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COMMENTS RECEIVED ON PROPOSED GUIDANCE

Land Recycling Program Technical Guidance Manual – Section IV.A.4 Vapor Intrusion into Buildings from Groundwater and Soil under the Act 2 Statewide Health Standard

DEP Guidance Document Number 253-0300-001

Published July 20, 2002

Public Comment Period July 20, 2002 through August 19, 2002

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DRAFT Comment/Response Document


List of Commentators*

ID

Name/Address Zip

1 Ed Dziedzic, P.G. Project Manager Groundwater & Environmental Services, Inc. 410 Eagleview Blvd., Suite 110 Exton, PA 19341 (610) 458-1077 x154

19341

2 Cullen Flanders, P.E. Geologic Services Corporation 129 McCarrell Lane Zelienople, PA 16063 (724) 452-7150 (724) 452-5446 (fax)

16063

3 Fred M. Anderson Environmental Advisor, Northeast ExxonMobil Refining and Supply 3225 Gallows Road, Room 8B0427 Fairfax, VA 22037 (703) 846-3209 (703) 846-5599 (fax) [email protected]

22037

4 Gary J. Buterbaugh, P.G. Earth Tech 2 Market Plaza Way Mechanicsburg, PA 17055 (717) 796-8011 (717) 795-8280 (fax)

17055

5 Eric D. Stahl, P.E. Client Service Manager Weston Solutions, Inc. 610.701.7553 (Office) 610.701.3187 (Fax) [email protected]

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List of Commentators*

ID

Name/Address Zip

6 Richard A. Blackburn GEM Company, Environmental Business Manager BP 1 West Pennsylvania Avenue Suite 915 Towson, MD 21204 (410) 821-4586

21204

7 Mr. Jim Nairn Civil & Environmental Consultants, Inc. 333 Baldwin Road Pittsburgh, PA 15205 (412) 429-2324 [email protected]

15205

8 Andrew Clibanoff RCRA Corrective Action Project Manager PA Operations Branch U.S.EPA Region III 1650 Arch Street Philadelphia PA 19103-2029 (215) 814-3391

19103-2029

*Commentators are identified by the number in parentheses at the end of each comment.

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Proposed Vapor Intrusion Guidance

LIST OF ACRONYMS

API American Petroleum Institute

BTEX Benzene, toluene, ethylbenzene and xylene

COC Contaminant of concern

COPIAC Chemical of Potential Indoor Air Concern

CSSAB Cleanup Standards Scientific Advisory Board

DEP or PADEP Pennsylvania Department of Environmental Protection

EPA or USEPA U.S. Environmental Protection Agency

GW Groundwater

IAQ Indoor air quality

J-E Model or JEM Johnson and Ettinger model

MADEP Massachusetts Department of Environmental Protection

MSC Medium-specific concentration

MSCGW or MSCGW Medium-specific concentration for groundwater

MSCIAQ or MSCIAQ Medium-specific concentration for indoor air quality

MSDS Material Safety Data Sheet

MTBE Methyl- tert-butyl ether

NAPL Non-aqueous phase liquid

OSHA Occupational Safety and Health Administration

PEL Permissible Exposure Limit

POC Point of compliance

SHS Statewide health standard

SPL Separate phase liquid

SSS Site-specific standard

SVOC Semivolatile organic compound

TO-14 EPA Methodology TO-14 from Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air, Second Edition

TPH Total petroleum hydrocarbons

VOC Volatile organic compound

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Comment/Response Document*


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Comment 1

Apparently, the referenced guidance only applies to Statewide Health Standard residential and non-residential exposure scenarios. Does it make sense, or is it acceptable to use the guidance to evaluate and eliminate pathways and demonstrate attainment under the Site-Specific Standard? Specifically, where fate and transport analysis indicates that a dissolved contaminant may exist within 15 feet below an offsite (beyond the POC) basement, could the decision matrix in the guidance be used to evaluate the pathway via indoor air sampling? If the indoor air sample results are below the MSCs for indoor air quality, could the pathway be eliminated? (1, 4)

Response 1 This Vapor Intrusion Guidance is only intended as a screen under the Statewide Health Standard (SHS) and is not to be used under the site-specific standard. If the general criteria are met as indicated in the groundwater flowchart, the decision matrix process can be used to evaluate the indoor air pathway. If the indoor air samples are below the established MSCIAQ no further remedial activity is required.

Comment 2

Since this is a screening documents and the media is indoor air, why are vapors emanating from soil and groundwater not considered cumulatively. Note that according to Act 2:

(b) Carcinogens.--For known or suspected carcinogens, soil and groundwater cleanup standards shall be established at exposures which represent an excess upper-bound lifetime risk of between 1 in 10,000 and 1 in 1,000,000. The cumulative excess risk to exposed populations, including sensitive subgroups, shall not be greater than 1 in 10,000.

