesignificant swings in the population score that are more artifacts of when the sampling occurre

VOC exposure. The concern regarding accurately characterizing indoor exposure levels is pa

indoor air concentrations measured within a short 2 indoor air concentrations measured, within a short 2 3- day period day period. 

Potential Ways to Mitigate Errors and Uncertainties

Two ways to mitigate this uncertainty and potential error is to characterize exposure levels usisampling periods, or alternatively increase the number of (shorter period) air samples that targ

intrusion. In short, use sampling technologies are approaches that provide better representatA different approach would be to apply a scheme that has more than two designations for con

detected/observed exposures that are <0.5x the benchmark health value, a value of 3 for valu

occupying buildings with exposures greater than the benchmark value. 

30
Commenter Charge 

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Larsen 4 (con't) Weighting of Population Targets in ASC

In the proposed approach for weighting target populations within the ASC it appears there is a indoor data. Under the proposed scheme, subslab concentrations greater than 10x the health

0.75 (weighted slightly less than a level II exposure) irrespective of the specific concentration opportunities for robust statistical analyses including the derivation of attenuation rate percent

used to help appropriately weight targets where only subslab data is available. For example, 

factor is 0.03, thus it can be concluded that if subslab levels exceed benchmarks by a factor obeing exposed to levels above the corresponding health-based criteria and that the appropriatIn section 5.2.1.3.2.3, the proposed rule indicates subslab data and crawlspace data will be si

are equivalent, however, EPA and others have generally assumed the attenuation factor betwassumed 1and thus is a reasonable surrogate for actual indoor air data. So, this would sugge

space should be weighted under the proposed scheme at a value of 1 and that if concentratioappropriate weighting would be 10.In general there appears to be a undervaluing of susbslab data, even when that is the only typprimary type of data available at a site and the population component of the scoring may be bscored risk may be substantially lower if the primary data source is subslab measurements thwas indoor measurements. 

RecommendationUse EPAs database of paired subslab and indoor air data to perform more refined weighting o

the probability a Level I or Level II exposure is occurring based on subslab data. Additional Comment

The example scenario described in the Charge Question #4 is highly unusual contamination f

Under this scenario I would expect all floors beneath the 4th floor to be considered and actualscenario and the actual proposed rule indicates all floors beneath the observed exposure wou

Larsen 5 I agree with the proposed weighting for workers. Generally, workers do spend more time indo

Larsen 1.1 7 2 It seems, the question of non-occupancy should consider how long a residence has been vac

Larsen 1.1 8 21 Might consider discussing effective air-filled porosity since this is the actual porosity that coun

1.1 8 31 I would add a definition of crawl space type construction and crawl space sample. 

Larsen 2.1.1 10 27 Equation I agree with the form of the equation and how vapor intrusion pathway was incorporated. It al

typically will be different substances driving the two pathway components. 

Larsen 2.4.1.1 16 18 Table 2-4 [Referring to "0.0001 ≤ RfC < 0.006"]: Factor of 60 difference

Larsen 2.4.1.1 2.4.1.1 16 18 Table 2 Table 2 4- [Referring to [Referring to "0 006 . ≤ RfC < 0 2 RfC < 0.2 ]: " Factor of 33 difference Factor of 33 differenceLarsen 2.4.1.1 16 18 Table 2-4 [Referring to "0.2 ≤ RfC < 2.0"]: Factor of 10 differenceLarsen 2.4.1.1 16 18 Table 2-4 [Referring to "0"]: Changes in RFC are directly proportional to benchmark values and calculat

of magnitude) the way the assigned values do. I do not see the justification for abandoning th

Larsen 2.4.1.2 18 35 Within large chlorinated solvent plumes, risk drivers can change depending on location. Thus 

substance. This should be accounted for in the general approach.

Larsen 2.4.2.2 23 21 As indicated in my responses to the charge questions, these calculations should consider the 

buildings. This would make better comparisons to hazardous waste quantities in other media pathway with respect to waste quantity.

Larsen 5.2.1.1.2.1 45 40 Table 5-12 [Referring to "Evidence of intrusion by biogas, inert gases or other non-hazardous substances

circumstance I typically come across or information that is not typically gathered.

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Commenter Charge 

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Larsen 5.2.1.1.2.1 45 40 Table 5-12 [Referring to "Existence of maintained vapor migration barrier system but not addressing all p

somewhere between No. 2 and No.3 – there should be one or more categories added to repre

Larsen 5.2.1.1.2.2 46 11 Treating subslab and water media as equivalent make work for overall predictions of VI. But d

may score differently based on whether soil gas or only groundwater data was collected. I sco

based on soil gas came out at 500, the same site scored 380 based on groundwater data. 

Larsen 5.2.1.1.2.2 46 13 Table 5-13

Last Row

[Referring to ">150ft 0"]: These values should mirror predicted changes in diffusive flux as pre

Larsen 5.2.1.1.2.3 46 20 Use the most sensitive structure.

Larsen 5.2.1.1.2.3 47 4 Table 5-14 There is no consideration of moisture content and its affects on diffusive/advective flux. This 

to climate. However, it is an important factor that does not appear in the scheme at all.

Larsen 5.2.1.1.2.3 47 4 Table 5-14 True clays are unusual and are very effective barriers. They seem overvalued in Table 5-15.

Larsen 5.2.1.1.2.4 48 14 Table 5-18 I don’t understand why we average the transport potential of three substances then use only t

Lofstrom/Klein 1 There is no provision for significant volatile organic chemical (VOC) concentrations detected i

Alternative: Provide default structure properties.

The vertical migration factor ranking considers certain geologic factors and identifies karst, lav

allow channelized flow. Manmade preferential pathways such as utility corridors and sewer liin the site inspection. Alternative: Expand the definition of channelized flow to include most c

expanded list in the regulatory language (Perhaps as part of Table 5-15 Vertical Migration Fac

Lofstrom/Klein 2 The hazardous waste quantity ranking is based on the assumption that a structure or structure

case at the site being evaluated, the approach seems appropriate. But it is difficult to imagine be accomplished within a 1 -2 day site inspection. Soil gas/groundwater sampling should be d

substances to be analyzed for in indoor air (substances associated with subsurface contaminaHowever, the approach does not allow for the determination of the hazardous waste quantity isubstance (VOC) contamination exists in soil/groundwater where structures could or will be co

estimating indoor air concentrations from measured environmental media concentrations (soiparameters for a default structure. Provide default volume values (a default area value is provregulations explicit direction on “where no home is subject to actual contamination”. 

Lofstrom/Klein 3 This approach is consistent with the California Department of Toxic Substances Control (DTS

Lofstrom/Klein 4 This is a reasonably conservative approach. However, there is much uncertainty surrounding 

depth discussion of this approach in the proposal Technical Support Document with reference

Lofstrom/Klein 5 Assuming a relative risk of three times greater for indoor workers vs. outdoor workers for vola

since indoor workers would be exposed to contaminated air in a limited volume over much of constrained in a limited space but is immediately diluted by atmospheric air. Other direct expo

cont ib t littl t t k /i t k b f th l til t f th h i l d di 

tribute very little to uptake/intake because of the volatile nature of the chemicals under dis

proposal Technical Support Document should discuss and provide support for any factor chos

Lofstrom/Klein 1.1 6 16 Definitions [The word 'agent']: Should be changed to ‘hazardous substance’ to be consistent with the langLofstrom/Klein 1.1 7 1 Definitions [The word 'was']: should be 'were'.Lofstrom/Klein 1.1 7 34 Definitions [The word 'toxicant']: Should be changed to ‘substance’ or ‘hazardous substance’.Lofstrom/Klein 1.1 8 42 Definitions [The word 'agent']: Change to ‘hazardous substance’. Lofstrom/Klein 1.1 9 7 Definitions [Regarding weight of evidence classification system] This classification scheme is no longer b

Lofstrom/Klein 5.2.1 44 41 There should be a bullet addressing area of subsurface contamination not containing a structu

Lofstrom/Klein 5.2.1.1.1 45 14 [Regarding word 'by']: Replace with ‘from’.Lofstrom/Klein 5.2.1.2.2 49 28 Table 5-19 The superscripts for C and D are incorrect.

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Lofstrom/Klein 5.2.1.3.2.3 52 3 There should be an approach for evaluating a potential population over an area of subsurface 

current structure.

33
Peer Reviews

Tonia Burk (ATSDR)

• Charge Question Comments

• CV

• COI Certification

34
Peer Review Charge for:

U.S. Environmental Protection Agency (EPA). Proposed Rule: Addition of a Subsurface Intrusion 

Component to the Hazard Ranking System; 40 CFR Part 300; EPA-HQ-SFUND-2010-1086; FRL_XXXX-X

(review draft). 

Background

The U.S. Environmental Protection Agency (EPA) is proposing to include a subsurface intrusion (SsI) 

component to the Hazard Ranking System (HRS). Subsurface intrusion is the migration of hazardous 

substances from the unsaturated zone and/or the surficial ground water into overlying structures. The HRS is 

the principal mechanism the EPA uses to evaluate sites for placement on the National Priorities List (NPL). 

The subsurface intrusion component addition (this addition) would primarily 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 and the environment from releases of hazardous substances. 

This addition will allow the HRS evaluation to directly consider human exposure to hazardous substances 

that enter building structures through subsurface intrusion, and thus enable sites with subsurface intrusion 

contamination to be evaluated for placement on the NPL. This addition will make the HRS more accurate in 

assessing a site’s relative potential risk. The Agency is not considering changes to the remainder of the HRS 

except for minor updates reflecting changes in terminology related to revised toxicological parameters. This 

proposed regulatory change does not affect the status of sites currently on or proposed to the NPL. 

Expertise Required

The peer review panel for U.S. EPA’s Proposed Rule: Addition of a Subsurface Intrusion Component to the 

Hazard Ranking System should include expertise in: 

Federal Agency Panelist: Panelist must have a strong working knowledge of policy and technical issues 

related to topic of vapor intrusion. Knowledge of recent developments in vapor intrusion technologies and 

research is required, in addition to working knowledge of federal vapor intrusion response programs. 

Expertise in hydrogeology, chemistry, knowledge of public health risks associated with indoor air threats, 

and the subsurface migration of volatile hazardous substances is necessary. Field experience conducting 

vapor intrusion investigations, while not required, is highly desirable. Experience conducting field 

investigations for the purpose of listing sites on the NPL and/or experience working with the HRS to 

evaluate sites for inclusion on the NPL is highly recommended, but not necessary. 

35
Peer Review Charge Questions

1. Potential for subsurface exposure (intrusion) into occupied structures

Background: The current HRS evaluates the likelihood of a release of a hazardous substance when an actual 

release has occurred through either chemical analysis or direct observation. The current HRS also evaluates 

the potential for a release to occur within the ground water, surface water and air pathways (see section 2.3 

of the current HRS). The potential for a release is determined by the consideration of pathway specific 

factors that aid the site evaluator in predicting whether a release to the pathway is likely to occur. These 

factors are based on containment features of the source of contamination (whether or not hazardous 

substance can get out), route characteristics specific to each pathway (how far hazardous substances could 

migrate based on knowledge of site conditions) and include physical/chemical properties of the hazardous 

substances being evaluated (how the hazardous substances act in the environment). 

Proposed Approach: EPA is proposing a parallel approach for evaluating potential and actual exposure of 

intruded hazardous substances for the subsurface intrusion addition to the HRS. In determining which route 

characteristics are appropriate for evaluating potential exposure to subsurface contaminants, EPA examined 

present modeling methods such as the Johnson-Ettinger model and also considered multiple lines of evidence 

approaches which estimate the levels of contaminant exposure based on numerous route characteristics. In 

addition, EPA examined the relationship between these factors to determine which have the greatest 

influence on the likelihood that an exposure would occur, and then incorporated these factors within its 

proposed approach. EPA also gave careful consideration to ensure that the data necessary to obtain route 

characteristic factors could be measured or calculated on a site-specific basis and in a manner consistent with 

current HRS evaluations. Based on the Agency’s analysis, the following three factors for which sufficient 

site-specific information could be collected during a site inspection represented the greatest impact on the 

potential for exposure: (1) depth to contamination; (2) vertical migration; and (3) vapor migration potential 

(see Figure 1). 

36
Figure 1 

Charge Question #1 : Is EPA’ s p roposed approa ch scientifically reasona ble for evaluating and assigning 

proportional weightings for the following whe n evaluating potential for exposure ? If no, what al ternative 

approach would you recommend? 

a. Consideration of the construction/structure type for which sufficient site-specific information

could be collected during a site inspection for the occupied structure;

b. Distance between occupied structure and depth of contamination; and

c. Evaluation of the vertical migration factor based on the thickness and porosity/permeability of

geologic materials in the interval between the lowest point of an occupied structure and the highest

known point of hazardous substances in the subsurface.

Response 1.a. No mention of the potential for intrusion from wet basements or factors affecting indoor air 

pressure and exchange rate, such as HVAC systems or structural integrity (“leakiness”) of building, was 

identified. Section 5.2.1.1.2.1 Structure Containment of the HRS Rule document may be an appropriate place 

to add consideration of these topics.

Response 1.b. Agreed, reasonable. 

Response 1.c. Consideration of the possibility for hydraulic pumping in areas prone to rapid rise of the 

groundwater table may warrant a higher ranking. For example, vapor intrusion events in Hartford, IL have 

been correlated with rise in the Mississippi River and, to a lesser extent, rainfall 

37
(http://www.atsdr.cdc.gov/HAC/pha/HartfordResidentialCommunity/HartfordResidentialCommunityLHC02

-24-2010.pdf).

38
2. Hazardous Waste Quantity

Background: In the current HRS, the hazardous waste quantity factor reflects the risk consideration related 

to the magnitude and duration of either the release for ground water, surface water, and air pathways, or the 

exposure for the soil exposure pathway (see section 2.4.2 of the current HRS). Hazardous waste quantity is 

evaluated for all four pathways. At each site evaluated, EPA uses a four-tiered hierarchy for calculating the 

hazardous waste quantity that is based on (1) constituent quantity; (2) waste stream; (3) volume; and (4) area 

of the sources of hazardous waste at the site. EPA uses minimum waste quantity factors when there is 

insufficient information to estimate hazardous waste quantity. In the ground water, surface water, and air 

pathways, the HRS evaluates the total quantity of hazardous substances available to migrate from the original 

sources (how much has migrated and how much can be released in the future). In the soil exposure pathway, 

the hazardous waste quantity does not include the total amount of hazardous substances in all site sources, 

but rather is based on the amount of hazardous substances to which a receptor can be exposed where actual 

contamination has been documented. In other words, for the soil exposure pathway, the risk posed by a 

release of hazardous substances is directly related to the amount of hazardous substances that receptors are 

exposed to, as opposed to how much of the hazardous substances from the original sources may migrate to 

the receptors. 

Proposed Approach: EPA is proposing a parallel approach to the soil exposure pathway to calculate 

hazardous waste quantity for the subsurface intrusion addition to the HRS. Since the subsurface intrusion 

component also focuses on exposure, the waste quantity factor value for this component should also reflect 

only the amount of hazardous substances that people actually are exposed to (the amount present in occupied 

structures). EPA is proposing to use a similar four-tiered hierarchical approach to calculate hazardous waste 

quantity within occupied structures with contamination. In cases where no home is subject to actual 

contamination, EPA is proposing to use minimum waste quantity factors. In situations where there is an 

observed release within a structure above benchmarks (Level I), a default value of 100 is proposed for the 

hazardous waste quantity factor value. This value is not used in the current soil exposure pathway, but is 

consistent with the ground water, surface water, and air pathways and reflects the increased exposure risk of 

a release within an occupied structure. 

Charge Question #2: Is EPA’s approach of basing the hazardous waste quantity on the amount of 

contaminants that could be found in the intruded structures appropriate? If no, what alternative approach 

would you recommend? 

Response 2. Agreed, appropriate.

39
3. Population score

Background: Within the current HRS, receptors are evaluated in two main categories: whether they are 

exposed to 1) actual contamination; or 2) potential contamination (see section 2.5 of the current HRS). If 

receptors are exposed to contaminant levels meeting observed release criteria, they are identified as actually 

contaminated; however, if the receptors are not exposed to contaminants that meet the observed release 

criteria but are within the target area being evaluated, they are considered potentially contaminated. Actual 

contamination is further divided into two sub-categories based on whether the hazardous substance is present 

at or above a health-based benchmark. If the concentration of the hazardous substance released at the 

receptor is greater than a health-based benchmark, the receptors are identified as Level I receptors and are 

weighted (multiplied by a factor of 10) in scoring. If the release concentrations are less than a health-based 

benchmark, the receptors are identified as Level II receptors and are not weighted (multiplied by a factor of 

1). Potential receptors are distance/dilution weighted; in other words, the farther away a receptor is located 

from a source, the less the population contributes to the site score. 

Proposed Approach: EPA is proposing to generally use the same receptor weighting structure in the 

subsurface intrusion component as the one used in the current HRS. Those receptors in the area(s) of 

observed exposure (AOE) are considered actually contaminated, and those in the area(s) of subsurface 

contamination (ASC) are considered potentially contaminated (See Figure 2). The receptors in an AOE are 

further differentiated based on whether the contaminant concentrations are at levels above identified 

benchmarks (Level I) or are at levels establishing a release but below identified benchmarks (Level II). The 

benchmarks that EPA is proposing to use for the subsurface intrusion component are: 

• Screening concentration for cancer effects; and

• Screening concentration for non-cancer effects (systemic toxicants).

Consistent with the weighting of populations throughout the HRS, the proposed subsurface intrusion 

component will weight targets within the AOE subject to Level I contaminant concentrations by a factor of 

10 and weight targets subject to Level II contaminant concentrations by a factor of 1. 

EPA is proposing to evaluate the weighting of targets within the ASC based on sub-slab, soil gas, and/or 

ground water samples. Potential receptors within the ASC receive less weight (population multiplied by a 

factor of 0.1), except in cases where a sub-slab sample indicates contaminant levels are at least 10 times 

higher than a health-based benchmark (population is multiplied by a factor 0.75). The value of 0.75 was 

determined based on an evaluation of paired data when both a sub-slab and indoor air sample were collected. 

The 0.75 weighting reflects the observation that for approximately 80 percent of the sampling events where 

contamination was detected in the sub-slab, contamination was also detected in the indoor air sample. The 

order of magnitude adjustment applied to the health-based benchmark reflects EPA’s finding that, in such 

paired sampling events, the indoor air sample concentration is, on average, 10 times lower than the sub-slab 

sample concentration. 

40
Figure 2 

Charge Question #3: Is it appropriate to consider individuals/populations located within the area of 

subsurface contamination (ASC) to be at a higher relative risk in situations when sub-slab contaminant 

concentrations are at least ten times greater than a health-based benchmark? If no, please explain. 

Response 3. Agreed, however, the last bullet in section 5.2.1.2.2 of the HRS Rule document includes 

enclosed crawl spaces in this criteria. Since EPA’s default attenuation factor for crawl space intrusion to 

indoor air is 1, the crawl space criteria may be better stated as considering populations when crawl space 

concentrations are greater than a benchmark (instead of 10 times a benchmark). 

41
4. Multi-story and multi-tenant structures

Background: In the current HRS, multi-story and multi-tenant buildings are evaluated based on population 

associated with an actually or potentially impacted target. In the ground water pathway, all residents who are 

served by a well are considered subject to the actual or potential contamination of the well. In the air 

pathway, all residents who have an opportunity to breathe ambient air are considered subject to the actual or 

potential contamination of the ambient environment within a distance category. All receptors within a 

contaminated surface water stretch are subject to the level of contamination associated with that surface 

water stretch. In the soil exposure pathway, receptors must be able to come in contact with areas of 

contamination. In determining the likelihood a person will come in contact with areas of contamination, the 

HRS uses a 200 foot rule (see section 5.1.3 of the current HRS) because it is reasonable to assume that that a 

person will walk/use areas within a 200 foot areal extent of their residence/property. The 200 foot rule is 

used regardless of whether a building is multi-tenant or multi-story (the assumption being that is reasonable 

for people to use the outside of their properties). 

Proposed Approach: EPA is proposing to evaluate multi-story/multi-tenant buildings utilizing a similar 

approach as soil exposure, limiting the receptors to those individuals that reasonably can be exposed to 

subsurface intrusion within an occupied multi-tenant/multi-story building. EPA is proposing to consider all 

receptors exposed to actual contamination as the population inhabiting the floor of the intruded space and the 

population inhabiting the floor above and the floor below the intruded space when calculating waste quantity 

and population. EPA considers that this approach will more accurately reflect risk to both actual and 

potential receptors, while also minimizing the potential for over counting (Figure 3). 

Figure 3 

42
Charge Question #4: When calculating waste quantity and population, is it scientifically reasonable for 

populations in multi-story or multi-tenant structures to be evaluated based on using only the population 

inhabiting the intruded space and the population on the floor above and below the intruded space (For 

example, if contamination is found on the first floor, population from the basement and second floor would 

be used in the calculation. If contamination is found on the fifth floor, population from the fourth floor and 

sixth floor would be used in the calculation – for further explanation, see detailed discussion in above 

paragraph “Proposed Approach”)? If no, what alternative approach would you recommend? 

Response 4. The charge question seems to be worded differently than the description in the HRS Rule 

document on this topic. The charge question considers only the contaminated floor and one floor below and 

above the contaminated floor. Sections 5.2.1.3.2.1 and 5.2.1.3.2.2 say to consider those populations living 

within the story with Level I/II concentrations and those stories below that story. Section 5.2.1.3.3 says to 

count those workers in the highest story with observed exposure, one story above and all stories below. I 

agree with either approach with a caveat: preferential pathways, such as elevators and ventilation systems, 

may serve to transport hazardous vapors to distant floors. It may be prudent to consider the possibility of 

discontinuous contamination from floor to floor and not rule out floors that have not been sampled in such 

cases. Also, if a preferential pathway has not been identified to contamination in an isolated upper floor, all 

floors below seem at risk. 

5. Factor Value for Workers

Background: In the current HRS, 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 of observed 

contamination. These factor values range from 0 to15, depending on the number of workers exposed to 

outdoor contamination (see section 5.1.3.3 of the current HRS). 

Proposed Approach: EPA is proposing to mirror the procedures for the resident population threat in the soil 

exposure component when 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 and 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., factor values ranging from 0 to 45).

Charge Question #5: Because of longer exposure times indoors, is it reasonable to assume that the relative 

risk is three times greater for workers exposed to subsurface intrusion within the workplace than it is for 

workers exposed to outdoor surface contamination at the workplace? If no, please explain. 

Responst 5. Agreed reasonable. 

43
WORK EXPERIENCE

Position: Environmental Health Scientist 

Dates Employed: 11/2006 - present 

Employer: U.S. Department of Health and Human Services, Agency for Toxic 

Substances and Disease Registry, Division of Health Assessment and 

Consultation, Site and Radiological Branch 

Address: 4770 Buford Hwy, Mailstop F-59, Atlanta, GA 30341 

Responsibilities: Review information on environmental contamination and make 

recommendations to protect public health using the recent scientific 

body of knowledge, writing skills and interpersonal communication 

skills. Serve as agency expert on vapor intrusion. 

Position: Human Health Risk Assessment Analyst 

Dates Employed: 5/2002 - 11/2006 

Employer: State of Georgia, Department of Natural Resources, Environmental 

Protection Division, Hazardous Waste Management Branch, 

Corrective Action Program 

Address: Suite 1154, East Floyd Tower, 2 MLK Jr Dr, Atlanta, GA 30334 

Responsibilities: Review and critique risk assessment reports, policies and regulations. 

Assist field teams with environmental sampling. Provide technical 

assistance regarding environmental contaminants for internal and 

external inquiries. Speak to concerned citizens. 

EDUCATION 

Ph.D. Chemical Engineering, May 2001 

 Minor: Biochemistry/Genetics 

Dissertation: Surface Characterization and Interactions in a Dry 

Powder Inhalant Drug Delivery System 

Auburn University, AL US 

Dual Degree Undergraduate 

B.S., Chemical Engineering, Auburn University, AL, Aug 1994

B.A., Math, Huntingdon College, Montgomery, AL Jun 1995

CERTIFICATIONS 

OSHA, 29 CFR 1910.120 (HAZWOPER) 

Heartsaver First Aid, American Heart Association 

Tonia R. Burk 

4770 Buford Hwy NE 

Mailstop f-59 

Atlanta, GA 30341 

fxt9@cdc.gov

44
SUBJECT MATTER EXPERT EXPERIENCE 

Teaching

ATSDR Vapor Intrusion Workshop, course coordinator, Aug 2007, Agency for Toxic 

Substances and Disease Registry, Atlanta, GA 

Public Health Assessment of Vapor Intrusion, ATSDR Basic Health Assessor Course, 

presenter, Jun 2008-9, Agency for Toxic Substances and Disease Registry, Atlanta, GA 

Presentation

ATSDR Health Assessment of Vapor Intrusion at Military Facilities (Abstract #10073),

Environment Energy & Sustainability Symposium & Exhibition: Soil and Groundwater 

Contamination Session, Denver, CO, June 16 2010. 

Current {Vapor Intrusion} Evaluations at ATSDR Associated with DoD, Multi-services 

DoD Panel, Crystal City, VA Aug 2009 

ATSDR Health Assessment of TCE Exposure by Vapor intrusion at Military Facilities,

Environment Energy & Sustainability Symposium & Exhibition in Denver CO, May 4 

2009. 

Public Health Assessment of Vapor Intrusion, Board of Scientific Counselors Meeting, 

November 2008, Atlanta, GA. 

Public Health Effects from Vapor Intrusion, Morehouse School of Medicine Grand 

Rounds, October 2008, Atlanta, GA. 

Vapor Intrusion at Military Sites: An ATSDR Overview, Joint Services Environmental 

Management Training Conference & Exposition: Environment and Energy Management 

in a Transforming DoD, May 5, 2008, Denver, CO. 

Public Health Assessment of Vapor Intrusion, Region 6 ATSDR Partnership meeting in 

Dallas, TX, February 2008. 

An Approach to Protecting the Public from Vapor Intrusion at a Well Defined Site: A 

Screening Procedure for Kelly AFB, San Antonio, TX, Regions 2 ATSDR/EPA 

Meeting, Bear Mountain, NY, October 2007 

An Overview of ATSDR's Perspective on Vapor Intrusion, Region 8 & 9 ATSDR/EPA 

Meeting, Las Vegas, NV, September 2007 

An Overview of the ITRC Guidance on Vapor Intrusion Guidance, ATSDR Vapor 

Intrusion Workshop, August 2007 

Risk Assessment of Air Toxics in Georgia, in the US EPA Regional Risk Assessors 

Conference, San Francisco, CA, 2006. 

45
46
47
Peer Reviews

Blayne Hartman  

(Hartman Environmental Geoscience)

• Charge Question Comments

• CV

• COI Certification

48
Comments on Proposed HRS Rule 

Addition of a Subsurface Intrusion Component 

to the Hazard Ranking System 

Dr. Blayne Hartman 

858-204-6170

blayne@hartmaneg.com

February 10, 2012 

Key Comments on this Document 

• There needs to be a distinction in this rule between petroleum hydrocarbon VOCs

which readily bioattenuate and recalcitrant VOCs (typically those containing

halogens) that do not bioattenuate. I do not see any allowance for this under

vapor migration potential factors.

• One idea to distinguish between VOCs that bioattenuate versus those that don’t

would be to come up with a bioattenuation factor. These factors would be 0.1,

0.01, 0.001, and 0.0 using exclusion criteria that EPA-OUST is now considering.

• Setting benchmarks for cancer effects at 1e-6 risk level and for non-cancer at a

HI=1is going to suck in almost every site as the screening levels for many

compounds are below ambient levels. Since your goal is to rank the highest

priority sites, you should set the benchmarks for cancer at 1e-4 risk and noncancer at HI=10. This will accomplish the HRS goal of ranking the highest

priority sites but not bog down your ranking with a large number of sites to rank

that are unlikely to have a vapor intrusion concern.

• In some places (such as table 5-13 and section 5.2.1.3.2.3), the rule is inconsistent

with current & forthcoming EPA vapor intrusion guidances. This rule needs to be

compliant with the two guidances coming out in March by EPA-OSWER & EPAOUST.

Feel free to contact me with any questions on these comments. 

Blayne Hartman 

49
Peer Review Charge for:

U.S. Environmental Protection Agency (EPA). Proposed Rule: Addition of a Subsurface Intrusion 

Component to the Hazard Ranking System; 40 CFR Part 300; EPA-HQ-SFUND-2010-1086; FRL_XXXX-X

(review draft). 

Background

The U.S. Environmental Protection Agency (EPA) is proposing to include a subsurface intrusion (SsI) 

component to the Hazard Ranking System (HRS). Subsurface intrusion is the migration of hazardous 

substances from the unsaturated zone and/or the surficial ground water into overlying structures. The HRS is 

the principal mechanism the EPA uses to evaluate sites for placement on the National Priorities List (NPL). 

The subsurface intrusion component addition (this addition) would primarily 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 and the environment from releases of hazardous substances. 

This addition will allow the HRS evaluation to directly consider human exposure to hazardous substances 

that enter building structures through subsurface intrusion, and thus enable sites with subsurface intrusion 

contamination to be evaluated for placement on the NPL. This addition will make the HRS more accurate in 

assessing a site’s relative potential risk. The Agency is not considering changes to the remainder of the HRS 

except for minor updates reflecting changes in terminology related to revised toxicological parameters. This 

proposed regulatory change does not affect the status of sites currently on or proposed to the NPL. 

