Shock Chlorination — Well Maintenance
Site: http://www.agric.gov.ab.ca/water/wells/module6.html |
Shock chlorination is a relatively inexpensive and straightforward procedure used to control bacteria in water wells.
Many types of bacteria can contaminate wells, but the most common are iron and sulfate-reducing bacteria. Although not a cause of health problems in humans, bacteria growth will coat the inside of the well casing, water piping and pumping equipment, creating problems such as:
Reduced well yieldBacteria may be introduced during drilling of a well or when pumps are removed for repair and laid on the ground.
Restricted water flow in distribution lines
Staining of plumbing fixtures and laundry
Plugging of water treatment equipment
Rotten egg odor.
However, iron and sulfate-reducing bacteria (as well as other bacteria) can exist naturally in groundwater.
A well creates a direct path for oxygen to travel into the ground where it would not normally exist. When a well is pumped, the water flowing in will also bring in nutrients that enhance bacterial growth.
Wells can also be contaminated with harmful bacteria such as fecal coliforms. Shock chlorination is the most effective method to eliminate them.
Note: All iron staining problems are not necessarily caused by iron bacteria. The iron naturally present in the water can be the cause.
Ideal Conditions for Iron Bacteria
Water wells provide ideal conditions for iron bacteria. To thrive, iron bacteria require 0.5-4 mg/L of dissolved oxygen, as little as 0.01 mg/L dissolved iron and a temperature range of 5 to 15°C. Some iron bacteria use dissolved iron in the water as a food source.
Signs of Iron and Sulfate-Reducing Bacteria
There are a number of signs that indicate the presence of iron and sulfate-reducing bacteria. They include:
Slime growthSlime Growth
Rotten egg odor
Increased staining
The easiest way to check a well and water system for iron bacteria is to examine the inside surface of the toilet flush tank. If you see a greasy slime or growth, iron bacteria are probably present. Iron bacteria leave this slimy by-product on almost every surface the water is in contact with.
Rotten Egg Odor
Sulfate-reducing bacteria can cause a rotten egg odor in water. Iron bacteria aggravate the problem by creating an environment that encourages the growth of sulfate-reducing bacteria in the well. Sulfate-reducing bacteria prefer to live underneath the slime layer that the iron bacteria form. Some of these bacteria produce hydrogen sulfide as a by-product, resulting in a “rotten egg” or sulfur odor in the water. Others produce small amounts of sulfuric acid which can corrode the well casing and pumping equipment.
Increased Staining Problems
Iron bacteria can concentrate iron in water sources with low iron content. It can create a staining problem where one never existed before or make an iron staining problem worse as time goes by.
Use the following checklist to determine if you have an iron or sulfate-reducing bacteria problem. The first three are very specific problems related to these bacteria. The last two problems can be signs of other problems as well.
Checklist to Determine an Iron or Sulfate-Reducing Bacteria ProblemGreasy slime on inside surface of toilet flush tank
Increased red staining of plumbing fixtures and laundry
Sulfur odor
Reduced well yield
Restricted water flow
Shock Chlorination Method
Shock chlorination is used to control iron and sulfate-reducing bacteria and to eliminate fecal coliform bacteria in a water system. To be effective, shock chlorination must disinfect the following:
The entire well depth The formation around the bottom of the well The pressure system Some water treatment equipment The distribution system.
To accomplish this, a large volume of super chlorinated water is siphoned down the well to displace all the water in the well and some of the water in the formation around the well.
Before you shock chlorinate, consult your water treatment equipment supplier to ensure the appropriate steps are taken to protect your treatment equipment.
Don't mix acids with chlorine. This is dangerous.
Effectiveness of Shock chlorination
With shock chlorination, the entire system (from the water-bearing formation, through the well-bore and the distribution system) is exposed to water which has a concentration of chlorine strong enough to kill iron and sulfate reducing bacteria (see Figure 1, Water System). Bacteria collect in the pore spaces of the formation and on the casing or screened surface of the well. To be effective, you must use enough chlorine to disinfect the entire cased section of the well and adjacent water-bearing formation.
Figure 1 Water System
The procedure described below does not completely eliminate iron bacteria from the water system, but it will hold it in check. To control the iron bacteria, you may have to repeat the procedure each spring and fall as a regular maintenance procedure. If your well has never been shock chlorinated or has not been done for some time, it may be necessary to use a stronger chlorine solution, applied two or three times, before you notice a significant improvement in the water.
You might also consider hiring a drilling contractor to thoroughly clean and flush the well before chlorinating in order to remove any buildup on the casing.
