首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
Aerobic biodegradation can contribute significantly to the attenuation of petroleum hydrocarbons vapors in the unsaturated zone; however, most regulatory guidance for assessing potential human health risks via vapor intrusion to indoor air either neglect biodegradation in developing generic screening levels or allow for only one order of magnitude additional attenuation for aerobically degradable compounds, which may be overly conservative in some cases. This paper describes results from three-dimensional numerical model simulations of vapor intrusion for petroleum hydrocarbons to assess the influence of aerobic biodegradation on the attenuation factor for a variety of source concentrations and depths for residential buildings with basements and slab-on-grade construction. The simulations conducted in this study provide a framework for understanding the degree to which bioattenuation will occur under a variety of scenarios and provide insight into site conditions that will result in significant biodegradation. This improved understanding may be used to improve the conceptual model of contaminant transport, guide field data collection and interpretation, and estimate semi-site-specific attenuation factors for combinations of source concentrations, source depth, oxygen distribution, and building characteristics where site conditions reasonably match the scenarios simulated herein.  相似文献   

2.
Hazardous waste site investigations have shown that volatile organic compounds (VOCs) can be transported via sewer pipes and migrate into indoor spaces. Despite field data confirming the presence of this exposure pathway, there is lack of context-based numerical models that provide guidance to characterize and predict VOCs concentration in sewer gas at vapor intrusion sites. Particularly, this poses a challenge when assessing and mitigating risks associated with these exposure pathways. Therefore, a numerical model has been developed to simulate the concentration of VOCs in sewer gas in different stages throughout the sewer lines. The developed model considers various input parameters, including temperature, sewer liquid depth, groundwater depth, and sewer construction characteristics to incorporate local and operational conditions. The model's output is verified using field data from a sewer system constructed near a Superfund site. Moreover, a sensitivity analysis was conducted to evaluate the model's response to variation of the external input parameters. To the best of our knowledge, this study is the first attempt to model VOCs concentration in sewer gas, particularly to address vapor intrusion. The developed model can be used as a numerical tool to support the development of sewer assessment guidelines, risk assessment studies, and mitigation strategies.  相似文献   

3.
Different types of data can be collected to evaluate whether or not vapor intrusion is a concern at sites impacted with volatile organic compound (VOC) contamination in the subsurface. Typically, groundwater, soil gas, or indoor air samples are collected to determine VOC concentrations in the different media. Sample results are evaluated using a “multiple lines of evidence” approach to interpret whether vapor intrusion is occurring. Data interpretation is often not straightforward because of many complicating factors, particularly in the evaluation of indoor air. More often than not, indoor air sample results are affected by indoor or other background sources making interpretation of concentration‐based data difficult using conventional sampling approaches. In this study, we explored the practicality of compound‐specific isotope analysis (CSIA) as an additional type of evidence to distinguish between indoor sources and subsurface sources (i.e., vapor intrusion). We developed a guide for decision‐making to facilitate data interpretation and applied the guidelines at four different test buildings. To evaluate the effectiveness of the CSIA method for vapor intrusion applications, we compared the interpretation from CSIA to interpretations based on data from two different investigation approaches: conventional sampling and on‐site GC/MS analysis. Interpretations using CSIA were found to be generally consistent with the other approaches. In one case, CSIA provided the strongest line of evidence that vapor intrusion was not occurring and that a VOC source located inside the building was the source of VOCs in indoor air.  相似文献   

4.
Detailed site investigations to assess potential inhalation exposure and risk to human health associated with the migration of petroleum hydrocarbon vapors from the subsurface to indoor air are frequently undertaken at leaking underground storage tank (UST) sites, yet documented occurrences of petroleum vapor intrusion are extremely rare. Additional assessments are largely driven by low screening‐level concentrations derived from vapor transport modeling that does not consider biodegradation. To address this issue, screening criteria were developed from soil‐gas measurements at hundreds of petroleum UST sites spanning a range of environmental conditions, geographic regions, and a 16‐year time period (1995 to 2011). The data were evaluated to define vertical separation (screening) distances from the source, beyond which, the potential for vapor intrusion can be considered negligible. The screening distances were derived explicitly from benzene data using specified soil‐gas screening levels of 30, 50, and 100 µg/m3 and nonparametric Kaplan‐Meier statistics. Results indicate that more than 95% of benzene concentrations in soil gas are ≤30 µg/m3 at any distance above a dissolved‐phase hydrocarbon source. Dissolved‐phase petroleum hydrocarbon sources are therefore unlikely to pose a risk for vapor intrusion unless groundwater (including capillary fringe) comes in contact with a building foundation. For light nonaqueous‐phase liquid (LNAPL) hydrocarbon sources, more than 95% of benzene concentrations in soil gas are ≤30 µg/m3 for vertical screening distances of 13 ft (4 m) or greater. The screening distances derived from this analysis are markedly different from 30 to 100 ft (10 to 30 m) vertical distances commonly found cited in regulatory guidance, even with specific allowances to account for uncertainty in the hydrocarbon source depth or location. Consideration of these screening distances in vapor intrusion guidance would help eliminate unnecessary site characterization at petroleum UST sites and allow more effective and sustainable use of limited resources.  相似文献   

