Back pressure on new well pump

[fourwells]

This year my main domestic well began producing more fine sediment than usual (most of my neighbors have some amount of sediment.) The well was drilled in 2000. It is 660ft and the old Jacuzzi Sandmaster pump had been set at 360. I had a well/pump company pull the pump, inspect the casing, swab develop the well, and install a new pump with a sleeve over it. In the warm weather season the well produces about 6gpm after 12 hours of testing. Static is around 300ft and the new pump was re-set at 440. Other than the sediment, the water quality is good. Some tannins but other than that doesn't need much treatment.

During redevelopment of this well, the flow was throttled back to 5gpm at the well head and the well ran on a timer: 1hour on/1 hour off for three days. This was two months ago. The timer was removed and I have been advised to keep the throttle on at 5gpm primarily because the back pressure will reduce the amount of sediment I'm pulling and because the flow is less than my well gpm.

Since that time I have installed a 5,000 gallon storage tank and booster pump. The tank is filled with a mechanical float. For the initial fill I am using an irrigation hose/timer that flows at about 3gpm for 40 minutes. I noticed my filters would clog a bit after these fill sessions; this well is still used for domestic supply until my booster pump is wired next week. To address this I dropped each fill to 20-25 minutes and noticed improvement in the amound of sediment I'm pulling up.

Questions: 1. Do you agree that applying back pressure to the well pump would decrease the amount of sediment drawn up? 2. Would you argue that back pressure on the pump can increase the amount of sediment? 3. Is constant back pressure good for the pump long term? 4. Would it make sense that when I reduced the time for each of my fill cycles, I drew in less sediment (I've made the change a couple days ago)? 5. If Q4 is plausible, would it make sense to add a 240v timer to my well pump so that when the float is open, I only fill in say, 15 minute increments? (Theory being as well refills, the sediment would have time to sink.)

Finally, a thank-you is in order since this is my first time posting. I have four wells on my property (and one dry hole). No real experience with wells, or even plumbing for that matter until I bought this place 4 years ago. We've had a lot of water issues this summer and it is downright frightening. I appreciate all of you who contribute. I often find diagnoses/solutions in these forums, not just for the wells, but other things like replacing a recirc pump on a tankless heater. Most importantly I know I'm not alone! Thank you.

Looking forward to your ideas.

 

[Bannerman]

The lower flow rate maybe prolonging how long sediment will continue to be delivered to the surface, maybe forever.

Normally, a well will be developed by causing the pump to run continuously with the least amount of flow restriction, to allow it to pump out as much sediment and debris to the surface as possible. Disconnecting the drop pipe at the well head, will reduce the amount of flow restriction, thereby increasing the velocity of water flowing through the pump and being pumped to the surface. This will increase the amount of fine sediment drawn into the pump, which is then usually discarded into the field surrounding the well. Developing a well will often require only a few hours of constant pumping before the discharge becomes and remains clear, but sometimes, several days of continuous pumping will be needed.

You didn't state how deep the casing is installed, nor the depth of the inlet screen if utilized.

If the water is entering the well above the pump location, such as through an inlet screen located above the pump, sediment entering with the well inflow will also be dropping from above the pump, allowing the sediment to be drawn into the pump whenever the pump is operating.

By properly developing a well, the fine sediment particles that are passing through the inlet screen, will eventually reduce, allowing larger sediment particles that can't pass through the screen, to pack around the outside of th3 screen, thereby acting as an additional sand filter to further prevent smaller sediment particles from within the surrounding soil, from even coming into contact with the screen.

Pump's are designed for continuous duty, so there is no harm if runing 24/7/365. Restricting the flow output will not harm the pump as long as at least 1 GPM is being drawn into the inlet, to provide cooling flow over the electric motor. The flow inducer shroud now installed, will help to ensure cooling flow over the motor, even if the flow rate is only 1 GPM.

