Article

Comparison of the Johnson-Ettinger Vapor Intrusion Screening Model Predictions with Full Three-Dimensional Model Results

School of Engineering, Brown University, Providence, Rhode Island 02912, United States.
Environmental Science & Technology (Impact Factor: 5.48). 02/2011; 45(6):2227-35. DOI: 10.1021/es102602s
Source: PubMed

ABSTRACT The Johnson-Ettinger vapor intrusion model (J-E model) is the most widely used screening tool for evaluating vapor intrusion potential because of its simplicity and convenience of use. Since its introduction about twenty years ago, the J-E model has become a cornerstone in guidance related to the potential for significant vapor intrusion-related exposures. A few papers have been published that claim it is a conservative predictor of exposure, but there has not been a systematic comparison in the open literature of the J-E model predictions with the results of more complete full three-dimensional descriptions of the phenomenon. In this paper, predictions from a three-dimensional model of vapor intrusion, based upon finite element calculations of homogeneous soil scenarios, are directly compared with the results of the J-E model. These results suggest that there are conditions under which the J-E model predictions might be quite reasonable but that there are also others in which the predictions are low as well as high. Some small modifications to the J-E model are also suggested that can bring its predictions into excellent agreement with those of the much more elaborate 3-D models, in some specific cases of homogeneous soils. Finally, both models were compared with actual field data.

1 Bookmark
 · 
124 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Vapor intrusion from volatile subsurface contaminants can be mitigated by aerobic biodegradation. Laboratory column studies with contaminant sources of chlorobenzene and a mixture of chlorobenzene, 1,2-dichlorobenzene, and 1,4-dichlorobenzene showed that contaminants were rapidly degraded in thin reactive zones with high biomass and low substrate concentrations in the vicinity of the capillary fringe. Such behavior was well characterized by a model that includes oxygen, substrate- and biomass-dependent biodegradation kinetics along with diffusive transport processes. An analytical solution was derived to provide the theoretical support for the simplification of reaction kinetics and the approximation of reactive zone location and mass flux relationships at steady state. Results demonstrate the potential of aerobic natural attenuation in the capillary fringe for preventing contaminant migration in the unsaturated zone. The solution indicates that increasing contaminant mass flux into the column creates a thinner reactive zone and pushes it toward the oxygen boundary, resulting in a shorter distance to the oxygen source and a larger oxygen mass flux that balances the contaminant mass flux. As a consequence, the aerobic biodegradation can reduce high contaminant concentrations to low levels within the capillary fringe and unsaturated zone. The results are consistent with the observations of thin reactive layers at the interface in unsaturated zones. The model considers biomass while including biodegradation in the capillary fringe and unsaturated zone and clearly demonstrates that microbial communities capable of using the contaminants as electron donors may lead to instantaneous degradation kinetics in the capillary fringe and unsaturated zone.
    Environmental Science and Technology 12/2014; DOI:10.1021/es503086p · 5.48 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The basis upon which recommended attenuation factors for vapor intrusion (VI) have been derived arereconsidered. By making a fitting curve to the plot showing the dependence of observed indoor air con-centration (cin) on subslab concentration (css) for residences in EPA database, an analytical equation isobtained to identify the relationship among cin, cssand the averaged background level. The new rela-tionship indicates that subslab measurements may serve as a useful guide only if cssis above 500 �g/m3.Otherwise, cinis independent of css, with a distribution in good agreements with other studies of back-ground levels. Therefore, employing this screening value (500 �g/m3), new contaminant concentrationattenuation factors are proposed for VI, and the values for groundwater-to-indoor and subslab-to-indoorair concentration attenuation factors are 0.004 and 0.02, respectively. The former is applied to examin-ing the reported temporal variations of cinobtained during a long-term monitoring study. The resultsshow that using this new groundwater-to-indoor air concentration attenuation factor also provides areasonably conservative estimate of cin.
    Journal of Hazardous Materials 01/2015; 286:583-561. DOI:10.1016/j.jhazmat.2015.01.013 · 4.33 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this study, the development and partial validation are presented for an analytical approximation method for prediction of subslab contaminant concentrations in PVI. The method involves combining an analytic approximation to soil vapor transport with a piecewise first-order biodegradation model (together called the Analytic Approximation Method, including Biodegradation, AAMB), the result of which calculation provides an estimate of contaminant subslab concentrations, independent of building operation conditions. Comparisons with three-dimensional (3-D) simulations and another PVI screening tool, BioVapor, show that the AAMB is suitable for application in a scenario involving a building with an impermeable foundation surrounded by open ground surface, where the atmosphere is regarded as the primary oxygen source. Predictions from the AAMB can be used to determine the required vertical source-building separation, given a subslab screening concentration, allowing identification of buildings at risk for PVI. This equation shows that the "vertical screening distance" suggested by U.S. EPA is sufficient in most cases, as long as the total petroleum hydrocarbon (TPH) soil gas concentration at the vapor source does not exceed 50-100mg/L. When the TPH soil gas concentration of the vapor source approaches a typical limit, i.e. 400mg/L, the "vertical screening distance" required would be much greater.
    Journal of Hazardous Materials 05/2014; 279:336-347. DOI:10.1016/j.jhazmat.2014.05.065 · 4.33 Impact Factor

Full-text

Download
37 Downloads
Available from
May 20, 2014