Static Water Level in Well - Stone Drop Method

[Carl_NH]

Saturday AM - could not figure out why irrigation didnt run... Hmm took cap off well and can hear the pump running even tho I thought there was no water being drawn, so dropped a stone to check the water level - 15 seconds or about 350' is static level - this is lowest I have ever seen.

Long story short wife left the valve open on 200' of manual drip irrigation for 20 hrs Fri-Sat AM.

So solved that problem but lingering issue now is the pump likely ran dry when I thought we had in excess of 10 GPM flow in the well. (don't have a low pressure cutoff switch installed but will by tomorrow!)

My question is determining the static water level using the stone drop method. As close as I can tell by my searches is its about 24' per second so @ 8 seconds = 192' to the water level. Is this accurate - what do you water well guys/gals say?

The well is 6" casing, 410' deep, pump is 1.5HP 10GS15 Goulds set at 375' +- so my next step this AM was to monitor the static depth when irrgation was running. At the beginning of the cycle the water level (by my stone drop test) was 5 sec or about 120' to static water level. At the end of the cycle, 13 sec or 300', then 30 minutes later after the end of the irrigation cycle the level was 8 seconds or 190'.

What this told me was the recovery (300'-190=110x1.5 Gal) rate in 30 minutes was roughly 165 gallons or 5.5 GPM is the flow rate of the well.

What will skew the numbers is if my estimate of 24' per second is accurate on the stone drop test..

A little more detail on the well is when it was drilled (thru 400' granite) it produced 1.5 GPM, so we had it hydrofracked and after the fracking it was reported "over 10GPM". So the other question is can or does a hydrofracked well "close up"? Can it be fracked again?

Thanks in advance..

 

[Mickey_Fx]

Don't think you want to be dropping rock down the well as you never know what can happen at the other end.

Think you need to find a better way to measure water depth. A method I use was to measure by pressure. Run a length of tubing down the well to a known depth (add a weight to the end so it will keep the tubing straight). Water weighs .43 lbs per ft of depth. At the top end have a pressure gage and schrader valve attached. I always pressurized i.e. purged the tube a little prior to taking a reading to make sure if there was a slight leak in the tubing/fittings I'd purge the water from the tube and get an accurate reading.

Check the pressure on the gage, now its time for a little math. Pressure X 2.325 = water depth from lower end of the tube. Subtract that from depth of tubing in the well and that give you the the static water level. You do need to have tube as short as you can above the well head to make the measurement as accurate as possible.

 

[SPIKER]

Those stones can wedge your pump tight when time comes to pull it and can also cause issues. Low pressure switch is good to have and running modern pumps without water flow is not as bad as days past, motor and pump are below the intake level so they stay submerged and cool in the well water. Though doing so can lessen the pumps life with seals and such not getting full water pressure cooling/lubrication. n

A better method it to get a fishing pole and use some braided line that absorbs water, (not fishing line but a cotton masons line type material to drop into the well. The Gauge method is great too but cost for a long length of tubing is pretty high to get 300+ feet of tubing vs 350 or 400 feet of the cotton line. mark line at the top of the casing & pull out until the wet line comes out and use measuring wheel.

Mark

 

[KTurner]

As close as I can tell by my searches is its about 24' per second so @ 8 seconds = 192' to the water level. Is this accurate - what do you water well guys/gals say?

Ignoring the well aspect of this and just looking at physics... Something falling does not fall at a constant speed. Gravitational acceleration on Earth is 32 feet per second per second. At the end of one second, your rock is going about 32 feet per second. At the end of two seconds, your rock is going about 64 feet per second, three seconds is 96 feet per second. And so forth. At some point, it will reach terminal velocity, where the air resistance keeps it from going any faster. This will depend on the object in question. A feather and a marble accelerate at the same rate, but the feather reaches its terminal velocity much sooner than the marble.

Keith

 

[Carl_NH]

Thank you gentlemen for the replies.

Kturner On the speed of a rock falling - per your analogy after 3 seconds the rock would have traveled 32+64+96 = 192' so I cannot imagine how that is possible.