Reducing the flow rate by restricting the outflow, will be equal to what will occur when the water level in the well drops lower than the 300' static level. While most consider increasing flow restriction will cause the pump to work harder, in actual fact, the opposite will be true. Since the pump will be moving less than it's maximum flow capability, it won't need to work as hard and as a result, power consumption will be usually reduced.

 

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[fourwells]

The well casing is installed to 660 feet. Perforations at 200-220, 320-340, 420-440, 480-520, and 580-660. Each perf is .032" and the filter pack is 1/4 minus.

Thanks for your explanation of the effects of restricting flow. Count me among those who speculate that adding back pressure would cause the pump to work harder. My logic is that it would have to overcome the additional pressure therefore suction would be stronger at the end of the pipe than it would be unrestricted. Further, the added pressure will cause greater suction at the end which could also cause more sediment to stir, suspend, and be drawn up.

In your explanation I could see the restriction giving the pump some "free" pressure to use so that it wouldn't have to build it up on its own to meet the demand. Am I interpreting correctly?

If the real concern is keeping the motor cool by passing 1GPM I wouldn't need to be concerned under my current conditions. I believe the pressure tank is about 30-35 gallons drawdown.

Re: the well (re)development, I believe they did develop the well directly from the head without restriction for awhile. It was a Friday and in the afternoon they took away the probe, set the restriction at 5gpm, and set the timer. Came back on Tuesday to put things back together. Two weeks later I needed a well yield test for a building permit. That was also run unrestricted. After the first couple hours, only trace amounts of sand/sediment were detected. Just another data point to throw out there.

 

[Valveman]

The real problem is the 1/4 minus gravel. I would have used much smaller gravel, something just larger than the .032 slots. I might have even use .020 slots instead. But .032 should be small enough, just need smaller gravel. But it is too late for that. As was said developing the well usually means higher flow rates. I don't think the sand will even come up 1" or 1.25" pipe as it is barely at 1 FPS. The water is coming up so slow that in the 6-7 minutes it takes to get to the top the sand just settles back down to the bottom. I think you can still develop the well if you run it wide open until it pulls the well down, shut off the pump for a time, and do it all over again. You will need a dry run protector like the Cycle Sensor to keep this going for hours or days if needed.

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[Btrouse]

I have an 80' deep well on my property which is obviously constructed differently (casing to 75', kpacker and screen @ 0.010 from 75-80), it sounds like our wells behave very similarly. In my well, I ran for about 60hrs (on a generator) at 5gpm, hoping it would clear, but it did not. I speculate the sediment is silt because it does settle out but takes about 24hrs, and it doesnt feel like clay between my fingers (therefore its silt). Because of the time it takes to drop out of suspension, i don't think the diameter of the drop pipe, or the water velocity in it makes any difference in how the water coming out the top looks.

I noticed that i got different amounts of silt, depending on the flow rate. So I decided to perform what is called a "well step test". I measured the depth to water every 10minutes using a 1/2 full water bottle attached to some fishing line. Determining the flow rate using a bucket and stop watch, then making a plot similar to below. I also took water samples at the end of each flow step, and photographed them for reference.

The exercise described above took about half a day (which explains why my driller didn't perform anything like this). BUT it has really helped me to understand my connection with the aquafer, and helped me determine how long to pump for, at what flow rate (how much backpressure to apply), and I'm hoping it will help me asses if the well performance ever changes in the future. and that will help me justify paying for re-development or fracking.

My conclusion, the silt only really occurs near 5gpm, which is almost over-pumping my well, so I plan to dial in the backpressure so that i can get 3gpm. then i'll pump into a cistern, and supply the home from there.

 

[Valveman]

I wouldn't give up on developing the well. A few hours of running is nothing. It may take a few days to get it to clear up. If 5+ GPM is what causes the sediment, then run it at 5+ GPM to get the sediment out.

But after days of doing this if the sediment doesn't stop, restricting flow to 1-3 GPM and using a cistern is another way to deal with it.

