Introduction to Contaminated Site Management - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 26

For a long time, risk assessors seemed quite helpless with regard to the risk-
based assessment of TPH. In some countries (e.g., the USA, the UK, Australia,
and the Netherlands) expert judgement-based Soil Quality Standards have been
implemented. An elegant approach for dealing with these complex mixtures was
provided by Franken et al. ( 1999 ). They described a procedure for dealing with the
human health risks of petroleum hydrocarbons, based on five groups of aliphatic
hydrocarbons and five groups of aromatic hydrocarbons. Analogous to the US
Total Petroleum Hydrocarbon Criteria Working Group, these hydrocarbon groups
are characterized by a specific equivalent carbon number index range, representing
equivalent boiling points.
An overview of the detection and remediation of soil and groundwater contami-
nated with petroleum products is given in Nadim et al. ( 2000 ).

1.3.3.9 Asbestos

The contaminant that provided the ultimate challenge for risk assessors, maybe even
more than oil and petrol-like mixtures, is asbestos. Asbestos is also frequently found
in soils. First of all, asbestos distinguishes itself from almost all other contaminants
by the fact that asbestos is a mineral. It also is completely different from other
contaminants in its behaviour: asbestos does not adsorb to soil particles and does
not migrate through soils via the pore water, or soil gas. It is also not taken up by
plants. The only pathway by which asbestos can give rise to adverse effects is by
inhalation. These effects, although very serious (mesothelioma, that is, cancer of
the pulmonary membrane and peritoneum, asbestosis, and increased risks for lung
cancer), will reveal themselves over the longer term, that is, decades after exposure.
A concrete way of dealing with asbestos is described in Swartjes and Tromp
( 2008 ). They derived a Soil Quality Standard (Intervention Value) from measured
data and described a tiered approach (as preferably used for other (composited)
contaminants) to assess the site-specific risks of asbestos in soils. In the first step,
measured asbestos concentrations in soil are compared with the Intervention Value
of 100 mg/kg dw asbestos equivalents (0.01% by weight). 'Asbestos equivalents' is
the sum of the concentration of chrysotile asbestos (also serpentine asbestos or white
asbestos) and 10 times the concentration of amphibole asbestos (other asbestos
types), for both friable and bound asbestos. When this value is exceeded, a tiered
approach is used for the determination of site-specific human health risks. A site-
specific human risk is assumed, unless it can be proved otherwise ('risk, unless

... .').

The three tiers are as follows:

• Tier 1, Simple test: investigating the possibilities/likelihood of exposure;

• Tier 2, Determination of the respirable fraction in soil: investigating the pos-

sible site-specific exposure to humans, independent of the actual site use or
site-specific elements, based on the determination of the respirable concentration
of asbestos fibres in soil, in conformity with the Dutch standard NEN 5707.

• Tier 3, Measurement and testing of the concentration of asbestos fibres in outdoor

and indoor air under standardised conditions.