water well turbidity 2

[hunter82]

I have a water well that was recently drilled. The initial tests indicate that the water had a turbidity of 7. The well pumped several million gallons into the distribution system and the utility started getting complaints that the water was cloudy. We checked the turbidity agian and it was 20. The well has been pumping for about a month now and there has been no change in the turbidity. What is the problem-please help.

Just some background info.
The driller installed a 30 minute timer on the well so that it turns on and off to surge the well-mimicing development.
Also before the production well was drilled the client wanted to do a test well approximately 75 feet away from the production well location. The well was abondoned once satisfactory water quality results were obtained. A turbidity of 2. But could there be some drilling mud influence from the test well causing the increase in turbidity from the production well.

Thanks

 

[bimr]

You have not provided enough information to make any conclusion. For example, is the well 60 feet deep or 1600 feet deep.

1. Would hope that you have properly disinfected the well before use.

2. You need to obtain a complete water analysis. That will tell you what is in the water.

3. Some wells may pump sand. Other wells may have iron, manganese, or sulfur present. All these materials will cause turbidity.

4. The part about the 30 minute timer sounds questionable and perhaps ill advised. Surging the well may cause turbidity. If you have a sandstone well for example, you may be causing material to break off down in the well causing the turbidity.

Also, after wells are developed, the well water is run to waste until the well water is clear.

5. Do you have any water treatment equipment?

6. The wells located 75 feet apart are not likely to influence each other unless you are in a fractured rock formation.

 

[hunter82]

bimr

The well is 700 feet deep in a sand aquifer that has clay above and below it. It is a 1000 gpm well

1. The well was properly disinfected before use. Bacteriological tests were performed to ensure there was no problem

2. I have done a complete water analysis. I attached it.

3. There doesn't appear to be any sand problems

4.The idea of the timer was to remove any drilling mud that might be causing turbidity. The well is screened in a sand aquifer

The well was pumped/developed for a month and after that is when we got a turbidity of 7. this was before we put it online.

5. No I don't have any water treatment equipment. The TSS is 2 mg/L and the TDS is 208 mg/L

6. We are not in a fractured rock formation. I highly doubted the drilling mud from the test well would be the cause of the turbidity but why else would the well pump clear and then turn turbid.


Just a side note. this utility has always had a turbidity problem but the wells will clear up after about an hour of pumping to waste then the they put in in the system.

 

[bimr]

A well should not typically have turbidity.

Reducing the pumping rate may alleviate sand/turbidity production. Decreasing the pumping rate lowers the water entrance velocity. Therefore, the energy of the water to carry suspended solids is reduced.

The 30 minute timer may be aggravating the problem by surging the well.

A well will also generally remain sand free if the permanent pumping rate is lower than the discharge rate used during final development.Is the well subject to the influence or surface water or recharge?

http://www.michigan.gov/documents/deq/deq-wd-gws-wcu-wellsproducingsandorturbidity_270759_7.pdf

 

[hunter82]

bimr

The well was pumping 1100 gpm and we reduced the pumping rate to 800 gpm and the turbidity did not change noticably.

As far as influence from surface water recharge I guess that it does get recharged from surface water but I don't know where.

No other wells that are screened in the aquifer have this type of turbidity problem.

I haven't seen any sign of sand particles in the samples that I have taken.

Did you take a look at my water quality analysis? Anything out of the ordinary?

Thanks for your help with this

 

[bimr]

The water analysis that you have is not complete. However, what you do have does not indicate anything unusual with the water that would cause the turbidity.

Groundwater is usually turbidity free since the well water is naturally filtered underground.. Results from analytical methods represent both the dissolved and colloidal fractions of the solution. The colloidal fraction may be caused by improper well design, insufficient well development, and/or operational parameters. Turbidity may be associated with the aluminum concentrations since many colloids, are composed of aluminosilicates.

Your next step is to identify what material is causing the turbidity. The lab should be able to assist you with that. With that information, you can go back to the well installer and determine if installer can rectify the problem.

 

[thewellguy]

The timer confuses me. Why would you need to "develop" a well that is already in production? Without knowing what the material is, its hard to tell. Did they do a seive test to size the well screen? What type of well casing was used? Have the joints been inspected?

