Deepening An Existing Dug Well On Rock

I have a dug well which is about 9' deep. Local lore has it that they hit a large rock when digging and then stopped. I have been down in the well and confirmed it sits on large rock. It is lined with rock and has a modern concrete cap. This well is next to a marshy area. Neighbors' well are down about 13' and do not ever go dry.

We have periodically had droughts where the well level gets too low to use. We collect rainwater for our garden so when droughty we use that water to flush toilet, wash etc. Solar shower for especial enjoyment. With fall rains, the well comes back and we are good until following summer.

Even though we happily live around this, the droughts are getting worse and more frequent. I am loathe to drill a well. Lots of stories about arsenic, using water purifiers, etc. Plus the cost. Plus the loss of an existing resource.

SO, since the existing well sits on a large rock, I am wondering if it might be possible to pump the well out, keep pumping it out and go down the well and drill numerous holes down about four feet into the rock. Then use explosives or some other means to fracture the rock. (Local lore has it also that explosives were commonly used in well construction but the use today tightly controlled.) Or, absent explosives to jackhammer four feet into the well base.

The last obstacle in all this would be the size of the rock. Let's say the base rock is 6' thick then its integrity would have to be shattered in order to allow the water below and to the side to filter through. Alternatively if the base rock is only 2' thick then a further 2' of digging needed.

One very important consideration is all this is to be sure that the integrity of the existing well walls and structure is maintained.

I have looked on the net regarding my situation and can find nothing similar. I also note that there are a lot of folks around here in a similar well situation yet there seems to be no one offering a Well Augmentation Service. Usually, their wells are not on rock but simply need to be deepened.

Thanks for any help or suggestions.

You can do what you propose: pump the well out, then fracture the rock, and you can legally buy Sierra Blasters to do that.

You coud also start a fire down there on the rock, and then douse the rock with water and it will shatter into small pieces, able to be worked.

But a cheaper, easier method might be to dig lateral trench's away from the well, and then put in drain tile. It is kind of a misnomer because it is just flexible, perforated black plastic pipe 4 inches in diameter. It costs $55 for 100 ft roll. By running that through trenches into your wet area around your well, the water will be funneled from a very wide area, and feed your well so that it has more water supply. That would be your cheapest option, and you would not get blasting residue in your drinking water either.

But blasting is still done today, and is very common. They literally drop dynamite down deep wells and it helps fracture the rock at the bottom, hopefully opening up more seams. This nets more water from a previously drilled well.

Blasting system

Perhaps some investigation first may assist.
Using an SDS drill system [ rotary hammer] you may be able to drill through the rock or at least down as far as you drill bit will reach.
If its shallow you can think of other methods to keep drill and break up the rock.

e trench method ay be a god start if you can get low with the trench, but remember trenching deep can be dangerous.

rocks can be cracked with kaboom

here are some methods, like drilling holes and filling with quicklime
http://www.sciencemadness.org/talk/viewthread.php?tid=73463

While there are many ways to break rock, the original poster will still have the trouble of bringing those rock fragments out of the well, and then will have to continue to dig down. That is a lot of work, and might not net that much gain. However if he uses horizontal pipes, the collection area will be much, much larger and save a lot of underground digging.

If lateral pipes do not work, then the original poster could then break up the rock and dig deeper. But I would try the cheapest, easiest method first. It is going to make your existing well that much more efficient because you are funneling more water to it.

If it is still not enough water, dig deeper then.

The most common reason why you will need to stop digging when you hit a rock is the unknown nature of the rock (and soil). You can't see the underground, as so its size. It might be 10 times bigger than what you think or it might be barely big. When you remove the rock there are 4 possible scenarios. The first one is what we all hope for, nothing happens. The second scenario involves a theme of sides collapsing (clay layer around the rock). The third scenario is my favorite. When you remove the rock it is like unplugging a madness (rock over sand). It gets destabilized. It looks as if it boils from beneath. The fourth one is opening a hole through a house-size rock, which is a very expensive undertaking. This problem was a common widow maker before the caisson technique became common. People used to go and dig another one and blame on their luck or if the rock was closer to the surface they would dig all around the rock, relieve the horizontal and vertical pressure and then continue. Usually, it is a dead-end.

I would not recommend using explosives. But if you are going to go down that path, try to remove in layers not thicker than 4-6 inches. Many small booms are better than one bigger boom. You don't want to destabilize the zone.

The solution Travis recommended is one very good but temporary option. I would do that instead of taking any risks. I might also bite the bullet and call professionals to do the job. I am biased though, I have seen workers getting buried up to their knees and won't able to escape by themselves when a side wall collapsed.