5.
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.  相似文献   

6.
A detailed seasonal study of soil vapor intrusion at a cold climate site with average yearly temperature of 1.9 °C was conducted at a house with a crawlspace that overlay a shallow dissolved‐phase petroleum hydrocarbon (gasoline) plume in North Battleford, Saskatchewan, Canada. This research was conducted primarily to assess if winter conditions, including snow/frost cover, and cold soil temperatures, influence aerobic biodegradation of petroleum vapors in soil and the potential for vapor intrusion. Continuous time‐series data for oxygen, pressure differentials, soil temperature, soil moisture, and weather conditions were collected from a high‐resolution monitoring network. Seasonal monitoring of groundwater, soil vapor, crawlspace air, and indoor air was also undertaken. Petroleum hydrocarbon vapor attenuation and biodegradation rates were not significantly reduced during low temperature winter months and there was no evidence for a significant capping effect of snow or frost cover that would limit oxygen ingress from the atmosphere. In the residual light nonaqueous phase liquid (LNAPL) source area adjacent to the house, evidence for biodegradation included rapid attenuation of hydrocarbon vapor concentrations over a vertical interval of approximately 0.9 m, and a corresponding decrease in oxygen to less than 1.5% v/v. In comparison, hydrocarbon vapor concentrations above the dissolved plume and below the house were much lower and decreased sharply within a few tens of centimeters above the groundwater source. Corresponding oxygen concentrations in soil gas were at least 10% v/v. A reactive transport model (MIN3P‐DUSTY) was initially calibrated to data from vertical profiles at the site to obtain biodegradation rates, and then used to simulate the observed soil vapor distribution. The calibrated model indicated that soil vapor transport was dominated by diffusion and aerobic biodegradation, and that crawlspace pressures and soil gas advection had little influence on soil vapor concentrations.  相似文献   

7.
Diminishing rates of subsurface volatile contaminant removal by soil vapor extraction (SVE) oftentimes warrants an in-depth performance assessment to guide remedy decision-making processes. Such a performance assessment must include quantitative approaches to better understand the impact of remaining vadose zone contamination on soil gas and groundwater concentrations. The spreadsheet-based Soil Vapor Extraction Endstate Tool (SVEET) software functionality has recently been expanded to facilitate quantitative performance assessments. The updated version, referred to as SVEET2, includes expansion of the input parameter ranges for describing a site (site geometry, source characteristics, etc.), an expanded list of contaminants, and incorporation of elements of the Vapor Intrusion Estimation Tool for Unsaturated-zone Sources software to provide soil gas concentration estimates for use in vapor intrusion evaluation. As part of the update, SVEET2 was used to estimate the impact of a tetrachloroethene (PCE) vadose zone source on groundwater concentrations, comparing SVEET2 results to field-observed values at an undisclosed site where SVE was recently terminated. PCE concentrations from three separate monitoring wells were estimated by SVEET2 to be within the range of 6.0–6.7 μg/L, as compared to actual field concentrations that ranged from 3 to 11 μg/L PCE. These data demonstrate that SVEET2 can rapidly provide representative quantitative estimates of impacts from a vadose zone contaminant source at field sites. In the context of the SVE performance assessment, such quantitative estimates provide a basis to support remedial and/or regulatory decisions regarding the continued need for vadose zone volatile organic compound remediation or technical justification for SVE termination, which can significantly reduce the cost to complete for a site.  相似文献   

