Inadequate sewage treatment and disposal in the national capital territory is contaminating city’s groundwater
Delhi residents who depend on groundwater for their drinking water needs be warned. The latest data of the Central Ground Water Board (CGWB) shows that groundwater samples taken from observation wells in the national capital are getting contaminated because of their unhygienic catchments and untreated sewage, which is discharged in the open and into drains, and percolates into the groundwater.
Nitrate concentrations in the water samples, known to cause methaemoglobinemia or blue baby syndrome (a blood disorder wherein hemoglobin is unable to release oxygen effectively to body tissues), have been recorded at a high 1,500 mg/l (See map). The World Health Organisation advice is that nitrate levels in drinking water should be below 50 mg/l, as “an effective preventive measure”. The Bureau of Indian Standards states that the desirable limit is 45 mg/l, and there is “no relaxation” for this maximum value. The CGWB report, compiled in November last year, states that “the nitrate pollution in the groundwater is mostly anthropogenic and may be due to improper disposal of sewage and unhygienic conditions around the well”.
These findings may be of less concern to three fourths of Delhi’s population which is connected to the official piped water network operated by the Delhi Jal Board (DJB). DJB officials say that they test 300 to 400 samples at the consumer end each day and that “the percentage of unsatisfactory water samples ranges between 1 to 2 per cent”. The CGWB finding, however, is a matter of serious concern for those unconnected to the network as they have little choice but to rely on private abstraction wells or tankers that supply untreated ground water. Although this water can be made safe for drinking by an ion exchange or reverse osmosis purifier, market research studies have found that less than a quarter of Delhi’s households have an in-house water purifier.
CGWB also monitored the electrical conductance of water to get an idea of the mineral content in groundwater, as well as the total dissolved salts content of a water sample. Out of the total 124 analysed samples, 42 samples were recorded with values in the range of 2,000 to 16,700 µs/cm. But it is the rising nitrate levels that are alarming. The levels have been attributed to “combined effect of contamination from domestic sewage, livestock rearing, landfills and runoff from fertilized fields, unlined drains and cattle sheds”. According to the report, Delhi’s groundwater has more nitrate contents at shallow levels but they decrease with depth, substantiating the argument that levels are high where “domestic effluent is discharged into open unlined drains”.
Delhi has 162 hydrograph monitoring stations, ranging from one monitoring station per 1.4 sq km in the New Delhi district to a monitoring station for every 30 sq km in the North and East district. “Given the importance of groundwater, we are striving to increase and improve our monitoring capacity,” says A D Rao, officer-in-charge of the state unit CGWB office in Delhi. Rao and his team have found a correlation between open drains carrying untreated sewage and groundwater contamination. They are currently conducting a study looking into the quality of observation wells around the Najafgarh drain, which carries approximately half of the wastewater generated in the national capital territory, which is partially treated sewage at best. The report is expected to be finalised by end May. Refusing to divulge any further details, Rao says that the water quality results point to how detrimental poor septage management and lack of adequate sewage treatment and disposal systems can be for groundwater in not just the immediate localities but even in ground water up to two kilometers away from the drain.
As per the inception report of the Master Plan for Sewerage System of Delhi for 2031, the existing sewerage system in Delhi is grossly inadequate, as only about 55 per cent of the population have a connection to the sewer lines, while 15 per cent of the population has on site sanitation systems such as septic tanks. It is also well known that there are 27 urban villages, 150 rural villages and 1,575 unauthorised colonies which are yet to be connected to the sewer network. Therefore, approximately 35 per cent of the sewage treatment facilities, woefully inadequate, is currently under-utilised, and roughly 2,900 million litres of sewage is discharged untreated into the 19 major stormwater drains, and ultimately into the river Yamuna.
Authorities pay lip service
Preparing themselves for a peak summer water demand, the environment department of the Delhi government is planning to map borewells in the national capital territory and enforce metering in commercial establishments. How and when this will happen is yet being worked out, and at the moment it is just paying lip service to the need for conservation of water in the city. There is also admission on the part of the government that under the guise of rainwater harvesting bore wells are being used for extraction. The Centre for Science and Environment, a New Delhi based nonprofit, has been advocating designing of borewell shafts at approximately 5-8 metres above the water table. The natural percolation allows some degree of filtration, given that catchments are often poorly maintained. It also prevents shafts from puncturing those aquifers which are beyond recharge, and at the same time prevent extraction of water from such aquifers. CGWB is yet to decide on this matter.
The other issue of concern is the operation of tankers that are not licensed to sell water in the city. The demand is highest in areas where the groundwater levels are the lowest. CGWB records the water level depth four times a year in Delhi—in January, May, August and November—to gauge the seasonal fluctuations in the water table. The pre-monsoon measurement is an important indicator of use and depletion of reserves. According to the report, the north-east, central, south and southwest recorded a fall in the range of 0.02 to 5.70 metre, year on year, between May 2010-11. “The overall data indicates that south and southwest districts are showing falling trends,” mentions the report. Moreover the maximum decadal fall is recorded in north-west, south and south-west districts—9.76 to 14.07 metre on mean levels in the month of May.
Given that demand outstrips supply, the fact that the piped network remains iniquitous and incomplete in its reach, groundwater abstraction, be it official or otherwise, is here to stay. Moreover, even after a planned expenditure of Rs 25,000 crore under the sewerage master plan 2031, the choice of costly, energy intensive sewage treatment technologies will ensure that capacity will remain woefully inadequate, although the city agency maintains high hopes that the national capital territory will be fully sewered by then. With previous experience of sewage generation outstripping that forecast by the planning department, the quality of groundwater is bound to remain an area of concern.
Click here to read the full CGWB report on Delhi groundwater
Ground water year book 2011-12: NCT Delhi
Ground water scenario in major cities of India
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