A numerical investigation of vapor intrusion - The dynamic response of contaminant vapors to rainfall events

Rui Shen, Kelly G. Pennell, Eric M. Suuberg

Research output: Contribution to journalArticlepeer-review

44 Scopus citations

Abstract

The U.S. government and various agencies have published guidelines for field investigation of vapor intrusion, most of which suggest soil gas sampling as an integral part of the investigation. Contaminant soil gas data are often relatively more stable than indoor air vapor concentration measurements, but meteorological conditions might influence soil gas values. Although a few field and numerical studies have considered some temporal effects on soil gas vapor transport, a full explanation of the contaminant vapor concentration response to rainfall events is not available. This manuscript seeks to demonstrate the effects on soil vapor transport during and after different rainfall events, by applying a coupled numerical model of fluid flow and vapor transport. Both a single rainfall event and seasonal rainfall events were modeled. For the single rainfall event models, the vapor response process could be divided into three steps: namely, infiltration, water redistribution, and establishment of a water lens atop the groundwater source. In the infiltration step, rainfall intensity was found to determine the speed of the wetting front and wash-out effect on the vapor. The passage of the wetting front led to an increase of the vapor concentration in both the infiltration and water redistribution steps and this effect is noted at soil probes located 1. m below the ground surface. When the mixing of groundwater with infiltrated water was not allowed, a clean water lens accumulated above the groundwater source and led to a capping effect which can reduce diffusion rates of contaminant from the source. Seasonal rainfall with short time intervals involved superposition of the individual rainfall events. This modeling results indicated that for relatively deeper soil that the infiltration wetting front could not flood, the effects were damped out in less than a month after rain; while in the long term (years), possible formation of a water lens played a larger role in determining the vapor intrusion risk. In addition, soil organic carbon retarded the transport process, and damped the contaminant concentration fluctuations.

Original languageEnglish
Pages (from-to)110-120
Number of pages11
JournalScience of the Total Environment
Volume437
DOIs
StatePublished - Oct 15 2012

Bibliographical note

Funding Information:
This project was supported by Grant P42ES013660 from the National Institute of Environmental Health Sciences . The authors also appreciate the valuable discussions with Xiong Tao and Mingge Deng from Brown University.

Keywords

  • Numerical modeling
  • Rainfall
  • Soil gas sampling
  • Vapor intrusion

ASJC Scopus subject areas

  • Environmental Engineering
  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution

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