Environmental Engineering Reference
In-Depth Information
2008 ). By adding information on sediment management costs for each of the han-
dling options, the cost-effectiveness of the alternative classification systems could
be explored.
14.14.3.5 Outcome Assessment
Since the removal of sediments was considered urgent to prevent flooding, the
new policies were implemented before the system was validated. A real Outcome
Assessment could consist of a regular monitoring of terrestrial soils, in a chronose-
quence, to study whether the new policies result in terrestrial soils that are less
contaminated than the soil quality standards, and/or result in lower net risks than
predicted. Due to the urgency of the problem given the water quantity management
needs, the Management Assessment is currently being conducted. Hence, there is
as yet no Outcome Assessment showing that the new approach is both sufficiently
safe as well as cost-effective. However, Harmsen ( 2004 ) demonstrated that long-
term deposition of slightly contaminated (Class-2) sediments on adjacent land did
result in slight but significant increases of, e.g., PAH-levels in top soils. However,
the net toxic pressure did not increase proportionately, due to the sigmoid associa-
tion between PAH-concentration and ecological risk. It appeared that the observed
concentration increases were taking place at the level of the near-horizontal lower
tail of the SSDs of the different PAHs.
14.14.4 Soil Quality Classes and Local Risks to Manage
Local Soils
14.14.4.1 Problem Setting
As mentioned in Section 14.14.1 , a toolbox for site-specific Risk Assessment has
been provided since 2008 by the national Dutch government, to assist local soil
authorities in soil management. This toolbox is applied for complex situations, such
as management of the reuse of excavated soils in built areas. This example shows
the soil use classification in a municipality, demonstrating that different soil uses do
imply different sensitivities related to those soil uses (e.g., man can be more sen-
sitive than ecosystems), which could consequently imply the use of different soil
quality standards for appraising soil quality implications. So far, all appraisals used
the national standards (Target and Intervention Values), which were usually based
on the most sensitive endpoints. Since 2008, three soil quality classes have been
implemented in the soil appraisal system (a class with sites with soil concentrations
below the background concentration, and a class “residential” and a class “indus-
try”). Class boundaries were derived so that the local soil use is not at risk, with
higher class boundaries going from “background” to “residential” to “industry”.
Further, the example shows a hypothetical outcome of the use of the Risk Toolbox
for such soil use areas, given certain degrees of contamination.
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