|The present study therefore investigates the groundwater potential of SRRBDA Zamfara State Talata mafara using the self potential values (sp)|
BACKGROUND OF THE STUDY
Zamfara state is one of the 36 federating states in Nigeria with the state capital located in Gusau,It has immensely witnessed all round infrastructural developments and a corresponding population growth. The increased population has led to rapid increase in the demand for potable water for domestic, irrigational and industrial uses which public water by government could not meet. The consequential effect of the situation is that some inhabitants making alternative arrangements for water through wells and boreholes and others that could not afford that get water of uncertain quality from water vendors in carts and tankers and also from surface water sources. However, available bodies of water on the Earth’s surface which include streams, rivers, oceans and lakes are often not very safe for direct consumption due to their exposure to atmospheric pollutants (from natural and anthropogenic sources) and pathogenic organisms that make these water sources not as clean as the groundwater, and this has necessitated subjecting them to chemical treatments before consumption or industrial use. Groundwater, the water held in porous and permeable rocks deep within the earth called aquifers, is relatively pure and grossly protected from surface pollutants perhaps due to their depth of storage and natural filtration through different subsurface layers (soil horizons). Groundwater is enormous and therefore its development is essential to supplement the expensive surface water to relieve stress which population growth often places on water availability and supply. The provision of groundwater supply in Zamfara state as part of a coordinated development programme for rural development is seen as an essential service imperative to the entire state’s development (Macdonald’s and Partners, 1986). Three governmental organizations were responsible for provision of groundwater for the entire state; namely, Water Resources Engineering and Construction Agency (WRECA), Zamfara State Water Board, Ministry of Water Resources. In addition, a number of local governments are also promoting their own groundwater supply programmes. Groundwater exploitation by these agencies is carried out by sinking of hand-dug, concrete limed wells and drilling of abstraction boreholes all located in geologies. However, despite the efforts of these organizations, it is estimated that out of the 7,500 hand dug wells in the state in 1981, about 3,300 had either fallen into disrepair or were in need of being re-evacuated due to collapse/slumping-cave-in e.t.c. Thus, village water supply sources essentially that consisted of seasonal streams, rainfall pools and other such reservoirs. These sources are invariably polluted and constitute hazards to health (Imerbore et al 1987). In alleviating the hardships endured by rural population, the objective of the international drinking water supply and sanitation decade will have been considerably satisfied (WHO 1990). Various potentials are produced in native ground or ground within the surface altered by our actions, natural potentials occur about dissimilar materials, near varying concentrations of electrolytic solutions, and due to the flow of fluids. Sulfide ore bodies have been sought by the self potential generated by ore bodies acting as batteries. Other occurrences produce spontaneous potentials, which may be mapped to determine the information about the subsurface. Spontaneous potentials can be produced by mineralization differences, electro-chemical action, geothermal activity, and bioelectric generation of vegetation. Recognition of different spontaneous-potential sources is important to eliminate noise, the low background voltages, some engineering and environmental occurrences may be mapped by contouring surficial voltages between base/refrence electrode(s) and the mobile electrodes. Flow of gasses and fluids in pipes, leakage of a reservoir within the foundation or abutment of a dam, movement of ionic fluids to or within the groundwater, flow of geothermal fluids, and movement of water into or through a karst system can be the origin of streaming potentials; these potentials may exceed the background voltage variation of a site.
STATEMENT OF THE PROBLEM
The present study therefore investigates the groundwater potential of SRRBDA Zamfara State Talata mafara using the self potential values (sp). This present study is more detailed than the work of previous workers, and adds to the existing geophysical database for groundwater development activities in the area.
AIM AND OBJECTIVES
The aim of this study is to assess the ground water potential using self potential values.
The main objective is to investigate the:-
The ground water development
Get the sp data
Plot the sp data with depth
Identify location of greater depth
SIGNIFICANCE OF THE STUDY
This study investigates the ground water potential of SRRBDA Talata mafara Zamfara state with a view to delineating the suitable aquifer for ground water development.
1.4. LOCATION OF THE STUDY AREA
The Bakalori Dam is in Zamfara State in the Northwest of Nigeria, completed in 1978 and its reservoir filled by 1981. It is a major reservoir on the Sokoto River, a tributary of the Rima River, which in turn feeds the Niger River. Water from the dam supplies the Bakalori Irrigation Project.
The dam has a capacity of 450 million cubic meters, with reservoir Covering 8,000 hectares extending 19 km (12 mi) upstream.
The dam construction project displaced many Peasant farmers without providing alternative land or financial compensation. Many people died in protests over their loss of livelihood.
The project has become known as a classic example of development failure. The Sokoto River runs through the semi-arid Sudan Savannah zone of northern Nigeria. Annual rainfall is Unpredictable, ranging from 500 mm to 1,300 mm per year during the June–September period.
