This short report summarises activities and conclusions
from a visit to Nigeria by Alan MacDonald (6-21 January
2001), other relevant information is attached. The terms of
reference for the visit were:
• to train WaterAid/WASU/BERWASSA staff to find
dolerite intrusions in Obi and Oju;
• to train staff in the use and interpretation of resistivity
equipment in Oju and Obi;
• carry out a desk study of the geological conditions of 7
LGAs in Benue State.
To meet these terms of reference a seven-day workshop
was undertaken in Oju/Obi comprising mainly fieldwork.
Three days were spent in Makurdi consulting geological
information available at the Geological Survey of Nigeria.
A summary of the main activities and recommendations
from the visit are given below.
1. Boreholes drilled into dolerite intrusions offer the
cheapest and most sustainable water supply for much of
Obi. Therefore considerable time (1-2 days per community)
should be given to try to locate dolerite in communities
in Obi. The best method for finding it is to use EM34
and magnetics together and then validate using EM34 with
40-m coil separations. WaterAid and WASU are competent
to carry out these activities.
2. All workshop participants could competently use the
magnetic and EM34 equipment. Most could interpret the
data to identify areas with dolerite. However, for this year,
it is advisable for the WaterAid Engineer to validate interpretations
of any surveys.
3. Resistivity is not a particularly useful technique in Oju
and Obi. Similar information is given by using EM34 at
20-m spacings and then repeating with 40-m coil separation.
All participants recognised the pros and cons of using
resistivity and as a group we decided that we do not need to
continue using it in Oju and Obi. Most participants can
now roughly interpret resistivity data.
4. The geological conditions of the 7 LGAs vary greatly.
The most difficult area for finding groundwater is probably
Gwer West. The geological conditions of all seven LGAs
are summarised in Table 3.
5. The records from the 2000 drilling programme highlighted
several important issues.
• The boreholes were drilled and tested during the rainy
season when yields are artificially high.
• They were only grouted to a depth of one metre, therefore
leaving the laterite unsealed.
• The depth ranged from 22-51m (average 32.4 m) –
well short of the minimum depth of 40 m suggested by
BGS.
• The bailer tests were not carried out properly (and the
raw data not given) therefore it is impossible to assess
the yields of the boreholes.
6. Several other issues arose during the visit, such as
the future use of the drilling rig; the distribution of reports
(both within the project and to other stakeholders). These
are discussed later in the report.
Summar
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