1.0 EPA/AEHS Vapor Intrusion Attenuation Workshop

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1 May 17, 2004 To: From: Subject: Karen Tomimatsu and Henry Schuver, EPA/OSW Robert Truesdale, RTI Final report describing VI attentuation workshop, database, analysis of attenuation factors, precluding factors, and recommendations for VI Guidance modifications; Subtasks 2.10 deliverable, EPA Work Assignment 5, EPA Contract No. 68-W RTI is submitting this memo report as the technical deliverable under Subtask 2.10 of this work assignment. As such it: # documents results and conclusions of the VI workshop # portrays new and existing data in VI database # identifies factors that can influence vapor attenuation measurements # discusses attenuation at sites with precluding factors # describes possible factors to consider for improving guidance based on available data.. Because the March VI conference provided additional data and insights about vapor intrusion phenomena, and our expert consultants put together the analyses needed to support this report during the conference, the deliverables listed individually under previous tasks have been combined into this single report. This report incorporates comments and revisions from the consultants on the April 7 draft report, along with their additional recommendations for possible improvements in the guidance suggested by data from the San Diego VI attenuation workshop. Section 1.0 describes the workshop and its content. Section 2 summarizes the conference results, as assembled by the experts at the conference, which also includes portrayals and analyses of both new and existing data in the VI database. 1.0 EPA/AEHS Vapor Intrusion Attenuation Workshop On March 16 and 17, the U.S. Environmental Protection Agency (EPA), in cooperation with the Association for Environmental Health and Sciences (AEHS), conducted a workshop on measured subsurface vapor-to-indoor-air attenuation factors. As a major activity under this work assignment, RTI supported this workshop, including subcontracting AEHS to reserve the conference facilities and procuring the services of nationally recognized vapor intrusion experts (Dr. Paul Johnson, Ian Hers, and Todd McAlary) to help review and select papers and provide questions, insights, and analyses during the conference. RTI also provided support in terms of preparing and distributing a call for papers and workshop announcement; selecting, notifying, and preparing presenters; preparing, and distributing the workshop agenda; working with AEHS to

2 VI Attenuation Workshop Report May 17, 2004 work through conference facilities and logistics; and providing direct support during the workshop in terms of organizing, moderating, and facilitating the proceedings. The two-day VI attenuation workshop focused specifically on what is known from measurements about the attenuation factor and vapor attenuation processes in the subsurface. EPA organized the workshop as part of their continuing work to update the draft Vapor Intrusion Guidance, recognizing that their efforts could be meaningfully informed by the increased experience and empirical data that practitioners and regulators continue to gain concerning VI attenuation. The workshop call for papers (Attachment A) was for presentations describing (1) preexisting and newly gathered attenuation-related data sets, (2) methods for correctly and effectively sampling and analyzing soil gas and indoor air data in the context of a vapor intrusion investigation, and (3) approaches for correctly interpreting VI attenuation data in the light of background concentrations from other vapor sources and site conditions that can impact results. 1.1 Workshop Attendance and Evaluation By all measures the workshop was a success. The call for papers resulted in 44 abstract submittals. Of these, the RTI team of experts and EPA selected 18 for platform presentations and 17 for a poster session that was added to the agenda to accommodate the larger than anticipated response to the call (the final agenda for the workshop is provided in Attachment B). In addition to the 35 presenters, 129 participants signed up and attended the workshop (the list of attendees is provided in Attachment C), with attendees from 31 states and 8 foreign countries. Organizations represented include industry, defense, EPA offices and Regions, state regulators, and consultants. Because the total attendance (172, counting experts, EPA, and RTI support staff) was much larger than the 100 that was originally planned for, RTI worked with AEHS to rent a larger hall, which could hold up to 200 along with the poster session. This hall was close to full for every session of the workshop. An evaluation was sent out after the conference to all attendees, and 33 forms have been returned to date. Table 1 summarizes the evaluation scores. As can be seen, responses have been very positive so far, with 82 percent of the question responses being in the two highest rating categories and 46 percent being in the highest. In terms of the rating the overall conference, all responses but one were in the highest two categories. 1.2 Workshop Content and Results As can be seen from the agenda in Attachment B, the presentations and posters held to the main topic of the conference and most presented data from studies that measured vapor intrusion attenuation, with a fewer number addressing measurement methods. Attachment D summarizes each of the platform presentations by summarizing results, information about the sites and buildings pertinent to vapor intrusions processes, and information about the attenuation factors presented. Attachment E summarizes selected poster presentations. Copies of the full presentations can be downloaded from the Indoor Air Vapor Intrusion Website at (look under Resources/Document Library). -2-

3 VI Attenuation Workshop Report May 17, 2004 Table 1. Summary of VI Workshop Evaluation Responses (33 responses) Number of Responses by Score Category 1 Question nr Did the workshop content adequately cover the subject matter (measured vapor attenuation coefficients)? Did workshop content meet your expectations? Will the information from this program be useful in your job? Did the workshop increase your knowledge of measuring vapor attenuation and interpreting vapor attenuation factors? How would you rate this program overall? Were the questions and presentations from the experts helpful in interpreting and conveying the workshop information? Cumulative percentages 46% 36% 14% 0.5% 1% 3% 1 5 = yes, definitely; 3 = somewhat; 1 = no, not at all; nr = no response 2 5 = excellent; 1 = poor Vapor Attenuation Factors The conference did include several sets of attenuation factors that are likely suitable for inclusion in the VO database. Some of the more notable attenuation factor datasets presented include: # Ron Mosely and Dominic Digiulio (EPA ORD) presented data from the Raymark Superfund site, where a chlorinated solvent plume underlies a neighborhood of older homes in Connecticut. This high-quality dataset (from an EPA ORD/Region 1 study) has subslab-to-indoor air attenuation factors for 6 chlorinated VOCs at 15 houses. Radon attenuation factors are also available. # Bill Wertz (NYSDEC) and Gerald McDonald (NYSDOH) presented data from the Endicott site in New York, where a chlorinated solvent plume from a former IBM facility underlies an older mixed commercial and residential neighborhood. This very large (over 400 homes total), high quality dataset of subslab-to-indoor air attenuation factors. Groundwater-to-indoor air attenuation factors are also possible, but will require reading groundwater concentrations off an isopach map. Phase 1 data from this site (27 buildings) is in the current VI database. Bill Wertz has just sent the Phase 2 data, which includes data on 66 buildings. # David Folkes (EnviroGroup Limited) presented a couple of talks based on data from the Redfields site in Colorado, where a residential/commercial neighborhood lies over a chlorinated solvent plume. This large, high-quality dataset contains over 5-years of groundwater and indoor air monitoring data for over 700 homes. Mean groundwater-to-indoor air attenuation factors are in the 10-5 to 10-7 range, with 10-3 values rarely occurring (usually near the plume boundary). There is some -3-