Expertise Required

The peer review panel for U.S. EPA’s Proposed Rule: Addition of a Subsurface Intrusion Component to the 

Hazard Ranking System should include expertise in: 

Panelist from non-specified sector: Panelist must have a strong working knowledge of policy and technical 

issues related to the topic of vapor intrusion. Knowledge of recent developments in vapor intrusion 

technologies and research is required, in addition to working knowledge of federal vapor intrusion response 

programs. Expertise in hydrogeology, chemistry, knowledge of public health risks associated with indoor air 

threats, and the subsurface migration of volatile hazardous substances is necessary. Field experience 

conducting vapor intrusion investigations, while not required, is highly desirable. Experience conducting 

field investigations for the purpose of listing sites on the NPL and/or experience working with the HRS to 

evaluate sites for inclusion on the NPL is highly recommended, but not necessary. 

Peer Review Charge Questions

1. Potential for subsurface exposure (intrusion) into occupied structures

Background: The current HRS evaluates the likelihood of a release of a hazardous substance when an actual 

release has occurred through either chemical analysis or direct observation. The current HRS also evaluates 

the potential for a release to occur within the ground water, surface water and air pathways (see section 2.3 

of the current HRS). The potential for a release is determined by the consideration of pathway specific 

factors that aid the site evaluator in predicting whether a release to the pathway is likely to occur. These 

factors are based on containment features of the source of contamination (whether or not hazardous 

substance can get out), route characteristics specific to each pathway (how far hazardous substances could 

migrate based on knowledge of site conditions) and include physical/chemical properties of the hazardous 

substances being evaluated (how the hazardous substances act in the environment). 

50
Proposed Approach: EPA is proposing a parallel approach for evaluating potential and actual exposure of 

intruded hazardous substances for the subsurface intrusion addition to the HRS. In determining which route 

characteristics are appropriate for evaluating potential exposure to subsurface contaminants, EPA examined 

present modeling methods such as the Johnson-Ettinger model and also considered multiple lines of evidence 

approaches which estimate the levels of contaminant exposure based on numerous route characteristics. In 

addition, EPA examined the relationship between these factors to determine which have the greatest 

influence on the likelihood that an exposure would occur, and then incorporated these factors within its 

proposed approach. EPA also gave careful consideration to ensure that the data necessary to obtain route 

characteristic factors could be measured or calculated on a site-specific basis and in a manner consistent with 

current HRS evaluations. Based on the Agency’s analysis, the following three factors for which sufficient 

site-specific information could be collected during a site inspection represented the greatest impact on the 

potential for exposure: (1) depth to contamination; (2) vertical migration; and (3) vapor migration potential 

(see Figure 1). 

Figure 1 

Charge Question #1: Is EPA’s prop osed approa ch scientif ically reasonable f or evaluating and assigning 

proportional weightings for the following whe n evaluating potential f or exposure? I f no, what al ternative 

approach would you recommend? Comment [B1]: No, it is not 

scientifically reasonable using these 3 

factors alone. 

51
a. Consideration of the construction/structure type for which sufficient site-specific information

could be collected during a site inspection for the occupied structure;

b. Distance between occupied structure and depth of contamination; and

c. Evaluation of the vertical migration factor based on the thickness and porosity/permeability of

geologic materials in the interval between the lowest point of an occupied structure and the highest

known point of hazardous substances in the subsurface. Comment [B2]: This is a better 

approach than the one written above. 

However, this approach is also flawed if 

bioattenuation is not included into the 

vertical migration factor/potential. As now 

written, Section 5.2.1.1.2.3 & 4 & 5 have 

no allowance for bioattenuation, so the 

approach is fundamentally flawed for any 

VOCs that can bioattenuate such as vinyl 

chloride and petroleum VOCs. 

52
2. Hazardous Waste Quantity

Background: In the current HRS, the hazardous waste quantity factor reflects the risk consideration related 

to the magnitude and duration of either the release for ground water, surface water, and air pathways, or the 

exposure for the soil exposure pathway (see section 2.4.2 of the current HRS). Hazardous waste quantity is 

evaluated for all four pathways. At each site evaluated, EPA uses a four-tiered hierarchy for calculating the 

hazardous waste quantity that is based on (1) constituent quantity; (2) waste stream; (3) volume; and (4) area 

of the sources of hazardous waste at the site. EPA uses minimum waste quantity factors when there is 

insufficient information to estimate hazardous waste quantity. In the ground water, surface water, and air 

pathways, the HRS evaluates the total quantity of hazardous substances available to migrate from the original 

sources (how much has migrated and how much can be released in the future). In the soil exposure pathway, 

the hazardous waste quantity does not include the total amount of hazardous substances in all site sources, 

but rather is based on the amount of hazardous substances to which a receptor can be exposed where actual 

contamination has been documented. In other words, for the soil exposure pathway, the risk posed by a 

release of hazardous substances is directly related to the amount of hazardous substances that receptors are 

exposed to, as opposed to how much of the hazardous substances from the original sources may migrate to 

the receptors. 

Proposed Approach: EPA is proposing a parallel approach to the soil exposure pathway to calculate 

hazardous waste quantity for the subsurface intrusion addition to the HRS. Since the subsurface intrusion 

component also focuses on exposure, the waste quantity factor value for this component should also reflect 

only the amount of hazardous substances that people actually are exposed to (the amount present in occupied 

structures). EPA is proposing to use a similar four-tiered hierarchical approach to calculate hazardous waste 

quantity within occupied structures with contamination. In cases where no home is subject to actual 

contamination, EPA is proposing to use minimum waste quantity factors. In situations where there is an 

observed release within a structure above benchmarks (Level I), a default value of 100 is proposed for the 

hazardous waste quantity factor value. This value is not used in the current soil exposure pathway, but is 

consistent with the ground water, surface water, and air pathways and reflects the increased exposure risk of 

a release within an occupied structure. 

Charge Question #2: Is EPA’s approach of basing the hazardous waste quantity on the amount of 

contaminants that could be found in the intruded structures appropriate? If no, what alternative approach 

would you recommend? Comment [B3]: This approach is 

appropriate, but what is not appropriate is 

defining the level I & II benchmarks at a 1 

in 1 million risk level. Much too low. You 

should set benchmarks at a 1 in 10,000 risk 

level. 

53
3. Population score

Background: Within the current HRS, receptors are evaluated in two main categories: whether they are 

exposed to 1) actual contamination; or 2) potential contamination (see section 2.5 of the current HRS). If 

receptors are exposed to contaminant levels meeting observed release criteria, they are identified as actually 

contaminated; however, if the receptors are not exposed to contaminants that meet the observed release 

criteria but are within the target area being evaluated, they are considered potentially contaminated. Actual 

contamination is further divided into two sub-categories based on whether the hazardous substance is present 

at or above a health-based benchmark. If the concentration of the hazardous substance released at the 

receptor is greater than a health-based benchmark, the receptors are identified as Level I receptors and are 

weighted (multiplied by a factor of 10) in scoring. If the release concentrations are less than a health-based 

benchmark, the receptors are identified as Level II receptors and are not weighted (multiplied by a factor of 

1). Potential receptors are distance/dilution weighted; in other words, the farther away a receptor is located 

from a source, the less the population contributes to the site score. 

Proposed Approach: EPA is proposing to generally use the same receptor weighting structure in the 

subsurface intrusion component as the one used in the current HRS. Those receptors in the area(s) of 

observed exposure (AOE) are considered actually contaminated, and those in the area(s) of subsurface 

contamination (ASC) are considered potentially contaminated (See Figure 2). The receptors in an AOE are 

further differentiated based on whether the contaminant concentrations are at levels above identified 

benchmarks (Level I) or are at levels establishing a release but below identified benchmarks (Level II). The 

benchmarks that EPA is proposing to use for the subsurface intrusion component are: 

• Screening concentration for cancer effects; and

• Screening concentration for non-cancer effects (systemic toxicants).

Consistent with the weighting of populations throughout the HRS, the proposed subsurface intrusion 

component will weight targets within the AOE subject to Level I contaminant concentrations by a factor of 

10 and weight targets subject to Level II contaminant concentrations by a factor of 1. 

EPA is proposing to evaluate the weighting of targets within the ASC based on sub-slab, soil gas, and/or 

ground water samples. Potential receptors within the ASC receive less weight (population multiplied by a 

factor of 0.1), except in cases where a sub-slab sample indicates contaminant levels are at least 10 times 

higher than a health-based benchmark (population is multiplied by a factor 0.75). The value of 0.75 was 

determined based on an evaluation of paired data when both a sub-slab and indoor air sample were collected. 

The 0.75 weighting reflects the observation that for approximately 80 percent of the sampling events where 

contamination was detected in the sub-slab, contamination was also detected in the indoor air sample. The 

order of magnitude adjustment applied to the health-based benchmark reflects EPA’s finding that, in such 

paired sampling events, the indoor air sample concentration is, on average, 10 times lower than the sub-slab 

sample concentration. 

54
Figure 2 

Charge Question #3: Is it appropriate to consider individuals/populations located within the area of 

subsurface contamination (ASC) to be at a higher relative risk in situations when sub-slab contaminant 

concentrations are at least ten times greater than a health-based benchmark? If no, please explain. Comment [B4]: EPA OSWER has 

released a paper evaluating attenuation 

factors, including sub-slab to indoor air 

attenuation factors. The factor of 10 you 

refer to in the above paragraph is not an 

average. It is a 95th percentile. If you are 

going to use an average as you indicate, 

than the factor of 10 should be significantly 

higher. A paper released in 2011 says that a 

more reasonable subslab to indoor air 

attenuation factor is 50x. So, while it is 

appropriate to consider 

individuals/populations located within the 

area of subsurface contamination (ASC) to 

be at a higher relative risk in situations 

when sub-slab contaminant concentrations 

are high, the weighting factor of 0.75 

should not apply until sub-slab values are at 

least 50 times higher than indoor air values 

rather than 10x higher. 

55
4. Multi-story and multi-tenant structures

Background: In the current HRS, multi-story and multi-tenant buildings are evaluated based on population 

associated with an actually or potentially impacted target. In the ground water pathway, all residents who are 

served by a well are considered subject to the actual or potential contamination of the well. In the air 

pathway, all residents who have an opportunity to breathe ambient air are considered subject to the actual or 

potential contamination of the ambient environment within a distance category. All receptors within a 

contaminated surface water stretch are subject to the level of contamination associated with that surface 

water stretch. In the soil exposure pathway, receptors must be able to come in contact with areas of 

contamination. In determining the likelihood a person will come in contact with areas of contamination, the 

HRS uses a 200 foot rule (see section 5.1.3 of the current HRS) because it is reasonable to assume that that a 

person will walk/use areas within a 200 foot areal extent of their residence/property. The 200 foot rule is 

used regardless of whether a building is multi-tenant or multi-story (the assumption being that is reasonable 

for people to use the outside of their properties). 

Proposed Approach: EPA is proposing to evaluate multi-story/multi-tenant buildings utilizing a similar 

approach as soil exposure, limiting the receptors to those individuals that reasonably can be exposed to 

subsurface intrusion within an occupied multi-tenant/multi-story building. EPA is proposing to consider all 

receptors exposed to actual contamination as the population inhabiting the floor of the intruded space and the 

population inhabiting the floor above and the floor below the intruded space when calculating waste quantity 

and population. EPA considers that this approach will more accurately reflect risk to both actual and 

potential receptors, while also minimizing the potential for over counting (Figure 3). 

56
Figure 3 

Charge Question #4: When calculating waste quantity and population, is it scientifically reasonable for 

populations in multi-story or multi-tenant structures to be evaluated based on using only the population 

inhabiting the intruded space and the population on the floor above and below the intruded space (For 

example, if contamination is found on the first floor, population from the basement and second floor would 

be used in the calculation. If contamination is found on the fifth floor, population from the fourth floor and 

sixth floor would be used in the calculation – for further explanation, see detailed discussion in above 

paragraph “Proposed Approach”)? If no, what alternative approach would you recommend? Comment [B5]: This protocol is okay so 

long as there are no elevators in the 

building or pipe/electrical chases that act as 

vapor conduits between lower & upper 

floors. 

57
5. Factor Value for Workers

Background: In the current HRS, 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 of observed 

contamination. These factor values range from 0 to15, depending on the number of workers exposed to 

outdoor contamination (see section 5.1.3.3 of the current HRS). 

Proposed Approach: EPA is proposing to mirror the procedures for the resident population threat in the soil 

exposure component when 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 and 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., factor values ranging from 0 to 45).

Charge Question #5: Because of longer exposure times indoors, is it reasonable to assume that the relative 

risk is three times greater for workers exposed to subsurface intrusion within the workplace than it is for 

workers exposed to outdoor surface contamination at the workplace? If no, please explain. Comment [B6]: There’s no explanation 

as to where the factor of 3 came from. 

Hence, while it is reasonable to assume the 

risk is greater, I feel the basis for the factor 

of 3 should be explained. 

58
Vapor Intrusion Support Services 

Hartman Environmental specializes in vapor intrusion support services. Blayne Hartman 

has been performing vapor intrusion assessments since the mid 90s and has performed 

soil gas sampling since the mid 80s. Hartman’s vast connections throughout the vapor 

intrusion community enable him to call in additional expertise as needed for a specific 

project. Hartman typically works with the local consultant to provide the necessary 

expertise for assessing the vapor intrusion pathway. These services include: 

• Assessment program design (type of samples, where to sample)

• Determination of site-specific screening levels

• Indoor air and soil gas field sampling and/or sampling supervision

• On-site analysis of indoor air and/or soil gas samples by 8021, 8260, TO-15, TO-17

• Data review and interpretation.

• Risk calculations using J-E models.

• Preparation of workplans and interpretive reports.

• Review of workplans prepared by others.

• Review of interpretive reports prepared by others.

• Interaction with regulatory agencies.

• Training on the vapor intrusion pathway and sampling methods.

• Mitigation system design & installation

• Expert witness and litigation support

59
Biosketch - Dr. Blayne Hartman 

Blayne Hartman received his Ph.D. in geochemistry from the University of Southern 

California. He co- founded & operated H&P Mobile GeoChemistry, a business 

partnership offering on-site laboratory analysis, direct push environmental sampling, soil 

vapor surveys, and vapor intrusion services for twenty years. He sold H&P in 2008 and 

is currently an independent consultant offering vapor intrusion and soil gas support. 

Dr. Hartman is a nationally recognized expert on soil vapor sampling, soil vapor analysis, 

and vapor intrusion. He has provided training on soil gas methods and vapor intrusion to 

County and State regulatory agencies in over 30 states, many of the EPA regions, the 

DOD, and numerous stakeholder groups and consultants. He has written numerous 

articles on the collection, analysis, and interpretation of soil vapor data, including 

chapters in four textbooks. He has participated in technical workgroups on soil vapor 

methods for EPA, CA-EPA, CA Regional Water Boards, County of San Diego, ITRC & 

ASTM and has reviewed/edited instructional manuals for the EPA OUST and Superfund 

groups. Over the past four years, Dr. Hartman has been a contributing author/editor to 

vapor intrusion and soil gas guidance documents to federal EPA, CA-EPA, San Diego 

County, ITRC, DOD, API, and more than 25 individual State documents. He is currently 

a trainer in the EPA-OUST, ITRC, and API vapor intrusion courses and was formerly a 

co-trainer of the ASTM vapor intrusion course. 

60
Complete Resume – Blayne Hartman, Ph.D.

EDUCATION

Ph.D., Geological Sciences - 1983; University of Southern California, Los Angeles, CA 

M.S., Geological Sciences - 1978; University of Southern California, Los Angeles, CA

B.S., Chemical Engineering- 1975; Clarkson University, Potsdam, New York

EMPLOYMENT HISTORY 

Present: Hartman Environm ental Geoscience, Vapor Intrusion Assessm ents of 

methane and volatile organic compounds (VOCs), Soil Gas Support 

1998 to 2008: H&P Mobile Geochemistry, Carlsbad, CA, 92010 

Founder, partner, principal geochemist. 

1988 to 1998: Transglobal Exploration and Geoscience (TEG), Inc., Solana Beach, CA 

President , founder, principal geochemist. 

1986 to 1988: InterOcean Systems, Inc., San Diego, California, 

Chief Geochemist 

1982 to 1986: Unocal Science and Technology Division, Brea, California 

 Research Geochemist 

SUMMARY OF PROFESSIONAL EXPERIENCE 

Dr. Hartman is a nationally recognized expert on soil vapor sampling, soil vapor analysis, 

and vapor intrusion of volatile compounds and methane. He has provided training on soil 

gas m ethods and vapor intrusion to County and State regulatory agencies in over 30 

states, m any of the EPA regions, the DOD, and num erous stakeholder groups and 

consultants. He has written num erous articles on the collection, analysis, and 

interpretation of soil vapor data, includi ng chapters in four textbooks. He has 

participated in technical workgroups on soil vapor m ethods for EPA, CA-EPA, ITRC, 

ASTM, CA Regional W ater Boards, Count y of San Diego, has reviewed/edited 

instructional manuals for the EPA OUST a nd Superfund groups, and lectured on soil gas 

methods in the EPA-OSW ER vapor intrusion se minars. He has been involved with five 

research studies with EPA-ORD on soil gas methods, soil gas tem poral variations and 

indoor air variations in 2011, 2010, 2009, 2008, & 2007. 

61
At H&P Geochem istry, Dr. Hartm an was prim arily responsible for geochem ical data 

interpretation, corporate and business developm ent, and method development. As Founder and 

President of TEG, Dr. Hartm an was personally responsible for geochem ical technical 

development, equipment design and m aintenance, laboratory director, applications developm ent, 

and implementation of exploration programs, analyses, and reporting. Prior to co-founding TEG, 

Dr. Hartman was chief m arine geochemist with InterOcean Systems, where his responsibilities 

included direction of marine sediment and bottom-water geochemical exploration programs. As a 

research chem ist with Unocal Research, Dr. Hartm an was responsible for development of 

geochemical prospecting techniques in onshore and offs hore applications including 

fingerprinting of methane and light hydrocarbons using isotopes. 

PRESENTATIONS & TRAINING ON SOIL GAS METHODS & VAPOR 

INTRUSION 

Too numerous to list. Go to www.handpmg.com, Presentations & Training for a partial 

list. 

RECENT PUBLICATIONS ON SOIL GAS METHODS & VAPOR INTRUSION 

Hartman, B. (2010). Vapor Intrusion Pathway: Regulatory Updates and Issues 

Specifically for Petroleum Hydrocarbons, LustLine, November 2010. 

McHugh, Thomas E., Hammond, Douglas E., Nickels, Tim & Hartman, Blayne (2008) 

'Use of Radon Measurements for Evaluation of Volatile 

Organic Compound (VOC) Vapor Intrusion', Environmental Forensics, 9:1, 107 - 114 

Hartman, B. et. al., (2007). Results from EPA Funded Research Programs on the 

Importance of Purge Volume, Sample Volume, Sample Flow Rate and Temporal 

Variations On Soil Gas Concentrations. Proceedings AWMA Vapor Intrusion 

Conference, Providence, RI, September 2007 

Hartman, B. (2006). How to Collect Reliable Soil Gas Data for Risk Based 

Applications, Part 4: Updates on Soil Gas Collection & Analytical Procedures,

LustLine #53, September 2006. 

Hartman, B. (2004). How to Collect Reliable Soil Gas Data for Risk Based 

Applications, Part 3: Answers to Frequently Asked Questions, LustLine, November 

2004. 

Hartman, B. (2003). How to Collect Reliable Soil Gas Data for Risk Based 

Applications, Part 2: Surface Flux Chamber Method, LustLine #44, NEIWPIC, 

August 2003. 

62
Hartman, B. (2002). How to Collect Reliable Soil Gas Data for Risk Based 

Applications, Part 1: Active Soil Gas Method, LustLine #42, NEIWPIC, October 

2002. 

Hartman, B. (2002). Reevaluating the Upward Vapor Migration Rick Pathway, 

LustLine #41, NEIWPIC, June 2002. 

Hartman, B. and J. Jacobs (2000a). Soil vapor principles, in Standard Handbook of 

Environmental Science, Health, and Technology, Lehr, J. and J. Lehr, eds., Mc Graw 

Hill, ISBN#0-07-038309-X. 

Hartman, B. and J. Jacobs (2000b). Applications and interpretation of soil vapor data 

to volatile organic compound contamination, in Standard Handbook of Environmental 

Science, Health, and Technology, Lehr, J. and J. Lehr, eds., Mc Graw Hill, ISBN#0-

07-038309-X.

Hartman, B. (1999). Applications and Interpretation of Soil Vapor Data, in 

Chlorinated Solvent Contamination: Legal and Technical Issues, Morrison et.al., eds., 

Argent Communications Group, Foresthill, CA. 

Hartman, B. (1998a). Applications and Interpretation of Soil Vapor Data, in 

Petroleum Hydrocarbon Contamination: Legal and Technical Issues, Morrison et.al., 

eds., Argent Communications Group, Foresthill, CA. 

Frez, W.A., Tolbert, J.N., Hartman, Blayne, and T.R. Kline (1998), Determining Risk 

Based Remediation Requirements Using Rapid Flux Chamber Technology, in 

proceedings, Remediation of Chlorinated and Recalcitrant Compounds, Monterey, 

CA, Battelle Press 

Hartman, B. (1998). The Downward Migration of Vapors, LUSTLine Bulletin 28, 

NEIWPCC, Wilmington, MA, December 1998. 

Hartman, B. (1997). The Upward Migration of Vapors, LUSTLine Bulletin 27, 

NEIWPCC, Wilmington, MA, December 1997. 

63
RECENT PROJECTS/PUBLICATIONS WITH EPA 

USEPA (2010) Vertical Distribution of VOCs in Soils from Groundwater to the 

Surface/Subslab Soil Vapor Probe Equilibration Study, EPA Contract No. EP-C-05-061 

Task Order No. 65, Modification 7 

http://www.epa.gov/nerlesd1/cmb/research.htm#schumacher

USEPA (2009). Vertical distribution of VOCs in soils from groundwater to the 

surface/subslab. EPA/600/R-09/073, August 2009. 

http://www.epa.gov/nerlesd1/cmb/research.htm#schumacher 

USEPA (2007a). Final project report for the development of an active soil gas sampling 

method. EPA/600/R-07/076, July 2007. 

http://www.epa.gov/nerlesd1/cmb/research.htm#schumacher

USEPA (2007b). Final project report for investigation of the influence of temporal 

variation on active soil gas/vapor sampling. EPA/600/R-07/141, December 2007. 

http://www.epa.gov/nerlesd1/cmb/research.htm#schumacher

DiGiulio, D., C. Paul, R. Cody, R. Willey, S.Clifford, P. Kahn, R. Mosley, A. Lee, K. 

Christensen (2006b). Assessment of vapor intrusion in homes near the Raymark 

superfund site using basement and sub-slab air samples. EPA/600/R-05/147, March 

2006 (paid reviewer) 

DiGiulio, D., C. Paul, R. Cody, R. Willey, S.Clifford, R. Mosley, A. Lee, K. Christensen 

(2006a). Comparison of Geoprobe PRT and AMS GVP soil-gas sampling systems 

with dedicated vapor probes in sandy soils at the Raymark superfund site. 

USEPA/600/R-06/111, October 2006. (paid reviewer) 

Hartman, B. et. al., (2007). Results from EPA Funded Research Programs on the 

Importance of Purge Volume, Sample Volume, Sample Flow Rate and Temporal 

Variations On Soil Gas Concentrations. Proceedings AWMA Vapor Intrusion 

Conference, Providence, RI, September 2007 (primary author) 

64
REGULATORY GUIDANCE DOCUMENTS CONTRIBUTED TO 

• CA Leaking Underground Fuel Tanks (LUFT) Manual, 2011

• EPA-OUST Vapor Intrusion Guidance, 2011

• San Diego County Dept. Env. Health Soil Gas Collection Guidance, 2011

• San Diego County Dept. Env. Health Soil Gas Analytical Guidance, August 2011

• CA-EPA (DTSC) Soil Gas Collection Guidance, March 2010

• CA-EPA (DTSC) Soil Gas Collection Guidance, 2011 & 2003

• ASTM Vapor Intrusion Standard, March 2008

• ITRC Vapor Intrusion Guidance, February 2007

• States of CA, MO, MI, TN, AZ, NY, NJ, KS, IN, WA, NH, WI, AK, OH, HI

• San Diego County Building Dept. Methane Testing Ordinance, 2001

• EPA OUST Site Assessment Manual, 1997

• LA-RWQCB Soil Gas Analytical Guidance, 1997-1992

REFERENCES 

• Jeff Kuhn, MT-DEP, jkuhn@mt.gov, 406-841-5055

• John Boyer, NJ-DEP, john.boyer@dep.state.nj.us, (609) 984-9751

• Kevin Graves, CA-SWQCB, kgraves@waterboards.ca.gov, 916-341-5782

• Robin Davis, UT-DEP, rvdavis@utah.gov, 801-512-4767

• Brian Schumacher, EPA-ORD, schumacher.brian@epa.gov, 702-513-2661

• Lorraine LaFreniere, Argonne Nat’l Lab, lafreniere@anl.gov, 630-252-7969

• Todd Ririe, BP-Arco, TODD.RIRIE@BP.COM, 714-670-3062

• Robin Mongeon, NH-DEH, rmongeon@des.state.nh.us

• Richard Spiese, VT-DEP, Richard.Spiese@state.vt.us

• John Menatti, UT-DEP, jmenatti@utah.gov, 801-536-4159

65
CURRENT & RECENT PROJECT DESCRIPTIONS 

Site: Clocktowers Site, Lancaster PA 

Date Conducted: March 2011 to Present (project in progress) 

Client: General Dynamics OTS

Oversite Agency: PA-DEP & EPA Region 3 

Project Description: Vapor intrusion assessment of TCE to existing school and 

residential units located on a former watch manufacturing facility property. Hartman 

providing work scope, conducted soil gas, sub-slab soil gas, and indoor air sampling 

programs, on-site analysis by Method TO-14, and data interpretation. 

Site: Research House, Indianapolis, IN 

Date Conducted: August 2011 to Persent (project in progress) 

Client: Dr. Brian Schumacher, EPA-ORD, Las Vegas

Oversite Agency: EPA-ORD 

Project Description: Research program by EPA studing temporal variation of soil gas 

and indoor concentrations. Hartman proving real-time, continuous (24 hour) 

monitoring of chloroform, TCE, and PCE by method TO-14 for a period of 4 months. 

Site: Residential neighborhood, Phoenix AZ 

Date Conducted: June 2011 to Present (project in progress) 

Client: Motorola/Freescale Semiconductor

Oversite Agency: EPA Region 9 

Project Description: Vapor intrusion assessment of over 100 residential units located 

over a TCE groundwater plume. Hartman providing work scope, conducted soil gas, 

sub-slab soil gas, and indoor air sampling programs, and data interpretation. 

Site: Residential neighborhood, Miles City, MT 

Date Conducted: May 2011 to present (project in progress) 

Client: Trinity Industries, Dallas TX

Oversite Agency: Montana DEQ 

Project Description: Vapor intrusion assessment of houses neighboring a rail yard 

located over diesel contamination. Hartman providing work scope, conducted soil gas, 

sub-slab soil gas, and indoor air sampling programs, and data interpretation. 

66
Site: 20 townships in rural Kansas 

Date Conducted: 2008 through 2011 

Client: USDA & Argonne National Laboratory

Oversite Agency: Kansas DHE 

Project Description: Hartman consucted a preliminary vapor intrusion screening 

assessment of approximately 20 townships in rural Kansas with former or current 

grain storage silos using carbon tetrachloride. In Hanover KS, Hartman provided a 

detailed vapor intrusion assessment of carbon tetrachloride in ~ 20 residences located 

near a former US grain storage site. Hartman provided work scope, conducted soil 

gas, sub-slab soil gas, and indoor air sampling programs, and data interpretation. 

Site: Residential neighborhood, Seal Beach, CA 

Date Conducted: 2009 - 2010 

Client: Arco

Oversite Agency: CA-EPA 

Project Description: Vapor intrusion assessment of ~ 50 houses neighboring a 

operating Arco service station. Hartman providing work scope, conducted soil gas, 

sub-slab soil gas, and indoor air sampling programs, and data interpretation. 

67
Peer Reviewer Conflict of Interest Certification 

Peer Review: Proposed Rule: Addition of a Subsurface Intrusion Component to the Hazard Ranking System; 40 

CFR Part 300; EPA-HQ-SFUND-2010-1086; FRL_XXXX-X (review draft). 

A conflict of interest or lack of impartiality exists when the proposed peer reviewer personally ( or the peer 

reviewer's immediate family), or his or her employer, has financial interests that may be affected by the results of the 

peer review; or may provide an unfair competitive advantage to the peer reviewer (or employer); or if the peer 

reviewer's objectivity in performing the peer review may be impaired due to other factors. When the Peer Reviewer 

knows that a reasonable person with knowledge of the facts may question the peer reviewer's impartiality or 

financial involvement, an apparent lack of impartiality or conflict of interest exists. 

The following questions, if answered affirmatively, represent potential or apparent lack of impartiality (any

affirmative answers should be explained on the back of this form or in an attachment): 

• Did you contribute to the development of the document under peer review, or were you consulted during its

development, or did you offer comments or suggestions to any drafts or versions of the document during its

development?

