Contractor Multiplex carries out remedial works to limit damage of yet another setback for troubled stadium.
Multiplex has been forced to carry out remedial works on the drainage system at Wembley stadium after it emerged the stadium could flood with sewage.
The Australian-owned contractor, which will next week give a progress report on the stadium, ordered an urgent survey of drainage systems on the project to identify the extent of the problem and are carrying out remedial works.
A senior Football Association source confirmed that the additional works had been carried out and that Multiplex had notified them of the problem. He said: "This is on our radar. It is not a massive problem in the bigger scheme of things - but it is a problem, all the same, that we can certainly do without."
The source said the cause could be that heavy machinery on site had impacted on the drainage foundations. He said: "It seems that a certain amount of settlement has affected the systems."
The source said it remained unclear whether this would affect the project's programme. However, Martin Tidd, Multiplex managing director, said last month the project would have to run "as smoothly as a Swiss watch" for the project to be ready for the FA Cup Final in May.
A union source close to the project told Building that the problem could present a huge health and safety risk at the stadium. He said there was a significant risk that the walkway outside the stadium would be flooded by sewage, given the positions of the drains, and that there would be 2618 toilets in use at the stadium once it is operational.
The source close to the project said: "The drainage has been poorly developed. There is a problem, and it is anticipated this could cause sewage to leak around the stadium. It is a particular concern given the low-lying land that leads down to Wembley station."
Building also understands that work on some areas of the stadium had to be stopped this week after concrete joins were breached by heavy rainfall over the weekend.
Multiplex declined to comment on the suggestions.
Meanwhile the project was hit by more worker unrest this week among electricians and its crucial roofing workforce.
The T&G union is understood to be investigating claims that workers from roofing contractor Weatherwise have been paid below the agreed minimum wage for their sector.
Representatives from M&E union Amicus were due to meet electrical firms on site as Building went to press on Wednesday. The aim was to quell further unrest among workers employed by labour agency BMS, which employs about 500 workers on the stadium.
BMS this week agreed to reduce its membership fee from £35 a week to £22 to prevent a further walkout after workers took unofficial action against working hours last month. BMS' workers are now complaining that they are not receiving enough rest breaks.