4 VI Attenuation Workshop Report May 17, 2004 correlation with groundwater depth but no apparent correlation with building or soil type. Redfield data for 27 homes are included in the VI database (from the original Region 8 database), and Region 8 is working to incorporated additional data from this site. # Todd McAlary (GeoSyntec Consultants, Inc.) presented soil gas to indoor air attenuation factors from a large set of data collected near a former industrial landfill site in Runcorn, United Kingdom. High quality data are available for 145 houses overlying bedrock and quarry fill deposits. The data generally support the generic attenuation factor of 10E-2 for deep soil gas to indoor air used in the Draft VI Attenuation Workshop Report April 7, 2004 OSWER VI Guidance. Upper limit alpha factors may be attributable to unique site conditions (highly permeable backfill subsurface, and possible pressure gradients from ocean winds). # Dave Mickunas (EPA ERTC) presented attenuation factors calculated using measurements by EPA s trace atmospheric gas analyzer (TAGA) mobile laboratory. In his study, 24-hour Summa canister and TAGA indoor air measurements compare favorably and the real-time TAGA data were very useful in tracking down indoor sources of VOCs. His data include both subslab- and groundwater-to-indoor air attenuation factors for 2 chlorinated hydrocarbons from a groundwater plume underlying 23 homes in Hopewell, NY. # Paul Sanders (NJDEP) presented results of a high quality study of vapor intrusion from a gasoline plume into 11 homes in Stafford, NJ. Indoor air, outdoor air, subslab, soil gas, and groundwater data are available and indicate that benzene, toluene, ethylbenzene, or xylene did not clearly impact indoor air quality even when present at parts-per-million levels in underlying groundwater. MTBE did appear in indoor air when underlying groundwater concentrations were above 500 ppm, with a groundwater-to-indoor air attenuation factor of about # Steve Washburn (ENVIRON) presented results of an indoor air investigation for a site in Philadelphia, PA, where a light nonaqueous phase liquid (LNAPL) petroleum hydrocarbon plume lies under residential and commercial buildings. On-plume and off-plume indoor air data do not show discernible differences, indoor air concentrations are not discernibly higher than outdoor concentrations and are similar to similar to literature background, suggesting little or no indoor air impacts in spite of free product under the buildings. # Lindsay Breyer (Walsh Environmental) presented a screening level investigation to evaluate the vapor intrusion pathway at a site in Mandan, ND, where a spilled diesel fuel LNAPL plume underlies a residential neighborhood. Although the data were limited to a single, one-day sampling event, concentrations of diesel-related compounds in indoor air were relatively low, suggesting significant attenuation between the LNAPL and the residences. Groundwater and soil gas attenuation factors could be suitable for the VI database. # Jeff Kurtz (EMSI) provided a poster describing measured versus model-predicted vapor intrusion attenuation at Alliant Techsystems Dry Creek Road site in Littleton, -4-

5 VI Attenuation Workshop Report May 17, 2004 CO, where a solvent plume in shallow groundwater underlies homes near the site. Shallow soil vapor to indoor air attenuation factor was around 0.01 and the measured groundwater to indoor air attenuation factor was about 10-5, which is appropriate for the weathered clayey, silty, sandstone at the site and consistent with the JE model predictions. Paired samples, information on the methodology, and good agreement between measurements and model predictions suggest a high quality dataset. # Carolyn Mayer (Philip Services) and Chris Waldron (Pioneer Technologies) presented a poster about the Philip Services site in Seattle, WA, where releases of chlorinated solvents and petroleum products have contaminated groundwater at a former TSD facility and in the surrounding area, a mixed industrial and residential neighborhood. Attenuation data from this site is currently being added to the indoor air vapor intrusion database by EPA Region Evaluation of Vapor Intrusion Data: Observed Attenuation Factors The primary focus of EPA s March 2004 workshop was to determine (1) what can be learned from measurements of vapor attenuation processes in the subsurface and (2) how this knowledge can be applied to improve the default vapor attenuation factors in the draft Vapor Intrusion Guidance. An attenuation factor represents the ratio of indoor air concentrations to subsurface soil gas or groundwater concentrations at some depth below a building. In EPA s guidance, the media-specific generic screening attenuation factors (also known as alphas) are # groundwater to indoor air: # soil gas to indoor air: 0.1 (shallow); 0.01 (deep) # subslab to indoor air: 0.1 # crawlspace to indoor air: 1. These attenuation factors play a key role in regulatory guidance for the vapor intrusion (VI) exposure pathway as they are used to calculate media-specific VI action levels in draft EPA, state, and local regulatory guidance. They are designed to calculate concentrations in the media of interest (groundwater and soil gas) at which regulators can confidently assert that VI does not and will not in the future pose an unacceptable health risk to occupants of overlying buildings. During the VI attenuation workshop, Dr. Helen Dawason (EPA Region 8) and Ian Hers (Golder Associates) reviewed the experience and empirical data that practitioners and regulators have provided before and during the workshop and evaluated these data in the light of the current VI guidance. Their insights and conclusions from this preliminary evaluation of preexisting and newly gathered attenuation-related data sets and methods are summarized herein. 2.1 VI Attenuation Data Review and Evaluation Past and current efforts to evaluate VI attenuation data focus on several steps that are designed to identify and select attenuation factors representative of VI processes and conditions across the United States. This selection process is necessary to address the challenges associated with evaluating a large dataset of attenuation measurements, including: -5-

