Henry’s Equilibrium Partitioning between Ground Water and Soil Air: Predictions versus Observations

Jeroen Provoost, Robbe Ottoy, Lucas Reijnders, Jan Bronders, Ilse Van Keer, Frank Swartjes, Daniel Wilczek, David Poelmans
DOI: 10.4236/jep.2011.27099                

Abstract

Humans spend 64% - 94% of their time indoors; therefore, indoor air quality is very important for potential exposure to volatile organic compounds (VOC). The source of VOC in the subsurface may come from accidental or intentional releases, leaking landfills or leaking underground and above-ground storage tanks. Once these contaminants are present near or beneath buildings, they may move as a vapour through soil gas and enter the building. A large number of vapour intrusion (VI) algorithms have been published in peer-reviewed publications that link indoor VOC concentrations to the contamination of soils. These models typically include phase partitioning calculations of VOC based on Henry’s law to estimate the concentration of a particular contaminant in soil gas. This paper presents the results from a series of laboratory experiments concerning the use of the Henry’s Law constant for the calculation of toluene concentrations in equilibrium between ground water and soil air. A series of column experiments were conducted with various toluene concentrations in artificial (ground) water to contrast the predicted and observed (soil) air concentrations. The experiments which exclude soil material show a toluene fugacity behaviour roughly in line with Henry’s law whereas the experiments which include soil material result in equilibrium soil concentrations which were around one order-of-magnitude lower than was expected from a Henry Law-based estimation. It is concluded that for toluene inclusion of Henry’s Law in VI algorithms does not provide an adequate description of volatilisation in soils and may lead to an overestimation of health risk. Instead, a model based on a simple description of the relevant intermolecular interactions could be explored.

Keywords

Henry Law Coefficient, Equilibrium Partitioning, Ground Water, Soil Air, Toluene, Algorithm

