Burying a well pipe

[Notwhitevanman]

I have to lay a new water pipe from my well to the storage tanks as the old one is shot!
The pipe will be going up a 100m incline through all kinds of scrub/bracken etc. No chance of getting machinery up there so I may just do it by hand. I know!!! The other option would be to use a mole but I’m not sure if it would feasible up a hill like that. So my first question is does anybody know if a mole would work in this situation? And roughly how much would that cost me (100m)?
Next question - if I do end up digging it by hand what is the lowest depth I could possibly get away with? (To prevent freezing).
I know the general consensus is 600mm but obviously I would prefer to dig a lot less than that.
Where the pipe will be buried it will quickly become completed covered in several feet of scrub etc so would that help to protect the soil from freezing and therefore allow me to bury the pipe at say 300mm?
The pipe that is already there is probably only about 300mm down. But I have no way of knowing if it ever freezes up in the winter.
Thank you for reading and hope there is somebody out there will some helpful advice

My experience relates to replacement of our mains water pipes (and 10 years in the water industry!).
For mains water pipes new and replacement pipes have to go in at 2ft 6in to prevent frost damage. So that might be worth considering.
We replaced our leaky old lead pipe. We started digging the trench and because of the depth we only managed about a yard of the distance to the house before admitting defeat.
We managed to hire a man with a mini digger who dug the hole 10 yards from the pavement to the house in about an hour.