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
