One bore well was constructed in Khondalite. The saturated fracture was encountered at depths of 55 - 57 metres with discharge of about 5 litres per second. Upon development the water was clear initially. However, as and when the well is operated after a gap of a day or so, turbid (white) water comes out for nearly 15 minutes and then slowly starts clearing up. What could be the possible reason and how to solve this permanently?
Dear Arnivan
There can be several reasons to this matter of fact, but the most probable one is that the discharge of the well is much higher when you begin to pump and thus when the piezometric level is very high than after a few minutes of pumping, when the piezometric level decreased. You could check this by measuring discharge and piezometric level just after starting the pump, and also comparing these data with the caracteristic curve of the pump.
In such a case, the solutions are : 1. install a device (an electronic variator) that will progressively increase the discharge after any stop of pumping and/or 2. (re)develop the well at a higher discharge than previously done in order to "clean" the fractures in the vicinity of the well. However, this must be done carefuly and according to the detailed geological log and completion of the well in order not to produce adverse effects such as clogging, filling the well with sand, etc..
Moreover, this phenomenon can also result from other reasons, such as a bad grouting of the well, particularly at shallow depth, so this point should also be carefully examined.
I hope these few elements may help you. Best regards PL
looks to me this is related to the aquifer material or the material used to construct the well. there could possibly be some leakage via the annular seal (this is usually clay or grout) or the filter material it self was not good and contains some clay and silt. how is the pH of this water? may be this can also help to findout the problem.
Chemical treatment by alum OR PHOSPHATE may clear the water
I don't know if you are using a pump or not and witch type of pump. But if there is white coloured water it is possible that pump vibration is the cause. Pumps could vibrate when NPSH is close to critical or almost there (cavitation). To escape this ==> Just increase the immersion of the pump by 1 m and see if the problem is fixed or not.
First, I note that people tended to answer without asking questions, so... Is the turbidity permanent, or is it gas? If the latter, no likely problem. But, that would be too easy! Is the khondalite aquifer highly weathered? If so, you could be getting kaolin and other clays, or sillimanite, or ??? In that case, serious redevelopment with rigorous surging are might be needed to cleanse the fractures far enough from the well to reduce water velocity through/over the white mineral(s). What was drilled through before hitting the khondalite aquifer? Is it khondalite saprolite, for example? The one respondent could be right in implying that resting the well for "recovery" allows water to contact not only packing and sealing materials but also a white mineral that is entrained until water drains below it. In this case, reducing initial pumping rate, filtering, or pumping to waste may be the solutions. White does not sound like a microorganism infection of the well, but a test might be in order to check that wild possibility AND more to see if there are signs of contamination from above. Did drillers or others pour something like lime or calcium hypochlorite (powder or pellets) into the well for disinfection? Again, after water level recovery, the resulting calcium hydroxide could be entrained until the level drops during pumping. Each start of pumping is like one suction surge, as in well development. How many times have the operators cycled through the off-on sequences? Some stuff could be shaken loose each time, so time and repeated use might also be a solution, though Mother Nature is rarely so kind. Are there other questions I should have asked? Bob
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