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	J. Kliest, T. Fast, J. S. M. Boley, H. van de Wiel and H. Bloemen, “The Relationship between Soil Contaminated with Volatile Organic Compounds and Indoor Air Pollution,” Environment International, Vol. 15, No. 1-6, 1989, pp. 419-425.
[2]	J. C. Little, J. M. Daisey and W. W. Nazaroff, “Transport of Subsurface Contaminants into Buildings. An Exposure Pathway for Volatile Organics,” Environmental Scientific Technology, Vol. 26, No. 11, 1992, pp. 2058-2066. doi:10.1021/es00035a001
[3]	F. D. Tillman and J. W. Weaver, “Temporal Moisture Content Variability Beneath and External to a Building and the Potential Effects on Vapour Intrusion Risk Assessment,” Science of the Total Environment, Vol. 379, 2007, pp. 1-15.
[4]	M. B. Kaplan, P. Brandt-Rauf, J. W. Axley, T. T. Shen and G. H. Sewell, “Residential Releases of Number 2 Fuel Oil: A Contributor to Indoor Air Pollution,” American Journal of Public Health, Vol. 83, No.1, 1993, pp. 84-88.
[5]	D. Fugler and M. Adomait, “Indoor Infiltration of Volatile Organic Contaminants: Measured Soil Gas Entry Rates and Other Research Results from Canadian Houses,” Journal of Soil Contamination, Vol. 6, No. 1, 1997, pp. 9-13. doi:10.1080/15320389709383542
[6]	D. A. Olson and R. L. Corsi, “Fate and Transport of Contaminants in Indoor Air,” Journal of Soil and Sediment Contamination, Vol. 11, No. 4, 2002, pp. 583-601.
[7]	F. A. Swartjes, “Evaluation of the Variation in Calculated Human Exposure to Soil Contaminants Using Seven Different European Models,” Human and Ecological Risk Assessment, Vol. 15, No. 1, 2009, pp. 138-158. doi:10.1080/10807030802615733
[8]	M. C. Underwood, “Assessing the Indoor Air Impact from a Hazardous Waste Site: A Case Study,” Toxicology and Industrial Health, Vol. 12, No. 2, 1996, pp. 179-188.
[9]	B. Eklund, D. Folkes, J. Kabel and R. Farnum, “An Overview of State Approaches to Vapor Intrusion,” Environmental Manager, Air & Waste Management Association, February 2007, pp. 10-13.
[10]	J. F. Foster and B. D. Beck, “Basement Gas: Issues Related to the Migration of Potentially Toxic Chemicals into House Basements from Distant Sources,” Advanced Modelling Environmental Toxicology, Vol. 25, 1998, pp. 219-234.
[11]	S. Chowdhury and S. L. Brock, “Indoor Air Inhalation Risk Assessment for Volatiles Emanating from Light Nonaqueous Phase Liquids,” Soil and Sediment Contamination, Vol. 10, No. 4, 2001, pp. 387-403.
[12]	M. J. Moran, J. S. Zogorski and P. J. Squllace, “Chlorinated Solvents in Groundwater of the United States,” E nvironmental Science and Technology, Vol. 41, No. 1, 2007, pp. 74-81. doi:10.1021/es061553y
[13]	J. Roy and G. Bickerton, “Proactive Screening Approach for Detecting Groundwater Contaminants along Urban Streams at the Reach-Scale,” Environmental Science and Technology, Vol. 44, No. 16, 2010, pp. 6088-6094.
[14]	D. R. Williams, J. C. Paslawski and G. M. Richardson, “Development of a Screening Relationship to Describe Migration of Contaminant Vapours into Buildings,” Journal of Soil Contamination, Vol. 5, No. 2, 1996, pp. 141-156. doi:10.1080/15320389609383519
[15]	T. McAlary, J. Provoost and H. Dawson, “Chapter 10—Vapour Intrusion,” In: F. Swartjes, Ed., Dealing with Contaminated Sites—From Theory towards Practical Application, Springer Publishers, Netherlands, January 2011, pp. 409-453.
[16]	J. Provoost, F. Tillman, J. Weaver, L. Reijnders, J. Bronders, I. Van Keer and F. Swartjes, “Chapter 2 Vapour Intrusion into Buildings—A Literature Review,” In: J. A. Daniels, Ed., Advances in Environmental Research, Nova Science Publishers Inc., New York, 2010, pp. 69-111.
[17]	R. J. Millington, “Gas Diffusion in Porous Media,” Science, Vol. 130, No. 3367, 1959, pp. 100-102. doi:10.1126/science.130.3367.100-a
[18]	H. L. Penman, “Gas and Vapour Movements in Soil I, the Diffusion of Vapours through Porous Solids,” Journal of Agricultural Science, Vol. 30, 1940, pp. 463-462.
[19]	W. W. Nazaroff, “Radon Transport from Soil to Air, Review of Geophysics,” American Geophysical Union, Vol. 30, No. 2, 1992, pp. 137-160.
[20]	W. A. Jury, W. F. Spencer and W. J. Farmer, “Behavior Assessment Model for Trace Organics in Soil: I. Model Description,” Journal of Environmental Quality, Vol. 12, No. 4, 1983, pp. 558-563. doi:10.2134/jeq1983.00472425001200040025x
[21]	J. A. Currie, “Movement of Gases in Soil Respiration, Sorption and Transport Processes in Soils,” SCI Monograph Series, Vol. 37, 1970, pp. 152-171.
[22]	R. J. Millington and J. P. Quirk, “Permeability of Porous Solids,” Transactions of the Faraday Society, Vol. 57, 1961, pp. 1200-1207. doi:10.1039/tf9615701200
[23]	W. Malesinski, “Azeotropy and Other Theoretical Problems of Vapour-Liquid Equilibrium,” InterScience, 1965, pp. 222.
[24]	W. F. Spencer, M. M. Cliath, W. A. Jury and L. Z. Zhang, “Volatilization of Organic Chemicals from Soil as Related to their Henry’s Law Constants,” Journal Environmental Quality, Vol. 17, No. 3, 1988, pp. 504-509. doi:10.2134/jeq1988.00472425001700030027x
