Performance Evaluation of RBF Wells with Special Reference to Water Quality Parameters in Hard Rock Region of Tungabhadra Catchment

. Tungabhadra River is the chief source for drinking water and agriculture developments in Davangere and adjoining districts of Karnataka. It is reported that the water of Tungabhadra is getting polluted by the direct / indirect effluent discharges due to which people living on the river bank are facing the problem of drinking water. River Bank Filtration (RBF) wells which will naturally treat the polluted surface and ground water have been drilled in perpendicular to the river at a distance of 30m, 50m and 80m to understand the extent of treatment of RBF wells to provide clean and safe drinking water. The present study deals with the problems of water quality in a selected village (Somlapura) located in a hard rock terrain of river Tungabhadra, Karnataka, India. As a part of the investigation, water samples were collected from River Bank Filtration wells and adjoining river and aquifers were analyzed using standard methods. Outcomes of water quality presents that the concentrations of turbidity and total coliform were lesser in the RBF well water samples when compared to Tungabhadra River water samples. The water from RBF wells contained fresh water, which is highly mineralized and free from bacterial contamination relative to the water from river. However, groundwater of the adjoining aquifers showed wide variations in various physio-chemical parameters. From the analysis, unsafe levels of total coliforms (included E.coli and F. Coli) were detected in Tungabhadra River i.e., It varied between 1680 and 3179 MPN/100 ml. It is observed that the average removal efficiency of coliform bacteria from RBF well 1 & 2 was 99.84% and 99.82% respectively.


Introduction
Water is known as the universal solvent and the existence of life on the earth mostly depends on its distribution.However, due to several geo-genic processes and anthropogenic activities like agriculture, urbanization, industrialization etc., are liable for water pollution, which make it unsuitable for drinking and other domestic usages.Majority of the seasonal rivers in India, acts as waste water conduits and are likely to be contaminated with high loads of pathogenic microorganisms and other physical and chemical contaminants.As the water requirement as a whole and also for drinking purposes increases tremendously, it is reported that the natural resources of groundwater are rapidly depleting in many parts of the country.According to a study, in India groundwater currently provides 85% of the country's domestic water, but in 20 years, about 60% of all of India's aquifers will be critically degraded [1].One strategy for making up for depleting groundwater resources is to use natural water-treatment systems that permit the cost-effective technology and re-use of polluted surface water resources.One such treatment method which is widely used is Riverbank Filtration (RBF) technique.RBF is one of the alternative sustainable water treatment rather a pre-treatment technique which is proved to be cost-efficient technology for extracting safe drinking water [2].In the present study, the performance of RBF in solving the water quality problems of a selected village (Somlapura) located in a hard rock terrain of river Tungabhadra, Karnataka, India was studied.
In recent years, (Kalashetty et.al, 2014), studied both the river and groundwater quality of selected villages and recommended the necessity of treatment of drinking water supplied to village.It is also opined that as the concentration of pollutants exceeding the permissible limits due to the industrial discharge on the upstream end of the village, treatment by conventional methods will be costlier.Hence it is convenient to go for alternative method which can be natural, low-cost & sustainable.In this study, a RBF wells were drilled on the bank of Tungabhadra near a village called Somlapura (As per CGWB report this area comes under a hard rock region).Water quality of these wells was compared with River and ambient groundwater quality.

Study Area
A Somlapura village on the bank of Tungabhadra River is selected as a study site.Somlapura is a small village of Ranebennur (tq.), Haveri (dist.),Karnataka state, India.It is situated 48 km towards an East of district headquarters, 20 km from Ranebennur and 319 km from capital of state i.e., Bengaluru.According to 2011 census the population of the village is 1484.The Figure1 displays the geographical position of the study area.

Methodology
Methods followed for the water quality analysis are as follows: In the present study, the water samples were collected (May, 2017 to April, 2020) from the RBF wells drilled in Somlapura village and also from river Tungabhadra (stretch of the river close to RBF wells) to compare the water quality.The concentration of physio-chemical parameters such as pH, Turbidity, TDS (Total dissolved solids), EC (Electrical Conductivity), Calcium and Magnesium hardness, Total hardness, Alkalinity, Chloride, Sulphate, Potassium, Sodium, Iron, Nitrates, Fluoride, and biological parameters (Total and Fecal coliform) were analyzed (APHA, 2005).

