Assessment of Surface and Ground water Quality of Hebbal Lake, Bangalore-Case Study

Transcription

1 Sengupta, M. and Dalwani, R. (Editors) Proceedings of Taal2007: The 12 th World Lake Conference: Assessment of Surface and Ground water Quality of Hebbal Lake, Bangalore-Case Study Usha N M 1, Jayaram K C 2 and Lakshmi Kantha H 3 ABSTRACT Hebbal tank is situated in the Northern part of the Bangalore city, covering an area of about 76 hectares. Being one of the biggest tanks in Bangalore, the tank receives untreated domestic sewage from Bharath Electronics Ltd (BEL) residential layout, Vidyaranyapura residential area, Hebbal residential area and the surrounding areas. The present study was undertaken to evaluate the quality of surface water and groundwater of Hebbal lake. The study was conducted for premonsoon and monsoon session. The assessment of groundwater quality is made through calculating the Water Quality Indices (WQI). In the formulation of WQI, all the nineteen parameters analyzed were considered; ph, EC, TDS, turbidity, Cl -, Total Alkalinity (TA), Total Hardness (TH), Ca 2+, Mg 2+, nitrate, Na +, K +, So 4 2-, F -, Fe, Zn, Pb, Mn and copper. In order to understand the spatial nature of groundwater quality in the study area, Isoconcentartion maps were prepared by using Arcview 3.2a GIS software for different water quality parameters. A systematic calculation of Karl-Pearson Correlation coefficients has been made and attempts have been made to develop the linear regression equations between significantly correlated parameters by using Statistical Package for Social Sciences (SPSS) software. The study showed a positive and significant correlation of TDS with chloride, total hardness, calcium and magnesium ion concentrations, whereas, total hardness was shown good correlation with calcium and magnesium ion concentrations. Key words: groundwater, lake, pollutant, sewage, remediation. INTRODUCTION Bangalore was a city well known for its green environment and was once called as a pensioners paradise. Pollen grain was major cause for prevalence of Asthma in Bangalore city. Bangalore city is witnessing high pace of growth in sectors of life viz; medicine, engineering, education, software, hardware technology, public transport, mass transport, urbanization etc. Nowadays, due to increase in population and increased usage of personal vehicles and other human activities have resulted in increased load of water pollution, soil pollution and air pollutants in the surrounding atmosphere. The number of vehicles registered at all RTO offices in Bangalore is around 20Lakhs which indicates the rapid growth rate of city and its population. Out of 20 lakh total vehicles, two wheelers and auto rickshaws alone are 13 Lakhs. The AAQM results indicated that Bangalore is one among the 7 non attainment cities from Air Quality point of view. The Government of Karnataka have constituted a Task Force for planning and coordinating the efforts of various Departments, Agencies and NGO s/publics such as Police, Transport, Food and Civil Supplies in order to reduce the air pollution in the city. Because of effective implementation of the task assigned to the task force, the pollution load has come down to substantial level though there is a tremendous increase in population of the city and registration of number of vehicles in the city limits. The Task Force has evolved a 14 point action plan which is being implemented and monitored periodically. Bangalore is getting its drinking water from river Kaveri, from a distance of almost 200km, from drinking water reservoir constructed across the tributary of river Kaveri near Bangalore city and also extracting ground water. Some of the pockets of ground water source around Banaglore city is reported to be contaminated due to unscientific disposal of domestic sewage and industrial effluents. Though, surface water bodies like lakes, tanks are not used for drinking water supply of the city but their contribution towards ground water recharge is of considerable point. In this study water quality assessment of one of the surface water tank is considerd and detailed study has been carried to assess the present surface and ground water quality, and suggest the possible remedial works to avoid/reduce the entry of sewage and industrial effluents into the water body and to improve the present water quality. Hebbal tank is situated in the Northern part of the city along Bellary road, covering an area of about 76 hectares. Hebbal Lake receives water inflow from its catchments that covers localities like Yeshwanthpur, Mathikere, RMV, BEL and HMT colonies, Nagavara, Narsipura and other layouts. The present study area selected lies between 13 5 N N latitude and to longitudes as shown in Figure 1.

