Acta Hydrologica Slovaca, Ročník 18, Č
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ACTA HYDROLOGICA SLOVACA Ročník 18, č. 2, 2017, 253 – 261 GROUNDWATER VULNERABILITY ASSESSMENT IN PRESPA REGION Zoran Kačeski The region around Lake Prespa in recent years is under the constant influence of the different activities (natural and human) that endangers the quality of groundwater. Namely, the characteristics of the basin, topographic and hydrogeological, contribute that the ground water in the region is under constant threat of being contaminated. For these reasons there was appeared a need to make a map of vulnerability of groundwater by the degree of vulnerability and, consequently, to create the conditions for assessment of protection measures for certain areas regarding level of vulnerability of underground water. For groundwater vulnerability assessment and vulnerability maps preparation DRASTIC method (Aller et al., 1987) and Italian hydrogeological settings (GNDCI-CNR basic method) were applied. KEY WORDS: vulnerability, pollution, DRASTIC, vulnerability map HODNOTENIE ZNEČISTENIA PODZEMNEJ VODY V OBLASTI PRESPA. Oblasť okolo jazera Prespa je v posledných rokoch pod neustálym vplyvom rôznych prírodných a ľudských činností, ktoré ohrozujú kvalitu podzem- ných vôd. Topografické a hydrogeologické charakteristiky povodia prispievajú k tomu, že podzemná voda v regióne je neustále ohrozená kontamináciou. Z týchto dôvodov sa ukázalo, že je potrebné vypracovať mapu zraniteľnosti podzemných vôd v závislosti od stupňa zraniteľnosti a v dôsledku toho vytvoriť podmienky na posúdenie ochranných opatrení v určitých oblastiach týkajúcich sa úrovne zraniteľnosti podzemných vôd. Pre hodnotenie zraniteľnosti a zrani- teľnosti podzemných vôd sa použila metóda DRASTIC (Aller et al., 1987) a talianske hydrogeologické nastavenia (základná metóda GNDCI-CNR). KĽÚČOVÉ SLOVÁ: zraniteľnosť, znečistenie, DRASTIC, mapa zraniteľnosti Introduction The study area is divided into two parts because it is not possible for the entire study area to determine the In the last several decades the assessment of vulne- vulnerability on the basis of one method. The part where rability of underground water become very important exist enough hydrogeological and geological data task due to different reasons. Among them the most obtained from wells, DRASTIC method was used for important reasons are: increasing of water demand for assessment of vulnerability of ground water basin. This different needs (human needs, agriculture, industry etc.), area is in the vicinity of Prespa Lake. Other part of increased production of pollutants that cause dete- study area which is on bigger distance from the lake is riorating of underground water and increased awareness evaluated by using hydrogeological mapping. The data of society for importance of underground water. The about Geological setting and Hydrogeological characte- assessment of vulnerability of underground water is ristic for investigated area is taken from “UNDP Project required due to risk assessment is obtained by known RFP 10/2013 Hydrogeological Study for the Lake vulnerability of underground water and the type and Prespa Watershed”. degree of danger polluters which is applied on particular area. Methods Proposed approach for evaluation of vulnerability of The Study area is located in one of the main tectonic underground water in Prespa region units, so called West-Macedonian zone. 253 Acta Hydrologica Slovaca, ročník 18, č. 2, 2017, 253 – 261 Fig. 1. Hydrogeological map of Lake Prespa region – Macedonian part. Obr. 1. Hydrogeologická mapa regiónu jazera Prespa – Macedónska časť. About the geological conditions of the Western- nerability of aquifer bodies is created by Aller at all, Macedonian zone we will note the following facts: 1987 and it is based on evaluation of 7 parameters - The area is covered with Paleozoic, Triassic, which together with the weight factors are calculated to Neogene and Quaternary geological units. obtain index of vulnerability of underground water, - The Paleozoic consists of metamorphic schist's DRASTIC index (DI). DRASTIC method was complex with Cambrian, Ordovician and Devonian developed with the intention to serve as like a tool for age from one, and Permian magmatic complex from determining the degree of vulnerability of any kind the other side. aquifers and DRASTIC index is relatively easy to - The schist complex is mainly built up of different calculate because it requires, comparatively speaking, kind of phyletic schist's, metasandstones, meta- a basic knowledge of hydrogeology and processes that conglomerates and rarely with marbled limestone. lead to pollution of the system groundwater. DRASTIC - Granitoides are present mainly for a zone Pelister methodology has two main parts: the determination of