Work will last over four years to deliver tunnels at Bleddfa, Ffrydd Wood and Nantmel and one pipeline project on the Elan Valley Aqueduct.
Barhale will deliver 4.5kms of new tunnel alongside North Midland Construction under the newly-formed BNM Alliance joint venture.
The project at the Elan Valley Aqueduct has seen the purchase of a new Earth Pressure Balanced Tunnel Boring Machine, supplied by Herrenknecht, to deal with rock strengths up to 190mpa and 10bar of external water pressure.
Work is due to start on site in October.
Liv Garfield, CEO of Severn Trent Water said: “This is a fantastic achievement for our One Supply Chain and demonstrates how they can deliver with pace for the benefit of our customers and our company.”