Healthy water - future of human life



On the base agreement between Šobot Milan and Grahovac Siniša, from Banja Luka, and Gaćeša Nenad, geology and geophisic engineer from Banja luka, there was carrying geophysics and geo-electric research of “Ograđeni bunar” environment in Bijakovac village – village part Rijeka near Moštanica, municipality of Kozarska Dubica as first stage of Hydro-geology research of larger environment, in aim to establish optimal condition for water operation.

Field works was made in May 2004 in relative favorable weather conditions, during the high water level and high level of underground water.

Field surveying is made by Vožni Zdenko, geologist technician, with assists. Processing of field surveying information is made by Nenad Gaćeša, geology and geophysics engineer.

Area position included by this research is present on topographic map of larger environment in 1:50.000 proportional.

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Report made by Nenad Gaćeša.

Geology of larger area

To take into consideration that we do not have details about geological material of tested area, in order to see disposition of some litho-facies and tectonic characteristics of area, we can give shortly geology characteristics according to Basic geology map SFRJ, 1 : 100 000, Kostajnica.

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On South edge of larger area is represent with Central ofiolit zone rock and ofiolit melanz of the Jurassic formation, present with stratum of diabase - horny formation – sandy terrain, clays with olistrolits and horn-like stones with olistoliths and olistroms Triassic limes, serpentinite, amfibolite, gabro-dolerits and diabase of relative big (kilometric) dimensions.

In the middle part of larger area is represent by younger, neogen and qaurtar stratum. Neogen stratum of middle Miocene (M 2 2) is presented with two facies – multi layered marl sandstones and facies of limestone Stratums of upper Miocene (M 3 1) is presented by two facies of marl sandstones, bio-classic and limestone and marl sandstones.

In north-eastern part of larger area, nearby tested area, is represented with metamorphose rocks of granite drain of Prosara, represent with meta-sandstones, and further on north, green quartz slates. In places, on surface, there is granite-porphyry and quartz-porphyry.

On tighter area of testing, on left shore of Kablovska Rijeka, on surface is find stratums of middle Miocene (M 2 2) represent with facies of multi – layered marl sandstones (toward Prosara) and stratums of upper Moocene (M 3 1) represent with facies of sandy Triassic marls and marl sandstones (on sauth), on right shore of upper Miocene stratum (M 3 1).

Geophysics tests

Method of testing:

Geophysics tests are done on 10 spots, approximately disposed along 4 profiles.

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With method of geo-electric ground sounding with four electrode symmetric (Schlumbergers) dispositive of electrodes A-M-N-B, with maximal half-interval of electrodes AB/2 to 200 m (see drawing). The depth of testing is approximately 100 m. Testing is reach borders of some litho-facies environment to depth of 70 m.

A ...........................M ......O .....N .......................B

Insincere resistance of ground is:

Where resistance is in ohms, potential difference between electrodes is in mV, and strength of electrodes is in m A.

Results of testing:

As result of geo-electric ground sounding we come to diagrams shown above every single profile for every single sonde.

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On base of information taken from diagram of geo-electric sounding we made maps of izo-ohms

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Which shoves distribution of insincere resistance of ground for depth which corresponding size AB/4. Profiles of izo-ohms shoves distribution of insincere resistance in profiles of ground.

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With graphic and analytic processing of diagrams geo-electric sounding we can define thickness of some litho-facies environment and truth resistance that characterize it, for very single spot and bring on geo-electric profiles.

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Interpretation of testing results:

Diagrams of geo-electric sounding

With field surveying we obtain four and five stratum diagram,

See diagrams in adjective 9 to 12

which shoves on relative complex “electric material” of ground. In shallow parts of ground “electric material” is some more complex, which we can clearly see on diagrams S-1, S-2, S-7 and S-10. For illustration, lower is the diagrams that illustrate this.

Here in shallow parts of ground, there is diagrams of H-K-H and K-H-A types which shows on often reduces of thin quart clayey, sandy and clay stratum, so diagrams for shallow parts is more complex.

In deep parts there is diagrams of K-H types which shoves that under environment of higher resist is environment of lower resist, which is characteristic for eastern parts of tested area (see diagram S-2), while diagram of A-K type (see diagram S-7) or H-K (se diagram S-9) shows that on depth part of ground under less resist environment is environment of larger resist, which is characteristic for western parts of tested area.