Self-potential methods measure naturally occurring electrical potentials in the earth. One source of these self-potentials is the “streaming potential” (or electro kinetic potential) which arises from the flow of fluid (e.g. groundwater) through a porous medium. For this reason self-potential is used in groundwater investigations and in geotechnical engineering application for seepage studies. Self-potential surveys are conducted by measuring electrical potential differences between pairs of electrodes that contact the surface of the earth (or water, in water covered area) at a number of survey stations in the area of interest. These stations may be along profiles or spaced so as to obtain a real coverage. One station is selected as a base station and all potentials are referenced to that point. The base station should be located at a point removed from expected anomalous activity. Potential (voltage) measurements are made by contacting the earth with non-polarizing electrodes. These electrodes, often called “porous pots,” are designed so as not to create any spurious chemical potential upon contact with the ground. Measurements are made by connecting a high impedance voltmeter between two electrodes, usually the base station and a roving electrode. Self potential interpretation can range from a simple a qualitative inspection of the plotted self potential profiles to complex computer modeling involving subtle interactions between temperature electrochemical reactions and earth geometry. For most groundwater investigations a simple qualitative analysis will provide the desired information about groundwater flow paths. Data are plotted as profiles (observed potential versus distance along the profile) or, if the data provides sufficient areal coverage, as contour plots. All else being equal, the anomaly location corresponds to the maximum groundwater flow. For “point sources,” some estimate of the depth of the source may be obtained from the width of the anomaly. There are several other sources of self potential variations which may act as noise or interference when mapping streaming potentials for groundwater investigations. These include: buried metal, temperature variations, soil property variation, electrochemical variations topographic effects and telluric (naturally occurring time varying electric potentials caused by distant thunder storms and ionospheric disturbance. NGA’s geophysical team has the expertise to deal with these interference and create sound geophysics create sound geophysical interpretations
2.1. MEANING OF SELF POTENTIAL
Self potential is also called spontaneous potential (sp) is a naturally occurring electric potential difference in the earth, measured by an electrode relative to a fixed reference electrode. Sp are often measured down boreholes for formation evaluation in the oil and gas industry, and they can also be measured along the Earth’s surface for mineral exploration or groundwater investigation. The phenomenon and its application to geology was first recognized by Conrad schlumberger, marcel schlumberger, and E.G. leonardon in 1931, and the first published examples were from Romanian oil fields. Sp are usually caused by cgarge separation in clay or other minerals, due to presence of semi-permeable interface impeding the diffusion of ions through the pore space of rocks, or by natural flow of a conducting fluid through the rocks
2.2. SELF POTENTIAL SURVEY
Standard SP surveys utilize non-polarizing, porous pot electrodes, which have been specially adapted to minimize contact voltages. Readings are typically taken with one electrode fixed at a base station and a second, mobile ‘field’ electrode that is moved around the survey area. Reading stations are spaced at regular intervals along linear profiles, closed loops or grids depending upon the desired application. The self potential method is traditionally used as a mineral exploration tool and for down hole logging in the oil industry. More recently it has been adapted for hydro geological and water engineering applications, by the use of more sensitive equipment and the careful application of data
2.3. FIELDS EQUIPMENTS OF SELF POTENTIAL SURVEY
The self potential method goes back to 1830, when Robert fox used copper plate electrodes and a spring galvanometer as a detector in attempt to final extension of underground copper deposits in common wall. Since 1920 it has been employed in base metal search, usually as a second method. The equipment required is electrodes connected by a wire to mill volt meter. There are however two restrictions on the electrodes and detector that are most important. If one were to use metal strokes driven into the ground as self potential electrode, the result, electrochemical action at the ground contacts would create spurious potential are erratic in different ground and at different time, so it would be possible to make a fixed correction consequently time, so it would not be possible to make a fixes correction consequently non polarizing electrodes are essential. A simple sp survey consists of a base electrode position and a roving electrode to determine potential differences on a gridded survey or along profile lines. The required equipment merely includes electrodes, wire, and a precise mill volt meter.
2.4.1. SURVEY ELECTRODES
The electrodes in contact with the ground surface should be the non-polarizing type, also called porous pots. Porous pots are metal electrodes suspended in a supersaturated solution of their own salts (such as a copper electrode suspended in copper sulfate) within a porous container. These pots produce very low electrolytic contact potential, such that the background voltages is as small as possible. Tinker and Rasor manufacture models of porcelain non-polarizing electrodes that are reliable and sealed to avoid evaporation of the salt solution. Sealed pot can take their supersaturated solution for more than a week, even in and locates, refilling the pot with solution must occur before a day’s work due to the possible contact potential change while performing a measurement set.
