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CHAPTER - IV

STUDY OF WATER QUALITY INDICES

INTRODUCTION

The inability to provide infrastructure keeping pace with the expanding

population, residential and industrial development has resulted in pollution of freshwater

systems. Conservation of water quality requires good sewage disposal systems and

compliance with current effluent regulations. Domestic effluent treatment including

installation and maintenance of on site treatment tanks is vital in maintaining the quality

of public waters.

There is presently an urgent need for introduction of additional measures against

organic pollutants particularly those which originate from non-point sources like urban

development and agricultural fields combined with rainfall. Hence, there arises the

necessity for a survey and documentation of the water quality. In the present work a

Water Quality Index (WQI) has been used for surveying the quality of different lentic

systems.

REVIEW OF LITERATURE

The WQI is a single numerical expression reflecting the composite influence of a

number of the water quality parameters significant for a specific beneficial use. It is a

tool for assessing the overall water quality of a freshwater system.

According to Pande & Sharma (1999) the important requirements of water quality

indices are as follows: (a) It should significantly decrease when some critical parameters

exceed the permissible quality level for a given use. (b) It should remain almost

unchanged when the value of a parameter changes within the permissible level. (c) The

change in an index should invariably be more in respect of a parameter, which has

greater significance. (d) The variation in the index should reflect the different levels of

significance of a single parameter for different uses.

Waiski & Parker (1974) analysed the consumers water quality index for freshwaters.

Harkins (1974) revealed the objectives and importance of water quality index. A review of

wo

literature in the study of water quality index in freshwater systems is given in the

Table - 34.

METHODOLOGY

Horton (1965) defined a water quality index based on chemical and physical

measurements by arranging its rating scales and weights.

Formation of Water Quality Index

Water quality indices were formulated for different water uses like public water

supply, agricultural use, bathing purpose and recreation. As per Horton (1965), the

formulation of the water quality indices is assessed by the following steps.

Selection of Water Quality Characteristics

Water quality characteristics can be obtained by measuring the standards of

quality of different physical, chemical and biological water parameters.

Establishment of Quality of Rating Scale for each Characteristics

The quality rating scale (qi) 100 signifies the best water quality condition and the

rating zero shows the worst water quality condition. The rating scale for the nine

physico-chemical parameters is given in the Table - 35. The values of the parameters

have been divided into 4 stages (permissible, slight, moderate and severe).

Weights for physico-chemical and biological parameters of water (WHOStandards)

The weight range is from 1 to 4. The maximum weight of 4 has been arranged

for parameters like p1-I, turbidity and DO due to their importance in water quality

assessment. Some of the parameters have been assigned the moderate weight of 3 and 2.

The parameters like sulphate have been assigned the minimum weight of 1, as they do

not play a very prominent role in the quality of freshwaters (Table - 36).

The water quality index has been obtained by following the method of

Tiwari & Mishra (1985) and Tiwari et al., (1986).

70

Table - 34

Review of Literatures in the Study of Water Quality Indexin Freshwater Systems

Area of StudyI

Reference

Freshwater Brown et al., (1970)

River Ganga Bhargava (1983)

Indian Rivers Tiwari & Mishra (1985)

River Jhelum, Kashmir Tiwari et al., (1986)

Halali River, Bhopal Sharma etal., (1996)

Ram Ganga River, Uttar Pradesh Pande & Sharma (1999)

River Yarnuna Ajit Pratab & Ghosh (1999)

Ram Ganga River, Uttar Pradesh Sharma & Pande (1999)

71

Table - 35

Rating Scale for Water Quality Parameters (qi)

Degree of pollution and rating (qi)Parameters (units) Permissible Slight Moderate Severe

(100) (80) (50) (0)

pH7.0- 8.5 8.6-8.8 8.9-9.2 > 9.2

6.8-7.0 6.5-6.7 <6.5

Turbidity (N.T.U) <5 5- 10 11 —25 > 25

Specific Conductance (jiS/cm) <20 21 - 30 31 -40 > 40

Total Alkalinity (mg/1) > 50 51 -85 86-120 > 120

Total Hardness (mg/1) < 100 101 —300 301 —500 > 500

Chloride (mg/1) <200 201-400 401 -600 > 600

Sulphate (mg/1) <200 201 - 300 301 —400 > 400

Dissolved Oxygen (mg/1) > 6 4.6-5.9 3.0 - 4.5 <3.0

Faecal Coliform (No./100 ml) ND <50 51 - 1000 > 1000

Table - 36

Rating Scale and Weights of Physico-chemicalParameters of Water (WHO Standards)

Parameters (units) Standards Weights Unit Weight

pH 7.0-8.5 4 0.16

Turbidity (N.T.U) 5.0 4 0.16

Specific Conductance (.iS/cm) 40.0 2 0.08

Total Alkalinity (mg/1) 120.0 3 0.12

Total Hardness (mg/1) 100-500 2 0.08

Chloride (mg/1) 201-600 2 0.08

Sulphate (mg/1) 200 —400 1 0.04

Dissolved Oxygen (mg/1) 6 4 0.16

Faecal Coliform (No./100 ml) 1 3 0.12

72

For calculating the WQI, the sub-index (SI) is first found out for each parameter,

which is

(SI) i = qw,

And thus the following formula is derived.

9 9WQ1 = E (SI)i/ E

i=1 i=l

9i.e., WQ1 = E q 1 w 1 as w 1 =

i=1

RESULTS

For the calculation of water quality indices, nine important parameters were taken

into account. Parameters like pH, chlorides and DO have already been discussed in

Chapter II and faecal coliform in Chapter III. The remaining parameters are turbidity,

specific conductance, total alkalinity, total hardness and sulphate.

