INTRODUCTION:

Ninety seven percent of the total water of the Earth (1,011 million cubic kilometer)) is in the oceans. Out of remaining three percent, 3 million cubic kilometer is buried underground leaving only 2.5% as the total fresh water. Again, twenty two percent of the fresh water is in frozen form in the polar ice cap and glaciers. The remaining small quantity estimated at 33, 400 cubic meter provides the water supply vital for life on the Earth¹. The report of the World Health Organization reveals that 18% of the total world’s population lack access to safe drinking water. Water related diseases account for 80 % of illness and deaths in developing countries. By 2025, two-thirds of the world’s population will lack clean and safe drinking water. Thirty two countries, including India, face water stress and scarcity. Ground water is the source of one third of total drinking water and along with other uses and is the only source of drinking water for many rural and small countries².

Water dissolves many substances like oxygen, nutrient, minerals etc. Some of them are beneficial in requisite amounts and some are harmful to us even in trace amount. Chemically contaminated water may lead to various diseases, may even lead to death. Chemical contaminants in water include iron, chloride, sulphate, nitrate, fluoride, lead, cadmium, mercury, chromium, arsenic etc. Amongst them iron, sulphate, chloride etc. are aesthetic contaminants, which mainly affect the taste or causes staining cloths, utensils etc. Fluoride, lead, cadmium, mercury, chromium, arsenic etc. are health-related inorganic constituents. Presence of the above chemical contaminants in drinking water beyond the permissible limits effect health of the people greatly.

More than sixty five percent of the Indian population now utilizes ground water for daily need. Potable water must be clear transparent, tasteless and odourless. It must not contain any kind of bacteria and dissolved harmful chemicals beyond the permissible limits that may cause diseases to our bodies.

Unscientific use of chemical fertilizers and pesticides in agricultural fields multiplies the problem by contaminating the sources of drinking water³. Faulty industrialization process leads to atmospheric pollution which is hazardous to man and other living organisms. Increased human population and manmade conditions are the key factors for day by day deterioration of ground water quality. Solid waste contaminates ground water in the nearby areas of disposal sites. It was found that the parameters like TDS, alkalinity, TH, chloride and nitrate exceeded the desirable limits, which infers that the ground water up to a radius of 1000m from the disposable sites of solid waste is not suitable for drinking purpose⁴. Agricultural pesticides and fertilizers also contain toxic chemicals. Bacteriological analysis shows that well water samples are highly contaminated with some fecal bacteria³. Fifteen Indian states experience high fluoride content in underground drinking water⁵.

Excess iron in the drinking water is very common in the North Eastern states of India. Iron is essential element for human health, but its excess in ground water causes staining of plumbing fixtures, clothes during laundering and porcelain, and imparts an astringent taste to drinking water. Excess iron in drinking water causes constipation along with other physiological problems. The presence of iron in ground water results in the growth of several kinds of reducing and oxidizing bacteria. These bacteria change certain types of dissolved iron to the insoluble ferric state⁶. Assam receives abundant rainfall and has a strong aquifer base to hold enough water for long durations. But the reality is that, there is scarcity of ground water in different parts of the state, or there is uneven storage in certain areas causing concern at the critical period of demand. As per information available with the Central Ground Water Board, Assam, the total ground water recharge as a whole in the state is 27.23 billion cubic meters (bcm). This has been obtained from rainfall during the monsoon season and other sources such as ice, glaciers, intrusion by percolation and lateral transmission of under water from other regions during the non-monsoon period. However, this amount and mode of recharge are not uniform throughout the state.

Dhaligaon is a well known site in the industrial map of India (Fig.1). Indian Oil Corporation (Bongaigaon Refinery), one of the few refineries of India is situated here. It is located along latitude 26.32 N and longitude 90.25 E and is about 3 km. distance away from the district head quarter of Chirang district, Kajalgaon. IOC LPG bottling plant is also commissioned in this locality. Some other Indian Oil Corporation (Bongaigaon Refinery) based downstream industries are also operating in this industrial place. So, contamination of water, air and soil is inevitable in and around of this area. Bongaigaon town which is touching Dhaligaon is an industrial town having a large number of industries of medium and small grades. All these are contributing to the pollution of water, air, soil and noise. Thus, there is a possibility of ground water being contaminated.

The present study area is deprived of proper drainage system and solid waste management. Unscientific use of chemical fertilizers and pesticides is a common phenomenon in this area .Recession of ground water level in February to April compelled people to use water from any available sources regardless of its potability.

