Eyecatchers-188: 2015 floods recharged Chennai's groundwater, but polluted it

2015 floods recharged Chennai's groundwater, but polluted it

Ram Sundaram | TNN | Oct 12, 2017, 08:08 IST

Researchers collected water samples from 22 spots along the adyar after the floods and in April 2016.

The 2015 floods may have recharged aquifers across the city, but it con taminated the groundwater with bacteria and chemical ions, a re search by Anna University has found. Bacterial counts and chemical ions in groundwater samples collected across the city exceeded Bureau of Indian Standard's (BIS) recommended limits, concludes the research recently published in `Nature'.

Researchers found presence of V Cholerae and S Typhi among other pathogens, which can cause cholera, typhoid, urinary tract and respiratory infections. These pathogens, when isolated from groundwater, have shown resistance to widely prescribed antibiotics like ceftriaxone, doxycycline and nalidixic acid.

Continued showers during the last fortnight of November 2015 and unprecedented rainfall on December 1 in the catchment area of Adyar inundated the bank of the river the next day . Samples were collected from 22 areas along the river soon after the floods and six months later in April 2016.

The research team during field visits found that several wells located on either side of the banks were flooded in December 2015 and in all the bore wells, the annular space between the casing and discharge pipe was not securely protected with water tight seals. One of the researchers, professor L Elango, said this led to the direct entry of surface water into the ground through the annular space.

The top few meters were highly weathered and turned into regolith, layer of unconsolidated solid material covering the bedrock, and a thin layer of alluvium (3m to 5 m) formed in some regions along the river, the research paper observed. "This supported sorption [a process by which a substance becomes attached to another] of contaminated urban run-off carrying sewage, water from industrial and domestic sources, printed papers, metal, batteries, oil and paint," said G Gowrisankar, who was also a part of this study .

The team compared the groundwater quality with drinking water standards specified by BIS and suggested that groundwater not only in flood-affected areas, but also in some non-affected locations were unsuitable for direct domestic use. Concern for water quality based on chemical constituents was mainly due to calcium (>200 miligraml) and sulphate (400 mgl) as they exceeded the BIS limits.

The study found that the total bacterial count (TBC) in groundwater was high in most of the affected locations. The runoff carrying domestic sewage entered the contaminated Adyar river and increased microbial counts in groundwater of affected areas. In non-affected regions, it was comparatively lower.Though these pathogens isolated from the groundwater showed resistance to antibiotics, namely ceftriaxone, doxycycline and nalidixic acid, they were sensitive to others including chloramphenicol, ciprofloxacin, norfloxacin, and tetracycline, the report concluded.

Courtesy: The Times of India dated

Grateful thanks to Mr.Ram Sundaram, TNN and The Times of India