Rapid In-Field Approaches for Delineating VOC in Both Soil Vapour and Groundwater for Vapour Intrusion Assessment

Liang Wang,Ying Cheng,Peter Gell,Mark Bowman,Ravi Naidu

doi:10.3389/fenvs.2021.746195

Liang Wang, Ying Cheng + Show 3 more

Open Access

https://doi.org/10.3389/fenvs.2021.746195

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Abstract

Traditional contaminated site characterisation approaches are time-consuming, labour-intensive, and demand a high level of expertise. This case study provides a rapid field-based solution to investigating a VOC contaminated site and its vapour incursion by combining soil vapour and groundwater survey. To fully assess the volatile organic compound (VOC) distribution in a contaminated site, a number of self-developed soil vapour sampling probes (SVSPs) were placed vertically at different locations in a grid with different depths. Hence, 3D subsurface contour maps for VOC concentrations in soil vapour can be obtained and used to help identify hot spots and the migration patterns of VOCs. This SVSP is “easy-to-install” in the field and a cost-effective solution for rapid assessment of soil vapour samples. The SVSPs can be installed both vertically and horizontally. If there is a requirement to take soil vapour samples beneath an existing building from a potential contamination source zone, SVSPs can be horizontally installed beneath the building without compromising its structural integrity. In addition, to ascertain the correct groundwater channels that are likely to carry contaminants from a potential source zone, an electrical resistivity tomography technique was employed to provide the preliminary information for groundwater delineation in a complex groundwater channel network.

Highlights

Groundwater flows through a contaminated area can carry volatile organic compound (VOC) contaminants off-site, where VOC vapours could migrate vertically and laterally through the soil in a residential area, and subsequently through building foundations to contaminate residential indoor air, a process known as vapour intrusion
This study showed that sampling with the soil vapour sampling probes (SVSPs) is a cost-effective way to rapidly identify a potential source zone
According to our hydrological report, the groundwater layer is around 10–12 m below the ground and the free-product and dissolved TCE is thought to be carried by groundwater that intersects with the source zone, which is released as a vapour which migrates to the ground surface as per vapour intrusion theory (Unnithan et al, 2021)

Summary

Introduction

Groundwater flows through a contaminated area can carry volatile organic compound (VOC) contaminants off-site, where VOC vapours could migrate vertically and laterally through the soil in a residential area, and subsequently through building foundations to contaminate residential indoor air, a process known as vapour intrusion. For a vapour intrusion risk assessment, the conventional method is to install a network of groundwater monitoring wells around targeted locations. Using this conventional method to locate and identify the correct groundwater channels that require the most treatment is costly and inefficient without firstly being able to identify the source zone. A solution for identifying the source zone is to install a network of soil vapour monitoring bores. Traditional vapour sampling bores take time to construct and install and is technically challenging.

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