Fig. 1 The study area

MATERIALS AND METHODS:

On the basis of the average rainfall, temperature, humidity and other conditions, three sampling seasons, namely, monsoon, post monsoon and pre monsoon have been selected for the present study. 10 drinking water samples (Table 1) were collected once in every season for a period of one year starting from June 2008 to May 2009. Water samples were collected from two ring wells, two tube wells, four tara pumps and two deep tube wells considering the people’s options of use of sources of drinking water in the study area. Samples were collected from the same site of sampling station in each set.

Table 1: Sources of drinking water samples

Sample No.	Site	Source
1	IOC(Bongaigaon Refinery)	Deep Tube Well
2	Dhaligaon Market	Ring Well
3	36 no. Dhaligaon L.P. school	Tara Pump
4	Kukurmari	Ring Well
5	Hatipota Daksinpuri	Tube Well
6	Chapaguri Shiva Temple	Tara Pump
7	Chapaguri Chowk	Tube Well
8	Eco Park ,Dolaigaon	Deep Tube Well
9	Bartola Madrasa	Tara Pump
10	Chatipur L.P. School	Tara Pump

Standard procedures were followed for storage of the samples and the analysis was completed within three months from the date of collection of samples^7,8. Altogether 19 physicochemical and two microbial parameters namely, total coliform and E. coli of drinking water samples were analyzed. For microbial analysis water samples were collected in sterile glass bottles followed by immediate steps for analysis.

RESULTS AND DISCUSSIONS:

The average temperatures of the water samples ranged 24.0⁰ C to 24.4⁰ C (Table 2).The lowest values and highest values were found to be in post monsoon and monsoon seasons respectively. The pH of the water samples ranged 5.1 to 6.4. The values reveal that all the water samples showed their values below the desirable limit (6.5-8.5). Acidic water (pH value bellow 7) interferes in water softening and water treatment processes and P^H value of 5.0 imparts sour taste to water^9,10. The turbidity of the water samples ranged 0.6 NTU to 19.5 NTU. Samples nos. 5, 7 and 9 showed much higher turbidity values than the permissible value. Samples no. 6, 8 and 10 also crossed the permissible limit of 5 NTU. The Electrical Conductance (EC) of the water samples ranged 78.7 µ S /cm to 301.7µ S/cm. One sample (samples no.2) crossed the permissible limit of 300 µ S /cm. The alkalinity of the drinking water samples were found to be in between 8.0 mg/L to 108.7mg/L. The values were well below the permissible limit of 200 mg/L. The hardness of the drinking water samples were found to be in between 21.0 mg/L to 104.0 mg/L. The values were well below the permissible limit of 300 mg/L. Total suspended solids (TSS) contents of the water samples ranged 13.7 mg/L to 78.8 mg/L. Total dissolved solids (TDS) contents of the water samples ranged 68.3 mg/L to 154.0 mg/L. Drinking water should not have dissolved solids beyond 500 mg/L. Thus, TDS contents of the water samples were within the permissible limit.

The chloride contents of the water samples ranged 2.1 mg/L to 6.4 mg/L, and were well below the permissible limit of 250 mg/L. The sulphate concentrations of the water samples ranged 2.2 mg/L to 12.1 mg/L, which were found to be below the permissible limit of 200 mg/L. The nitrate contents of the water samples ranged 0.1 mg/L to 11.6 mg/L, which were well below the permissible limit of 45 mg/L. The phosphate contents of the water samples ranged 0.0 mg/L to 0.3 mg/L. The fluoride contents of the water samples ranged 0.00 mg/L to 0.60 mg/L which were well below the permissible limit. The permissible limit of fluoride in drinking water is fixed at 1.0 mg/L.

Table.2: Average values of water quality parameters (Units are in mg/L for parameters except Temperature, pH, Turbidity, E.C., Coliform and E. Coli)

Sample no.	Temp. ( C)	pH	Turbidity (NTU)	EC (µS/ cm)	Alkalinity	Hardness	TDS	TSS	Cl^-	NO₃^-	SO₄^2-
1	24.2	6.4	0.6	183.7	74.7	60.7	135.3	16.0	2.1	3.4	5.9
2	24.3	6.2	0.7	301.7	108.7	104.0	154.0	16.3	5.7	3.3	12.1
3	24.4	5.4	0.8	85.3	25.0	22.7	72.6	13. 7	4.1	11.6	2.8
4	24.2	5.1	0.7	265.0	25.3	26.3	141.3	17.3	5.1	7.2	5.9
5	24.4	6.3	19.5	111.3	43.7	46.7	89.3	78.8	3.4	0.9	3.9
6	24.3	5.7	5.3	112.0	43.3	50.0	90. 7	30.3	2.1	1.0	2.2
7	24.2	5.5	15.3	125.0	57.3	40.0	70. 7	69.3	4.7	0.1	5.1
8	24.2	6.4	5.1	78.7	25.3	37.3	68.3	33.0	6.4	0.9	4.1
9	24.0	6.0	17.0	289.7	25.3	21.0	119.0	74.3	4.2	1.4	4.4
10	24.1	6.0	6.3	85.3	8.0	44.3	74.0	38.7	5.1	3.4	7.5

