CONTENTS
Introduction
Abstract
Map
Geology
Hydro-geology
Geophysics
Conclusion
Recommendation
Investigative summary
INTRODUCTION
HYDROGEOLOGICAL AND GEOPHYSICAL
INVESTIGATION FOR GROUNDWATER was
commission by (NAME HERE) BUILDING AND CONSTRUCTION NIGERIA LIMITED
to undertake the pre-drilling hydro geological and geophysical investigations
at (ADDRESS HERE) with the view of
making recommendation towards a design and construction of a water supply bore
hole to serve its purpose.
On Tuesday (DATE HERE) a geophysical survey was
carried out at the location.
Included
in the overall methods of investigation are:
• Desk
study to review the geology and hydrogeology of the areas around the sites.
• Reconnaissance
survey at the site to check the existing structures, area of coverage, local
relief, geology and suitable position for gravity survey, Geophysical
investigation by resistivity method to estimate the
disposition of the sub surface strata.
• Report
with recommendations based on the outcome of the above.
The
following is therefore an account of the work carried out, the results obtained
as well as the conclusion reached and on which our recommendations have been
based.
ABSTRACT
Global
positioning system imaging, Geo-electric studies, Geological logs based on
exploratory drilling and local surfacial geology have been employed for
groundwater investigation in Abakaliki, south eastern Nigeria.
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Results
from the study shows that the areas which vary in sub surface composition have
a common feature of lateritic surface and thick underlying shale which however
should be targeted for groundwater investigation within the consolidated
sedimentary Environment.
Using
the results of the study/investigation there is increase in the number of
successful boreholes drilled in the areas from 35% to 51% most especially
within the location. It is also observed that remote sensing, geo-electric and
exploratory drilling data are adequate for delineating the surface and
near-subsurface hydrogeology of this areas.
The
survey was carried out at the surrounding of the Areas for the purpose of
locating prolific aquifers/fractures for the sitting of a motorized boreholes
that will supply water at the areas.
The
survey sites are centered on the geographical coordinate of 60’ 20’N,
8006’E and have an average altitude of 179ft.
OBJECTIVES OF THE SURVEY
The
overall objective of the survey is to delineate saturation zones in the area
for the purpose of developing a motorized underground water scheme for PRIVATE
USE Consequently, the following set objectives were born in mind.
i.
To conduct Geophysical survey in
the area
ii. To
delineate zones of saturation with their thickness and depth.
iii. To
design and make recommendations for the drilling of a borehole.
LOCAL GEOLOGY OF LOCATION
SITE DESCRIPTION
TOPOGRAPHY
The
study area is located on consolidated sedimentary catchments. The area under
investigation is surrounded by low land which gives a goods sight view of
distant topographical formation characterized by consolidated sedimentary
shale. The highest point on the location is 205ft.
CLIMATE;
Abakaliki
experiences a humid tropical climate with annual temperature of 33OC
on the average.
GEOLOGICAL ASSESSMENT;
The
area under investigation is underlain by shale’s and table mountains with
gentle crest and troughs. The surface exposes light grey feldpathic and
micaceous laterite and blue black shally intrusives.
INTERPRETATION OF DATA
The interpretation of the survey is presented in the
table below:
COORDINATE: 6O20’N, 8O06’E
|
LAYER
|
DEPTH (M)
|
RESISTIVITY
|
INFERED LITHOLOGY
|
COMMENT
|
|
1
|
0.58
|
559.08
|
Lateritic over burden
earth.
|
Topsoil
|
|
2
|
1.02
|
892.00
|
Compact dry clay
|
|
|
3
|
2.70
|
934.37
|
Dry clay
|
|
|
4
|
5.82
|
582.09
|
Partly weathered shale
|
|
|
5
|
12.53
|
257.56
|
Fractured shale
|
|
|
6
|
18.39
|
146.78
|
Dark shale likely fractured
|
|
|
7
|
19.67
|
144.68
|
Shale
|
|
|
8
|
22.23
|
122.66
|
Shale
|
|
|
9
|
22.23
|
98.78
|
Weathered shale
|
|
DATA ACQUISITION
The
location was visited on the 3rd of December 2013. A Vertical
Electrical Sounding (VES) was carried out at spots shown. The maximum spread
was AB/2 = 250m and AB/2 =150m . The data were acquired under favorable weather
conditions. A variety of electrode arrangements are possible for resistivity
measurements in the field, but Schiumberger array has been found to be
convenient and reliable in most terrains. Electrode movement on the current
electrodes C are moved outward symmetrically, keeping P fixed at the center.
With this procedure often called electric drilling, the properties of the
subsurface may be explored.
INSTRUMENTATION
A
resistivity meter, Electrodes, and a wire which transmits a little amount of
current say 5mA to the homogenous ground surface.
The
Resistivity system consists of a basic unit called the Booster a method whereby
consecutive readings are taken and the results are averaged continuously.
DATA PROCESSING
All
raw field data were processed by using the appropriate constants and analyzed
using RESIXPLUS Inverse Computer program. The VES data are then presented as
sounding curves which are obtained by plotting graphs of apparent resitivity
versus half-current electrode spacing on double logarithmic graph sheets and
further verified using curve matching.
SITE VES (INTERPRETATION)
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RECOMMENDATIONS
From
the results minor saturation zones occur from depths of 55-60ft and 70- 9Oft
within unconnected joints. The fractionating zones within these saturation
points are good to accommodate a high capacity motorized. The over riding
inference is that there is 68% probability of success for drilling a borehole
at the site location selected.
SPECIFICATIONS
Drill-bit
diameter (minimum): 6-8”
Casing
diameter (minimum): 4
- 6inches
Borehole
depth: 45-48m
Screen
depth (total): 9m
(281t)
Screen
slot size (max): 0.5mm
Sump:
1m
(lOft)
Gravel
packing: quartzite
pebbles
 |
| BOREHOLE DESIGN |
Drilling
Techniques: The down the hole
drilling method should be employed in this area as it is consolidated and
compact.
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