6 VI Attenuation Workshop Report May 17, 2004 # a large range in number of measurements at the individual buildings and sites (from single measurement location and chemical to thousands of measurements) # widely varying site conditions # variable data quality # confounding influence of background VOC sources # variable data documentation # other measurement uncertainties. To meet these challenges, the review and evaluation of vapor attenuation data should apply criteria that analyze VI data to identify valid attenuation factors. These criteria include a screen of data quality, filters designed to winnow out inaccurate attenuation factors (e.g., background indoor air concentrations), and investigation to identify factors that influence vapor attenuation. Data quality screening The goal of data quality screening is to develop a subset of adequately qualified data that are representative of site conditions. Review of the sampling and analysis methodology, including the quality assurance/quality control (QA/QC) protocols, is a critical step in this process, both to confirm that the proper sampling and analysis methodologies were correctly applied and to determine whether the datasets adequately represent the site. Important factors to consider when determining whether samples are adequately representative include # Whether samples represent the same time frame. Concurrent analyses between indoor air and the media of concern are preferred, although if groundwater shows a consistent time trend indoor air samples may not need to be concurrent. # Whether background VOC concentrations are influencing results. Background investigations (e.g., indoor surveys) should show no obvious indoor sources and indoor air concentration should be less than subslab concentrations. In addition, widely disparate alphas for multiple chemicals in a single sampling event can indicate indoor sources. # Whether samples give reasonable estimates of the media concentrations of interest. For example, depending on methodology, soil gas samples may be biased, and vapor concentrations next to the house may not represent what is underneath. # Whether unusual circumstances are present, such as advective transport, that can result in an anomalously high attenuation factor. The data quality screen also should be based on the data quality objectives for the evaluation to be conducted. Background indoor air concentrations are perhaps the most common factor leading to inaccurate vapor attenuation measurements. In the context of a vapor intrusion investigation, background is defined as VOCs that originate from sources other than the vapor intrusion pathway. Background sources can be outdoor ambient air or VOC-containing products used in the home. The importance of background varies from chemical to chemical. Although there are a variety of sources for CHCs in indoor and outdoor air, background concentrations are particularly problematic for PHCs, as they are found in gasoline as well a a -6-

7 VI Attenuation Workshop Report May 17, 2004 variety of other household products. Because of this fact, it is very difficult to measure significant vapor intrusion for PHCs relative to background, especially for benzene, toluene ethylbenzene, and xylene (BTEX), which are common gasoline constituents and prevalent in household cleaning products, solvents, and glues. The potential effect of background on measured vapor attenuation factors is evident in the equations for the empirical attenuation factor versus the attenuation factor due only to vapor intrusion Empirical: " = (C vapor + C background ) / C source Vapor-derived: " = (C vapor / C source ) Thus, as background concentrations increase, the empirical vapor intrusion factor also increases, overpredicting the impact of vapor intrusion on indoor air quality. If one cannot distinguish a vapor intrusion indoor air concentration from background, the empirical attenuation factor becomes an upper bound value, but the effect from background is less significant when source concentrations are high. There were several methods presented during the workshop for distinguishing background indoor air concentrations from those from the vapor intrusion pathway. # Use a tracer compound found in the subsurface but not in indoor air (e.g, 1,1- dichloroethylene, radon, trimethylpentane) to calculate an attenuation factor that can then be applied to other chemicals of concern. # Use correlations between media concentrations and consistent ratios between different chemicals in different media to fingerprint the vapor intrusion source and distinguish background concentrations. # Compare indoor concentrations to literature values to determine when background concentrations might be present and what their contribution might be. # Compare indoor concentrations to concentrations in similar nearby homes. # Compare concurrent, nearby outdoor air concentrations to indoor concentrations. # Use pathway samples to measure concentrations at the point of entry (e.g., in a sump or above foundation crack). # Compare indoor air quality in a home under natural condition with indoor air quality under a positively pressurized condition. Contaminants that do not decrease (or disappear) with pressurization may be attributed to indoor sources. # Conduct site-specific predictive modeling to provide insight on a reasonable range for the measured attenuation factor. -7-

8 VI Attenuation Workshop Report May 17, 2004 A balance of evidence approach, using as many of these methods as possible, will provide the greatest chance of correctly determining the impacts of background concentrations in a building. Where background cannot be adequately distinguished, it is important to qualify the alpha as a possible upper bound value. Filters (to get at real alphas) To help select alphas that represent site conditions, filters can be applied to the data to screen out attenuation factors that are more prone to error, especially from the effect of elevated indoor air background concentrations. These filters establish a preference for attenuation factors based on media samples that # are greater than a site-specific background level (e.g., an outdoor air concentration) or orders of magnitude above typical background level # represent a high source concentration (i.e., a high source strength), which are less sensitive to errors from background indoor air concentrations, measurements near the detection limit, or measurements near the periphery of a groundwater plume # are greater than risk-based concentration limits. Filters can also be applied to eliminate selected chemicals where a concentration ratio evaluation or other information indicates suspect data. This takes advantage of the fact that true vapor intrusion alphas should be similar for different chemicals along with information about the relative likelihood a chemical may be from indoor sources. For example if a trichloroethylene (TCE) alpha is 10-5 and a tetrachloroethylene (PCE) alpha is 10-2, the TCE value would be the best to use for vapor intrusion because it is lower and because PCE is more likely to originate from an indoor source (such as dry cleaned clothes). Factors influencing alphas A final step in using empirical data to evaluate or develop attenuation factors is to identify the factors influencing VI attenuation factors. Based on analysis of available data to date, as well as studies of VI phenomena, the following factors are know to be significant in their effects on vapor intrusion: # Chemical class. With respect to vapor intrusion phenomena, a relevant classification is petroleum hydrocarbons (PHCs), which are nonchlorinated and are readily degraded under aerobic subsurface conditions, versus chlorinated hydrocarbons (CHCs) which are more resistant to degradation and therefore more persistent in the environment. Because of this difference, it has been argued that the default attenuation factors for PHCs should be lower than CHCs for groundwater and deep soil gas. PHCs also tend to be more common than CHCs in products around the house and in outdoor air. Therefore PHC indoor air concentrations are more prone to be confounded by background sources. # Chemical. There also can be significant differences between VI contaminants within a chemical class. Some chemicals are more likely than others to have indoor sources other than VI; for example, TCE has been removed from many consumer products and is less prevalent as a background contaminant than PCE, which is still -8-

