Evaluation of flow controllers used with evacuated canisters to assess VOC exposures in occupational and non-occupational environments.

Ideally, measuring exposures to volatile organic compounds should allow for modifying sampling duration without loss in sensitivity. Traditional sorbent-based sampling can vary sampling duration, but sensitivity may be affected when capturing shorter tasks. Diaphragm and capillary flow controllers allow for a range of flow rates and sampling durations for air sampling with evacuated canisters. The goal of this study was to evaluate the extent to which commercialized capillary flow controllers satisfy the bias (±10%) and accuracy (±25%) criteria for air sampling methods as established by the National Institute for Occupational Safety and Health (NIOSH) using the framework of ASTM D6246 Standard Practice for Evaluating the Performance of Diffusive Samplers to compare their performance with diaphragm flow controllers in a long-term field study. Phase 1 consisted of a series of laboratory tests to evaluate capillary flow controller flow rates with respect to variations in temperature (-15-24 °C). The results demonstrated a slight increase in flow rate with lower temperatures. In Phase 2, the capillary flow controller was evaluated utilizing a matrix of parameters, including time-weighted average concentration, peak concentration (50-100× base concentration), air velocity across the sampler inlet (0.41-0.5 m/s), relative humidity (20-80%), and temperature (10-32 °C). Comparison of challenge concentrations with reference concentrations revealed the aggregate bias and overall accuracy for four tested compounds to be within the range of criteria for both NIOSH and ASTM standards. Additionally, capillary flow controllers displayed lower variability in flow rate and measured concentration (RSD: 2.4% and 4.3%, respectively) when compared with diaphragm flow controllers (RSD: 6.9% and 7.2%, respectively) for 24-hr laboratory tests. Phase 3 involved further testing of flow rate variability for both diaphragm and capillary flow controllers in a field study. The capillary flow controller displayed a lower level of variability (RSD: 5.2%) than the diaphragm flow controller (RSD: 8.0%) with respect to flow rate, while allowing for longer durations of sampling.

Distribution of select per- and polyfluoroalkyl substances at a chemical manufacturing plant.

Per- and polyfluoroalkyl substances (PFAS) are used in various industrial products; however, they pose serious health risks. In this study, soil, soil gas, and groundwater samples were collected at a PFAS manufacturing facility in New Jersey, USA, to determine the presence and distribution of PFASs from the soil surface to groundwater and at various distances from the presumed source. Fluorotelomer alcohols (FTOHs) were detected in soil (< 0.26-36.15 ng/g) and soil gas (160-12,000 E µg/m3), while perfluorinated carboxylic acids (PFCAs) were found in soil (4.3-810 ng/g), soil gas (<0.10-180 µg/m3), and groundwater (37-49 µg/L). FTOH and PFCA concentrations decreased as the distance from the presumed source increased, suggesting that PFCAs are likely to migrate in groundwater, whereas FTOHs primarily move in the vapor phase. The presence of PFAS in the groundwater, soil, and soil gas samples indicate its potential for vapor intrusion; thus, some PFAS may contribute to indoor air inhalation exposure. To the best of our knowledge, this is the first report on the quantification of volatile PFAS in soil gas at a PFAS manufacturing facility.

Evaluation of Long-Term Flow Controller for Monitoring Gases and Vapors in Buildings Impacted by Vapor Intrusion.

This study evaluated the use of a long-term capillary flow controller paired with an evacuated canister for indoor air exposure monitoring in a vapor intrusion (VI) environment with trichloroethylene in comparison to the traditional method utilizing a diaphragm flow controller. Traditionally, air sampling with 6 L evacuated canisters equipped with diaphragm flow controllers has been best suited for 8 to 24 h samples. New advances in capillary flow controllers can extend sampling to up to 3 weeks by reducing flow rates to 0.1 milliliters min-1. During six 2 wk sampling events, conventional diaphragm flow controller canisters were used to collect 24 h samples simultaneously with capillary flow controllers collecting 2 wk samples. Testing was performed at four indoor locations in buildings impacted by VI with co-located samples for each method at each location. All samples were analyzed using GC/MS, and the results were statistically analyzed to produce a direct comparison of the two sampling systems. Ninety-two percent of the 14 d capillary samples were within the 95% levels of agreement of the average concentration of the diaphragm flow controllers. The ability to collect 14 days of data, with less occupant disturbance, allows for improved exposure assessments and thus improved risk management decisions.

