Well gpm after hydro fracture

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Old 08-06-20, 12:51 PM
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Well gpm after hydro fracture

We had a 500’ well with the pump at 450’. The supply was 1.5 gpm. Thec water level was noted at the time to be 90’ down.

The previous owner had an inground irrigation system in place.

we looked into drilling a new well for the irrigation system. The contractor told us that we still might have to go 500’ down and then possibly hydro fracture and between that and wiring and piping, it could run $15,000-20,000.

we decided to fracture our existing well instead. We do not want or need a lawn like a golf course, but would water when needed.

we were told that our supply after fracturing is now 4.5 gpm.

we have a 90 gallon pressure tank. Our pump is 5 gpm. If a given zone has 4 heads with 2.5 gpm nozzles, would the maximum flow be determined by our pump? So no more than 5 gpm would be used at any time?

i was going to set it up to run a zone or 2 at a time and then “rest” for a couple hours before running again.

of note, after we fractured, the water was filthy, so we ran our sprinklers to clear it up. We never noticed a big drop in flow despite running them for over 2 hours at a clip.

im just trying to figure out how to have some irrigation without running it dry. Thanks
 
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Old 08-06-20, 05:28 PM
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Your flow volume will vary depending on a number of things. When the pump isn't running all the water will be coming from the pressure tank so the pump's 5 gpm is not a factor. The pressure tank will deliver water as fast as your piping can carry it away. The gotcha is when the tank is almost empty and the pump kicks in and can only deliver 5 gpm when your emitters want 10 gpm. At that point you'll get the maximum capacity from your pump, about 5 gpm, and the pressure will be low.

Another issue is if you are using pop-up emitters. They draw considerably more water volume at the beginning of the cycle. Most leak a lot of water until the head is in the full up position. So, initially your irrigation zone could need a good deal more water than what the emitters spray. If you can't keep up the flow and pressure during this phase the emitters sit partially raised and gushing water. You can get around this by insuring your irrigation zone draws enough less than your delivery rate. Another option is to only used fixed emitters or enough fixed emitters that your water supply enough water for the difficult start up phase.
 
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Old 08-06-20, 07:06 PM
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Thank you. That makes a lot of sense. So, when the pump is pulling from the well, the pump is pulling 5 gpm. I’m not sure if the height of the water has risen at all from 90’. So, we are starting with a 6” diameter column of water approximately 360 feet long (pump is at 450’ and water is 90’ below surface. The pump is pulling 5 gpm, but the well is replacing the water with 4.5 gpm. I’m trying to get a rough, probably oversimplified idea of the conceivability and timeframe of the well potentially running out of water.
 
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Old 08-06-20, 09:56 PM
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I’m trying to get a rough, probably oversimplified idea of the conceivability and timeframe of the well potentially running out of water.
That's pretty hard to figure. Your well driller knowing the area could give you a better idea.
You have a replacement rate of 4.5gpm that may not remain constant.
4.5gpm recovery is comfortable for a house but you have a sprinkler system on top of that.
Then you need to consider as you start drawing more water is it affecting potability.

It's going to be experimental to get the best balance.
Well yield information

I started playing with measurements....
6" ID = 1.47 gallons per foot.
360' x 1.47gpf = 529 gallons capacity.
 

Last edited by PJmax; 08-06-20 at 10:33 PM.
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Old 08-07-20, 04:59 AM
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Yes. I figure it’s a very dynamic thing. I will ask well contractor when he comes to pull a water sample. I guess from the above calculation, with pump running and assuming well is adding 4.5 gpm, we would have a net deficit of 0.5 gpm. That would buy us 800-850 hours being conservative. I would run a zone or two and let it rest. If I ran 2 zones that each put out 10 gpm each for 20 min, that would be 400 gallons. The I would let it sit for 2 hrs which should totally refill it before running anything else. Does that make sense?
 
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Old 08-07-20, 05:14 AM
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Being on a well with irrigation system a little experimentation is required.

What you do not want is the pump cycling, that will just kill the life expectancy, a pump likes to run, not start/stop.

Basically you will need to play with the nozzle sizes to get each zone down to a GPM capacity of the pump/tank/well capacity.

If you have 2 sprinklers per zone, each head would be at 2.X GPM, 4 heads, 1.X GPM. The experimentation comes into play to correct misc pressure loss, water availability pressure tank set point etc.

It can be a little time consuming but get one correct and the others should be pretty much the same, maybe!

Dont worry about the low GPM at the heads, you just adjust run times to achieve the correct amount of water.

Now that you have each zone dialed in, just let the pump and controller do their thing!
 
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Old 08-07-20, 05:39 AM
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Thanks! Yes, I have already started to drop the nozzle sizes down. The heads had 3 gpm. I have dropped them to the lowest at 1.5 gpm. The most heads per zone we have is 4. Some have 3. I have noticed with any given zone running, pressure at the tank tends to stay around 45-50 psi with pump running. In other words, it doesn’t reach the 60 psi shutoff pressure until irrigation zone stops. It does not tend to cycle on and off with zones on.
 
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Old 08-07-20, 08:42 PM
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I have noticed with any given zone running, pressure at the tank tends to stay around 45-50 psi with pump running.
I'd say that's pretty good.
 
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Old 08-15-20, 06:07 AM
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I double checked. With a sprinkler zone running, the pressure drops over a minute or so to 40 and pump kicks on. It then gradually increases and stabilized at 45 psi with sprinklers going. Once the sprinklers stop, it quickly goes to 60 psi and shuts off.

i put a new pressure switch on that will shut off pump if pressure drops to 30 or below.

latest tests show static water level at 40 feet (up from 90), and 4.5 gpm.

theoretically, pump can only pump 5 gpm so with pump going and 4.5 gpm coming into well, we have .5 gpm deficit. With 600 gallon reservoir (400 feet of water), would it take approximately 1200 minutes to exhaust well (600 gallons and .5 gpm deficit)?
 
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Old 08-15-20, 09:53 AM
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Can only be figured in theory or determined under actual operation.
Your pump can pump up to 5 gpm but that would be into an open ended pipe..... not into a system that is restricting it. In other words.... under operation your pump may only be pumping 4 gpm.
 
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Old 08-15-20, 10:03 AM
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That makes sense. So assuming a relatively steady flow of water into well, we hopefully won’t run it dry.
 
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