8.
An investigation at a major industrial facility in the Midwestern United States provides insights regarding the amount of attenuation of sub-surface vapors occurring at industrial buildings. The buildings at the facility were ranked in terms of vapor intrusion potential and testing began in October 2016 and is ongoing. Results have been evaluated for data collected at 718 unique locations across 77 buildings. A total of 1646 sample pairs (sub-slab and indoor air) have been collected and analyzed for 65 analytes, resulting in a total of 106,990 data pairs. As many as 49 sample pairs were collected within a given building during a single sampling event and up to 11 rounds of seasonal testing have been performed at selected buildings. Seasonal variability in sub-slab soil-gas concentrations was found to be negligible. Data analysis was performed to look for data trends across the entire data set and identify inter-building comparisons. This data evaluation focused on individual volatile organic compounds (e.g., tetrachloroethylene, trichloroethylene) present in the sub-slab soil gas at concentrations exceeding 1000 μg/m3. A total of 157 building-specific attenuation coefficients (α) were evaluated. This evaluation demonstrated that large industrial buildings have a much greater attenuation than that assumed for single-family residential buildings. All attenuation coefficient values were lower than 0.03, which is the standard regulatory default for non-residential buildings. The median value was 9.3E-05 and the 95% upper confidence limit was 2.7E-04. There is some evidence of lower attenuation under wintertime conditions. The data suggests that the default attenuation factor of 0.03 over-predicts indoor air impacts at this industrial facility by at least two orders of magnitude.  相似文献   

9.
Generic indoor air:subslab soil gas attenuation factors (SSAFs) are important for rapid screening of potential vapor intrusion risks in buildings that overlie soil and groundwater contaminated with volatile chemicals. Insufficiently conservative SSAFs can allow high‐risk sites to be prematurely excluded from further investigation. Excessively conservative SSAFs can lead to costly, time‐consuming, and often inconclusive actions at an inordinate number of low‐risk sites. This paper reviews two of the most commonly used approaches to develop SSAFs: (1) comparison of paired, indoor air and subslab soil gas data in empirical databases and (2) comparison of estimated subslab vapor entry rates and indoor air exchange rates (IAERs). Potential error associated with databases includes interference from indoor and outdoor sources, reliance on data from basements, and seasonal variability. Heterogeneity in subsurface vapor plumes combined with uncertainty regarding vapor entry points calls into question the representativeness of limited subslab data and diminishes the technical defensibility of SSAFs extracted from databases. The use of reasonably conservative vapor entry rates and IAERs offers a more technically defensible approach for the development of generic SSAF values for screening. Consideration of seasonal variability in building leakage rates, air exchange rates, and interpolated vapor entry rates allows for the development of generic SSAFs at both local and regional scales. Limitations include applicability of the default IAERs and vapor entry rates to site‐specific vapor intrusion investigations and uncertainty regarding applicability of generic SSAFs to assess potential short‐term (e.g., intraday) variability of impacts to indoor air.  相似文献   

10.
A portable gas chromatograph‐mass spectrometer (GC/MS) was used to investigate sources of chlorinated volatile organic compound (cVOC) contamination in indoor air at 46 residences around Hill AFB, Utah, that were potentially affected by vapor intrusion. Analytical methods were developed to allow sample turnaround times of less than 10 min and method detection limits (MDLs) generally less than 1 μg/m3 for a selected list of cVOCs. Area‐by‐area sampling was used to identify the likely vapor source locations. In many cases, individual container/enclosure sampling and subsequent field emission rate measurements from isolated consumer products were used to determine if identified products were likely to be the primary source of vapors in the residence. The portable GC/MS was also used to characterize vapor intrusion in two residences. In one of these two residences, building pressure control was used to enhance vapor entry in order to facilitate the investigation resulting in confirmation of vapor intrusion and identification of a primary route of vapor entry. cVOCs were identified in 42 of the 46 homes investigated, subsurface vapor intrusion was identified in two homes, and two homes had inconclusive results.  相似文献   

11.
Subslab soil gas sampling and analysis is a common line of evidence for assessing human health risks associated with subsurface vapor intrusion to indoor air for volatile organic compounds; however, conventional subslab sampling methods have generated data that show substantial spatial and temporal variability, which often makes the interpretation difficult. A new method of monitoring has been developed and tested that is based on a concept of integrating samples over a large volume of soil gas extracted from beneath the floor slab of a building to provide a spatially averaged subslab concentration. Regular field screening is also conducted to assess the trend of concentration as a function of the volume removed to provide insight into the spatial distribution of vapors at progressive distances away from the point of extraction. This approach minimizes the risk of failing to identify the areas of elevated soil vapor concentrations that may exist between discrete sample locations, and can provide information covering large buildings with fewer holes drilled through the floor. The new method also involves monitoring the extraction flow rate and transient vacuum response for mathematical analysis to help interpret the vapor concentration data and to support an optimal design for any subslab venting system that may be needed.  相似文献   

