It was a group seminar geophysics course presentation in my year 3 of which I was asked to represent the group in giving an oral presentation of how we can apply resistivity in the geophysical investigation of groundwater, pollution ansd hydrogeology.

1. APPLICATION OF RESISTIVITY FOR
GROUNDWATER,HYDROGEOLOGY
AND POLLUTION RESEARCH
GROUP 1
MAT NO.001-16 GEOLOGY
MAT NO. 006,008,014,022,029 GEOLOGY AND MINING

2. PRESENTED BY
OMOKPARIOLA ELSHALOM CHIOMA
MATRICULATION NUMBER: U2013/5565012
COURSE LECTURER: PROF. N.F. UKAIGWE
COURSE TITLE: PRINCIPLES OF GEOPHYSICS
DEPARTMENT OF GEOLOGY, ‘
UNIVERSITY OF PORT HARCOURT,
2015/2016 ACADEMIC SESSION.
COURSE CODE: GLY 306.1
GROUP: 1

3. S/N NAMES OF GROUP ONE MEMBERS Matric Number
1 Wilson Ama Emmanuel U2013/5565001
2 Agomuo Kelechi Peace U2013/5565002
3 Chigozie Ifeanyi Paul U2013/5565003
4 Enyiayi Glory Marckson U2013/5565004
5 Inekigha Samson Ayebaikoko U2013/5565005
6 Temuru Stephen Olotu U2013/5565006
7 Egileoniso Endurance Oni U2013/5565007
8 Onyemachi Chibundu Miracle U2013/5565008
9 Njoku Chinemerem Precious U2013/5565009
10 Nwazuruoke Emmanuel Chinonso U2013/5565010
11 Tunebari Bernard Henrietta U2013/5565011
12 Omokpariola Elshalom Chioma U2013/5565012
13 Miller Dhulesh Emmanuel U2013/5565013
14 Ndubuishi Peter Onwelazu U2013/5565014
15 Egwurugwu Chisom Chijioke U2013/5565015
16 Nwonkwo Bright Stephen U2013/5565016
17 Tolulope Lebile U2013/5765006
18 Kaine Bobmanuel Scent U2013/5765008
19 Patrick Progress U2013/5765014
20 Phillip Wilson U2013/5765022
21 Simon Ebikefe Ogidikpe U2013/5765029

4. Introduction
Water is a very important nature’s gift to man and it constitute 79.1% of the
world’s total land space; due to this fact availability of good quality water for
drinking is a necessity; sometimes these water could be contaminated or polluted
due to various forms like landfill, pollutants, etc and so we apply some resistivity
method to resolve this problem and also know the best level to achieve a clean
water from the aquifer.
Resistivity can be defined as the longitudinal electrical resistance of a uniform rod
of unit length and unit cross- sectional area; it’s an important part of well logging
especially recording along spontaneous potentials. Several methods has been
used and these includes; Electrode resistivity devices, Spontaneous log,
Introduction logging, Microresistivity logs and LWD Induction tools.
The use of resistivity logs are the determination of Rt and Rₓₒ and, for the newer
imaging devices, and the mapping of resistivity profiles into and around the
borehole. One of the problems of field investigation of groundwater pollution is
to locate the contaminated plume. In most cases the goal is to positively locate
the pollutant and its movement by test holes and direct monitoring. Drilling of
sampling holes on a hit-or-miss basis is both time- consuming and expensive.
This study however integrated hydrogeologic and geophysical measurements in
the assessment of aquifer vulnerability and the maps derived are anticipated to
complement the efforts of the regional government on groundwater
management strategies, particularly the prevention of groundwater quality
degradation.

5. 1: To know at what depth one can drill up to obtain a portable
clean water.
2: To identify contaminated regions within the subsurface
aquifer formations.
3: To differentiate between the boundary between salt water
and fresh water interphase.
4: To evaluate the geoelectrical and hydrogeological
characteristics of the aquifer layer present in the study area.
OBJECTIVES
Aim
The Use of Resistivity in the Application of the Study Groundwater, Hydrogeology
and Pollution.

6. LOCATION MAP
Fig 1: A Location Map of the area (Source: Stephen O. Ariyo and Gabriel O. Adeyemi)

7. METHODOLOGY
This was a desk work with materials sourced from the internet and several articles were applied. The method applied for resistivity
groundwater, hydrogeology and pollution.
Methods of Study: The study involved two phases of measurements- the hydrogeologic and geoelectric measurements.
The hydrogeologic phase involved water level measurements in a total of forty five (45) existing non-flowing wells
across the area. The measurements engaged steel tape whose lower end was marked with carpenter’s chalk, as
practiced in Moore (2002). This was to enable a reading to be taken from the submerged portion. To ensure
two measurements were taken at each well location, and the average values were determined whenever there was
contrast. Since the depth to the static water level is considered an approximation of the interface between the
and phreatic zones in a non-confined aquifer setting (Moore. Et. Al., 2002), the measurements were used to
the thickness of the vadose zone across the area.
The geoelectric phase has to do with the protective near-surface geologic barriers with sufficient thickness and low
hydraulic conductivity usually act as efficient groundwater protection media (Lenkey et.al. 2005). Clay or silt,
characterized by low resistivity (1-100 Ohm-m) and very low permeability, and impervious or semi-impervious
(laterite and lateritic sand), characterized by high resistivity values (> 400 Ohm-m) constitute protective layers where
they cap vadose zones. They are known to effectively slow down contaminants percolation in the vadose zone, thus
allowing time for natural degradation. Permeable materials like sand and gravel readily allows access of
The north-south and west-east geoelectric sections showing spatial variation of resistivity across the geoelectric
in the area show the spatial variation of resistivity in first and second geoelectric layers across the area.
The resistivity parameters in these layers have been used to evaluate the vulnerability risk of the materials overlying
unsaturated zone. Figure 8 shows that resistivity values in the range of 1-100 Ohm-m, diagnostic of clay/silt in the
Nigerian geologic circumstance, occurring at the north central to south central portions, constitutes about 20%,
resistivity values greater than 300 Ohm-m, suggesting laterite/lateritic sand, and occurring at north-west, south-
north-east and southern segments, constitutes about 21% in the first layer.