On the tubing - I understand that but finding 300 or so feet of 1/4" tubing may be a challenge and costly especially if its the soft pliable type.

Then the string/line method with a weight on it is something I have done before but one issue is the line tends to get entangled with the wire. I might try some nylon line with something thin attached for a weight. I have used a 100' nylon tape measure with success in the past with a small wrench attached when the water level was higher.

On the rocks - these are 1/2-3/4" pebbles and the only thing that they would lodge on is the torque arrestor above the pump and when it cycles they likey would get dislodged falling below the pump. The 4" pump has a SST screen around the intake as well.

 

[Egon]

The formation fractures can plug up. It should be possible to do another frac.

 

[V1Rotate]

Instead of dropping a stone into your well, how about dropping an ice cube?

 

[Carl_NH]

Update:

Havent used much water since this AM, so I went out with my nylon 100' tape with a small wrench attached for a weight. It hit water at 56' so I then dropped a small 1/2" stone - took 3 seconds to hit the water. so rough calculations would be around 20' per second. Excluding acceleration - I still need to noodle on that..

The pitless adapter is 6' from the top of the casing so this means the pump is sitting in 325' of water or almost 500 gallon reserve.

By the way, I have now dropped 5 pebbles in the well in the last 2 days..raising the water level - I like the ice cube - GREAT idea!

Egon - thanks - i will speak to the driller Tuesday but for now I am going to cut back on the sprinkler use and let nature handle it until I get more info.

 

[Egon]

Distance equals 1/2 times acceleration times the time squared. assuming zero for initial velocity.

D=1/2 x at**

 

[Carl_NH]

Egon,

I didn't do well in Algebra in school - can you provide an example with the information given?

What I have seen on the web searches 9.8 meters/sec is the rate at which a object falls less the speed of sound traveling back but that doesnt compute with my measurements.

Thanks!

 

[KTurner]

Kturner On the speed of a rock falling - per your analogy after 3 seconds the rock would have traveled 32+64+96 = 192' so I cannot imagine how that is possible.

Not exactly. It continuously increases in speed (until it hits terminal velocity). So, at second 3, it's going 96 feet per second (ignoring drag), but it has just hit that speed. At second 2.9, it was going slower. This ignores air resistance/drag though, which slows things down some.

15 seconds sounds like a long time for something to be falling. A golf ball has a terminal velocity of 105 feet per second (~70mph). Even if it took 10 seconds to reach terminal velocity (dont know how long it would take), the golf ball would travel 525 feet (105 feet per second * 5 seconds) in the last five seconds.

Differently shaped rocks and different density rocks will have different terminal velocities. I.e., two dissimilar rocks dropped in the same well at the same time would reach the water at different times due to the differences in terminal velocities.

Keith

 

[Egon]

Differently shaped rocks and different density rocks will have different terminal velocities. I.e., two dissimilar rocks dropped in the same well at the same time would reach the water at different times due to the differences in terminal velocities./QUOTE]

Would the time difference measurement for that distance be within the capabilities of the ordinary person using his wristwatch?

Carl, my scholastic ability is also quite limited. Use the 9.8 ft/sec and forget about the sound time.

you could always work backwards from the distance measured and find the almost time it should take for the stone to fall that distance.

I'm best at stuff like that by putting a float on a fishing line and lowering that down the well.

Do you have a laser measurement device?

 

[Carl_NH]

Egon,

Agreed, keep it simple as possible. That's sort of my goal in this post to establish or determine somthing of a norm with this "stone drop" or "ice drop" as VIrotate appropriately suggested, as its simple, quick, yet effective to get a ballpark assessment +- 30' so to speak.