2.4.2. SURVEY WIRE
The wire used in sp surveys must be strong, hard, and are of low resistivity. were needs to have sufficient tensile strength to be able to withstand long-term pulls of survey work for multiple sites. For some field use, heavy twine or light rope may need to be twisted and knotted to long lengths of wire to add strength. Survey wire must have abrasion-resistant insulator wrapping. Pulling the wire over roadway surfaces can expose bare wire. Usually random bare wire positions will not fully ground to the soil, and the effected will be variables differing lengths of wire are unreeled and occupy differing positions for the survey. This error will only modify the signal by a few to tens of millivolts (mV). Twisted two-conductor, 18-gauge, multi strand (not solid conductor) copper wire has been found to be strong and abrasion resistant.
2.4.3 MILLI VOLT METER
An inexpensive, high-input-impedance voltmeter is used to read the potential in the millvolt range. Actual field voltage will be in error when the source potential is within a order of magnitude of the input impedance of the meter. The meter uses a bias current to measure the desired potential. The input impedance should exceed 50mΩ. Higher input impedance is desirable due to the impedance reduction of air’s moisture. The resolution of the meter should be 0.1 or 1.0mV
2.5. PAST GEOPHYSICAL WORKS USING SP
In the 1970’s, Bogoslovsky and Ogilvy (1973) observed a significant positive self-potential anomaly (¼ 40 mV) around a pumping well in response to a pumping test experiment in steady state conditions (Figure 1a).
Revil et al. (2003), proposed three methods to interpret these data: (1) a semi-empirical approach relating linearly the self-potential signal to the depth of the water (note that many authors, such as Jackson and Kauahikaua, (1987) and Aubert and Atangana (1996) have observed a similar relationship), (2) a tomography algorithm based on a normalized cross-correlation algorithm, and (3) an inversion scheme using the Simplex algorithm. Their analysis is based on the conceptual model of Fournier (1989), which considered each element of the water table, in steady state conditions, as an elementary dipole with an inclination locally perpendicular to the water table and strength proportional to the water table elevation. The three methods proposed by Revil et al. (2003) determine the shape and range of possible depthsof the water table from the study of the self-potential distribution recorded at the ground surface.
Naudet et al. (2003, 2004) have shown that it is possible to determine the redox potential values of a contaminated aquifer from self-potential measurements. They have performed intense self-potential measurements on the Entressen landfill site (Provence, Southern France). This landfill, which has been active since 1912, is responsible for an organic-rich contaminant plume spreading in a shallow unconfined aquifer. After removing the electrokinetic component associated with the groundwater flow, then, a strong negative anomaly (several hundreds of millivolts) was observed to be correlated with the contaminant plume. Moreover, as a first approximation, the strength of residual self-potential signals has been shown to be directly proportional to the redox potential (Naudet et al., 2004)
Naudet and Revil (2005) performed sandbox experiments in which self-potential signals and redoxpotential variations were monitored in presence of sulfate-reducing bacteria. A linear relationship was also observed apparently related to bacteria activity. From these considerations, these authors proposed a (bio)-geobattery concept in which biofilms and/or biominerals (precipitation of metallic particles induced by biomineralization) at the redox front allow electron transfer (therefore a net driving current density) between the reduced and oxidized parts of the system. In turn, this current is responsible for an electrical field measurable at the ground surface as self-potential anomalies.
Recently, Rizzo et al. (2004) performed a pumping test experiment and monitored both piezometric levels and self-potential signals during the steady-state and relaxation phases. Using hydraulic models during these two phases of experiment, they joined the hydraulic and electric theories to analyze the self-potential data.
Mohammed et al. (2007), in their regional study and investigation for groundwater potential in Minna area, identified Chanchaga as one of the locations in the area with less than the average aquifer’s thickness of 24 m.
Amadi et al. (2009) worked on the hydrogeology and water quality of southwestern part of Minna and concluded that the water is of good quality and occurs in the regolith and fractured bedrock.
Idris-Nda et al. (2013) also conducted a study on the occurrence and chemical composition of groundwater in Minna Metropolis and found that weathering in the granitic bedrock ranges from 3 – 25 m and constitutes the main source of water for shallow dug wells, chemically the water shows a gradual enrichment in manganese, arsenic and lle
The self-potential geophysical method is simple, a high quality non-polarizing electrodes combined with a precision millivolmeter is used to record the voltages, resulting from natural electrical current flow in the earth, at the earth surface. We will first map the 2D distribution of SP across the landfill and into keegan marsh within the vicinity of the landfill. The self-potential measurements on the keegan landfill will be made in a conventional manner by implanting the electrode into soil surface. The geophysical measurements are obtained “in survey” from a shallow-draft paddleboat and spatially geo-referenced with precision global positioning satellite (GPS). Self Potential (SP) geophysical surveys measure the potential difference between any two points on the ground produced by the small, naturally produced currents that occur beneath the Earth’s surface. The SP method is passive, non-intrusive and does not require the application of an electric current. Small potentials of the order of a few millivolts are produced by two electrolytic solutions of differing concentrations that are in direct contact, and by the flow of groundwater through porous materials (streaming potential). Larger ground potentials are produced by conductive mineralized ore bodies partially immersed below the water table.
