Groundwater-Related Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 767

is manipulated by pumping water out of the polder area into surrounding canals.
These polders are generally found in coastal areas and are most common in the
Netherlands.
Irrigation may also increase water recharge significantly. In the past few years,
new irrigation areas have been created in many parts of the world. They have con-
tributed to an increment of groundwater recharge. Clearing of native vegetation in
recharge areas, as in upper parts of a catchment (which usually correspond to the
lowest agricultural productivity areas), can increase the amount of recharge as well.
One side effect of such an increase in recharge can be that salt and contaminants in
the upper soil layers are leached into underlying aquifers, causing land salinity and
groundwater contamination.
Construction of roads can affect both recharge and discharge. If the road is in a
recharge area, contaminants may be released accidentally during the construction or
operation phases. In regions with colder climates, salt added to melt snow in winter
can leach into the groundwater. When the road is in a discharge area, contaminants
are washed into the surface water. Movement of equipment and supplies can have
an impact as well.
17.4 Calculating Contaminant Transport
17.4.1 Conceptual Models
Every appropriate model calculation must be preceded by the development of a
Conceptual Model. In Section 1.8.7.2 a Conceptual Model was defined as a (usually
visual) presentation of the relationship between the source, all the pathways
involved and the receptor. A cross-section of the contaminated site is the most
common format of a Conceptual Model. An example of a Conceptual Model, as a
cross-section of a groundwater body, is given in Fig. 17.5 (European Commission
2008 ). In this graph, sources, pathways and receptors are given. Moreover, several
Points Of Compliance ( POC ) are identified in the graph in the framework of the
Water Framework Directive, which help to determine whether a contaminated
discharge is acceptable or to decide upon required remediation levels (European
Commission 2008 ). POC 0 relate to the concentrations directly near the source in the
unsaturated zone. The groundwater at POC 1 to POC3 at different locations in the
saturated zone could be considered as receptor. There are two types of compliance
point, these are, a theoretical point within a model for calculating an acceptable dis-
charge concentration or required remediation level, and a physical monitoring point
(e.g., an observation borehole). A compliance point may either be at the receptor
itself or, for practical reasons, at a point between the source and the receptor.
The development of a Conceptual Model is essential for modelling contaminant
transport, as groundwater bodies are complex systems, and the Conceptual Model
helps in understanding and identifying the paths, receptors and points (or planes) of
compliance. Moreover, it provides a schematisation of the geometry of an aquifer. In
addition, a Conceptual Model provides support for explaining Groundwater-related
Risk Assessment to the stakeholders involved.