12.
The vapor intrusion impacts associated with the presence of chlorinated volatile organic contaminant plumes in the ground water beneath residential areas in Colorado and New York have been the subject of extensive site investigations and structure sampling efforts. Large data sets of ground water and indoor air monitoring data collected over a decade-long monitoring program at the Redfield, Colorado, site and monthly ground water and structure monitoring data collected over a 19-month period from structures in New York State are analyzed to illustrate the temporal and spatial distributions in the concentration of volatile organic compounds that one may encounter when evaluating the potential for exposures due to vapor intrusion. The analysis of these data demonstrates that although the areal extent of structures impacted by vapor intrusion mirrors the areal extent of chlorinated volatile organic compounds in the ground water, not all structures above the plume will be impacted. It also highlights the fact that measured concentrations of volatile organic compounds in the indoor air and subslab vapor can vary considerably from month to month and season to season. Sampling results from any one location at any given point in time cannot be expected to represent the range of conditions that may exist at neighboring locations or at other times. Recognition of this variability is important when designing sampling plans and risk management programs to address the vapor intrusion pathway.  相似文献   

13.
The area surrounding the Colorado Department of Transportation Materials Testing Laboratory in Denver was the subject of intense investigation, involving the collection of thousands of ground water, soil-gas, and indoor air samples in order to investigate indoor air impacts associated with a subsurface release of chlorinated solvents. The preremediation portion of that data set is analyzed and reduced in this work to ground water–to-indoor air attenuation factors (αgw= the ratio of the measured indoor air concentration to the soil-gas concentration predicted to be in equilibrium with the local ground water concentration). The empirical αgw values for this site range from about 10−6 to 10−4 with an overall average of 3 × 10−5 (μg/L indoor air)/(μg/L soil gas). The analysis of this data set highlights the need for a thorough data review and data screening when using large data sets to derive empirical relationships between subsurface concentrations and indoor air. More specifically, it is necessary to identify those parts of the data that contain a strong vapor intrusion pathway signal, which generally will require concentrations well above reported detection levels combined with spatial or temporal correlation of subsurface and indoor concentrations.  相似文献   

14.
The attenuation factor (AF) of 0.03 recommended by the U.S. Environmental Protection Agency (USEPA) is increasingly being used by regulatory agencies for the development of subsurface vapor screening levels for vapor intrusion (VI). There are concerns, however, over the database used to derive the AF and the AF's applicability to building types and geographies not included in USEPA database. To derive a more technically defensible AF for subsurface vapor screening in California, a database consisting of 8415 paired indoor and subsurface vapor samples collected from 485 buildings at 36 sites in California was compiled. Filtering was applied to remove data of suspect quality that were potentially affected by background (non-VI) sources. Filtering reduced the size of the database to 788 indoor air and subsurface vapor pairs, 80% of which were trichloroethylene (TCE) measurements. An AF of 0.0008 was derived from only TCE vapor data, based on the ability of the AF to reliably identify buildings with indoor air concentrations above screening levels in 95% of cases where subsurface vapor screening levels were exceeded. The AF derived from this study demonstrated limited sensitivity to the variables typically considered important in VI characterization, which was partially attributed to relatively weak correlation of indoor air and subsurface vapor concentration data. The results of this study can be used to improve VI screening in California and other states and help focus limited resources on sites posing the greatest potential risk.  相似文献   

