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Geophysical methods for hydrogeological

research, for the natural and artificial pollution

of underground water in the Kopais basin

G. Memou

Institute of Geology and Mineral Exploration, 115 27 Athens,

Greece

Abstract

The object of the present work is the evaluation of the geophysicalinformation for the formulation of proven hypothesis concerning thegeological structure of the Kopais basin. The target of the study was thesearch of the nature of artificial causes responsible for the aquifer pollutionwithin the neogene sediments or the karstified limestones cherts.

1 Introduction

The KOPAIS basin is situated in the region of BEOTIA 110 km fromATHENS. It's known that the basement of the study area belongs basicalyto the zone of the Eastern Greece and only at its western part appear partsof the Parnassos-Ghiona and Beotia zones, where limestones predominate.The flysch appears in both zones. The schist - sandstone - chert formationwith clayey schists, sandstones, conglomerates and ophiolites belongs tothe Eastern Greece zone and constitutes an impermeable formation withlow permeability in the weathering mantle and permeable in stronglyfissured zone. The neogene and quaternary formations are composed ofconglomerates and sandstones, gravels, sands, clayey marls beds etc. (G.Christodoulou, 1968).

According to G. Mastoris, 1968, the main tectonic directions (offaults) are WNW - ESE, ESE - WNW and E - W. Hydrogeologicaly theKOPAIS basin accepts a big volume of water based on the atmosphericalprecipitation as well as from the surface and underground flowouts.

The object of the study was to determine: The probable productiveaquifers. The underground formations of karstic cavities and fissured

Transactions on Ecology and the Environment vol 7, © 1995 WIT Press, www.witpress.com, ISSN 1743-3541

516 Water Pollution

limestones. The spread out and the depth of the schist-chert formationswith ophiolites. The geological structure, tectonics assessment, thickness ofthe quaternary and neogene formations, and the delineation of themetamorphic basement as well.

GEOPHYSICAL DATA

To accomplish the study, the following data were used: Theaeromagnetical map ( HUNTING, 1977 ) scale 1:100000 with a flight linespacing of 800m, and 300m ground clearance. The Bouguer map ( K.Lagios etc, 1988 ), scale 1:500000 with a density of 5 stations per Km*, ofthe regional area of Kopais, the total magnetic field measurements inprofiles and specific resistivity measurements with the Schlumbergerconfiguration .

The determination of the physical properties range, was done with "insitu" measurements which are presented in the following table.

Geological formations.

Quaternary and neogene.Flysch.Schist-chert formationswith ophiolites.

Karstifield limestone.Limestones and dolomites

Ps1020

35

1560

(Om)-50-30

-80

-60-3000

X

0.0.

0.

00

12

6

10-' (uCGS)-0.2-0.3

- 1.2

d(g/cn

2.12-2.40-

2.60-

2.67-2.70-

**)2.352.60

3.20

2.702.80

Table 1.

As it is shown from the given results there are differences and overlaps ofthe electrical properties of the formations. At the same time it is observedthat the only rocks in the zone, which have important magnetic propertiesare the ophiolites ( G. Memou and G. Skianis, 1990 ) while from thedensity results there is no clear difference between the limestone anddolomites and the only rocks with a density varying between 2,6-3,2 g /cmare the ophiolites with considerable outcrops in the regional area.

GEOLOGICAL DATA AND POLLUTION SOURCES

The basic formations which construct the area are :Quaternary formations.FlyschSchist- sandstone- chert formations with ophiolitesLimestones and dolomites.

Acquifers are distinguished in those which are hosted in grained(clastic) formations and those which are hosted in karstified limestones.Flysch is considered as the impermeable formation of local, water bearing,capacity. The schist - sandstone - chert formations with ophiolites , and atlower layers dolomites, are practically impermeable.


Water Pollution 517

The groundwater pollution tends to depend on:-The hydrogeological conditions prevailing in the local and regional area.-The development of the area.-The concentration of its populations.-The production and water consumption capacity of the area.

The pollution sources, according to the origin of waste waters whichcan provide with infiltration-percolation, are classified as follows:-Urban waste waters.-Industrial leachades (liquid residual).-Drainned wa ters of irrigated areas.-Nitrates resulting from fertilisers residues.-Disolution of corpses in cemeteries etc.

The reasons of groundwater pollution are :-Natural eg. transfusions of water from sinkholes, natural cavities andsurface drainage system.-Artificial eg. stables, cemeteries, cesspits, waste disposal sites agriculturalactivities etc.