Experimental Results
On a monthly basis, water samples were collected from Tungabhadra River, River bank wells (RBF wells) and also from adjoining aquifer covering riparian belt.Physical, biological and Chemical parameters which include pH, TDS (Total dissolved solids), Total coliform, Turbidity, Calcium and Magnesium hardness, EC (Electrical Conductivity), Total hardness (TH), Alkalinity, Chloride, Sulphate, Potassium, Sodium, Iron, Nitrates and fluoride were evaluated.In groundwater samples, the concentrations of Ca, Mg, Cl, SO4, and NO3 was found to be relatively higher and in majority of the cases exceeded the limits prescribed by BIS.TDS (740±270 mg/L) and TH (356±168 mg/L) were also higher in concentrations.It is noticed that the concentration of fluorides is above the BIS limits (1.5 mg/L) in various locations.The results of the investigation are discussed below.

pH and Turbidity
pH of water plays a vital role in characterizing water for various purposes.The pH of groundwater varies between 6.79 (on Sept.18) and 8.34 (July 17).Water is found to be slightly acidic to moderately alkaline.pH of surface water varies between 7.21 (Aug17) and 7.86 (May19).Though the water receives domestic waste disposal from the upstream industries and households, the pH value remains within the prescribed limits of drinking water (6.5-8.5) as per IS: 10500 (2012).It is found that the pH is relatively higher in river water than in groundwater.The turbidity of water plays a significant role by indicating the relative clarity of water in a medium.This is an optical feature representing the amount of light that is penetrated the water body (depth of penetration).If the scattered light has more intensity, the turbidity is more.Tungabhadra is one of the major tributaries of river Krishna and carries a large quantity of sediments as the fertile agricultural land that lies on either side of the river.River turbidity is significantly high and groundwater also showed a considerable level of turbidity during the study period (fig.2).

Electrical Conductivity and Total Dissolved Solids
Electrical conductivity and TDS are relative parameters and depend on the total concentration of ions, mobility, relative concentration, and valence.From the monthly observations on EC of groundwater, it is noticed that EC varies from 528 μS/cm (July 18) to 1441 μS/cm (April'20), whereas in the surface water it ranges from 270.18 μS/cm (June'17) to 496 μS/cm (May18).Meanwhile, it is noticed that the corresponding TDS of groundwater varied between 269 mg/l and 741 mg/l.In surface water, the variation observed was between 289.8 mg/l and 171.30mg/l.From the analysis of EC and TDS data, it is presumed that the variation of TDS across the study area could be attributed to the release of untreated sewage discharge in the upstream zone and due to the storm flow from urban and agricultural areas during the monsoon season.

Total Alkalinity
Alkalinity is the measure of the capability of acids to neutralize water.The common ions which are responsible for the Total alkalinity are carbonate (CO3 2− ), bicarbonate (HCO3), and hydroxide (OH).In the present investigation, groundwater alkalinity ranges from 157 mg/l (July 18) to 412 mg/l (Apr 19).In the surface water, it varied between 111.89 mg/l (Aug'19) and 182.31 mg/l (Feb.20).Along the stretch of the study area, alkalinity showed an increase towards the downstream of the river and a decline, close to the RBF site.

Chlorides
Chlorides and sulphates are two essential anions in water for identifying the aptness of water for public supply, agriculture and industrial usage.The average chloride content of groundwater was found to vary from 64 mg/l (Jul'19) to 192 mg/l (Apr'18) and in the river water, it ranged between 34.1 mg/l and 39.76 mg/l (Apr'20).

Fluoride
Fluoride content in the groundwater varied between 1.18 mg/l (Oct.19) and 1.94 mg/l (Feb.20).In majority of the observations, it is found that the concentration of fluoride is higher than the permissible limits (1.5 mg/l).However, in the surface water, it is much lower than the permissible limits.The minimum concentration observed was 0.38 mg/l and the maximum was 0.48 mg/l.

Sulphates and Nitrates
Sulphate concentration during the observation period showed variation from 6 mg/l (May 17) to 40.8 mg/l (Nov.19) in the groundwater, whereas in the river water it ranged from 7.10 mg/l (Aug'17) to 12.40 mg/l (Nov.18).In the case of nitrates, it varied from 3.32 mg/l (Oct & July' 17) to 14.18 mg/l (Jul'19).In the river water, the variation observed was between 7.58 mg/l (Aug'19) and 11.64 mg/l (May19).