(c) Systemic toxicants.--For systemic toxicants, soil and groundwater cleanup standards shall represent levels to which the human population could be exposed on a daily basis without appreciable risk of deleterious effect to the exposed population. Where several systemic toxicants affect the same target organ or act by the same method of toxicity, the hazard index shall not exceed one. The hazard index is the sum of the hazard quotients for multiple systemic toxicants acting through a single-medium exposure pathway or through multiple-media exposure pathways. Referring to the attached spreadsheet, the hazard index exceeds one for various target organs. (2)

Response 2 The commentator is quoting from Section 304 of Act 2, which addresses the site-specific standard. The Statewide Health Standard (SHS) does not address media contamination and risk from a cumulative perspective. Only the site-specific pathway does. This draft guidance only applies to the SHS.

* Comments are presented as received from individual commentators without editing.

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Comment 3 Refer to page 8, 3 paragraph …”these screening analyses use conservative assumptions”

Based on some calculations, this analysis does not appear to be conservative. Using the J-E model and PADEP default values, several chemicals exceed the cancer risk of 1 in 100,000 (Statewide Standard set to 1 to 100,000). Furthermore, if the systemic affects on target organs are considered, the hazard index exceeds 1. Since this is a screening document, consider using a hazard quotient of 0.1 and a cancer risk of 1 in 1,000,000. Using these values will ensure that this screening document will comply with Pa Code 25 § 250.402(b)(1)…between 1 in 10,000 and 1 in 1 million. Cumulative 1 in 10,000 and Pa Code 25 § 250.402(b)(2)…the hazard index may not exceed one. (2)

Response 3 The fate & transport of contaminants were set and evaluated at the worst-case scenario based on very conservative exposure factors. The CSSAB subcommittee did not want to use various toxicological endpoints which are not consistent with Chap. 250. Also, the CSSAB subcommittee, in the development of the generic SHS, addressed each medium separately and only single medium values are provided which is consistent with all currently available screening programs, e.g., Superfund SSLs. To address multi media exposure conditions, conservative assumptions are used. In this evaluation, conservative assumptions included an infinite source, no degradation, and lifetime exposures.

As a further check that the evaluation was protective, model runs were performed using the residential scenario and the GSI/ASTM version of the Johnson and Ettinger model (J-E model) (GSI, 1999). This software allows both soil and groundwater to be addressed simultaneously (whereas the EPA version does not) which typically provides more conservative values that the EPA model (because of inherent assumptions in the software that cannot is adjusted). The results indicate that the values derived separately using the PA defaults and EPA J-E version are protective of both media together.

This conclusion is further supported by the empirical findings by GSI (presented at the NGWA/API Petroleum Hydrocarbons Conference in Houston, 11/01).

Comment 4

It is not appropriate to identify specific chemicals to be considered. It is more appropriate to identify chemical properties that would indicate that there is little indoor air hazard. For example, based on default hazard quotient calculation, naphthalene does pose an inhalation hazard and it should be considered an indoor air hazard. . . Other VOCs and SVOCs may need to be added to the screening list. Instead of identify chemicals that should and should not be evaluated, consider identifying chemical properties (i.e. vapor pressure, water solubility, and Henry’s constant) that indicate that a chemical is not likely to pose a significant hazard. (2)


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Response 4 The Act 2 regulations are based on specific chemicals, not property based factors.

Comment 5

It would be helpful if PADEP generated a target organ list. Different reference documents identify different target organs. (2) Response 5

Identifying target organs would involve a lot of detail under a SHS approach and the DEP has chosen at this time not to establish a target organ list under the Statewide Health Standard. Target organs could be developed as part of remediations under the site-specific standard.

Comment 6

Indoor Air Background: Indoor air risk-based limits calculated using the method proposed in the guide are below background (i.e., concentrations expected to occur at sites not impacted by affected soil or groundwater) for key COCs such as benzene and PCE. For example, Benzene: risk-based limit is 2.7 ug/m3 but a typical background indoor air concentration is 10 ug/m3 (McHugh et al., 2002).

The consequence of setting a risk-based limit that is below background is that we can never use direct measurement to determine compliance with the standard. Instead, we have to rely on a conservative model that may indicate the need for corrective action when in fact, no problem exists. A conservative model is appropriate as a screening tool, but is problematic when used as a final decision making tool. (3)

Response 6 Sources of hazardous substances of concern in the form of VOCs are found in a variety of household products such as paints, fuels, varnishes, cleaning solvents, and from personal habits such as smoking. All of these factors may elevate background concentrations of such substances in indoor air. Therefore, the Department suggests caution in taking indoor air samples and interpreting the results in this context. Because sampling VOCs in indoor air can be complicated by these other sources of VOCs within a dwelling, the guidance gives an option of taking soil gas measurements at a distance not to exceed 5 feet from the dwelling and compared to MSCs for soil gas.

Comment 7

Use of OSHA Limits for Industrial Facilities: For industrial facilities, indoor air concentration limits should be consistent with OSHA standards. Some argue that only OSHA has the regulatory authority to establish exposure standards for industrial facilities. Aside from this issue, OSHA standards should be used to ensure consistent regulation of different sources. (In other words, why should benzene in air from groundwater be regulated differently from benzene in air from an industrial process?) * Comments are presented as received from individual commentators without editing.

