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I'm thrilled to share with you the program of Remtech Europe 2021. This important environmental conference is made of 23 sessions fully ONLINE. Any session is completely FREE.To follow any session you have to register in our website with a valid email. To reserve your seat, receive the presentations in pdf and receive your Certificate of Attendance of the session you will attend, you have to register in the Google form of each session. In each form you would find also the detailed program and beginning and end in different time zones. Reserve your seat today!SESSION 1 (Organized by JRC-European Commission) From policy talking to industry actions: Zero Pollution for Soil Mon 20 SEPTEMBER 09:00 – 13.00 CEST 2 (Organized by US Army Corps of Engineers) TRAINING COURSE - PFAS: characterization, environmental impact, remediation strategies Mon 20 SEPTEMBER 14.30 – 19.00 CEST 3 Sustainable management of contaminated sites Mon 20 SEPTEMBER 14.30 – 16.30 CEST 4 Waste tailings and acid mine drainage: challenges for Mining Sites Mon 20 SEPTEMBER 17.00 – 19.00 CEST 5 Bioremediation and phytoremediation in agricultural, industrial, and military sites Tue 21 SEPTEMBER 09.00 – 11.00 CEST 6 Oil and hydrocarbons impacted sites Tue 21 SEPTEMBER 11.30 – 13.30 CEST 7 HRSC, High Resolution Site Characterization Tue 21 SEPTEMBER 11.30 – 13.30 CEST 8 (Organized by ASTM) TRAINING COURSE - ASTM STANDARDS: PFAS, Sediment and Climate Resilience Tue 21 SEPTEMBER 14.30 – 19.00 CEST 9 Innovative, digital and smart characterization techniques tools Tue 21 SEPTEMBER 14.30 – 16.30 CEST 10 Circular Economy: how to apply it in the context of the next Generation EU Tue 21 SEPTEMBER 17.00 – 19.00 CEST 11 Soil remediation: can we deal in a sustainable way? Wed 22 SEPTEMBER 09.00 – 11.00 CEST 12 DNAPL and chlorinated compounds: optimize the process to achieve the target Wed 22 SEPTEMBER 11.30 – 13.30 CEST 13 (Organized by SERDP-ESTCP) TRAINING COURSE - Current Approaches for Vapor Intrusion Site Investigation and Mitigation Wed 22 SEPTEMBER 14.30 – 19.00 CEST 14 (Organized by Ramboll) TRAINING COURSE - Sustainability assessment as a tool for a more sustainable and resilient remediation of soils, groundwater and sediments Wed 22 SEPTEMBER 14.30 – 16.30 CEST 15 PFAS, remediating the forever chemical Wed 22 SEPTEMBER 17.00 – 19.00 CEST 16 Microplastics and sediments: two main threats for ports and coastal areas Thu 23 SEPTEMBER 09.00 – 11.00 CEST 17 Sustainathon Thu 23 SEPTEMBER 14.00 – Fri 24 SEPTEMBER 14:00 CEST 18 Aeriforms and vapor intrusion: measures and models Thu 23 SEPTEMBER 11.30 – 13.30 CEST 19 Groundwater remediation in difficult conditions Thu 23 SEPTEMBER 11.30 – 13.30 CEST 20 (Organized by AESAS) TRAINING COURSE - State of the art of contaminated sites in Brazil Thu 23 SEPTEMBER 14.30 – 19.00 CEST 21 River environment: managing impacts from different sources Fri 24 SEPTEMBER 09.00 – 11.00 CEST 22 Wastewater and sewer sludge, handling the last link in the chain Fri 24 SEPTEMBER 11:30 – 13.30 CEST 23 TRAINING COURSE: Wastewater control and seawater quality: it is possible to do it acting differently? Fri 25 SEPTEMBER 14.30 – 19.00 CEST free to share to your colleagues or to any contacts that you think he/she may be interested. REMEMBER THAT THE CONFERENCE IS FREE, NO FEES. JOIN US !See you online!Laurie A. ChilcoteRemtech Europe Ambassador ... See MoreSee Less
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Decontamination and Decommissioning of Warehouses - Gela Industrial Site. - Author: Mariangela Venco (ENI Rewind) RemTech Expo ... See MoreSee Less
We are excited to announce our Brazil Patent BR 11 2018 004186-6 has been granted!#remediation #vaporintrusion #contaminatedsites #vaporpin #vi #coxcolvin #patent #Brazil ... See MoreSee Less
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We are excited to participate in the virtual seminar Vapor Intrusion: Sampling with Confidence for the Mid-Atlantic region, with Mark Mank of the Maryland Department of the Environment, Todd Creamer of Geosyntec Consultants, Christina Lewis at Langan Engineering & Environmental Services, Craig Cox at Cox-Colvin and Associates, Inc. and our own William Elcoate and Andy Rezendes. This event is free. NJ LSRP CEC Application for credits is pending. Registration is open: ... See MoreSee Less
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Main Content

August 2018 Article

In 2012, EPA released a report titled, EPA’s Vapor Intrusion Database: Evaluation and Characterization of Attenuation Factors for Chlorinated Volatile Organic Compounds and Residential Buildings. The information in the database was critical to EPA’s derivation of soil-gas and groundwater Vapor Intrusion Screening Levels (VISLs).


