Vapor Intrusion - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 431

circumstances. Therefore, it may not be applicable in specific circumstances, with-
out modifications. Johnson ( 2002 ) provides a detailed discussion of the critical input
parameters for the J&E Model and guidelines for the model's use.
The National Institute for Public Health and the Environment (RIVM) in the
Netherlands developed the VOLASOIL model in the mid-1990s (Waitz et al. 1996 )
and used it for site-specific indoor air concentration predictions in a decision frame-
work for determining the urgency of remediation. The model includes both diffusive
transport and convective transport. Site-specific data can be used as input data.
The VOLASOIL model was reviewed, further verified and extended by Bakker
et al. ( 2006 ) and Van Wijnen and Lijzen ( 2006 ) and now includes three foun-
dation types (i.e., crawl space, concrete basement and slab-on-grade floor). More
information about the extended, commercial version can be found via the website:
http://www.risc-site.nl /. Van Wijnen and Lijzen ( 2006 ) used this model to com-
pare predicted and measured indoor air concentrations due to vapor intrusion from
contaminated groundwater into buildings with crawlspaces. The study showed that
tetrachloroethylene (PCE) concentrations in air were positively correlated to the
groundwater concentration for all compartments (soil, crawl space and indoor air)
and that the relationships are significant at the 95% confidence level. Indoor air con-
centrations were well predicted, with more than 50% of the observations within one
order-of-magnitude. However, the observed concentrations for biodegraded prod-
ucts, like vinyl chloride (VC) and cis 1,2-dichloroethene (DCE), were often much
lower than the predictions. The observed TCE concentrations in the soil air were
in general within one order-of-magnitude higher and lower, though some of the
observed concentrations were up to 2 orders-of-magnitude lower than the predic-
tions. Other scenarios (concrete basement and slab-on-grade floor) need to be further
evaluated.
Risc is a model for performing fate and transport modelling and Human Health
Risk Assessments for contaminated sites. Risc contains various soil vapor emis-
sion models for predicting indoor and outdoor air concentrations. Risc can model
volatilization from groundwater and the vadose zone to indoor and outdoor air and
includes diffusive and convective transport of soil air to the building (BP 2001 ).
The model for volatilization from groundwater to indoor air is derived from ASTM
( 2004 ) and for soil to indoor air from Johnson and Ettinger ( 1991 ). The model
includes consideration of a concrete basement or slab-on-grade floor, but not a
crawl space. Risc can be used to estimate the potential for adverse human health
impacts (both carcinogenic and non-carcinogenic) and includes nine exposure path-
ways. More information about the commercial version of Risc can be found on the
website http://www.bprisc.com .
An extensive evaluation of vapor intrusion screening models was done by Evans
et al. ( 2002 ), who evaluated nine vapor intrusions models (including the Risc,
J&E Model and VOLASOIL models) for the UK Environment Agency in terms
of their contents, benefits, limitations and suitability for modelling vapor intrusion
for United Kingdom conditions. According to Evans et al. ( 2002 ) no single model
was considered to satisfy all the criteria, although it was concluded that the Risc
model most closely satisfied the criteria for inclusion in the British contaminated