The RTA determined to construct a pilot filtration plant for the M5 East tunnel on the eastern side of Bexley Road. The filtration system includes electrostatic precipitators for the removal of PM10 particulates and a denitrification unit to remove nitrogen dioxide from the tunnel air. The construction of the filtration plant requires a building approximately 60 metres x 40 metres x 8 metres which is designed to minimise its height above ground. The building will house the filtration system, a water recycling plant, ventilation fans, and offices. A vent tunnel will be constructed approximately 300 metres long and will connect to the M5 East main westbound tunnel to extract air from the main tunnel, transfer it to the filtration plant and return the treated air to the main tunnel.
The excavation is in Hawkesbury Sandstone. The anchors required at the tunnel portal consisted of  11 No 19 strand anchors, 5 No 13 starand anchors, and 4 No 7 strand anchors with 11m bond length and 9m free length to RTA Specification. Water testing in the bore holes at the anchor locations indicated some pressure grouting was required prior to anchor installation.