2 Figure 1: Location Map of the Sampling Points MATERIALS AND METHODS The present study was undertaken to examine the quality of the surface water and ground water in the surrounding areas of the Hebbal Lake and to evaluate the possible migration of the contaminants from surface water to groundwater in the vicinity. For the surface water analysis, the lake water was sampled at the following points: Inlet, Centre 1, Centre 2 and Outlet. The water samples were collected at the following points between am to 12 pm. The physico (colour, temperature, odor, TDS and TSS), chemical (ph, electrical conductivity, turbidity, total hardness, total alkalinity, dissolved oxygen, BOD, COD, chloride, nitrate, sulphates, fluorides, sodium and potassium) and biological (Total coliform and fecal coliform) parameters were analyzed for the water samples. Heavy metals were also analyzed - total iron, zinc, manganese, lead and copper. The average mean values of different physico - chemical variables of Hebbal lake during pre-monsoon session and monsoon session were conducted. The data on 25 parameters is incorporated for the months May, June and July Procedure outlined by APHA (1989) is followed. A total of 27 ground water samples surrounding Hebbal Lake were analyzed. Out of which 19 samples were analyzed in areas lying within 1-2 kms radius of Hebbal Lake. And the remaining eight samples were analyzed in areas lying within 4-5 kms radius. Totally 7 areas were chosen for the sample collection namely: Kempapura, Neerbhavi layout, Nagashetti Halli, Kodige Halli, Sanjeevi Nagara, Sanjay Nagara and Sahakar Nagara. In each area about 3 to 4 samples were analyzed. 19 water quality parameters are selected, which are considered to be important as per the drinking water standards (IS ) ph, EC, TDS, Turbidity, Chlorides, Total Alkalinity, Total Hardness, Ca2+, Mg2+, Nitrate, Sodium, Potassium, Sulphate, Fluoride, Fe, Zn Pb, Mn and Copper. The analysis results were compared with drinking water standards (IS ) to assess the quality of groundwater in the study area. The drinking water quality standards are tabulated in Table 1. The assessment of groundwater quality is made through calculating the water quality indices. The understanding of the various parameters that causes the groundwater pollution is important in evaluating the water quality index. In order to understand the spatial nature of groundwater quality in the study area, Isoconcentartion maps are prepared by using Arcview 3.2a GIS software for different water quality parameters. 1738

3 Table 1. Analytical report of ground water for heavy metals. Sl.No. Parameters with Units Range in samples Mean WHO Standards ISI Standards Acceptable limits 1. ph EC (in µs) TDS Turbidity Chlorides Total Alkalinity Total Hardness Calcium Hardness Magnesium Hardness Nitrate Sodium Potassium Sulphate Fluoride Iron Lead Zinc Manganese Copper All parameters are in mg/l. Except EC in µs; Turbidity in NTU Maximum limits Existing bore wells of the study area were considered as the points to draw the samples. Twenty seven borewells were selected as the sampling points to collect the groundwater samples. The points selected were distributed in the entire area to represent true representative about the quality of groundwater. The locations of the sampling points are shown in the Figure 1. Sample Collection and Transportation: Groundwater samples were collected from selected borewells as per the standard procedure. Two liter precleaned PVC (polyvinyl chloride) cans thoroughly rinsed with distilled water were used for collection of samples. The borewell water was released for 3 to 5 minutes before collecting samples into the cans, so as to wash out the local impurities and to empty the water standing in the service pipe. The containers are labeled describing the date of collection, time of collection, sampling location, and conditions under which sampling is done. The collected samples were transported to laboratory and were analyzed. RESULTS AND DISCUSSION Surface water Analysis: The result of the physico-chemical analysis of surface water (as in Table 2 and 3) showed that ph was within the prescribed limits ( ).The electrical conductivity was found to range from 15 to µs. This was due to the presence of salts in the lake. The high value for dissolved solids indicated a high rate of sedimentation in the lake. The D.O was found ranging from 1.2 to 9.2 mg/lit. The high D.O was found only in the centre of the lake i.e., in the areas lying close to weed bed. The alkalinity ranged from to 288 mg/lit. The nitrate concentration was found to be between 4.8 to 47 mg/lit. The chlorides were also found to be between 70 to mg/lit. Sulphates ranged from 2.0 to 26 mg/lit. BOD was found to be very high, higher than the standard (3 mg/lit). BOD was found to be between 10.4 to 160 mg/l. This could be attributed to the inflow of sewage into the lake, which has stopped now. COD was found to be between 16 to 440 mg/l. COD was found to be much higher than the standard indicating the presence of various chemical compounds in the water. Sodium and potassium were also found to be high, being the essential nutrients along with phosphates for the microbial biota causing eutrophication of the lake. Sodium was found to be between 27 to 127 mg/l and potassium 4 to 15 mg/l. Phosphates was found to be between 0.09 to 0.23 mg/l. Fluorides were found to be between 0.15 to 0.57 mg/l. Heavy metals like Iron, zinc, manganese, lead and copper were found in the lake. The coliform count was very high, more than 1600 per 100ml of water. This result indicates sewage pollution and eutrophication of the lake. 1739

