Tunnel boring under the M4 motorway to build a new pipeline as part of the £15M Frome Valley relief sewer scheme has started.
Wessex Water is tunnelling under the motorway from a nature reserve in Bradley Stoke, South Gloucestershire to construct a 5km, 1.8m diameter pipeline that will run from Iron Acton, north of Frampton Cotterell and then west towards Bradley Stoke.
The relief sewer scheme will divert wastewater from South Gloustershire to Bristol sewage treatment works in Avonmouth.
Project manager Mike Bryant said: “Work is progressing well, with the M4 tunnel crossing works getting underway last week and due to last for approximately four months.
“We are currently sinking other shafts on the job, and we will be mobilising additional tunnel boring machines around the Winterbourne and Iron Acton areas in the coming months.
“Open excavation in rock around Iron Acton is proving to be tough but we are achieving the estimated outputs per day.
“In September we will be crossing the River Frome, which has all been agreed with the Environment Agency and conservation groups.”
The first sections of the Frome Valley relief sewer were laid in areas of North Bristol and Yate during the 1980s and 1990s.
Wessex Water said it is “taking painstaking care” to protect the nature reserve wildlife during the works.