Groundwater HIA post edit - FreshwaterLife

licensing (that may nevertheless be protected rights), and springs used for
stock watering.
• Records of domestic supplies, available from the Environmental Health
Officer in the local authority. These records are far from complete however,
and another approach is to examine records of public water supply pipes to
locate properties that are not connected to the public water supply.
• Records of boreholes and wells held by the British Geological Survey.
• Ordnance Survey maps.
• Databases of conservation sites (see Appendix 1).
Ideally, certain key pieces of information should be collected on the boreholes and
wells that are the licensed abstractions and protected rights, namely, total depth, depth
to pump intake, current typical pumping water level, and which aquifer is exploited.
This information is important for the assessment of potential derogation (see Step 11).
Depending on how far away the furthest flow impact feature is, the potential search
area is very large, and a great many potential drawdown impact features might be
present within the search area. How thoroughly Step 8 should be undertaken is a
matter of judgement. A door-to-door and field-by-field survey is the only sure way of
identifying all the relevant water features. This is obviously too onerous at Tier 1, but
may be necessary at Tier 3. The results of this step should be added to the sketch
map, as shown in Figure 4.2 (the water features coloured red).
4.2.9 Step 9: Predict maximum drawdown impacts
The water features identified in Step 8 should now be examined in turn, to predict the
magnitude and timing of the maximum drawdown impact. For predicting the magnitude
of the steady-state drawdown, it is suggested that the Thiem or Thiem-Dupuit equation
should be used as appropriate. These equations were introduced in Box 3.1, and a full
explanation of their derivation and the assumptions on which they are based can be
found in Kruseman and de Ridder (1990). For an abstraction in an unconfined aquifer,
the simplified situation is as shown in Figure 4.3.
Figure 4.3 Parameters for the Thiem-Dupuit equation
32 Science Report – Hydrogeological impact appraisal for groundwater abstractions