How do I chlorinate drilled wells?
A Word of Caution
The CRD Health Department via itself and local laboratories has for many years passed out instruction sheets containing valuable information for the disinfection of wells. However, these sheets also have some ineffective and outdated instructions as well. Following is a more detailed set of instructions which we believe will cover most cases.
CRD Health Department information sheets suggest pouring bleach into the well and running taps until bleach can be detected/smelled. In our opinion this is not a good idea for many wells. Low volume wells will be completely drained, leaving little water for houshold use and possibly running the pump dry. In high yield wells, the bleach can be excessively diluted before it reaches the pump, if it reaches it at all. Their instruction sheets also recommend removal of the plug from the top of the pressure tank to allow chlorinated water to contact all of the inside surfaces of the tank. This is a bad idea; most tanks no longer have a top plug and those that do must not have them removed because serious waterlogging problems can occur if they are not resealed perfectly. Also, these plugs are installed very tightly and are difficult to remove.
A Better Way
Our recommended method of disinfection requires being able to not only pour bleach (chlorine) into the well but also to fully circulate it within the well before finally filling the rest of the piping system with chlorinated water. This circulation, depending on well depth and pump capacity, can take ten minutes to two hours (or more) and is accomplished by pumping water back into the top of the well, typically via a garden hose. Circulation is complete when water coming out the hose smells of chlorine.
Our method of disinfection is as follows:
(Read all steps before proceeding!)
STEP 1 - Pour a bleach solution into well.
- For wells with a pitless adapter, removal of the wellhead cap provides ample room to pour in the bleach and push in the garden hose to circulate the water.
- Where a well seal has been used, chlorination can be much more difficult.
- Some well seals have a 1.25 inch plugged hole; removal of the plug provides ample access.
- Some well seals have a 1/2" or 3/4" threaded hole with a plug screwed in. By removing the plug and installing the appropriate garden hose adapter, chlorination can be carried out.
- When all the holes in the well seal are filled with wires, conduit, safety rope, etc. it may even be necessary to drill a hole in the casing. Obviously, extreme care must be taken in doing this.
- In cases where the well seal carries no weight it is often possible to lift it up to provide the necessary access. Never remove the well seal bolts Lifting up the well seal should only be done if you understand exactly what you are doing.
| Table of Quantities for 5% bleaching solution required for disinfection of wells (Approx. 50 ppm) | |
|---|---|
| Diameter of well, spring or pipe in inches | Amount of household bleach required for each 10 ft depth of water |
| 2" | 1 tsp or 5 ml |
| 4" | 4 tsp or 20 ml |
| 6" | 10 tsp or 50 ml |
| 8" | 7 tbsp or 105 ml |
| 10" | 10 tbsp or 150 ml |
| 12" | 13 tbsp or 195 ml |
| 24" | 3.5 cups or 875 ml |
| 36" | 2 qts or 2.2 L |
| 48" | 3 qts or 3.3 L |
| 60" | 5 qts or 5.5 L |
| 72" | 7 qts or 7.7 L |
| 96" | 3 gals or 13.5 L |
*Please note:
Excess of the recommended bleach may poison your septic field
STEP 2 - Feed a garden hose from the house or pressure tank into the top of the well and turn it on
Note: Some water filtration equipment such as water softeners must not be exposed to heavily chlorinated water and must be bypassed. By drawing water from the bottom of the well and feeding it in the top, the chlorine will be fully circulated within the well. Circulation is complete when water coming out the hose smells of chlorine. Depending on well depth and pump capacity, circulation can take ten minutes to two hours.
STEP 3 -Shut off the hose and run chlorinated water into all water lines
Wait for 12 to 24 hours then flush the system. Run each tap until chlorine smell appears, flush each toilet, run hot water for ten minutes or so.
Be careful; if you have a low yielding well, flushing must be done in stages to prevent running the pump/well dry.
Use outside taps; avoid running excessive amounts of this water into the septic tank.
STEP4 - Test water for bacteria
When all the chlorine has been flushed out, a water sample can be taken for a bacteria test. Coliform samples should not be more than 24 hours old and should be kept refrigerated at 4 degrees and be shipped with an ice pack. This is not necessary if the sample is to be in the lab within a few hours.
- Obtain a 250 ml sterilized plastic bottle from Cantest (385-6112) or MB Labs (656-1334) and carefully follow the instructions supplied. Handle the bottle with care to avoid contaminating the sample. Avoid touching the rim or the inside of the bottle. Hold the bottle by the base and do not pass your hand over the mouth of the bottle. Do not rinse the bottle. Open the bottle just before sampling and close immediately.
- If sampling a household source, use a cold water tap. Remove any plastic attachments or aeration screens. Run water for a few minutes then take the sample.
- Fill the bottle, leaving a small air space, and close the bottle securely.
- Take sample to lab; check with lab for hours of operation.
*Please note:
A total & fecal coliform test should be repeated 7 -14 days after bleach treatment.
If you are not certain of how to accomplish any of these steps, do not start. Consult a well pump professional or someone completely familiar with this information.
