Groundwater HIA post edit - FreshwaterLife

Finally, the reversibility (or otherwise) of the potential drawdown impact should be
taken into account. Whereas it may be relatively easy to reverse the effects of
derogation, the damage caused to a wetland or an archaeological site by a significant
or prolonged drop in water level may be irreversible. This will affect the degree of
confidence that it is necessary to achieve.
4.2.12 Step 12: Assess the water quality impacts
Groundwater quality is given great prominence in the WFD, with the achievement of
‘good’ status being just as dependent on quality as on quantity, and it is therefore
treated separately here. However, methods for determining water quality impacts are
not nearly as well-developed as for quantitative impacts. For example, in the RAM
Framework, the approach is just to capture and record comments on existing water
quality problems where they affect the ecology, so that they can inform the next step in
the overall CAMS process, which is the sustainability appraisal. In addition, the
uncertainty associated with impacts on water quality is inherently greater than with
quantity, as the impacts are much harder to identify, measure, and prove. The
Environment Agency is developing regional groundwater quality monitoring strategies,
and will soon be in a position to define the background groundwater quality of all the
principal aquifers at least, if not for all secondary aquifers. This is a requirement of the
WFD, and data on all groundwater bodies are being collected so that the water quality
status of each body can be defined. In fact, part of the WFD procedure includes
identifying specific water quality pressures on the aquifer.
Potential water quality impacts of groundwater abstraction are largely related to
changes in the groundwater flow pattern in the aquifer. In some cases a numerical
groundwater model will be available that is also suitable for modelling contaminant
transport. This should be used to examine the impact of the proposed abstraction on
the water quality. However, in the vast majority of cases there will not be this luxury.
For these cases, the approach should be to ask the question: How is the flow pattern in
the aquifer likely to be altered by the proposed abstraction? A basic picture of the flow
patterns in the aquifer should be available from the conceptual model, and the usual
combination of tools, professional judgement and expert opinion from technical
specialists should be used to assess how these flow patterns will be altered. A
judgement can then be made on whether or not the water quality impacts are likely to
be significant. Issues to watch out for include the following:
• Pollutant plumes from point sources (such as old landfills or industrial sites)
accelerating or changing direction. Briefly, plumes in groundwater move by
advection, that is with the water flow, and by dispersion. Dispersion is
largely independent of the flow velocity so that a new abstraction, unless
very large, is unlikely to
change the rate of
dispersion significantly.
Advection takes place with
the flow of water, so that
increased rates of flow will
increase the plume
movement in a similar
way. Groundwater
abstraction can therefore
draw pollution into
previously unpolluted parts
of the aquifer, as reported
by Morgan-Jones et al Potential point source of pollution
40 Science Report – Hydrogeological impact appraisal for groundwater abstractions