Table.2 (continued): Average values of water quality parameters

Sample no.	PO₄^3-	F^-	Fe	Cu	Pb	Cr	Hg	As	Coliform (MPN/100ml)	*E. Coli* (MPN/100ml)
1	0.2	0.01	0.08	0.00	0.01	0.00	0.00	0.00	0.0	0.0
2	0.0	0.01	0.12	0.01	0.03	0.00	0.00	0.00	270.3	8.7
3	0.3	0.03	0.03	0.00	0.02	0.00	0.00	0.00	28.3	3.3
4	0.1	0.03	0.45	0.01	0.65	0.00	0.00	0.00	305.7	13.3
5	0.1	0.05	1.40	0.20	0.05	0.00	0.00	0.00	3.3	0.0
6	0.1	0.04	0.47	0.01	0.04	0.00	0.00	0.00	8.3	0.7
7	0.1	0.03	0.46	0.00	0.00	0.00	0.00	0.00	45.0	3.0
8	0.1	0.60	0.03	0.00	0.00	0.00	0.00	0.00	0.0	0.0
9	0.0	0.0	0.82	0.00	0.00	0.00	0.00	0.00	4.3	0.0
10	0.0	0.0	0.53	0.00	0.00	0.00	0.00	0.00	2.3	0.0

The iron contents of the water samples ranged 0.03 mg/L to 1.40 mg/L. The permissible limit of iron in drinking water is 0.3 mg/L. Sixty percent of the samples crossed the permissible limit. The Copper contents of the water samples ranged 0.00 mg/L to 0.20 mg/L. No sample crossed the permissible limit (0.05 mg/L) of copper in drinking water of the samples collected under the present study. Chromium was found to be absent in all the drinking water samples. The lead contents of the water samples ranged 0.00 mg/L to 0.65 mg/L. One sample (Sample no. 4) crossed the permissible limit of lead, while another (Sample no. 5) touched the permissible limit. No sample showed the presence of mercury. The permissible limit of mercury in drinking water is 0.01 mg/L. No sample showed the presence of arsenic as well. The permissible limit of arsenic in drinking water is 0.05 mg/L.

The total Coliform contents of the samples were found to be 0 MPN/100 mL to 305.7 MPN/100 mL. The MPN value of Coliform per 100 mL water should be zero in drinking water. Eighty percent of the samples showed the presence Coliform bacteria in water. The E Coli contents of the samples were found to be 0.0 MPN/100 mL to 13.3 MPN/100 mL. The MPN value of E. Coli per 100mL water should be zero for drinking water. Fifty percent of the drinking water samples were found to be contaminated with E.Coli.

CONCLUSION:

Some of the parameters including fluoride and arsenic of drinking water samples studied were found to be non-objectionable. Contrary to this, cent percent of the samples showed the P^H values below the desirable limit. Sixty percent of the samples crossed the permissible limit of turbidity. One sample showed excess electrical conductance. Presence of TSS and phosphate in some of the samples indicates that water from such sources should not be directly used for drinking purpose. Although, the drinking water with respect to metals like arsenic, mercury and chromium were found to be not objectionable, 60% of the samples showed the presence of excess iron. One sample crossed the permissible limit of lead while another touched the permissible limit. The other physicochemical properties of the water samples were found to be bellow the respective permissible limits.

Eighty percent and fifty percent of the samples indicated the presence Coliform and E. coli in the drinking water respectively. The total Coliform and E Coli contents of the samples of the ring wells revealed that water from these sources were not at all fit for drinking purse. Other sources were also found to be not acceptable from potability point of view.

Therefore, the detailed study of the drinking water of Dhaligaon and its surrounding areas revealed that water should be properly treated before used for drinking.

ACKNOWLEDGEMENT:

Authors are grateful to University Grant Commission (NERO) for financial assistance to carry out the project works.

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Received on 30.07.2010 Modified on 28.08.2010

Asian J. Research Chem. 4(1): January 2011; Page 91-94