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In addition, if different standards are applied for different sources, then direct measurement of air cannot be used to demonstrate compliance with the lower standard. (3)

Response 7 OSHA regulations prescribe controls and monitoring of the environment including exposure to vapors and gases in the workplace. The regulations prescribe values that may not be exceeded during a workday called Permissible Exposure Limits (PELs) at enterprises that handle various volatile material to control exposure to employees. Where OSHA regulations are applicable at the site including PELs, OSHA-derived screens may be used as an alternative to the default EPA-derived screen if so documented.

Comment 8

Henry's Law Equilibrium: Both the JEM and the draft guide use the assumption of Henry's Law equilibrium between soil gas and groundwater to evaluate the GW-to-indoor air pathway. However, this assumption is not appropriate at most sites. Diffusion through water is 1000 to 10,000 times slower than diffusion through air. As a result, vertical diffusion through groundwater will limit groundwater-to-indoor air mass flux at most sites. The assumption of Henry's Law equilibrium will result in the greatest errors at sites with high soil permeability. Thus, the assumption of Henry's Law equilibrium in combination with conservative soil attenuation factor (intended to be protective for the highest permeability sites) results in unreasonably conservative GW screening values for the groundwater-to-indoor air pathway. (3)

Response 8 The Department believes it used very conservative assumptions in developing the screening values. The J-E model as applied uses conservative screening values that may indicate a potential indoor air problem, when in fact there is not one. The Department chose to err on the side of conservatism, since the option exists to further evaluate the pathway under the site-specific standard.

Comment 9

Conservative GW-to-Indoor Air Attenuation Factor: Available data indicate that an attenuation factor of 0.01 is too conservative for the GW-to-indoor air pathway even when applied as an initial screening step. An analysis of 32 sites with characteristics most likely to result in indoor air impacts (i.e., sandy soil and shallow groundwater) indicates that 0.0001 is a reasonably conservative attenuation factor for initial pathway screening for chlorinated solvents. (Note that this attenuation factor is calculated directly as the ratio of air concentration to GW concentration, with out the Henry's Law adjustment.) For petroleum hydrocarbons, there was no evidence of any impact on indoor air quality even for this group of high-risk sites (McHugh et al., 2002). (3)


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Response 9 See last sentence of Response 8 above.

Comment 10

Conservative Assumption that Impacted Soil and Ground Water Within 100' of an inhabited Building May Cause an Unacceptable Indoor Air Impact: The requirement to assume that a complete exposure pathway exists when an MSC is exceeded for ground water and a building exists within 100' of the impacted area is not supported by the facts. An evaluation of existing ground water and indoor air measurement data indicate that for petroleum hydrocarbons, only NAPL under a building or direct GW intrusion are likely to cause indoor air impacts (McHugh et al., 2002). (3)

Response 10 See Response 8 above. In addition, the 100 feet from the source to receptor (inhabited building) value was chosen as the criterion to define when sites need to be addressed for vapor intrusion and to be consistent with the USEPA. The USEPA concluded that 100 feet is a reasonable criterion when considering vapor migration fundamentals, typical sampling density, and uncertainty in defining the actual contaminant spatial distribution. The rationale, as cited by USEPA, is based on the fact that vapor concentrations generally decrease with increasing distance away from a subsurface vapor source, and at some distance the concentrations become negligible. The distance at which concentrations are negligible is a function of the mobility, toxicity, and persistence of the chemical, as well as the geometry of the source, subsurface materials, and characteristics of the building of concern.

Comment 11

Will this guidance document be applicable to the Storage Tank program cleanups? How will the short list of petroleum parameters used for soil and water sampling under the Storage Tank Program correlate or be used for vapor sampling? (4)

Response 11 The guidance is applicable under Chapter 250 for the Statewide Health Standard (SHS) when a responsible party is attaining the SHS for soil and/or groundwater. The 30+ constituents of concern are indicated in the guidance Tables for soil and groundwater. This standard, and the associated tables are relevant to cleanups performed in the storage tank program.

Comment 12

The definition of "preferential exposure pathway" is confusing/cloudy. How shallow is shallow? What length of a vertical soil fracture is significant? It may be healed, it could


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be a shallow desiccation crack. Is there a way to measure if it is a preferential pathway? (4)

Response 12 The Department chose not to define the vertical distance or length of fractures. This would be dependent on the site-specific geology. However, more importantly if such a feature exists and passes through or occurs within 30 feet of the source and has a direct pathway from the source to the receptor, a potential preferential pathway exists and would move the process into a sampling mode as indicated in the soil/groundwater decision matrix.

