Site-specific risk assessment and management of point and diffuse sources - Environmental Deterioration and Contamination: Problems and their Management - page 350

Uncertainties
The conservative estimates will certainly compensate the uncertainties, which derive
from the heterogeneities, and the quasi homogeneous black-box model approach,
without considering the differences in the composition, metal content, location of
the sources, and the watershed. The metal sorption and desorption on solid phases,
the solid transport which all may have a strong influence on the dissolved phase metals
and the metal resupply in runoffs are not taken into account either. These uncertainties
may be reduced in the Tier 3 risk assessment.
In summary: The three-tier risk reduction—natural contaminants retention,
removal and combined chemical and phytostabilization—can reduce metal concen-
tration to the desired threshold. Lead is the bottleneck of the system; risk reduction of
lead needs all three steps to reach acceptable risk level in surface water.
Tier 3
Concept
Modeling of the water flow by a numerical GIS-model and creating a more detailed,
numerical model of the contaminant transport to calculate the mobility influencing
changes due to partition, as well as chemical and biological transformation. When
creating such a model, one can consider the heterogeneities of the environment as well
as the increasing risk of the solid phase containing environmental compartments such
as the high sorption capacity soils and sediments.
Software for GIS-based modeling is available both as open source and on the
market. Geographic Resources Analysis Support System (GRASS, 2013) is a free and
open source (FOSS) tool which integrates process-based modeling and GIS. GRASS
have developed hydrological, sediment and stream modules for runoff and erosion
modeling, landscape structure analysis, solution transport, and watershed analysis.
Other available open source tools are geospatial libraries (PROJ.4, 2013; GEOS, 2013;
Geotools, 2013; Geoserver, 2013; TerraLib, 2013; Boost.Geometry, 2009), free Desk-
top GIS tools (GRASS GIS, 2008; SAGA GIS, 2013; uDIG, 2013; ILWIS, 2007), web
mapping tools (deegree, 2012; MapServer, 2013; MapGuide Open Source, 2005) and
geostatistics software (gstat 2013; R Project, 2013) which have made the widespread
use of GIS-based transport modeling possible.
For sediment transport modeling one can apply the distributed WaTEM/SEDEM
model (2013) and the HEC-RAS (2013) channel transport model. EEA PRAMS (2013)
quantitative risk assessment model fits well to contaminant transport modeling.
WaTEM/SEDEM is a spatially distributed soil erosion and sediment delivery model
specifically developed to simulate the impact of soil conservation and sediment control
measures as well as land use changes in the framework of an integrated watershed
management, on the local soil loss and sediment delivery to rivers.
WaTEM/SEDEM focuses on the spatial, and less the time-related variability of the
relevant parameters and allows the incorporation of landscape structure or the spatial
organization of different land units and the connectivity between them. The water ero-
sion component of WaTEM/SEDEM uses an adapted version of the Revised Universal
Soil Loss Equation (RUSLE) to calculate mean annual soil loss values. WaTEM/SEDEM