9 VI Attenuation Workshop Report May 17, 2004 used for dry cleaning. With respect to PHCs, methyl-tert-butyl ether (MTBE) is more soluble and resistant to degradation than benzene, toluene, and xylenes (BTEX), and therefore tends to lead a groundwater plume and show less attenuation along VI pathways. # Site conditions that can affect VI include geology, weather/climate, depth to source, water table depth, and whether nonaqueous phase liquids (NAPL) are present. # Building conditions that can influence attenuation include foundation type (slab, crawlspace, full basement); heating, ventilation, air conditioning (HVAC) system, age and weathertightness, pressure differential with outside air, and building air exchange rate; activities within the building (e.g., hobbies, equipment storage) that serve as background indoor air VOC sources. Although past and current data evaluation efforts have paid attention to such factors, the available information does vary considerably depending on the study or data source. A draft list of important factors influencing VI was distributed to workshop presenters prior to the conference and is included in Attachment F. Wider distribution of this list, especially to potential data providers for the VI database, could improve future analyses of the impact of these factors on VI attenuation. 2.2 Preliminary Results - Past and Current Data During the conference, both Dr. Helen Dawson and Ian Hers conducted a preliminary review of the VI data, including a comparison of the original November 2002 and new data. This review included groundwater, soil gas, subslab, and crawlspace attenuation factors, and preliminary data quality screening and filtering of the data based on the approach described above. Table 2 summarizes the sites included in this review. Table 2. Review of Sites in VI Database (Existing, New, and to be Added) Dataset State Contaminant class Number of buildings in database Description of Contamination Original Database (November 2002) Alliant 1 CO CHC 4 homes solvent plume CDOT CO CHC 6 apts. solvent plume Eau Claire MI CHC 3 homes solvent plume Hamilton-Sunstrand CO CHC 13 homes solvent plume Lowry AFB CO CHC 13 homes solvent plume Mountain View CA CHC 7 homes solvent plume MADEP MA CHC, PHC 12 homes (mult. sites) various Redfields 1 CO CHC 23 homes solvent plume Uncasville CN CHC 5 homes solvent plume Pilot Database (November 2003) Endicott 1 NY CHC 27 buildings solvent plume Davis Manufact. 1 MI CHC 1 home, 1 commercial solvent plume Strip malls TX CHC 2 commercial solvent plume -9-

10 VI Attenuation Workshop Report May 17, 2004 Table 2. (continued) Dataset State Contaminant class Number of buildings in database Description of Contamination Route 9B Landfill ME Misc. 6 homes, 1 commercial landfill plume Paulsboro NJ PHC 1 home gasoline plume Stafford 1 NJ PHC 1 home, 1 commercial gasoline plume Expanded Database (March 2004) Cowpens SC CHC 1 home solvent plume Endicott 1 NY CHC +66 buildings solvent plume Philips 1 WA CHC 2 homes solvent plume Jackson 1 WY CHC 1 apt., 3 homes solvent plume? Twins Inn CO CHC, etc. 1 school, 1 home chemical plume Philadelphia PA PHC 2 homes, 2 commercial LNAPL plume Runcorn UK CHC 145 homes landfill vapor plume Cibola NM CHC 6 homes solvent plume Juniper CHC Chatterton PHC Alameda CA PHC gasoline plume Virginia VA PHC gasoline plume 1 Indicates site was the focus of a presentation during the March 2004 VI Attenuation Workshop. Dr. Dawson showed graphs of the earlier attenuation factor data versus newer data (received since November 2002) that plotted indoor air versus media concentrations or attenuation factors versus media concentrations. Ian Hers focused on plotting the empirical data on the semisite-specific attenuation factors from Figure 3 in EPA s 2002 VI guidance. Because they worked independently to produce these graphs during the conference, their underlying datasets differ to some degree. Preliminary observations and findings are summarized below by media (groundwater, soil gas, subslab, and crawlspace). The figures referenced in the text below are attached immediately following the text of this report. Groundwater Attenuation Factors Figure 1 shows the new and original (November 2002) groundwater to indoor air data from the VI database, with the indoor air concentration plotted against the groundwater vapor concentration calculated using Henry s law. This figure shows that the new data lie within the same range as the original data. Figure 2 is the same plot except that it distinguishes between chlorinated hydrocarbon (CHC) and petroleum hydrocarbon (PHC) data. Although the PHC points tend to be in the higher concentration region, and include some of the lowest attenuation factors in the dataset, it does not appear that there are enough data at this time to conclude that PHC sites constitute a separate population or to establish a separate, lower attenuation fact for PHCs. Figure 3 plots the groundwater attenuation factors for CHCs against their corresponding groundwater vapor concentrations. This figure illustrates how source strength impacts the spread of attenuation factors, with a greater spread of attenuation factors occurring at a lower source strength. This is partly due to a greater impact of background concentration on the attenuation factors; as source strength decreases, so does the concentration of indoor air contaminants from -10-