Also, diameter of the well is proportional to the depth (depending on other parameters and also type of the well). If I remember correctly 4-5 m (13- 16 ft) deep well, generally speaking, should not have a diameter less than 140-150 cms (5 ft). You might want to check those too. If the diameter does not allow you to go deeper, don't go deeper. This recommendation comes from ages-old experiences.

Just remember too, you can be killed by a cave-in  without being fully buried.

If the soil comes to your chest, when you inhale, the soil packs against your body, and you cannot exhale. You suffocate, not by being fully buried, but just because you cannot expand your diaphragm. This is why any trench over 48 inches deep has to have those metal troughs according to OSHA rules.

Thanks for all the interesting replies and comments.

As mentioned the main concern and unknown is the size and integrity of the rock at the bottom of the well. There is, as has been mentioned, a great risk of destabilising the well walls. The diameter of the well now is 3' which makes going from 9' to 13' very dicey to say the least as also mentioned. I will have to explore and see if there are any professionals locally who do such work.

I did do some research and came up with these two explosive devices for those interested:

MIcro Blaster, apparently used by some folk to exploit old mine tailings amongst other things. Drill hole must be DRY so would not work in my case.


Then, Boulder Buster which actually works in a wet environment and uses the water for energy transfer and shock value.


Of course drilling down in a 9' hole with an internal combustion drill excellent ventilation would be needed for starters.

The best way to break up rock for a DIY homeowner is to use Hydraulic cement designed to expand so much it shatters the rock. you use a rotary hammer, blow out the hole and pour in the slurry. By the next day its fractured. We use it here all the time for footings and piers when there is a rock in the way... You would have to keep it pumped out but not dry... All the above warnings apply... I like the horizontal well tile as well.
 

How would you install lateral underground pipes to a 9 ft deep well?

Thanks,  David, I will consider the hydraulic cement technique.

As has been properly pointed out, drilling the rock and then removing it, particularly in an area 3' in diameter is quite problematic. Then there is the problem that the size of the rock is unknown and thus the risk of destabilizing the well walls.  

And as John asks: "How would you install lateral underground pipes to a 9 ft deep well?" I have the same question. Possibly, I did not explain my situation exactly enough. As the summer here progresses, the groundwater level drops down from say 3' down, to 4' down, etc. until the groundwater level is near or below the foot valve. If the drought continues the groundwater level continues to drop, say 9', 10' etc. So, since water seeks its own level, I don't see  how trenching and bringing more water in will help, since my well will still be only 9' down (and the foot valve is even above that.).

And here is an interesting Deepening An Existing Dug Well story:

I was at the gas station the other day and I saw a large pickup truck at the pumps with welldrilling stickers on it. It also mentioned a few other things like core drilling. Anyway, I took note of the company name and went inside the shop to get a coffee.

Shortly thereafter a fellow appeared at my side and asked "Are you interested in well drilling?" I was quite taken aback, thinking he was psychic or something.
I replied " Well, yes, I need my dug well deepened. How did you know I was interested in well drilling."

He explained that he saw the expression on my face when I saw his truck signs and that he could see " the wheels turning in my head." I found this most remarkable and asked if he was in sales. He laughed and said no.

I said "You are in the wrong business, you should be a professional poker player if you can read faces that well."
Anyway, we had a good yarn and he was quite interested in my project.

Thanks again for all the helpful and thoughtful  comments. This certainly is a very delicate project and safety is uppermost in my mind.

I've used Dexpan before.  It's really easy to use.  All you need is a 1/2 inch drive hammer drill and a good masonry bit, a funnel and a 5-gal. bucket.  You drill holes down into the rock, mix up the Dexpan into a slurry and pour it down into the holes.  Wait a day and you'll come back and the rock is busted.  Easy peazy, and only $40 for the product.  Obviously your budget will be more if you need to rent or buy the drill and bit.

https://www.homedepot.com/p/Dexpan-11-lb-Bucket-Type-2-50F-77F-Expansive-Demolition-Grout-for-Concrete-Rock-Breaking-and-Removal-DEXPAN11BKT2/204378788?MERCH=REC-_-pipsem-_-203335355-_-204378788-_-N

Depending up on the width of your well, you might be able to get in there and leave the outside of that big rock to keep the walls of the well stable, while cracking straight through the middle of it.  Basically, you'd create a tunnel through the core of the rock.  

Here's a video.  

John C Daley wrote:How would you install lateral underground pipes to a 9 ft deep well?

Backhoe