Comment 13 The guidelines only apply to sites remediated under the Act 2 SHS? Why not Site-Specific? (4)

Response 13 The vapor screen as designed is meant for the Act 2 Statewide Health Standard (SHS). By existing regulation, the site-specific standard (SSS) must identify pathways and perform a risk assessment. However, under SSS, one could utilize the J-E model as fate and transport to indoors and then apply risk assessment. One could NOT assume an incomplete pathway if vapor screen indoor air MSCs are met because an open exposure pathway still requires a risk assessment.

Comment 14

The example stated in the Introduction, bullet 3, that if groundwater meets the non-used aquifer MSC for chloroform (1000 µg/l) that further evaluation would be needed if it does not meet the Residential screening value of 414 µg/l. However, the Groundwater IAQ Decision Matrix (Fig. 1) indicates that chloroform concentrations greater than the MSCGW for used aquifers (100 µg/l) require further evaluation. This seems to contradict. Is the decision point at 100 or 414 µg/l? (4)

Response 14 The comment is referring to bullet 2 in the draft guidance and not bullet 3 in the Introduction. Groundwater concentrations for chloroform must meet the used aquifer MSC (not the nonuse aquifer MSC as stated in the comment) which would not be of concern for the indoor air pathway. The commenter correctly states that the Groundwater IAQ Decision Matrix (Fig. 1) indicates that chloroform concentrations greater than the MSCGW for used aquifers (100 µg/L) require further evaluation. There is no contradiction. If one would continue in the Figure 1 decision matrix process and not meet the vertical separation, then one would compare groundwater levels to the GW


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J-E default levels of 414 µg/L (residential) in Table 1. If the groundwater values are greater than the 414 µg/L, then the process continues in the decision matrix.

Comment 15

On pg. 4, next to last paragraph - Q: If SPL is present on site but >100 feet from inhabited building, then is soil gas or indoor air sampling required? The first sentence under Sampling on pg. 6 implies that sampling of soil gas or indoor air is required based on "the presence of SPL". We believe that this is intended to apply if the SPL is beneath or within 100 feet of an occupied building. (4)

Response 15 If SPL is greater than 100 feet from the receptor (inhabited building) the sampling mode would not be immediately conducted. However, the vapor evaluation process continues in the Decision Matrices in Figure 1 and Figure 2. Soil gas or indoor air sampling is intended to apply if the SPL is beneath or within 100 feet of the receptor at or above the water table.

Comment 16

COPIACS - last paragraph on pg.4, This paragraph uses the phrase "(those that should always be addressed)". What does this mean. It appears to imply that the COPIAC parameters must always be evaluated. If a site had a petroleum spill or more specifically a drum of toluene that spilled, does this imply that the soil, groundwater and/or vapors should be evaluated for all fifteen (15) COPIAC parameters (given a Residential setting)? This question ties to question #2, a typical situation may be that an unleaded gasoline spill occurred. soil and/or water samples were collected for characterization and analyzed for BTEX, cumene, MTBE and naphthalene. Only analytical data for these parameters would be available for evaluation with Figure 1 and/or 2. Some of these parameters are on the COPIAC list and some are not. It would not be logical or economical to include carbon tetrachloride or the other non-petroleum related compounds to the analytical list. (4)

Response 16 The Department did not intend to imply that the list of COPIACs “should always be addressed”. A responsible party needs only to sample and analyze for those constituents pertaining to the particular release at the site that are on the COPIAC list or in Tables 1 , 2, 4, 5. If the constituent is not listed in the tables and is found to be a concern at a particular site, then a site-specific analysis should be used. The Department will clarify the final guidance with additional language.


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Comment 17

Paragraph 2 on page 2 states that the guidance document applies to volatile and semivolatile compounds. None of the screening criteria (Table 1 , 2 , 3 & 4) appear to be semivolatiles. Have they all been screen out? Were any evaluated? I spoke to a local laboratory about analyzing for petroleum VOC/SVOCs and they indicated that EPA method TO-14 does not detect compound like Naphthalene that are borderline between volatile and semivolatile. (4)

Response 17 The dichlorobenzenes contained in Tables 1, 2, 3, 4 and 5 are considered to be semivolatiles, by the CSSAB subcommittee advising the DEP on this guidance. . The compound Naphthalene is not listed in those Tables.

Comment 18

PADEP has provided guidance on evaluating the Vapor Intrusion Pathway using Act 2. This guidance includes the requirement for collecting either indoor air quality or soil gas samples to compare to the PADEP Act 2 MSCIAQ and MSCSG values, respectively, for buildings that have preferential pathways. From conversations with PADEP regulators, it is clear that soil gas sampling is the preferred method for evaluating the vapor intrusion pathway for many reasons, not the least of which is the elimination of any potential indoor air contamination interferences from household sources (including paints, glues, dry cleaned clothing, cleaners, solvents, fuels, etc.).

