Environmental Engineering Reference
In-Depth Information
agriculture). For example, in the Netherlands, gasoline no longer contains lead. In
the future, a reduction in metal levels in the topsoil may be expected due to leaching,
for lead an extremely slow process. Associated to that, the toxic pressure in the top-
soil may decrease slowly. Such an effect may be counteracted by continuing diffuse
inputs.
14.14.2.5 Outcome Assessment
An Outcome Assessment related to emission reduction measures has not yet been
made, since the processes that change lead concentrations in the topsoil are very
slow, and there is no data yet on subsequent sampling periods to allow for time-trend
analyses.
14.14.3 Handling Slightly Contaminated Sediments
14.14.3.1 Problem Setting
The Netherlands is a country rife with water. Land parcels are lined by thousands
of kilometers of actively managed waterways. Waterways tend to accumulate sedi-
ment, and sediments tend to accumulate contaminants. Sediments pose problems to
water quantity management, so that sediments need to be removed regularly.
Given the occurrence of (slightly) contaminated sediments, policies have been
formulated in the 1980s and 1990s to prevent soil contamination which would result
from the old practice of depositing (slightly) contaminated sediments on adjacent
lands, to act as fertilizer. At the time of implementing those policies, it was expected
that preventive chemical and emission permit policies would be sufficiently effective
in reducing the accumulation of contaminants in newly formed sediments in the
future. In short, it was expected that all newly formed sediments could be spread on
adjacent land again in the year 2000.
However, the policy ban that was formulated on spreading slightly contaminated
sediment from ditches in the rural landscapes on land (based on sediment qual-
ity standards) resulted in increased sediment loads in waterways: water managers
could not get rid of the slightly contaminated material that was continuously formed
(AKWA
2001
). This seriously threatened water
quantity
management (“keeping the
country dry”), and possibly also affected water quality. In addition, spreading on
land costs (say) 3 C/m
3
, while removal from the system and off-site treatment or
storage costs up to 100 C/m
3
. The question is thus: how to balance water quan-
tity and quality management with soil quality protection and cost effective Risk
Management?
14.14.3.2 Approach
As a solution, a database containing the volumes of backlog sediments with their
contamination levels was created, and the risks of spreading these sediments on
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