Indeed, the stone is clacking off the walls of the well on the way down is reducing velocity, but as you say working backwards, 56' in 3 seconds should be around 6 seconds to 110' and 12 seconds at 220' and so on.. and yes using a wrist watch. So my goal was/is some standard or "rule of thumb" with this. I did a search on this subject on TBN and looked at 30 or so different posts but couldn't find anything definitive.

i DO have laser measurement devices - one of those thermometers which is very good to see hot spots in piping or cold spots in walls. Now you have me thinking about getting another laser measurement device (like a golfer uses to get distance to the pin) same concept, just dont know how well it would work in a deep well which isn't always straight down and has pipe obstructions.

Thanks again.

Carl

 

[Carl_NH]

Keith.

Thanks for the golf ball analogy, typically when I play golf (26+ handicap) in 3-4 seconds after I hit it usually lands left or right it - not where I intended

Most of the time I am hitting the golf ball 150-200 yards (450-600') so 105 feet per second sounds about right.

Thats an accelerated speed, much like shooting a (stone, pellet etc) down a well not the same as dropping a rock and timing the free fall.

This has been interesting and hope this might help others trying to ascertain static well depth as it has me.

Carl

 

[Carl_NH]

Further to this, I plan to install a CSV or a Cycle Stop Valve and the low pressure cutout switch. After much reading today the CSV keeps the pump running during the cycle diverting the flow to the source as required while keeping the pressure under the setpoint.

This keeps the pump running and reduces the cycles on the motor which is what kills sub pumps from most of the time. @ $150 not cheap, but the longer life it should yield from the Sub motor should pay off plus lower electric costs due to the non cycling surge at startup.

Any suggestions on which CSV to get?

 

[TheGoose]

Carl,

I have seen ads for sonic water level testers, but they are about $1,000. I use a regular tape/weight, but around here our water levels are usually about 30-80 ft. We have 4" wells here so it's not quite possible to drop anything into the well without it getting wedged between the pump/casing.

I believe the acceleration is 32.2 ft/sec/sec as stated above. The math required to figure out how far left my mind years ago. Distance/velocity/acceleration.....all runs together in my head LOL. If you figure it out (seconds = x distance) let me know. Next time I measure one I'll drop in some chlorine tablets and see how long it takes to hear the spalsh and then correlate that to the measured water level.

 

[Carl_NH]

TheGoose,

Well I did figure it out with a tape measure 56' to water (after letting it sit most of the day) then did the stone drop. it was 3 seconds with my wristwatch, of course it might have been 2.7 or 3.1 seconds.. so 20'/second.

The stone was clacking on the well casing but I think for my purposes this is good enough. I will use 20' / sec as the average looking forward..

The other good one was to use ice instead of stones VIrotate suggested - lots of good ideas came from this..

Thanks

Carl

 

[nikdfish]

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deleted when I decided not to trust my rusty brain ....
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Nick

 

[Egon]

http://upload.wikimedia.org/math/6/e/5/6e551b7718cf4ab08290ff74ddc45ded.png
:thumbsup:

 

[wrooster]

TheGoose,
The stone was clacking on the well casing but I think for my purposes this is good enough. I will use 20' / sec as the average looking forward.
Carl

Carl,
A number of folks in this thread have already opined, but I don't think you are hearing it. So again: a pebble dropped into a well does not fall 20 feet per second. This is not a valid rule of thumb, and in is not of any use for the general case. You may have back-calculated that value from one experiment you did at a given water depth, but that does not make it a valid formula for all depths. Here's why -- from the moment you let go of the pebble, it is accelerating -- that is, falling faster with every passing moment.

The theory you need to know is explained here:
Gravitational acceleration - Wikipedia, the free encyclopedia

The practice that you need to know is explained here:
Equations for a falling body - Wikipedia, the free encyclopedia

Pay attention to the graphic of the basketball on the right side of the second link above. This is key to understanding the continued acceleration of a falling body.

You can use online calculators, such as the following, to easily convert between time and distance of a falling body. The first example calculator on the page can be used to convert time to distance.
Gravity Calculations - Falling Body Equations at gravitycalc.com

For example, using the calculator above ... if the stone dropped at the wellhead takes 3 seconds to hit the water below, the distance to the water is about 44 meters, or about 143 feet.

wrooster