 

[fourwells]

I wouldn't give up on developing the well. A few hours of running is nothing. It may take a few days to get it to clear up. If 5+ GPM is what causes the sediment, then run it at 5+ GPM to get the sediment out.

But after days of doing this if the sediment doesn't stop, restricting flow to 1-3 GPM and using a cistern is another way to deal with it.

View attachment 103248
View attachment 103249

I have an 80' deep well on my property which is obviously constructed differently (casing to 75', kpacker and screen @ 0.010 from 75-80), it sounds like our wells behave very similarly. In my well, I ran for about 60hrs (on a generator) at 5gpm, hoping it would clear, but it did not. I speculate the sediment is silt because it does settle out but takes about 24hrs, and it doesnt feel like clay between my fingers (therefore its silt). Because of the time it takes to drop out of suspension, i don't think the diameter of the drop pipe, or the water velocity in it makes any difference in how the water coming out the top looks.

I noticed that i got different amounts of silt, depending on the flow rate. So I decided to perform what is called a "well step test". I measured the depth to water every 10minutes using a 1/2 full water bottle attached to some fishing line. Determining the flow rate using a bucket and stop watch, then making a plot similar to below. I also took water samples at the end of each flow step, and photographed them for reference.

View attachment 103233
View attachment 103234

The exercise described above took about half a day (which explains why my driller didn't perform anything like this). BUT it has really helped me to understand my connection with the aquafer, and helped me determine how long to pump for, at what flow rate (how much backpressure to apply), and I'm hoping it will help me asses if the well performance ever changes in the future. and that will help me justify paying for re-development or fracking.

My conclusion, the silt only really occurs near 5gpm, which is almost over-pumping my well, so I plan to dial in the backpressure so that i can get 3gpm. then i'll pump into a cistern, and supply the home from there.

That is an interesting experiment. Thank you for sharing.

I have kept the backpressure at 5GPM on the well pump and noticed a few things in the course of operating my 5k gallon storage tank for about a month and a half now. If open the storage tank fill valve all the way, I get sediment/silt clogging my filters fairly quickly. However if I slow down the fill rate (by using a flow restrictor on the end of the storage tank float) to 1.2GPM or 2GPM, I don't collect as much in my filters. My goal is to reduce the amount of sediment collected to what can be flushed out automatically in my daily ~30 second backwash. Since this well is way in the back of my property, I have a pressure gauge nearby to give me an indication that I'm getting flow up to the tank. So far I've been happy; although with the well pump throttled at 5GPM I imagine I'm still collecting sediment in my pressure tank. My logic is that by filling the storage tank slowly, I allow as much settling as possible in the well between pump cycles. I've been keeping the flow restrictor at 1.2GPM and trying not to use more than 1,440 x 1.2 gallons per day which isn't hard.

I'll be using more water for irrigation in the summer, but not close to 1,700 gallons/day. I'll be curious to see if drawing an additional couple hundred gallons a day will change the behavior.

 

[Valveman]

You either need to develop the well by pumping hard to get the sand out, or restrict the flow to a point where the well is not making any sand. At 5 GPM the velocity in the drop pipe is only about 1 foot per second. If the well is making any sand it won't get to the top of the drop pipe and just settles on top of the pump and check valve. You will see a slug of sand anytime the flow is increased above 5 GPM. At only 1-2 GPM the well may not be making any sand to be sucked into the pump, but you still won't know until the flow increases to see if a slug of sand comes up.

If you use a flow inducer on the pump and extend it a foot or two below the motor, the velocity in that piece of 4" pipe will be so slow the pump will not pick up sand. But it could settle to the bottom and eventually fill the well up to the bottom of the flow inducer.

A flow inducer will also help keep the pump/motor cool when the flow is restricted to a very low rate like 1-2 GPM.

