We have seen a trend with consultants specificizing directionally drilled Storm Water and Waste Water lines at shallow depths to avoid excavation that would cause disruption or damage tree roots or property.
Designers should consider ground conditions carefully when choosing install methods as Council may not accept pipes that do not meet the specifications around deviation of straightness tolerances. You can find guidance for directional drilled Storm Water lines in Guidelines for Horizontal Directional Drilling, Pipe Bursting, Microtunnelling and Pipe Jacking (The Australasian Society for Trenchless Technology).