mountain (Baba mountain). hydrogeological units or hydrogeological zoning and - Triassic complex lies transgressive over schist's, and application pattern of relative ranking DRASTIC its mainly composed of limestone's and conglo- method. merates at the bottom level. In this paper, the evaluation of vulnerability of under- - On some zones (especially from the Ohrid lake ground water on area near to the lake Prespa is side), there are occurrences of intrusions or diapiric conducted by DRASTIC method due to there are 15 magmatic bodies of diabases, gabbros and wells from which was obtained a view of Geology peridotites. The upper zones of the field are covered profile and groundwater levels. with thick overlay of Pliocene and Quarternary DRASTIC method is based on evaluation of 7 para- sediments. meters which have their own weight. The weight deter- mines the importance of a parameter in determining the DRASTIC method overall vulnerability of aquifer. These elements and corresponding weights are shown in DRASTIC methodology for assessment of the vul- the table 1. 254 Kačeski, Z.: Groundwater vulnerability assessment in Prespa region Table 1. Elements for DRASTIC Method Tabuľka 1. Zložky pre metódu DRASTIC Parameter Weight Agricultural Weight Depth to water D 5 5 Net Recharge R 4 4 Aquifer Media A 3 3 Soil Media S 2 5 Topography T 1 3 Impact of Vadose Zone I 5 4 Hydraulic Conductivity of Aquifer C 3 2 D - Depth to Water (Depth to Water affects the time available for a contaminant to undergo chemical and biological. A low depth to water parameter will lead to a higher vulnerability rating. R - Net Recharge Net Recharge is the amount of water which enters the aquifer. This value can be calculated on an annual or monthly basis with data available. Net Recharge can be calculated using climate data by applying a mass balance on the water. Net Recharge = Precipitation – Evaporation – Runoff A - Aquifer Media Aquifer Media is used to produce a rating based on the permeability of each layer of media. High permeability allows more water and therefore more contaminants to enter the aquifer. Therefore a high permeability will yield a high vulnerability rating. S - Soil Media Soil media is affects the transport of the contaminant and water from the soil surface to the aquifer. The soil media can affect the types of reactions which can take place. T - Topography The topography of the land affects groundwater vulnerability because the slope of the land is an important factor in determining whether the contaminant released will become run-off or infiltrate the aquifer. I - Impact of Vadose Zone The vadose zone is the typical soil horizon above and below the water table, which is unsaturated or discontinuously saturated. If the vadose zone is highly permeable then this will lead to a high vulnerability rating. C - Hydraulic Conductivity The hydraulic conductivity relates the fractures, bedding planes and intergranular voids in the aquifer. These components become pathways for fluid movement, and likewise pathways for contaminant movement once a contaminant enters the aquifer. The hydraulic conductivity is positively correlated with the vulnerability rating. DRASTIC method relies on ranking, rating and weight: Table 2. Class of vulnerability by Rang – Each parameter is divided in several ranges DRASTIC Method which have influence in vulnerability of aquifer. Tabuľka 2. Triedy zraniteľnosti metódou Rating – Each rang of each parameter is assessed in DRASTIC relation to the other ranks to determine its emollient Class of Vulnerability Points capacity. Each rank is evaluated with a rating from 1 to 10. Negligible 23 – 30 Weight – Each parameter is evaluated in relation to Small 30 – 90 other parameters to gain importance in determining Medium 90 – 140 vulnerability. High 140 – 200 Extreme >200 The vulnerability of aquifer, the DRASTIC Index (DI), is obtained by formula: Application of DRASTIC Method for assessment of vulnerability of underground water shall consider the DI = DR · DW + RR · RW + AR · AW + SR · SW + TR · TW + following assumptions: a. Contamination occurs at the IR · IW + CR · CW (1) ground surface; b. The pollutant enters the water table when rain falls on the surface and percolates into the where saturated zone; c. The contaminant travels with water, at Index R – Rating, the same rate and speed as water; d. The aquifer is Index W – Weight. unconfined (the method can be modified for a confined aquifer); e. The dominant pollutants are not pesticides From the parameters mentioned above the DRASTIC (the method can be modified to include pesticides) index or vulnerability rating of underground water can be obtained. The higher the value for the DRASTIC Calculation of DRASTIC Index index, the greater the vulnerability of underground water on that location of an aquifer. Data