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Chlorine solution pH test & adjustment: making sure that a chlorine disinfectant solution used to shock a water well or to disinfect building water piping or water treatment equipment can help determine a successful outcome. This article defines pH - the acidity or basic or neutral property of a liquid, and explains how to test and adjust the pH of a solution as needed when disinfecting a water supply system.
Well disinfection, shocking, & restoration procedures recommended by the BC Canada Ministry of Health & other expert sources include helpful details that can increase the chances that the disinfection is successful, producing potable water.
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Many experts have discussed the effect of solution pH on the effectiveness of disinfection, including the disinfection of wells and water treatment equipment. Dailloux (1999) for example, points out that certain nontuberculous mycobacteria include resistant strains that tolerate low pH and high temperatures, while other sources point out that high pH is an equally serious concern. (Yu-sen 2002).
And as we cite below, health professionals writing about optimum well disinfection procedures have elaborated the importance checking and adjusting the pH of water and disinfectant solutions.
Explanation of pH levels: the pH (power of hydrogen) of any liquid solution is a measure of how acidic or how basic the solution is. Low pH = acidic. High pH = basic. Solutions with a pH over 7 are considered basic or alkaline while solutions with a pH under 7 are considered acidic. A solution with a pH close to 7 is essentially neutral.
Lemon juice or vinegar and some soft drinks such as Coke® are common household acids; ammonia (NH3) is a common weak base while household bleach is very alkaline - a strong base.
What this means to a non-scientist is that when attempting to disinfect a well or water treatment equipment, taking the time to check and if necessary adjust the pH of a solution can make the difference between a successful disinfection and a failure. Essentially we want a neutral pH or a pH in the range of 6-7 by some sources or pH of 7-7 by others (Hua 2002).Reader Mark has encountered and discussed the importance of pH (and also well casing deposits) when chlorinating a water well. Mark posted as a comments on 3/22/2013 & 1/31/2014
Mark continued on 1/31/2014
Re: Mark's 2013 comment
Excellent points Mark - which explains why it can be difficult to sanitize a well, but ONLY if there is actual exfoliating rust inside the well casing - which is not usually the case. Normal surface rust is not a substantive block to disinfectants used in a well. But a thick mineral deposit that may build up in some wells (in the area of the casing or well borehole that is normally water-filled) can make disinfection more difficult in those wells unless disinfection is accompanied by mechanical cleaning.
Mark's 2014 comment was in regards to mine:
We agree completely.Just below for reader convenience and also at References  we have cited and link to a PDF file copy of the helpful BC ministry document to which Mark refers. My original comment was directed at typical residential well disinfection and the PROCEDURE & QUANTITY of BLEACH NEEDED to SHOCK A WELL - and did not adequately focus on on pH adjustment and on disinfecting a well contaminated by area flooding - a more extreme situation that may have forced floodwaters into the aquifer itself.
For a detailed procedure for disinfecting a well after area flooding see this helpful document cited both in our references and again just below:
In addition to the pH problem in disinfecting flooded wells, I add Manci's caution about giardia:
The document from the BC ministry makes a sound point that it can be difficult to disinfect a water well following a flood, giving two reasons why well disinfection may be unsuccessful.
pH Test Kits - litmus paper in rolls or strips read water or disinfectant solution pH level
You can purchase pH test kits and strips at drug stores, swimming pool suppliers, test equipment suppliers, some plumbing suppliers, and of course, online.
How to Adjust Water & Disinfectant pH when Shocking a Well
Adapted from "When Standard Water Well Chlorination Procedures are Ineffective:... " - British Columbia Ministry of Environment, retrieved 1/31/2014, original source: http://www.env.gov.bc.ca/wsd/ plan_protect_sustain/groundwater/ wells/factsheets/PFRA_well_recovery.pdf
Fresh potable water in the mixing tank to be used for preparing the disinfectant solution to be injected into the water well should be tested for pH level.
Before adding the chlorine solution, you can lower the pH of water by adding a safe weak acid such as household vinegar (acetic acid). Depending on the observed pH you may need to add 20 as much as Liters of 5% acetic acid (household vinegar) to 1000 Liters of water. Slowly add the acetic acid to the water while stirring the tank and then check the pH again as needed until you've reached the target pH.
How to Add the Chlorine (household bleach, sodium hypochlorite) to the Water to Prepare Well Disinfectant
When the water is at the proper pH, add the required amount of chlorine - see WELL DISINFECTANT TABLE, POST FLOODING for the quantity of bleach you will need.
Watch out: the Canadian Ministry of Environment warns in the source document that because we are adding chlorine to a weak acid (pH 4.5) some chlorine gas will form. Chlorine gas can be harmful or even fatal at high concentrations and exposures. The ministry recommends:
Watch out for hydrogen sulfide (H2S - which produces a rotten egg or sulphur smell) in the water. This gas is not just smelly, it can be dangerous, a health risk and een an explosive. If there is H2S in the water you will need to aerate the water to dissipate that gas before adding vinegar (or chlorine) to the water. - see CHLORINE SAFETY WARNING where we discuss both H2S and chlorine gas hazards.
The advice continues to explain that while some chlorine gas will form at pH 4.5 (you'll smell it), the addition of the chlorine raises the pH to a safe level - that is, the total quantity and duration of chlorine gas formation should be low. As you add chlorine the solution becomes alkaline.
Check the disinfectant solution pH again.
Step by step well disinfection procedures using pH adjusted disinfectant solution are given in these two articles:
Chlorine & Well or Water Equipment Disinfection Solution pH Adjustment & Target References
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