If indoor air quality sampling is needed at a particular site, PADEP has not provided any guidance on methods for evaluating that indoor air quality data, specifically regarding contamination interferences from indoor household sources. PADEP has referenced several guidance documents from other state agencies, including the Massachusetts Department of Environmental Protection (MADEP). The MADEP guidance provides very specific and clear recommendations on evaluating indoor air quality data, including the use of published ambient indoor background values in order to specifically screen out contaminants that may originate from “normal” household sources. MADEP also proposes methods of data analysis to compare sample results within a particular household that are designed to differentiate between contaminants that originate from household sources as opposed to those that originate from the external source via the vapor intrusion pathway.

Question: Does PADEP accept the methods recommended by MADEP for data evaluation and analysis, specifically regarding the use of published ambient indoor air background values and household-specific comparisons, to screen out contaminants potentially originating from household sources? (5)

Response 18 This comment appears to go beyond the standard default screening under the SHS and into a more site-specific analysis. The Department recognizes that there will always be * Comments are presented as received from individual commentators without editing.

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issues and unique situations that will warrant careful attention when sampling indoor air. If other indoor sources are a concern, the Department provides the option to conduct soil gas sampling. If indoor air sampling is conducted, the focus is on the proponent to identify and document extraneous sources, such that they may be removed from the analysis either by direct action or inference. Overall, the screening approach the Department has devised will eliminate sites that are clearly de minimis for this pathway. The other sites will likely move on from the SHS to the site-specific standard (SSS). That is why modeling is workable as a first step for the SSS.

Comment 19

PADEP cites several references on guidance for designing soil gas sampling investigations around buildings. These references include the U.S. Environmental Protection Agency (EPA), MADEP, and the American Petroleum Institute (API). MADEP references EPA for guidance on soil gas sampling design. EPA specifies that soil gas samples should be collected within 5 feet of the building foundation and at a depth just below the building foundation. API recommends collecting soil gas samples close to the source, because this depth is more representative of “steady-state” soil gas conditions that may take months or years to achieve at shallower depths (depths close to the building foundation) depending upon the litho logical conditions at the site. API also recommends collecting soil gas samples at various depths in order to determine the effects of biodegradation on contaminants.

Question: Has PADEP identified a “preferred” approach to soil gas sampling, specifically regarding sample depth and the evaluation of biodegradation affects on contaminants? (5)

Response 19 The Department has not specified a specific depth for soil gas sampling which would likely be at a point just below the slab or basement floor where vapors would most likely enter and be representative. Obviously, the deeper the sample point and closer to the source, the higher the soil gas concentrations. The Department used a conservative process when evaluating the vapor pathway and assumed no biodegradation of contaminants. Specifics concerning soil gas and indoor air sampling will be addressed in the Technical Guidance Manual (TGM) revision.

Comment 20

PADEP has provided guidance on how to evaluate the potential for vapor intrusion within a VOC plume when a complete preferential pathway (e.g., utility or drain/sewer lines, basement sumps, etc) exists.

Question: If one of the aforementioned types of preferential pathways are eliminated buy use of engineering controls (e.g., drains lines removed or blanked off from service, or sumps sealed), what, if any, type of sampling is required to evaluate the potential for


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vapor intrusion into structures within the area affected by VOCs in groundwater in these cases? (5)

Response 20 If preferential pathways are eliminated by use of engineering controls, as mentioned above, the immediate sampling would not be required. However, the vapor pathway evaluation would continue as indicated in the Groundwater/Soil Decision Matrices (Figures 1 & 2) under SHS.

Comment 21

The draft guidance may require soil gas or IAQ sampling as part of the initial screening level assessment of the indoor air pathway. If concentrations in soil or groundwater exceed the SHS for the respective matrices, a site specific risk assessment using the J&E model should be made available as an alternative to soil gas or IAQ sampling. That is, conducting a site specific risk assessment to identify soil and groundwater target levels should be an option to the investigator prior to conducting soil gas or IAQ sampling. (6)

Response 21 This Vapor Intrusion Guidance is only intended as a screen under the Statewide Health Standard (SHS) and is only acceptable to be applied and used under SHS and is not intended to be used under the site-specific standard. If the general criteria are met as indicated in the Decision Matrices (Figures 1 & 2), the decision matrix process can be used to evaluate the indoor air pathway. If the indoor air samples are above the established risk-based MSCIAQ, one could mitigate the IAQ contamination or conduct a site-specific risk analysis.

Comment 22

The draft guidance presents a comparison of groundwater concentration protective of indoor inhalation with the non-use aquifer standards. The leaching to groundwater and indoor inhalation pathways are separate issues that should be treated accordingly. It is not clear why the comparison to groundwater quality to the non-use aquifer MSCGW is part of the initial assessment flowchart. (6)

Response 22 The guidance is to be applied when a responsible party is attaining the SHS for soil and/or groundwater under Act 2. The Department used extensive worst-case modeling (Johnson-Ettinger Intrusion Model; version 2.3, 2001) using PA-specific inputs and MSCs. The results indicated that, in the absence of SPL, if the levels of regulated substances in groundwater are less than or equal to the MSC for a nonuse aquifer (with some exceptions), no further action is required.