11 VI Attenuation Workshop Report May 17, 2004 vapor intrusion, and background indoor air become a more significant component of the overall indoor air concentration. In addition, measured values near the detection limit, or near the periphery of a groundwater plume, are more subject to errors that can impact the accuracy of vapor intrusion estimates where source strength is low. The importance of source strength is further supported by the data shown in Figure 4, which is the Figure 3 plot with all attenuation factors based on an indoor air concentration with a risk of 10-6 or less removed from the dataset. Removing these low-concentration based alphas reduces the number of values above the current default groundwater to indoor air attenuation factor (0.001), although the shape of the plots remain similar. Figure 5 plots empirical groundwater attenuation factors against the semi-site-specific attenuation factors presented in Figure 3a of the 2002 VI guidance 1. The observed attenuation factors (which are mostly CHCs) are plotted by water table depth. Of the 17 residential and 5 commercial sites represented in the figure, about one-half of the sites are based on multiple data points, where the 90 th percentile value was plotted. The other one-half have fewer data points and are based on the maximum concentration. The data were filtered for significant vapor intrusion based on pathway analysis, tracer (1,1-DCE) and/or comparison to background. The figure shows that all attenuation factors are at or below the guidance attenuation factor curves, with the maximum groundwater attenuation factor approximately equal to 10-3, the VI guidance default. Figure 6 is a similar plot, limited to PHC compounds. Unlike the CHC data, most of these sites had limited data points, and maximum values are plotted on the figure. At all but two sites, it is not possible to distinguish indoor air from background; therefore, these attenuation factors are conservative upper bound values. In almost all cases, maximum alpha s are at least one order of magnitude lower than those from VI Guidance Figure 3. Soil Gas Attenuation Factors Figure 7 plots indoor air VOC concentrations against soil gas concentrations for sites in the original and new VI database. The variability in these results makes it difficult to say anything definitive about soil gas to indoor air attenuation except that better protocols are needed to generate more consistent soil gas data. Figure 8 plots a different set of empirical soil gas attenuation factors against the semi-sitespecific attenuation factors presented in Figure 3b of the 2002 VI guidance. The observed CHC attenuation factors are plotted by sampling depth. Of the 6 residential sites represented in the figure, two are based on multiple data points, where the 90 th percentile value was plotted, and 4 have fewer data points and are based on the maximum concentration. Although four of the sites are well above the VI guidance alphas, they are high because extraordinary site conditions, a shallow soil gas sampling depth (that may not represent sub-building conditions), or low source strength. As with the Figure 7 data, the high data variability and limited number of data points in Figure 8 make it difficult to draw more general conclusions about soil gas attenuation. 1 Figure 3 supports Question 5 (Q5) of the guidance, which allows users to apply lessconservative default attenuation factors when depth to groundwater and soil type are known. The attenuation factors lines in Figure 3 were derived using EPA s Johnson and Ettinger model spreadsheets with most variables set at conservative, default values. -11-

12 VI Attenuation Workshop Report May 17, 2004 Figure 9 shows data for soil gas attenuation factors from PHC sites and compares them with the Figure 3b alphas from the 2002 VI Guidance. Although the data are from a limited number of measurements (all site values are maximums), and the impact of background contributions has not been assessed, all measured values are one to several orders of magnitude below the guidance alphas, suggesting significant attenuation between soil gas and indoor air for these PHC sites. Sub Slab Attenuation Factors The empirical subslab attenuation factor dataset has expanded markedly from the original 2002 VI database, mainly from the measurements available from the Endicott site in NY State. Figure 10 plots subslab attenuation factors from Endicott and four other sites. Most values are below the 0.1 guidance default. Figure 11 plots this same dataset without attenuation factors based on indoor air concentrations below a 10-6 risk-based level. Removal of these low concentration values removes most of the attenuation factors above the 0.01 attenuation line, with the 4 values above this level being for chemicals that are often found in indoor sources. These data indicate that generic screening alpha of 0.1 is conservative. The higher concentration data suggest that a lower generic screening subslab to indoor air alpha of 0.05 or 0.01 may also be protective. Crawl Space Attenuation Factors Data on crawlspace to indoor air attenuation are still very limited. Figure 12 plots the available data against the VI Guidance default of 1. These data suggest that the generic screening alpha of 1.0 is a good upper bound value, but more data are needed. Precluding Factors Two factors, including a shallow (< 5 feet) water table depth and a fractured vadose zone, that preclude the application of the generic attenuation factors in the current vapor intrusion guidance. Data from several sites presented at the San Diego workshop and in the IAVI database suggest that the current generic attenuation factors are protective in some cases even when precluding factors are present. Two Michigan sites, including the wet basement site presented by Karen Berry-Sparks at San Diego and the Eau Claire site in the original VI database, have water tables within 5 feet of the basement floor and yet have attenuation factors below the generic soil-to-groundwater attenuation factors. The Redfields and CDOT sites in Colorado also exhibit high attenuation in spite of fractured bedrock in the vaodse zone underying the homes. These cases suggest that the applicability of these precluding factors be revisited. 3.0 Conclusions and Recommendations Conclusions of this preliminary evaluation of currently available VI attenuation measurements include: # For groundwater to indoor air, both the generic screening alpha of and the semi-site-specific screening values in Figure 3 of the 2002 VI Guidance are good upper bound values for CHCs, even for sites with precluding factors (including -12-