Turbidity

The turbidity was generally high during the summer season 22 and 25 NTU at

station I, 13 and 12 NTU at station II, 6 and 8 NTU at station III and 11 and 13 NTU at

station IV during 1998 and 1999 respectively (Tables 37 -40).

Specific Conductance

The specific conductance during the post monsoon in 1998 and 1999 were

51 hiS/cm and 49 hiS/cm at station 1, 41 hiS/cm and 44 hiS/cm at station II, 33 6/cm and

38 LS/cm at station III, and 46 hiS/cm and 51 LS/cm at station IV (Table - 37). The

specific conductance in summer 1998 and 1999 (Table - 38), south- west monsoon 1998

and 1999 (Table - 39) and north-east monsoon 1998 and 1999 (Table —40) are recorded.

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DISCUSSION

Turbidity

The turbidity values ranged between 17 and 25 NTU at station 1, 10 and 14 NTh

at station II, 4 and 8 NTU at station Ill and 7 and 14 NTU at station IV. This was well

under the range of prescribed standards. In lentic systems there was always a gradual

sedimentation of the suspended solids; had it not been so the turbidity values would have

been much higher than the present value. A comparative data of turbidity value of

different freshwater systems are set out in the Table - 41. Mohini Gadhia et al., (2000)

noted higher turbidity in four stations of Rotania - Moticher Reservoir during summer

seasons similar to the present work. This could be due to nature of surroundings or due

to the selected sampling stations having the sandy, gravelly and muddy bottom or due to

the addition of drainage.

Specific Conductance

The specific conductance of a sample correlates with the concentration of

dissolved minerals. An empirical relationship exists between the specific conductance

and TDS of most natural waters (Ramesh & Anbu, 1996). In the present study, the highest

value (57 tS/cm) was recorded at station I during north-east monsoon season and the

lowest value (13 hiS/cm) was recorded at station III during south-west monsoon. The

Table - 41 shows the comparative values of specific conductance in different freshwater

systems.

Total Alkalinity

All the lentic systems under study showed the rnaximuin total alkalinity in the

summer season (67 mg/1 at station I in 1998, 18 mg/1 at station III in 1999 and

61 mg/1 at station IV in 1998). This could be correlated with the increase in bicarbonate

due to the reduced level of water with high salt contents (Cook & Powers, 1958). Th

increase in salt contents is also indicated by the enhancement of hardness in summer.

The findings of Singhal et al., (1986) and Mohini Gadhia et al., (2000) and the results of the

current study are in good agreement. -

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81

Alkalinity

The total alkalinity ranged from 54 mg/i to 67 mg/I at station I, 19 mg/i to

46 mg/i at station II, 9.5 mg/i to 70 mg/i at station III and 16 mg/i to 56 mg/I at

station IV. The values of total alkalinity for post monsoon, summer, south-west

monsoon and north-east monsoon are presented in the Tables 37 - 40 respectively.

Total Hardness

The total hardness showed seasonal variations at all the stations. The amount of

total hardness for post monsoon (Table - 37), summer (Table - 38), south-west monsoon

(Table - 39) and north-east monsoon (Table - 40) is given. It ranged from 53 mg/I to

72 mg/i at station I, 32 mg/l to 49 mg/i at station II, 14 mg/1 to 30 rng/l at station III, and

36 mg/l to 61 mg/i at station IV.

Sulphate

The values of sulphate were very low for all the stations and for all seasons

(Tables 37 - 40).

Water Quality Indices

The water quality indices were calculated for each station and each season. The

water quality indices for 1998 post monsoon were 63 for station I, 72 for station II,

90 for station III and 77 for station IV and in summer, they were 70 for station I, 72 for

station II, 87 for station III and 66 for station IV. The water quality indices for south-

west monsoon were 66.4, 83.2, 90.8 and 83.2 and north-east monsoon were 69.6, 72, 82

and 72 for stations Ito IV respectively, whereas in 1999 the values were 63, 72, 87 and

72 for the post monsoon, 70, 72, 87 and 62 for summer, 66, 78, 94 and 80 for the south-

west monsoon and 70, 72, 86 and 72 for the north-east monsoon for stations I to IV

respectively.

82

Water Quality

Not all the quality variables are detrimental to all the beneficial uses. Any

variable may have great importance for one of the beneficial use, but may not be

important for another use. Each beneficial use has different water quality requirements.

Based on the water quality indices the water was classified into five categories A, B, C,

D and E. If the WQI value is greater than 90 it is classified under category A

(Excellent). Similarly WQI 65 - 89 comes under category B (Good), 35 - 64 under

category C (Satisfactory), 11 - 34 under category D (Poor) and less than 10 under

category E (Unacceptable).

According to the above classification the water quality at station I comes under

category B in summer, south-west and north-east monsoon seasons whereas it is under

category C during the post monsoon season. This may be due to the activities of local

inhabitants by way of waste discharge, workshops effluent discharge, washing and

agricultural practices. In all the seasons the water condition at stations II and IV fall

under category B. The values at station III during post monsoon and south-west monsoon

1999 (90 and 91 respectively) showed excellent nature indicating that it was less polluted

due to less anthropogenic influence since it was a private one (Figure - 23).

A similar type of classification has also been attempted by Pande & Sharma (1999)

in Ramganga river, Ajit Pratap Singh & Ghosh (1999) in the Yamuna. The present study is a

pioneer to open up a way for the best use of the water resources and it also underscores

the fact that it is essential to know the various end uses of water at a locality. Further,

the quality of the water has to be monitored at periodical intervals in order to maintain

the quality of water for human use and sustenance of the ecosystem.

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