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Comment 23

The draft guidance does not indicate the number of soil gas samples needed nor the depth at which the samples are to be taken. It does not indicate whether samples should be collected temporally, and whether the samples should be collected on a one-time basis or from permanent soil gas wells. (6)

Response 23 See Response 19 and page 18 under “Soil Gas Sampling”. Multiple collection events are typically needed to develop a representative soil vapor concentration and properly constructed soil gas wells would be considered as collection points. It is recommended that samples be collected periodically (e.g., four quarterly samples over a year). The MADEP guidance that is referenced recommends that 1-2 soil gas sampling probes be installed adjacent to the structure. Specifics concerning soil gas and indoor air sampling will be addressed in the Technical Guidance Manual (TGM) revision.

Comment 24

In the case of multiple data points (in time or space), the draft guidance does not indicate how to determine a representative concentration (highest recorded, average, etc.) for each media; soil, groundwater or soil vapor, which will be used for the comparison with the SHS. (6)

Response 24 Previous Act 2 guidance is consistent with the application of USEPA methods for the selection of representative concentrations and exposure point concentrations. For the purpose of making comparisons between environmental data sets and screening levels or criteria to establish the basis for de minimis conditions or the need for additional assessment. The Department believes it is reasonable to compare the maximum detected value or the 95% upper confidence limit of the mean of the appropriate distribution of the environmental data set to the standard or criteria. Specifics concerning soil gas and indoor air sampling will be addressed in the Technical Guidance Manual (TGM) revision.

Comment 25

The draft guidance does not specify the location where the soil gas sample should be taken in those sites where a building is not present at the site. (6)

Response 25


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This document provides guidance only for vapor intrusion into occupied buildings in which soil gas measurements can be taken at a distance not to exceed 5 feet from the slab or basement edge. Specifics concerning soil gas and indoor air sampling will be addressed in the Technical Guidance Manual (TGM) revision.

Comment 26

The draft guidance does not specify the specific inputs used in the preparation of the soil and groundwater concentrations protective of the indoor inhalation pathway. This would be helpful for review and comment on the draft guidance. (6)

Response 26 The Department can provide the PA specific input parameters as a Table in the guidance document.

Comment 27

The default values for soil appear to be very conservative when compared to the ones used in other States. For example, the PA default value for benzene is 0.37 mg/kg, while in Ohio this value is 0.95 mg/kg. (6)

Response 27 The default values for soil were established using the standard methodologies for volatilization to indoor air and standard exposure factors commonly in use throughout the country. Please be aware that these were derived using standard default generic values and they are intended to be conservative. Further, identification of conditions that exceed these values does not indicate a requirement for remediation, only that additional assessment or explanation is warranted. The Department considered this approach conservative but not unreasonable.

Comment 28

The draft guidance requires soil gas sampling or indoor air sampling when separated phase liquid (SPL) or impacted soil are within 100 feet of the receptor. It is not readily apparent why the distance of 100’ was selected and this distance may be overly conservative in most cases. (6)

Response 28


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The 100 feet from the source to receptor (inhabited building) value was chosen as the criterion to define when sites need to be addressed for vapor intrusion and to be consistent with the USEPA. The USEPA concluded that 100 feet is a reasonable criterion when considering vapor migration fundamentals, typical sampling density, and



DRAFT

uncertainty in defining the actual contaminant spatial distribution. The rationale, as cited by USEPA, is based on the fact that vapor concentrations generally decrease with increasing distance away from a subsurface vapor source, and at some distance, the concentrations become negligible. The distance at which concentrations are negligible is a function of the mobility, toxicity, and persistence of the chemical, as well as the geometry of the source, subsurface materials, and characteristics of the building of concern.

Comment 29

BP agrees with the concern expressed in Table 6 of the guidance regarding the uncertainties posed by the use of indoor air sampling. It is practically impossible to separate the contribution to the total concentration coming from indoor sources from that coming from the subsurface sources under the building. (6)

Response 29 The Department concurs with the comment. However, prior to any indoor air sampling care must be taken to eliminate any potential sources. See pg. 2-5 of MADEP Indoor Air Sampling and Evaluation Guide. The guide is referenced in the vapor guidance and also available for download at: http://www.state.ma.us/dep/new.htm Specifics concerning soil gas and indoor air sampling will be addressed in the Technical Guidance Manual (TGM) revision.

Comment 30

Guidance, page 3, second paragraph:

Under SHS, if separate phase liquid is encountered beneath the site or within 100ft of the receptor at or above the water table, soil gas sampling or indoor air sampling is required.

Comment: Further clarification is necessary as to the location of the SPL that defines a complete exposure pathway. For example, if a site has SPL within 100 feet of a receptor, but a number of soil and groundwater samples collected 50 feet from the receptor identify no unacceptable risk to the receptor, the guidance does not indicate whether soil gas samples are still required to be collected. (6)

Response 30

If separate phase liquid (SPL) exists within 100 feet of a receptor, then sampling in or around the receptor to attain the Statewide Health standard is required. One may choose to assess the risk through sampling and assessment between the SPL and receptor. This however, represents procedures under the site-specific standard, which may be applied through a combination of standards remediation.