15.
A value of 0.001 is recommended by the United States Environmental Protection Agency (USEPA) for its groundwater‐to‐indoor air Generic Attenuation Factor (GAFG), used in assessing potential vapor intrusion (VI) impacts to indoor air, given measured groundwater concentrations of volatile chemicals of concern (e.g., chlorinated solvents). The GAFG can, in turn, be used for developing groundwater screening levels for VI given target indoor air quality screening levels. In this study, we examine the validity and applicability of the GAFG both for predicting indoor air impacts and for determining groundwater screening levels. This is done using both analysis of published data and screening model calculations. Among the 774 total paired groundwater‐indoor air measurements in the USEPA's VI database (which were used by that agency to generate the GAFG) we found that there are 427 pairs for which a single groundwater measurement or interpolated value was applied to multiple buildings. In one case, up to 73 buildings were associated with a single interpolated groundwater value and in another case up to 15 buildings were associated with a single groundwater measurement (i.e., that the indoor air contaminant concentrations in all of the associated buildings were influenced by the concentration determined at a single point). In more than 70% of the cases (390 of 536 paired measurements in which horizontal building‐monitoring well distance was recorded) the monitoring wells were located more than 30 m (and one up to over 200 m) from the associated buildings. In a few cases, the measurements in the database even improbably implied that soil gas contaminant concentrations increased, rather than decreased, in an upward direction from a contaminant source to a foundation slab. Such observations indicate problematic source characterization within the data set used to generate the GAFG, and some indicate the possibility of a significant influence of a preferential contaminant pathway. While the inherent value of the USEPA database itself is not being questioned here, the above facts raise the very real possibility that the recommended groundwater attenuation factors are being influenced by variables or conditions that have not thus far been fully accounted for. In addition, the predicted groundwater attenuation factors often fall far beyond the upper limits of predictions from mathematical models of VI, ranging from screening models to detailed computational fluid dynamic models. All these models are based on the same fundamental conceptual site model, involving a vadose zone vapor transport pathway starting at an underlying uniform groundwater source and leading to the foundation of a building of concern. According to the analysis presented here, we believe that for scenarios for which such a “traditional” VI pathway is appropriate, 10?4 is a more appropriately conservative generic groundwater to indoor air attenuation factor than is the EPA‐recommended 10?3. This is based both on the statistical analysis of USEPA's VI database, as well as the traditional mathematical models of VI. This result has been validated by comparison with results from some well‐documented field studies.  相似文献   

16.
Shallow trichloroethene (TCE) groundwater and soil contamination associated with a Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) Superfund Site in Michigan resulted in a vapor intrusion (VI) investigation of overlying condominium units. Units with data suggesting a complete VI pathway received subslab depressurization systems (SSDs). Performance monitoring following the installation of an SSD at one unit indicated that the indoor air TCE concentrations remained elevated, despite pressure field extension tests that showed the system should effectively reduce VI from soil gas. Therefore, a cost-efficient and incremental investigation was launched to identify other potential source(s) of TCE using a field-portable gas chromatograph/mass spectrometer (GS/MS). The combination of room-by-room air sampling, potential VI entry point sampling, and emission tests of potential sources were used, which resulted in successfully identifying a bedroom furniture set as an indoor source of TCE for the unit. Although many common household products are recognized as indoor sources of TCE, emissions from finished furniture products have not been widely discussed in the VI literature. The findings of this study indicate that off gassing from furniture can lead to TCE concentrations in indoor air that exceed regulatory guidelines.  相似文献   

17.
Groundwater contamination associated with two former industrial facilities in Denver, Colorado, has led to concerns about vapor intrusion into residences adjacent to the facilities. 1,1,1-Trichloroethane (1,1,1-TCA), 1,1-dichloroethene (1,1-DCE), and trichloroethene (TCE) are the main contaminants of concern in groundwater, with trace levels of 1,2-dichloroethane (1,2-DCA) present at one of the sites. Indoor air monitoring programs have been ongoing at these two sites since 1998 and recent results have suggested that background, indoor source, 1,2-DCA has been increasing in the frequency of detection, and median and maximum concentration over the past several years. A lines of evidence evaluation was undertaken for both sites in order to document the predominance of indoor sources of 1,2-DCA. Evidence utilized included spatial evaluation of 1,2-DCA in indoor air; comparison of 1,2-DCA concentrations in mitigated and unmitigated homes; a phone survey to evaluate the potential for smoking to contribute to indoor air 1,2-DCA levels; evaluation of mitigation system effluent data; and an evaluation of volatile organic compound (VOC) ratios in groundwater and indoor air. The results of this evaluation indicated that smoking had no demonstrable influence on measured indoor air concentrations. In addition, it appears that consumer products have had a markedly increased influence on indoor air concentrations since 2005. Data from one of the industrial facilities at one of the sites also indicated that polyvinyl chloride (PVC) and vinyl composite floor adhesive used in a building remodel in 2005 apparently generated elevated levels of indoor 1,2-DCA and vinyl chloride, which have been sustained up to the present time.  相似文献   

