According to data collected from an advocacy group here in Chennai, the city’s groundwater table has increased by about 10 feet - thanks to northeast monsoon showers! There is also substantial improvement in the quality of groundwater, as all the impurities present in shallow aquifers underneath the ground have got diluted with rainwater.
In areas including A1 Block in Anna Nagar, Ramakrishna Mission in Mylapore, Hindi Prachar Sabha Street in T. Nagar, Chamiers Road in Nandanam, etc. the groundwater is seen at just 6 feet depth. The advocacy group surveyed groundwater levels in 88 different observation wells.
Thanks to end-of-October showers
On inspecting an open well on Hindi Prachar Sabha Street, since October, the groundwater level has drastically improved from 18 to 5 feet. Compared to September and October data, there is not much improvement in the groundwater level. With incessant rain showers during the end of October, there is uptick in groundwater levels across places in the city.
In Shastri Nagar, the level of groundwater was least favorable and could obtain only 15 feet under the ground. In October, the level was 25 feet. In fact, the observation well of 30-feet in Adyar neighborhood remained dry in September.
Type of soil decides percolation
Depending on the soil condition, the groundwater level may vary, say experts from the advocacy group. There is clayey type of soil in Nungambakkam High Road and surrounding areas. Hence, it takes time for rainwater to percolate in the ground surface. There is sandy soil in Adyar and Besant Nagar, and hence, the water can easily percolate into the ground surface within a very few hours of downpour.
TDS - the measuring key
The Total Dissolved Solids (TDS) is the key to know whether water is potable. Accordingly, the best quality water is observed in West Mambalam and Virugambakkam. Here, the TDS was 250mg per litre, whereas the desirable limit is 500 mg per litre.
At Nesapakkam and Ashok Nagar, the TDS is 813 mg per litre, and 698 mg per litre respectively. In fact, most parts of the city had potable groundwater, say sources.