J

i(°Klo D Yes

• Do you know of any reason that you might be unable to provide impartial advice on the matter under

consideration in this peer review, or any reason that your impartiality in the matter might be questioned? 

)tNo D Yes 

• Have you had any previous involvement with the review document(s) under consideration? J(No D Yes

• Have you served on previous advisory panels, committees, or subcommittees that have addressed the topic

under consideration�o D Yes

• Have you made any public statements (written or oral) on the issue?)(Noo Yes

• Have you made any public statements that would indicate to an observer that you have taken a position on

the issue under consideration?}(No D Yes

• Do you, your family, or your employer have any financial interest(s) in the matter or topic under peer review,

or could someone with access to relevant facts reasonably cone)� that you (or your family or employer)

stand to benefit from a particular outcome of this peer review?

' � No D Yes

With regard to real or apparent conflicts of interest or questions of impartiality, the following provisions shall apply 

for the duration of this peer review: 

(a) Peer Reviewer warrants, to the best of his/her knowledge and belief, that there are no relevant facts or

circumstances that could give rise to an actual, apparent, or potential organizational or personal conflict of interest,

or that Peer Reviewer has disclosed all such relevant information to EMS or to EPA.

(b) Peer Reviewer agrees that if an actual, apparent, or potential personal or organizational conflict of interest is

identified during performance of this peer review, he/she immediately will make a full disclosure in writing to EMS.

This disclosure shall include a description of actions that Peer Reviewer ( or his/her employer) has taken or proposes

to take after consultation with EMS to avoid, mitigate, or neutralize the actual, apparent, or potential organizational

conflict of interest. Peer Reviewer shall continue performance until notified by EMS of any contrary action to be

taken.

D Check here if any explanation is attached 

s;� Date 

Ziu 'f Al� /../rt/t.f'MM 

Printed Name 

/bAfittM fsv,Au/J�Pt� f%tb?!� 

Affiliation/Organization 

68
Peer Reviews

Paul Johnson

(Arizona State University)

• Charge Question Comments

• CV

• COI Certification

69
Peer Review Charge for:

U.S. Environmental Protection Agency (EPA). Proposed Rule: Addition of a Subsurface Intrusion 

Component to the Hazard Ranking System; 40 CFR Part 300; EPA-HQ-SFUND-2010-1086;

FRL_XXXX-X (review draft). 

Background

The U.S. Environmental Protection Agency (EPA) is proposing to include a subsurface intrusion (SsI) 

component to the Hazard Ranking System (HRS). Subsurface intrusion is the migration of hazardous 

substances from the unsaturated zone and/or the surficial ground water into overlying structures. The 

HRS is the principal mechanism the EPA uses to evaluate sites for placement on the National Priorities 

List (NPL). The subsurface intrusion component addition (this addition) would primarily 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 and the environment from releases of hazardous 

substances. 

This addition will allow the HRS evaluation to directly consider human exposure to hazardous 

substances that enter building structures through subsurface intrusion, and thus enable sites with 

subsurface intrusion contamination to be evaluated for placement on the NPL. This addition will make 

the HRS more accurate in assessing a site’s relative potential risk. The Agency is not considering 

changes to the remainder of the HRS except for minor updates reflecting changes in terminology related 

to revised toxicological parameters. This proposed regulatory change does not affect the status of sites 

currently on or proposed to the NPL. 

Expertise Required

The peer review panel for U.S. EPA’s Proposed Rule: Addition of a Subsurface Intrusion Component to 

the Hazard Ranking System should include expertise in: 

Academia: Panelist must have experience working, researching, and developing opinions on the topic of 

vapor intrusion. Expertise in the history and recent developments of vapor intrusion research and 

development, remediation, and mitigation technologies is required. Expertise in hydrogeology, 

chemistry, knowledge of public health risks associated with indoor air threats, and the subsurface 

migration of volatile hazardous substances is necessary. Experience working on Superfund issues is 

highly recommended, but not necessary. 

Peer Review Charge Questions

1. Potential for subsurface exposure (intrusion) into occupied structures

Background: The current HRS evaluates the likelihood of a release of a hazardous substance when an 

actual release has occurred through either chemical analysis or direct observation. The current HRS also 

evaluates the potential for a release to occur within the ground water, surface water and air pathways 

(see section 2.3 of the current HRS). The potential for a release is determined by the consideration of 

pathway specific factors that aid the site evaluator in predicting whether a release to the pathway is 

likely to occur. These factors are based on containment features of the source of contamination (whether 

or not hazardous substance can get out), route characteristics specific to each pathway (how far 

hazardous substances could migrate based on knowledge of site conditions) and include 

70
physical/chemical properties of the hazardous substances being evaluated (how the hazardous 

substances act in the environment). 

Proposed Approach: EPA is proposing a parallel approach for evaluating potential and actual exposure 

of intruded hazardous substances for the subsurface intrusion addition to the HRS. In determining which 

route characteristics are appropriate for evaluating potential exposure to subsurface contaminants, EPA 

examined present modeling methods such as the Johnson-Ettinger model and also considered multiple 

lines of evidence approaches which estimate the levels of contaminant exposure based on numerous 

route characteristics. In addition, EPA examined the relationship between these factors to determine 

which have the greatest influence on the likelihood that an exposure would occur, and then incorporated 

these factors within its proposed approach. EPA also gave careful consideration to ensure that the data 

necessary to obtain route characteristic factors could be measured or calculated on a site-specific basis 

and in a manner consistent with current HRS evaluations. Based on the Agency’s analysis, the following 

three factors for which sufficient site-specific information could be collected during a site inspection 

represented the greatest impact on the potential for exposure: (1) depth to contamination; (2) vertical 

migration; and (3) vapor migration potential (see Figure 1). 

Figure 1 

71
Charge Question #1: Is EPA’s proposed approach scientifically reasonable for evaluating and assigning 

proportional weightings for the following when evaluating potential for exposure? If no, what alternative 

approach would you recommend? 

Overall, the structure of this section seems to be based more on conventional wisdom (and c ommon 

pathway misconceptions) than on th e latest understanding gained from theory/modeling and criticallyreviewed empirical observations. 

For example, field data and modeling show that the si ngle-most significant influence on vapor intrusion 

impacts is whether or not a chemical is aerobically biodegradable, and that is not considered here. 

In addition, for chemicals that do no t significantly biodegrade during va por transport (i.e., chlorinated 

solvents), the potential significance of vapor intrusion impacts is pr imarily related to the quantity {(C 

Deff/L AB)/(QB Ctarget)}, where C is the source concentra tion, Deff is the overall effective vapor d iffusion 

coefficient, L is the dep th to the concentration C, A B and E B are the building footprint and exchange 

rate, and Ctarget is the target concentration for adverse impacts. Of these quantities, the ones that might 

vary most from site to site and have the greatest influence on the pot ential for adverse impacts are the 

ratios (C/Ctarget) and (D eff/L). The first is a meas ure of how strong the source is, while the second is a 

measure of the overall resistance to transport through the soil. The relative interplay between these 

quantities, the strength of the source, and the realistic sensitivity of (Deff/L) to depth and soil type are not 

reflected in the proposed approach. 

The proposed approach could be replaced by a simp ler one based on only two primary factors: one 

derived from (C/Ctarget) ratios and one from a soil type vs. depth t able. There could also be a modifying 

factor for chemical degradabilit y that would be based on (total of all biodegradable 

concentrations/oxygen content in air and depth). 

a. Consideration of the construction/structure type for which sufficient site-specific information

could be collected during a site inspection for the occupied structure;

With respect to Table 5-12 (structure containment), I am not aware of definitive studies or significant 

anecdotal experiences that support the inclusion of Items 4, 5, or 7. USEPA’s empirical database does 

not show a clear dependence on foundation construction (Item 4) and I am not aware of any definitive 

validation studies of the performance of passive systems (Items 5 and 7). It is also not clear that Item 3 

is needed either, especially given its value and the reality that it is not feasible to identify all intrusion 

points to buildings. Item 1 should include evidence of intrusion of hazardous contaminants (not just nonhazardous contaminants). This table could probably be reduced to three items (current Item 1 combined 

with Item 2, a combined Item 6 and Item 8, Item 9) 

b. Distance between occupied structure and depth of contamination; and

72
There are ambiguities and potential issues with application of Table 5-13 (depth to contamination) and 

its associated discussion. In particular, it is not clear if the authors intended for contaminant 

concentrations to be below background or detection levels for all distances less than this depth, or if it is 

simply the depth to the closest detection above background or detection levels? These are two very 

different concepts and have different implications for use in a scoring system like this. 

For example, if the authors intended contaminant concentrations to be below background or detection 

levels for all distances between the foundation and this depth, then Table 5-13 is likely overly 

conservative. 

On the other hand, if the depth to be used is the depth to the closest detection above background or 

detection levels (independent as to whether or not there are non-detect/background-level samples until 

that point is encountered), then the table might not be sufficiently protective. For many sites, there may 

only be groundwater data available, and so people will be using depth to groundwater with Table 5-13. 

The vapor intrusion impact dependence on depth to groundwater has not been shown through field data 

or modeling to be as significant as suggested by this table (e.g., modeling would show that at most 

intrusion rates would be 10X less for a 200 ft depth than for a 20 ft depth for comparable groundwater 

concentrations and soils, and empirical data show little dependence on depth for the range of depths 

represented in the empirical data set). 

The following revisions are suggested: 

1) Clarify the meaning of “depth to contamination”.

2) If contaminant concentrations are supposed to be below background or detection levels for all

distances less than this depth (unlikely to be verified with typical data used for ranking), then

only two or three depth categories are justified and the value should be 0 for all depths greater

than about 10 or 20 ft.

3) If it is the depth to the closest detection above background or detection levels, then Depth to

Contamination Assigned Values should not decline as significantly with depth as happens in

Table 5-13. It is justified to have a high value for cases with liquid intrusion or very shallow

depths to groundwater, but depths to about 100 ft (most sites) should probably all have about the

same value and depths greater than 100 ft (few sites) should probably have values that are within 

50% of the <100 ft values. This is in part because there is a second important dimension not 

considered here in the factors – contaminant concentration. For example, a groundwater plume 

with a 20 ug/L concentration at 10 ft depth poses the same risk as a groundwater plume with a 

200 ug/L concentration at a 100 ft depth and a groundwater plume with a 400 ug/L

concentration at a 200 ft depth (all other factors being equal, and a non-biodegradable

chemical).

c. Evaluation of the vertical migration factor based on the thickness and porosity/permeability of

geologic materials in the interval between the lowest point of an occupied structure and the

highest known point of hazardous substances in the subsurface. 

73
The vertical migration factor should be presented as being related to “soil type” and not effective 

porosity/permeability as these quantities are irrelevant to the vapor intrusion pathway and only soil 

descriptions are used in Table 5-14 anyway. 

Categories 2 and 3 in Table 5-14 should be adjusted so that “silty loams; loesses; silty clays; sediments 

that are predominantly silts; moderately permeable till (fine-grained, unconsolidated till, or compact till 

with some fractures)” should be included in Table 2. EPA’s own modeling in its pathway assessment 

guidance document (as well as other publications) and empirical data show little difference in behavior 

across this range of soil types. 

Depth creeps in as an overly-sensitive modifying factor in Table 5-15, compounding its use already in 

Table 5-13.

2. Hazardous Waste Quantity

Background: In the current HRS, the hazardous waste quantity factor reflects the risk consideration 

related to the magnitude and duration of either the release for ground water, surface water, and air 

pathways, or the exposure for the soil exposure pathway (see section 2.4.2 of the current HRS). 

Hazardous waste quantity is evaluated for all four pathways. At each site evaluated, EPA uses a fourtiered hierarchy for calculating the hazardous waste quantity that is based on (1) constituent quantity; (2) 

waste stream; (3) volume; and (4) area of the sources of hazardous waste at the site. EPA uses minimum 

waste quantity factors when there is insufficient information to estimate hazardous waste quantity. In the 

ground water, surface water, and air pathways, the HRS evaluates the total quantity of hazardous 

substances available to migrate from the original sources (how much has migrated and how much can be 

released in the future). In the soil exposure pathway, the hazardous waste quantity does not include the 

total amount of hazardous substances in all site sources, but rather is based on the amount of hazardous 

substances to which a receptor can be exposed where actual contamination has been documented. In 

other words, for the soil exposure pathway, the risk posed by a release of hazardous substances is 

directly related to the amount of hazardous substances that receptors are exposed to, as opposed to how 

much of the hazardous substances from the original sources may migrate to the receptors. 

Proposed Approach: EPA is proposing a parallel approach to the soil exposure pathway to calculate 

hazardous waste quantity for the subsurface intrusion addition to the HRS. Since the subsurface 

intrusion component also focuses on exposure, the waste quantity factor value for this component should 

also reflect only the amount of hazardous substances that people actually are exposed to (the amount 

present in occupied structures). EPA is proposing to use a similar four-tiered hierarchical approach to 

calculate hazardous waste quantity within occupied structures with contamination. In cases where no 

home is subject to actual contamination, EPA is proposing to use minimum waste quantity factors. In 

situations where there is an observed release within a structure above benchmarks (Level I), a default 

value of 100 is proposed for the hazardous waste quantity factor value. This value is not used in the 

current soil exposure pathway, but is consistent with the ground water, surface water, and air pathways 

and reflects the increased exposure risk of a release within an occupied structure. 

74
Charge Question #2: Is EPA’s approach of basing the hazardous waste quantity on the amount of 

contaminants that could be found in the intruded structures appropriate? If no, what alternative 

approach would you recommend? 

It is suggested that this be eliminated as a factor in assessing the relative risk of vapor intrusion, as 

hazardous waste quantity has little relevance to vapor intrusion impacts, except to the extent that it 

might impact the longevity of the contaminant vapor source. 

The proposed approach makes little sense and is not technically defensible. The mass of contaminant in 

the residence is irrelevant for this pathway; instead it is the duration of time that the vapor source will 

produce vapor concentrations of significance that is the relevant quantity. That in turn is related to 

source zone longevity (under natural or remediation conditions) and groundwater migration rates for 

dissolved plume sources. That is likely to be a very long time – probably decades for most sites 

evaluated by this process, unless source removal and or control are going to reduce the time frame to 

less than a decade. 

Source concentrations should be included somewhere in the analysis as discussed above.

3. Population score

Background: Within the current HRS, receptors are evaluated in two main categories: whether they are 

exposed to 1) actual contamination; or 2) potential contamination (see section 2.5 of the current HRS). If 

receptors are exposed to contaminant levels meeting observed release criteria, they are identified as 

actually contaminated; however, if the receptors are not exposed to contaminants that meet the observed 

release criteria but are within the target area being evaluated, they are considered potentially 

contaminated. Actual contamination is further divided into two sub-categories based on whether the 

hazardous substance is present at or above a health-based benchmark. If the concentration of the 

hazardous substance released at the receptor is greater than a health-based benchmark, the receptors are 

identified as Level I receptors and are weighted (multiplied by a factor of 10) in scoring. If the release 

concentrations are less than a health-based benchmark, the receptors are identified as Level II receptors 

and are not weighted (multiplied by a factor of 1). Potential receptors are distance/dilution weighted; in 

other words, the farther away a receptor is located from a source, the less the population contributes to 

the site score. 

Proposed Approach: EPA is proposing to generally use the same receptor weighting structure in the 

subsurface intrusion component as the one used in the current HRS. Those receptors in the area(s) of 

observed exposure (AOE) are considered actually contaminated, and those in the area(s) of subsurface 

contamination (ASC) are considered potentially contaminated (See Figure 2). The receptors in an AOE 

are further differentiated based on whether the contaminant concentrations are at levels above identified 

benchmarks (Level I) or are at levels establishing a release but below identified benchmarks (Level II). 

The benchmarks that EPA is proposing to use for the subsurface intrusion component are: 

• Screening concentration for cancer effects; and

75
• Screening concentration for non-cancer effects (systemic toxicants).

Consistent with the weighting of populations throughout the HRS, the proposed subsurface intrusion 

component will weight targets within the AOE subject to Level I contaminant concentrations by a factor 

of 10 and weight targets subject to Level II contaminant concentrations by a factor of 1. 

EPA is proposing to evaluate the weighting of targets within the ASC based on sub-slab, soil gas, and/or 

ground water samples. Potential receptors within the ASC receive less weight (population multiplied by 

a factor of 0.1), except in cases where a sub-slab sample indicates contaminant levels are at least 10 

times higher than a health-based benchmark (population is multiplied by a factor 0.75). The value of 

0.75 was determined based on an evaluation of paired data when both a sub-slab and indoor air sample 

were collected. The 0.75 weighting reflects the observation that for approximately 80 percent of the 

sampling events where contamination was detected in the sub-slab, contamination was also detected in 

the indoor air sample. The order of magnitude adjustment applied to the health-based benchmark reflects 

EPA’s finding that, in such paired sampling events, the indoor air sample concentration is, on average, 

10 times lower than the sub-slab sample concentration. 

Figure 2 

Charge Question #3: Is it appropriate to consider individuals/populations located within the area of 

subsurface contamination (ASC) to be at a higher relative risk in situations when sub-slab contaminant 

concentrations are at least ten times greater than a health-based benchmark? If no, please explain. 

76
It should be recognized that this approach is predicated on two assumptions, both of which have 

weaknesses: 

1) It is assumed that areas of subsurface contamination have a 10X lower relative potential for

impact than areas of observed contamination, and

2) Sub-slab soil gas samples are reliable indicators of vapor intrusion.

With respect to (1), the preamble document contains the paragraph: 

“When an observed exposure has not been established, the EPA is proposing to evaluate the potential 

for exposure within structures located in the ASC within the subsurface intrusion component. Given that 

contamination within an ASC is documented as present below these structures, there is a potential that 

intrusion and exposure to the intrusion has occurred but that sampling has not been performed at the 

time the exposure was taking place. As explained in section XXXX of the Proposal TSD, the factors 

affecting when intrusion will occur and the rate of subsurface intrusion are extremely time-, site- and 

climatic-specific. Sampling may not have been performed in these structures, or, even if performed 

during the limited time period of a site inspection, the sampling may have been during conditions that 

the intrusion was not occurring or occurring at levels not detectable or differentiable from background 

sources of the contaminant. Site inspections are conducted over a limited period (usually 1 to 3 days). 

Therefore it is important that the potential for exposure be included as a consideration when evaluating 

subsurface intrusion threats.” 

This paragraph reasonably captures the current state of the practice – namely that conventional point in 

time and point in space sampling (e.g., Summa canisters) has been shown to be inadequate for 

confidently assessing the presence or absence of vapor intrusion. In addition, empirical data have 

shown unacceptable and highly variable indoor air impacts at chlorinated solvent sites with 

groundwater concentrations as low as 10 ug/L, with no clear dependence on groundwater 

concentration, soil type, or depth. Thus, the reality is that we are unable to confidently identify a priori 

whether homes are expected to be impacted, and which homes are likely to be the most impacted above 

a dissolved groundwater plume. 

This proposed approach seems to ignore this. There is no basis for assigning lower risks to areas of 

subsurface contamination having similar subsurface conditions as nearby areas of observed impacts 

simply because impacts have not been observed. It is arguably more appropriate to assume that the 

potential for exposure is the same in all areas having similar conditions, unless there has been extensive 

data collection to prove otherwise. The other factors discussed above already reflect differences in 

potential for impacts based on soil type and depth. 

USEPA’s database (raw data – not the alpha factor analysis) should be reviewed carefully in dealing 

with the issue of relative risk of observed areas of exposure vs. areas of subsurface contamination. For 

example, the figure below is from this database, and to it has been added lines and text by P.C. Johnson 

77
(2011, presentations) to point out that indoor air concentrations of concern have been observed across 

the full concentration range of interest for chlorinated solvent sites: 

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08

Indoor Air Concentration (ug/m3)

EPA Data (IA > RL)

Alpha = 1.0

Alpha = 1E-1

Alpha = 1E-2

Alpha = 1E-3

Alpha = 1E-4

Alpha = 1E-5

Groundwater Vapor (ug/m3)

U.S. EPA’s Vapor Intrusion Database: 

Preliminary Evaluation of Attenuation Factors 

0.1 – 10 ppbv 

OSWER Draft - March 4, 2008 - http://iavi.rti.org/OtherDocuments.cfm 

10 – 10,000 μg/L 

in ground water 

With respect to (2), the approach ignores the debate and recent technical advances regarding the utility 

of sub-slab soil gas samples for pathway assessment. It has been shown at a field study site in Utah that 

indoor air sources can cause sub-slab contaminant vapor plumes; thus, the nearly 1:1 correlation 

between indoor air and sub-slab soil gas detections is not validation that sub-slab samples are good 

indicators of vapor intrusion as stated above (as 1:1 correlation would occur with indoor sources as 

well). 

There are also field study results showing temporal and spatial variability in sub-slab soil gas samples 

and experience that sub-slab sampling may not even have been done for pathway assessment by the time 

that HRS calculations are being done. 

78
4. Multi-story and multi-tenant structures

Background: In the current HRS, multi-story and multi-tenant buildings are evaluated based on 

population associated with an actually or potentially impacted target. In the ground water pathway, all 

residents who are served by a well are considered subject to the actual or potential contamination of the 

well. In the air pathway, all residents who have an opportunity to breathe ambient air are considered 

subject to the actual or potential contamination of the ambient environment within a distance category. 

All receptors within a contaminated surface water stretch are subject to the level of contamination 

associated with that surface water stretch. In the soil exposure pathway, receptors must be able to come 

in contact with areas of contamination. In determining the likelihood a person will come in contact with 

areas of contamination, the HRS uses a 200 foot rule (see section 5.1.3 of the current HRS) because it is 

reasonable to assume that that a person will walk/use areas within a 200 foot areal extent of their 

residence/property. The 200 foot rule is used regardless of whether a building is multi-tenant or multistory (the assumption being that is reasonable for people to use the outside of their properties). 

Proposed Approach: EPA is proposing to evaluate multi-story/multi-tenant buildings utilizing a similar 

approach as soil exposure, limiting the receptors to those individuals that reasonably can be exposed to 

subsurface intrusion within an occupied multi-tenant/multi-story building. EPA is proposing to consider 

all receptors exposed to actual contamination as the population inhabiting the floor of the intruded space 

and the population inhabiting the floor above and the floor below the intruded space when calculating 

waste quantity and population. EPA considers that this approach will more accurately reflect risk to both 

actual and potential receptors, while also minimizing the potential for over counting (Figure 3). 

79
Figure 3 

Charge Question #4: When calculating waste quantity and population, is it scientifically reasonable for 

populations in multi-story or multi-tenant structures to be evaluated based on using only the population 

inhabiting the intruded space and the population on the floor above and below the intruded space (For 

example, if contamination is found on the first floor, population from the basement and second floor 

would be used in the calculation. If contamination is found on the fifth floor, population from the fourth 

floor and sixth floor would be used in the calculation – for further explanation, see detailed discussion in 

above paragraph “Proposed Approach”)? If no, what alternative approach would you recommend? 

It is not clear why possible exposures in the lowest floors (closest to the vapor source) would ever be 

discounted? Otherwise, I have no comments on this approach as I have little experience with impacts in 

multi-story buildings to draw from at this point in time. It is difficult to imagine many scenarios where 

this issue will be a determining factor in HRS calculations. 

80
5. Factor Value for Workers

Background: In the current HRS, 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 of 

observed contamination. These factor values range from 0 to15, depending on the number of workers 

exposed to outdoor contamination (see section 5.1.3.3 of the current HRS). 

Proposed Approach: EPA is proposing to mirror the procedures for the resident population threat in the 

soil exposure component when 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 and 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., factor values ranging from 0 to 

45). 

Charge Question #5: Because of longer exposure times indoors, is it reasonable to assume that the 

relative risk is three times greater for workers exposed to subsurface intrusion within the workplace than 

it is for workers exposed to outdoor surface contamination at the workplace? If no, please explain. 

This seems to be a comparison of apples and oranges (indoor vapor inhalation vs. outdoor soil 

exposure), so assuming some fixed correlation between the two would be inappropriate. 

 It might be reasonable to assume that worker inhalation risks would be less than those of residents in 

homes in similar conditions because of differences in exposure durations. The type of work might affect 

both the building ventilation and worker breathing rates, so indoor concentration rates might be lower 

and inhalation higher in more industrial settings vs. office and residential settings. 

81
Paul C. Johnson, Ph.D. 

Dept. of Civil and Environmental Engineering Office of the Dean 

Ira A. Fulton School of Engineering Ira A. Fulton School of Engineering 

P.O. Box 875506 P.O. Box 879309 

Arizona State University Arizona State University 

Tempe AZ 85287-5506 Tempe AZ 85287-9309 

(480) 965-9115 (phone) (480) 965-9115 (phone)

(480) 965-8293 (FAX) (480) 965-8855 (FAX)

paul.c.johnson@asu.edu paul.c.johnson@asu.edu

Home Address: 11030 N. Royal Ct., Fountain Hills, AZ; (480) 837-2005 

Area of Expertise:Recognized for contributions to the fields of soil and groundwater remediation and risk 

assessment; more specifically, the design, monitoring, and optimization of soil and groundwater 

remediation systems and the monitoring and modeling of human exposure pathways. Much of this work 

forms the basis for current practice for the most widely applied technologies and for federal and state 

regulatory guidance in the area of risk and exposure assessment. 

Education:

1987 Ph.D. - Princeton University - Chemical Engineering 

1984 M.A. - Princeton University - Chemical Engineering

1983 B.S. - University of California, Davis - Chemical Engineering

Academic and Administrative Experience:

2011 – present Ira A. Fulton Schools of Engineering, Dean 

2006 – 2011 Ira A. Fulton Schools of Engineering, Executive Dean 

2006 – 2007 Ira A. Fulton School of Engineering, Executive and Interim Dean 

2004 – 2006 ASU Associate Vice President – Research

2003 – 2004 Ira A. Fulton School of Engineering, Associate Dean – Research 

2002 – 2003 College of Engineering and Applied Science Interim Associate Dean - Research 

2000 – present Assistant Chair – Graduate Programs Dept. of Civil and Environmental 

Engineering 

2003 – present Professor, Arizona State University 

1997 - 2003 Associate Professor, Arizona State University (tenured) 

1994 - 1997 Associate Professor, Arizona State University (untenured) 

Industrial Experience:

1994 – present Consultant to industry and federal and state agencies 

1993 - 1994 Senior Research Engineer, Shell Development, Houston 

1990 - 1993 Research Engineer, Shell Development, Houston 

1987 - 1990 Associate Research Engineer, Shell Development, Houston 

Other:

2003 – 2011 Editor-In-Chief, National Ground Water Association Journal – 

Ground Water Monitoring and Remediation

2010 – present National Research Council Committee on 

Future Options of the Nation’s Subsurface Remediation Effort

82
Awards & Honor Societies:

National Ground Water Association Keith E. Anderson Award 2011 

Strategic Environmental Research and Development Program 

(SERDP) Project of the Year 2011 

Outstanding Educator (AZ Society of Professional Engineers) 2011 

2006 AEHS Academic Career Recognition Award 2006 

ASCE/CERF Charles Pankow Award for Innovation Finalist 2005 

White House Closing the Circle Award Winner 2003 

National Pollution Prevention Roundtable Most Valuable 

Pollution Prevention Project Award 2003 

ASCE/CERF Charles Pankow Award for Innovation Finalist 2003 

Environmental Security Technology Certification Program 

(ESTCP) Project of the Year 2002 

ASU College of Engineering Teaching Excellence Award 2002 

CEAS Alumni SOAR Outstanding Faculty Advisor Award 2002 

National Ground Water Association (NGWA) 2001 Outstanding 

Ground Water Remediation Project Award 2001 

ASCE Journal of Environmental Engineering Editor’s Award 2001 

AWPCA Quentin Mees Research Award (w/C. Bruce) 2000 

ASU Parents Association Teacher of the Year Finalist 2000 

ASU College of Engineering Teaching Excellence Award 1998 

ASCE Student Chapter Best Teacher Award 1996 

AWPCA Quentin Mees Research Award 1995 

NGWA/API National Conference Best Paper 1994 

Shell Oil Company Recognition Award 1990, 1991, 1993, 1994 

Princeton University Wallace Memorial Fellowship in Engineering 1986-1987 

University of California Stauffer Chemical Scholarship 1983 

University of California ARCO Scholarship 1982 

American Military Engineers Scholarship 1982 

Associate Western Universities DOE Research Fellowship 1981 

Phi Kappa Phi - National Honor Society 

Tau Beta Pi - National Engineering Honor Society 

Pi Mu Epsilon - National Mathematics Honor Society 

Patents

1. Salanitro, J.P., P.C. Johnson, S.M. Stearns, P.M. Maner, J.H. Miller, and G.E. Spinnler. 2004. In

Situ method and Apparatus for Biodegradation of Alkyl Ethers and Tertiary Butyl Alcohol. U.S.

Patent 6,808,632. 

2. Salanitro, J.P., P.C. Johnson, S.M. Stearns, P.M. Maner, J.H. Miller, and G.E. Spinnler. 2004. In

Situ method and Apparatus for Biodegradation of Alkyl Ethers and Tertiary Butyl Alcohol. U.S.

Patent 6,776,910 B2. 

3. Salanitro, J.P., P.C. Johnson, S.M. Stearns, P.M. Maner, J.H. Miller, and G.E. Spinnler. 2003. In

Situ method and Apparatus for Biodegradation of Alkyl Ethers and Tertiary Butyl Alcohol. U.S.

Patent 6,503,395 B1. 