An alternative generic groundwater-to-indoor air attenuation factor for application in commercial, industrial, and other nonresidential settings.

The default groundwater-to-indoor air attenuation factor (AF) of 10-3 (0.001) to assess the vapor intrusion (VI) pathway and generate VI screening levels for groundwater was developed by the United States Environmental Protection Agency (EPA) based on chlorinated volatile organic compound (VOC) indoor air and groundwater data collected in residential buildings and compiled in EPA's 2012 VI database. In their VI guidance published in 2015, EPA recognized that this default AF may be overly conservative for nonresidential buildings. In 2015, the Department of Defense (DoD) began developing a first-of-its-kind VI database to assess AFs at commercial and industrial buildings at DoD installations and support the development of alternative generic AF values. This database was expanded in 2019 to include 76 buildings at 22 DoD installations across the United States and is comparable in size to the EPA VI database. The DoD database includes chlorinated VOC data from groundwater and indoor air samples collected from multiple sampling zones within these buildings. Empirical groundwater-to-indoor air AFs were calculated using similar screening methods employed by EPA, including a source strength screen, to filter out potential background source contributions unrelated to VI. Analysis of indoor air-groundwater data pairs found that there is more attenuation occurring from groundwater to indoor air in DoD commercial and industrial buildings relative to residential buildings and that the DoD buildings' AFs are one to four orders of magnitude lower than EPA's residential-based default of 10-3. The results support the use of a generic groundwater AF of 10-4 (0.0001) to support VI assessment and develop groundwater screening levels specific to large commercial and industrial buildings as an alternative to the residential default AF.Implications: The use of groundwater-to-indoor air attenuation factors (AFs) is a key component of vapor intrusion (VI) pathway assessments and VI screening-level development for groundwater. Currently, the United States Environmental Protection Agency (EPA) and many state regulatory agencies use a default groundwater AF of 10-3 (0.001) based on chlorinated volatile organic compound (VOC) data collected in residential buildings. VI assessment data collected at Department of Defense (DoD) installations indicate that there is significantly more groundwater-to-indoor air attenuation occurring at DoD commercial and industrial buildings. For that reason, the default AF of 10-3 results in groundwater screening levels that are overestimating VI-related risks in these types of building. The DoD data support the use of a generic groundwater AF of 10-4 (0.0001) for conducting VI assessment and developing groundwater screening levels at large commercial and industrial buildings.

Neutral Per- and Polyfluoroalkyl Substances, Butyl Carbitol, and Organic Corrosion Inhibitors in Aqueous Film-Forming Foams: Implications for Vapor Intrusion and the Environment.

Per- and polyfluoroalkyl substances (PFAS), butyl carbitol, and corrosion inhibitors are components of aqueous film-forming foams (AFFFs). Volatile (neutral) fluorotelomerization (FT)- and electrochemical fluorination (ECF)-based PFAS, butyl carbitol, and organic corrosion inhibitors were quantified in 39 military specification (MilSpec), non-MilSpec, and alcohol resistant-AFFF concentrates (undiluted) from 1974 to 2010. Fluorotelomer alcohols were found only in FT-based AFFFs and N-methyl- and N-ethyl-perfluoroalkyl sulfonamides, and sulfonamido ethanols were found only in ECF-based AFFFs. Neutral PFAS and benzotriazole, 4-methylbenzotriazole, and 5-methybenzotriazole occurred at mg/L levels in the AFFFs, while butyl carbitol occurred at g/L levels. Neutral PFAS concentrations in indoor air due to vapor intrusion of a nearby undiluted AFFF release are estimated to be anywhere from 2 to >10 orders of magnitude higher than documented background indoor air concentrations. Estimated butyl carbitol and organic corrosion inhibitor concentrations were lower than and comparable to indoor concentrations recently measured, respectively. The wide range of neutral PFAS concentrations and Henry's law constants indicate that field, soil-gas measurements are needed to validate the estimations. Co-discharged butyl carbitol likely contributes to oxygen depletion in AFFF-impacted aquifers and may hinder the natural PFAS aerobic biotransformation. Organic corrosion inhibitors in AFFFs indicate that these are another source of corrosion inhibitors in the environment.

