Assessing Community Vulnerability to Extreme Events in the Presence of Contaminated Sites and Waste Management Facilities: An Indicator Approach.

Communities across the world are facing extreme events, such as excessive heat, droughts, floods, and wildfires. In the presence of contaminated sites and waste management facilities, communities must consider the impacts of potential releases from these sites due to such events. Impacts of extreme events on sites and consequently on surrounding, often disadvantaged communities result from complex interactions between natural, physical, and social factors. A conceptual framework was developed to identify and provide a shared understanding of key vulnerabilities and pathways that transcend disciplines. A transparent and replicable method was developed to create mappable indicators that represent contaminated sites, waste facilities, contaminant transport via air and water, and population sensitivities. This method can be applied as a screening step to assist states and local communities in prioritizing targeted strategies and resources and determining where in-depth assessments are needed. These indicators can facilitate communication with a broad audience more easily than complex modeling approaches or aggregated indices. Case study results demonstrate the importance of considering indicators in conjunction with each other. The indicator method was developed together with U.S.-based partners, but can be adapted for other countries seeking to understand the potential impacts of extreme events on contaminated sites and communities.

Building resilience to extreme weather events in Phoenix: Considering contaminated sites and disadvantaged communities.

The interplay of contaminated sites, climate change, and disadvantaged communities are a growing concern worldwide. Worsening extreme events may result in accidental contaminant releases from sites and waste facilities that may impact nearby communities. If such communities are already suffering from environmental, economic, health, or social burdens, they may face disproportionate impacts. Equitable resilience planning to address effects of extreme events requires information on where the impacts may be, when they may occur, and who might be impacted. Because resources are often scarce for these communities, conducting detailed modeling may be cost-prohibitive. By considering indicators for four sources of vulnerability (changing extreme heat conditions, contaminated sites, contaminant transport via wind, and population sensitivities) in one holistic framework, we provide a scientifically robust approach that can assist planners with prioritizing resources and actions. These indicators can serve as screening measures to identify communities that may be impacted most and isolate the reasons for these impacts. Through a transdisciplinary case study conducted in Maricopa County (Arizona, USA), we demonstrate how the framework and geospatial indicators can be applied to inform plans for preparedness, response, and recovery from the effects of extreme heat on contaminated sites and nearby populations. The indicators employed in this demonstration can be applied to other locations with contaminated sites to build community resilience to future climate impacts.

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.

Observation of Conditions Preceding Peak Indoor Air Volatile Org Compound Concentrations in Vapor Intrusion Studies.

Temporal and spatial variability of indoor air volatile organic compound (VOC) concentrations can complicate vapor intrusion (VI) assessment and decision-making. Indicators and tracers (I&T) of VI, such as differential temperature, differential pressure, and indoor radon concentration, are low-cost lines of evidence to support sampling scheduling and interpretation of indoor air VOC sampling results. This study compares peak indoor air chlorinated VOC concentrations and I&T conditions before and during those peak events at five VI sites. The sites differ geographically and in their VI conceptual site models (CSM). Relative to site-specific baseline values, the results show that cold or falling outdoor temperatures, rising cross slab differential pressures, and increasing indoor radon concentrations can predict peak VOC concentrations. However, cold outdoor air temperature was not useful at one site where elevated shallow soil temperature was a better predictor. Correlations of peak VOC concentrations to elevated or rising barometric pressure and low wind speed were also observed with some exceptions. This study shows how the independent variables that control or predict peak indoor air VOC concentrations are specific to building types, climates, and VI CSMs. More I&T measurements at VI sites are needed to identify scenario-specific baseline and peak related I&T conditions to improve decision-making.

Field Study of Soil Vapor Extraction for Reducing Off-Site Vapor Intrusion.

Soil vapor extraction (SVE) is effective for removing volatile organic compound (VOC) mass from the vadose zone and reducing the potential for vapor intrusion (VI) into overlying and surrounding buildings. However, the relationship between residual mass in the subsurface and VI is complex. Through a series of alternating extraction (SVE on) and rebound (SVE off) periods, this field study explored the relationship and aspects of SVE applicable to VI mitigation in a commercial/light-industrial setting. The primary objective was to determine if SVE could provide VI mitigation over a wide area encompassing multiple buildings, city streets, and subsurface utilities and eliminate the need for individual subslab depressurization systems. We determined that SVE effectively mitigates offsite VI by intercepting or diluting contaminant vapors that would otherwise enter buildings through foundation slabs. Data indicate a measurable (5 Pa) influence of SVE on subslab/indoor pressure differential may occur but is not essential for effective VI mitigation. Indoor air quality improvements were evident in buildings 100 to 200 feet away from SVE including those without a measurable reversal of differential pressure across the slab or substantial reductions in subslab VOC concentration. These cases also demonstrated mitigation effects across a four-lane avenue with subsurface utilities. These findings suggest that SVE affects distant VI entry points with little observable impact on differential pressures and without relying on subslab VOC concentration reductions.

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.

Evidence of a sewer vapor transport pathway at the USEPA vapor intrusion research duplex.

The role of sewer lines as preferential pathways for vapor intrusion is poorly understood. Although the importance of sewer lines for volatile organic compound (VOC) transport has been documented at a small number of sites with vapor intrusion, sewer lines are not routinely sampled during most vapor intrusion investigations. We have used a tracer study and VOC concentration measurements to evaluate the role of the combined sanitary/storm sewer line in VOC transport at the USEPA vapor intrusion research duplex in Indianapolis, Indiana. The results from the tracer study demonstrated gas migration from the sewer main line into the duplex. The migration pathway appears to be complex and may include leakage from the sewer lateral at a location below the building foundation. Vapor samples collected from the sewer line demonstrated the presence of tetrachloroethene (PCE) and chloroform in the sewer main in front of the duplex and at multiple sample locations within the sewer line upstream of the duplex. These test results combined with results from the prior multi-year study of the duplex indicate that the sewer line plays an important role in transport of VOCs from the subsurface source to the immediate vicinity of the duplex building envelope.

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.

Industrial surface impoundments: environmental settings, release and exposure potential and risk characterization.

This paper presents the results of a national scale evaluation of the environmental impact of surface impoundments that contain non-hazardous wastewaters. In the 1990s, it was found that approximately 18,000 surface impoundments existed in the US for treating, storing or disposing of non-hazardous wastewater. In this study, the focus was on the subset of 11,900 impoundments that contain at least one of 256 chemicals of interest or high or low pH wastewater. Questionnaires were sent to facilities chosen in a two-phase nationally representative random sample. The nature, extent and use of surface impoundments across manufacturing industries were characterized using the information collected in the survey. Also, the chemical composition of impounded wastewaters; the potential for chemical releases to the environment from the impoundments; and the risk from these releases were assessed. It is estimated that only approximately 5-6% of facilities with impoundments have the potential to pose risks to human health, although approximately 19-46% of facilities with impoundments release chemicals of concern to the environment. The information in this study should help environmental managers evaluate and avoid those risk factors that have the potential to result in environmental harm, particularly when present in combination.