13 VI Attenuation Workshop Report May 17, 2004 high water tables and fractured bedrock). Data also suggest that these values are probably too high for PHCs, but additional data are needed to set an appropriate level. # For soil gas to indoor air, measurement variability makes it difficult to conclude as to the appropriateness of the default values. A standard sampling methodology, careful implemented with clear data quality objectives, is needed for more consistent measurements. # For subslab to indoor air, the generic screening alpha of 0.1 is conservative. Attenuation factors based on higher concentration data suggest that a lower generic screening alpha may also be protective. # For crawlspace to indoor air, very limited data suggest that the generic screening alpha of 1.0 is a good upper bound value. Other conclusions and recommendations that may drawn from the various workshop presentations include: # Measurements of actual ventilation rates using radon indicate that the EPA default Q soil flowrate may be too low (Mosely). # Radon can be useful as a tracer and surrogate chemical for determining vapor attenuation factors for a building, but radon attenuation factors tend to be about a factor of 3 higher than VOC attenuation factors (Mosely). # Expect consistent alphas across contaminants for VOC intrusion into a building. Contaminants that exhibit lower attenuation may be influenced by background indoor air sources (Mosely and others). # Comparing the ratios of the contaminant of concern (COC) to 1,1-dichlorotheylene or trichloroethylene in indoor air to the ratios in the source media (soil gas or groundwater) may be useful for identifying background influences (Folkes). # Subslab sampling is very useful for evaluating background influences (various). # Several subslab samples, taken along transects of a basement floor may be needed to adequately characterize subslab vapor concentrations (DiGuilio). # For larger sites, deep soil gas surveys (mapping profiles across the area of concern), along with accurate groundwater plume maps, can provide the information needed to demonstrate that the VI pathway is incomplete, which can in turn reduce the need for subslab sampling (McAlary). # The scatter in available soil gas data suggests that more consistent, effective sampling methodologies are needed. Soil gas probes should be installed and sampled with the same care as groundwater monitoring wells. Accurate methods, -13-

14 VI Attenuation Workshop Report May 17, 2004 including procedures that do not add much to sampling costs, are available but need to be formalized and used more widely (McAlary). # There is a seasonal variation in indoor air due to differences in HVAC system operation. For Colorado sites, the highest concentrations occur in the winter and the lowest concentrations are observed in the summer. Spring or fall is the best time to sample to estimate annual average indoor air concentrations. (Folkes) # Several studies and available data in the IAVI database suggest that PHCs attenuate (most likely by way of biodegradation) more than CHCs in soil vapor. However additional data are needed to support lower attenuation factors (Hers). # Non-BTEX PHCs (e.g., trimethylpentane, TMP) may serve as tracers as these components are not common in houseold products other than PHC fuel (Sanders). # For studies where both compounds are present, MTBE, TMP, and cyclohexane appear to be attenuated less than other petroleum constituents (e.g., BTEX) (Sanders). # The identification of reliable criteria for delineating the areal extent of soil-gas contamination (for the protection of indoor air) could help regulators cost-effectively address the vapor intrusion pathway by using well-delineated institutional controls (Schuver and Sowinski). # Better techniques for reliably characterizing the extent of contamination in the subsurface soil-gas environment, and the verifiable prediction of the concentrations that may be found near the building foundation (e.g., subslab, adjacent samples), may be some of the major challenges for the future (Schuver). # Several studies illustrate that soil vapor samples taken close to the building foundation can underestimate subslab concentrations. This suggests that additional methodological work is needed before adjacent samples can reliably predict the subsurface vapor concentrations entering the building (Hers). # Trees can extract and volatilize VOCs from shallow groundwater plumes to ambient air (Berry Spark). -14-

15 VI Attenuation Workshop Report May 17, 2004 Indoor Air versus Groundwater (Vapor) Concentrations Original versus New Data 1000 Indoor Air Concentration (ug/m3) Original Data New Data Alpha = Groundwater (Vapor) Concentration (ug/m3) Figure 1. Comparison of original and new groundwater to indoor air attenuation data. -15-

16 VI Attenuation Workshop Report May 17, Indoor Air versus Groundwater (Vapor) Concentrations CHC versus PHC Indoor Air Concentration (ug/m3) CHC PHC Alpha = Figure Groundwater (Vapor) Concentration (ug/m3) Comparison of petroleum and chlorinated hydrocarbon groundwater to indoor air attenuation data -16-

17 VI Attenuation Workshop Report May 17, 2004 GW-IA Alphas vs Groundwater (Vapor) Concentrations CHCs 1.00E E-01 ~ 5 ug/l GW-IA Alpha 1.00E E E-04 Alpha = E E E Groundwater (Vapor) Concentration (ug/m3) Figure 3. Comparison of groundwater to indoor air attenuation factors with groundwater source strength (groundwater vapor concentration). -17-

18 VI Attenuation Workshop Report May 17, 2004 GW-IA Alphas vs Groundwater (Vapor) Concentrations CHC Indoor Air Concentration > 10-6 Screening Level 1.00E E-01 ~ 5 ug/l GW-IA Alpha 1.00E E E-04 Alpha = E E E Groundwater (Vapor) Concentration (ug/m3) Figure 4. Comparison of groundwater to indoor air attenuation factors with groundwater source strength - alphas with indoor air concentrations below 10-6 cancer risk removed. -18-

19 VI Attenuation Workshop Report May 17, 2004 Groundwater to Indoor Air Attenuation Factors - Figure 3a (Q5) All Data - Residential 1.E-02 Sand Sandy Loam Loamy Sand 1.E-03 Loam CDOT 90th Redfields 90th Hamilton 90th Alpha 1.E-04 Lowry 90th Juniper 90th Davis Max cis-12-dce (sand & gravel) 1.E-05 MAPEP 1 Max TCE (sand) MAPEP 2 Max TCE (sand) Eau Claire Max TCE Uncasville Max PCE (Sand) 1.E-06 Figure Depth (m) Alliant Max TCE Mountainview Max TCE (Silty, Clayey Sand) Chatterton BTX (sand, DP=0 Pa) Empirical groundwater attenuation factors (90 th percentile or maximum by site) plotted against semi-site-specific attenuation factors from Figure 3 (Question 5) in EPA s 2002 VI guidance (solid symbols indicate indoor air levels well above typical background; open symbols indicate levels within typical background range). -19-