Cost Comparison of Soil Vapor Extraction and Subslab Depressurization for Vapor Intrusion Mitigation.

Soil vapor extraction (SVE) can be applied for remediation, and also as an alternative to sub-slab depressurization (SSD) for vapor intrusion (VI) mitigation. This study compares capital, operation, and treatment costs of SVE and SSD systems using data collected during a multi-year demonstration project conducted at eight buildings in an urban setting. The capital cost of the SVE system is substantially less than the estimated total capital cost of individual SSD systems. The SVE operating costs are higher, especially in the early operating years when it is being operated for mass removal and treatment. As a result, the cumulative SVE system cost rises above that of the SSD systems in the sixth year of operation. A significant portion of the operations and maintenance cost advantage of the SSD systems comes from the assumption that off-gas treatment is not required. Alternative cases show SVE costs are likely to be lower in scenarios where numerous small buildings requiring independent SSD systems overlie the SVE zone of influence. Conversely, SSD systems are less costly for cases with few small buildings overlying the SVE zone of influence. An additional benefit of SVE is continued mass removal. In a situation where an existing SVE can be repurposed for VI protection from residual volatile organic carbon (VOC) mass, the SVE cumulative costs over 30years can remain lower than the cost of installing and operating SSD systems in multiple buildings.

An alternative generic subslab soil gas-to-indoor air attenuation factor for application in commercial, industrial, and other nonresidential settings.

The default subslab soil gas (SSSG)-to-indoor air attenuation factor (AF) of 0.03 to assess the vapor intrusion (VI) pathway and generate VI screening levels for SSSG was developed by the United States Environmental Protection Agency (EPA) based on chlorinated volatile organic compound (VOC) indoor air and SSSG data collected in residential buildings and compiled in EPA's 2012 VI database. In their VI guidance published in 2015, EPA recognized that this default AF may be overly conservative for nonresidential buildings. In 2015, the Department of Defense (DoD) began developing a first-of-its-kind VI database to assess AFs at commercial and industrial buildings at DoD installations and support the development of alternative generic AF values. This database was expanded in 2019 to include 76 buildings at 22 DoD installations across the United States and is comparable in size to EPA's VI database. The DoD database includes chlorinated VOC data from SSSG and indoor air samples collected from multiple sampling zones within these buildings. Empirical SSSG-to-indoor air AFs were calculated using the same screening methods employed by EPA to filter out potential background source contributions unrelated to VI, including a source strength screen. Analysis of indoor air-SSSG data pairs found that there is substantially more attenuation occurring from SSSG to indoor air in DoD commercial and industrial buildings relative to residential buildings, and that the DoD buildings' AFs are one to three orders of magnitude lower than EPA's residential-based default of 0.03. The results support the use of a generic SSSG-to-indoor air AF of 10-3 (0.001) to support VI assessment and develop SSSG screening levels at large commercial and industrial buildings as an alternative to the residential default AF.Implications: The use of subslab soil gas (SSSG)-to-indoor air attenuation factors (AFs) is a key component of vapor intrusion (VI) pathway assessments and VI screening level development for SSSG. Currently, the United States Environmental Protection Agency (EPA) and many state regulatory agencies use a default AF of 0.03 based on chlorinated volatile organic compound (VOC) data collected in residential buildings. VI assessment data collected at Department of Defense (DoD) installations indicate that there is significantly more SSSG-to-indoor air attenuation occurring at DoD commercial and industrial buildings. For that reason, the default AF of 0.03 results in SSSG screening levels that are overestimating VI-related risks in these types of building. The DoD data support the use of a generic SSSG-to-indoor air AF of 10-3 (0.001) for conducting VI assessment and developing SSSG screening levels at large commercial and industrial buildings as an alternative to the residential default AF.

Key Design Elements of Building Pressure Cycling for Evaluating Vapor Intrusion-A Literature Review.

Building pressure cycling (BPC) is becoming an increasingly important tool for studying vapor intrusion. BPC has been used to distinguish subslab and indoor sources of vapor intrusion as well as to define reasonable worst case volatile organic compound mass discharge into a structure. Analyses have been performed both semi-quantitatively with concentration trends and quantitatively with more rigorous flux calculation and source attribution methods. This paper reviews and compares the protocols and outcomes from multiple published applications of this technology to define the key variables that control performance. Common lessons learned are identified, including those that help define the range of building size and type to which BPC is applicable. Differences in test protocols are discussed, recognizing that the complexity of the test protocol required depends on the particular objectives of each project. Research gaps are identified and tabulated for future validation studies and applications.

