What’s under our streets (and why does the digging cost so much)?

This summer there’ll be roadcones, diggers and safety fencing aplenty in all Wellington’s towns, as councils dig holes to get the water (and poo) going where they should. So, what’s down there?

This is a companion discussion topic for the original entry at https://talkwellington.org.nz/2023/whats-under-our-streets-and-why-does-the-digging-cost-so-much/