Groundwater-Related Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 776

17.5.3 Regional Approaches
It is recognised that it is much more cost-efficient to simultaneously remediate a
series of groundwater plumes in a region than to do this site by site, certainly in the
case of intermingling groundwater plumes (see Section 17.7.2 on mingling ground-
water plumes). Moreover, it is advisable to manage groundwater and surface water
as an integrated whole (Environment Agency 2009 ).
To be able to bring this regionally based groundwater Risk Management into
practice some tough judicial problems have to be overcome. Firstly, the responsible
parties who caused the different plumes need to be identified. This is sometimes dif-
ficult, especially in the case of intermingling groundwater plumes that were caused a
long time ago. Secondly, depending on the responsible parties identified, the contri-
bution to the total costs of the different stakeholders has to be negotiated. Given
the complexity of the legal and technical situation and the costs involved with
regionally-based groundwater remediation, hydrogeologically trained mediators can
play an important role in this process.
17.6 Sampling and Monitoring
17.6.1 Purpose
The most common purpose of groundwater sampling is to gain insight into the actual
contamination pattern in the groundwater. Besides this, time series of concentra-
tions of contaminants in groundwater, assessed through monitoring , are important
in evaluating the developments in groundwater quality. Monitoring networks are
also constructed for feeding data to models that allow simulation of groundwater
flow and contaminant transport. In Fig. 17.6 an example of a groundwater sampling
activity at a site in Ft. McMurray, Canada, is given.
Sampling and modelling should be intimately linked in an iterative way. Data
feed models which predict outcomes. If the outcomes are not validated, then often
the data are deficient, and so the data input needs to be modified.
Sampling or monitoring objectives must be defined at the early stages of a
contaminated site investigation.
17.6.2 Groundwater Concentration Pattern
Generally, the spatial variation in groundwater concentrations is less than the spatial
variation in soil concentrations due to the mixing of groundwater and contaminants
in groundwater. Nevertheless, accurate measurements and monitoring are burdened
with several difficulties. For bigger sites, for example, the spatial representation of
samples is often limited, since groundwater sampling is relatively expensive. Even
when a high density of sampling wells is applied, the total surface of the wells
generally is only a small part of the area under investigation. Besides this, problems