Calcium, Magnesium, and Iron
From the study it is noticed that the calcium concentration of groundwater during the study period varied from 23.30 mg/l (Sept.17) to 64.16 mg/l (Apr.19).In the river sample, calcium varied from 20.12 mg/l (Aug.17) to 49.64 mg/l (May.20).Interestingly, a steady increase in the concentration was observed towards downstream.A rise in calcium content was noticed along the river stretch which could be due to the anthropogenic activities.
Magnesium also showed a similar trend.The variation of Mg content lies between 12.20 mg/l (Sept.18) and 44.90 mg/l (Mar'18).In the river water, it varied between 4.60 mg/l (June.17 & Aug.19) and 6.90 mg/l (May.20).Therefore, it is presumed to be from the same source.
Iron concentration in the groundwater varied from 0.78 mg/l (Sept.19) to 1.92 mg/l (Mar.19).In the upstream region, the concentration varied from a minimal of 0.06 mg/l (Aug.19) to a maximum of 0.23 mg/l (Apr'19).In the downstream, at Nadiharahalli, the iron content was reduced to 0.08 mg/l from 0.24 mg/l (observed at the upstream point).The sampling stations in the upper reaches (near Kumarapatnam) showed higher iron content (As per IS 10500-2012, the desirable limit of iron is 0.3 mg/l).

Total Hardness
Hardness is the concentration of multivalent metallic cations in a solution.Hardness would be represented by the sum of magnesium and calcium ions for all calculation purposes.The current investigation showed a variation of total hardness from 56.9 mg/l as CaCO3 during the rainy season to 160.33 mg/l as CaCO3 in the dry season.In some of the stations a rise in hardness was observed mainly because of the release of untreated household sewage discharged in the upstream region.
Based on water hardness, river water showed hardness less than the desirable limit (range is between 50 to 150 mg/l as CaCO3), both during monsoon and post-monsoon seasons.

Sodium and Potassium
The sodium concentration varies from 22 mg/l (Jun.19 & Mar.20) to 57 mg/l (Nov.18) and in the river water, concentration ranged from 14.85 mg/l (Apr'19) to 89.52 mg/l (Nov'18).Observations on potassium indicated that it varies between 6 mg/l (Aug'17 & 18) and 19 mg/l (Nov.19).However, it is noticed that both the concentration of sodium and potassium are found to be within the permissible limits.

Dissolved Oxygen
Dissolved Oxygen (DO) is among the very necessary component of natural water.The atmospheric oxygen solubility in fresh water is between 14.6 mg/l (at 0

Bio-chemical Characteristics of Surface water
Biochemical Oxygen Demand (BOD) refers to the volume of oxygen used in organics microbial utilization.The corresponding BOD, in all eight stations where the DO were monitored (BOD observed are 2.9, 5.5, 6.5, 10.95, 9.10, 7.10, 5.04, and 4.1 mg/l) showed variation between 2.9 mg/l and 10.95 mg/L.It is also noticed that, the BOD values were higher in the pre-monsoon period as against other seasons.The increase of BOD from in selected locations is mainly due to domestic waste water discharge from the adjoining villages.
As per the CPCB norms, when BOD is higher than 3 mg/l, the river can classified as stream 'D' for which the most beneficial uses are regulated, particularly for wastewater disposal, propagation of wildlife fisheries, and industrial cooling and irrigation.Stream 'C' refers to the BOD value between 2 and 3 mg/l.From the present observation, the river up to 3 km from the headwater may be classified as stream 'C' type and further downstream (between 3 and 40 km) it is grouped under the stream "D" category.

Chemical Oxygen Demand
Chemical Oxygen Demand (COD) is the quantity of oxygen, that is required to oxidize organic matter using an oxidizing agent under an acidic state.