In more severe cases, the pump may have to be removed and chemical solutions added to the well and vigorous agitation carried out using special equipment. This is to dislodge and remove the bacterial slime. This should be done by a drilling contractor.
Shock chlorination Procedure for Drilled Wells
A modified procedure is also provided for large diameter wells.
Caution: If your well is low yielding or tends to pump any silt or sand, you must be very careful using the following procedure because overpumping may damage the well. When pumping out the chlorinated solution, monitor the water discharge for sediment.
Follow these steps to shock chlorinate your well.
Step 1 Store sufficient water to meet farm and family needs for 8 to 48 hours.Step 2 Pump the recommended amount of water
(see Table 1, Amount of Chlorine Required to Obtain a Chlorine Concentration of 1000 PPM) into clean storage. A clean galvanized stock tank or pickup truck box lined with a 4 mil thick plastic sheet is suitable. The recommended amount of water to use is twice the volume of water present in the well casing. To measure how much water is in the casing, subtract the non-pumping water level from the total depth of the well. See the example below.
Shock Chlorination — Well Maintenance
Site: http://www.agric.gov.ab.ca/water/wells/module6.html |
Step 3 Calculate the amount of chlorine that is required, as shown in Table 1. Mix the chlorine with the previously measured water to obtain a 1000 ppm chlorine solution.
Calculating Amount of Chlorine Example
If your casing is 6 in. and you are using 12% industrial sodium hypochlorite, you will require .091 L per ft. of water in the casing. If you have 100 ft. of water in the casing, you will use 0.091 L x 100 ft. = 9.1 L of 12% chlorine.
Using Table 1, calculate the amount of chlorine you will need for your well.
Shock Chlorination — Well Maintenance
Site: http://www.agric.gov.ab.ca/water/wells/module6.html |
Casing diameter_______ Chlorine strength_______ L needed per 1 ft. of water_______ x _______ ft. of water in casing = _______ L of chlorine.
Step 4 Siphon this solution into the well (see Figure 2, Siphoning Chlorine Solution).If you have an old well that has not been routinely chlorinated, consider hiring a drilling contractor to thoroughly clean the well prior to chlorinating. Any floating debris should be removed from the well and the casing should be scrubbed or hosed to disturb the sludge buildupStep 5 Open each hydrant and faucet in the distribution system (including all appliances that use water such as dishwasher, washing machine, furnace humidifier) until the water coming out has a chlorine odor. This will ensure all the plumbing fixtures are chlorinated. Allow the hot water tank to fill completely. Consult your water treatment equipment supplier to find out if any part of your water treatment system should be bypassed, to prevent damage.
Step 6 Leave the chlorine solution in the well and distribution system for 8 to 48 hours. The longer the contact time, the better the results.
Step 7 Open an outside tap and allow the water to run until the chlorine odor is greatly reduced. Make sure to direct the water away from sensitive plants or landscaping.
Step 8 Flush the chlorine solution from the hot water heater and household distribution system. The small amount of chlorine in the distribution system will not harm the septic tank.
Step 9 Backwash and regenerate any water treatment equipment.
Figure 2 Siphoning Chlorine Solution
Modified Procedure for Large Diameter Wells
Due to the large volume of water in many bored wells the above procedure can be impractical. A more practical way to shock chlorinate a bored well is to mix the recommended amount of chlorine right in the well. The chlorinated water is used to force some of the chlorine solution into the formation around the well. Follow these steps to shock chlorinate a large diameter bored well.
Shock Chlorination — Well Maintenance
Site: http://www.agric.gov.ab.ca/water/wells/module6.html
|
Step 1 Pump 200 gal. (1000 L) of water into a clean storage tank at the well head.Step 2 Mix 20 L of 5 1/4% domestic chlorine bleach (or 8 L of 12% bleach or 1.4 kg of 70% calcium hypochlorite) into the 200 gal. of stored water.
This mixture will be used later in Step 5.Step 3 Using Table 1 calculate the amount of chlorine you require per foot of water in the casing and add directly into the well. (Note that the 70% hypochlorite powder should be dissolved in water to form a solution before placing in the well.)
Step 4 Circulate chlorine added to the water in the well by hooking a garden hose up to an outside faucet and placing the other end back down the well. This circulates the chlorinated water through the pressure system and back down the well. Continue for at least 15 minutes.
Step 5 Siphon the 200 gal. bleach and water solution prepared in Steps 1 and 2 into the well.
Step 6 Complete the procedure as described in Steps 5 to 9 for drilled wells.