The conditions of protection of groundwater from the pollutiondepend on and are relative to :The nature and the permeability, the thickness and the extend of stratathat exist above the aquifer. The degree of self-purification capacity of theproductive aquifer ( the sedimentary formation has a grain size less than0,4 mm ). The depth of the aquifer formations. The velocity ofgroundwater movement.

THE INTERPRETATION OF THE GEOPHYSICAL DATA

The application of geophysical methods in the KOPAIS basin can helpseriously to the observation of the parameters for the protection of theenvironment.

Geophysical data were studied in correlation to the geologicalformations, which construct the area and the following conclusions werederived:1. From the aeromagnetic data it comes out that:-The majority of the aeromagnetic anomalies is related to the rocks of theophiolitic complex, so it is possible to give the location and the form ofsuch rocks even in places where there are not any surface information as itis shown in fig.l These rocks are considered as impermeable formationswith local aquifers ( G. Christodoulou, 1968).-The main strike of the anomalies is NW-SE, there is also the NE directionand the E-W as well, fig. 2.-The morphology of the anomalies with the intense orientations and localdisturbances suggests that these are large fault zones and smaller tectonicstructures which lead to useful! conclusions for the tectonic structure of thearea, fig. 2.2. The Bouguer anomaly gravimetric map for the Kopais zone presents aclassic form of a basin anomaly ( Nettleton, 1976 ). The gravimetric


518 Water Pollution

anomaly is a "minimum" anomaly with main direction NW-SE and asecondary direction NE-SW which delineates the nowadays Kopais.Thegravimetric anomaly remains open in the NW and NE side of the basinand a dense gradient W and S of the present flow of the Kifissos river, isobserved fig.3.3. In the same section is presented also the isobathometric map of thekarstified limestone of the Kopais basin, where it is shown that the Kopaisbasin is a result of a tectonic submersion with the principal directionsNW-SE and a secondary direction NE-SW, which is probably the cause ofa horst in the lower levels of the basin.4. The construction of the physico-geological profiles was based on thegeophysical ( electrical, aeromagnetic and gravimetric data ) andgeological data. The profiles are located perpendicularly to the great axisthe basin.

The profile between the community PETRA-PAVLOS exists in thecentre of the basin of Kopais. The conclusions of the quantitative andqualitative interpretation of the geophysical data are :a. The north part of the basement has a smooth ( regular) submersion with10°- 15* degrees.b. Up^the depth of 200- 250m, sedimentary deposition is consisted ofalternating strata of conglomerates, marls, sands, sandstones and clays.c. In the lower levels of the basin a system of clayey depositions (in general)is perceived . Their thickness, in some places amounts to 500m.d. The more basic intervention offered by the geophysical data, is at thelimit of sediments to the basement where it is clearly discernible, thepresence of a stratum of the schist-chert formation with ophiolites.e. In the south side of the section faults cause large displacement of thebasement.f. The karstifeid limestones ( north and south of the section ) host largequantities of water.g. Considerable groundwater flow exists due to faults.

The profile of St. Georgios- Karia -Pirgos is situated at the west ofKopais, area and from the interpretation of the geophysical data thefollowing conclusions can be derived:a. In the north side of the basin section, the sedimentary formations arealternating beds of: conglomerates, marls, sandstones, sands and clays etc.where their thickness is 100- 250m.b. The faults caused heterogenous evolution at different levels of the basin.c. The existence of intense rupture (faulting) accommodated thegroundwater circulation at great depths.d. The high values of the specific resistivity allude to the existence of eithera compact neogen deposition or the basement of basin. The aquiferformation is located into the neogen sediments but the large quantities ofwater are hosted in the karstified limestones from the centre to the south ofthe profile.f. The schist-sandstone-chert formation and ophiolites manifest theirpresence at the south area of profile.


Water Pollution 519

Fig. 1 Aeromagnetic interpretation results, Kopais areascale 1:100.000

Fig. 2 Probable faults from aeromagnetic interpretation map,Kopais area, scale 1:100.000


520 Water Pollution

Fig. 3 Isobathometric map of the karstified limestone roof andBouguer anomaly map, Kopais area scale 1:100.000

CONCLUSIONS

The object of the present work is the evaluation of the geophysicalinformation for the formulation of proven hypothesis concerning thegeological structure of the Kopais basin. The target of the study was thesearch of natural and artificial causes responsible for the aquifer pollutionwithin the neogene sediments or the karstified limestones.