83
4. Marsden, A.R. Jr., D.A. Weingaertner, L.W.R. Dicks, A.L. Otermat, P.C. Johnson. 1997. Enhanced

Deep Soil Vapor Extraction Process and Apparatus Utilizing Sheet Metal Pilings. U.S. Patent

5,660,500. 

5. Johnson, P.C.. 1993. In Situ Soil Heating Press/Vapor Extraction System. U.S. Patent 5,244,310.

6. Johnson, P.C., D.A. Weingaertner, L.W.R. Dicks, A.L. Otermat, and A.R. Marsden, Jr.. 1993.

Enhanced Deep Soil Vapor Extraction Process and Apparatus for Removing Contaminants Trapped

in or Below the Water Table. U.S. Patent 5,271,693.

7. Dicks, L.W.R., P.C. Johnson, A.R. Marsden, Jr., D.A. Weingaertner. 1993. Modified Heater for In

Situ Soil Heating. U.S. Patent 5,233,164.

8. Marsden, A.R., A.L. Otermat, D.A. Weingaertner, P.C. Johnson, L.W.R. Dicks, H.B. Wilde. 1993.

Heater Blanket for In Situ Soil Heating. U.S. Patent 5,221,827.

9. Johnson, P.C. and D.A. Weingaertner. 1993. In Situ Thermal Desorption of Contaminated Surface

Soil. U.S. Patent 5,193,934.

10. Johnson, P.C. and D.A. Weingaertner. 1992. In Situ Soil Decontamination Process With

Subsurface Vapor Recovery. U.S. Patent 5,169,263.

11. Johnson, P.C., J.D. Colthart, A.L. Otermat, D.A. Weingaertner, C.C. Chou, D.L. Byers, S.M.

Stearns, A.R. Marsden Jr., and G.M. Deeley. 1992. Soil Decontamination. U.S. Patent 5,114,497.

12. Johnson, P.C., A.L. Otermat, and C.C. Chou. 1991. In Situ Decontamination of Spills and Landfills

by Focused Microwave/Radio Frequency Heating and a Closed-Loop Vapor Flushing and Vacuum

Recovery System. U.S. Patent 5,076,727.

PUBLICATIONS AND PRESENTATIONS

Refereed Archival Journal Papers:

1. Kingston, J.T, P.R. Dahlen, and P.C. Johnson. 2010. State of the Practice Review of In Situ

Thermal Technologies. Ground Water Monitoring and Remediation. 30 (4). 64 – 72.

2. Lesser, L.E., P.C. Johnson, G.E. Spinnler, C.L. Bruce, and J.P. Salanitro. 2010. Spatial Variation in

MTBE Biodegradation Activity of Aquifer Solids Samples Collected in the Vicinity of a FlowThrough Aerobic Biobarrier. Ground Water Monitoring and Remediation. 30 (2). 63 – 72.

3. Johnson, P.C., C.L. Bruce, K.D. Miller. 2010. A Practical Approach to the Design, Monitoring,

and Optimization of In Situ MTBE Aerobic Biobarriers. Ground Water Monitoring and

Remediation. 30 (1). 58-66.

4. Luo, H., P. Dahlen, P.C. Johnson, T. Peargin, and T. Creamer. 2009. Spatial Variability of SoilGas Concentrations near and beneath a Building Overlying Shallow Petroleum Hydrocarbon–

Impacted Soils. Ground Water Monitoring and Remediation. 29 (1). 81-91.

84
5. Johnson, P.C., R.A. Ettinger, J.P. Kurtz, R. Bryan, and J.E. Kester. 2009. Empirical Assessment of

Ground Water–to-Indoor Air Attenuation Factors for the CDOT-MTL Denver Site.Ground Water

Monitoring and Remediation. 29 (1). 153-159.

6. McAlary, T. and P.C. Johnson. 2009. Vapor Intrusion. Ground Water Monitoring and

Remediation. 29 (1). Editorial.

7. Lesser, L.E, P. C. Johnson, R. Aravena, G.E. Spinnler, C.L. Bruce, and J.P. Salanitro. 2008. An

Evaluation of Compound-Specific Isotope Analyses for Assessing the Biodegradation of MTBE at

Port Hueneme, CA. Environmental Science and Technology.42 (17). 6637–6643.

8. Odencrantz, J.E., H. O’Neill, S.J. Steinmacher, J.D. Case, and P.C. Johnson. 2008. Residential

Vapor Intrusion Evaluation: Long-Duration Passive Sampling vs. Short-Duration Active Sampling.

Remediation. Autumn. 49-54.

9. Lundegard, P.D., P.C. Johnson, and P. Dahlen. 2008. Oxygen Transport from the Atmosphere to

Soil Gas Beneath a Slab-on-Grade Foundation Overlying Petroleum-Impacted Soil. Environmental

Science and Technology.42 (15). 5534–5540.

10. Xu, Y., L.A. Baker, and P.C. Johnson. 2007. Trends in Groundwater Nitrate Contamination in the

Phoenix, Arizona, USA Region. Ground Water Monitoring and Remediation. 27 (2). 49 – 56.

11. P.Lundegard, P.D., P.C. Johnson, and Z. Liu. 2006. Source Zone Natural Attenuation at Petroleum

Hydrocarbon Spill Sites – I: Site-Specific Assessment Approach. Ground Water Monitoring and

Remediation.26 (4). 82 – 92.

12. Johnson, P.C., P.D. Lundegard, and Z. Liu. 2006. Source Zone Natural Attenuation at Petroleum

Hydrocarbon Spill Sites – II: Application to Source Zones at a Former Oil Production Field.

Ground Water Monitoring and Remediation.26 (4), 93–106

13. Abreu, L. and P.C. Johnson. 2005. Abreu, L. D. V. and P.C. Johnson. Modeling the Effect of

Aerobic Biodegradation on Soil Vapor Intrusion into Buildings - Influence of Degradation Rate,

Source Concentration, and Depth. Environmental Science and Technology. 40 (7). 2304-2315.

14. Abreu, L. and P.C. Johnson. 2005. Effect of Vapor Source-Building Separation and Building

Construction on Soil Vapor Intrusion as Studied with a Three-Dimensional Numerical Model.

Environmental Science and Technology. 39(12). 4550-4561.

15. Johnson, P.C.. 2005. Sensitivity Analysis and Identification of Critical and Non-Critical Parameters

for the Johnson and Ettinger Vapor Intrusion Model. Ground Water Monitoring and Remediation

Winter 2005.25 (1). 63-78.

16. Vangelas, K., F.H. Chapelle, J. Cummings, P.C. Johnson, K.A. Lovelace, E.K. Nyer, R. Norris.

2005. Monitored Natural Attenuation Forum: A Panel Discussion on the Use of Integrated Mass

Flux and MNA Inconsistencies Within Federal and State Agencies. Remediation. 16 (1). 141 -152.

17. Lundegard, P.D. and P.C. Johnson. 2004. A Composite Plume Approach for the Analysis of

Dissolved Contaminants in Ground Water versus Distance from Source Areas. Ground Water

Monitoring and Remediation. Summer 2004. 24 (3). 69 - 75.

18. Sigley, J.L., P.C. Johnson, and S.P. Beaudoin. 2003. Use of Nonionic Surfactant to Reduce

Sulfuric Acid Mist in the Copper Electrowinning Process. Hydrometallurgy. 70 (2003). 1 – 8.

85
19. Hers, R. Zapf-Gilje, P. C. Johnson, and L. Li. 2002. Evaluation of the Johnson and Ettinger Model

for Prediction of Indoor Air Quality. Ground Water Monitoring and Remediation. 23 (2). 119 –

133.

20. Amerson, I.L., C.L. Bruce, P.C. Johnson, and R.L. Johnson. 2001. A Multi-Tracer Push-Pull

Diagnostic Test for In Situ Air Sparging Systems. Bioremediation Journal, 5(4):349-362.

21. Bruce, C.L., I.L. Amerson, R.L. Johnson, and P.C. Johnson. 2001. Use of an SF6-Based Diagnostic

Tool for Assessing Air Distributions and Oxygen Transfer Rates during IAS Operation.

Bioremediation Journal, 5(4):337-347.

22. Johnson, P.C., A. Leeson, R.L. Johnson, C.M. Vogel, R.E. Hinchee, M. Marley, T. Peargin, C.L.

Bruce, I.L. Amerson, C.T. Coonfare, and R.D. Gillespie. 2001. A Practical Approach for the

Selection, Pilot Testing, Design, and Monitoring of In Situ Air Sparging/Biosparging Systems.

Bioremediation Journal, 5(4):267-281.

23. Johnson, P.C., R.L. Johnson, C.L. Bruce, and A. Leeson. 2001. Advances in In Situ Air

Sparging/Biosparging. Bioremediation Journal, 5(4):251-266.

24. Johnson, R.L., P.C. Johnson, T.L. Johnson, and A. Leeson. 2001. Helium Tracer Tests for

Assessing Contaminant Vapor Recovery and Air Distribution During In Situ Air Sparging.

Bioremediation Journal, 5(4):321-336.

25. Johnson, R.L., P.C. Johnson, T.L. Johnson, N.R. Thomson, and A. Leeson. 2001. Diagnosis of In

Situ Air Sparging Performance Using Transient Groundwater Pressure Changes During Startup and

Shutdown. Bioremediation Journal, 5(4):299-320.

26. Johnson, R.L., P.C. Johnson, I.L. Amerson, T.L. Johnson, C.L. Bruce, A. Leeson, and C.M. Vogel.

2001. Diagnostic Tools for Integrated In Situ Air Sparging Pilot Tests. Bioremediation Journal,

5(4):283-298.

27. Abranovic, D., P. C. Johnson, R. J. Charbeneau, and T. Hemstreet. 2000. A Graphical Approach

for Determining Dilution-Attenuation Factors: Basic Theory and Approach for Submerged Sources.

Groundwater Monitoring and Remediation.

28. Salanitro, J. P., P. C. Johnson, G. E. Spinnler, P. M. Maner, H. L. Wisniewski and C. L. Bruce.

2000. Field-Scale Demonstration of Enhanced MTBE Bioremediation through Aquifer

Bioaugmentation and Oxygenation. Environmental Science and Technology. 34(19). 4152-4162

29. Johnson, P.C., A. Das, and C. Bruce. 1999. Effect of Flowrate Changes and Pulsing on the

Treatment of Source Zones by In Situ Air Sparging. Environmental Science and Technology. 33

(10). 1726-1731.

30. Johnson, P.C., R.L. Johnson, and M.W. Kemblowski. 1999. Assessing the Significance of Vapor

Migration to Enclosed-Spaces on a Site-Specific Basis. Journal of Soil Contamination. 8 (3). 389 -

421.

31. Johnson, P.C., C. Bruce. R.L. Johnson, and M.W. Kemblowski. 1998. In Situ Measurement of

Effective Vapor-Phase Porous Medium Diffusion Coefficients. Environmental Science and

Technology. 32. 3405-3409.

86
32. Johnson, P.C.. 1998. An Assessment of the Contributions of Volatilization and Biodegradation to

In Situ Air Sparging Performance. Environmental Science and Technology. 32 (2). 276-281.

33. Rutherford, K..W., D.H. Bass, W., W. McPhee, P.C. Johnson. 1997. Estimation of Oxygen Mass

Transfer Coefficients During Air Sparging. Bioremediation. 4 (1). 153-158.

34. Johnson, P.C., R.L. Johnson, C. Neaville, E.E. Hansen, S.M. Stearns, and I.J. Dortch. 1997. An

Assessment of Conventional In Situ Air Sparging Tests. Ground Water. 35 (5). 765 - 774.

35. Rutherford, K.W. and P.C. Johnson. 1996. Effects of Process Control Changes on Aquifer

Oxygenation Rates During In Situ Air Sparging in Homogeneous Aquifers. Ground Water

Monitoring and Remediation. 16 (4). 132 - 141.

36. Johnson, P. C. and R. A. Ettinger. 1994. Some Considerations for the Design of In Situ Vapor

Extraction Systems: Radius of Influence -vs- Radius of Remediation. Ground Water Monitoring

and Remediation. 14 (3). 123 - 128.

37. Johnson, R.L., P.C. Johnson, D.B. McWhorter, R. Hinchee, and I. Goodman. 1993. An Overview

of In Situ Air Sparging. Ground Water Monitoring and Remediation. 13 (4). 127 - 135.

38. Benson, D.A., D. Huntley, and P.C. Johnson. 1993. Modeling Vapor Extraction and General

Transport in the Presence of NAPL Mixtures and Nonideal Conditions. Groundwater. 31 (3). 437 -

445.

39. Johnson, P.C. and R.A. Ettinger. 1991. Heuristic Model for the Intrusion Rate of Contaminant

Vapors Into Buildings. Environ. Sci. Technol.. 25(8). 1445-1452.

40. Johnson, P.C., C.C. Stanley, M.W. Kemblowski, D.L. Byers, and J.D. Colthart. 1990. A Practical

Approach to the Design, Operation, and Monitoring of In Situ Soil-Venting Systems. Ground

Water Monit. Rev.. 10 (2). 159 - 178.

41. Johnson, P.C., M. W. Kemblowski, and J. D. Colthart. 1990. Quantitative Analysis for the

Cleanup of Hydrocarbon-Contaminated Soils by In Situ Soil Venting. Ground Water. 3 (28):413-

429.

42. Johnson, P.C., P. Nott, and R. Jackson. 1990. Friction-Collisional Equations of Motion for

Particulate Flows and Their Application to Chutes. J. Fluid Mech.. 210. 501-535.

43. Johnson, P.C. and R. Jackson. 1987. Friction-Collisional Constitutive Relations for Granular

Materials, with Application to Plane Shearing. J. Fluid Mech.. 176. 67-93.

44. Johnson P.C., M.C. Lagunas-Solar, and M.J. Avila. 1984. The Indirect Production of No-CarrierAdded 57Co via the 59Co(p,3n)57Ni->57Co Reaction. Int. J. Applied Radiat. Isot. 35(5). 371-

376.

45. Lagunas-Solar, M.J. Avila, and P.C. Johnson P.C.. 1984. Cyclotron Production of 101mRh via

Proton-Induced Reactions on 103Rh Targets. Int. J. Applied Radiat. Isot. 35(8). 743-748.

87
46. Lagunas-Solar, M.C., M.J. Avila, N.J. Navarro, and P.C. Johnson. 1983. Cyclotron Production of

No-Carrier-Added 97Ru by Proton Bombardment of 103Rh Targets. Int. J. Applied Radiat. Isot.

34(6). 915-922.

Other Peer-Reviewed Reviewed Publications:

1. Johnson P.C., R.L. Johnson, C.L. Bruce CL. 2010. In Situ Air Sparging for the Treatment of

Dissolved Hydrocarbon Groundwater Plumes. In Stroo HF, Ward CH, eds, In Situ Remediation of

Chlorinated Solvent Plumes, Vol 2, SERDP/ESTCP Remediation Technology Monograph Series.

Springer Science+Business Media, LLC, New York, NY, USA, In Press.

2. Johnson R.L. and P.C. Johnson. 2010. In SituSparging for the Delivery of Gases in the Subsurface.

In Kitanidis, P.K. and P.L. McCarty eds, Delivery and Mixing in the Subsurface: Processes and

Principles for In Situ Remediation. SERDP/ESTCP Remediation Technology Monograph Series.

Springer Science+Business Media, LLC, New York, NY, USA, In Press.

3. McAlary, T., R.A. Ettinger, P.C. Johnson, B. Eklund, H. Hayes, D.B. Chadwick, I. Rivera-Duarte.

2009. Review of Best Practices, Knowledge and Data Gaps, and Research Opportunties for the U.S.

Department of Navy Vapor Intrusion Focus Areas. Technical Report 1982. May. SPAWAR

Systems Center Pacific.

4. Hay-Wilson, L., P. C. Johnson, and J. Rocco. 2005. Collecting and Interpreting Soil Gas Samples

from the Vadose Zone: A Practical Strategy for Assessing the Subsurface-Vapor-to-Indoor-Air

Migration Pathway at Petroleum Hydrocarbon Sites. American Petroleum Institute. Publication

Number 4741. November.

5. McAlary, T., R.A. Ettinger, and P.C. Johnson. 2005. Reference Handbook for Site-Specific

Assessment of Subsurface Vapor Intrusion to Indoor Air. EPRI Technical Report 1008492. Palo

Alto, CA.

6. Johnson, P.C.., K. Miller, and C. L. Bruce. 2004. A Practical Approach to the Design, Monitoring,

and Optimization of In Situ MTBE Aerobic Biobarriers. http://docs.serdpestcp.org/viewfile.cfm?Doc=CU0013%2DTR%2D01%2Epdf.

7. Johnson, P.C.., K. Miller, and C. L. Bruce. 2004. In Situ Bioremediation of MTBE in Groundwater

– Final Technical Report.http://docs.serdpestcp.org/viewfile.cfm?Doc=CU%2D0013%2DFR%2D01%2Epdf.

8. Johnson, P.C.., K. Miller, and C. L. Bruce. 2004. In Situ Bioremediation of MTBE in Groundwater

– Cost and Performance Report. http://www.estcp.org/documents/techdocs/CU-0013.pdf.

9. Johnson, P.C., P.D. Lundegard, J. Catts, D. Eley, K. Schroeder, E. Nichols, David Peterson. 2004.

Dissolved Total Petroleum Hydrocarbons (TPH) Groundwater Plume Stability at the Former

Guadalupe Oil Field.

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10. Johnson, P.C., P.D. Lundegard, J. Catts, K. DiSimone, D. Eley, K. Schroeder. 2003. Source Zone

Natural Attenuation Field Measurements, Data Interpretation, and Data Reduction at the Former

Guadalupe Oil Field (Version 2.1). Ratified December 18.

11. Roggemans, S., C.L. Bruce, and P.C. Johnson. 2002. Vadose Zone Natural Attenuation of

Hydrocarbon Vapors: An Empirical Assessment of Soil Gas Vertical Profile Data. American

Petroleum Institute Technical Report.

12. Spinnler, G.E., P.C. Johnson, K. Miller. 2002. Bioaugmentation Field Testing for MTBE

Treatment. USEPA Ground Water Currents. October. Issue 41.

13. Johnson, P.C.. 2002. Sensitivity Analysis and Identification of Critical and Non-Critical Parameters

for the Johnson and Ettinger (1991) Vapor Intrusion Model. American Petroleum Institute Technical

Report.

14. Johnson, P.C., R.A. Ettinger, J. Kurtz, R. Bryan, and J.E. Kester. 2001. Empirical Assessment of

Subsurface Vapor –to- Indoor Air Attenuation Factors and Comparison with Theory for the CDOTMTL Denver Site. American Petroleum Institute Technical Report.

15. Johnson, P.C., M. W. Kemblowski, and R.L. Johnson. 1998. Assessing the Significance of

Subsurface Contaminant Migration to Enclosed Spaces: Site-Specific Alternatives to Generic

Estimates. American Petroleum Institute Publication No. 4674. December.

16. Johnson, P.C., D. Abranovic, R.J. Charbeneau, and T. Hemstreet. 1997. Technical Background

Document for the Graphical Approach for Determining Site-Specific Dilution-Attenuation Factors

(DAFs). American Petroleum Institute Publication 4659.

17. Johnson, P.C., D. Abranovic, R.J. Charbeneau, and T. Hemstreet. 1997. User’s Guide for the

Graphical Approach for Determining Site-Specific Dilution-Attenuation Factors (DAFs). American

Petroleum Institute Publication 4659.

18. American Society for Testing and Materials. 1997. Standard Guide for Risk-Based Corrective

Action (RBCA) at Chemical Release Sites.

19. Johnson, P.C.. 1997. Application of Risk-Based Corrective Action at a Petroleum Release Site.

United States Environmental Protection Agency.

20. American Society for Testing and Materials (P.C. Johnson lead author). 1995. Standard Guide for

Risk-Based Corrective Action (RBCA) at Petroleum Release Sites. E1739-95 (updated and modifed

version of ASTM ES-38 below).

21. American Society for Testing and Materials (P.C. Johnson lead author). 1994. Emergency Guide

for Risk-Based Corrective Action (RBCA) at Petroleum Release Sites. ES-38.

Books, Book Chapters, Monographs, and Dissertations:

1. Johnson P.C., R.L. Johnson, C.L. Bruce CL. 2010. In Situ Air Sparging for the Treatment of

Dissolved Hydrocarbon Groundwater Plumes. In Stroo HF, Ward CH, eds, In Situ Remediation of

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Chlorinated Solvent Plumes, Vol 2, SERDP/ESTCP Remediation Technology Monograph Series. 

Springer Science+Business Media, LLC, New York, NY, USA, In Press. 

2. Johnson R.L. and P.C. Johnson. 2010. In SituSparging for the Delivery of Gases in the Subsurface. In

Kitanidis, P.K. and P.L. McCarty eds, Delivery and Mixing in the Subsurface: Processes and

Principles for In Situ Remediation. SERDP/ESTCP Remediation Technology Monograph Series.

Springer Science+Business Media, LLC, New York, NY, USA, In Press.

3. Johnson, P.C. 2000. Chapter 14: Aquifer Restoration via In Situ Air Sparging. In Standard

Handbook of Environmental Science, Health, and Technology (J. Lehr, ed.). McGraw-Hill.

4. Johnson, P.C.. 1999. Chapter 23: Hydraulic Design for Groundwater Contamination. Hydraulic

Design (L. Mays, ed.). McGraw-Hill. 23.1 – 23.68.

5. Dablow, J.F., J.A. Pearce, P.C. Johnson. 1998. Steam and Electro-Heating Remediation of Tight

Soils. Ann Arbor Press.

6. Johnson, P. C. and R. A. Ettinger. 1997. Some Considerations for the Design of In Situ Vapor

Extraction Systems: Radius of Influence -vs- Radius of Remediation. Subsurface Restoration (C.H.

Ward, J.A. Cherry, M.R. Scalf, editors). Ann Arbor Press. 209 - 216.

7. Hinchee, R.L., R.N. Miller, and P.C. Johnson. 1995. In Situ Aeration: Air Sparging, Bioventing,

and Related Remediation Processes. Battelle Press. ISBN 1-57477-003-9.

8. Johnson, P.C., G.E. Hoag, R.H. Hinchee, R.A. Brown, and A.L. Baehr. 1994. Innovative Site

Remediation Technology: Vapor Extraction-Based Technologies (Soil Vapor Extraction,

Bioventing, Air Sparging, and Thermally-Enhanced Soil Vapor Extraction). USEPA/AAEE

WASTECH Monograph. ISBN 1-883767-08-3.

9. Johnson, P.C. and A.J. Stabenau. 1991. HyperVentilate - A Software Guidance System Created for

Vapor Extraction Applications - Users Manual. USEPA 600/R-93/028.

10. Johnson, P.C., R.L. Johnson, C. Neaville, E.E. Hansen, S.M. Stearns, and I.J. Dortch. 1995. Do

Conventional Practices Indicate In Situ Air Sparging Performance?. In Situ Aeration: Air Sparging,

Bioventing, and Related Remediation Processes (Hinchee, Miller, Johnson, eds.). Battelle Press. 1 -

20.

11. Bedient P.B. and P.C. Johnson. 1992. Soil Vapor Extraction Systems. Groundwater Remediation.

Charbeneau, R.J., P.B. Bedient, and R.C. Loehr Eds.. Technomic Publishing Inc.. 143-160.

12. Johnson, P.C., C.C. Stanley, D.L. Byers, D.A. Benson, and M.A. Acton. 1991. Soil Venting at a

California Site: Field Data Reconciled with Theory. Hydrocarbon Contaminated Soils and

Groundwater: Analysis, Fate, Environmental and Public Health Effects, Remediation, Vol I." P.T.

Kostecki and E.J. Calabrese (eds.). Lewis Publishers. 253 - 282.

13. Rixey, W.G., P.C. Johnson, G.M. Deeley, D.L. Byers, and I.J. Dortch. 1991. Mechanisms for the

Removal of Residual Hydrocarbons for Soils by Water, Solvent, and Surfactant Flushing. In

Petroleum Contaminated Soils Volume 4 (P.T. Kostecki and E.J. Calabrese Eds.). Lewis Publishers.

90
14. Johnson, P.C., Hertz, M.B. and D.L. Byers. 1990. Estimates for Hydrocarbon Vapor Emissions

Resulting from Service Station Remediations and Buried Gasoline-Contaminated Soils. In

Petroleum Contaminated Soils Volume 3 (P.T. Kostecki and E.J. Calabrese Eds.). Lewis Publishers.

295-326.

15. Johnson, P.C.. 1987. Frictional-Collisional Relationships for Particulate Flows and Their

Application to Plane Shear Flows. Ph.D. Thesis. Department of Chemical Engineering. Princeton

University

Invited Presentations/Papers:

1. Johnson, P.C., P. Dahlen, H. Luo, C. Holton, K. Gorder, E. Dettenmaier. 2011. Temporal Changes

in VI Behavior:Considerations for Pathway Assessment. U. Washington/USEPA Superfund

Research Center. June 15. Seattle, WA.

2. Johnson, P.C., P. Dahlen, H. Luo, C. Holton, K. Gorder, E. Dettenmaier. 2011. Temporal Changes

in VI Behavior:Considerations for Pathway Assessment. 21at Annual Training Program – National

Association of Remedial Program Managers. May 16-20. Kansas City, MO.

3. Johnson, P.C. and E. Nichols. 2011. Session Keynote: Measurement and Control of Subsurface

Contaminant Discharge and Its Use in Decision-Making. RemTEC Summit. May 16-19. Chicago,

IL.

4. Kavanaugh, M., K. Pennell, Johnson, P.C., and Anna Willett. 2011. Panel Discussion -Future of

Subsurface Remediation Efforts in the United States: Barriers to Success. RemTEC Summit. May

16-19. Chicago, IL.

5. Johnson, P.C. 2011. Soil and Groundwater Remediation: Issues, Advances, and Challenges.

Engineers Club of the West Valley. April. Sun City, AZ.

6. Johnson, P.C., P. Dahlen, H. Luo, C. Holton. 2011. Temporal Changes in VI

Behavior:Considerations for Pathway Assessment. USEPA Workshop on Addressing Regulatory

Challenges in Vapor Intrusion: A State of the Science Update Focusing on Chlorinated VOCs.

AEHS 21st Annual Meeting and West Coast Conference on Soils, Sediments, Water. San Diego, CA.

7. Johnson, P.C. 2010.Session Keynote: Vapor Intrusion Pathway Assessment: State of the Practice and

Opportuntites for v3.0. SERDP/ESTCP Partners Conference. December, 2010.

8. Johnson, P.C., P. Dahlen, H. Luo, C. Holton, K. Gorder, E. Dettenmaier. 2011. Integrated Fieldscale, Lab-scale, and Modeling Studies for Improving Our Ability to Assess the Groundwater to

Indoor Air Pathway. SERDP Technical Exchange Meeting on Vapor Intrusion. August 16 - 17.

Salt Lake City, UT.

9. Johnson, P.C. 2010.Vapor Intrusion Pathway Assessment: Challenges, Developments, and Ongoing

Research. Air Force Restoration and Technology Transfer Workshop. April 6 – 8, 2010.

91
10. Johnson, P.C. 2009. Subsurface Vapor to Indoor Air Pathway: Consideration of Multiple Lines of

Evidence in Pathway Assessment. . CA Department of Toxic Substances Control (DTSC), Asilomar,

CA. November.

11. Johnson, P.C. 2008. Aeration-Based Remediation Technologies. Remediation Technology

Symposium. CA Department of Toxic Substances Control (DTSC). Sacramento. May 14 – 16.

12. Johnson, P.C., J. Triplett-Kingston, P. Dahlen, E. Foote, S. and Williams. 2008. Critical Evaluation

of In Situ Thermal Treatment Technologies for DNAPL Source Zone Treatment. 2008 AFCEE

Technology Transfer Workshop. March 25-28, 2008.

13. Johnson, P.C. 2008. The Path to More Confident and Cost-Effective Vapor Intrusion Pathway

Assessment. 18th Annual AEHS Meeting and International Conference on Soils, Sediments & Water.

San Diego. March 10 - 13.

14. Johnson, P.C. and R.A. Ettinger. 2008. An Empirical Analysis of Data From the Colorado DoT

Materials Laboratory Testing Site, Denver CO. 18th Annual AEHS Meeting and International

Conference on Soils, Sediments & Water. San Diego. March 10 - 13.

15. Johnson, P.C., 2007. Vapor Intrusion – Conceptualizing and Dealing with Spatial and Temporal

Variability. Air and Waste Management Association: Vapor Intrusion – A Rapidly Developing

Environmental Challenge. November 13 – 15, 2007.

16. Dahlen, P. and P.C. Johnson. 2007. Field Comparison of Oxygen Delivery Technologies.

University Consortium for Field-Focused Groundwater Contamination Research. April 17 – 19.

Ontario, Canada.

17. Triplett-Kingston, J.. and P.C. Johnson. 2007. Empirical Assessment of Thermal Technology

Performance. April 17 – 19. Ontario, Canada.

18. Johnson, P.C.. 2007. Vapor Intrusion Field Studies and Modeling. April 17 – 19. Ontario, Canada.

19. Johnson, P.C.. 2007. Subsurface Vapor to Indoor Air Pathway Assessment: Lessons-Learned and

Challenges for the Future. Keynote Presentation at the 6th State of Washington Hydrology

Symposium. May 1 – 3.

