Periodic Sediment Problem in Well

[techinstructor]

We have a deep well, 420', with a static water level of 40' and a recovery of 2 GPM. Usually our water runs clear, though we do get some sediment buildup over time as is evidenced in a container that we keep filled for filtering our drinking water through a Sterasyl ceramic candle. However, we have had 2 or 3 occasions in the past 2 years when the sediment increased dramatically for a short time. This occurred again last night.

The water because very cloudy and when left to settle, there were lots of fine, dark gray particles in the water. This condition persisted through three baths. This morning after washing dishes, it ran clear again. I'm trying to find out why this could be happening. We have had a relatively dry year for my area, in fact I think NOAA has declared our area to be in drought. It's been a while since we had a long soaking rain, but we've had plenty of thunderstorms as of late. The last heavy rain was on Aug. 6 and the sediment occurred on Aug. 10 so I don't think there is a connection there. However, the last time I remember this happening it did follow a heavy rain which was preceded by a dry period.

Any suggestions as to the cause of this periodic increase? Should I worry about my well being contaminated? We have plans to install a sediment filter, but I still am curious as to the cause.

[LLigetfa]

Well drillers will often use a product like Benseal to seal the casing borehole. Sometimes during heavy draws and/or heavy rains, the Benseal may leak into the well. The more Benseal that leaks in, the greater the leak becomes. Of course it could also be naturally occurring clay.

You don't say what size the casing is so we cannot calculate how much storage the casing has. The more the storage is drawn down, the greater the hydrostatic pressure between the groundwater and the well. A 2 GPM recovery is nothing to write home about, so not drawing down the storage too far should help reduce the leakage.

[techinstructor]

Well drillers will often use a product like Benseal to seal the casing borehole. Sometimes during heavy draws and/or heavy rains, the Benseal may leak into the well. The more Benseal that leaks in, the greater the leak becomes. Of course it could also be naturally occurring clay.

You don't say what size the casing is so we cannot calculate how much storage the casing has. The more the storage is drawn down, the greater the hydrostatic pressure between the groundwater and the well. A 2 GPM recovery is nothing to write home about, so not drawing down the storage too far should help reduce the leakage.

The well casing is 6" PVC. The casing is 74' deep. It was grouted with bentonite to a depth of 35.' The casing extends 12" above the ground surface as is required by code. According to the well report, the static water level is 30' though it says 40' on the well tag. The well report also said the formation was "dirt" from 0-60' and below 60', granite. The well was drilled in Nov. 2008.

I think what I'm seeing in the water is bentonite, but I'm still unsure as to how it is getting in there if this data is correct. (All the clay around here is either red or yellowish and this sediment was dark gray.) If the casing extend into the granite by 14' then how could the bentonite leak into the well.

Thanks for the information.

[Porky]

Well casing should be grouted from the bottom of the casing to the top of the ground even though state regulations in most states require 20 foot minimum. I suspect the casing isn't sealed in the rock and is leaking. Specially if it occures more after a local rain. Bentonite is a clay from Wyoming and doesn't contain any fine dark particles so I doubt that it is the cause. I would say that this is a well installation problem. This can be rectified by a qualified driller but it isn't simple or cheap. Check the well tag on the well casing then call the NC Health Department in your area and report the problem. It may be the driller that installed the well's responsibility to rectify the problem.

[techinstructor]

I would say that this is a well installation problem. This can be rectified by a qualified driller but it isn't simple or cheap. Check the well tag on the well casing then call the NC Health Department in your area and report the problem. It may be the driller that installed the well's responsibility to rectify the problem.

Thanks for the explanation. This is what I feared may be happening. I am reluctant to contact the Health Department; I'd be in a hard spot if they decide the driller is not responsible and the well cannot be used. I will probably call them anonymously and try to get information. I'm not hopeful however. I called them before about discrepancy in the well report and the well tag and the health department inspector was defensive of the driller, so I really doubt that he'll do anything. What a disappointment to spend so much money - this well wasn't cheap at 420' - and not have it done right.

[LLigetfa]

The amount of storage in the 74 feet of 6 inch casing is not a lot. I think it is somewhere around a gallon per foot so 74 - 30 - 1 = 43 gallons. A well and/or pump man may correct me with more accurate numbers. So, once you draw all the water out of the casing at a rate much faster than the well can recover, the static level falls to below the bottom of the casing and whatever surface water pressure there is within the 60 feet of overburden, is now at full force against the seal. If you draw at a slower rate and use less so that the well can recover, the pressure differential against the seal is less so less surface water might enter the well. Besides the obvious turbidity, the other concern may be the potability of the surface water.

If you have a high GPM pump and a very large tank, it might yoyo the water level considerably even if you don't constantly draw a lot of GPM.

One other thing... depending on the terrain and geology, the static level in the well might be different than the static level of the surface water.

[Porky]

I understand your concern with the health department (I am reluctant to contact the Health Department; I'd be in a hard spot if they decide the driller is not responsible and the well cannot be used. I will probably call them anonymously and try to get information. I'm not hopeful however.) I'm sorry that we can't talk privately but I understand that it's against the rules, Privacy Issues and all!
However my previous statement stands, the casing is leaking at the lower end!

[techinstructor]

LLigetfa
Thank you for the explanation. This makes sense and explains why it would only happen periodically. I really don't think I have any recourse, as the well was installed according to code - at least the paperwork says that. We already have plans to filter the water for sediment, iron/manganese, and then a carbon to remove and chemical contaminants. We already filter all of our drinking water with a British Berkefeld which uses a ceramic filter. As long as we continue to filter the water, I guess we'll be ok.

I'm sorry that we can't talk privately but I understand that it's against the rules, Privacy Issues and all!
However my previous statement stands, the casing is leaking at the lower end!

I agree and I'd love to hear more. You can email me at techinstructor @ mindspring.com.