Vapor Intrusion (VI) is the process in which chemicals associated with gasoline, dry cleaning fluid, and various other volatile substances, migrate from soil or groundwater sources and enter buildings. Readers of this column will recognize the term “attenuation”, which is the decline in concentration as vapors migrate from source to receptor. Understanding how much attenuation takes place during vapor migration is useful in two ways. If we understand the amount of attenuation between, say, a groundwater source and an overlying building, we can use groundwater concentration data to predict indoor-air vapor concentrations. Groundwater is usually far less costly to analyze than indoor air. Conversely, if we start with a chemical’s Regional Screening Level (RSL) or some other maximum allowable concentrations in indoor air, we can use our understanding of attenuation to determine the screening levels for soil gas and groundwater.

In EPA’s 2012 Draft VI guidance, EPA derived soil-gas and groundwater screening levels by modeling the amount of vapor attenuation. They estimated that vapor concentrations in indoor air equaled approximately 1/10th of concentrations directly beneath the floor in subslab soil gas, and expressed this ratio as an Attenuation Factor (AF) of 0.1. Deep soil gas and groundwater AFs were assumed to equal 0.01 and 0.001, respectively. Accordingly, subslab soil-gas, deep soil-gas, and groundwater screening levels equaled indoor-air screening levels times 10, 100, and 1,000, respectively. (Groundwater VISLs were also adjusted for groundwater-to-air vapor partitioning using Henry’s constants, as discussed in the January 2018 Focus on the Environment newsletter). Due to the complexities of soil-to-indoor-air attenuation, EPA only briefly attempted to predict VI from soil, with their Johnson & Ettinger spreadsheets, last updated in 2004.

To refine their understanding of AFs, EPA compiled data from their own investigations and from outside investigators, which would allow them to compare indoor vapor concentrations to subsurface concentrations. The dataset was limited to chlorinated volatile organic compounds (CVOCs) from residential settings. The results were published in EPA’s 2012 Vapor Intrusion Database publication.

A graph showing the ratio of indoor air to subslab soil gas, (EPA’s Figure 12), is shown below.

Had the AF for subslab soil gas actually equaled 0.1, all of the data points would have fallen on the second diagonal line from the top. Instead, the points fall, on average, between the third and fourth diagonal lines, corresponding to an AF of 0.003. So one’s best guess of indoor air vapor concentrations would equal subslab concentrations x 0.003, and the subslab screening levels would equal indoor-air screening levels / 0.003. Because there’s a fair amount of scatter in the data, EPA updated their default subslab soil-gas AF and attenuation factors using a ratio of 0.03, to allow for uncertainty.

The ratio of indoor air to exterior soil gas, which is typically collected below 5 feet with a drilling rig, (EPA’s Figure 20), is shown graphically below.

The exterior soil-gas plot shows approximately the same 0.003 ratio of indoor air / soil gas concentrations as subslab soil gas. Accordingly, EPA revised both the subslab and the exterior soil-gas default AFs to 0.03, so that all soil-gas screening levels equal indoor-air screening levels / 0.03. Notice that the exterior soil-gas plot also shows far more scatter than the subslab-soil-gas plot, which suggests that subslab is better for predicting VI. Subslab soil gas is also cheaper and easier to collect than exterior soil gas, if you don’t mind putting holes in the floor.

The ratio of indoor air to vapor concentrations directly above groundwater, (EPA’s Figure 16), can be seen in the plot below.

Had the AF for groundwater vapor actually equaled the default AF of 0.001, the data points would have fallen on the fourth diagonal line from the top. Instead, the data points surround the fifth line, corresponding to an actual groundwater AF of 0.0001. EPA kept the default AF of 0.001 to allow for uncertainty.

Thus, EPA’s indoor-air VISLs are divided by 0.03 (multiplied x 33) to derive soil-gas VISLs, and indoor VISLs are divided by 0.001 (multiplied x 1,000) to derive groundwater VISLs.

But there’s more to the story. Besides EPA’s tenfold multiplier to account for uncertainty, other factors make soil-gas and groundwater VISLs unrealistically low in many situations. Among them:

  • The VI database was based on residential data. Commercial/Industrial (CI) buildings often have far higher indoor-air exchange rates, and higher ceilings, which dilutes soil gas and reduces VI more than in residential settings.
  • The database was built on data from CVOCs, which resist chemical breakdown. The attenuation of Petroleum Hydrocarbons (PHCs) is often far greater.
  • Most of EPA’s groundwater data did not meet the Agency’s own criteria for inclusion in the database. Yao, Verginelli, Suuberg, and Eklund’s article in Groundwater Monitoring & Remediation, (2018) describes how 70% of the indoor-air-to-groundwater pairs were separated by more than 30 meters (98 feet) laterally. EPA’s 2015 VI Guidance considers the VI lateral separation distance, or “footprint”, to be 100 feet from the source for CVOCs, and 30 feet for PHCs (EPA’s 2015 Petroleum VI Guidance). Yao, et al. estimate that vapor attenuation from groundwater is 10 x greater than EPA’s estimate.
  • VI-risk is usually estimated on the basis of the highest subsurface concentration. Actual VI results from a mix of lower and higher soil-gas vapor concentrations, especially near source areas typical of industrial facilities.

Accordingly, in our experience, the risk of VI based on subsurface data is hugely exaggerated, at least at CI sites. Assuming that indoor-air vapor concentrations equal the maximum subslab concentration x 0.03 overestimates risk by 1,000 or more. Also, consider that the risk from constituents in indoor air may already be exaggerated to account for uncertainties. For example, the cancer risk for tetrachloroethene (perchloroethene, PCE) is exaggerated by 1,000, after applying three uncertainty factors of 10x. It’s appropriate to take subsurface contamination seriously and investigate the risk of VI, but an exceedance of subsurface VISLs by a factor of 10x or 100x, especially at CI sites, rarely indicates a VI problem, and treating it as a crisis brings fear to occupants and unnecessary expense to responsible parties.