We are part-way having our borehole system installed. The hole itself is dug and lined, and the contractor says they found water at 70 metres, which is normal for this part of the country (West Wales). It slowly rose to only 5 metres, but that's OK as it gives more of a settlement sump.
We are now awaiting a site visit from the installation company, who will do a flow test, take samples for basic testing of water quality, and install the well-head apparatus and pop the pump and cable down the hole attached to about 100 metres of pipe.

Standard procedure in open fields is now to dig a trench, but our route has to go down a wood , quite close to a lot of fairly mature trees. I'm a bit concerned about the possible damage to tree roots - apparently the formula is don't cut roots closer than 5 X Diameter of trunk at the base, which would necessitate hand excavation around every tree the pipe passes, and feeding the pipe under all the roots it crosses.
Chatting to the engineer who visited, he suggested instead just taking the pipe down the middle of an old and thick hedge and burying it in the dead leaves and humus at the bottom, which runs virtually all the way. He says that will easily be free from any risk of freezing.

Our grown-up children say that is risky, and it should be trenched regardless of cost, which of course they will not be paying for.

Any thoughts, observations, experience anyone?

(I've also discovered that the Earth is pretty uniformly at about 12 degrees C 70 metres down, regardless of season because the heat comes from the Core, not the Sun. So the water being pumped down the pipe will surely be at about 10 degrees to start with?)

West Wales, it'll probably be fine. If it's being run regularly/constantly , almost definitely. As you mention, the groundwater temperature is significantly above freezing to start with. But, if the property is unoccupied for periods and there's a big cold weather event.... maybe. Instead of down the middle of the hedge, maybe consider scratching it in the foot of the hedge, if that's feasible. It'll be more prone to damage but the shelter of the hedge will help and less likely to get parts exposed. If it does get caught, it's not an expensive fix.

Running a bigger bore pipeline will help provide more thermal mass too. And give longer service intervals if silting is an issue. At least 32mm

Posted By: Cliff Popethe contractor says they found water at 70 metres, which is normal for this part of the country (West Wales). It slowly rose to only 5 metres, but that's OK as it gives more of a settlement sump.

The bore hole will only provide a settlement sump whilst the water column is static. If you are drawing water then any sediment will be carried up with the water. If you do have sediment in the water then you will need a (cleanable) filter preferably at the well head. The pump will be placed at a level dependant upon the flow of the well and the required output. A pump will be put in and run and the level of the water will be monitored to see how much the water level drops and how long it takes to recover after pumping, this will determine the flow rate and therefore the size of the appropriate pump. If the borehole is of low flow you will need a holding tank to provide an instant capacity that can then be slowly filled from the borehole. If the flow is low then you might also need a sensor just above the pump to shut the pump off in the event that that water column gets that low to avoid the pump dry running.

If the bore hole is supplying a house or alike with taps then you will need a pressure vessel to provide static pressure, usually about 80 - 100 lts of water (which gives about 20 -30 lts of water between pump cycles) otherwise every time a tap is turned on for 1/2 a glass of water the well pump will have to start, this short cycling will significantly affect the life of the pump.

Given that the location of underground water is a large amount of guess work I wonder why the borehole was drilled 100 m away from point of use and not closer.

When we were living in Hampshire I ran a thick wall rubber pipe with metal jointing fittings down the plot (100 yds) to the barn. it was just laid down the fence line but over a few years it got buried by natural detritus. When I laid it I reckoned that if it froze I could do without water until it thawed - It never froze.

Over here I had a water pipe coming vertically out of the ground (as an animal drinker supply) after a week of night time temps at -18 and daytime temps of -10 I needed the pipe to function and found that after a week of such temps the ice only went down about 25 cm.

The standard pipe here and I presume in the UK is KPE pipe will take repeated freeze / thaw cycles without degradation.

From my experience I would agree with the visiting engineer about the (very very) low risk of the pipe freezing tucked up nicely at the bottom of a hedge.

I would put in standard 25 mm KPE pipe without additional insulation other than the detritus that the hedge can provide.

You don't say what the borehole will be supply and how critical the supply will become. This should govern the choice of installation and what to have on the shelf when something happens on Saturday evening.

For what it is worth I have 3 boreholes on the farm, one at 120 m, one at 25 m and one at 7 m, all potable quality and the 120 m borehole has an estimated max flow of 200 lts / min with the others about 30 lts / min. The 120 m borehole pumps to a holding tank and then from this another pump pumps to the pressure vessel supplying the house and the low areas and then a second pump in series goes to another pressure vessel to boost the pressure to the top pastures. The holding tank is primarily to reduce the cycling of the submersible pump (this pump cycles at about 1000 lts). The 25 m borehole has a submersible pump directly feeding the pressure vessel and the 7 m borehole has a surface pump directly feeding the pressure vessel. (you can't use a surface pump where the water surface is greater than 9 m down).

A conventional pneumatic pipe mole might also be an option for feeding through the roots.

If the holding tank is higher than the tank in the loft it may be worth considering removing the tank in the loft and have the holding tank gravity feed straight to the house which (if the holding tank is higher than the tank in the loft) would give a bit more pressure for showers and remove a potential failure point.

The decision about the depth of the pump should be based on a combination of flow rate of the borehole and capacity of the pump. Lower capacity pumps are cheaper than higher capacity ones and if once a day filling is enough then a lower capacity pump could suffice.

Generally the flow of a borehole will increase with usage as waterways are opened up by flow.

FWIW my deep pump is a Grundfos which has been down the hole for 20 years without problems. (probably tempting fate saying that)

Regarding not needing a massive flow, don't be tempted to skimp on the pipe sizing. Larger bore piping is so much easier to blast out with compressed air, should the need arise because the quality isn't perfect. And, in the scheme of it, 25mm to 32mm isn't a big cost upgrade. Fittings are quite a lot cheaper but reduced back down at either end.

If you have a frost risk free supply as backup, sounds like lying it in the foot of the hedge is a no brainer. It'll be grown in before you know it.

Edit, what about the power supply? That will be a bit vulnerable? Float controlling to a tank 50m up a hill sounds potentially more expensive than pressure controlling. But I don't know what cables/conduits you may already have.

SWA I presume for the power?