18.
Petroleum hydrocarbon vapors biodegrade aerobically in the subsurface. Depth profiles of petroleum hydrocarbon vapor and oxygen concentrations from seven locations in sandy and clay soils across four states of Australia are summarized. The data are evaluated to support a simple model of biodegradation that can be used to assess hydrocarbon vapors migrating toward built environments. Multilevel samplers and probes that allow near‐continuous monitoring of oxygen and total volatile organic compounds (VOCs) were used to determine concentration depth profiles and changes over time. Collation of all data across all sites showed distinct separation of oxygen from hydrocarbon vapors, and that most oxygen and hydrocarbon concentration profiles were linear or near linear with depth. The low detection limit on the oxygen probe data and because it is an in situ measurement strengthened the case that little or no overlapping of oxygen and hydrocarbon vapor concentration profiles occurred, and that indeed oxygen and hydrocarbon vapors were largely only coincident near the location where they both decreased to zero. First‐order biodegradation rates determined from all depth profiles were generally lower than other published rates. With lower biodegradation rates, the overlapping of depth profiles might be expected, and yet such overlapping was not observed. A model of rapid (instantaneous) reaction of oxygen and hydrocarbon vapors compared to diffusive transport processes is shown to explain the important aspects of the 13 depth profiles. The model is simply based on the ratio of diffusion coefficients of oxygen and hydrocarbon vapors, the ratio of the maximum concentrations of oxygen and hydrocarbon vapors, the depth to the maximum hydrocarbon source concentration, and the stoichiometry coefficient. Whilst simple, the model offers the potential to incorporate aerobic biodegradation into an oxygen‐limited flux‐reduction approach for vapor intrusion assessments of petroleum hydrocarbon compounds.  相似文献   

19.
Groundwater contamination associated with an industrial facility in Utah has led to concerns about potential vapor intrusion into residences outside the facility boundary. Trichloroethylene (TCE) is the main contaminant of concern with 1,2-dichloroethane (1,2-DCA) present in some areas. An air-monitoring program implemented to detect vapor intrusion of these compounds found 1,2-DCA in homes outside areas of groundwater contamination, suggesting indoor sources in these cases. Investigative indoor air and product sampling were conducted to isolate consumer products emitting 1,2-DCA and to quantify the emission rates of identified products. The combination of room-by-room air sampling and emission measurements was successfully used to identify molded plastic holiday ornaments, having measured emission rates as high as 0.3 µg 1,2-DCA/min. Subsequent testing of seven comparable retail items found similar 1,2-DCA emissions. Screening-level calculations show that the measured emission rates of 1,2-DCA from these items can lead to indoor concentrations high enough to be of regulatory concern (0.094 to 9.4 µg/m3 based on 10–6 to 10–4 cancer risk levels).  相似文献   

20.
A model is presented for estimating vapor concentrations in buildings because of volatilization from soil contaminated by non- aqueous phase liquids (NAPL) or from dissolved contaminants in ground water. The model considers source depletion, diffusive- dispersive transport of the contaminant of concern (COC) and of oxygen and oxygen-limited COC biodecay. Diffusive-advective transport through foundations and vapor losses caused by foundation cross-flow are considered. Competitive oxygen use by various species is assumed to be proportional to the product of the average dissolved-phase species concentration and a biopreference factor. Laboratory and field data indicate the biopreference factor to be proportional to the organic carbon partition coefficient for the fuel hydrocarbons studied. Predicted indoor air concentrations were sensitive to soil type and subbase permeability. Lower concentrations were predicted for buildings with shallow foundations caused by flushing of contaminants by cross-flow. NAPL source depletion had a large impact on average exposure concentration. Barometric pumping had a minor effect on indoor air emissions for the conditions studied. Risk-based soil cleanup levels were much lower when biodecay was considered because of the existence of a threshold source concentration below which no emissions occur. Computed cleanup levels at NAPL-contaminated sites were strongly dependent on total petroleum hydrocarbon (TPH) content and COC soil concentration. The model was applied to two field sites with gasoline-contaminated ground water. Confidence limits of predicted indoor air concentrations spanned approximately two orders of magnitude considering uncertainty in model parameters. Measured contaminant concentrations in indoor air were within model-predicted confidence limits.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号