3.1. CHARACTERIZATION OF GROUNDWATER QUALITY
For the purpose of risk assessment of contaminated sites and the use of remediation methods, it is very important to know how and where the anaerobic contamination can spread or decline over time. In this situation, the self-potential method appears as an economical and fast reconnaissance tool to monitor redox conditions and to delineate the shape of the contamination plume. In the case of contaminated groundwater, the main self-potential sources are associated with
Groundwater flow (electrokinetic effect),
Concentration gradients (diffusion or membrane potential) and
Redox potential gradients (electro-redox effect). To further evaluate the potential role of bacteria in the generation of an electrical current.
3.2. FIELD PROCEDURES OF SELF-POTENTIAL GEOPHYSICAL SURVEY
Background potentials for these surveys may be at a level of a few tens of millivolts. Self-potential must exceed the background to be apparent. Potentials exceeding 1.0v have occurred for shallow or down hole measurements of large sources. Measurements with the electrodes may require a system of reversing the electrode position to resolve contact potentials at the electrodes. Previously measured locations may need to be premeasured on a systematic or periodic basis. Reoccupation if s necessary when very accurate surveys are being conducted and for sites with temporal potential changes or spatial variations of electrode potential. Changes temporally in the electrodes or due to the self potential of the field require the survey to be conducted in a gridded or loop array. Loops should have closure voltages of zero or only a few millivolts. High closure potential requires re measuring several to all of the loop station. Station reoccupation should be in the same exact position of the earlier reading (s). in -closed lines should be avoided. Reoccupation of particular station intervals should be made when closed loops are not possible. The traveling electrode should periodically re-measure the base location to observe contact potential, dirty electrodes, or other system changes. Reversing the survey electrodes or changing the wire polarity should only change the voltage polarity. Electrodes may have contact differences due to varying soil types, chemical variations, or soil moisture. Temporal and temperature variations are also possible, which may require the reoccupation of some of the survey positions on some arranged loop configuration. Electrode potentials have minor shifts with temperature change. Variations in the flow, or change of surface elevation where measurements are obtained are sources of variation of streaming potential. Self potentials may have temporal or spatial changes due to thunderstorm cloud passage, dissention of mineralization or electrolytic concentration, and in the groundwater flow conduits and location. High telluric potential variations may require the SP survey to be delayed for a day.
Some simple procedures are required to perform accurate and precise SP surveys. Good maintenance of porous pots, wires, and voltmeters must be observed through the survey. The traveling pot needs to be kept clean of soil with each position. Contact with moist oil, or more elaborate measures for good electrical contact with roadways or tock, must be assured. A water vessel may be varied to moisten the soil hole and clean the porcelain surface. Wire reels speed the pulling of cable and wire recovery for changing loops, and lessen wear on the cable. Reversing the wire polarity for some measurements and reoccupation of adjacent stations assures the cable has not been grounded or stripped. Repair and checking of the wire must be made between loops and is easily done when rewinding the cable reel.
Quality assurance in the field is conducted by reoccupation of loop closure points with the same base position. Repeated and reversed readings of particular loop end stations and checking base locations provide statistics for the assessment of measurement quality. Grid surveys offer some advantages in planning SP surveys. Changes in elevation (changing the distance to the potential source) and cognizance of cultural effects can be minimized with planning survey grids or loops. AC power lines, metal fences and underground utilities are cultural features that affect the potential field extraneous to the normal sources of interest.
The research work title assessment of ground water using self potential method in the Sokoto rima river basin development authority (SRRBDA) Mafara shows that the SP result for the ground water are more likely to flow around station one with sp value 46.574 (mV), at latitude 11.9671(N0) and longitude 8.4292(E0), for station two with SP value 59.67(mV) at latitude 11.9661 and longitude 8.4293, station 3with SP 63.507(mV) at latitude 11.9646(N0) and longitude 8.4290(E0), station four with SP 69.415(mV), latitude 11.9699(N0) and longitude 8.4399(E0), station five with SP value 47.136(mV), latitude 11.9717(N0) and longitude 8.4393(E0), station six with SP value 28.333(mV), latitude 11.9731(N0) and longitude 8.4385(E0), stations even with SP value 86.024(mV), latitude 11.9742 and longitude 8.4388(E0), station eight with SP value 98.080(mV), latitude 11.9917(N0) and longitude 8.4387(E0), station nine with SP value 30.597(mV), latitude 11.9754(N0) and longitude 8.4380(E0), and station ten with SP value 26.981(mV), latitude 11.9922(N0) and longitude 8.4371(E0).