Temporary vs. Permanent Sub-slab Ports: A Comparative Performance Study.

Vapor intrusion (VI) is the migration of subsurface vapors, including radon and volatile organic compounds (VOCs), from the subsurface to indoor air. The VI exposure pathway extends from the contaminant source, which can be impacted soil, non-aqueous phase liquid, or contaminated groundwater, to indoor air-exposure points. Therefore, contaminated matrices may include groundwater, soil, soil gas, and indoor air. VOC contaminants of concern typically include halogenated solvents such as trichloroethene, tetrachloroethene, and chloroform, as well as petroleum hydrocarbons, such as the aromatic VOCs benzene, toluene, and xylenes. Radon is a colorless radioactive gas that is released by radioactive decay of radionuclides in rock and soil that migrate into homes through VI in a similar fashion to VOCs. This project focused on the performance of permanent versus temporary sub-slab sampling ports for the determination of VI of halogenated VOCs and radon into an unoccupied house. VOC and radon concentrations measured simultaneously in soil gas using collocated temporary and permanent ports appeared to be independent of the type of port. The variability between collocated temporary and permanent ports was much less than the spatial variability between different locations within a single residential duplex. The agreement of the majority of VOC and radon concentrations, 0-36% relative percent difference, and 2-19% relative standard deviation respectively, of each sub-slab port (SSP) type was achieved even though the clay portion of the seal of the temporary ports was visibly desiccated and cracked. Post sampling leak test results suggested that the temporary SSP desiccation and cracking were not as detrimental to the port seal performance as would have been expected, this suggests that the Teflon tape portion of the seals served an important function. Post sampling leak tests are advisable (in addition to pre-sampling leak tests) when temporary ports are used to collect a time-integrated sample over a period of several hours. These results suggest that temporary sub-slab sampling ports can provide data equivalent to that collected from a permanent sub-slab sampling port. However, (1) only one type of seal material was tested in one location, (2) the seals were installed by experts with rigorous quality control, and; thus, (3) these results may not apply to all types of temporary seals and all building foundations.

Variables affecting emissions of PCDD/Fs from uncontrolled combustion of household waste in barrels.

The uncontrolled burning of household waste in barrels has recently been implicated as a major source of airborne emissions of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). A detailed, systematic study to understand the variables affecting emissions of PCDD/Fs from burn barrels was performed. The waste composition, fullness of the barrel, and the combustion conditions within the barrel all contribute significantly to determining the emissions of PCDD/Fs from burn barrels. The study found no statistically significant effect on emissions from the Cl content of waste except at high levels, which are not representative of typical household waste. At these elevated Cl concentrations, the impact of Cl on PCDD/F emissions was found to be independent of the form of the Cl (inorganic or organic). For typical burn conditions, most of the PCDD/F emissions appear to be associated with the later stages of the burn when the waste is smoldering. Polychlorinated biphenyls (PCBs) were also measured for a subset of the tests. For the nominal waste composition, the average emissions were 76.8 ng toxic equivalency units (TEQ)WHO98/kg of waste combusted, which suggests that uncontrolled burning of household waste could be a major source of airborne PCDD/Fs in the United States.

Aquatic ecological risks due to cyanide releases from biomass burning.

Aquatic toxicity due to the creation and mobilization of chemical constituents by fire has been little studied, despite reports of post-fire fish kills attributed to unspecified pyrogenic toxicants. We examined releases of cyanides from biomass burning and their effect on surface runoff water. In laboratory test burns, available cyanide concentrations in leachate from residual ash were much higher than in leachate from partially burned and unburned fuel and were similar to or higher than the 96-h median lethal concentration (LC50) for rainbow trout (45 microg/l). Free cyanide concentrations in stormwater runoff collected after a wildfire in North Carolina averaged 49 microg/l, again similar to the rainbow trout LC50 and an order of magnitude higher than in samples from an adjacent unburned area. Pyrogenic cyanide inputs, together with other fire-related stressors, may contribute to post-fire fish mortalities, particularly those affecting salmonids.