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Comment 31 Guidance, page 4, second paragraph:

If the groundwater concentration is greater than the J&E PA default screening levels, or if groundwater is less than 5 feet below the receptor, then the need to further evaluate or mitigate can be determined by comparison of measured soil gas or indoor air concentrations.

Comment: Why is the J&E model not considered valid when the groundwater is < 5 feet below the receptor? The Agency should consider not requiring further evaluation whenever the groundwater concentrations are below the default values, even when the depth to groundwater is < 5 feet. (6)

Response 31 The Department concluded through J-E modeling that groundwater concentrations between the appropriate MSC and J-E default levels when groundwater is less than 5 feet below the receptor could pose an indoor air problem and therefore require sampling.

Comment 32

Guidance, page 4, second paragraph:

The MSCIAQ are found in Table 3 and MSCSG is a function of the MSCIAQ and a transfer (or attenuation) factor of 0.01, from outside to inside the building.

Comment: The attenuation factor of 0.01 is not defined, as no transfer distance is given for the pathway. It appears to indicate that the transfer is from directly beneath the slab to directly into the building.

The attenuation factor depends on a number of site-specific parameters including, but not limited to (i) soil type, (ii) chemical, (iii) air exchange rate in the building, (iv) cracks in the slab, (v) the pressure difference between the soil and the building, and (vi) the distance from the source to the building. (6)

Response 32 The Department chose to use the transfer factor, from soil gas to indoor air, of 0.01 which is a conservative value relating concentrations in indoor air to concentrations in soil gas adjacent to a building based on a data report in Management of Manufactured Gas Plants Sites, Volume III: Risk Assessment, Gas Research Institute, 1987, pages 6-30 and 6-31. The Department chose to err on the side of conservatism, since the option exists to further evaluate the pathway on a site-specific basis if warranted.

Comment 33

Guidance, page 4, first paragraph in the Process for Soil Section:


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Also, if preferential exposure pathways are present and pass through the source or occur within 30 feet of the source, then the decision matrix requires that soil gas or indoor air sampling be performed.

Comment: This appears to indicate that a conduit or trench located 30 feet laterally away from the source is a preferential pathway, and therefore requires soil gas or indoor air sampling. A preferential pathway should be a subsurface feature that connects the source to the receptor. A subsurface feature located 30 feet laterally away from the source should not be considered to be a preferential pathway. (6)

Response 33 Page 22 of the draft guidance states that “a preferential pathway is defined as a natural (e.g., shallow rock or vertically fractured soil) or manmade (e.g., buried utilities) feature that creates a sufficiently direct pathway from a source to a receptor….” In addition, the preferential pathway can either pass through the source or occur with 30 feet of the source.

Comment 34

Guidance, page 19, Table 7

Comments: The Exposure Time, 24 hr/day, given in the Table may be too high. A more realistic number is 16 hr/day.

The Inhalation rate, 1.25 m3/h or 30 m3/day, for the nonresidential case may be too high. A more reasonable value is 20 m3/day. (6)

Response 34 The Department chose to use the same assumptions as promulgated in 25 Pa. Code250.307 under Inhalation Numeric Values.

Comment 35

Upon review of the “Vapor Intrusion into Buildings from Groundwater and Soil, Technical Guidance Manual”, Civil & Environmental Consultants, Inc. (CEC) believes that DEP has omitted from this guidance an EPA methodology that has been proven to accurately measure emissions from subsurface contamination. In 1986, EPA published the “Measurement of Gaseous Emission Rates from Land Surfaces Using an Emission Isolation Flux Chamber, User’s Guide1.” This guidance described a methodology to directly measure the surface emission rates of organic chemicals that volatilize from subsurface contamination. Once the emission rates from the subsurface contamination are measured, ambient air concentrations of these contaminants can be calculated and health risks to humans and the environment can be assessed. In recent years work has been completed using the flux chamber to measure vapor intrusion into buildings 2,3. The flux chamber methodology allows a direct measurement of vapor intrusion into the building. Once the intrusion rate is measured, the indoor air concentration due to


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volatilization from subsurface contamination can be calculated. The flux chamber methodology offers several advantages over the methods used in the Vapor Intrusion Guidance document. First, because the flux chamber measures only the chemicals being emitted from the subsurface contamination, there is no interference from chemicals that may be present in the ambient air environment that would be measured on indoor air samples. The resulting health risk assessment will not be complicated by the presence of chemicals measured on indoor air samples but that are not associated with the subsurface contamination. Second, because the flux chamber methodology is an actual measurement, there is no need to rely on the uncertainties of modeling, resulting in a more accurate assessment of indoor air concentrations due to volatilization of subsurface contamination. In addition, often the input values used in these models are not standardized and can be disputed, creating a more complicated process. These types of disputes are eliminated through using the flux chamber methodology. The State of California is working on guidance for using the flux chamber to assess vapor intrusion into indoor air. Frank Dellechaie of the California Department of Toxics Substances Control (DTSC) can be contacted at [email protected] , if you have questions regarding this application.

