Groundwater HIA post edit - FreshwaterLife

should match the required level of confidence. Further guidance on sources of
information and data, and useful methods of processing, interpreting and displaying
information during the development of a conceptual model can be found in
Environment Agency (2002a).
The outline regional conceptual model should now be refined by adding more detail
about the local area around the proposed abstraction, to form a local conceptual
model. The information in the local conceptual model should of course be consistent
with that in the regional conceptual model. Information should be collected on, and an
understanding gained of, local factors including:
• Geology: use borehole lithological logs and large-scale geological maps
(1:10,000 for example), to build up a three-dimensional picture of the local
geology. Useful information can be obtained from site investigation,
geotechnical, mineral exploration, and abstraction boreholes. At the local
level, it is important to include drift and other superficial deposits, as they
may have considerable significance. Try to construct several crosssectional
diagrams of the local geology, to refine your understanding of the
structure of the aquifer.
• Hydrogeology: refine your understanding of the location and nature of
hydrogeological boundaries (vertically and horizontally), local groundwater
flow directions, the hydraulic properties of the aquifer and surrounding
formations, and interaction with surface water features. Look for reports of
test pumping already carried out in the area, and examine hydrographs
from observation boreholes to gain information on local trends in
groundwater level. Comparison of the hydrographs with annual recharge
estimates or abstraction records from nearby boreholes may help identify
whether the trends are natural or artificial.
• Hydrology: refine your understanding of the local surface water system,
including catchment boundaries, losing and gaining stretches of streams
and rivers, seasonal flow variations, behaviour of springs, and relationships
to wetlands, lakes, meres, etc.
• Groundwater quality: collect information on local groundwater quality
(including trends over time), and historical, existing and potential sources of
groundwater pollution.
At this point, readers may be asking the question, for what area should the local
conceptual model be developed, as the zone of influence of the abstraction has not yet
been defined? Unfortunately, this is a chicken-and-egg situation, in that the zone of
influence cannot be defined without a conceptual model, but the area for the
conceptual model is not yet clear. This is where the cyclical approach to conceptual
modelling comes into its own. An educated guess should be made of the area over
which to collect information for the first attempt at the conceptual model, with the area
being revised at the start of each cycle. If the abstraction is from a karstic aquifer or
fractured crystalline rock, the shape and size of the zone of influence is likely to be
highly uncertain, and will need careful consideration (see Appendices 3 and 4 for
further information).
4.2.3 Step 3: Identify water features susceptible to flow impacts
The starting point for this step is the question: Which water features are likely to be
deprived of water by the abstraction? In other words, at which places will quantities of
water (totalling the abstraction quantity) eventually be stopped from leaving the aquifer
(or additional flows induced), when the system has eventually achieved a new
24 Science Report – Hydrogeological impact appraisal for groundwater abstractions