20. Johnson, P.C.. 2006. Field Studies of Oxygen and Hydrocarbon Vapor Transport Beneath and

Around Buildings Located Over NAPL Sources. 16th Annual AEHS Meeting and International

Conference on Soils, Sediments & Water. San Diego. March.

21. Johnson, P.C. 2005. Vapor Intrusion – Lessons Learned Through Numerical Simulation. 15th Annual

AEHS Meeting and International Conference on Soils, Sediments & Water. San Diego. March.

22. Johnson, P.C. and L. D. V. Abreu. 2004. Advances in the Modeling of Vapor Migration to

Buildings. Annual International Conference on Soils, Sediments & Water. University of

Massachusetts. October.

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23. Johnson, P.C. and L. D. V. Abreu. 2004. Advances in the Modeling of Vapor Migration to

Buildings. Annual International Conference on Soils, Sediments & Water. University of

Massachusetts. October.

24. Johnson, P.C.. 2002. Confusion and Delusion in the World of Vapor Intrusion. Keynote Speech –

First Annual Midwestern States Risk Assessment Symposium. July 16 – 17. Indianapolis, Indiana.

25. Johnson, P.C.. 2002. Arizona Groundwater Study – Preliminary Results. Fourth Annual

Underground Storage Tank Program Conference, Arizona Department of Environmental Quality.

June 5. Phoenix, AZ.

26. Johnson, P.C.. 2001. Assessing Risks From Vapor Migration To Enclosed Spaces. Pennsylvania

Department of Environmental Protection Annual Conference. June 7. Harrisburg, PA.

27. Johnson P. C.. 2000. Advances in Vapour Intrusion Modelling for Risk-Based Decision Making.

2000 Contaminated Site Remediation Conference. December 4 – 8. Melbourne Australia

28. Johnson, P.C.. 2000. A Retrospective Look to the Future of LUST Issues. Third Annual

Underground Storage Tank Program Conference, Arizona Department of Environmental Quality.

September 29. Phoenix, AZ.

29. Johnson, P.C. and R.A. Ettinger. 2000. Progress Towards Gaining a Better Understanding of

Subsurface Vapor Migration. RCRA: Visions for the Future Conference. USEPA. August 15 –18.

Washington, D.C..

30. Johnson, P.C. and R.A. Ettinger. 2000. An Empirical Analysis of Data From the Colorado DoT

Materials Laboratory Testing Site, Denver CO. RCRA: Visions for the Future Conference. USEPA.

August 15 –18. Washington, D.C..

31. Johnson, P.C., C. Bruce, J. P. Salanitro, G. E. Spinnler. 2000. MTBE Biobarrier Studies at Port

Hueneme, CA. 2000 National LUST Conference – U.S. Environmental Protection Agency. March.

Portland, OR.

32. Johnson, P.C. and J.P. Salanitro. 1999. MTBE Bioremediation. New Jersey Department of

Environmental Protection. August 17, 1999. Trenton, NJ.

33. Ward, C.H., P.C. Johnson, and J.B. Hughes. 1999. Plenary Lecture: Enhanced BioAttenuation for

Subsurface Remediation. In Situ and On Site Bioremediation – Fifth International Symposium.

April 19-22, 1999. San Diego, CA.

34. Johnson, P.C. 1998. An Introduction to Natural Attenuation. First National Stakeholders Forum on

Monitored Natural Attenuation. San Francisco. August 31 – September 1. (voted best presentation

by attendees)

35. Johnson, P.C.. 1997. Keynote Lecture: Vadose Zone Natural Attenuation - Issues, Modeling

Challenges, and Critical Measurements. NGWA Petroleum Hydrocarbons and Organic Chemicals

in Groundwater: Prevention, Detection, and Restoration. November 12 - 14. Houston. (voted best

presentation by attendees)

93
36. Johnson, P.C. and R.L. Johnson. 1997. Plenary Lecture: It Looks Good on Paper and You’ve Paid

a Bunch, But is Your Remediation System out to Lunch? The Fourth International Symposium - In

Situ and On-Site Bioremediation. April 28 - May 1, 1997. New Orleans, LA.

37. Johnson, P.C.. 1997. Keynote Lecture: US Field and Research Experiences with In Situ Air

Sparging. ATV Danish National Groundwater Conference. March 11 - 12. Billund, Denmark.

38. Johnson, P.C.. 1997. Conventional and Innovative In Situ Air Sparging Pilot Test Procedures. ATV

Danish National Groundwater Conference. March 11 - 12. Billund, Denmark.

39. Johnson, P.C.. 1996. Risk-Based Corrective Action. Santa Fe Pacific Pipeline Partnership. Los

Angeles. August 23.

40. Johnson, P.C.. 1996. Risk-Based Corrective Action Training. USEPA/OUST/ADEQ. Phoenix

Arizona. August 15 - 16.

41. Johnson, P.C.. 1996. An Engineer’s Introduction to Bioremediation. First Arizona Soil

Remediation Conference. Phoenix. May 3.

42. Johnson, P.C.. 1996. Soil Vapor Extraction - Mass Transfer Effects. First Arizona Soil

Remediation Conference. Phoenix. May 3.

43. Johnson, P.C.. 1996. Risk-Based Corrective Action for Tribal Lands. USEPA/OUST. Denver

Colorado. March 25 - 29.

44. Johnson, P.C.. 1996. Risk-Based Corrective Action. USEPA/OUST and State of Colorado.

Denver Colorado. March 19 - 22.

45. Johnson, P.C.. 1995. Risk-Based Corrective Action Demonstration Project. USEPA/OUST and

West Virginia Department of Environmental Quality. September 28 - 29.

46. Johnson, P.C.. 1995. Hydrocarbon Removal - How Much is Enough? USEPA OUST Strategic

Research Planning Meeting. Las Vegas. September 20 - 21.

47. Johnson, P.C.. 1995. Risk-Based Corrective Action for UST Sites. Arizona Department of

Environmental Quality. Phoenix. September 18.

48. Johnson, P.C.. 1995. Research Needs for the Remediation of DNAPL Sites. USAF Research

Planning Meeting. Tallahasee. August.

49. Johnson, P.C.. 1995. Modeling Biodegradation in Groundwater - Analytical Models. API

Biodegradation Modelling Workshop. Dallas. May 8 - 9.

50. Johnson, P.C.. 1995. In Situ Remediation Technologies. Arizona Water Pollution Control

Association. Phoenix. March 17.

94
51. Johnson, P.C.. 1995. Risk-Based Corrective Action. South Dakota Dept. of Environmental Quality.

March 8.

52. Johnson, P.C.. 1995. Aeration-based Remediation Technologies. ARCO Research. Los Angeles.

February 7.

53. Johnson, P.C.. 1994. Considerations for the Design and Optimization of Soil Vapor Extraction

Systems. Invited presentation at the 1994 API/NGWA Conference: Petroleum Hydrocarbons and

Organic Chemicals in Groundwater. Houston.

54. Johnson, P.C., R.L. Johnson, C. Neaville, and E.E. Hansen. 1994. Performance Monitoring and

Pilot Testing of In Situ Air Sparging Systems. Invited Presentation at the AGWSE National

Education Program. October 9-12. Las Vegas, Nevada.

55. Johnson, P.C.. 1994. Pilot Testing of In Situ Air Sparging Systems. Invited Presentation at the

Annual Air Force Center for Environmental Excellence (AFCEE) Conference. San Antonio.

56. Johnson, P.C. and D. Mohr. 1994. Soil Vapor Extraction, Bioventing, and Air Sparging. Invited

presentation at the 1st USEPA Strategic Technology Evaluation Workshop. February.

57. Johnson, P.C.. 1993. Risk-Based Corrective Action: Developments and Opportunities. Presented at

the 14th Annual Society of Toxicology and Chemistry Meeting. November 14-18. Houston, TX.

National Conference Proceedings Reviewed Papers, Abstracts, and Presentations:

1. Luo, H., C. Holton, P. Dahlen, and P.C. Johnson. 2011. Field and Modeling Studies of Temporal

Variability of Sub-Slab Soil Gas and Indoor Air Concentrations at a House Overlying a Chlorinated

Compound-Impacted Groundwater Plume. Bioremediation and Sustainable Environmental

Technologies. Reno, NV. June 27-30, 2011.

2. Escobar, E., P. Dahlen, and P.C. Johnson. 2011. Biodegradation of Petroleum Hydrocarbon Vapor

Components in the Subsurface: A Laboratory Soil Column Study. Bioremediation and Sustainable

Environmental Technologies. Reno, NV. June 27-30, 2011.

3. Escobar, E., P. Dahlen, P. C. Johnson. 2011. Transport and Biodegradation of Petroleum

Hydrocarbon Vapor Components in the Subsurface – A Soil Column Study. USEPA Workshop on

Addressing Regulatory Challenges in Vapor Intrusion: A State of the Science Update Focusing on

Chlorinated VOCs. AEHS 21st Annual Meeting and West Coast Conference on Soils, Sediments,

Water. San Diego, CA.

4. H. Luo and P. C. Johnson. 2011. Incorporating Barometric Pressure and Wind Effects into Vapor

Intrusion Simulations. USEPA Workshop on Addressing Regulatory Challenges in Vapor Intrusion:

A State of the Science Update Focusing on Chlorinated VOCs. AEHS 21st Annual Meeting and

West Coast Conference on Soils, Sediments, Water. San Diego, CA.

95
5. Luo. H., P. Dahlen, T. Peargin, P.C. Johnson. 2010. Proof-of-Concept Study of an Engineering

Bio-Attenuation Barrier Beneath a Building at a Petroleum Hydrocarbon-Impacted Site.

Remediation of Chlorinated Solvents and Recalcitrant Compounds. May 24- 27. Monterey, CA.

6. P.Lundegard, P., P. Johnson, and P. Dahlen. 2008. Oxygen Transport from the Atmosphere to Soil

Gas Beneath a Slab-on-Grade Foundation Overlying Petroleum-Impacted Soil. 18th Annual AEHS

Meeting and International Conference on Soils, Sediments & Water. San Diego. March 10 - 13.

7. Spinnler, G.E., P.C. Johnson, L. Lesser, C.L. Bruce, R. Aravena, J.P. Salanitro, R.L. Johnson. 2003,

MTBE and TBA Biodegradation Assessment Under Natural and Engineered Conditions Using

Compound-Specific Carbon Isotope Analysis at Port Hueneme, CA. NGWA/API Petroleum

Hydrocarbons and Organic Chemicals in Groundwater. August 20- 22. Costa Mesa, CA.

8. Johnson, P.C. and L. Abreu. 2003. Learning Through the Simulation of Vapor Intrusion Scenarios.

NGWA/API Petroleum Hyrocarbons and Other Organic Chemicals in Groundwater. August 20 –

22. Costa Mesa, CA.

9. Johnson, P.C., P. Dahlen, E. Henry, and M. Matsumura. 2003. It’s Not About Plume Lengths – The

Arizona Groundwater Study. NGWA/API Petroleum Hyrocarbons and Other Organic Chemicals in

Groundwater. August 20 – 22. Costa Mesa, CA.

10. P.C. Johnson, and K. Miller. 2002. Large-Scale Mixed MTBE-BTEX Plume Containment at Port

Hueneme, CA, Using A Combination of Biostimulation and Bioaugmentation. Third International

Conference on Remediation of Chlorinated and Recalcitrant Compounds. Monterey, CA. May 20 –

23.

11. Bruce, C.L. and P.C. Johnson. 2001. Effect of Chemical Properties on IAS Treatment: An

Evaluation of Field and Lab Data Comparing MTBE vs. BTEX Removal. API/NGWA Conference:

Petroleum Hydrocarbons and Organic Chemicals in Groundwater. Houston, TX. November 14 –

16.

12. Johnson, P. C.. 2001. Gaining a Better Understanding of the Johnson and Ettinger Model Through

Sensisivity Analysis. API/NGWA Conference: Petroleum Hydrocarbons and Organic Chemicals in

Groundwater. Houston, TX. November 14 – 16.

13. Spinnler, G.E., J.P. Salanitro, and P.C. Johnson. 2001. MTBE Remediation at Retail Gas Stations

by Bioaugmentation. API/NGWA Conference: Petroleum Hydrocarbons and Organic Chemicals in

Groundwater. Houston, TX. November 14 – 16.

14. Salanitro, J.P., P.C. Johnson, C.L. Bruce, Spinnler, G.E., P.M. Maner, D.L. Tharpe, H.L.

Wisniewski. 2001. In Situ Bioremediation of MTBE Using Biobarriers of Single or Mixed Cultures.

In Situ and On-Site Bioremediation – The Sixth International Symposium. San Diego. June 4 - 7.

15. Spinnler, G.E., P.M. Maner, J.P. Salanitro and P.C. Johnson. 2001. Demonstration of the

BioRemedy Process for MTBE Remediation at Retail Gasoline Stations. In Situ and On-Site

Bioremediation – The Sixth International Symposium. San Diego. June 4 - 7.

96
16. Johnson, P.C. and R.A. Ettinger. 2000. Progress Towards Gaining a Better Understanding of

Subsurface Vapor Migration. RCRA: Visions for the Future Conference. USEPA. August 15 –18.

Washington, D.C..

17. Johnson, P.C. and R.A. Ettinger. 2000. An Empirical Analysis of Data From the Colorado DoT

Materials Laboratory Testing Site, Denver CO. RCRA: Visions for the Future Conference. USEPA.

August 15 –18. Washington, D.C..

18. Kemblowski, M.W. and P.C. Johnson. 2000. Environmental Monitoring, Modeling, and

Management and Bayesian Belief Networks. Envirosoft. June. Bilbao, Spain.

19. Arulantham, R., P. C. Johnson, and M. W. Kemblowski. 2000. Identifying Low-Risk MTBEImpacted Sites. Pacific Focus Ground Water Conference. February 17 – 18. San Francisco, CA.

20. Salanitro, J.P., P.C. Johnson, G.E. Spinnler, C.C. Neaville, P.M. Maner, S.M. Stearns, C.L. Bruce.

1999. Demonstration of the Enhanced MTBE Bioremediation (EMB) IN Situ Process. In Situ and

On Site Bioremediation – Fifth International Symposium. April 19-22, 1999. San Diego, CA.

21. Bruce, C.L., I.L. Amerson, P.C. Johnson, R.L. Johnson. 1999. Diagnostic Tools for Quantifying

Oxygen Mass Transfer Rates. In Situ and On Site Bioremediation – Fifth International Symposium.

April 19-22, 1999. San Diego, CA.

22. Bruce, C.L., P.C. Johnson, and R.L. Johnson 1998. Methyl Tert-Butyl Ether Removal by In Situ

Air Sparging in Physical Model Studies. The First International Conference on Remediation of

Chlorinated and Recalcitrant Compounds. May 18-21. Monterey, CA.

23. Johnson, P.C., A. Das, R.L. Johnson, C. Bruce, A. Leeson, D. McWhorter, and R.E. Hinchee. 1997.

Removal of Immiscible-Phase Hydrocarbons - Effects of Process Control Changes, Chemical

Properties, and Distribution. In Situ and On-Site Bioremediation: The Fourth International

Symposium. April 28 - May 1, 1997. New Orleans.

24. Johnson, R.L., P.C. Johnson, A. Leeson, C.M. Vogel. 1997. Air Distribution During In Situ Air

Sparging: Tracer and Geophysical Measurements. In Situ and On-Site Bioremediation: The Fourth

International Symposium. April 28 - May 1, 1997. New Orleans.

25. Rutherford, K.W., D. Bass, W. McPhee, and P.C. Johnson. 1997. Estimation of Oxygen Mass

Transfer Coefficients During In Situ Air Sparging. In Situ and On-Site Bioremediation: The Fourth

International Symposium. April 28 - May 1, 1997. New Orleans.

26. Johnson, R.L., P.C. Johnson, A. Leeson, C.M. Vogel. 1997. Air Distribution During In Situ Air

Sparging: Tracer and Geophysical Measurements. The Fourth International Symposium - In Situ

and On-Site Bioremediation. April 28 - May 1, 1997. New Orleans, LA.

27. Johnson, P.C.., A. Das, R.L. Johnson, A. Leeson, D. McWhorter, R. Hinchee, and C.M. Vogel.

1997. Effects of IAS Process Changes on the Removal of Immiscible-Phase Hydrocarbons. The

Fourth International Symposium - In Situ and On-Site Bioremediation. April 28 - May 1, 1997.

New Orleans, LA.

97
28. Rutherford, K.W., D. Bass, W. McPhee, and P. C. Johnson. 1997. Estimating Oxygen Mass

Transfer Coefficients During Air Sparging. The Fourth International Symposium - In Situ and OnSite Bioremediation. April 28 - May 1, 1997. New Orleans, LA.

29. Westerhoff, P., L. Baker, P. Fox, P. Johnson, and S. Houston. 1997. A Low-Cost Strategy to

Treating and Reuse Wastewater in Nogales, AZ. AWRA Long Beach ‘97. October 19-23.

30. Johnson, P.C., K. Balshaw-Biddle, T. Reeves, and C. Bruce. 1997. In Situ Air Sparging Studies

Using the AATDF ECRS Large-Scale Physical Model. AATDF Conference. Rice University.

February.

31. Johnson, P.C., R.L. Johnson, C. Neaville, and E.E. Hansen. 1995. Short-Term Pilot Tests - Reliable

Indicators of Long-Term In Situ Air Sparging Performance? In Situ and On-Site Bioreclamation

Conference - 3rd International Symposium. San Diego. April 24-27.

32. Johnson, R. L., N. R. Thomson, and P. C. Johnson. 1995. Does Sustained Groundwater Circulation

Occur During In Situ Air Sparging. In Situ and On-Site Bioreclamation Conference - 3rd

International Symposium. San Diego. April 24-27.

33. Rutherford, K. and P.C. Johnson. 1995. Interfacial Mass Transfer During In Situ Air Sparging -

Effects of Process Changes and Lithology. API/NGWA Conference: Petroleum Hydrocarbons and

Organic Chemicals in Groundwater. Houston, TX. November.

34. Johnson, P.C., R.L. Johnson, C. Neaville, and E.E. Hansen. 1995. Short-Term Pilot Tests - Reliable

Indicators of Long-Term In Situ Air Sparging Performance? AWPCA Annual Conference - Quentin

Mees Award. Phoenix. May.

35. Wheeless, W., S. Hicken, C. Beitler, J. Rowe, M.A. Robbins, R.E. Hinchee, P.C. Johnson, R.L.

Johnson, and D.B. McWhorter. 1995. In Situ Air Sparging - Technology Demonstration for

Remediating Groundwater Contaminated with Dissolved-Phase Constituents at Hill Air Force Base.

API/NGWA Conference: Petroleum Hydrocarbons and Organic Chemicals in Groundwater.

Houston, TX. November.

36. Johnson, P.C., Rounds, D., and C.C. Stanley. 1994. Risk-Based Corrective Action (RBCA) at

Petroleum Release Sites. API/NGWA Conference: Petroleum Hydrocarbons and Organic Chemicals

in Groundwater. Houston, TX. November.

37. Neaville, C., P.C. Johnson, and R.L. Johnson. 1994. Evaluation of Air Sparging Technology at a

Gasoline UST Site. AEHS Petroleum Contaminated Soils Conference. Long Beach, CA.

38. Sabadell, G.P., J.B. Gustafson, P.C. Johnson, E.R. Cruz, L.W.R. Dicks and C.C. Wang. 1993.

Evaluation of Soil Vapor Extraction System Design and Operation Utilizing Tracer Tests. Presented

at the CSCE-ASCE National Conference on Environmental Engineering. July.

39. Johnson, P.C. and C.C. Stanley. 1993. An Integrated Exposure/Risk-Based Corrective Action

Approach for Underground Storage Tank Sites. Presented at the 86th Annual Meeting and

Exhibition of the Air & Waste Management Association. Denver, Colorado.

98
40. Stanley, C.C., P.C. Johnson, R.K. Wenzlau, J.L. Rous, J.F. Vargas, and J.L. Peterson. 1992. An

Exposure/Risk-Based Corrective Action Approach for UST Sites. Proceedings of Petroleum

Hydrocarbons and Organic Chemicals in Groundwater. Houston, TX. November.

41. Johnson, P.C., M.W. Kemblowski, and J.D. Colthart. 1988. Practical Screening Models for Soil

Venting Applications. Proceedings; Petroleum Hydrocarbons and Organic Chemicals in Ground

Water Conference, National Water Well Association, American Petroleum Institute; Houston, TX.

Sponsored Research - External Grants and Gifts:

1. Johnson P.C. and P. Dahlen. Improving Our Understanding of Dissolved Groundwater Plume

Sources at Petroleum-Impacted Sites Through Physical Model, Mathematical Model, and Field-Site

Studies. Chevron.$500,000. 9/1/2010 – 8/31/2012.

2. Johnson, P.C. and P. Dahlen. Integrated Field-Scale, Lab-Scale, and Modeling Studies for

Improving Our Ability to Assess the Groundwater to Indoor Air Pathway at Chlorinated Solvent

Impacted Sites. SERDP. $1,256,000. 10/1/2009 – 9/30/2012.

3. Johnson, P. C. and P. Dahlen. Chemical Oxidation Technologies. Johnson. Shell Global

Solutions. $120,000. 12/1/08 – 6/31/11.

4. Johnson, B. Rittmann. Assessment of the Natural Attenuation of NAPL Source Zones and PostTreatment NAPL Source Zone Residuals. ESTCP. $899,424. 4/1/07 – 3/30/10.

5. Johnson, P.C. Capillary Properties of Soils and Residual Fluid Levels. American Petroleum

Institute. $50,000. 1/1/2010 – 12/31/2010.

6. Johnson. Field Study of Vapor Intrusion of Petroleum Hydrocarbon Vapors. Chevron. $40,000.

1/1/08 – 1/1/09

7. Johnson. Vapor Migration Studies. Chevron. $80,000. 1/1/06 – 12/31/07.

8. Johnson. Oxygen Delivery Technologies. Shell Global Solutions. $20,000. 1/1/07 – 12/31/07.

9. Johnson. Critical Evaluation of State-of-the-Art In Situ Thermal Treatment Technologies for

DNAPL Source Zone Treatment. Battelle (from ESTCP). $325,000. 2/1/05 – 9/31/07.

10. Johnson. Computer Simulation Of Subsurface Hydrocarbon Vapor Migration In The Vicinity Of

Homes And Buildings. Arco/Atlantic Richfield. $30,000. 9/1/05 – 8/31/06.

11. Razdan, Johnson. East Valley Water Forum Simulations. East Valley Water Forum. $117,500.

9/1/05 – 9/1/06.

12. Johnson. Bench-Scale Evaluation Of Long-Term Biosparging Effect On Ground Water Quality In

Diluent Source Areas At The Guadalupe Restoration Project. Unocal. $57,860. 6/14/04 – 6/1/06.

99
13. Johnson. Field Evaluation of Oxygen Delivery Technologies. Shell Global Solutions. $50,000.

1/1/05 – 5/31/06.

14. Johnson. Modeling of Vapor Intrusion of Petroleum Hydrocarbon Vapors. Chevron. $30,000.

1/1/05 – 12/31/06.

15. Johnson. Numerical Modeling of Vapor Intrusion of Petroleum Hydrocarbon Vapors. British

Petroleum. $20,000. 1/1/04 – 1/31/05.

16. Johnson. Mobil Foundation Gift. $10,000. 1/1/04 – 1/31/04.

17. Johnson. Innovative Technologies for Assessing and Treating Impacted Aquifers. U.S. Navy.

$275,000. 10/1/02 – 9/30/04.

18. Anderson-Rowland and Johnson. Collaborative Interdisciplinary Research Community

/Maricopa Engineering Transition Scholars (CIRC/METS). National Science Foundation.

$400,000. 7/1/03 – 6/30/07.

19. Johnson. Predicting Groundwater Quality Downgradient of Permeable Reaction Barriers. U.S.

Navy. $200,000. 10/1/03 – 5/30/06.

20. Johnson. Release of Regulated Substances to Arizona Ground Water – Supplemental Data

Collection. Arizona Department of Environmental Quality. 7/1/2002 – 12/31/2002. $150,000.

XCT9312.

21. Johnson. Release of Regulated Substances to Arizona Ground Water. Arizona Department of

Environmental Quality. 2/1/2001 – 12/31/2002. $331,143. XCT9312.

22. Johnson. Remediation of MTBE-Impacted Aquifers. Gift – Shell Oil Foundation. $10,000.

1/1/02 – 12/31/02.

23. Johnson. Environmental Restoration and Risk Assessment. Mobil Research Foundation.

$10,000. 1/1/02 – 12/31/02.

24. Johnson. Demonstration of the Enhanced MTBE Bioremediation Process at Port Hueneme, CA.

Equilon Enterprises. $80,114. 9/15/99 – 12/31/02. ORCA00310.

25. Johnson. Innovative Technologies for Assessing and Treating MTBE-Impacted Aquifers – Phase

1, 2, and 3. US Navy. $374,198. 8/30/99 – 5/31/02. XCA6526.

26. Johnson. Assessing the Longevity of Hydrocarbon Source Zones. Rio Tinto. $51,528. 9/1/99 –

12/31/01.

27. Johnson. NEX MTBE Plume Characterization. US Navy. $5,000. 6/8/99 – 6/1/00. XCA6525.

28. Johnson. Gift – Remediation of MTBE-Impacted Aquifers. Equilon Enterprises. $20,000.

12/1/99 – 12/1/00

100
29. Johnson. Gift – Remediation of MTBE-Impacted Aquifers. Equilon Enterprises. $10,000.

10/19/99 – 10/18/00.

30. Baker and Johnson. Management of Nitrate Contaminated Aquifers. Salt River Project.

$22,306. 6/1/99 – 5/16/01. XCT9292.

31. Johnson. Gift - Environmental Restoration and Risk Assessment. Mobil Research Foundation.

$12,000. 12/1/98 – 12/1/99.

32. Johnson. Gift - Remediation of MTBE in Ground Water. Equilon Enterprises. $86,000. 6/29/98 –

6/1/02.

33. Westerhoff and P.C. Johnson (40%). A Zero-Valent Treatment Process for Removing Nitrate and

Perchlorate from Groundwater. American Water Works Association. $64,812. XCT9283.

34. Johnson and R. Johnson (Oregon Graduate Institute). Vadose Zone Natural Attenuation.

American Petroleum Institute. $95,058. XCT9272. 2/12/97 - 6/1/99.

35. Johnson (Oregon Graduate Institute) and P. Johnson (10%). Natutal Attenuation of Dissolved

MTBE Plume. American Petroleum Institute. $90,000. 970060. 2/12/97 - 6/1/99.

36. Johnson (33%), R. Johnson (Oregon Graduate Institute), and M. Kemblowski (Utah State

University). Diagnostic Tools for the Monitoring and Optimization of In Situ Air Sparging

Systems. American Petroleum Institute. $133,117. XCT9255. 1/1/96 - 12/31/99.

37. Johnson and M. Kemblowski (Utah State University). Vadose Zone Natural Attenuation.

American Petroleum Institute. $45,864. 970060. 2/12/97 - 12/31/97.

38. Johnson. In Situ Bioremediation of Contaminated Aquifer Soils. Battelle/SERDP/USAF.

$223,152. XCJ 6230. 11/1/96 - 12/31/98.

39. Johnson. Chlorinated Hydrocarbon Remediation. Salt River Project. $22,000. 5/1/95 - 11/1/97.

GFT4628.

40. Johnson. Gift - Environmental Restoration and Risk Assessment. Mobil Research Foundation.

$20,000. 2/1/97 -. XC51001.

41. Johnson and R. Charbeneau (U. Texas). Graphical Tools for Determining Site-Specific RiskBased Soil Screening Levels for the Soil to Groundwater Transport Pathway - A Practical

Alternative to Generic Dilution Attenuation Factors. American Petroleum Institute. $105,000.

2/1/95 - 7/31/96. XCT 8786.

42. Johnson. Iron-Induced Hydrocarbon Degradation. Arizona Department of Water Resources.

$24,470. 95-0483. 11/1/95-2/1/97.

43. Johnson. Regional Water Quality and Supply Management Strategies for the Phoenix

Metropolitan Area. Arizona Department of Water Resources. $24,220. XCT1465. 11/1/95-

2/1/97.

101
44. Fox, S. Houston, W. Houston, P.C. Johnson (25%). Direct Well Recharge of Tertiary Effluent.

Arizona Department of Water Resources. $77,558. XCT9251. 11/1/95 - 2/28/97.

45. Westerhoff, L. Baker, P. Johnson (20%). Linking Nitrate Models to Existing Salt River Project

Canal Hydraulic Models to Predict Water Quality Impacts of Well Pumping. Salt River Project.

$25,358. GFT 4653. 6/1/96 - 5/31/97.

46. Johnson. An Evaluation of EPA-Recommended Stack Emissions Monitoring Using Tracer Gas

Mass Balance Approach. Salt River Project. $14,327. GFT 4654. 6/1/96 - 5/31/97.

47. Johnson. Evaluation of the Use of Elemental Iron to Treat DBCP-Impacted Groundwater. Salt

River Project. $9,327. GFT 4654. 6/1/96 - 5/31/97.

48. Baker, P. Westerhoff, P. Fox, S. Houston, P. Johnson (15%), C. Klopotek. US-Mexico Border

Water Resource Management Technologies for Sustained Development - Low Cost Strategy for

Treating and Reusing Wastewater. SCERP/USEPA. $135,000. 96287. 9/1/96 - 8/31/97.

