Tikrit Journal of Pure Science

N ear surface soil and subsurface self-potential investigations were carried out in farming land nearby Quldara Village/Northeast Kikruk town about 15 km at area about 63000 m 2 . Nine soil samples has been taken to determine texture, organic materials percentage , PH, electric conductivity Ec and electric resistivity in the laboratory. Geophysical Self-potential method survey applied through six lines, the separation was teen meters between the electrodes of the employed instrument and teen measurement points has been taken , each line was 100 m. The self-potential data processed and presented as profiles and contour maps. Soil analysis proved that it is composed of homogeneous sandy clayey silt with normal content of organic materials and salt with moderate acidity, it is suitable for crop growin. Self-potential data interpretations indicated that the possibility of ground water in the study area.


1-Introduction
The present research concerning a land nearby Quldara village at Shuwan Suburb 15 km northeast of Kirkuk town fig.(1), Its area is about 63000 m 2 .The aim is to change it to farming area of different vegetable grown in the future, especially there no any knowledge about the nature of soil and water resources which important to any agriculture projects.

Fig.(1): Location map of the study area
The Self-potential method is playing a good role in achievement of great problems in geophysics, its principle is the measurement of natural occurring potential difference in the earth.The methods that can be used for the identification of underground water, it can be produces from electrochemical, electro kinetic and thermoelectric sources.It has been increasingly applied in groundwater and geothermal investigations, environmental and engineering applications mapping seepage flow associated with dams, geological mapping, delineate shear zones and near surface faults.The Self-Potential method has been used in worldwide applications in many geophysical problems, it used to propose a least squares inversion algorithm [1] and determine the spatially variable depth of the water table in shallow unconfined aquifers.It applied in derivative analysis method to higher derivatives to estimate the depth and shape of buried structure from self-potential (SP) data [2].A researcher studied the problem of a polarized cylinder with a small cross-section [3], the polarization geometry simulates the self-potential field produced by a horizontal flow.The SP was conducted in a study to map underground river flow in the karst area [4] to reduce the impact of drought during the dry

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season.A study of Water flow in the subsoil generates electrical currents measurable at the ground surface with the self-potential method has been conducted [5] to estimate the water-table elevation from SP data measured at the ground surface.The geological research which enclosed in the study area are, the application of the electrical resistivity method in hydrogeology of Jolack basin by [6] and the study of Salinity of groundwater of Kirkuk by [7].The objective of the study is to explore near surface soil characteristics and possible underground water existence.

2-Geological setting
The study farming land is situated in the basin area which is a part of the foothill zone in the folded area of unstable shelf in Iraq [8], structurally is located between the Kalkalan Dagh Mountain and Kirkuk with a width ranging from (15 -20 km).The area is characterized by the presence of some seasonal valleys nearby the site ranging from (20 -100 m) in width with a depth of (1-3 m) and its deposition consists mainly of Sand, Clay and Gravel, there is alluvial plain deposit (river terraces) which covers the site, the sediment composed of silt, clay, fine gravel and sand [9].

3-Material and methods.
The Self-potentials survey was carried out using the field techniques electrode configurations Potential gradient method fig.
(2) which called (dipole/leap frog/gradient configuration), the separation between the 2 electrodes is 10 m which measures the potential difference between the two electrodes .

Fg.(2): leap frog configuration survey.
Self-potentials measurement was carried out using two non polarizable porous pot electrodes connected to precision voltmeters capable of measuring to at least 1 mV.Each electrode is made up of a copper electrode dipped in a saturated solution of copper sulphate which can percolate through the porous base to the pot.Six survey line were conducted in the study area (line1, line2, lin3, line4, East line, west line) fig.(3), the separation between the two electrodes was (10) m ,ten leap points was taken in every line ,the total profile length line was (100)m.To hold near surface soil investigations in the agriculture laboratory nine soil samples was taken in (0.3) m depth at the site subjected to particles analysis, pH ,electric conductivity (Ec), organic material content percentage .Electric resistivity was determined for soil samples in the physics department table (1).

Table 1: Soil samples analysis results.
The self potential measured observed constructed as contour maps using Surfer (8) Software, the gridding data procedure is applied by kriging data interpolation fig.(4).For construct regional contour map third order polynomial regression fig.
(5) was applied by subtraction it from the observed one, the residual contour map fig.( 6) could be interpreted.

4-Result and Discussion
The The divergence of Self-potential anomalies in value is maintained by its source [10].In case of the value of self-potential is negative of hundreds mV, at that time the source is probably sulfide ore deposits and deposits of conductive minerals.Whether the selfpotential positive of tens mV, the possible source will be quartz or pegmatite occurrence.If the selfpotential value is less than hundred mV, it might because of chemical reactions.In condition the selfpotential is positive or negative of one to hundred mV, it denotes the movement of ground water.
Finally the self-potential will be negative value of three hundred mV due to bioelectric plants, but in our present research the geological setting in addition to wide information concerning present of ore or a likes deposit, in this situation we could infer that the selfpotential anomalies are due to streaming of ground water.In other side the observed self potential contour map fig.( 4) is consists of different source effects in geophysical term, some are from near surface others are from depth ones, the regional map fig.(5) indicates that deep effect, it shows wide broad shape regional anomalies spread all over the map.The operation of construct residual anomaly map fig.( 6) which more likely represent the near surface effect relates the electrokinetic potential of soil source .The process of isolation the regional anomalies from the observed anomalies also indicates present of deep source which is more likely denote to existing of underground water situation print its effect upon the observe self potential measurements.That assumption of availability of underground water in subsurface of the study area which yield from geophysical self potential data processing supported by the borehole section fig.(8) (ground water table is 21 m depth) which confirm the possibility of ground water existing through its impact upon the observed Self-potential measured data especially in the regional scheme.

5-Conclusions
Near surface soil analysis results which are in a good correlation proved that the nearby Quldara village land is a homogeneity contents composed of sandy clayey silt and normal amount of salt and organic materials with moderate acidity those properties are suitable for crop growing.Geophysical self potential survey and its data processing and qualitative interpretation in different presenting schemes could contribute as active tool to predict the possible existing of shallow ground water.
soil samples results showing that the site is compose of sandy clayey silt generally ,the electric resistivity tests (2.8-30.8)ohm.m reflect the constituent nature of that lithology of low values.Electric conductivity value (0.03-0.1) mS denote little amount of total salt the soil content, with low percentage of organic materials(1.3-3.9), the soil sample have moderate reaction between acidic and basic (7.52-7.95)pH.The self potential line profiles rapid view shows sinusoidal forms, it might reflect the effects of different sources in geophysical term upon the SP measurements ,it compose of low and relatively high amplitude of potential readings with negative and positive polarity ,minimum value is (-27.26)mV (line 3)and the maximum is (+28.01)mV(west line) .