 

[fourwells]

We redeveloped the well and put a sleeve over it as you suggest, details above. After three-plus days of pumping the water was clear. A few weeks after that we also ran a 12-hour warm weather well test (required where I live in No Cal), and when pumping full throttle, the amount of sediment drawn up decreased over time. During my initial storage tank fill, I noticed similar behavior. I was doing the fill about 1" at a time (about 70-80 gallons) using an irrigation timer to spread it out over a month; we also were using the well directly for domestic use while I was plumbing the pump and runs to the houses.
Sounds like we've done things as you suggest which is makes me feel we've done what we can. Now I'm trying to find the steady state, i.e. the fill rate from this well, size of filters, timing for backwash, etc. so I don't have to worry about it.
I suppose one thing to keep in mind is your suggestion of throttling the flow at the pump even more, which is a good card to keep up my sleeve. Now that storage is implemented I think more about quality than quantity, so that is an option, especially if the sand/silt will harm the motor.

 

[Reach4]

Sounds like we've done things as you suggest which is makes me feel we've done what we can.

How about a baffle to make the sand settle before it hits your intake to the pressure pump.

Then suck out the accumulated sand as needed, which may not be much.

 

[fourwells]

How about a baffle to make the sand settle before it hits your intake to the pressure pump.

Then suck out the accumulated sand as needed, which may not be much.

Is a baffle like the Lakos product that accumulates and then dumps the sand back in the well? I had suggested a product like that but the pump company thought the sand was too fine for it to work. They recommended, if needed, a separator above ground. I am currently filtering it out with a 50 micron separator (like a Rusco), but auto flushing, and a 20 micron 10" filter.

 

[Reach4]

Suppose your tank is cube-like. The baffle I was thinking of would be like a plate/curtain between the input from the well and the intake for the pump taking water out of the cistern. Thus a particle from the well would have a longer path, toward the bottom of the cistern, to reach the intake. If your tank is enclosed, that would make adding a baffle harder.

Is your tank similar to one of these? https://www.plastic-mart.com/water-tanks/ Those are smaller than yours, probably.

Is your current filtering performing as you hope, or if not, what is lacking?

If you take some of your fine sediment, and stir it into water in a water glass, how long does it take for the sediment to settle out?

 

[fourwells]

I can picture what you have in mind. Yes, the tank I have is like one of their 5,000 gallon above-ground tanks. 12' diameter. My goal is to put sediment-free water into the storage tank. Inside the tank it is treated with ozone and then flows through a DAB e.symax booster pump for distribution.
My current filtering is done between the storage tank and the pressure tank down by the well head, about a five iron away. I'd give the setup a B-. I recently put back the automatic backwashing filter in front of the GE 10" housing, so we'll see how that goes. (I took that part out of the line when I was using the well water directly as my domestic supply; even though it can be set to backwash once a day it clogged too quickly.) I'll give it a higher grade if I get consistent results throughout the seasons as my water usage fluctuates. (And I really hate changing filters on those 10" housings...) I've only had the storage tank implemented for about 6 weeks.
When the well is pumping cloudy water, I'd say it takes about 20-30 seconds for the material to settle in a jar.

 

[Reach4]

When the well is pumping cloudy water, I'd say it takes about 20-30 seconds for the material to settle in a jar.

That would be fairly fine.

Another possibility, which may be more than you need, would be to use a backwashing filter (looks like a softener) for mechanical filtration. An example media is https://www.clackcorp.com/products/filter-ag/

Another possibility would be to route the water through a cone-bottom tank, that has a blow off valve at the bottom that lets you dump the sand. But this tank would be many gallons, so it could collect a lot of sand before you have to release the sand.

a 20 micron 10" filter.

A 4.5 x 20 inch filter will hold twice as much as a 4.5 x 10 inch filter. Some can be changed by changing the sump, and leave the attached part unchanged.

But a 20 inch filter housing full of water is heavy. You don't want to try to lift that at arm's length.