Nowadays, for many countries, a major resource of drinking water is karst groundwater. In the world, millions of people are provided by drinking water from karst aquifers, which contain valuable freshwater resources, and also, karst groundwater plays a crucial role for economic development of various countries and regions   . At the same time, we should consider that karst aquifers are particularly vulnerable to contamination resulting from human activities      .
Today, groundwater contamination is the most concern problem in karstic regions around the world. Karst groundwater is a potentially faster contaminated freshwater resources, due to increasing population density, rapid urbanization, as well as domestic and industrial usage  -  . Thus, karst groundwater quality and permanent ecological monitoring are very important, because the hydrochemical investigation provides significant information about water quality and characteristics of karst system     .
In this paper, we present a new study of karst groundwater including geochemical compositions in the Racha limestone massif, where karst ground- water is one of the most important sources of drinking water, which represents considerable natural resource for the study area.
The novelty of this work lies in the fact that such a survey was conducted for the first time in the karst springs. For the first time, the content of heavy metals in karst waters was identified by laboratory studies. Based on the methods used, it is possible to conduct similar surveys on other limestone massifs of Georgia.
Also, in the future, if we foresee the predicted increase in fresh drinking water demand, a comprehensive study of karst groundwater is very important both for the chosen area and the whole country as well. Quality of drinking water is one of the big problems in this country. In the different regions of Georgia, local population has water supply problems, which are caused by various factors (agriculture, urbanization and other).
Therefore, the results of this study present important information on karst groundwater quality of the study area. Based on our research, we can say that the quality of karst groundwater is completely good and safe for human health.
2. Study Area and Geological Settings
In Georgia, karst is represented only western part of the country, and occupies 6.4% of the entire territory of Georgia, that is about 4475 km2   . Karst line along the southern slope of the Caucasus mountain range extends 325 km in length from the Psou River to the Ertso Lake area.
The Racha limestone massif is the biggest karst massif in Georgia (the total area of which exceeds 590 km2), which is located in the eastern part of the karst zone of western Georgia (Figure 1). Geographically, the limestone massif is lo cated in the Oni and Ambrolauri municipalities. The study area belongs to the medium and high mountainous regions in Georgia. The highest elevation of the Racha limestone massif is 2402 m above sea level   . Also, at high hypso- metric altitudes are located Dolabistavi (1170 m a.s.l), Kidobana (1177 m a.s.l), and Sakishore (1165 m a.s.l) karst springs, which are significant fresh water reserves. Krikhula karst spring is located at a relatively low hypsometric altitude (701 m a.s.l).
The Racha limestone massif is a classic karst region throughout the Caucasus in terms of karst processes development. The Bajocian porphyritic suite is the basis of the massif and Cretaceous carbonate rocks also influence the structure of the stratigraphy  . Rocks from almost every part of the Early and Late Cretaceous exist in the region.
The massif consists mainly of upper and lower Cretaceous and Paleogene limestones, which have an important influence on the origin and development of the surface and underground karst features and on the water table and its fluctuations due to their geologic characteristic  .
The prominence of karst processes in the region is considerably high, due to the rapid movement of water along the structural weaknesses in the limestones. The fault dislocations provide groundwater infiltration; there is a rapid infiltration and inflow of surface water and almost no surface flow on the surface of the massif. Some small surface streams are mostly associated with the rainy and snowmelt periods.
Figure 1. (a) Location of the Racha limestone massif (west Georgia). (b) Geological settings of the study area  .
3. Research Methods
Water samples were collected in 1000 ml (HDPE) plastic bottles. The plastic bottles were washed and rinsed 3 times with distilled water. Preservation of water samples was done by adding 2 drops of concentrated HNO3 (trace metal grade) to each sample. Each bottle was labeled according to the sampling location and time. The samples were then put into the insulated box and taken to the laboratory for further processing.
Water samples were filtered with Whatman 0.45 µm filter paper in a Buchner funnel and heated at 100˚C until the volume was reduced to 50 ml in the normal volumetric flask of 50 ml. The volume was made up with acidified water (made up with acidified water: 3 mL concentrated HNO3 + 1 L distilled water). Samples were analyzed by Atomic Absorption Spectroscopy (which identifies data by minimum errors) in the chemical laboratory of the Ivane Javakhishvili Tbilisi State University, country of Georgia.
4. Results and Discussion
We studied the following parameters in the water samples: the water chemical indicator (pH); oxygen chemical requirement in the organic substances and ammonium ions. In addition, the microbiological indicator―Escherichia coli (E. coli) was identified in the water samples that was not observed in any of the water samples (Table 1).
Content of heavy metals were identified in the same samples, including nickel (Ni), silver (Ag), cobalt (Co), lead (Pb), zinc (Zn), aluminum (Al), fluorine (F), manganese (Mg), iron (Fe), cadmium (Cd), and copper (Cu).
The study revealed that the heavy metal content in the karst waters does not exceed the Environmental limits, which makes possible to use the karst springs as drinking water. The research results are important, as in the study area, the population faces the seasonal water problems. Figures 2-5 show the data obtained through the chemical analysis.
According to the laboratory studies of the karst water samples, collected in summer of 2014, it was identified that out of the present water samples only in the Krikhula karst water was detected the excessive amount of the lead (Pb) ions, which was 0.07 mg/l; in this case, environmental limit is 0.03 mg/l according to Georgian standards (Figure 6).
Table 1. Content of some of the chemical characteristics in the karst waters.
Figure 2. Heavy metals concentration in the Krikhula karst spring.
Figure 3. Heavy metals concentration in the Dolabistavi karst spring.
Figure 4. Heavy metals concentration in the Kidobana karst spring.
Figure 5. Heavy metals concentration in the Sakishore karst spring.
Figure 6. Heavy metals numerical data found in the water samples. (a). Krikhula karst spring, (b). Dolabistavi karst spring, (c). Kidobana karst spring, (d). Sakishore karst spring.
Important surveys were conducted in the years of 2014-2015 in the Racha limestone massif, where the drinking water supplies are important, in order to study the karst waters’ chemical and microbiological characteristics. However, nowadays, unfortunately, by the Georgian legislation, the special characteristics of drinking water within karst regions are not very seriously taken into consideration in determining the criteria for karst water sources protection.
The results of our study provide important information for groundwater quality on the Racha limestone massif. By laboratory studies, conducted by us in the Dolabistavi, Kidobana and Sakishore karst springs, we found that in the study area, the chemical characteristics of the presented water samples meet the national standards, which means that the water samples do not include excessive amounts of various pollutants traces. Also, laboratory studies have found that none of the water samples showed any bacteriological indicators (E. coli). Thus, karst groundwater quality of the Racha limestone massif is good and quite safe for drinking purposes.
Based on this, we can state that the karst waters are completely safe for human health and in the future, it may facilitate the development of a strategic plan, which implies the karst waters to be used as drinking water for the Racha limestone massif.
Our intention was to conduct surveys in different smaller karst springs and carry out their laboratory testing, but due to financial shortages, we could not implement such surveys.
We would like to thank the Shota Rustaveli National Science Foundation for the research funding within the Doctoral Programs Grant No. DO/80/9-280/14. We also would like to thank the Vakhushti Bagrationi Institute of Geography for the financial support in the presented research.