Diagrams are showed in minimized logarithm scale on geo-electric profiles,

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as illustration of field measurements.

Maps of izo-ohms AB2=5m, AB/2=9m, AB/2=20m, AB/2=60m, AB/2=120m

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Map shows distribution of insincere ground resistance in depth approximately same as size AB/4, which for some maps are 3, 5, 10, 30, and 60 m.

It is visible that on all maps insincere ground resistance is about 50 and 200 ohm. In shallow parts of ground higher resistance, as well as water drain, have same stratum in domain of sonde S-5 and S-6, while zone of higher resistance in deeper part of ground considerable spreads, which manifest on larger space of waterproofing layers in depth parts.

Profile of izo-ohms

Profile of izo-ohms,

See adjective 9 to 12

which represents distribution of insincere resistance in ground profile shown as illustration and contrast show different resistant zone in ground profile. Bigger resistance (lighter shade) in domain of alluvial stratum point to presents of gravel-sandy stratum with considerable water proofing, and in foundation alluvial stratums domain on relative compact rocks which can be porous, also with considerable water proofing. Smaller resistances (darker shade) in ground profile show reduced water proofing of stratum.

It is very noticeable zone of bigger illusory resistance subsurface stratums on south part profile GEP-I and on eastern parts profile GEP-II and GEP-III for AB/2 approximately 50 – 60 m, with tendency to deepen in domain sonde S-5. This deepen is probably stratum of deeper parts of ground.

It is also characteristic increase of stratum resist in deeper parts profiles GEP-III and GEP-IV, on western parts of profile.

Geo-electric profiles

On geo-electric profiles,

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On every sonde we can see “geo-electric structure” In ground profile, in other words thickness of some diagrams of separated environment and sizes of truth resistance which characterize it. With correlation of thickness and sizes of resistances between sondes on sides of profile we can set aside some geo-electric environment which is on condition of litho-facies environment presents in ground profile.

Because there is information of testing drilling, litho-facies decree of some geo-electric environment along the profiles in deeper parts is not defined. It is not rare in practice that different litho-facies environment have same electric resistance. That is why is difficult to notice them on diagrams. That is why description of environments shown on geo-electric profiles is given conditional in legend, especially for deeper parts of ground.

On all profiles in shallow parts we can see two environments with different alectric resistance included with environment of:

1. Relativity thin surface of quartar clayed stratum and delluvial layer with crush have characteristic of specific electric resistance (SER in far text) between 55 and 110 ohms. It is not considerable waterproofs. Gravel – sandy stratums in alluvial surface of River, which have relative big resistance, between 110 and 485 ohms, have considerable resistance.

Deeper, nearby under quartar, on all profiles is separated middle with lower resistance:

2. Subsurface, some deeper (5-20 m) marl – clay stratums originate from rock decay, which is characteristic with reduce resistance, 40 – 100 ohms is low or none waterproof rocks.

In deeper parts of ground two environment is selected:

3. Layers of deeper parts of ground with resistance between 55 and 150 ohms, according to size of SER represent reduced waterproof, and in domain of smaller sizes of SER probably is not waterproof.

4. Layers of deeper parts of ground which is represent with very large SER, between 150 and 350 ohms, have considerable waterproof.

Map of suffice deep of waterproof rocks

On map, with izo-lines is shown deep of waterproof layers of deeper parts of ground, shown on geo-electric profiles as environment 4, which is characteristic with very large electric resist, between 150 and 350 ohms.

Expressed difference in deep of suffice of this layers on some parts of tested area probably is cause of tectonic dislocation, marked on geo-electric profiles and on map as assumed cleft.


On base of geophysical efforts we can conclude this:

Waterproof layers on smaller tested area is environment with very large SER, over 150 ohms.

Further tests with drilling must be direct to environment with larger SER, over 200 ohms.

In goal to make water works, from environments of deeper parts of ground, drilling must direct on western parts of profiles GEP-III and GEP-IV. Deep of drilling, according to results shown on geo-electric profiles is need to be about 60 and 80 m.





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