Sciknow Publications Ltd.
ER 2013, 1(1): 33-36 DOI: 10.12966/er.05.05.2013
Earth Resources ©Attribution 3.0 Unported (CC BY 3.0)
Environmental Assessment of Water Quality in Nagarjuna Sagar Reservoir, India K. Brindha* and L. Elango Department of Geology, Anna University, Chennai- 600 025, India *Corresponding author (Email:
[email protected])
Abstract – The quality of water determines its usage for any intended purpose. We studied the quality of water in the Nagarjuna Sagar reservoir, one of the biggest surface water reservoirs in India with an aim to determine the suitability of the water for domestic and agricultural use. This reservoir supplies water to the irrigational needs of five districts and the drinking water supplies of nearby towns. We collected water samples once in two months between July 2008 and January 2010 from the reservoir. We measured pH and EC of the samples in the field. The concentration of calcium, magnesium, sodium, potassium, bicarbonate, chloride, sulphate, fluoride, nitrate and uranium were analysed in the laboratory using standard procedures. The suitability of water for drinking purpose was determined by comparing the results of the analysis with the drinking water guidelines of the Bureau of Indian Standards and World Health Organisation. Even though the groundwater in this area is rich in fluoride and uranium, this does not affect the water quality of the reservoir for drinking water supply. The comparison of the water samples with the irrigational water quality assessing factors such as percent sodium, residual sodium carbonate, magnesium hazard, sodium absorption ratio and permeability index also indicated the suitability of water for agricultural use. As the water in the Nagarjuna Sagar reservoir is suitable and good for drinking and irrigational use, not much treatment needs to be carried out except for disinfection before supplying it for domestic use. Keywords – Surface Water Quality, Drinking Water Standard, Irrigational Water Use, BIS, WHO, Nalgonda District, Andhra Pradesh
1. Introduction Surface water is normally more prone to pollution as it is exposed to the environment. The composition of surface water may depend on various factors such as topography, rainfall, geology, biology, temperature, land use, impact of humans etc. Intentional storage of surface water has many purposes like hydroelectric power generation, irrigational supply through canals, prevent wide damage from floods in the downstream, recreational purpose like boating, swimming etc. The Nagarjuna Sagar dam which has a capacity of 11,560 million cubic meters is one of the largest dams in India and it was built on the Krishna River to facilitate the irrigation supplies of Nalgonda, Guntur, Prakasam, Krishna and Khammam districts of Andhra Pradesh, India. The dam also supplies drinking water to the Nalgonda town and to some extent to the needs of the Hyderabad city, the capital of Andhra Pradesh state. Rao et al. (2004) carried out geotechnical investigations on the downstream side of the Nagarjuna Sagar dam for the construction of a bridge across the Krishna River. Though groundwater quality in parts of Nalgonda district has been studied extensively (Brindha and Elango, 2013; Brindha and Elango, 2012; Elango et al. 2012; Rajesh et al. 2012; Brindha et al. 2011a, b), the surface
water quality of Nagarjuna Sagar reservoir has not been reported. The objective of our study is to determine the quality of surface water in the Nagarjuna Sagar reservoir for domestic and irrigational use. This reservoir is located at a distance of about 120 km from Hyderabad in Nalgonda district, Andhra Pradesh, India (Fig. 1). This area experiences an arid to semi-arid climate. The temperature ranges from 30o to 46.5oC during April to June (summer) and from 17o to 38oC during November to January (winter). Most of the rainfall occurs during the southwest monsoon i.e. from June to September. The average annual rainfall in this area is 600 mm.
2. Methodology One surface water sample was collected from the downstream side of the Nagarjuna Sagar reservoir from July 2008 to January 2010 once every two months. The samples were analysed for major ions and concentration of uranium. The samples were collected in 500 ml capacity bottles that were washed prior to sampling by soaking in 1:1 diluted nitric acid solution for 24 hours and then washed with distilled
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Earth Resources (2013) 33-36
water. The bottles were washed again before each sampling with the water to be sampled. The pH and electrical conductivity (EC) were measured in the field using portable digital meters that were calibrated beforehand. The surface water samples were brought to the laboratory and filtered using 0.45 μm millipore filter paper before carrying out the chemical analysis. The concentration of calcium, magnesium, sodium, potassium, chloride, sulphate, fluoride and nitrate were determined in an ion chromatograph using appropriate standards. The uranium concentration was determined in a laser fluorimeter. Blanks and standards were run simultaneously during the measurement for en-
suring accuracy of the result. The concentration of carbonate and bicarbonate were determined by titrating against H2SO4 as per standard method (APHA, 1998). The accuracy of the chemical analysis was verified by ion balance error method which was generally within 5%. Total dissolved solids (TDS) was calculated by using the formula TDS = EC X 0.64 (Lloyd and Heathcote, 1985). Total hardness (TH) of the groundwater was calculated using, TH (as CaCO3) mg/l = (Ca + Mg) meq/l x 50 (Sawyer and McCarty, 1978).
Fig. 1. Location of the Nagarjuna Sagar Reservoir in Andhra Pradesh, India Table 1. Minimum, Maximum and Mean Concentration of Various Parameters in Surface Water Parameter
Unit
Minimum
Maximum
Mean
pH
-
7.0
8.5
7.7
EC
µS/cm
150.0
720.0
404.1
TDS
mg/l
96.0
460.8
258.6
TH
mg/l
118.3
200.2
153.7
Calcium
mg/l
30.1
59.0
42.5
Magnesium
mg/l
9.1
14.2
11.6
Sodium
mg/l
35.1
61.1
53.6
Potassium
mg/l
1.2
4.0
2.5
Bicarbonate
mg/l
92.0
189.0
148.1
Chloride
mg/l
40.2
62.2
49.9
Sulphate
mg/l
38.6
59.2
48.2
Fluoride
mg/l
0.1
0.4
0.3
Nitrate
mg/l
0.0
0.2
0.1
Uranium
µg/l
0.4
4.0
2.0
3. Results and Discussion The chemical composition of major ions in surface water was in the order of Na>Ca>Mg>K=HCO3>Cl>SO4. The maximum, minimum and mean concentration of various parameters analysed is given in Table 1. 3.1 Drinking Water Quality The chemical composition assessed in the water samples were compared to the standards of drinking water quality given by the Bureau of Indian Standards (BIS, 2003) and World Health Organisation (WHO, 2004). All the surface water samples were within the permissible limits of BIS and WHO for pH and other ions measured during this study. The water from the Nagarjuna Sagar reservoir was fresh water type (
