GIS based Ground Water Quality Analysis in Kabul City Region

Ahmad Shah frahmand Msc Geoinformatics (Senior), College of Science, Osmania University, Hyderabad, India

Ground water assumes greater significance as a resource for utilization under various sectors as it is a confined resource within the layer beneath the surface of the earth and supposedly less polluted due to limited interaction with atmospheric agents. In fact, it is observed that more than 75% of irrigated areas in the countries east of Afghanistan are ground water based. Especially, in India ground water is over used as it is considered as a free resource. Political sops like free electricity for pumping the ground water have depleted them so much that there is an alarming situation faced by every user in the country.

Afghanistan lies along the great tectonic upheaval that has produced the world’s highest mountain ranges including the Hindu Kush Mountains. In the Kabul area Orogeny has been accompanied by a complex sequence of faulting. Deep Grabens in crystalline rocks have formed and are filled with hundreds of meters of alluvial, culluivial and lacustrine deposits. Ground water flow in the Kabul basin is mainly through saturated alluvium and other basin fill sediments. The water surface table generally mirrors topography and ground water generally flows in the direction of surface water discharge. (USGS, Afghanistan project 001, 2005)

As far as Kabul is concerned, the bulk of urban and rural water supplies for domestic and other municipal purposes in kabul are obtained from ground water sources like springs, karezes and manmade wells. (http: //www. afghan-engineers. org/water -supply. html) Though, there are many alluvial ground water aquifers in the basin, Logar, Kabul and Paghman are important for providing drinking water for Kabul as they are rich in ground water potential. Properties of three main groundwater aquifers are given in (table 1).

Table (1): Properties of Three Main Ground Water Aquifers around Kabul City

Source: Afghanistan Geological Survey

In fact, it is found that due to the strategy for supplying drinking water is to develop ground water resources, water table has dropped approximately 6-7m with in forty years from 1965-2005. (Tunnemeier and Houben 2005). However, the over exploitation of ground water is an environmental hazard, which may not only cause the salinity of ground water, but also enhance the rate of land subsidence (Lashkaripour & Hussini 2008 )

The quality of ground water is also an important issue to be considered as it affects the human health, both directly as well as indirectly. The quality of ground water in the vicinity of Kabul city varies. In some areas, the high concentration of dissolved solids and the presence of some constituents at concentrations are deemed harmful to humans and crops alike. However, the quality of ground water is significantly affected by sewage in the vicinity of the built up areas. Of particular concern are higher concentrations of Nitrate, Boron and Dissolved solids. (Broshears et al 2005).

In the context of above findings, a further Physical, chemical and microbiological analysis is carried on for major and minor constituents of water samples that have been collected from 170 wells (map 1) within the city region of Kabul. Along with this, other important indicators of ground water quality namely PH, Specific Conductivity, Alkalinity, Coli & E_Coli are also analysed to have an idea about their spatial distribution and concentration. A detailed description of each parameter along with maps generated through GIS (Arc Info 9.3) is given below. As the data was available for only the specified sample wells around the city, the maps generated too pertain to the Kabul city surroundings only.

Ground water quality in and around Kabul city

Average thickness of aquifers(m)

Mean porosity (%)

Transmissivity (Sqm/day)

Average range of permeability

(m/s)

Stored volume (m*10

Aquifer

30-40

40-80

30-70

7. 5

7. 5

7. 5

4. 1 · 10–2–9 · 10–2

1. 0 · 10–5–6. 8 · 10–2

1. 4 · 10–4–1. 3 · 10–3

5. 0 · 10–5–7. 5 · 10–4

81

31

90

Logar

Kabul

Paghman

It is generally recognized that the quality of ground water is as important as its quantity. The quality required of a groundwater supply depends on its purpose; thus needs for drinking water, irrigation water and industrial water vary widely. To establish quality criteria, measures of chemical, physical, biological and radiological constituents must be specified. Accordingly a few major and minor constituents have been analyzed from the sample data derived from the wells in the study region (map 1). The location of the wells is derived by GPS.

Sodium

The values of sodium show a range between less 10mg/l to more 365mg/l. The highest concentration is found in southeastern part of the city region with a grading down towards peripheries of the city (Map 2). The high concentration that is more than 50mg/l in water can cause corrosion and aid in chemical weathering. (David Ketith Todd 1980)

Nitrate

Nitrate is another constituent whose presence in water may change the taste of water. Usually > 100mg/l result in bitter taste of water. The analyzed values for the study region have a range from a low value around 0 to a high value around 128. The high values are found once again nearer to the city center and slowly grade down towards margins (map 3). The high values near 120mg/l near city indicate the bitter taste of the water.

