The move followed a complaint by a group of local residents, which had been submitted to the police and the Bangkok Metropolitan Administration (BMA).

"We will find out whether the depot has considered environmental-protection and traffic measures. We have to make sure there is minimal environmental impact," Apirak said.

He said the BMA Environmental Division and the Sai Mai District Office had already been instructed to look into the details of the planned project.

He has also assigned Deputy Bangkok Governor Puttipong Punnakan to follow up on the investigation.

Asked whether the project site would be changed, Apirak said a decision on this would hinge on the investigation's findings.

"After the investigation concludes, I will go to Sai Mai district and explain (the) relevant matters myself," he said.

Bangkok Deputy City Clerk Pichai Chaipotpanich said he had asked the BMA Environmental Division to report the investigation's findings next week.

According to him, the project was approved when Samak Sundaravej was at the helm of the BMA.

It envisaged the construction of a depot for 253 garbage trucks and a waste-water treatment system.

"We have found that the contractor has [the] proper … licence and strictly complies with [a] regulation not to do any construction work at night," Pichai said.

However, a source said many people suspected irregularities in the project, given that the constructor was in a new, limited partnership and had won the project as its first job.

The source revealed that the Sai Mai District Office had previously opposed the idea of having a garbage truck depot in its area as the proposed site was considered too close to people's homes.

Both BMA Environmental Division director Thirachai Tiensanchai and Sai Mai District Office director Jantana Panpiriya declined to comment yesterday.