Hi all, I have a need to correct the pH level of a borehole water which services a fish pond. The borehole water was initially tested okay with pH level ranging b/w 6-8 sometimes last year, but now has dropped to b/w 2-3. The water borehole depth is in the range of 100 to 120 ft. and this range is acceptable within the locality where the borehole was drilled. The Fish pond is located 80ft away from the borehole with the waste water discharged within this space to service a nearby garden.
Could the sudden change in pH level be as a result of contamination from the waste water from the fish pond or as result of acid rain and how best can it be corrected?
If the borehole well waterbhas dropped that much, I would be surprised. Acid rain can have a low pH, and in swimming pools, people have to continue to add alkalinity and chemicals to raise pH to above neutral. Low alkalinity water has no buffering capacity, so pH can change abruptly. People who service swimming pools may be able to test water and offer solutions, just remind them it is a fish pond, so no chlorine needed. We treat some low alkalinty lakes and waters with lime to raise pH, but I dont know if you need a special grade of lime. Low pH will make aluminum more soluble and perhaps other contaminants harmful to fish. If you have any zoos or aquariums, they too may be able to give advice. But the fish may not be able to tolerate this too long, so quick response is probably needed first to raise alkalinity and pH, then search for answers on why.
Such low pH in groundwater is almost unbelievable. The fish should be dead and it is hard to find a mechanism that could explain such a large pH drop.
I advise that you first try to verify the low pH and try to understand the nature of it. E.g. aerate a water sample overnight and measure the pH again. Try to measure the pH with different pH meters and if possible measure it with indicator paper to see if the pH indication match your measurement. Also try to titrate the water with base to measure the acidity.
If the pH is really this low and you treat by adding an alkaline chemical like lime or sodium hydroxide into the well it is likely that there would be precipation of minerals that would 'cement' the well so it cannot fill with groundwater. A neutralisation tank between the well and the fish tank would be more safe and controllable.
Dr Anderson had a point about dumping chemicals down a well. The liming of lakes and flowing waters does not include dumping lime down a well. I would also suggest adjusting quickly, but not too abruptly, and at least try to get pH to 5-6. Pool instructions suggest adjusting alkalinity first, then pH. I would try to get alkalinity up to at least 40 ppm or mg/l. Swimming pool test strips or testing kits may be available at hardware stores. The pool chemical used to raise pH from a hardware store is Sodium Carbamate and instructions say to add 20 ounces per 10000 gallons for water under pH 6.5. You may need more, but dont go overboard, giving chemical time to work and dump them in fish pond and not well. You may need to address well water later, and I would shut that off until you have time to figure out. pH 2-3 is like acid coal mine influnced water as I have seen in Missouri in Cedar Creek below some coal mining activity years ago. Rainfall can have low pH, but 2-3 is low for that. I am not sure if you should relocate fish, and some fish may be more tolerant to these extremes than others. Consulting with a fish biologist, aquarium manager or animal vet, or internet searches about this may be appropriate. If your fish are not already dead, if they exhibit signs of stress, you may need to put them in a more controlled environment. Do not dump them in stream, lake or river, as if they are not native species, they can damage or even destroy native fish or consume all the food if they are invasive.
Dear Charles,
It is quite unusual to have ground water with such low pH, In my opinion you must look for surroundings of bore-well it appears that bore-well is connected to some untreated industrial disposal system.
Do you have any dumping of Industrial waste-water particularity distillery/ chemical units nearby to bore-well?
I have encountered similar problem In one of Industrial zone in India , where one Industry was disposing off its untreated waste water into ground.
As far as acidic rain is considered it is difficult have such a pH in ground water as percolating rainwater water passing through carbonate-rich rocks (e.g., limestones and marbles) will usually have pH values greater than 7 as the acidic water is “neutralized.”
If the geology of the aquifer containing the ground water has few carbonate rocks (e.g., sandstone, metamorphic granitic schists and gneisses; volcanic rocks, etc.) the ground water will tend to remain acidic but not 2 ~3. except hot sulfur springs, which can have pH up-to 1.5. due to microbial reaction.
Mitigation:
Best possible low cost mitigation in my opinion is to have horizontal bed of broken limestone with sufficient length & Hydraulic Retention Time (HRT) for neutralizing the pH and make it safe for fish pond.
regards
dinkar
Thanks all for your valuable contributions and suggestions. I will quickly swing into actions to correct the borehole pH so as to save the fishes. I promise to share the outcome of the results to all after the correction.
Just in case you have some funds to monitor the well water quality, you can buy a water quality sonde (such as Global Water company - search on Global water quality sonde will probably get you there). They can record various water quality components such as TDS, specific conductance, pH, salinity (if you need that), depth if corrected by barometric pressure, etc. The sonde I used was self contained and you could put on a long cable or rope, but the depth measurement had to be adjusted for nearby barometric pressure. These sondes are programmable for recording frequency and the batteries for the one I had lasted 5 years. These sondes probably range from $1000 plus alot, depending on what you want to measure. Some of these are very complex and there are alot of options. The data collected can be at nearly any interval. They require some maintenance and calibration, and the one I used was in a freshwater, saltwater interface wilderness type stream on the national forest where under certain low flow conditions in the Santee River, salt water would come up into the wilderness area. This would be a great teaching tool for students or a tool useful to help in graduate study. I am glad you will let us know the outcome because I think we have consensus that the pH is probably not natural. You must have some tough fish. As I said though, if the water alkalinity is extremely low (ie, no buffering capacity), small inputs could produce large change. I know we have certain leaves in the mountains that are acidic that are a concern in low alkalinity waters of the mountains, and in extreme cases they have gone to lime additions to streams to raise pH.
