With the city facing drought for the third year in a row, there is more pressure on the already plummeting groundwater level

Every day, at least one resident in Triplicane goes for a deeper borewell in search of water that has become elusive in most parts of the city.

As the city has faced drought for three years in a row, there is more pressure on the already plummeting groundwater level. In the absence of piped water supply and owing to difficulty in getting a tanker load of water, residents are sinking borewells even up to 600 feet in suburban areas such as Ambattur, Pallavaram, Chromepet and Avadi.

"Unlike many parts of the city, added areas have to manage with poor supply from Chennai Metrowater," says S. Raghuraman, a resident of Ambattur. “We heavily depend on groundwater to meet our needs and manage with water supplied by private tanker at ₹7 per pot. Many people sink borewells up to 600 feet and settle for saline water. Some of them have no choice but to spend on private tankers as their borewells have gone dry this summer,” he said.

On an average, one borewell contractor sinks about 30-40 borewells a month and there is nearly 10-20% increase in the demand. Residents in several areas have opted to sink double the depth in the past two months. "It is difficult to replenish groundwater in deep borewells," said S. Yuvaraj of the Chennai Borewell Rig Owners and Contractors Association. Though the number of enquiries has escalated from 45 to 200 per month, contractors are unable to meet the demand due to heat and shortage of manpower.

Contractors like S.R. Parthasarathy of Triplicane note that residents are willing to spend ₹2.5 lakh to dig 500 feet borewells in Triplicane and Royapettah. But there are areas such as Mylapore, where water is available at 150 feet.

Soil conditions

Chennai has limited potential to tap deep aquifers through borewells as there is not much thick alluvial soil, which is deposited over flood plains and river basin. The city largely has a geological formation of crystalline gondwana and shale rocks that restrict the volume of groundwater storage. "It is advisable to dig up to 500-600 feet for yield. The neighbourhood of Porur lake would have a good yield at 200-300 feet,” said L. Elango, professor, Geology Department, Anna University.

Pointing out that the borewells in the same locality may not be connected, V. Ravichandran, a borewell contractor, said deeper borewells would only help store water and not lead to a new source. The fear of losing source if the neighbour digs deeper is unnecessary, he said.

Though the level of shallow groundwater is being monitored by many agencies, there is not much official data on deep aquifers. The Chennai Metropolitan Area Groundwater (Regulation) Act does not lay any restrictions on groundwater for domestic purpose.

"When the freshwater column decreases, salinity or iron content increases in groundwater, depending on the geological conditions," says J. Saravanan, consulting hydrogeologist for water sources assessment and management.

Government agencies must step in to create awareness on the depth in borewells suited in areas of different soil formations. Besides this, the city must focus on greywater recycling. “We need foolproof designs for various areas to recycle waste water and cannot rely on canna plants alone,” he said.

Private suppliers to be monitored

Indiscriminate drawal through borewells for commercial purposes by private water suppliers is a major concern in the city fringes. In a bid to address the issue, the State Ground and Surface Water Resources Data Centre, Water Resources Department, is coming up with a proposal to provide licence at source. Officials of the Data Centre said there may be restrictions on the number of hours of extraction from borewells and assessment of yield through monitoring litres of drawal per minute. Instead of licence, private water tankers could carry a tripsheet.

Though Chennai Metrowater is the competent authority for implementing the provisions of the Chennai Metropolitan Groundwater (Regulation) Act, it often does not intervene for lack of manpower. Moreover, there is not enough monitoring or data on groundwater level in deep aquifers.The WRD has piezometers in 1,570 locations across the State to monitor water level in borewells. But, it is limited in Chennai and neighbourhood. “We are planning to increase the number and also place digital water level recorders for better understanding of deep aquifers,” said an official.The WRD also plans to regulate groundwater extraction in residential apartment complexes with more than six flats through a committee soon.Water level in borewells of packaged drinking water units would also be monitored.

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Analysis of groundwater level

Each number in the table depicts the average water level in metres below the ground level in the pre-monsoon period (April-June) in various years. The higher the number, the worse the situation.

The table shows that 2004-05 remains the worst period.

Ground water levels in Aminjikarai and T.Nagar dropped to 11-12 metres below ground level (BGL). They saw a recovery of sorts since then, improving to 3-6 metres BGL in the following years.

Chennai is heading towards a crisis again. In 2017-18, many areas saw the highest BGL in many areas. In Guindy and T.Nagar, the 2018 average was 8.4 and 8.5, the worst numbers since 2004-05