Groundwater HIA post edit - FreshwaterLife

2 Basic concepts
2.1 Introduction
Before delving into the detail of the HIA methodology, it is useful to discuss some basic
concepts that are fundamental to HIA, namely uncertainty, risk, and conceptual
modelling. This section also deals with some common misconceptions about the way
in which groundwater abstractions behave. Unfortunately, there is no magic tool for
assessing the hydrogeological impacts of groundwater abstraction; the emphasis is on
developing good conceptual models, taking uncertainty and risk into account, and
using appropriate tools and techniques to answer specific questions.
2.2 Uncertainty and risk
The Environment Agency’s approach to environmental risk assessment is based on the
guidelines published by the Government (DETR 2000). In these guidelines, the
following definitions are given:
Hazard: a property or situation that in particular circumstances could lead
to harm.
Risk: a combination of the probability (or frequency) of occurrence of a
defined hazard and the magnitude of the consequences of the occurrence.
In groundwater abstraction licensing, the hazard is the act of abstracting water, and the
risk relates to potential impacts on the environment, or other impacts such as
derogation of the rights of existing abstractors. In order to evaluate and use risk
assessments effectively as a credible basis for decision-making, it is important to
understand how different sources of uncertainty contribute to the final risk estimates.
Uncertainty can affect all stages of risk assessment, and environmental scientists are
increasingly being required to provide information on how certain their decisions are.
Analysing the sources and magnitudes of uncertainties can help to focus discussion,
identify knowledge gaps, and feed into decisions about risk management.
Uncertainties generally fall into the following categories (DETR 2000):
• Model uncertainty: where models provide only an approximation of the
real environment. Model uncertainty may have two components: (i)
conceptual modelling uncertainty due to insufficient knowledge of the
system; and (ii) mathematical model uncertainty arising from the limitations
of the model selected in accurately representing reality.
• Sample uncertainty: where uncertainties arise from the accuracy of
measurements or the validity of the sample (number and location of
sampling points).
• Data uncertainty: where data are interpolated or extrapolated from other
sources.
• Knowledge uncertainty: where there is inadequate scientific
understanding of the processes involved.
• Environmental uncertainty: where the inherent variability of the natural
environment leads to errors in our approximations. For groundwater
4 Science Report – Hydrogeological impact appraisal for groundwater abstractions