The important conclusions are as follows:a. The Kopais is a submergence basin^raben) with maximum depth of 700mand the basement is composed of limestone rocks.b. Differentiation of the type of sedimentation is observed from the centertowards the west of the basin and particularly by the north side of theKopais basin where the thickness of the alternating strata exceeds the 250mand the dip of the sedimentary deposits is 15° degrees. c.The faultshave affected the basement and the basin sediments . At the NW side theNW-SE directions dominate, at the NE side, the NE-SW directions whileat the southern and central part of the basin both directions are observedas well as E- W one.d. The impermeable schist-chert formation occupies important extensionand width westwards and southwards of Kopais basin.

The Kopais basin is one of the areas of the Greek territory which aregreatly developed, where there is a great concentration of population, withgreat agricultural and industrial possibilities, with large irrigated surfacewhere increasing quantities of fertilisers are used.


Water Pollution 521

SW

-300-•400-•5OC--6OO-

Section PETRANE

61 85 62 63 68 6O 67 59 53 52 51

W^k_WUWi--l^A^

-* ^ ( :-:V± :: ~2±M l

5 62 63 68 60 67 59 53 52

S¥e

200J- __g.

Section ST. GICR3IOS - K/WRIA - ST.

81 84 96 65* 97 98 66 80 75 * 76 38 137

NE

100-0 •

-1OC--20C-ooc--4OO--5OO-- 600-

i i i L ^ L ^a?*... »&" . •• X • > . <*"£'^#^Y '"[" ••. '••~.». ".'1-2'?'.jfet"—". ,\ ""* r

Fig.4 Scale 1:100.000


522 Water Pollution

in<u

cn

c(U£

<u 52 o3 E

co>o£ •oc.

O

TJC <U

o —V) O

c Itj *>

o<uO

S 2o. *_

: i.2 I>- 33 —

OOJ£(UQ.>sU.a»

«uc

•c oo -*-•(/* in<Ucr u


Water Pollution 523

Proposals

Having into consideration all these data plus the prevailinghydrogeological conditions in the local . and regional area it ispossible to suggest areas of the basin where due to natural and artificialcauses groundwater pollution is probable.

The northern and eastern part of the basin where intense tectonicsand the existence of alternating neogene formations with the basicdomina don of coarse grained^ meterial, gravels and conglomerates andtheir smooth submersion at 15*,made possible the natural and artificialpollution of groundwater.

In the central and southern areas of the basin, fine-grained material isdominated which has the ability of self-purification of the drainned waterof the irrigated areas. So the high production procedure does not affect thedeeper groundwater.

Westwards and southwards of the Kopais basin, schist-chertformation with ophiolites and the overlain strata, mainly composed ofclays and sandstones, occupy significant area. It is known that mainindustrial activity and population is gathered in this area of the basin. Sothe drained wate% infiltrated in the subsurface aquifers contain fertiliserresidues, urban wastes and industrial wastes.

But the existence of the large coverage of the schist-chert formationmakes possible the protection of the acquifer which results from thepresent study on the karstified limestones. The karstified limestones whichunderlain the schist-chert formation are the most hopefull strata wherefuture search for water should be directed.

Taking into account the complicated tectonics of the basin, it isindinspensable that detailed gephysical study should precede the futurelocation of the cemeteries, waste disposal sites of the domestic wastes andindustrial wastes , in order to determine the physical-geological parametersof the superficial strata.

Acknowledgments

The authour would like to express his gratitude to her colleaque Mr. M.Nikolaidis for his valuable interest and constructive criticism during thepreparation of this last manuscript, including the translation to the englishlanquage.

References

1. Books1. Nettleton, L.L. Gravity and Magnetics in Oil Prospecting, Me.

Graw-Hill, New-York, 1976.2. Karous, M. R. Application of ground geoelectrical method to

hydrogeological, engineering-geological and environmental studies,Montreal, Ecole Polytechnique, September -December, 1993.


524 Water Pollution

3. Ward, S. H. Geotechnical and Environmental Geophysics, S.E.G.Tusla, Oklahoma, 19902. Papers

1. Mastoris, K. Hydrogeological research in the limestone area ofSouth Giona. Doctoral thesis in the N. M. Politechny, Athens, 1968.

2. Memou, G. and Skianis, G. Geophysical research in lake Iliki,I.G.M.E. 1990

3. Christodoulou, G. and etc. Geological maps of Greece, Levadia,Vayia, Thiva sheets, sc. 1: 50000, I.G.M.E. 1968-1974

4.Hunting, 1976. Aeromagnetic map of Greece , Levadia, Vayia,Thiva sheets, sc. 1 :50000 .

5.Gatzogiannis, A. Hydrogeological maps of Greece, Levadia, Vayiasheets, sc. 1:50000, I.G.M.E. 1989


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