Burying the water line

I'm considering trying to bury the water line at the camp.  
Problem is, it's on the coast of Maine and my soil depth runs between 2 and 8 inches, below that, it's solid granite ledge.  
Frost line in dirt here is near 4 feet.  

Question is, does the frost penetrate ledge to the same depth as in dirt?  'Cuz I'm sure not going to dig a 100 foot long trench four feet deep!

Any folks in the "cold" belt have input?

Thanks,
Randy

When I buried my Water line in northern MN, I went the full depth ......yes, we had some excitingly large rocks.

Randy said, "Question is, does the frost penetrate ledge to the same depth as in dirt?  'Cuz I'm sure not going to dig a 100 foot long trench four feet deep!

If I were doing this I would use the tube insulation for pipes buried as deep as possible then cover the area where it is not possible to get below the frost line with hay bales.

Those two thing will probably give all the added protection needed.

Yeah, that's a toughie.  If you can't dig down, I think you have to add insulation above.  Either 4' of dirt or something more insulative.  The other concern is how well the rock transfers heat/cold.  If you tuck the line under hay bales but the frozen rock it's sitting on just sneaks the frost under the arrangement, you're still screwed.  I guess I'd ask around at the local feed store, cafe or other places where farmers or homesteaders hang out.

It may depend on how cold it gets.

I know Maine gets cold and stays cold.

Our land is mostly caliche with rock.

We recently had to dig up our waterline at the wellhead due to a water leak at the timer that supplies the water for the deer tank.

After the leak was fixed we temporarily used whatever was handy as insulation, things like old clothes.

This worked for below freezing.

We then wrapped the lines with some fiberglass insulation, threw the old clothes back in, and covered with some dirt maybe about 3".

This has worked for -07 degrees.

I have always found this post about using sheep manure and hay intriguing:

Travis said, "Sheep manure will not break down.

I use this around my pipes buried underground so they do not freeze. Sheep manure by its nature has a lot of hay mixed in with those convenient-to-work-with pellets!

BTW, Travis is also in Maine.

https://permies.com/t/101428/Insulating-underground-perimeter-greenhouse-materials#836204

Randy,   I just gotta think there is a local county extension agent, .... if not nearby neighbors,......who could help you answer this very site-specific question.  Certainly parts of Maine could get cold enough for you to make sure water line installation is done right.  Even though you are coastal, I don't think it's worth gambling on frozen pipes for water that you deem necessary to have running in winter.  A county extension agent should have enough knowledge about soil structure and stratification with rock, along with local techniques on how to get water lines below frost depth, to get you where you need to be in your design and plans.  Take it from someone who's had to deal with my own and other's mistakes on buried water lines not sufficiently protected that you want this done right so that you don't have to dig up in the near future to repair/replace an inadequate job.  Good luck!

Could your line be pressurized on demand, and then be quickly depressured and gravity drained to a lower non-freezing location? It would be a different design, but I think with some insulation it could work. Beware of low spots in the line that will hold enough water to freeze and block the line.

Is this a permanent, summer or seasonal cabin?  If only used in summer, I would skip the dig, and simply run it through a larger pipe so that it is easily pulled/serviced if necessary, and drain it when shutting down for the season. This also protects it from the nibblers who love to munch through water lines in times of limited access to water.

Heat tape is another option for less than depth water lines; perhaps not permie friendly, as it would need continuous power through out the cold months (a 100% guaranteed source of power); perhaps a solar option, but then how to keep the batteries from freezing...

Otherwise, speak with the locals and find out how they handle this...even the local hardware store or plumbing dude should be able to provide the most common solutions suitable to your area.

Really appreciate everyone's input.  I've not yet contacted the local Co-op, but that's a great lead.  
To answer some of the questions, and/or clarify my situation:
Yes, this is a seasonal cottage. And we do currently drain everything for the winter.  It would be really nice to avoid that chore.
The pipe runs about 100 feet from the well with half of it running under the middle of the gravel driveway.  Not conducive to piling 4 feet of insulation over it!
Cellar wall penetration is only a foot below grade ('cuz that's where the bedrock starts). And it's only a crawlspace on that end.
As for heat tape - definitely not "green", but since we may not go there for a month or more when it's really cold, I can't know for certain if the place has power.  Lot's of really tall red spruce trees with widespread but very shallow root systems on most of the property. Power outages are not quite guaranteed, but pretty likely - three so far this winter (2021/2022) with broken lines tangles under 16" diameter downed trees.
Again - thanks folks for all the suggestions.  What a great resource!
Randy

Randy Butler wrote:
Yes, this is a seasonal cottage. And we do currently drain everything for the winter.  It would be really nice to avoid that chore.

Well, given that it is Maine, I think that chore is a fact of life. Easier than digging 4 feet down into bedrock. And when you are not in the house for months, it's best to have the water shut off and pipes drained. What if you had the water attached all winter while you're not there. Couldn't the taps in the unheated kitchen and bathroom freeze and break? Then, in spring unlimited water could flow out of the broken pipes.