BOREHOLE PROPOSAL | HYDROGEOLOGICAL AND GEOPHYSICAL INVESTIGATION FOR GROUNDWATER | SAMPLE

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.

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 6^0’ 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 33^OC 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:  6^O20^’N,  8^O06^’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 3^rd 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)

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

Drilling Techniques: The down the hole drilling method should be employed in this area as it is consolidated and compact.

Click on the related links below and read more.

Do you like this article? Share this article