White foam on Chengdu river traced to metro construction site

White foam seen on a river in Chengdu, Sichuan province, was caused by wastewater containing a foaming agent from a metro construction site, the Chengdu High-tech Industrial Development Zone's environmental and urban management bureau said on Friday.

The foam appeared on Wednesday near the confluence of the Gaopan and Jinjiang rivers, according to a statement published on the bureau's official WeChat account.

It had disappeared by 6:40 pm that day, and the river had returned to normal. Rapid on-site tests showed the water met quality standards. Later laboratory results on Thursday night confirmed the finding.

Officials said no source of pollution was found along the river section within the High-tech Zone.

A separate investigation by the Wuhou ecological environment bureau traced the foam to a metro construction site upstream in Wuhou district.

Muddy water containing a foaming agent used in tunnel-boring operations entered the Gaopan River through the stormwater drainage system after workers flushed drainage channels to reduce the risk of flooding.

Authorities in Wuhou have opened an investigation into the site over suspected environmental violations. River inspections in the zone would continue, the statement said.