Total Coliform
The fecal coliform bacteria are one subgroup and Escherichia coli is the most common associate.The microorganism grows at higher temperatures and is only related to fecal materials of animals (warm-bodied).
In river water, the excess concentrations of coliform bacteria 1700 MPN per 100 mL) was detected during the post-monsoon season.High concentrations of Total coliforms (>800 MPN per 100ml) were observed during the pre-monsoon period (April-May 2018).During monsoon, huge deviations in amounts of Total coliform was noticed which varied from nil to about 800 MPN per 100ml.At the outset, yearly mean of total coliforms was relatively lower in RBF wells (avg: 2MPN per 100ml) than that for river samples (avg: 1121 MPN per 100ml;).Statistical parameters such as ranges, averages (arithmetic mean), standard deviations of river and RBF water samples were summarized in Table 1.In river samples, concentrations of Ca and Mg are below the desirable BIS limits, with an average of 35.18 mg/l and 6.02 mg/l respectively.Chloride and SO4 are also below desirable BIS limits with an average value of 39.47 mg/l and 8.73 mg/l respectively.The average NO3 was 9.31 mg/l which is lower than desirable limit (i.e., 45 mg/l).The concentrations of TDS, Alkalinity, Fe, Fluoride, Sodium and Potassium are well within the BIS limits.Whereas, the concentrations of parameters such as Turbidity, Total Coliform and E.coli are exceeding BIS limits.Water samples from both RBF well-1 and well-2 were examined for Temperature, pH, EC and Total coliform.The average concentration of Total coliform varied from undetectable to 2 MPN per 100mL (Table 1), with a peak value being detected in the rainy season (10 MPN per 100 mL).Overall, percentage removal of coliforms is about 99.9%.The coliform concentrations in a river is low (<600MPN per 100ml).The least bacteria elimination capabilities of RBF wells vary between 90% and 99%.The average EC was 529.64 μS/cm (Table 1); which is 0.54 times lesser than that of groundwater samples (average: 985μS/cm) but 1.34 times higher than that of river water samples (Table 1).Total hardness (avg.: 233.19 mg/l) was twice than that for the water sample from the river, however it is 1.14 times less than that for groundwater.Limits of all major ions often exceeded BIS limits in Groundwater samples.The fluoride concentrations were recorded well within the acceptable limits for all samples (<1.5 mg/L).In terms of concentrations of major ions (Table 3), the hydro geochemical features of water samples from RBF system are closer to groundwater features than the features of water samples obtained from a river (Fig. 4).In case of anions, in RBF water Cl was the dominant anion, tailed by SO4 followed by HCO3 + CO3.Average concentrations of NO3 differs from 41.61 to 42.17mg/l (as NO3), whereas Fluoride was <1.36 mg/l.A Piper diagram (fig.5) was used for further examination of hydro geochemical character of RBF well water (n = 36) relative to groundwater and river water.The diagram shows that 22.2% and 16.3% of water samples from river plot in the Ca-Mg-HCO3 (I) and Na-Cl (III) The above water quality outcomes represent that turbidity and total coliform concentrations were lesser in the RBF wells when compared to the Tungabhadra River.While RBF water was extremely mineralized relative to the river, some of the major ion concentrations in RBF well water crossed the limits recommended by BIS.

Conclusions
Conclusions drawn from the experimental study are as follows: • Outcomes of Water quality analysis represent that turbidity and concentrations of E. coli were lesser in the RBF wells when compare to Tungabhadra River.While water from RBF found extremely mineralized than the water from a river, but it was not as saline as that of ambient groundwater source.
• The results of E. coli test show that the average removal efficiency of E. coli in RBF well 1 & RBF well 2 was 99.84% and 99.82% respectively.During rainy season, water quality of both RBF wells was 99.81% to 99.83% greater than the river.And it was 99.81% to 99.86%greater during dry season.
• The average removal efficiency of total coliform at RBF well 1 was 99.82% in dry season and it is reduced to 99.11% in rainy season.While at RBF well 2, the average total coliform removal efficiency was 99.85% in dry season and it is reduced to 99.16% in rainy season.• In conclusion, this study reveals that RBF is a suitable water treatment technology in case of hard rock terrain.

Fig. 1 .
Fig. 1.Location of the Study Area

Fig. 2 :
Fig. 2: Concentrations of Turbidity in the river (left side) and RBF (right side) water
• C) and 7 mg/l (at 35 • C) under one atmospheric pressure.The complete loss of DO is a result of decay and the prevailing temperature range.The mean values of DO during the study period were 7.65, 8.10

Table 1 .
Turbidity, EC & Total coliform ranges for water samples of river and RBF well.
, while the majority of river water samples (54.2%) are of mixed kind (Ca-Mg-Na-Cl-HCO3; V).In contrast, 45.3% of RBF well samples are of mixed kind (Ca-Mg-Na-Cl-HCO3), 27.8% Na-Cl (III), and 26.0%Ca-Mg-Cl (II).Groundwater Samples were a mixture of Ca-Mg-Cl (II), Na-Cl (III), and Ca-Mg-Cl-HCO3 (V) types.The hydrogeochemical signs of the RBF water have the features of mainly mixed kind River water and Na-Cl/Mg-SO4 type groundwater.