Groundwater HIA post edit - FreshwaterLife

i. Establish a preliminary conceptual model of the river-aquifer system, and
choose whichever analytical solution available in IGARF is closest to the
conceptual model.
ii. Using IGARF, make initial predictions of the likely impacts of the
abstraction, carrying out sensitivity analysis on the input parameters to give
a range of likely impacts.
iii. Design a field pumping test based on the predictions, using IGARF to
indicate whether these changes are large enough to be observed, and if so,
over what time-period monitoring should be maintained, and how far
upstream and downstream the river flow should be monitored.
iv. Conduct the pumping test, analyse and interpret the results to evaluate
impacts on the river and to calculate aquifer physical properties.
v. Review the conceptual model, the selection of analytical solution and the
range of parameter values used in IGARF.
vi. Make predictions of the long-term impacts, using IGARF as a guide, and
taking into account all uncertainties.
3.3.3 Tier 3 tools
The main tools likely to be used at the level of Tier 3 are spatially-distributed, timevariant
and usually three-dimensional numerical groundwater models, calibrated and
validated against historical data. Such models should only be used by experienced
hydrogeologists and groundwater modellers, as their use is by no means intuitive. The
main modelling codes likely to be used are:
• MODFLOW: a freely available code developed by the United States
Geological Survey, which has become the industry standard. Many pre-
and post-processors and other useful software modules have been
developed for MODFLOW.
• ZOOMQ3D: a relatively new code being developed jointly by the University
of Birmingham, the Environment Agency, and the British Geological
Survey.
• MIKE-SHE: a package of models and graphical user interface developed
and marketed by DHI Water and Environment, Denmark.
• FEFLOW: a finite-element model (the other three are finite-difference
models) developed by WASY GmBH, Germany.
The Environment Agency's current preferred numerical groundwater modelling
software is MODFLOW, with Groundwater Vistas as the user interface.
3.3.4 Other useful techniques
Many other investigative techniques may be useful when undertaking HIA at any level.
If considered appropriate, and used carefully, these techniques can provide additional
information that may help with the development of conceptual models, and the
prediction of impacts. Such techniques include the following:
• Tracer tests: which involve adding a suitable tracer (such as a fluorescent
dye) to groundwater, with the aim of establishing a flow connection
18 Science Report – Hydrogeological impact appraisal for groundwater abstractions