HELP! Please help interpret well report...

[topspin]

Hi everyone..new 2000sq foot house build. Considering purchasing nice lot with low yield well drilled in 2003....1gpm. I have full report here summarized and would like to ask a couple questions if I may...

Specs:
800 ft depth.
51 foot 6 inch PL casing
open hole (no screen)
grouted with cement

Well log:
0 til 48 feet soil
48 til 800 feet Med Hard Grey Rock
- 94 feet is checked under the column "water bearing"

Pumping test:
Hours pumped: 6
pumping rate: 1gpm
H20 level before pumping 22'
level when pumping 406'


Questions if I may....

1) I understand a deeper well (800) has more storage but isn't that dependent on where the groundwater is in the well? Do I conclude that I have storage from 406 (level when pumping) to 800....or 94 until 800 since 94 is the level noted as "water bearing"?

2)Since this is an open hole well (presume because rock was hit at 48 feet) and only 50 foot casing....how do I calculate storage in the non-cased rock...would it still be 6 inch diameter and calculate at the same formula as if it were actually cased?

3) That 406 ' level when pumping...is that the draw down level (406-22) and does that seem high?


4)Any thoughts from any experts how they would feel about the well and what specific tests they would test for as part of the contract.

...I know this is a lot of info...thanks very much for your time. I am a well newbie...

WALLACE

 

[Boycedrilling]

Your numbers don't add up. If you pump 1 gpm for 6 hours you have pumped a total of 360 gallons. 1x60x6=360. You started with a static water level of 22 ft. After the 360 minutes of pumping the water level was now 406 ft. 406 ft minus 22 ft equals 384 ft of drawdown. 406-22=384. A six inch hole contains 1 1/2 gallons per foot of depth. 384x1.5=576 gallons. You are saying that pumping 360 gallons of water removed 576 gallons from the well.

Recheck your numbers, or email me your well log and pump test data and I will review it.

 

[Sponsor]

 

[topspin]

Understand your reasoning completely which is why I am confused myself. Sending you a copy of the report and thanks so much for your time and help.

 

[Reach4]

Your question 2 is intersting.. a 6 inch casing would be 6.5 inches OD, plus there would be some margin. I don't know if they drill a 5 or 6 inch hole and ream the the top of the hole to fit the casing, or if the whole hole is actually dug to maybe 7 inches.

I would also wonder how consistent that 1 GPM is. Is that the pump rating when pumping from 900 feet, or is there some kind of constant-flow mechanism to hold the flow at 1 GPM?

I don't know. Interesting.

 

[topspin]

Thanks for all the responses...here is a very hard to read copy of the well report...

 

[LLigetfa]

...low yield well drilled in 2003....1gpm.
...
Pumping test:
Hours pumped: 6
pumping rate: 1gpm
H20 level before pumping 22'
level when pumping 406'

If it were a 1 GPM well, then pumping at 1 GPM from the get-go should not have drawn it down that much. That much drawdown suggests they were actually pumping more than 1 GPM or the well does not produce 1 GPM.

Based on that and the numbers that Boycedrilling ran, I have to contend that they were not pumping 1 GPM from the get-go, but rather that they drew down the well first and then were able to sustain 1 GPM at the 406 foot mark. The GPM a well produces can be affected by the level it is drawn down. Drawing down the level changes the downhole pressure which can change the rate of recovery.

 

[Reach4]

I liked "METHOD USED TO MEASURE PUMPING RATE: 'Watch Bucket' "

That seems to support LLigetfa's analysis.

 

[LLigetfa]

My guess is they pumped it as fast as the pump would go and that once it reached 406 feet, the pump was at 1 GPM on the curve.

 

[VAWellDriller]

Its also possible that they measured the static level well after they ran the test.....in a scenario that may have gone like this...they drill the well, know it's low yielding, water is low and slowly recovering in the well and they want to know the yield so they immediately put in a test pump and perform the test (without waiting the 6 or 8 or 10 hours it might take for the well to recover after air lifting with the drill rig).... then check the static the next day or something. I've actually done the exact same thing.

 

[topspin]

Two very strong ideas. In MD the limit is 1gpm. VAWellDriller may be right on that they just dug and did the pump test wherever the water was at at the moment (406 I presume), then the next day observed the recovery rate as the static level depthof 94 ..DO I have this right VA?
OR...according to LLigetfa pumped at a higher rate drew down to 406 and then set the pump to 1gpm to see if the level would hold...? ...or perhaps 406 is where when decreasing the pump rate to the min of 1gpm the level seemed to hold?
In either case...how would you feel about this well and what test would you consider and want to see happen to buy the lot what is now 12 years later? To me it seems like I want to make sure it is 1gpm....but 1 gpm with still significant enough storage if the "open hole" storage in the rock is substantial and recoverable. If it held at 406 truly at 1gpm...do I have another 400 foot of some diameter storage (6 inch?) in the open hole in the rock as available stored water? thanks guys..

 

[LLigetfa]

In MD the limit is 1gpm...

Maybe the well made more but they were only concerned about meeting minimum? Around here one needs 5 GPM to get a building permit and to secure a mortgage so that is all the drillers test to.

It doesn't mean the well makes as much now as it did then.

What are the spec's on the pump in the hole? HP? GPM? Depth?
Are they pumping into a holding tank or directly into the house?

Maybe they found 1 GPM at 100 feet and kept going, hoping for more. The pump might not be set at the bottom of the well so it might not all be a reserve. It takes a lot of pump to lift 800 feet.

 

[Craigpump]

I would give some thought to having the well tested again with a test pump at the same level and compare the results. Better to spend a little now and know for sure, you might use the results as a negotiating tool for a lower purchase price.

1 gpm is 1440 gallons per day, more than enough for domestic purposes unless you have a large family. Combined with a usable 700' of water or 1050 gallons, you should have no problems.

 

[topspin]

LLigetfa- Pump height...yes that is another variable in the water storage equation I didn't even consider. There is no pump in the hole now....just a vacant lot with a well cap showing. I have no idea on cost of pumps...and increasing cost to try to lift 800 feet. What would you target as a sensible pump height based on cost of the pump? I'm thinking if the well recovers to 94 feet overnight (testable) I could rely on storage from 94 down to whatever is a "reasonable" pump height...

 

[LLigetfa]

I will leave that to the pros to suggest the right pump.

H20 level before pumping 22'

That is a bit of concern to me. When a pump is selected to lift from 800 feet, it will be way off the curve at 22 feet and careful consideration need be given to limit upthrust. This was discussed here before and valveman provided good insight.