SINGAPORE - A contractor conducting upgrading works for national water agency PUB was to blame for a black substance that polluted a Potong Pasir outlet drain last month.
In response to queries from The Straits Times, the National Environment Agency (NEA) and PUB said on Friday (Feb 8) that enforcement action by NEA would be taken against UGL (Singapore) over its illegal discharge.
PUB said that it takes the incident seriously and has instructed the contractor to put in place additional engineering controls. The agency has also stepped up supervision to prevent a recurrence.
On Jan 20, ST had reported that PUB and NEA were investigating after a black discharge was seen in an outlet drain near Potong Pasir Avenue 1.
Videos shared with ST had shown an inky black substance flowing into the canal, which then spread and clouded the water rapidly.
In their Friday joint reply to ST, NEA and PUB said they traced the source of the discharge to Woodleigh Waterworks located near Potong Pasir Avenue 1, currently undergoing upgrading works. UGL is the main contractor in charge of the works.
Public records on PUB's website indicate that UGL was awarded $67.5 million on March 20, 2017, to conduct "Process Upgrading and Equipment Replacement at Woodleigh Waterworks".
UGL was washing activated carbon filters used in water treatment from 9am to 10.30am on Jan 19.
"The backwash water was to flow into a holding tank for discharge into the sewers. However, the tank overflowed twice into the nearby outlet drain," the agencies said, adding that each overflow lasted around three minutes.
The black discharge came from fine residual particles from the activated carbon filters.
NEA and PUB said that activated carbon is a non-toxic substance commonly used to remove impurities in the water treatment process, and has no adverse impact on water quality.
It is an offence under the Environmental Protection and Management Act to discharge or to cause or permit the discharge of any trade effluent into any drain or land without approval. Any company found guilty may be fined up to $50,000.
As defined in PUB's requirements for its discharge, "trade effluent" means any liquid, including particles of matter and other substances in suspension in the liquid, flowing out from any trade, business or manufacturer or of any works of engineering or building construction.
Veteran wildlife expert Subaraj Rajathurai said that while the water may be non-toxic for humans to drink, a "proper study" still needs to be done to ascertain the effect on wildlife.
"We simply don't know yet if it will harm animals. If there is oil, for example, it could stick to birds' wings," he said.
He added that even though the overflow was a mistake, there should have been a secondary outflow as a backup to prevent the substance from reaching the canal.
ST has contacted NEA and PUB for more information.