 

[hunter82]

The thought was that maybe there was some drilling mud that wasn't pulled out and rise and fall of the water in the well would help to pull any mud out that might have been in there. It was really a shot in the dark because why would a well pump well for a time and then get turbid.

They did a sieve test of the aquifer material and sized the gravel pack and screen size off of that.

The well casing is 16" steel pipe that was welded together. The screen was 10 inch welded steel pipe.

I have taken the water to the lab and they performed an X-ray defraction test on it but they couldn't really tell me what it might be. I attached it in this post.

I just want to thank the people that have provided input on this issue. I am trying to figure something out and any input won't hurt. The driller and all the other local drillers have never heard of this so I am grasping at straws.
thanks

 

[cvg]

did they install slotted screen in the the clay material? Are they sure the bottom and top elevations of slot match up with the bottom and top of the sandy layer?

 

[hunter82]

yes they installed a slotted Muni-Pak screen in the aquifer and placed a gravel pack outside of the screen between the aquifer.
Yes I thought about running a camera down to the bottom of the hole just to check and make sure that the screen is installed where it is supposed to be. My thought about that is if it was in the clay why would the well clear up for a little bit.

 

[bimr]

The surficial and intermediate aquifers occasionally contain intervals with a relatively high content of clay material in the unconsolidated geologic formations. When water flows within unconsolidated sediments, the majority of particulates settle out because of the tortuosity of the flow path around the intergrannular porosity and gravitational effects. However, substantial research has documented that colloidal size particles can travel notable distances in unconsolidated formations. Many researchers conclude that sediment produced from monitor wells in unconsolidated formations is due to sloughing of particulate material from the borehole under the turbulent flow conditions induced by well development and pumping, and only minimal colloidal matter in ground water samples is from natural ground water flow. Obviously, this problem must be evaluated site by site.

http://www.dep.state.fl.us/water/groundwater/docs/filter-guidance.pdf

See "Common Correction Methods"

http://www.michigan.gov/documents/deq/deq-wb-dwehs-gwwfwim-section10_183036_7.pdf

You should have in your specifications some wording to the effect:

1.06 GUARANTEE
A. Guaranteed Conditions. For a period of one year after acceptance of the well by the Owner, the Contractor shall make the following guarantees and accept the following responsibilities concerning his work;
1. Sand production shall be less than 5 ppm within 15 minutes after start of pumping at the constant pump test rate of the well.
2. Sand production shall be less than 1 ppm within two (2) hours after start of pumping at the constant pump test rate of the well.
3. The well casing and screen shall remain intact throughout its entire length.
4. Plumbness and alignment shall remain within tolerances set forth in specifications.
B. Demonstration of Compliance.
1. To demonstrate compliance with the above, the Contractor shall perform after six (6) months of operation, and again, after eleven (11) months of operation, a test of the well. These tests shall be witnessed by representatives of the Owner and certified copies of the test results shall be
furnished to the Owner. The Owner shall be notified 48 hours prior to the scheduled test. The tests shall consist of a Rossum sand test of the well in accordance with Section 1.06 A.
2. To insure compliance with the terms of this section, the Contractor shall furnish a one (1) year maintenance bond. The one (1) year maintenance bond period shall begin at the time of notice of final acceptance.

In summary, the problem needs to be resolved by the well drilling Contractor.

 

[hunter82]

Our specs said something to the effect that the well shall have a turbidity less than 5 but didn't say anything about the sand production.

thanks

 

[hunter82]

I just talked to the water operator and the well has been inopperative for the last 2 months. They started it up yesterday at 700 gpm and the first turbidity reading was 6. They checked it again this morning and the turbidity was 10. Why would this happen when for last month of pumping we had a turbidity of 20.

My thoughts are that whatever is causing the turbidity has settled out over the last 2 months and it is slowly being resuspended as the well pumps more and more.

Any thoughts on why this might be happening or what we can do to fix this.

thanks

 

[bimr]

IF you are in a sandstone formation, the sandstone may be breaking off and being carried out. You may have a piece break off and then clear out over time.

When wells are developed with these characteristics, the practice is to pump (develop) the well at a higher flow so that when the well operates at the normal flow (lower flow rate), less material is likely to break off.

 

[hunter82]

yeah we are probably going to pump it at a lower flow rate but the aquifer is sand not sandstone.