20 VI Attenuation Workshop Report May 17, 2004 Groundwater to Indoor Air Attenuation Factors - Figure 3a Petroleum Hydrocarbon - Residential 1.E-02 Maximum values, limited number data points Sand Sandy Loam Vapour Attenuation Factor 1.E-03 1.E-04 1.E-05 1.E-06 Golder Associates Figure 6. Solid symbols indicate measured indoor air concentrations above typical background levels, open symbols indoor air concentrations within range typical background, therefore upper bound alpha Depth (m) Loamy Sand Loam MADEP 3 Max BTEX (sand) MADEP 5 Max BTEX (sand) MADEP 6 Max BTEX (sand, sm. gravel) MADEP 7 Max BTEX (sand, sm. gravel) Paulsboro Max BTEX (sand, sm. silt) Alameda Max BTEX (sand) Stafford Max BTEX (sand) Stafford MTBE (sand) MADEP 4 Max BTEX (sand) Empirical groundwater attenuation factors for PHCs plotted against attenuation factors from Figure 3 (Question 5) in EPA's 2002 VI guidance (solid symbols indicate indoor air levels well above typical background; open symbols indicate levels within typical background range). -20-

21 VI Attenuation Workshop Report May 17, 2004 Indoor Air versus Soil Gas Concentrations 1000 Indoor Air Concentration (ug/m3) Uncasville, CT Alliant, CO Jackson, WY Marble, MA Mountain View, CA Georgetown, WA Alpha = 0.1 Alpha = Figure Soil Gas Concentration (ug/m3) Empirical soil gas attenuation factors (alphas). -21-

22 VI Attenuation Workshop Report May 17, E+00 Soil Vapor to Indoor Air Attenuation Factors Figure 3b Chlorinated Solvents & HCBD - Residential Sand 1.E-01 UK site advection significant Borderline site based on source strength screening criteria Shallow Depth (0.4 m) Sandy Loam Loamy Sand Loam Alpha Figure 8. 1.E-02 1.E-03 1.E Depth (m) Uncasville Max PCE (Sand) Mountain View Max TCE (Silty, Clayey Sand) Juniper 90th TCE (sand & gravel) Davis Manu Max cis-12- DCE (sand & gravel) UK Runcorn 90th HCBD (fill) Cibola TCE Max (Sand) Golder Associates Empirical soil gas attenuation factors (90 th percentile or maximum by site) plotted against semi-site-specific attenuation factors from Figure 3 (Question 5) in EPA s 2002 VI guidance. -22-

23 VI Attenuation Workshop Report May 17, 2004 Soil Vapor to Indoor Air Attenuation Factors Figure 3b Petroleum Hydrocarbon - Residential 1.E-02 1.E-03 Maximum values, limited number data points Sand Sandy Loam Loamy Sand Loam Alpha 1.E-04 1.E-05 1.E-06 Figure 9. Solid symbols indicate measured indoor air concentrations above typical background levels, open symbols indoor air concentrations within range typical background, therefore upper bound alpha Depth (m) Chatterton BTX (sand, DP=0 Pa) Chatterton BTX (sand, DP>=10 Pa) Paulsboro BTEX (sand, sm. silt) Virginia BTEX (clay stone saprolite) Stafford Max BTEX (sand) Stafford MTBE (sand) Stafford 224 TMP (sand) S. Philadelphia Benzene (sand, silt layer) Golder Associates Empirical soil gas attenuation factors for PHC sites plotted against semi-sitespecific attenuation factors from Figure 3 (Question 5) in EPA s 2002 VI guidance. -23-

24 VI Attenuation Workshop Report May 17, 2004 Indoor Air versus Subslab Vapor Concentrations (Sites) Indoor Air Concentration (ug/m3) Endicott LAFB Georgetown Stafford Jackson alpha = Subslab Vapor Concentration (ug/m3) Figure 10. Subslab to indoor air attenuation factors from the VI database. -24-

25 VI Attenuation Workshop Report May 17, 2004 Indoor Air versus Subslab Vapor Concentrations (Indoor Air Concentration > OSWER 10-6 Screening Level) Indoor Air Concentration (ug/m3) DCA Benzene PCE Endicott LAFB Georgetown Stafford Jackson alpha = Subslab Vapor Concentration (ug/m3) Figure 11. Subslab to indoor air attenuation factors from the VI database with lower concentration data (indoor air < 10-6 risk level) removed. -25-

26 VI Attenuation Workshop Report May 17, 2004 Indoor Air versus Crawlspace Vapor Concentrations (Sites) 100 Indoor Air Concentration (ug/m3) LAFB Jackson alpha = Crawlspace Vapor Concentration (ug/m3) Figure 12. Crawlspace to indoor air attenuation factors. -26-