49. Johnson. Environmental Restoration and Risk Assessment. Mobil Research Foundation. $20,000.

10/1/94 -. XC51001.

Sponsored Research - Equipment Loans:

1. Experimental Controlled Release System.DOE/DOD/ AAATDF/ Rice University. 1/1/97 - 12/31/98.

970936.

2. Geoprobe Unit. University of California at Santa Barbara. 6/1/98 – 11/1/05

Sponsored Research - Internal Grants:

1. Johnson, P. Westerhoff, S. Beaudoin. Assessing the Impact of New Products and Process Changes on

Environmental Resources. $22,000. CEAS. 7/29/97 - 7/29/98.

2. Johnson. Chemistry Module for Undergraduate Civil Engineers. FEIGIA. $6000. 6/1/95 - 5/31/96.

ST1001.

3. Johnson. Restoration of Aquifers Contaminated with Solvents. FGIA. $6000. XCRG0110. 4/1/95 -

3/31/96.

4. Johnson. Bioremediation of Contaminated Aquifer Soils. $8000. OVPR. 9/1/94 - 8/31/95.

XCR230.

STUDENT THESES AND DISSERTATIONS SUPERVISED

Masters Degrees Awarded:

Student Date M.S. Thesis Title

102
Lisa Clifton 12/08 Effect of Dissolved Oxygen Manipulation on the 

Benzene Flux from a Low Permeability Soil Layer 

Pamela Maass 12/05 Modeling Groundwater Quality Changes Down-gradient 

of Permeable Reactive Barriers 

Roberta Lenski 12/04 Source Longevity Estimates for Ground Water Impacts 

at the Former Williams AFB Site 

Maikel Mendez 5/03 Use of MFI Tests to Project Secondary Effluent 

Recharge Well Performance in Costa Rica 

Makiko Matsumuro 12/02 Occurrence of Fuel Oxygenates in Groundwater at 

Arizona Leaking Underground Fuel Sites 

Suzanne Braunschneider 12/00 Visualization Studies for Bioaugmentation 

Jennifer Sigley [w/ S. 

Beaudoin – ChE] 

12/99 Use of Nonionic Surfactants for Reducing Sulfuric Acid 

Mist Emissions During the Copper Electrowinning 

Process 

JeskoSollner 6/99 Bioremediation of a MTBE-Contaminated Site – Factors 

Influencing the Transport of Bacteria Through Soil and 

Aquifer Sand [Technical University Berlin]

Victoria Hermes 12/98 Numerical Modeling of Vadose Zone Natural 

Attenuation 

Sophie Roggemans 12/98 An Empirical Assessment of Natural Attenuation in the 

Vadose Zone 

Patricia McSparren 12/98 Regional Scale Groundwater Flow Modeling and 

Assessment of the Impacts of Treated Effluent 

Discharge near the US-Mexico Border at Nogales 

Illa Lyn Amerson 12/97 Diagnostic Tools for the Monitoring and Optimization 

of In Situ Air Sparging Systems 

Angie Luckie 5/97 Long-Term Pump Test Performance of a Deep 

Horizontal Well in a Highly Heterogeneous Formation 

Amar Das 12/96 Laboratory-Scale Study of Volatilization from Residual 

Source Zones During Air Sparging 

David Abranovic 5/96 Graphical Tools for Determining Site-Specific RiskBased Soil Screening Levels 

Kyle Wayne Rutherford 12/95 Effects of Process Control Changes on Interfacial Mass 

Transfer Rates During In Situ Air Sparging 

Jennifer Campbell 12/96 Iron-Induced Degradation of Chlorinated Solvents in 

Groundwater [MSE Project] 

Cindy Barker 5/96 Learning Tools for Undergraduate Students - Chemistry 

Module for Civil Engineers [MSE Project] 

Doctoral Degrees Awarded:

Student Date Ph.D. Project Title 

Hong Luo 5/09 Field and Modeling studies of Soil Vapor Migration into 

Buildings at Petroleum Hydrocarbon Impacted Sites 

Jennifer Triplett-Kingston 5/08 Critical Evaluation of Thermal-Based Remediation 

Technologies 

Luis Lesser 5/08 Spatial and Temporal Variations in MTBE Degrading 

103
Activity 

LilianDeize de Abreu 3/05 A Three-Dimensional Numerical Model for Subsurface 

Vapor Migration to Enclosed Spaces 

Zhuang Liu 12/04 Accelerated Bench-Scale Weathering Tests for 

Petroleum Hydrocarbons 

Paul Dahlen 12/04 Impact of Leaking Underground Storage Tanks on 

Arizona Groundwater Resources 

Ying Xu 4/02 Empirical Analysis of Historical Trends and Prediction 

of Future behavior of Nitrate Concentrations in 

Groundwater in the SRP Service Area, AZ 

Cristin Bruce. 6/01 Performance Expectations for In Situ Air Sparging 

Systems 

STUDENT THESES AND DISSERTATIONS SUPERVISED

Current Graduate Projects in Progress:

Student Degree Project 

Ryan Ekre Ph.D. Source Zone Natural Attenuation of DNAPL Sources 

Elsy Escobar Ph.D. Vapor Co-Migration of Aerobically Biodegradable 

Components 

Bridgette Cavanagh Ph.D. Assessing the Impact of Chemical Oxidation for 

Treatment of Petroleum-Impacted Sites 

Chase Holton Ph.D. Vapor Migration of Chlorinated Solvents from 

Groundwater to Indoor Air 

Post-Doctoral Students:

Paul Dahlen (2004 – 2007) 

Hong Luo (2009 – present) 

Eric Henry (2001) – currently at University of North Carolina , Wilmington 

Cristin Bruce (2001 – 2003) – currently at Shell Global Solutions, Houston, TX. 

Undergraduate Projects Supervised:

1. Shawn Whitmer - Iron-Induced Chlorinated Hydrocarbon Degradation Studies

2. Makiko Matsumuro – WISE Program. Vapor Transport Studies.

PROFESSIONAL AND SCIENTIFIC SERVICE

Local Professional Committees and Appointments:

1. Governor Appointment to the Arizona UST Technical Appeals Board (1998 - 2002)

2. Governor Appointment to the Arizona Water Quality Assurance Revolving Fund (WQARF)

Advisory Panel (1997 - 2000)

104
3. ADEQ Ground Water Study Working Group (1999 - 2000)

4. Arizona Groundwater Clean-up Standards Task Force (1996 - 1997)

5. Arizona Department of Environmental Quality Director’s Advisory Panel on Soil Clean-up

Standards (1996)

Scientific and Professional Society Memberships:

1. American Society for Testing and Materials - Co-Chairman, Risk-Based Corrective Action for

Superfund and Self-Directed Cleanups Task Group (1995 - 1997)

2. Groundwater Remediation Technologies Analysis Center - Guidance Committee Member (1995 -

1998).

3. Advanced Applied Technology Demonstration Facility (DoD - AATDF) Program - Advisory

Committee Member (1994 - 1998)

4. National Ground Water Association

5. American Chemical Society

6. American Society of Civil Engineers

Conference Activities:

1. Session Chairman, Annual SERDP/ESTCP Partners in Innovation Conference. Vapor Intrusion.

Washington, D.C.. (2010).

2. Session Chairman, International Conference on Chlorinated Solvents and Other Recalcitrant

Compounds. Combining Thermal with Other Remediation Technologies. Monterey, CA (2010).

3. Session Chairman, Annual SERDP/ESTCP Partners in Innovation Conference. Vapor

Intrusion.Washington, D.C.. (2009).

4. Session Chairman, International Conference on Chlorinated Solvents and Other Recalcitrant

Compounds. Combining Thermal with Other Remediation Technologies. Monterey, CA (2008).

5. Session Chairman, Third International Conference on Chlorinated Solvents and Other Recalcitrant

Compounds. Monterey, CA (2002).

6. Session Chairman, In Situ and On-Site Bioreclamation Conference - 6th International Symposium.

June 4- 7. San Diego, CA (2001).

105
7. Session Chairman, Second International Conference on Chlorinated Solvents and Other

Recalcitrant Compounds. Monterey, CA (2000).

8. Session Chairman, In Situ and On-Site Bioreclamation Conference - 5th International Symposium.

San Diego, CA (1999).

9. Session Chairman, First International Conference on Chlorinated Solvents and Other Recalcitrant

Compounds. Monterey, CA (1998).

10. Session Chairman, In Situ and On-Site Bioreclamation Conference - 4th International Symposium.

New Orleans, LA (1997).

11. Session Chairman, Advanced Applied Technology Demonstration Conference. Rice University.

Houston, TX (1996).

12. Session Chairman, In Situ and On-Site Bioreclamation Conference - 3rd International Symposium.

San Diego, CA (1995).

13. Session Chairman, API/NGWA Conference: Petroleum Hydrocarbons and Organic Chemicals in

Groundwater. Houston, TX (1993).

Journal Editor Service:

1. Ground Water Monitoring and Remediation – Editor-in-Chief (2003 - )

2. Journal of Bioremediation (1996 - 2003) - Associate Editor

3. International Journal of Soil Contamination (1996 - 2003) - Editorial Advisory Board

Journal Referee Service:

1. Bioremediation Journal (Associate Editor)

2. Ground Water

3. Ground Water Monitoring and Remediation

4. Environmental Science and Technology

5. Environmental Engineering Science

6. Water Resources Research

7. Separation Science and Technology

8. ASCE Journal of Environmental Engineering

106
9. Soils (Associate Editor)

10. Water Environment Research

11. Biotechnology and Bioengineering

12. International Journal of Bioremediation

Proposal Reviewer:

1. National Science Foundation - Directorate for Geosciences (1993)

2. USEPA OUST Program (1994 - 1995)

3. Department of Energy/Department of Defense - AATDF Program (1993 - 1997)

4. DOE SERDP Program (1995, 1999, 2003, 2004, 2005)

Other:

Mentor - USEPA EarthVision Program (high school students; 1996 - 1997) 

UNIVERSITY COMMITTEE SERVICE AND OTHER SERVICE

University-Level Service

Associate Vice President – Research (2004 – 2006) 

College of Engineering and Applied Sciences/Ira A. Fulton School of Engineering:

Ira A. Fulton School of Engineering: Dean (2011 – ) 

Ira A. Fulton School of Engineering: Executive Dean (2006 –2010) 

College of Engineering and Applied Science Associate Dean – Research (2003 - 2004) 

College of Engineering and Applied Science Interim Associate Dean – Research (2002 - 2003) 

Dean’s Personnel Advisory Committee – Chair (2000 – 2001, 2001 – 2002) 

Dean’s Personnel Advisory Committee (1999 - 2000) 

College of Engineering and Applied Science Research Committee (1998 – 1999) 

College of Engineering and Applied Science ECE-100 Curriculum Committee (2000 – 2001, 2001 – 

2002) 

107
Department of Civil and Environmental Engineering:

Associate Chair – Graduate Programs (2000 – 2001, 2001 – 2002) 

ASCE Student Chapter Advisor (2001 – 2002) 

CEE Personnel Committee - Chair (1997 – 1998, 1998 - 1999) 

CEE Advisory Committee (1999 – 2000, 2001 – 2002) 

CEE Self-Study Committee (2001 – 2002) 

CEE Faculty Search Committee – Chair (1996 – 1997) 

CEE Faculty Search Committee (1995 – 1996) 

CEE Scholarship Committee (2001 – 2003) 

EVALUATION OF INSTRUCTION – AWARDS

ASU College of Engineering Teaching Excellence Award 2002* 

ASU Parents Association Teacher of the Year Finalist 2000 

ASU College of Engineering Teaching Excellence Award 1998* 

ASCE Student Chapter Best Teacher Award 1996 

* - The College of Engineering and Applied Sciences (CEAS) presents this award only to two faculty each

year.

108
EVALUATION OF INSTRUCTION – SUMMARY OF STUDENT EVALUATIONS

[max. score = 5.0] 

Year and 

Term 

Course # Course 

Title 

No. 

Students 

Instructor 

Evaluation 

Course 

Evaluation 

2011 CEE564 Contaminant

Fate and 

Transport 

22 4.73 4.16

2010 ASU101 Introduction to 

ASU 

18 4.94 4.57

2010 CEE560 Soil and

Groundwater 

Remediation 

23 4.44 4.12

2009 CEE564 Contaminant

Fate and 

Transport 

25 4.85 4.43

2009 CEE560 Soil and

Groundwater 

Remediation 

9 4.92 4.49

2009 ASU101 Introduction to 

ASU 

19 NA NA

2008 CEE564 Contaminant

Fate and 

Transport 

16 4.55 4.39

2007 CEE560 Soil and

Groundwater 

Remediation 

13 4.59 4.39

2007 ASU101 Introduction to 

ASU 

14 NA NA

2007 CEE598 Special Topics: 

Data Systems – 

Environmental 

7 4.85 4.74

2006 CEE591 Seminar 25 NA NA

2006 CEE564 Contaminant

Fate and 

Transport 

24 4.61 4.25

2006 CEE 598 Special Topics: 

Advanced 

Environmental 

Chemistry 

9 4.40 4.41

2005 CEE 598 Special Topics: 

Data Systems – 

Environmental 

10 4.86 4.71

2005 CEE 564 Contaminant

Fate and 

Transport 

29 4.55 4.04

2003 CEE 564 Contaminant

Fate and 

23 4.38 3.98

109
Transport 

2002 CEE 560 Soil and 

Groundwater 

Remediation 

25 4.77 4.40

2002 Spring CEE 598 Contaminant 

Fate and 

Transport 

18 4.79 4.43

2001 Fall CEE 540 Groundwater 

Hydrology 

(new course) 

23 4.73 4.42

110
EVALUATION OF INSTRUCTION – SUMMARY OF STUDENT EVALUATIONS [CONT.] 

[max. score = 5.0] 

Year and 

Term 

Course # Course 

Title 

No. 

Students 

Instructor 

Evaluation 

Course 

Evaluation 

2001 Spring CEE 598 Contaminant 

Fate and 

Transport 

18 4.84 4.45

2000 Fall CEE 540 Groundwater 

Hydrology 

(new course) 

23 4.73 4.42

1999 Fall ECE 100 M Introduction to 

Engineering: 

Modeling 

45 4.47* 3.71

1999 Fall CEE 598 Contaminant 

Fate and 

Transport 

11 4.88 4.49

1998 Fall ECE 100 M Introduction to 

Engineering: 

Modeling 

32 4.68** 3.46

1998 Fall CEE 560 Soil and 

Groundwater 

Remediation 

12 4.79 4.32

1998 Spring CEE 598 Contaminant 

Fate and 

Transport 

21 4.63 4.31

1998 Fall CEE 560 Soil and 

Groundwater 

Remediation 

12 4.79 4.32

1998 Spring CEE 598 Contaminant 

Fate and 

Transport 

21 4.63 4.31

1997 Fall CEE 560 Soil and 

Groundwater 

Remediation 

20 4.65 4.27

1997 Fall ECE 300 Intermediate 

Engineering 

Design 

39 4.50*** 4.30

1996 Fall CEE 361 Introduction to 

Environmental 

Engineering 

26 4.81 4.18

* - highest rating of ECE100 M instructors that semester - and highest rating achieved by any

ECE100 modeling instructors in the three-year period

** - highest rating of ECE100 M instructors that semester

*** - highest rating of ECE300 instructors that semester

For reference, the average ECE100 M instructor rating is approx. 3.9

For reference, the average ECE300 instructor rating is approx. 3.8

111
EVALUATION OF INSTRUCTION – NEW COURSES DEVELOPED

CEE560 – Soil and Ground Water Remediation 

CEE598 – Contaminant Fate and Transport 

ECE100 – Curriculum Development Committee (ECE100 revisions) 

CEE598 – Environmental Data Systems and Analysis 

WORKSHOPS/SHORT COURSES DEVELOPED

USEPA Vapor Intrusion Workshop

P. C. Johnson, T. McAlary, I. Hers, H. Dawson, R. Truesdale, H. Schuver and others

• March and October 2004, March 2005, March 2006

Vapor Intrusion Workshop

P. C. Johnson, R.A. Ettinger, T. McAlary, E. Nichols, and others

• September and October 2003

In Situ Air SpargingDoD Field Camp Course

P. C. Johnson, R.L Johnson, C. Bruce, P. Dahlen, J. Osgood

• May 2002, July 2002 (twice)

MTBE Remediation

[requested by USEPA and CA State Water Quality Control Board] 

• April 1999, May 1999, June 1999, September 1999

Risk Assessment

J. Rocco, L. Hay-Wilson, J. Mercer, J. Till, Johnson, P.C.

Santa Fe, NM.

• April 1998, April 1999.

USEPA/ASTM ES-38 Risk-Based Corrective Action Workshop

ASTM ES-38 Task Group 

• August 1996, March 1996, October 1995, September 1995, May 1995, December 1994

Air Sparging Workshop

International Network for Environmental Training 

P.C. Johnson, R.E. Hinchee

• December 1994

Risk-Based Corrective Action Workshop

P.C. Johnson, C.C. Stanley, G.E. DeVaull, R.A. Ettinger, P.M. McAllister

• AWMA Conference March 1994, AEHS Conference March 1994

Aeration-Based Technologies (Soil Venting, Air Sparging, Bioventing) - Environmental Education 

Enterprises 

P.C. Johnson, R.E. Brown and G.E. Hoag

• October 1995, January 1995, June 1994, March 1994, June 1993, December 1993

Groundwater Contamination from Petroleum Hydrocarbons

112
University of Texas - College of Engineering, Austin, TX. 

Charbeneau, R., P. Bedient, C.Y. Chiang, D.Daniel, P.C. Johnson, R. Loehr, G.E. Speitel Jr., and J. 

Weaver. 

• April 1994, April 1993, October 1992, April 1992, April 1991

USEPA Strategic Technology Evaluation Workshop

P.C. Johnson and D. Mohr

• February 1994

Soil Remediation Workshop - Petroleum Contaminated Soils Conferences 

Johnson, P.C. J.P. Salanitro, L.W.R. Dicks, M.H. Huesemann, G.M. Deeley, A.R. Marsden, Jr., W.G. 

Rixey, and J.B. Gustafson. 

• March 1993, September 1992, March 1992, September 1991, March 1991

USEPA Corrective Action Technology Transfer Workshop on NAPL Recovery and Residual 

Hydrocarbon Removal.

Johnson, P.C., J. Parker, T. Peargin 

• January 1993

An Exposure/Risk-Based Corrective Action for UST Sites - Petroleum Contaminated Soils Conferences 

Johnson P.C. and C.C. Stanley 

• March 1993

HyperVentilate© - A Software Guidance System for Vapor Extraction - Applications. 

P.C. Johnson

• USEPA Region VII - March 1994, USEPA Region VII - February 1994

Other Professional Information 

Past or Current Consultant to:

US Environmental Protection Agency IT Corporation 

US Department of Defense Battelle 

US Department of Energy Envirogen 

 Rice University Siemens 

Parsons-Engineering Science Phillip Environmental 

Baker Environmental BP Oil 

Mobil Oil Corporation GeoMatrix 

 Lockheed Chevron 

Occidental Chemical State Regulatory Agencies 

 Motorola Lawrence Livermore National Laboratory 

Unocal Oxygenated Fuels Association 

Allied Signal/Honeywell Woodward-Clyde Consultants 

Equilon Enterprises California Water Quality Control Board 

 Groundwater Services, Inc. Geosyntec 

Shell Global Solutions Haley and Aldrich 

113
Peer Reviewer Conflict of Interest Certification 

Peer Review: Proposed Rule: Addition of a Subsurface Intrusion Component to the Hazard Ranking System; 40 

CFR Part 300; EPA-HQ-SFUND-2010-1086; FRL_XXXX-X (review draft). 

A conflict of interest or lack of impartiality exists when the proposed peer reviewer personally ( or the peer 

reviewer's immediate family), or his or her employer, has fnancial iinterests that may be affected by the results of the 

peer review; or may provide an unfair competitive advantage to the peer reviewer (or employer); or if the peer 

reviewer's objectivity in performing the peer review may be impaired due to other factors. When the Peer Reviewer 

knows that a reasonable person with knowledge of the facts may question the peer reviewer's impartiality or 

financial involvement, an apparent lack of impartiality or conflict of interest exists. 

The following questions, if answered affirmatively, represent potential or apparent lack of impartiality (any

affirmative answers should be explained on the back of this form or in an attachment): 

• Did you contribute to the development of the document under peer review, or were you consulted during its

development, or did you offer comments or suggestions to any drafts or versions of the document during its

development? 0"No O Yes

• Do you know of any reason that you might be unable to provide impartial advice on the matter under

conJi<leration in this peer review, or any reason that your impartiality in the matter might be questioned?

GtNo O Yes . 

•

/ 

Have you had any previous involvement with the review document(s) under consideration? E'.'l"No D Yes

• Have you served on previous advisory panels, committees, or subcommittees that have addressed the topic

under consideration? � o O Yes

• Have you made any public statements (written or oral) on the issue? i:1"Noo Yes

• H.avc you made any public statements that would indicate to an observer that you have taken a position on

the issue under consideration? �o o Yes

• Do you, your family, or your employer have any financial interest(s) in the matter or topic under peer review,

or could someone with access to relevant facts reasonably conclude that you ( or your family or employer)

stand to benefit from a particular outcome of this peer review? t&o o Yes

With regard to real or apparent conflicts of interest or questions of impartiality, the following provisions shall apply 

for the duration of this peer review: 

(a) Peer Reviewer warrants, to the best of his/her knowledge and beliet: that there are no relevant facts or

circumstances that could give rise to an actual, apparent, or potential organizational or personal conflict of interest,

or that Peer Reviewer has disclosed all such relevant information to EMS or to EPA.

(b) Peer Reviewer agrees that if an actual, apparent, or potential personal or organizational conflict of interest is

identified during perfonnance of this peer review, he/she immediately will make a full disclosure in writing to EMS.

This disclosure shall include a description of actions that Peer Rcvie\ver ( or his/her employer) has taken or proposes

to take after consultation with EMS to avoid, mitigate. or neutralize the actual, apparent, or potential organizational

�-

conflict of interest. Peer Reviewer shall continue performance until notified by EMS of any contrary action to be

'--.-Q_ l-;g,12. c Check here if any explanation is attached 

Signature Date ? U>'--\ 

Printed Name 

(_ So �(1�

&,30t>f4 �Jak lhtcJ��:h 

Affiliation/Organization 

114
Peer Reviews

Kimi Klein & Dot Lofstrom

(Joint Reviewers, California DTSC)

• Charge Questions Comments

• CVs

• COI Certifications

115
Peer Review Charge for:

U.S. Environmental Protection Agency (EPA). Proposed Rule: Addition of a Subsurface Intrusion 

Component to the Hazard Ranking System; 40 CFR Part 300; EPA-HQ-SFUND-2010-1086; FRL_XXXX-X

(review draft). 

Background

The U.S. Environmental Protection Agency (EPA) is proposing to include a subsurface intrusion (SsI) 

component to the Hazard Ranking System (HRS). Subsurface intrusion is the migration of hazardous 

substances from the unsaturated zone and/or the surficial ground water into overlying structures. The HRS is 

the principal mechanism the EPA uses to evaluate sites for placement on the National Priorities List (NPL). 

The subsurface intrusion component addition (this addition) would primarily 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 and the environment from releases of hazardous substances. 

This addition will allow the HRS evaluation to directly consider human exposure to hazardous substances 

that enter building structures through subsurface intrusion, and thus enable sites with subsurface intrusion 

contamination to be evaluated for placement on the NPL. This addition will make the HRS more accurate in 

assessing a site’s relative potential risk. The Agency is not considering changes to the remainder of the HRS 

except for minor updates reflecting changes in terminology related to revised toxicological parameters. This 

proposed regulatory change does not affect the status of sites currently on or proposed to the NPL. 

Expertise Required

The peer review panel for U.S. EPA’s Proposed Rule: Addition of a Subsurface Intrusion Component to the 

Hazard Ranking System should include expertise in: 

Panelist from non-specified sector: Panelist must have a strong working knowledge of policy and technical 

issues related to the topic of vapor intrusion. Knowledge of recent developments in vapor intrusion 

technologies and research is required, in addition to working knowledge of federal vapor intrusion response 

programs. Expertise in hydrogeology, chemistry, knowledge of public health risks associated with indoor air 

threats, and the subsurface migration of volatile hazardous substances is necessary. Field experience 

conducting vapor intrusion investigations, while not required, is highly desirable. Experience conducting 

field investigations for the purpose of listing sites on the NPL and/or experience working with the HRS to 

evaluate sites for inclusion on the NPL is highly recommended, but not necessary. 

Peer Review Charge Questions

1. Potential for subsurface exposure (intrusion) into occupied structures

Background: The current HRS evaluates the likelihood of a release of a hazardous substance when an actual 

release has occurred through either chemical analysis or direct observation. The current HRS also evaluates 

the potential for a release to occur within the ground water, surface water and air pathways (see section 2.3 

of the current HRS). The potential for a release is determined by the consideration of pathway specific 

factors that aid the site evaluator in predicting whether a release to the pathway is likely to occur. These 

factors are based on containment features of the source of contamination (whether or not hazardous 

substance can get out), route characteristics specific to each pathway (how far hazardous substances could 

migrate based on knowledge of site conditions) and include physical/chemical properties of the hazardous 

substances being evaluated (how the hazardous substances act in the environment). 

116
Proposed Approach: EPA is proposing a parallel approach for evaluating potential and actual exposure of 

intruded hazardous substances for the subsurface intrusion addition to the HRS. In determining which route 

characteristics are appropriate for evaluating potential exposure to subsurface contaminants, EPA examined 

present modeling methods such as the Johnson-Ettinger model and also considered multiple lines of evidence 

approaches which estimate the levels of contaminant exposure based on numerous route characteristics. In 

addition, EPA examined the relationship between these factors to determine which have the greatest 

influence on the likelihood that an exposure would occur, and then incorporated these factors within its 

proposed approach. EPA also gave careful consideration to ensure that the data necessary to obtain route 

characteristic factors could be measured or calculated on a site-specific basis and in a manner consistent with 

current HRS evaluations. Based on the Agency’s analysis, the following three factors for which sufficient 

site-specific information could be collected during a site inspection represented the greatest impact on the 

potential for exposure: (1) depth to contamination; (2) vertical migration; and (3) vapor migration potential 

(see Figure 1). 

Figure 1 

Charge Question #1 : Is EPA’s proposed approach scientifically reasonable for evaluating and assigning 

proportional weightings for the following when evaluating potential for exposure? If no, what alternative 

approach would you recommend? 

117
a. Consideration of the construction/structure type for which sufficient site-specific information

could be collected during a site inspection for the occupied structure;

b. Distance between occupied structure and depth of contamination; and

c. Evaluation of the vertical migration factor based on the thickness and porosity/permeability of

geologic materials in the interval between the lowest point of an occupied structure and the highest

known point of hazardous substances in the subsurface.

1) There is no provision for significant volatile organic chemical (VOC) concentrations detected in

soil and/or surficial groundwater but without structures. Alternative: Provide default structure

properties.

2) The vertical migration factor ranking considers certain geologic factors and identifies karst, lava

tubes, open fractures (5.2.1.1.2.2) as features that would allow channelized flow. Manmade

preferential pathways such as utility corridors and sewer lines should be included in the HRS

assessment, if identified in the site inspection. Alternative: Expand the definition of channelized

flow to include most commonly encountered features and/or include that expanded list in the

regulatory language (Perhaps as part of Table 5-15 Vertical Migration Factor Values). 

118
2. Hazardous Waste Quantity

Background: In the current HRS, the hazardous waste quantity factor reflects the risk consideration related 

to the magnitude and duration of either the release for ground water, surface water, and air pathways, or the 

exposure for the soil exposure pathway (see section 2.4.2 of the current HRS). Hazardous waste quantity is 

evaluated for all four pathways. At each site evaluated, EPA uses a four-tiered hierarchy for calculating the 

hazardous waste quantity that is based on (1) constituent quantity; (2) waste stream; (3) volume; and (4) area 

of the sources of hazardous waste at the site. EPA uses minimum waste quantity factors when there is 

insufficient information to estimate hazardous waste quantity. In the ground water, surface water, and air 

pathways, the HRS evaluates the total quantity of hazardous substances available to migrate from the original 

sources (how much has migrated and how much can be released in the future). In the soil exposure pathway, 

the hazardous waste quantity does not include the total amount of hazardous substances in all site sources, 

but rather is based on the amount of hazardous substances to which a receptor can be exposed where actual 

contamination has been documented. In other words, for the soil exposure pathway, the risk posed by a 

release of hazardous substances is directly related to the amount of hazardous substances that receptors are 

exposed to, as opposed to how much of the hazardous substances from the original sources may migrate to 

the receptors. 

Proposed Approach: EPA is proposing a parallel approach to the soil exposure pathway to calculate 

hazardous waste quantity for the subsurface intrusion addition to the HRS. Since the subsurface intrusion 

component also focuses on exposure, the waste quantity factor value for this component should also reflect 

only the amount of hazardous substances that people actually are exposed to (the amount present in occupied 

structures). EPA is proposing to use a similar four-tiered hierarchical approach to calculate hazardous waste 

quantity within occupied structures with contamination. In cases where no home is subject to actual 

contamination, EPA is proposing to use minimum waste quantity factors. In situations where there is an 

observed release within a structure above benchmarks (Level I), a default value of 100 is proposed for the 

hazardous waste quantity factor value. This value is not used in the current soil exposure pathway, but is 

consistent with the ground water, surface water, and air pathways and reflects the increased exposure risk of 

a release within an occupied structure. 