Nitrite

Nitrite is also a Nitrogen compound with two molecules of Oxygen. It occurs with Nitrates in association with other compounds. Nitrite for the study region shows a range from 004 mg/l to 15mg/l. High values are concentrated in the city center and southern part of the city, whereas the medium values are distributed towards the eastern part of the city (Map 4).

Map 1 Map 2

Map 3 Map 4

Chloride

The presence of Chlorides in water indicates saltiness. Chloride in excess of 100mg/l imparts a salty taste. Concentrations greatly in excess of 100mg/l may cause physiological damage. It is a general fact that presence of salts in water is related to temperature. The concentration of Chlorides in Kabul city depicts a range from <10mg/l to > 570mg/l. The high concentrations are once again observed in the city region reducing in their values towards outer margins (Map 5).

Calcium, Magnesium & Bicarbonates

These constituents in a given water sample make the water hard and alkaline with high PH values. A crust like scale of Calcium Carbonate is formed in the presence of exchange of ions from above elements. All these constituents have high values in the city center, more towards south and south eastern parts indicating the hardness or water. The values for calcium range between 50 to 163mg/l (map 6), whereas Magnesium and Bicarbonates show a range between 15 to 167mg/l (map 7) and 225 to 572 mg/l(map 8) respectively Though the desirable values should be around 100mg/l, the high values in the city proximity call for immediate attention for proper water treatment.

Map no (5) Map no (6)

Map no (7) Map no (7)

Alkalinity

In the study region, the locational values of Bicarbonate and Alkalinity show high correlation. The two maps look alike and are identical. The Alkalinity values show a range between 184 to 469mg/l. South eastern part of the region shows a clear cut grading of values from 469 to 280mg/l (Map 9). In this part of the city the waters are highly alkaline.

Zinc, Copper, Manganese, Uranium, Arsenic and Lead

These are considerd as minor constituents. As the name denotes these usually have a range between 0001 to 0.1 mg/l. However, in some cases the values maybe high. in the study region

excepting for Zinc and Copper, rest of the elements are concentrated in the southeastern part of the city region.

Zinc

Zinc is the only element which is concentrated in the northwestern part of the city with extremely high values ranging around 1200mg/l. Otherwise, the other parts of the region show low values of around 10mg/l, once again much higher than desirable limits (Map 10).

Copper

Copper has a more or less all around distribution surrounding the city. The high values are around 5. 66 mg/l and low values are around 1. 04 mg/l. The high values occur in northern, western and southeastern parts of the city. (map 11)

Manganese

The presence of Manganese in water causes undesirable tastes, deposits on foods during cooking and fosters growth in reservoirs, filters and distributions systems. Most industrial users object to water containing more than 0.2 mg/l. In the city region, the Manganese values show a range between 1.8mg/l to 179 mg/l. However, the high concentration pockets bearing 160 to 169mg/l can be evidenced only in small center towards southeastern part of the city. The values around 60 to 80mg/l are widespread all around the city, with concentration of high values towards southern region (Map 12).

Map no (9) Map no (10)

Map no (11) Map no (12)

Uranium

Uranium, a radio isotope also has adverse affects on human health. It ranges from a low value of 3.24mg/l to a maximum value of 18. 5mg/l. However, the high values are concentrated once again towards southeastern part of the city (Map 13).

Arsenic

Arsenic too has a similar pattern of distribution, with the highest values of 6.24mg/l occurring in the southeastern corner. The rest of the region shows low values of around 0. 38mg/l (Map 14).

Lead

Lead is also an equally harmful substance when associated with food products. In the study region, this shows a range of values from. 06 to 2.4mg/l. The concentration of high values is more south and southeasterly in nature.

The changes in chemical composition may be attributed to weathering of rock that may include gypsum (Lashkaripour G. R. Æ Hussaini S. A. 2008) (Map 15).

Map no (13 map no (14)

Water temperature

Water temperature, is also an important physical analysis parameter. It reflects the nature of water. The high temperature of a particular sample readily becomes chemically more active and therefore more reactive. The ground water temperature is accounted by both conduction and convection in the subsurface. The values are usually recorded in Celsius. The obtained values for the study region do not show much variation as the range is only from 130 C -170 C. However, high temperatures are recorded in the north eastern part of the city, making the southern part more chemically active, as major and minor constituents of water show higher values in south and southeast (Map 16).