27 Attachment A EPA/AEHS Vapor Intrusion Attenuation Workshop Call for Papers

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29 CALL FOR PAPERS Vapor Intrusion Attenuation Workshop A Study of Observed Vapor Intrusion Attenuation 14 th Annual West Coast Conference on Soils, Sediments and Water March 15-18, 2004, Marriott Mission Valley, San Diego, California On the behalf of the U.S. Environmental Protection Agency s (EPA s) Office of Solid Waste and Emergency Response (OSWER), you are invited to submit an abstract for consideration for presentation at an EPA-sponsored workshop on subsurface vapor-to-indoor-air attenuation factors. This attenuation factor plays a key role in regulatory guidance for the vapor intrusion (VI) exposure pathway. This quantity represents the ratio of indoor air concentrations to subsurface soil gas concentrations at some depth and is used to calculate VI action levels in draft EPA, state, and local regulatory guidance. In these guidance documents, selection of an appropriate attenuation factor involves a combination of empiricism and modeling. This one and one-half day, EPA-sponsored workshop focuses specifically on what is known from measurements about the attenuation factor and vapor attenuation processes in the subsurface. As EPA continues working to update the draft Vapor Intrusion Guidance, we recognize that our efforts may be meaningfully informed by the increased experience and empirical data that practitioners and regulators continue to gain concerning VI attenuation. This call for papers is for presentations describing (1) preexisting and newly gathered attenuation-related data sets, (2) methods for correctly and effectively sampling and analyzing soil gas and indoor air data in the context of a vapor intrusion investigation, and (3) approaches for correctly interpreting VI attenuation data in the light of background concentrations from other vapor sources and site conditions that can impact results. Session 1 -- Sampling and Analysis of VI Attenuation Setting the stage for VI attenuation data discussions, the first segment of this workshop will cover recently developed VI sampling techniques, including real-time and composite sampling methods. Presentations should convey the latest knowledge on topics such as soil gas sampling, subslab sampling, indoor and outdoor air sampling, field and laboratory analytical methods, flux chambers, high purge-volume sampling, pneumatic testing, and/or ventilation testing. Presentations may also address methods of VI attenuation data interpretation, statistical analysis, temporal trends, and data reliability, as well as issues related to identifying and accounting for background sources of indoor air contamination and accounting for site-specific factors that are influencing results. Session 2 -- Observed VI Attenuation -- Empirical Evidence This segment covers the main focus of the workshop. Presenters will provide an overview of currently available VI attenuation data, including recent VI attenuation studies. Presentations may cover any of three distinct attenuation scenarios: (1) attenuation observed between subslab or crawlspace vapor and indoor air, (2) attenuation between deeper soil gas and indoor air, and/or (3) attenuation between groundwater and indoor air. Presentations may address VI attenuation for chlorinated solvents, petroleum hydrocarbons, or other compounds of interest and should cover ways to identify site-specific factors that affect the extent of VI attenuation, account for background concentration, and develop reliable empirical attenuation factors.

30 Conference/Workshop Information Information on the 14 th Annual West Coast Conference on Soils, Sediments and Water can be found at The Vapor Intrusion Attenuation Workshop will be an all-day workshop held on the first day of the conference (March 15, 2004). Up to 100 participants will be accepted into the workshop. The workshop will be followed the next evening by a interactive discussion and wrap up where presenters and workshop participants will engage in a moderated discussion to exchange opinions concerning the meaning of the VI attenuation data as it relates to broader issues of vapor intrusion. Paper/Presentation Submission Guidelines Interested parties should submit an abstract by January 15, 2004, to the following address for evaluation and selection ( submittals are preferred): Henry Schuver 5303W USEPA Headquarters - Ariel Rios Building 1200 Pennsylvania Avenue, N.W. Washington, DC schuver.henry@epa.gov ; and please cc: Robert Truesdale at rst@rti.org. Abstracts should be 500 words or less and should include a title and, for each author, name, degree, affiliation, complete address, telephone number, and address. Abstracts will selected based on relevance to the workshop topics described above. Preference will be given to papers that describe high quality empirical data sets that contribute to the understanding of vapor intrusion phenomena. Submitters may attach additional information (e.g., information related to data quality, citations for prior published work) if it will aid in the selection process. Submitters also may be asked for additional information as we proceed through the evaluation process. Selected authors will prepare a 20 minute presentation for the workshop and are expected to submit a paper for publication in the Fall 2004 issue of Ground Water Monitoring & Remediation (GWMR), which will be dedicated to papers from the workshop. Instructions and guidelines for submitting papers to GWMR can be found at -2-

31 Attachment B EPA/AEHS Vapor Intrusion Attenuation Workshop Agenda

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33 AGENDA Vapor Intrusion Attenuation Workshop A Study of Observed Vapor Intrusion Attenuation 14 th Annual West Coast Conference on Soils, Sediments and Water March 15-18, 2004, Marriott Mission Valley, San Diego, California The U.S. Environmental Protection Agency s (EPA s) Office of Solid Waste and Emergency Response (OSWER), welcomes you to our workshop on subsurface vapor-to-indoor-air attenuation factors. This attenuation factor plays a key role in regulatory guidance for the vapor intrusion (VI) exposure pathway. This quantity represents the ratio of indoor air concentrations to subsurface soil gas concentrations at some depth and is used to calculate VI action levels in draft EPA, state, and local regulatory guidance. EPA has sponsored this one and one-half day workshop to gather the latest data and interpret what is known from attenuation measurements and subsurface vapor attenuation processes. Platform Session - Monday, March 15 Time Title and Presenter 9:00 AM Welcome - Objectives & Overview Henry Schuver, U.S. EPA, Office of Solid Waste Background, Indoor Sources, and Measurement Methods 9:15 AM Use of Radon and Perfluorocarbons Measurements to Allocate VOCs Measured in Indoor Air Among their Various Sources Ronald. B. Mosley, U.S. EPA, Office of Research and Development 9:30 AM A COC Ratio Approach for Defining Extent of Vapor Intrusion and Background David J. Folkes, P.E., EnviroGroup Limited 9:45 AM Upward Vapor Intrusion Assessment: Real-time, Continuous Monitoring Data to the Rescue? Dr. Blayne Hartman, H&P Mobile Geochemistry 10:00 AM Sub-Slab Air Sampling Protocol and Analysis to Support Assessment of Vapor Intrusion Dr. Dominic DiGiulio, U.S. EPA, Office of Research and Development 10:20 AM Questions 10:30 AM Break Observed Attenuation Factors - Chlorinated Hydrocarbon Data 11:00 AM Vapor Intrusion in Endicott, NY: Observed Differences in the Concentrations of Chlorinated Volatile Organic Vapors (CVOCs) in Basement and Subslab Samples Dr. William E. Wertz, New York State Department of Environmental Conservation Gerald McDonald, New York State Department of Health 11:20 AM Attenuation Factors and Multiple Lines of Evidence for Evaluation of Potential Vapor Intrusion Pathways - Experience with the Grants Chlorinated Solvents Plume Site, Cibola County, New Mexico John Lowe and Jeff Minchak, CH2M HILL