Charge Question #2: Is EPA’s approach of basing the hazardous waste quantity on the amount of 

contaminants that could be found in the intruded structures appropriate? If no, what alternative approach 

would you recommend? 

Response from K. Klein 

1) The hazardous waste quantity ranking is based on the assumption that a structure or structures currently

exist on the site being evaluated. If this is the case at the site being evaluated, the approach seems

appropriate. But it is difficult to imagine that the sampling necessary to carry this approach out can be

accomplished within a 1 -2 day site inspection. Soil gas/groundwater sampling should be done prior to

indoor air sampling in order to identify those substances to be analyzed for in indoor air (substances

associated with subsurface contamination).

119
2) However, the approach does not allow for the determination of the hazardous waste quantity in the

absence of structures but where significant hazardous substance (VOC) contamination exists in

soil/groundwater where structures could or will be constructed. Alternative: Provide a simple approach for

estimating indoor air concentrations from measured environmental media concentrations (soil gas,

groundwater) using default attenuation factors and parameters for a default structure. Provide default

volume values (a default area value is provided (Table 5-19)). I could not find in the proposed regulations

explicit direction on “where no home is subject to actual contamination”.

120
3. Population score

Background: Within the current HRS, receptors are evaluated in two main categories: whether they are 

exposed to 1) actual contamination; or 2) potential contamination (see section 2.5 of the current HRS). If 

receptors are exposed to contaminant levels meeting observed release criteria, they are identified as actually 

contaminated; however, if the receptors are not exposed to contaminants that meet the observed release 

criteria but are within the target area being evaluated, they are considered potentially contaminated. Actual 

contamination is further divided into two sub-categories based on whether the hazardous substance is present 

at or above a health-based benchmark. If the concentration of the hazardous substance released at the 

receptor is greater than a health-based benchmark, the receptors are identified as Level I receptors and are 

weighted (multiplied by a factor of 10) in scoring. If the release concentrations are less than a health-based 

benchmark, the receptors are identified as Level II receptors and are not weighted (multiplied by a factor of 

1). Potential receptors are distance/dilution weighted; in other words, the farther away a receptor is located 

from a source, the less the population contributes to the site score. 

Proposed Approach: EPA is proposing to generally use the same receptor weighting structure in the 

subsurface intrusion component as the one used in the current HRS. Those receptors in the area(s) of 

observed exposure (AOE) are considered actually contaminated, and those in the area(s) of subsurface 

contamination (ASC) are considered potentially contaminated (See Figure 2). The receptors in an AOE are 

further differentiated based on whether the contaminant concentrations are at levels above identified 

benchmarks (Level I) or are at levels establishing a release but below identified benchmarks (Level II). The 

benchmarks that EPA is proposing to use for the subsurface intrusion component are: 

• Screening concentration for cancer effects; and

• Screening concentration for non-cancer effects (systemic toxicants).

Consistent with the weighting of populations throughout the HRS, the proposed subsurface intrusion 

component will weight targets within the AOE subject to Level I contaminant concentrations by a factor of 

10 and weight targets subject to Level II contaminant concentrations by a factor of 1. 

EPA is proposing to evaluate the weighting of targets within the ASC based on sub-slab, soil gas, and/or 

ground water samples. Potential receptors within the ASC receive less weight (population multiplied by a 

factor of 0.1), except in cases where a sub-slab sample indicates contaminant levels are at least 10 times 

higher than a health-based benchmark (population is multiplied by a factor 0.75). The value of 0.75 was 

determined based on an evaluation of paired data when both a sub-slab and indoor air sample were collected. 

The 0.75 weighting reflects the observation that for approximately 80 percent of the sampling events where 

contamination was detected in the sub-slab, contamination was also detected in the indoor air sample. The 

order of magnitude adjustment applied to the health-based benchmark reflects EPA’s finding that, in such 

paired sampling events, the indoor air sample concentration is, on average, 10 times lower than the sub-slab 

sample concentration. 

121
Figure 2 

Charge Question #3: Is it appropriate to consider individuals/populations located within the area of 

subsurface contamination (ASC) to be at a higher relative risk in situations when sub-slab contaminant 

concentrations are at least ten times greater than a health-based benchmark? If no, please explain. 

Response from K. Klein 

This approach is consistent with the California Department of Toxic Substances Control (DTSC) vapor 

intrusion guidance. 

122
4. Multi-story and multi-tenant structures

Background: In the current HRS, multi-story and multi-tenant buildings are evaluated based on population 

associated with an actually or potentially impacted target. In the ground water pathway, all residents who are 

served by a well are considered subject to the actual or potential contamination of the well. In the air 

pathway, all residents who have an opportunity to breathe ambient air are considered subject to the actual or 

potential contamination of the ambient environment within a distance category. All receptors within a 

contaminated surface water stretch are subject to the level of contamination associated with that surface 

water stretch. In the soil exposure pathway, receptors must be able to come in contact with areas of 

contamination. In determining the likelihood a person will come in contact with areas of contamination, the 

HRS uses a 200 foot rule (see section 5.1.3 of the current HRS) because it is reasonable to assume that that a 

person will walk/use areas within a 200 foot areal extent of their residence/property. The 200 foot rule is 

used regardless of whether a building is multi-tenant or multi-story (the assumption being that is reasonable 

for people to use the outside of their properties). 

Proposed Approach: EPA is proposing to evaluate multi-story/multi-tenant buildings utilizing a similar 

approach as soil exposure, limiting the receptors to those individuals that reasonably can be exposed to 

subsurface intrusion within an occupied multi-tenant/multi-story building. EPA is proposing to consider all 

receptors exposed to actual contamination as the population inhabiting the floor of the intruded space and the 

population inhabiting the floor above and the floor below the intruded space when calculating waste quantity 

and population. EPA considers that this approach will more accurately reflect risk to both actual and 

potential receptors, while also minimizing the potential for over counting (Figure 3). 

123
Figure 3 

Charge Question #4: When calculating waste quantity and population, is it scientifically reasonable for 

populations in multi-story or multi-tenant structures to be evaluated based on using only the population 

inhabiting the intruded space and the population on the floor above and below the intruded space (For 

example, if contamination is found on the first floor, population from the basement and second floor would 

be used in the calculation. If contamination is found on the fifth floor, population from the fourth floor and 

sixth floor would be used in the calculation – for further explanation, see detailed discussion in above 

paragraph “Proposed Approach”)? If no, what alternative approach would you recommend? 

Response from K. Klein 

This is a reasonably conservative approach. However, there is much uncertainty surrounding the stated 

assumptions. Therefore, there should be an in-depth discussion of this approach in the proposal Technical 

Support Document with references to support it. 

124
5. Factor Value for Workers

Background: In the current HRS, 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 of observed 

contamination. These factor values range from 0 to15, depending on the number of workers exposed to 

outdoor contamination (see section 5.1.3.3 of the current HRS). 

Proposed Approach: EPA is proposing to mirror the procedures for the resident population threat in the soil 

exposure component when 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 and 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., factor values ranging from 0 to 45).

Charge Question #5: Because of longer exposure times indoors, is it reasonable to assume that the relative 

risk is three times greater for workers exposed to subsurface intrusion within the workplace than it is for 

workers exposed to outdoor surface contamination at the workplace? If no, please explain. 

Response from K. Klein 

Assuming a relative risk of three times greater for indoor workers vs. outdoor workers for volatile organic 

chemicals (VOCs) may be an underestimate, since indoor workers would be exposed to contaminated air in a 

limited volume over much of their work day; whereas, contamination in outdoor air is not constrained in a 

limited space but is immediately diluted by atmospheric air. Other direct exposure pathways (incidental soil 

ingestion; dermal contact) contribute very little to uptake/intake because of the volatile nature of the 

chemicals under discussion in the subsurface intrusion component. The proposal Technical Support 

Document should discuss and provide support for any factor chosen to reflect the greater relative risk for 

indoor workers. 

125
CURRICULUM VITAE 

August 2010 

Kimiko A. Klein

9 Noah Court 

Sacramento, CA 95831 

(916) 422-8355

403 Main Street, Unit 312 

San Francisco, CA 94105 

(415) 546-6405

EDUCATION 

1986 Ph.D., Comparative Pathology, University of California, Davis 

1962 Medical Technology Internship, U.S. Public Health Service Hospital, Staten 

Island, New York 

1961 B.S. with honors, Public Health Laboratory Technology, University of 

California, Berkeley 

HONORS 

2006 Superior Accomplishment Silver Team Award, Department of Toxic Substances 

Control 

1998 Sustained Superior Accomplishment, Department of Toxic Substances Control 

1982 Special Performance Award, University of California, Davis 

1980 Citation for Excellence in Supervision, University of California, Davis 

1979 Outstanding Service to the Laboratory, Radiobiology Laboratory, University of 

California, Davis 

POSITIONS HELD 

3/10 – Present Staff Toxicologist Emerita, California Department of Toxic Substances 

Control, Berkeley 

6/90 – 11/09 Staff Toxicologist, California Department of Toxic Substances Control, 

Sacramento 

10/87 - 6/90 Staff Toxicologist; Environmental Hazards Scientist, California 

Department of Food and Agriculture, Sacramento 

126
1974 - 1987 Staff Research Associate IV, Laboratory for Energy-Related Health 

Research, University of California, Davis 

1965 - 1970 Laboratory Technician III, Radiobiology Laboratory, University of 

California, Davis 

1962 - 1965 Laboratory Technician II, University of California, San Francisco 

ACTIVITIES 

1992 Membership Officer, Genetic and Environmental Toxicology Association of 

Northern California. 

2000 Secretary, Genetic and Environmental Toxicology Association of Northern 

California 

1979-1982 Member, FDA Advisory Committee, Hematology Section of the Clinical 

Chemistry and Hematology Devices Panel, Washington, DC. Consumer 

representative to the panel. 

1976-1977 Member, Task Force on Long-Term Care, Golden Empire Health Systems 

Agency, Sacramento 

DISSERTATION 

Canine Lymphohematopoiesis - June 1986 

PUBLISHED PAPERS 

– 17 published papers from 1967 through 1995 on hematopoiesis and toxicology

The following are papers in toxicology: 

1987 Klein, A. K., M. L. Nasr and M. Goldman. The effects of in vitro exposure to 

the neurotoxins Sarin (GB) and Soman (GD) on unscheduled DNA synthesis 

by rat hepatocytes. Toxicology Letters 38:239-249. 

1988 Nasr, M. L., M. Goldman, A. K. Klein, and J. C. Dacre. SCE induction in 

Chinese Hamster Ovary cells (CHO) exposed to G agents. Mutation 

Research 204:649-654. 

1995 Klein, A. K., J. P. Christopher. Evaluation of crystalline silica as a threshold 

carcinogen. Scandinavian Journal of Work, Environment & Health 21 

suppl2:95-98. 

– 3 chapters on toxicology and risk assessment in books from 1993 through 2002

127
The following are the chapter citations: 

1993 Wade, M. J., B. K. Davis, J. S. Carlisle, A. K. Klein, L. M. Valoppi. 

Environmental Transformation of Toxic Metals. In: De Novo Toxicants: 

Combustion Toxicology, Mixing Incompatibilities, and Environmental 

Activation of Toxic Agents. State of the Art Reviews, Occupational Medicine. 

Eds. D. J. Shusterman, J. E. Peterson. Volume 8/Number 3. Hanley & 

Belfus, Inc. Philadelphia. 

1995 Davis, B. K., A. K. Klein. Medium-specific and multimedium risk assessment. 

In: Toxicology and Risk Assessment, Principles, Methods, and Applications. 

Eds. A. M. Fan, L. W. Chang. Marcel Dekker, Inc., New York. 

2002 Klein, Kimiko, Marilyn Underwood. Remediation. In: Encyclopedia of 

Agrochemicals. Eds. Jack R. Plimmer, D. W. Gammon, N. N. Ragsdale. 

John Wiley & Sons, Inc. 2003. 

PUBLICATIONS OF THE CALIFORNIA DEPARTMENT OF FOOD AND AGRICULTURE 

1988 Oudiz, D. and A. K. Klein. Evaluation of Ethyl Parathion as a Toxic Air 

Contaminant. 179 pp. CDFA EH-88-5. NTIS PB90-134909. 

PUBLICATIONS OF THE CALIFORNIA DEPARTMENT OF TOXIC SUBSTANCES 

CONTROL (DTSC) 

2009 Klein, K. and D. L. Berry. Remedial Goals for Dioxins and Dioxin-like 

Compounds for Consideration at California Hazardous Waste Sites. Human 

Health Risk Assessment (HHRA) Note 2. DTSC. May 2009. 

 COURSES TAUGHT 

1. 1990 - 1993. Risk and Decision Making Workshop. Three-day course sponsored

by the US EPA Region IX and the Department of Toxic Substances Control for

governmental regulatory agency personnel. Team instructor. .

2. 1993 - 1994. Critical Issues in Risk Assessment: Risk Assessment Guidance for

Superfund and DTSC Supplemental Guidance. One-day course for staff of the

Department of Toxic Substances Control. Team instructor with Dr. Brian Davis.

3. 1994. Risk and Decision Making at Petroleum Impacted Sites. Three-day course

sponsored by the San Francisco Bay Regional Water Quality Control Board for

governmental regulatory agency personnel. Team instructor with Dr. Brian Davis

for the sections on risk assessment.

128
4. 1996 -1997, 2001. Environmental Toxicology 146. Spring quarter course given at

the University of California at Davis for upper division students. Team instructor for

sections on topics related to regulatory risk assessment.

5. 1996, 1997. Risk Assessment Modeling: The CalTOX Model. Three-day extension

course sponsored by the University of California at Davis for interested parties.

Team instructor.

6. 1996. Risk-based Cleanup: What’s Acceptable? One-day extension course

sponsored by the University of California at Davis for interested parties. Team

instructor responsible for the topic of calculating human health-based safe soil

levels.

7. 1997. Health Risk Assessment at Hazardous Waste Sites. Two-day short course

on human and ecological risk assessment principles at Chulalongkorn University,

Bangkok, Thailand.

8. 1997, 1998. Integrated Multimedia Exposure Modeling with Sensitivity and

Uncertainty Analysis. One-day course sponsored by the International Society of

Exposure Analysis. Team instructor with Dr. Ned Butler.

9. 1998. Modeling Environmental Risk – Demonstration of California Toxic Risk

Models. One-day course sponsored by the Harvard School of Public Health. Team

instructor with Dr. Ned Butler.

10. 2000. Advanced Health Risk Assessment. Three-day short course at Chiang Mai

University, Chiang Mai Thailand. Given also for Pollution Control Department staff,

Ministry of Science Technology and Environment, at Chulalongkorn University,

Bangkok, Thailand. Team instructor with Dr. Brian Davis.

11. 2009. Vapor Intrusion Guidance. Two-day short course on evaluating vapor

intrusion into indoor air spaces from sub-surface sources. Team instructor

responsible for the topic of proper application of California Human Health Screening

Levels (CHHSLs) in estimating the risk from this exposure pathway.

PRESENTATIONS 

Davis, B.K., Klein, A.K., Wade, M.J., Valoppi, L.M., and Carlisle, J.S., 1994. 

Environmental transformation of metals and risk assessment. The Toxicologist 14:39. 

Davis, B.K., Christopher, J., Wade, M.J., and Klein, A.K., 1995. Risk assessment for 

multiple source exposures. The Toxicologist 15:36. 

Christopher, J.P., Butler, E.G., Klein, A.K., Davis, B.K., and Wade, M.J., 1996. CalTOX 

Stochastic Risk Assessment Compared to Standard CERCLA Methods. The 

Toxicologist, (Fundamental and Applied Toxicology) 30:113. 

129
Butler, E.G., Klein, A.K., Davis, B.K., Christopher, J.P., Wade, M.J., Wong, J.J., and 

McKone, T.P., 1996. Use of CalTOX to Guide Site Characterization and Risk 

Management Decisions for Contaminated Soil. Fundamental and Applied Toxicology, 

(The Toxicologist) 30:113-4. 

Davis B.K., Klein, A.K., and Wade, M.J., 1998. Approaches to Screening Level Risk 

Assessment at California Hazardous Waste Sites. Toxicological Sciences 42:231. 

Christopher, J.P., Carlisle, J.C., Davis, B.K., Klein, A.K., Renzi, B.E., and Wade, M.J., 

2000. Comparison of Updated Leadspread to Integrated Uptake, Exposure and 

Biokinetic Model (IEUBK) for predicting blood lead in children. The Toxicologist, 

Supplement to Toxicological Sciences 54:72. 

Carlisle, J.C., Christopher, J.P., Davis, B.K., Klein, A.K., Renzi, B.E., and Wade, M.J., 

2000. Updated version of Cal/EPA’s Leadspread model for predicting blood lead in 

children and adults. The Toxicologist, Supplement to Toxicological Sciences 54:72. 

Renzi, B., Wade, M.J., Davis, B.K., Klein, A.K., and Christopher, J.P., 2001. LeadBased Paint in Soil: When Worlds Collide – CERCLA Meets HUD. The Toxicologist, 

Supplement to Toxicological Sciences 60:422. 

Davis, B.K., J.F. Beach, M.J. Wade, A.K. Klein, and K. Hoch, 2002. Risk Assessment 

of Polychlorinated Biphenyls (PCBs) in Indoor Air. The Toxicologist, Supplement to 

Toxicological Sciences 66:106. Abstract number 516. 

DiBiasio, K., K. Klein, 2003. Human Health Risk Evaluation of Structural Surfaces 

Contaminated with Metals, presented at the Society of Toxicology Annual Meeting. 

DTSC WORK GROUPS/TEAMS – I was a member of the following work groups/teams 

involved in developing guidance or resolving issues associated with risk assessment: 

2005 HERD Work Group on Environmentally Acceptable Endpoints for Lampblack 

and Lampblack-Impacted Soils – Polycyclic Aromatic Hydrocarbons available for 

dermal and ingestion absorption 

2006 Cal/EPA Work Group on Use of California Human Health Screening Levels 

(CHHSLs) in Evaluation of Contaminated Properties 

2005; 2010 DTSC Work Group on Guidance for the Evaluation and Mitigation of 

Subsurface Vapor Intrusion to Indoor Air 

2005 HERD Work Group on Default Exposure Parameters for Non-Residential 

Receptors at Abandoned Mining Sites 

130
2006 DTSC Voluntary Cleanup Program Team charged to review voluntary 

cleanup operations and recommend changes to make the process go more 

quickly, more effectively and better. 

2010 Co-author revising the DTSC Preliminary Endangerment Assessment 

Guidance Manual 

RESEARCH INTERESTS AND SKILL SET 

Toxicologists in the Human and Ecological Risk Office of the Department of Toxic 

Substances Control perform and review human and ecological health risk assessments. 

Our primary focus is assessment of exposure by humans and non-human receptors to 

chemicals that have been released to the environment and have the potential to cause 

adverse health effects. My principal scientific interest is alternative approaches to 

exposure assessment that address site-specific characteristics of locations affected by 

past manufacturing activities. Technical writing and risk communication are particular 

skills I possess. These skills are important in the clear transmittal of critiques and reviews 

of documents submitted to the Department and in the teaching of risk assessment to 

students and individuals in the community. 

The following is a summary of my experience in and knowledge of environmental 

fate and transport. 

1. 1987-88. As an environmental hazards scientist in the environmental monitoring

program of the California Department of Food and Agriculture, I was responsible for

reviewing the protocol, performance, and results of field experiments designed to

measure residual pesticide concentrations in environmental media after legal

application. I was a co-author of a report on the evaluation of ethyl parathion as a toxic

air contaminant with responsibility for the sections on the environmental fate of this

pesticide.

2. 1993-98. As a member of the team overseeing the development and use of a

spreadsheet model, called CalTOX, that relates the concentration of an organic

chemical in soil to the risk of an adverse health effect for a person living or working on

or near the contaminated soil. I was responsible for writing the technical reports

describing the model for the California Department of Toxic Substances Control

(DTSC). CalTOX was developed by the University of California and has been

extensively peer-reviewed. The spreadsheet model consists of two parts. The first part

uses equations based on conservation of mass and chemical equilibrium to predict the

time-dependent concentrations of a chemical in the eight environmental compartments

of air, surface water, groundwater, three soil layers, sediment, and plants at a site. The

second part relates those calculated chemical concentrations in environmental media

over time to concentrations in personal air, tap water, food, household dusts, etc.,

thereby combining environmental fate and transport of the chemical to potential

exposure to the chemical by human receptors.

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3. 1996-98. I was part of a DTSC team teaching courses that emphasized multi-media

exposure modeling as a screening tool in human health risk assessment.

Environmental fate processes were discussed in depth in these courses.

4. 2005- present. I was part of a DTSC team writing guidance on evaluating the intrusion

of subsurface vapors intruding into indoor air. This evaluation is based on a

spreadsheet model that considers diffusion and advective forces in the transport of

volatile chemicals in sub-surface soil and/or groundwater to indoor air spaces. This

model is called the Johnson and Ettinger Model and has been extensively peerreviewed and modified by the DTSC for use in human health risk assessment.

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Dot Lofstrom

Section Chief, Geological Services Unit

California Environmental Protection Agency – Department of Toxic Substances Control (DTSC)

8800 Cal Center Drive

Sacramento, California   95826

• Lead Author of Vapor Intrusion Mitigation Advisory (DTSC 2011)

• Co‐Author of Advisory‐ Active Soil Gas Investigations (Cal/EPA –expected publication date

February 2012)

• Technical Editor for the Guidance for the Evaluation and Mitigation of Subsurface Vapor

Intrusion to Indoor Air (Vapor Intrusion Guidance) (DTSC 2011).

M.S. – Geology, University of Missouri, 1988

B.S. – Geology, Missouri State University, 1981

Professional Geologist #7022

Summary of Work Experience: 24 years with primary emphasis on soil and groundwater investigations

under RCRA and CERCLA.   Background includes State government, consulting, federal government

(Department of the interior) and academics (Arizona Western College).

Summary of Vapor Intrusion Experience: Actively  working on vapor intrusion guidances at DTSC since

2008; presented papers on DTSC guidance at Air and Waste Management Association (San Diego 2009),

National Brownfield Association (Sacramento 2009), and the Batelle conference in Monterey (2010).   

2009 to present

DTSC, Sacramento CA‐ Supervisor for Cal Center Geological Services Unit.  As a supervisor, provide

technical and professional leadership to nine registered geologists working on investigation and

remediation of soil, soil gas, and groundwater within the State of California, under the RCRA and CERCLA

processes.  Serve as Vapor Intrusion/Soil Gas Collection Specialist within DTSC.   

2005 to 2009

DTSC, Sacramento CA ‐Senior Engineering Geologist.Remedial Project Manager for the NPL site Naval Air

Station‐Alameda, California.Worked closely with EPA RPM Anna‐Marie Cook, San Francisco Region 9,

following the CERCLA process from remedial investigation through the Record of Decision and Remedial

Design.Reviewed and commented on technical documents and represented DTSC in public meetings.

2001 to 2005

DTSC, Sacramento CA‐ Engineering Geologist.  Provided geologic support the RCRA sites, primarily

focused on post‐closure permits or corrective action for treatment, storage and disposal facilities.

2000 – 2001

San Joaquin County, Stockton CA – Registered Geologist.Provided technical guidance and leadership for

six registered environmental health specialists, ensuring proper investigation and remediation of leaking

underground storage tanks.

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Dot Lofstrom (page 2)

1998 – 2000

Tetra Tech, EMI, Sacramento CA – Senior Environmental Geologist.Remedial Project Manager for Naval

Computer and Telecommunication Station‐ Stockton.  Lead investigator for ten landfill sites, collecting

relevant soil and groundwater data, and managing writing/production of remedial investigation reports

for U.S. Navy.

1993 ‐ 1998

Arizona Western College, Yuma AZ – Professor of Environmental Technology.  Lead faculty instructor

and creator of Department of Environmental Technology, a program designed to give students a

practical background to prepare them for work as environmental technicians.  Taught courses in

Environmental Regulations, Sampling and Analysis, Hazardous Waste Management, and Physical

Geology.

1991‐1993

Department of Defense (USBR and BLM), Yuma AZ

• USBR ‐ Hydrogeologist.  Responsible for installation and development of large‐diamater

irrigation and drinking water wells.

• BLM –District Geologist.  Responsible for administering the Minerals program in the Yuma

District, reviewing mining and reclamation plans.

1988 – 1993

IT Corporation, Irvine CA – Assistant Project Scientist.  Responsible for investigation of leaking

underground storage tanks and pesticide contaminated sites.  Conducted site investigations, analyzed

soil and groundwater data, and wrote subsequent reports.

134
135
136
137
138
Peer Reviews

Henning Larsen

(Oregon DEQ)

• Charge Questions Comments

• CV

• COI Certification

139
Peer Review Charge for:

U.S. Environmental Protection Agency (EPA). Proposed Rule: Addition of a Subsurface Intrusion 

Component to the Hazard Ranking System; 40 CFR Part 300; EPA-HQ-SFUND-2010-1086; FRL_XXXX-X

(review draft). 

Background

The U.S. Environmental Protection Agency (EPA) is proposing to include a subsurface intrusion (SsI) 

component to the Hazard Ranking System (HRS). Subsurface intrusion is the migration of hazardous 

substances from the unsaturated zone and/or the surficial ground water into overlying structures. The HRS is 

the principal mechanism the EPA uses to evaluate sites for placement on the National Priorities List (NPL). 

The subsurface intrusion component addition (this addition) would primarily 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 and the environment from releases of hazardous substances. 

This addition will allow the HRS evaluation to directly consider human exposure to hazardous substances 

that enter building structures through subsurface intrusion, and thus enable sites with subsurface intrusion 

contamination to be evaluated for placement on the NPL. This addition will make the HRS more accurate in 

assessing a site’s relative potential risk. The Agency is not considering changes to the remainder of the HRS 

except for minor updates reflecting changes in terminology related to revised toxicological parameters. This 

proposed regulatory change does not affect the status of sites currently on or proposed to the NPL. 

Expertise Required

The peer review panel for U.S. EPA’s Proposed Rule: Addition of a Subsurface Intrusion Component to the 

Hazard Ranking System should include expertise in: 

State Environmental Program Panelist: Panelist must have strong technical experience and working 

knowledge of policy and technical issues (e.g., mitigation and remediation) related to the topic of vapor 

intrusion. Expertise in hydrogeology, chemistry, knowledge of public health risks associated with indoor air 

threats, and the subsurface migration of volatile hazardous substances is necessary. Knowledge of recent 

developments in vapor intrusion technologies and research is required, in addition to working knowledge of 

state vapor intrusion response programs. Field experience conducting vapor intrusion investigations, while 

not required, is highly desirable. Experience related to conducting field investigations for the purpose of 

listing sites on the NPL and/or experience working with the HRS to evaluate sites for inclusion on the NPL is 

highly recommended, but not necessary. 

Peer Review Charge Questions

1. Potential for subsurface exposure (intrusion) into occupied structures

Background: The current HRS evaluates the likelihood of a release of a hazardous substance when an actual 

release has occurred through either chemical analysis or direct observation. The current HRS also evaluates 

the potential for a release to occur within the ground water, surface water and air pathways (see section 2.3 

of the current HRS). The potential for a release is determined by the consideration of pathway specific 

factors that aid the site evaluator in predicting whether a release to the pathway is likely to occur. These 

factors are based on containment features of the source of contamination (whether or not hazardous 

substance can get out), route characteristics specific to each pathway (how far hazardous substances could 

migrate based on knowledge of site conditions) and include physical/chemical properties of the hazardous 

substances being evaluated (how the hazardous substances act in the environment). 

140
Proposed Approach: EPA is proposing a parallel approach for evaluating potential and actual exposure of 

intruded hazardous substances for the subsurface intrusion addition to the HRS. In determining which route 

characteristics are appropriate for evaluating potential exposure to subsurface contaminants, EPA examined 

present modeling methods such as the Johnson-Ettinger model and also considered multiple lines of evidence 

approaches which estimate the levels of contaminant exposure based on numerous route characteristics. In 

addition, EPA examined the relationship between these factors to determine which have the greatest 

influence on the likelihood that an exposure would occur, and then incorporated these factors within its 

proposed approach. EPA also gave careful consideration to ensure that the data necessary to obtain route 

characteristic factors could be measured or calculated on a site-specific basis and in a manner consistent with 

current HRS evaluations. Based on the Agency’s analysis, the following three factors for which sufficient 

site-specific information could be collected during a site inspection represented the greatest impact on the 

potential for exposure: (1) depth to contamination; (2) vertical migration; and (3) vapor migration potential 

(see Figure 1). 

Figure 1 

141
Charge Question #1: Is EPA’s proposed approach scientifically reasonable for evaluating and assigning 

proportional weightings for the following when evaluating potential for exposure? If no, what alternative 

approach would you recommend?

a. Consideration of the construction/structure type for which sufficient site-specific information

could be collected during a site inspection for the occupied structure;

Potential for Exposure Equation

I agree generally with the mathematical set up of the equation (2a*(2b+2c+2d) and the decision to make the 

potential for exposure a product (in the mathematical sense) of a building’s characteristics and the subsurface 

conditions that lay beneath it. It mimics the two compartment model that many professionals and researchers 

conceptualize the vapor intrusion pathway to be. Furthermore, I believe it accurately replicates the 

“breaking” of the pathway by assigning a value of 0 to structures that employ demonstrated effective vapor 

control measures. 