[25]	J. E. Dunn and T. Chen, “Critical Evaluation of the Diffusion Hypothesis in the Theory of Porous Media Volatile Organic Compound (VOC) Sources and Sinks,” In: N. L. Nagda, Ed., Modelling of Indoor Air Quality and Exposure, American Society for Testing and Materials, Philadelphia, 1993, pp. 64-80.
[26]	A. L. Robinson, R. G. Sexto and W. J. Fisk, “Soil-Gas Entry into an Experimental Basement Driven by Atmospheric Pressure Fluctuations—Measurements, Spectral Analysis, and Model Comparison,” Atmospheric Environment, Vol. 31, No. 10, 1997, pp. 1477-1485. doi:10.1016/S1352-2310(96)00304-4
[27]	A. L. Robinson, R. G. Sexto and W. J. Riley, “Soil-Gas Entry into an Experimental Basement Driven by Atmospheric Pressure Fluctuations—The Influence of Soil Properties,” Atmospheric Environment, Vol. 31, No. 10, 1997, pp. 1487-1495. doi:10.1016/S1352-2310(97)83264-5
[28]	J. Grifoll and Y. Cohen, “Chemical Volatilization from the Soil Matrix—Transport through the Air and Water Phases,” Journal of Hazardous Materials, Vol. 37, No. 3, 1994, pp. 445-457. doi:10.1016/0304-3894(93)E0100-G
[29]	R. L. Scott, “Azeotropy and Other Theoretical Problems of Vapour-Liquid Equilibrium,” Journal of American Chemistry Society, Vol. 88, No. 21, 1966, pp. 5053. doi:10.1021/ja00973a070
[30]	K. U. Goss, “Adsorption of Organic Vapours on Polar Mineral Surfaces and on a Bulk Water Surface: Development of an Empirical Predictive Model,” Environmental Science and Technology, Vol. 28, No. 4, 1994, pp. 640-645. doi:10.1021/es00053a017
[31]	K. U. Goss, “Effects of Temperature and Relative Humidity on the Sorption of Vapours on Quartz Sand,” Environmental Science and Technology, Vol. 26, No. 11, 1992, pp. 2287-2294. doi:10.1021/es00035a030
[32]	K. U. Goss and S. J. Eisenreich, “Adsorption of VOCs from the Gas Phase to Different Minerals and a Mineral Mixture,” Environmental Science and Technology, Vol. 30, No. 7, 1996, pp. 2135-2142. doi:10.1021/es950508f
[33]	K. U. Goss, J. Buschmann and R. P. Schwarzenbach, “Linear Free Energy Relationships Used to Evaluate Equilibrium Partitioning of Organic Compounds,” Environmental Science and Technology, Vol. 35, No. 1, 2001, pp. 1-9. doi:10.1021/es000996d
[34]	K. U. Goss, “The Air/Surface Adsorption Equilibrium of Organic Compounds under Ambient Conditions, Critical Reviews,” Environmental Science and Technology, Vol. 34, No. 4, 2004, pp. 339-389. doi:10.1080/10643380490443263
[35]	K. U. Goss, J. Buschmann and R. P. Schwarzenbach, “Adsorption of Organic Vapours to Air-Dry Soils: Model Predictions and Experimental Validation,” Environmental Science and Technology, Vol. 38, 2004, pp. 3667-3673. doi:10.1021/es035388n
[36]	J. Provoost, J. Nouwen, C. Cornelis, G. Van Gestel and R. Engels, Technical Guidance Document, Part 4—Background Document for Chemical Properties and Specifications, Advise on Behalf of the Flemish Public Waste Agency OVAM, Dutch, 2004.
[37]	D. Mackay, W.-Y. Shiu, K. C. Ma and S. C. Lee, “Handbook of Physical-Chemical Properties and Environmental Fate for Organic Chemicals,” Second Edition, Vol. 1-4, CRC Press, 2006.
[38]	S. Matula, M. Mojrova and K. Spongrova, “Estimation of the Soil Water Retention Curve (SWRC) Using Pedotransfer Functions (PTFs),” Soil and Water Research, Vol. 2, No. 4, 2007, pp. 113-122.
[39]	ASTM, “Astm Standard C136-06 Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates,” ASTM International, West Conshohocken, PA, 2006. doi:10.1520/C0136-06
[40]	R. B. Brown, “Soil Texture,” Fact Sheet SL-29, Institute of Food and Agricultural Sciences, University of Florida, 2003.
[41]	ASTM, “ASTM Standard D2974-07a Standard Test Methods for Moisture, Ash, and Organic Matter of Peat and Other Organic Soils,” ASTM International, West Conshohocken, PA, 2007. doi:10.1520/C0136-06
[42]	US EPA, Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air, Second Edition, Compendium Method TO-15, Determination of Volatile Organic Compounds (VOCs) in Air Collected in Specially-Prepared Canisters and Analyzed by Gas Chromatography/Mass Spectrometry (GC/MS), Center for Environmental Research Information, Office of Research and Development, U.S. Environmental Protection Agency, Cincinnati, 1999. http://www.epa.gov/ttnamti1/airtox.html
[43]	S. W. Webb and K. Pruess, “The Use of Fick’s Law for Modeling Trace Gas Diffusion in Porous Media,” Transport in Porous Media, Vol. 51, 2003, pp. 327-341.
[44]	J. Provoost, L. Reijnders, F. Swartjes, J. Bronders, P. Seuntjens and J. Lijzen, J, “Functionality and Accuracy of Seven Vapour Intrusion Screening Models for VOC in Groundwater,” Journal of Soils and Sediments—Protection, Risk Assessment, and Remediation, Vol. 9, 2008. doi:10.1007/s11368-008-0036-y
[45]	J. Provoost, A. Bosman, L. Reijnders, J. Bronders, K. Touchant and F. Swartjes, “Vapour Intrusion from the Vadose Zone—Seven Algorithms Compared,” Journal of Soils and Sediments—Protection, Risk Assessment, and Remediation, 2009. doi:10.1007/s11368-009-0127-4
[46]	P. C. Johnson, M. W. Kemblowski and R. L. Johnson, “Assessing the Significance of Subsurface Contaminant Vapour Migration to Enclosed Spaces: Site-Specific Alternatives to Generic Estimates,” Journal of Soil Contamination, Vol. 8, 1999, pp. 389-421.