Led by managing director Jeff Brill, RDG already owns rail projects business Engenium, engineering and construction contractor Pacer Corporation and specialist engineering firm Intellect Systems.
It has agreed to pay $6.25 million for Ecologia, comprising about 60 per cent cash plus 12 million shares.
Established in 1989, West Perth-based Ecologia has about 30 staff, servicing the mining, oil & gas, construction, utilities and infrastructure sectors.
The acquisition is part of RDG's strategy to build a vertically-integrated service provider. It is targeting annual turnover of $200 million.