It isa very strange. case. Rasmussen is right..
One way is to neutralize with sodium carbonate. to pH 5,5 -6. It will result in a hydrogencarbonate solutyion that is not harmful.
I have thought about how the described drop in pH could be explained by a plausible mechanism.
I like to suggest that an explanation for the change of the well water to such low pH could be that that extracting water has lowered the groundwater table around the well below some sulfide/disulfide minerals like pyrite which are now being oxidized in a reaction that produces sulfuric acid: 2FeS2 + 7O2 + 2H2O => 2Fe2+ + 4SO42- + 4H+
We see this sometimes in Denmark in connection with drainage of wet agriculture soils. The pH of the drainwater can be 2-3 in soils without carbonate minerals.
If this can be verified (high sulphate concentration in the acidic well water) the problem can be solved by managing the extraction so the groundwater level is prevented from decreasing.
Hello,
Low pH levels in groundwater may be due to geological factors. If that is the case, it will be difficult to have it corrected in-situ. To correct this, you need to construct a chamber and dose it with lime after abstraction before distribution.
Hi Charles,
Could the bore have been drilled into acid sulphate soils? Although I'm not sure how long it would take after the bore has been drilled for the sulfides to oxidise and drop the pH. Has the water been tested for heavy metals as this may be a problem with the acid water especially if the fish will be used for human consumption? Also the equipment being used to pump out of the bore will need to be able to handle the corrosive nature of the low pH (plastic or stainless steel). The water can be treated once it has been pumped out, however, the treatment method will depend on 1) other aspects of the water quality (EC, metals, etc) and 2) economics.
Naturally such sudden change is impossible, there is possibility intrusion of some industrial effluent. For correction of pH, lime pond should be constructed between borehole and fish pond.
Pyrite oxidation could be the origin of the pH decrease. As the water table was lowered oxigen was brought into areas where formerly no remarkable oxidation processes have been. This is a very common experience in mining areas. If you want to prevent this process you have to stop pumping water or pump less water to rise the water table. The only alternative is to treat the water with neutralizing agents (like lime).
Hi Stephanie
If it new borehole, pump (flush) the water for while (10 minutes to 30 minutes). In situ measurement is more recommended. First calibrate your pH meter. Take the water sample into clean container . Measure the pH at the different interval (after each 10 minutes) See if there is any descrepancy in values, if not , take record of the value against the temperature.
Otherwise , for more information you may read from book " Standard Methods for Examination of Water and Wastewater (22nd Edition)- 2012. Published by APHA"
Chanzi, H
Tanzania
Hi Chanzi,
I have been taking many water samples and done a lot of in situ measurements of pH (in the beginning of my professional life) and I agree completely. (pH- measurement problems by the way are very nicely analysed by Guenther Meinrath (2007): Quality assurance for chemistry and environmental science: Metrology from pH-measurements to nuclear waste disposal)
Anyway, what I was describing is not a measurement problem, but a hydrogeochemical process in the aquifer that results in pH-decrease.
The process starts or may establish when the water table is lowered. As a result of this process after some time (e.g. one year) the pH is decreasing. This of course is dependant of the specific geochemical boundary conditions. The process itself is described in numerous publications e.g. on acid mine drainage (AMD) or acid rock drainage (ARD),
See also e.g.: https://brownfieldstsc.org/pdfs/amdinnovativetrttech_03.pdf
pH of Bore hole water varies from 6 - 8, to 2-3 , indicate contamination of acidic water. Source of such water can be identify by tracer technique. monitoring of water sample and their complete analysis may be useful. Once source of contamination is identify and taken care of that, the problem will be solved.
Very useful. I am having a similar problem with borehole water having pH of 3 to 4. my problem is which type of lime should I use for correcting the pH in a rubber tank before distributing the water to the concrete tanks containing the fish.
Sixthy year ago I asssisted a similar case. It was derived from a contamined hiole at around 100 m. Authorities gives permisision to a factory of Ethylchloride ( from EtOH and HCl) to dump the remains to a hole without treatment. The pump and tubes of a neighbour appeared very oxidised and so the water. We discovered the source because the eater in the opposite direction ( to the slope of the land) ramain normal. The factory was dismantled, the borehole neutralized. No more!
I am a homeowner in rural Maine with a dug well with 24 inch tiles. The pH of the water is approximately 6. 2. Is it possible to raise the pH by placing a block of marble ( calcium carbonate) in the well, or will I need to install a system that has to be backwashed? Water use is a concern as the well gets low during dry spells.
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