Vapor Intrusion - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 410

10.3.3 Soil Gas Advection ..................................

422

10.3.4 Mixing Inside the Building ............................. 423

10.4 Mathematical Modeling .................................... 423

10.4.1 Mathematical Model Formulation ......................... 424

10.4.2 Available Vapor Intrusion Models .........................

428

10.5 Sampling and Analysis ....................................

433

10.5.1 Sampling and Analysis Challenges ........................ 433

10.5.2 Pros and Cons of Sampling for Various Soil Compartments ......... 434

10.5.3 Analytical Methods ................................. 441

10.5.4 Field Screening Considerations ..........................

442

10.6 Mitigation ............................................ 444

10.6.1 Methods/Technologies for Existing Buildings .................

444

10.6.2 Methods/Technologies for Future Buildings ................... 447

References ................................................ 448

10.1 Introduction

Vapor intrusion is a pathway of potential exposure to volatile and semi-volatile con-
taminants (collectively referred to here as VOCs or vapors) that migrate from the
subsurface to the air inside occupied buildings. This particular pathway has gained
increasing attention in the past decade because of several highly publicized cases
where volatile contaminants were detected in indoor air samples at concentrations
higher than human health risk-based quality standards. To date, the practical experi-
ence with assessing vapor intrusion has demonstrated that this pathway can be very
challenging to assess for several reasons. The risk-based quality standards for indoor
air are very low, so extra care is required to avoid positive bias from contaminated
sampling equipment. Several common contaminants are typically found in indoor
air in residences at concentrations at or above risk-based quality standards due to
emissions from consumer products, building materials and even outdoor air sources,
so the relative contribution from the subsurface is often difficult to resolve. Indoor
air concentrations vary with the weather and building ventilation rate, and concen-
trations of VOCs in soil gas and groundwater samples show spatial and temporal
variability. All of these issues contribute to a relatively high level of uncertainty in
the assessment of vapor intrusion.
This chapter describes the factors affecting the vapor intrusion pathway, provides
information that can help in assessment of the pathway, and includes references to
much more detailed literature on the topic.

10.2 Conceptual Models

A conceptual model provides a framework for interpreting the processes influenc-
ing the fate and transport of contaminants as they move from a source to a receptor.
A conceptual model is not the same as a mathematical model, but should be the