USEPA. Measurement of Gaseous Emission Rates from Land Surfaces Using an Emission Isolation Flux Chamber, User’s Guide. US EPA Monitoring Systems laboratory, Las Vegas, Nevada. EPA/600/8-86/008, February, 1986.

Schmidt, C.E., Zdeb, T. “The Measurement of Indoor Infiltration Through a Concrete Slab Using the US EPA Flux Chamber,” Presented at the Annual 1998 AWMA Conference, 98-TA9C.01, June, 1998, San Diego, CA.

Schmidt, C.E., Rubin, J. “Indoor Infiltration Assessments of VOC’s from Contaminated Groundwater Using the US EPA Flux Chamber.” Presented at the Annual 2000 AWMA Conference, June 2000, Salt Lake City, UT. (7)

Response 35 The Department wants to allow flexibility in the selection of sampling devices for soil gas. We do not endorse any one sampling device method but recommend in the guidance the most widely used, available, and accepted devices. The Department indicated on page 5 of the guidance “sampling soil and indoor air is complex and should be approached with caution”. Also, as indicated in Table 6 “there are significant difficulties with sampling indoor and soil gas. Therefore, it is beyond the scope of this document to fully define processes for sampling these media.” The Department would accept the flux chamber methodology as long as all data quality objectives have been met.

Comment 36

EPA released its draft “Supplemental Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway” in October 2001. EPA is planning to publish a substantially modified version of this guidance document in the Federal Register for public comment in September 2002 or as soon as it is ready. A comparison of the latest version of EPA’s


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guidance and PADEP’s guidance indicates a few significant differences which are summarized below.

Maximum depth limitation in process for groundwater: In the groundwater screening process for determining the residential/nonresidential volatilization to indoor air criteria, a maximum depth to contamination limit of 30 feet for sand and 15 feet for non-sand soils is given in PADEP’s guidance. EPA’s guidance specifies a 100-foot maximum depth limitation for all soils. EPA is concerned that the depths chosen by PADEP may not be conservative enough. Available data have indicated that certain volatile organic compounds (“VOCs”) in groundwater at these depths could pose an indoor air threat above a tolerable risk level. EPA believes that PADEP may have arrived at the 15-foot and 30-foot depths based on studies related to petroleum-based compounds, which tend to attenuate rapidly over relatively small distances. EPA suggests that PADEP should reexamine whether the depth limitations contained in the guidance are appropriate.

Soil screening table: PADEP’s Vapor intrusion Guidance uses the Johnson-Ettinger (J-E) Model to back calculate soil concentrations that will be protective of indoor air. EPA does not recommend using soil sampling analytical results for assessing whether or not the vapor intrusion pathway is complete, unless the soil samples are preserved immediately upon collection with methanol. The uncertainties associated with soil partitioning calculations and the uncertainties associated with soil sampling/chemical analyses (see EPA/600/SR-93/140) are so great that use of soil concentration for assessment of this pathway is not technically defensible. Soil vapor concentrations are more stable than soil concentrations near the source and since collecting soil vapor samples provides direct measurement and is not any more difficult than collecting soil samples, EPA has made a decision not to pursue soil concentration tables. Soil concentration data could be used in a qualitative sense to delineate a source. For example, high soil concentrations (e.g., > 1000 mg/kg TPH) would indicate impacted soils; unfortunately, the opposite is not always true and non-detect analytical results should not be interpreted to conclude the absence of a vapor source.

Comparison – PADEP vs. EPA groundwater screening levels: Although both EPA and PADEP utilized the Johnson-Ettinger model to back-calculate groundwater screening criteria for the protection of indoor air, the two agencies calculated vastly different results. PADEP’s values seem to be much less conservative (several orders of magnitude) than EPA’s/. This is because the State used a combination of less conservative model assumptions in its calculation, such as choosing a sandy clay loam as the vadose zone soil type rather than a more porous material such as sand. PADEP also input a very low soil air porosity that, in conjunction with the soil type chosen, served to minimize the modeled soil vapor diffusion. As a result, PADEP came up with an attenuation factor of 0.00001 which is outside EPA’s recommended scenario range of 0.1 to 0.0001. Very slight manipulation of certain model assumptions can result in drastically different results. EPA recommends that PADEP reevaluate the default values in the Johnson-Ettinger model so that the risk based groundwater screening criteria for individual VOCs are based on more conservative assumptions. (8)


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Response 36 The Department will consider new and previously unavailable information that will improve the scientific bases of our analyses and guidance. As new information becomes available over time, we will continue our efforts to update and make revisions to the guidance as deemed necessary. The Department believes that the factors and assumptions incorporated into our approach are representative of the conditions in Pennsylvania. The commenter was not able to provide the additional information noted in the comment above with respect to general references to data that disavow soil sampling in favor of soil gas sampling.


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