New well, lots of sand. How to develop?

[lovetoknow]

Long time lurker here...I have found LOTS of answers to previous questions by searching the forums.
But nothing quite specific enough for my current situation. Sorry in advance for the long setup.
I'm just getting power to the site of my 1 year old well. There is no house yet on the property, but I do want to start irrigating (planting some trees this fall). Ready to install pump, tanks, etc. and need advice.
Wells in the area are commonly sandy/silty, so I used a driller with experience in the area.
Well was drilled with hollow stem auger. No drilling fluids used. Total depth - 100 ft. Bore hole - 11 inches, well casing - 4 inch PVC, solid cased from 0 to 20 ft, then slot screen (.020) from 20 to 100 ft. Annular space - 0 to 20 ft cement, 20 to 22 ft bentonite, 22 to 100 feet sand pack. The driller "surged" the well several times after the casing was down. He did a preliminary well test (6 hours @ 18gpm, did not have a larger pump on truck, unfortunately). Static water level - 18 ft. If I remember correctly, draw down was to 56 ft and held rock steady the for the whole 6 hours. He said production was likely well over 20gmp. Water started dark gray thick with silt and sand. Silt cleared up in about an hour, but very fine gray sand was present the whole time, although slowly decreasing. The driller recommended I call a local pump company to finish developing.
So I talked to two local pump companies with experience in my actual neighborhood and got conflicting advice.
One recommended a high flow production test to essentially "flush" the fines out of the sand pack. He said it would take a 35 to 50 gpm pump for 3/4 hours. Estimated cost - about $1000. (it's California so...).
The guy from the other pump company told me to save my money and just install my system with a sand tolerant pump (he recommended Gould's stainless). Since there won't be any residential use yet he figured the combination of irrigation, site development and building next spring would be plenty to develop the well to clean water. And didn't think a few months of sand would significantly shorten the pump life.
So my question is...which way should I go?
Thank you in advance for any insights that will help me make an informed decision!

 

[Valveman]

I would try to develop the well with a pump first. Just run the pump wide open for a while, until it clears fairly well. Then shut it off, wait for a while and do it all over again. You could even put it on a timer if needed. If the pump doesn't clean out the well fairly soon, then an air jetting or heavy bailing maybe in order.

 

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[Reach4]

Would that first while be about 48 hours, or would it be until you cannot detect materiel in the flow, even if that is just 30 minutes?

 

[Valveman]

Pump until it is clean, no matter how long it takes.

 

[lovetoknow]

Oh, thank you! That was what I was hoping to hear. I am planning on using a cycle stop valve and small tank to pressurize the system. Will the sand be a problem for the CSV?

 

[Valveman]

Oh, thank you! That was what I was hoping to hear. I am planning on using a cycle stop valve and small tank to pressurize the system. Will the sand be a problem for the CSV?

The CSV1A was designed to handle some sand, but not the CSV125. A little sand you can deal with. A lot of sand and it will cost too much to maintain the pump and equipment.

The CSV can help reduce the amount of sand a well makes. When a pump is cycling on and off it is pulling full flow, and then no flow from the well. So cycling the pump also surges the well, which can stir up the sand. When using a CSV the pump is drawing a steady amount at a smaller flow rate from the well. The CSV's steady and continuous draw from the well eliminates the surging. Reducing the flow rate also reduces the velocity of water into the well, which is another way the CSV keeps from drawing in as much sand.

Sand is a problem for every thing from the pump/motor up. It is best to try and clean the well so there is no sand. But using a CSV to reduce the velocity and keep from stirring up the well can help.

 

[lovetoknow]

So would it be better to just use a dole valve to restrict the pump flow while I'm doing the developing? With no back pressure up top, my TDH will only be 60-70 ft. That's way outside the pump curve for the 18gpm 1hp I was planning on using.

 

[Valveman]

With a little friction loss from the pipe and fittings, 60-70' is fine for an 18 GPM, 1HP. It will try to pump about 30 GPM, but that should help purge the well better. But if you are pumping the well dry too quickly, just restrict the flow with a ball valve. That way it can be adjusted to any flow rate needed. Sand and restriction will eventually wear out the ball valve, but that is a minor problem on a major job.

 

[lovetoknow]

Thank you, Valveman! Now I am actually looking forward to this next part of the project.