Map no (15) Map no (16)

Specific Conductivity and PH

Specific electrical conductance defines the conductance of a cubic centimeter of water at a standard temperature of 25 0 C. An increase of 10 C increases the conductance by about 2%. Specific conductance is measured in microsiemens/cm (ms/cm). It is because natural water contains a variety of ionic and undissociated species, conductance cannot be simply related to total dissolved solids. However, conductance is easily measured and gives results that are convenient as a general indication of dissolved solids. For most natural water, the range can be between 100 to 5000 ms/cm.

The specific conductance values in the study region show a range from 467 – 3170 ms/cm. This is in confirmation with the dissolved solvents found in the water samples. As has been the distribution trend for various constituents, similar is the trend for specific conductance too. The high values are once again distributed in the eastern portion of Kabul city (Map 17).

PH

PH refers to hydrogen ion concentration in a given sample of water. This is an important physical parameter to assess the quality of water. The Ph scale which shows a range from 0 – 14 can be categorised into three classes, namely 0 – 7 is considered as acidic and 7 – 14 is considered as basic or alkaline. The value around 7 is considered as neutral.

The values of PH in the study region are all above 7 indicating the alkaline character of the water which is also proved by the heavy concentration of major basic constituents in the water samples. The said values range from 7. 26 – 8. 1. The concentration of high values is mostly is in the eastern part of the city, where the water is alkaline. On the contrary, the rest of the region has values around 7. 26 – 7. 6 indicating a less alkaline character (Map 18).

Oxygen

The presence of O2 in the water makes it ready for oxidation and reduction process. The iron compounds present in rocks automatically react with oxygen and become oxides. The study region’s water is rich in O2 in the western part of the city indicating the source from snow melt waters of Hindukush Mountains to the west. The eastern portion of the city lacking in 02 is not considered to be potable as it is hard and unsuitable for domestic consumption. In contrast, the waters in the west of the city region ranging around 7 – 8 mg/l are highly suitable for drinking purposes (Map 19).

Map no (17) Map no (18)

Map no (19)

Biological Analysis: COLI &E COLI

Bacteriological analysis is important for detecting biological pollution of ground water. Most pathogenic bacteria found in water are indigenous to the intestinal tract of animals and humans, but isolating them from natural water is difficult in the laboratory. Because bacteria of the coliform group are relatively easy to isolate and identify, Standard tests to determine their presence or absence in a water sample are taken as a direct indication of the safety of the water for drinking purposes. Coliform test results are reported as the most probable number (MPN) of coliform group organisms in a given volume of water. (David Keith Todd 1980)

Coli

The values of Coli in the region range from a minimal value of 1.5 to a maximum value of 2271. The concentration of Coli is markedly observed in the city center where the population concentration is more. The presence of Coli in water is directly linked to domestic sewage. The high range in values is mainly due to this aspect. Away from city center, the values are as good as non existing (Map 20).

E Coli

On the other hand E Coli has maximum values in the south eastern and extreme northern portion of the city, depicting the values around -2 col/100ml to 40 col/100ml. The city center and surroundings show lesser values. This can also be treated as an indicator to measure the quality of water for human consumption (Map 21).

Map no (20) Map no (21)

Conclusion

From the above analysis, it is clear that the ground water in Kabul city and its environs is not of good quality there is a high concentration of lead, Arsenic aling with Coli and E-Coli within the city. Similarly Specific conductivity of water too is high. Alkalinity along with Bi carbonates also shows higher values near the city. It is clearly evident that as one moves away from the city center the concentration level of major constituents gets decreased showing a distant decay postulation. Therefore, there is a high correlation between concentration of population and concentration of major constituents in ground water in city region.

References

1. Broshears, R. E. , Akbari, M. A. , Chornack, M. P. , Mueller, D. K. , &Ruddy, B. C. (2005). Inventory of ground-water resources in the Kabul Basin, Afghanistan, U. S. Geological Survey, Scientific Investigations Report 2005–5090, http: //pubs. usgs. gov/sir/2005/5090

2. David Keith Todd (1980) Ground water hydrology, Elsiver publisher New York page 267-310

3. Georg Houben, Torge Tünnermeier (2005) Hydrogeology of Kabul Basin Ground water Geochemistry and Microbiology. Improving groundwater protection for the preventative avoidance of drought problems in the Kabul Basin, Afghanistan" funded by the Foreign Office of the Federal Republic of Germany

4. http: //www. afghan-engineers. org/water -supply. htm l

5. Lashkaripour G. R. Æ Hussaini S. A. (2008) Water resource management in Kabul river basin, eastern Afghanistan Environmentalist 28: 253–260DOI 10. 1007/s10669-007-9136-2