Overall, the term for the structure (a) ranges from 0-10 while the subsurface term (the sum of b+c+d) ranges 

from 1-50. Ideally the subsurface term should range as low as zero to reflect the absence of vapor intrusion 

risks associated with high molecular weight semi-volatile compounds like cPAHs, PCBs, and most 

pesticides. Thus, either term could have a zero value and the exposure pathway would then be considered 

broken or incomplete under two conditions: 1) in cases where a demonstrated effective vapor control 

technology is used, and 2) when a contaminant has sufficiently low volatility. 

Mathematically, this could be accomplished by multiplying the Depth to Contamination (b) and Vertical 

Migration (c) terms by the Vapor Migration Potential (d) term. Thus a zero Vapor Migration Potential

value would yield a zero for the entire Potential for Exposure factor. If the equation is changed in this way, 

the range in values for the Depth to Contamination and Vertical Migration terms would likely have to be 

adjusted so that Potential for Exposure results fall into the intended range of values (0-500). 

Table 5-12 Structure Containment

I suggest revisions to Table 5-12 with respect to the number of building types distinguished, their 

description, and their value assignments. 

• There does not appear to be a category that describes maybe the commonly encountered type of

residence: a slab-on-grade constructed home with no apparent open preferential pathways or vapor

migration barrier system. This is a significant omission that I believe will lead to confusion in

categorizing structures. On the scale of 1-10 that is used for this factor I would assign this category

of building a value of 9. It is vulnerable to vapor intrusion, but it is not the most vulnerable of

residential structures.

• Homes that are underlain by a combination of basement and crawl space, and which do not have any

form of vapor mitigation system, should be described as such and placed in Category 2. This is a

common type of residential construction and it would be an omission to leave it out of Table 5-12.

142
With this type of building there usually is a 4-5 ft high stem wall that separates the crawl space from 

the basement and generally there is no seal or a very poor seal between the crawl space and basement 

areas. This allows vapors to freely migrate into the basement and living spaces making these homes 

some of the most sensitive and vulnerable with respect to vapor intrusion. This type of structure 

should be assigned a value of 10 in Table 5-12. 

• In my experience, residences that are completely underlain by vented crawl spaces generally have

fairly small attenuation factors and their vulnerability to vapor intrusion is considerably less than

other building types. This was observed at a chlorinated solvent release at the Eugene Rail Yards

site in Eugene, Oregon. At this site, crawl space concentration showed a broad range of attenuation

factors and a poor correlation to soil gas values. It appeared crawl space concentrations were most

influenced by background and insignificantly by soil gas that spanned a range of PCE concentrations.

Based on my experience I would assign a value of 6 rather than 8 to this type of construction.

However, I acknowledge that nationally there may be regional/climatic differences that affect the

degree of communication between the crawl space and the overlying building and justify the value of

8.

• Evidence of biogas, inert gases. Is this referring to methane and radon? Typically this type of

information is not available for relatively short inspections.

b. Distance between occupied structure and depth of contamination; and

At the depths beyond the 0-10 ft range presented in Table 5-13 chemical diffusion is generally considered to 

be the dominant transport mechanism. Diffusion and diffusive flux is typically described using Fick’s Law 

J= -D(dc/dz). Using Fick’s Law and assuming 100 ug/m3

 at the source and zero in indoor air, concentration 

gradients as a function of depth are plotted below. 

143
Using this approach and assuming a Depth to Contamination value of 10 for a source 10 ft below the 

occupied base of a structure, 20 ft would then have a value of 5, 50 feet would have a value of 2, 100 ft a 

value of 1 and 150 ft of 0.66. Since this term is evaluating the strength of diffusive flux in the subsurface 

and not attempting to consider geologic heterogeneity, the values should be based on Fick’s Law of diffusion 

which has been empirically demonstrated to be accurate in numerous column tests of porous media; this is 

unless there is sufficient empirical field data that supports the numerical assignments in Table 5-13. 

Considering Depth to Groundwater Contamination and Depth to Soil Vapor Contamination Equivalently

An important concern in the assignment of Depth to Contamination values under section 5.2.11.2.2 is the 

approach treats groundwater and soil gas as equivalent media and at any given site there depths are 

presumably comparable. However, it isn’t an either or situation, if there is a groundwater plume of 

contamination at the water table, there will be corresponding soil gas contamination above it and by 

definition the soil gas will always be shallower than the groundwater contamination. Depending on where 

the soil gas measurement is taken it could be 20, 30, 50 ft or more shallower than the depth the groundwater 

contamination is measured at. Thus, the depth to contamination that is entered into this table may in large 

part be a consequence of which media was sampled and not the actual site conditions. 

I ran one of our bigger vapor intrusion sites (Tarr Oil, Portland, OR) through the Potential for Exposure 

calculation and it scored a 380 based on the initial groundwater data, and a 500 based on soil gas data. The 

location of the measurement also affects assignment of the Vapor Migration Potential value. The depth of 

measurement and choice of media to sample potentially introduces a bias that should ideally be eliminated 

from the calculations. 

c. Evaluation of the vertical migration factor based on the thickness and porosity/permeability of

geologic materials in the interval between the lowest point of an occupied structure and the

highest known point of hazardous substances in the subsurface.

Assignment of Vertical Migration Factor Values 

Vertical migration values for soils assigned a porosity/permeability value of 4 (clays, low permeability till, 

unfractured igneous rocks etc.) appear to be excessively high when compared to the values of other soils and 

thicknesses in Table 5-15 and relative to values assigned to the Depth to Contamination factor. True clays 

and unfractured igneous rocks have extremely low effective porosities and if they have any appreciable 

thickness should act as a virtually complete barrier to vapor transport. The only exception would be if the 

clays were or had been desiccated leaving fractures for preferential flow. 

It is difficult to say the 0-5 ft thickness value of 15 for soils assigned a porosity/permeability value of 4 is 

disproportionately high given the thickness ranges down to zero. However, I suggest revising the value for 

the 5-10 ft thickness to 8 rather 12, and the 10-20 ft thickness range 6 rather than 9 and the 20-50 ft range to 

3 rather than 6 and the 50-100 ft and 100-150 ft ranges both should be 1. I cannot think of a more restrictive 

barrier to vapor transport than 50-100 ft of true clay. 

The values in Table 5-15 applied to soils assigned a permeability/porosity value of 1-3 appear appropriate. 

144
Although not discussed, effective porosity for gas transport (diffusion rates through water-filled pore spaces 

are generally 100,000x or more lower than through air-filled) is highly sensitive to moisture content in the 

soil and I assume this consideration is embedded in the values of Table 5-15. Finer-grained soils typically 

retain a higher moisture content that further reduces effective porosity. This degree to which soils are 

saturated is largely a consequence of annual precipitation rates and their seasonal distribution. Therefore, for 

identical soils it’s anticipated that there would be regional differences in the vertical migration factor. 

Ideally the moisture content factor would be considered in the scoring, however, there may be insufficient 

information to confidently develop values. 

145
2. Hazardous Waste Quantity

Background: In the current HRS, the hazardous waste quantity factor reflects the risk consideration related 

to the magnitude and duration of either the release for ground water, surface water, and air pathways, or the 

exposure for the soil exposure pathway (see section 2.4.2 of the current HRS). Hazardous waste quantity is 

evaluated for all four pathways. At each site evaluated, EPA uses a four-tiered hierarchy for calculating the 

hazardous waste quantity that is based on (1) constituent quantity; (2) waste stream; (3) volume; and (4) area 

of the sources of hazardous waste at the site. EPA uses minimum waste quantity factors when there is 

insufficient information to estimate hazardous waste quantity. In the ground water, surface water, and air 

pathways, the HRS evaluates the total quantity of hazardous substances available to migrate from the original 

sources (how much has migrated and how much can be released in the future). In the soil exposure pathway, 

the hazardous waste quantity does not include the total amount of hazardous substances in all site sources, 

but rather is based on the amount of hazardous substances to which a receptor can be exposed where actual 

contamination has been documented. In other words, for the soil exposure pathway, the risk posed by a 

release of hazardous substances is directly related to the amount of hazardous substances that receptors are 

exposed to, as opposed to how much of the hazardous substances from the original sources may migrate to 

the receptors. 

Proposed Approach: EPA is proposing a parallel approach to the soil exposure pathway to calculate 

hazardous waste quantity for the subsurface intrusion addition to the HRS. Since the subsurface intrusion 

component also focuses on exposure, the waste quantity factor value for this component should also reflect 

only the amount of hazardous substances that people actually are exposed to (the amount present in occupied 

structures). EPA is proposing to use a similar four-tiered hierarchical approach to calculate hazardous waste 

quantity within occupied structures with contamination. In cases where no home is subject to actual 

contamination, EPA is proposing to use minimum waste quantity factors. In situations where there is an 

observed release within a structure above benchmarks (Level I), a default value of 100 is proposed for the 

hazardous waste quantity factor value. This value is not used in the current soil exposure pathway, but is 

consistent with the ground water, surface water, and air pathways and reflects the increased exposure risk of 

a release within an occupied structure. 

Charge Question #2: Is EPA’s approach of basing the hazardous waste quantity on the amount of 

contaminants that could be found in the intruded structures appropriate? If no, what alternative 

approach would you recommend? 

I disagree with the proposed approach to calculating hazardous waste quantities for the subsurface intrusion 

component. Compared to soil and water, air is a much less dense medium and as a consequence, for 

equivalent risk levels between various media, it typically contains much less contaminant mass. Essentially 

airborne contaminants can generate equivalent human health risks to those resulting from contact with other 

media, although with far less mass. For example, the State of Oregon assumes benzo(k)anthene has an oral 

slope factor of 0.073 and has calculated a residential soil screening level of 6.2 mg/kg (equating to 1x10-6 

risk). Assuming a 5000 ft2 property that is 70% land 30% impervious surface, a 1 foot thick layer of soil 

contaminated up to the screening level would contain approximately 1,190 grams of benzo(k)fluoranthene. 

In comparison, a 1300 ft2 residence with vinyl chloride (inhalation slope factor of 0.031) contamination at a 

concentration 0.14 ug/m3

 (equivalent to 1x10-6 risk) has 0.000047 grams in the indoor air at any one time. 

146
Assuming an air exchange rate of 6 exchanges/day, approximately 3.1 grams would have moved through the 

home over a 30 year period of time. Assuming an identical toxicity and slope factor to that of 

benzo(k)fluoranthene, the mass of vinyl chloride in the air over the 30 year period is 6.3 grams for the 

equivalent risk. Humans contact and take up air contaminants much more efficiently than contaminants in 

water or soil, therefore, it requires far less mass for equivalent risk. 

Using Table 2-6 (pg. 22) and the methods outlined in 5.2.1.2.2 to assign a Hazardous Waste Quantity Factor 

value, it is likely most vapor intrusion sites would get a quantity of 1 unless an exposure is documented then 

it defaults to 100. It appears very unlikely any VI site would have hazardous quantity factor larger than 100. 

This results in relatively low Waste Characteristic Factor values compared to what can calculated for other 

media and pathways. In this respect it appears to underestimate the risk of the subsurface intrusion pathway 

relative to others. 

Suggested Alternative Proposed HRS Method of Estimating Hazardous Waste Quantity 

Quantify and include contaminant sources in the subsurface in addition to the contamination found within the 

buildings. These sources constantly feed the contamination within the buildings and so could be legitimately 

included in the inventory of waste quantities. For this particular factor, the change would make the 

magnitude/mass of sources of vapor intrusion more comparable to those contaminating other media. 

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3. Population score

Background: Within the current HRS, receptors are evaluated in two main categories: whether they are 

exposed to 1) actual contamination; or 2) potential contamination (see section 2.5 of the current HRS). If 

receptors are exposed to contaminant levels meeting observed release criteria, they are identified as actually 

contaminated; however, if the receptors are not exposed to contaminants that meet the observed release 

criteria but are within the target area being evaluated, they are considered potentially contaminated. Actual 

contamination is further divided into two sub-categories based on whether the hazardous substance is present 

at or above a health-based benchmark. If the concentration of the hazardous substance released at the 

receptor is greater than a health-based benchmark, the receptors are identified as Level I receptors and are 

weighted (multiplied by a factor of 10) in scoring. If the release concentrations are less than a health-based 

benchmark, the receptors are identified as Level II receptors and are not weighted (multiplied by a factor of 

1). Potential receptors are distance/dilution weighted; in other words, the farther away a receptor is located 

from a source, the less the population contributes to the site score. 

Proposed Approach: EPA is proposing to generally use the same receptor weighting structure in the 

subsurface intrusion component as the one used in the current HRS. Those receptors in the area(s) of 

observed exposure (AOE) are considered actually contaminated, and those in the area(s) of subsurface 

contamination (ASC) are considered potentially contaminated (See Figure 2). The receptors in an AOE are 

further differentiated based on whether the contaminant concentrations are at levels above identified 

benchmarks (Level I) or are at levels establishing a release but below identified benchmarks (Level II). The 

benchmarks that EPA is proposing to use for the subsurface intrusion component are: 

• Screening concentration for cancer effects; and

• Screening concentration for non-cancer effects (systemic toxicants).

Consistent with the weighting of populations throughout the HRS, the proposed subsurface intrusion 

component will weight targets within the AOE subject to Level I contaminant concentrations by a factor of 

10 and weight targets subject to Level II contaminant concentrations by a factor of 1. 

EPA is proposing to evaluate the weighting of targets within the ASC based on sub-slab, soil gas, and/or 

ground water samples. Potential receptors within the ASC receive less weight (population multiplied by a 

factor of 0.1), except in cases where a sub-slab sample indicates contaminant levels are at least 10 times 

higher than a health-based benchmark (population is multiplied by a factor 0.75). The value of 0.75 was 

determined based on an evaluation of paired data when both a sub-slab and indoor air sample were collected. 

The 0.75 weighting reflects the observation that for approximately 80 percent of the sampling events where 

contamination was detected in the sub-slab, contamination was also detected in the indoor air sample. The 

order of magnitude adjustment applied to the health-based benchmark reflects EPA’s finding that, in such 

paired sampling events, the indoor air sample concentration is, on average, 10 times lower than the sub-slab 

sample concentration. 

148
Figure 2 

Charge Question #3: Is it appropriate to consider individuals/populations located within the area of 

subsurface contamination (ASC) to be at a higher relative risk in situations when sub-slab contaminant 

concentrations are at least ten times greater than a health-based benchmark? If no, please explain. 

An obvious answer to the Charge Question #3 is: yes, in general occupants of buildings where sub-slab 

concentrations exceed 10x a health-based benchmark are at higher risk relative to occupants of 

buildings with sub-slab concentrations that are less than this value. However, the scheme for weighting 

individual targets/receptors is crude in the ASC, does not appear consistent with the results of EPA’s 

compilation of paired sub-slab and indoor data, and potentially underestimates population risks. 

As described in sections xxxx of the draft HRS rule revisions, for targets/receptors occupying buildings over 

an ASC and where subslab contaminant concentrations exceed 10x the benchmark screening level should 

assigned a weighting of 0.75. The explanation given is that the review of the compiled paired data indicate 

80% of the time a subslab concentration exceeds 10x its respective health based benchmark, the contaminant 

is detected in indoor air. 

• Why wasn’t a value of 0.8 used instead 0.75 since the correlation described above was observed 80%

of the time?

• 0.75 is used in all where a subslab VOC concentration greater than 10x its corresponding healthbased benchmark has been observed within the ASC. However, subslab VOC concentrations at

many sites are routinely observed at levels from 100-100,000 times their corresponding benchmarks.

Yet in the proposed HRS scheme for weighting targets, irrespective of the concentration observed,

149
any time it exceeds 10x the benchmark a value of 0.75 is used. Using a single value (such as 0.75) 

may be reasonable for weighting receptors when subslab levels are just 1-2 orders of magnitude 

above benchmark values, and indoor concentrations are likely detectable but below benchmark 

values. However, as subslab contaminant levels increase, eventually a concentration threshold is 

crossed where the results of EPA data compilation indicate the probability of exceeding a 

benchmark value in indoor air is very high. For these cases assigning a weighting factor that is 

closer to10 is more appropriate. 

The proposed target weighting approach may introduce a low bias to population risks, particularly at 

sites where the primary medium sampled is subslab and not indoor air. soil gas and not 

• It is not clear from the rule revision whether the appropriate weighting for targets within the ASC is

based on the maximum observed subslab concentration or whether some form of average value is

considered (i.e. arithmetic mean, UCL, etc.) My recommendation, since this is a screening process,

would be to use the maximum subslab concentration observed, and that this expectation should be

specified in the rule if it isn’t already.

• The EPA database on paired subslab and indoor air data has been reviewed by many states and

individual practitioners. Statistics have been performed on both filtered and unfiltered data. The

filtering was done in an effort to eliminate the influence of ambient background concentration on

calculated attenuation factors. EPA has recognized the need to perform the data filtering to remove

outlier attenuation rates. A strategy that Oregon DEQ used in an attempt to separate out background

influences was to only consider data from sites with strong sources, for examples sites with subslab

concentrations greater than 1000 ug/m3

.

The results of the data analysis indicate unfiltered paired subslab-indoor air data had an average

attenuation factor of 0.003 and median value of approximately 0.002. An analysis of highly filtered

similar to data by ODEQ produced an average attenuation factor of 0.0007 and a median value of

0.0002. Thus the statement that approximately half of the vapor intrusion sites had an average

attenuation factor of 0.1 is not supported by EPA previous analysis of VI data.

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Derivation of Attenuation Factors

1,000,000

100,000

10,000

1,000

100

1

1

0

0.1

0.01

100,000

10,000

1,000

100

10

1

0.1

0.01

Subslab vapor (ug/m3)

Attenuation Factor

Attenuation Factors vs. Subslab Vapor Concentration

A verage 352

10th 680

25th 222

50th 33

75th 3.2

90th 1.1

Percentile A F Value

Deriving Attenuation Factors

1,000 10,000 100,000 1,000,000

100,000

10,000

1,000

100

10

Subslab Vapor Concentrations >1,000 ug/m3

Attenuation Factor

Attenuation Factors vs. Subslab Vapor Concentration (High Range)

Average 1,558

10th 3,324

25th 1,348

50th 516

75th 196

90th 125

Percentile AF Value

ODEQ, March 2010

Recommendation

Based on: statistical analyses of the EPA Database, and the recognition that it does not necessarily 

populated by the most sensitive structure types, I recommend that within defined ASCs assign a target 

weight factor of: 

• 0.1 to occupants of buildings with subslab contaminant concentrations less than 50x the health-based

benchmark value.

• 1 to occupants of buildings with subslab contaminant concentrations between 50x-500x the healthbased benchmark value.

• 10 to occupants of buildings with subslab contaminant concentrations greater than 500x the healthbased benchmark value

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4. Multi-story and multi-tenant structures

Background: In the current HRS, multi-story and multi-tenant buildings are evaluated based on population 

associated with an actually or potentially impacted target. In the ground water pathway, all residents who are 

served by a well are considered subject to the actual or potential contamination of the well. In the air 

pathway, all residents who have an opportunity to breathe ambient air are considered subject to the actual or 

potential contamination of the ambient environment within a distance category. All receptors within a 

contaminated surface water stretch are subject to the level of contamination associated with that surface 

water stretch. In the soil exposure pathway, receptors must be able to come in contact with areas of 

contamination. In determining the likelihood a person will come in contact with areas of contamination, the 

HRS uses a 200 foot rule (see section 5.1.3 of the current HRS) because it is reasonable to assume that that a 

person will walk/use areas within a 200 foot areal extent of their residence/property. The 200 foot rule is 

used regardless of whether a building is multi-tenant or multi-story (the assumption being that is reasonable 

for people to use the outside of their properties). 

Proposed Approach: EPA is proposing to evaluate multi-story/multi-tenant buildings utilizing a similar 

approach as soil exposure, limiting the receptors to those individuals that reasonably can be exposed to 

subsurface intrusion within an occupied multi-tenant/multi-story building. EPA is proposing to consider all 

receptors exposed to actual contamination as the population inhabiting the floor of the intruded space and the 

population inhabiting the floor above and the floor below the intruded space when calculating waste quantity 

and population. EPA considers that this approach will more accurately reflect risk to both actual and 

potential receptors, while also minimizing the potential for over counting (Figure 3). 

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Figure 3 

Charge Question #4: When calculating waste quantity and population, is it scientifically reasonable for 

populations in multi-story or multi-tenant structures to be evaluated based on using only the population 

inhabiting the intruded space and the population on the floor above and below the intruded space (For 

example, if contamination is found on the first floor, population from the basement and second floor 

would be used in the calculation. If contamination is found on the fifth floor, population from the fourth 

floor and sixth floor would be used in the calculation – for further explanation, see detailed discussion in 

above paragraph “Proposed Approach”)? If no, what alternative approach would you recommend? 

Regarding the Calculation of Waste Quantity

See comments and responses to Charge Question #2 

In the above scenario, if level I and level II exposures are observed on the 

first floor I would assign level I values to the basement dwellings also. 

They are overwhelming the most sensitive locations and having a reverse 

gradient scenario as depicted, where higher concentrations overlie lower 

concentrations would be very unusual for a VI site. A more likely 

explanation for this type of observed distribution would be simply being 

temporal variability in indoor air levels.

I would weight the occupants 

of the first floor based on the 

concentration observed in the 

basement. These residences 

and their occupants may be 

under weighted just because 

of the absence of direct 

observations – to remedy this 

use the EPA database to make 

educated inferences of 

exposure levels 

In this contaminant distribution, I 

would assume all basement 

residences are Level I due to error 

and uncertainty from temporal 

variability of indoor air quality

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Regarding Assumptions and Weighting of Occupants/Targets in Multi-Family Residences

Some comments are made directly on the Figure 3 – see boxed text. Aside from those suggested 

modifications, the general scheme looks appropriate. 

Regarding the Weighting of Population Targets in AOE

In my opinion the weighting is disproportionately influenced by data type – specifically the difference in 

weighting directly observed impacts as compared to inferred impacts based on subslab sampling. Whereas 

an individual or population directly observed (through indoor air sampling) to be exposed to levels above the 

health-based benchmark is indoor exposure directly observed to be over a benchmark is assigned 

The weighting of targets/receptors exposed to Level 1 contamination 10x higher than those exposed to 

 Level II concentrations by a factor of 10, coupled with the recognized temporal variability in indoor air 

concentrations (See Paul Johnson’s recent work at Hill Air Force Base, Arizona) could produce significant 

swings in the population score that are more artifacts of when the sampling occurred than true differences in 

the magnitude of the average VOC exposure. The concern regarding accurately characterizing indoor 

exposure levels is particularly relevant if site inspections are conducted and indoor air concentrations 

measured, within a short 2-3 day period. 

Potential Ways to Mitigate Errors and Uncertainties 

Two ways to mitigate this uncertainty and potential error is to characterize exposure levels using ambient air 

sampling methods that accommodate long sampling periods, or alternatively increase the number of (shorter 

period) air samples that target meteorological conditions particularly conducive to vapor intrusion. In short, 

use sampling technologies are approaches that provide better representations of long term exposure levels. 

A different approach would be to apply a scheme that has more than two designations for confirmed 

exposure levels. Perhaps the value 1 for detected/observed exposures that are <0.5x the benchmark health 

value, a value of 3 for values 0.5 -1.0 x the benchmark value, and 10 for those occupying buildings with 

exposures greater than the benchmark value. 

Weighting of Population Targets in ASC

In the proposed approach for weighting target populations within the ASC it appears there is a 

disproportionate undervaluing of susbslab data relative to indoor data. Under the proposed scheme, subslab 

concentrations greater than 10x the health-based benchmark value would weighted with a factor of 0.75 

(weighted slightly less than a level II exposure) irrespective of the specific concentration measured. EPA 

compiled a large database that provides opportunities for robust statistical analyses including the derivation 

of attenuation rate percentiles and confidence intervals. This information should be used to help 

appropriately weight targets where only subslab data is available. For example, using unfiltered statistics the 

50th percentile attenuation factor is 0.03, thus it can be concluded that if subslab levels exceed benchmarks by 

a factor of 33 or greater then there is 50% chance occupants are being exposed to levels above the 

corresponding health-based criteria and that the appropriate weighting is 10 rather than 0.75. 

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In section 5.2.1.3.2.3, the proposed rule indicates subslab data and crawlspace data will be similarly 

evaluated and weighted. The implies the data types are equivalent, however, EPA and others have generally 

assumed the attenuation factor between the crawl space and the residence interior should be assumed 1and 

thus is a reasonable surrogate for actual indoor air data. So, this would suggest detection of COCs below 

benchmark values in the crawl space should be weighted under the proposed scheme at a value of 1 and that 

if concentration exceeds benchmark values in the crawl space the appropriate weighting would be 10. 

In general there appears to be a undervaluing of susbslab data, even when that is the only type of data 

available. However, susbslab data may be the primary type of data available at a site and the population 

component of the scoring may be biased low as consequence. Thus, at any given site, the scored risk may 

be substantially lower if the primary data source is subslab measurements than compared to the same site if 

the primary source of data was indoor measurements. 

Recommendation

Use EPAs database of paired subslab and indoor air data to perform more refined weighting of targets in an 

ASC. Ideally, the weighting would relate to the probability a Level I or Level II exposure is occurring based 

on subslab data. 

Additional Comment

The example scenario described in the Charge Question #4 is highly unusual contamination found on 5th

floor consider tenants on 4th and 6th floors. Under this scenario I would expect all floors beneath the 4th floor 

to be considered and actually most of them contaminated. Overall, it’s an unrealistic scenario and the actual 

proposed rule indicates all floors beneath the observed exposure would be considered in the calculations, as 

they should be. 

5. Factor Value for Workers

Background: In the current HRS, 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 of observed 

contamination. These factor values range from 0 to15, depending on the number of workers exposed to 

outdoor contamination (see section 5.1.3.3 of the current HRS). 

Proposed Approach: EPA is proposing to mirror the procedures for the resident population threat in the soil 

exposure component when 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 and 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., factor values ranging from 0 to 45).

Charge Question #5: Because of longer exposure times indoors, is it reasonable to assume that the relative 

risk is three times greater for workers exposed to subsurface intrusion within the workplace than it is for 

workers exposed to outdoor surface contamination at the workplace? If no, please explain. 

I agree with the proposed weighting for workers. Generally, workers do spend more time indoors and that 

this pathway is more likely to be complete. 

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Henning Larsen, R.G.

2805 NE 28th Avenue

Portland, OR 97212

(503)281‐4770

Current Employer:  Oregon Department of Environmental Quality, 2020 SW 4th Avenue, Suite 400,

Portland, Oregon.  Ph: 503‐229‐5527.  Supervisor: Bruce Gilles (503‐667‐8414 x55009)

Education:          B.A. in Geology, Humboldt State University, Arcata, CA;  M.S. in Civil Engineering,

Oregon State University, Corvallis, OR.  

Certifications:    Registered Geologist, State of Oregon  

Work History:   1987‐1989 – Geologist, Newmont Mining Corporation

1992 – Geologist, Oregon Health Division  

1992‐1994 ‐ Hydrogeologist, Oregon Department of Environmental Quality

1994‐1998 – Cleanup Project Manager, Oregon Department of Environmental Quality

1998‐current ‐  Senior Hydrogeologist, Oregon Department of Environmental Quality

Current Duties/Responsibilities:  Develop and provide senior level review of hydrogeological

investigations;  develop statewide policy, guidance and rule recommendations for the  State of Oregon

Cleanup Program; Agency expert on contaminant fate and transport modeling; represents DEQ at

hearing, public meetings, and conferences to explain the bases for soil, soil vapor, and groundwater‐

related cleanup requirements.      

Professional Work Groups

Participant in EPA Groundwater Forum since 2007

Vapor Intrusion Related Guidance Work  

1996 – co‐author of State of Oregon Risk‐Based Corrective Action for Petroleum Cleanups .  Document

used J&E models to assess indoor vapor intrusion and outdoor volatilization pathways.

1999 – co‐author of State of Oregon Risk‐Based Decision Making at Petroleum Cleanup Sites.  Document

used J&E  level models to assess indoor vapor intrusion.

2006 –author of Guidance for Managing Hazardous Substance Air Discharges From Remedial Systems

2010 – co‐author/primary author of State of Oregon Guidance for Assessing and Remediating Vapor

Intrusion in Buildings.

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Vapor Intrusion Training Given

February 2003 – Developed and presented Risk‐Based Decision Making training including training on  VI

pathway, State of Oregon

November 2007 – Developed and presented 2‐day course on vapor intrusion pathway for the Northwest

Environmental Training Center (NWETC).  I gave the 2‐day course three separate times in Seattle, WA

and Portland, OR.  

April 2010 – Developed and led 1‐day training course on use of State of Oregon Guidance on Assessing

and Remediating Vapor Intrusion in Buildings .

Vapor Intrusion Presentations   

1998 – National UST‐LUST Conference, Albuquerque, NM – Vapor Intrusion – The Oregon Experience

2007 – Oregon Brownfields Conference, Salem OR,  Primer on Vapor Intrusion

2009 – Northwest Environmental Conference, Portland, OR, Vapor Intrusion Continues to Mature: Legal,

Regulatory and Technical Updates

2010 – EPA, Region 10 All States Meeting ‐ Assessing and Remediating Vapor Intrusion in Buildings

2011 – Northwest Environmental Business Conference, Portland, OR, Vapor Intrusion‐ Evaluating the

Marginal Cases

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