4 Table 2. Physico Chemical parameters carried out for 3 months on lake water Sl.No. Parameters May June July 1. ph Temperature C 27.2 C C 3. Turbidity EC Total Hardness Ca Mg D.O B.O.D C.O.D Chlorides Total Alkalinity TDS TSS Nitrate Sulfate Phosphate Sodium Potassium Fluorides Iron Zinc Manganese Lead Copper NIL NIL All parameters are in mg/l. Except Temperature - C; Turbidity NTU; EC - µs/cm Table 3. Physico chemical data for ground water in the studied area. All parameters are in mg/l. Except EC - µs/cm; Turbidity NTU; Locality Sl.No. ph EC TDS T Cl - TA TH Ca 2+ Mg 2+ NO 3 Na + K + 2- SO 4 F - Kempapura G G G G G Neerubhavi G G NIL Nagashetti G Halli G NIL G NIL G NIL Sanjeevi G Nagara G NIL Kodige Halli G NIL G G G Shantivana G NIL Hebbal Main Road G Sanjay Nagar G NIL G NIL G NIL Sahakar Nagar G G G G G

5 Groundwater Analysis: In the studied localities ground water was free from color and odor. The physico-chemical characteristics and heavy metals of the analyzed water sample have been presented in Table 2 and 3. The data revealed that there was a considerable physical chemical variation in the examined samples. The variations were not only in the samples collected from different localities, but the samples collected from the same locality were also having considerable variations in water quality. This may be due to the irregular distribution of the rocks or due to the difference in the depth of hand pump installations. A comparison of the depth of the hand pump installation indicated that deep installations were better than the shallow installations with respect to the water quality in the study area. Since shallow hand pumps draw water from the topmost bearing structure, which is most liable to contamination by various natural as well as anthropogenic sources percolating in the vicinity and taking with it minerals, etc,. In the study area, ph ranges from with a mean of 7.1. The Drinking Water Standards (IS ) for turbidity specify 10 NTU as the permissible limit and can be used up to 25 NTU in the absence of alternative source. In the study area, turbidity value ranges from 0.03 to NTU with a mean of 1.1 NTU). It is pertinent to note that in the study area, turbidity falls within the permissible limits. EC as well as TDS signify the inorganic pollution load of a water system. In the study area, Electrical Conductivity value ranges from to 1709 µmhos/cm with a mean µmhos/cm (Table 5.5). Out of the twenty seven samples, twenty six samples were found to be exceeding the permissible limit and is unfit for drinking purpose. This might be due to the gradual deposition of salts, over the years. In ground water, hardness is primarily due to presence of carbonates, bicarbonates, sulphates and chlorides of calcium and magnesium. In the study area, the total hardness (as CaCO 3 ) ranged from ppm to ppm with a mean of ppm (Table 5.5). Out of the 27 samples, 15 (55%) samples were found to be exceeding the permissible limits. The hardness was found to be quite high in the ground water in some areas. These were rural areas and the water was not being used regularly. This might have led to the accumulation of salts in the well. The observed result of TDS also correlates to the hardness result. According to hardness classification (Durfor and Becker, 1964), ground water was moderately hard at 3 locations (i.e., one at kempapura and the remaining two in sahakar nagar) and very hard at 24 locations in the studied area. CONCLUSIONS From the results of this study it has been concluded that: The physico chemical analysis of the study revealed that the lake was highly sedimented. High values of BOD indicate that the sewage inflow has severely polluted the lake and high values of COD indicate the presence of various chemical compounds in the lake water. Sodium and potassium was also found to be high, being the essential nutrients along with phosphates to the microbial biota causing eutrophication of the lake. Heavy metals like Iron, zinc, manganese, lead and copper were found in the lake. The coliform count was very high, more than 1600 per 100ml of water. This result indicates sewage pollution and eutrophication of the lake. All the 27 groundwater samples collected were having the concentrations of many parameters above the permissible limit. The quality of groundwater is objectionable in almost all the samples. Possible Remedial Measures: The sewage must be de linked with the water body and passed only through sewer systems. Clean up weeds in the lake and use it as compost and raw material to produce biogas. The water already present must be completely drained before any restoration work is implemented. Disposing of domestic/industrial wastes and carcasses must be stopped. Public awareness must be created among the citizens about the importance of lakes/tanks and suitability of groundwater for drinking purpose. REFERENCES Professor, Department of Civil Engineering, UVCE, Jananabharathi, Bangalore. Professor, Depaertment of Civil Engineering, BIT, KR Road, Bangalore. AEO, No.49, Parisara Bhavan, Church Street, Karnataka State Pollution Control Board, Bangalore , Ph , Fax: , E Mail. Lkdp2k@rediffmail.com. 1741