8. Fig 4: Adapted from NIOT,Rourkela,Orissa-769 008
Fig 5: Adapted from NIOT,Rourkela,Orissa-769 008
Fig 6: Adapted from Google Earth

9. EQUIPMENTS USED IN THE APPLICATION OF RESISTIVITY LOGGING
Fig 2: A Terrameter and its conductors
(Google Earth)
Fig 3: An application Of Resistivity of an Area
(Google Earth)
Fig 7:Soil resistivity meter
Fig 8: Voltage indicator
Fig 9: Null Balance
Fig 10: Adaptor

10. DISCUSSION
DEFINITION OF MAIN HYDROGEOLOGICAL PARAMETERS
Groundwater is characterized by a certain number of parameters which geophysical methods are trying to
determine from surface measurements, mostly indirectly, but sometimes directly. The most usual parameters are
the porosity, the permeability, the transmissivity and the conductivity.
THE POROSITY: The porosity is the ratio between the volumes of the pores and that of the rock. When dealing
with saturated layers (under the water level, that is to say under the vadose zone where the pores are filled with
air and with water), the water content is equal to the porosity.
Porosity = (volume of pores) / (volume of the rock)
Being a ratio, the porosity is expressed in %. The total porosity also includes the water located in clay, even if clay
is impermeable. For the exploitation of water, it is important to determine the porosity of free water (water
which can move), and hydrogeologists speak of the effective porosity which is the ratio of the volume of the
pores which are interconnected to the volume of the rock. As an order of magnitude, the effective porosity can
be for instance 80% of the free water porosity. The porosity of a fissured rock can be a few percents, that of a
gravel or a sand of the order of 30 percents.

11. THE CONDUCTIVITY: The electrical conductivity of the water is usually expressed in micro Siemens / cm: Conductivity
(microS/cm) = 104 / Resistivity (ohm.m) The electrical conductivity is the ability of a material to let an electric current flow
through it when an electrical voltage is applied. It is linked to the quantity of salts dissolved in the water: Conductivity
(microS/cm) = 1.4 x Total Dissolved Salts (mg/l).A usual rule for drinkable water is 10 ohm.m, or 1000 microS/cm, or 0.7 g/l

13. VERTICAL AND LATERAL INVESTIGATIONS
For measuring the ground resistivity, a current has to be transmitted with two electrodes, while the potential created on the
surface by the circulation of this current into the ground is measured with two other electrodes. Increasing progressively the
distance between the transmitting and the receiving electrodes permits to increase the depth of investigation (sounding array for
aquifer depth and thickness determination); translating the four electrodes together permits to detect lateral change of
resistivity (profiling array, for fault or fracture localization).
APPLICATION OF RESISTIVITY TO GROUNDWATER DETECTION
To identify the presence of groundwater from resistivity measurements, one can look to the absolute value of the ground
resistivity, through the Archie law: for a practical range of fresh water resistivity of 10 to 100 ohm.m, a usual target for aquifer
resistivity can be between 50 and 2000 ohm.m.
Most of the time it is the relative value of the ground resistivity which is considered for detecting groundwater: in a hard rock
(resistant) environment, a low resistivity anomaly will be the target, while in a clayey or salty (conductive) environment, it is a
high resistivity anomaly which will most probably correspond to (fresh) water in a confined aquifer.
In sedimentary layers, the product of the aquifer resistivity by its thickness can be considered as representative of the interest of
the aquifer. However, electrical methods cannot give an estimation of the permeability but only of the porosity.
The contrast of resistivity between a fresh water and a salted water (coming from a sea intrusion for instance) is high and the
depth of the water wedge is usually well determined with electrical methods.
In addition to this; in the aspect of resistivity value ratio determination: Water has the highest resistivity level compared to oil
and gas of which gas has the least resistivity value. Also polluted water due to land filling, sewage leakage, oil spillage, industrial
wash outs, etc tends to have a low resistivity value compared to clean water.

14. CONCLUSION:
The hydrogeological and surface geoelectric measurements conducted at the area enabled the delineation of the vadose
zone and assessment of invulnerability of the geoelectric layers capping the vadose zone. The depth to groundwater
(water table) ranges from 2.3m to 9.6m across the area. Based on DRASTIC index rating concerning classification of
depth to groundwater, shows that the unconsolidated layer encourages polluted water while consolidated layer
encourages clean water and it is in a confined aquifer.
I was also able to understand the application if resistivity log to know if an aquifer is polluted or contaminated and also
know that at every level water has the highest resistivity followed by oil and finally gas which has lowest resistivity due
to the ratio of their viscosity.
Since surface activities pose potentially great threat to groundwater quality, coupled with the growing demand for
groundwater for water supplies worldwide, vulnerability assessment thus become imperative. This assessment will
enable the delineation of zones of high or low aquifer sensitivity,
In addition to constituting a reliable guide to the delineation of zones of high or low aquifer sensitivity and effective
planning and groundwater management, in either local or regional scale.

15. THANK YOU!