10. Test Hole & Dewatering Well Exemption & Recommended Activity: Disinfection

Chapter Description

This chapter covers the importance of disinfecting test holes or dewatering wells during initial construction, equipment installation and alteration activities. Test holes and dewatering wells are exempt from the disinfection requirements in the Wells Regulation; however, there are many situations where disinfection would help protect the aquifer after well construction and equipment installation. This chapter provides recommended activities to disinfect a test hole or dewatering well and where appropriate best management practices.

Recommendations on proper sampling and testing of water after treatment and when test hole or dewatering well disinfection should not take place are provided. Information on safety issues and some hazards are also described.

This chapter does not cover ongoing well maintenance for existing test holes and dewatering wells. For information on maintenance, see Chapter 14: Test Hole & Dewatering Well Maintenance & Repair.

Regulatory Requirements – Disinfection Exemption

Relevant Sections – The Wells Regulation

• Disinfection – Section 15
• Disinfection exemption - Subsection 15(14)

The Requirements – Plainly Stated

Relevant Standards

American Water Works Association (AWWA). 2003. ANSI/AWWA C 654 -03 – “Disinfection of Wells.” AWWA, Denver, CO. 2003. AWWA website.

American Water Works Association (AWWA). 2006. ANSI/AWWA A100-06 – “Minimum Requirements for Vertical Water Supply Wells.” AWWA, Denver, CO. 2006. AWWA website.

NSF International Standard/American National Standard 60, 2009. “Drinking Water Treatment Chemicals - Health Effects.” NSF International, Ann Arbor, MI 2009. NSF website.

Reminder: The standards cited in this document are current at the time of printing. Check current documents for recent updates.

Well Record – Relevant Sections – Disinfection

Figure 10-1 shows a sample of the details to be completed on the well record relating to disinfection.

Figure 10-1: Well Record – Relevant Sections

Reminder: This section of the well record must be completed by the person constructing the well. By checking “Yes” in the “Disinfected?” section of the well record, the person constructing the well is confirming that the disinfection requirements in the Wells Regulation have been followed. A person can only select “No” when exemptions to disinfection apply, such as test holes or dewatering wells, flowing wells and minor alterations.

Key Concepts

Considerations if a Person Chooses to Disinfect a Test Hole or Dewatering Well

Purpose of Disinfection

Disinfection protects Ontario’s waters by reducing pathogens.

The disinfection steps provide an adequate level of removal or inactivation of pathogenic organisms that may be present in the well or groundwater^{footnote 1[1]} or introduced during the well construction process and prevent heavily chlorinated water from affecting crops, surface water courses or other activities.

This chapter covers a suggested disinfection process during and after test hole or dewatering well construction and installation of equipment in a test hole or dewatering well. This chapter does not include disinfection treatment (primary or secondary) on municipal distribution systems or treatment on wells.

Process of Disinfection

With respect to well construction and installation of equipment in a well, the process of disinfection involves the following^{footnote 2[2]}:

• initial steps, including:

  • following sanitary practices when constructing a new well,
  • properly developing a new well, and
  • removing any debris from a well,
• thorough flushing of the well,
• treating with a properly prepared chlorine solution,
• discharging of heavily chlorinated water from the well, and
• collecting and analyzing water samples.

When Should Disinfection Take Place?

A well can become contaminated during well construction and the installation of a pump or other equipment.

While every effort should be made to keep the equipment used and the environment worked in contaminant free, where appropriate, disinfection should be done after:

• constructing a new test hole or dewatering well,
• installing, including re-installing, the pumping equipment that will be dedicated to a test hole or dewatering well over an extended period of time,
• deepening or extending a test hole or dewatering well, or
• conducting other alterations (except minor ones) or repairs on an existing test hole or dewatering well or on equipment in a well.

When Should Disinfection Not Take Place?

In many cases, test holes or dewatering wells are located on contaminated sites. Disinfection of well water is not appropriate if the chlorinated water could:

• react with the contaminated water and create toxic byproducts that may pose health and safety risks to people on site and further contaminate groundwater. For example, in areas contaminated with petroleum hydrocarbons, benzene reactions with chlorinated water can create other chemicals such as chlorobenzene.
• introduce bias into samples.

Use of Chlorinated Water if a Person Chooses to Disinfect

Chlorine, in its various delivery forms, is generally a good disinfectant for indicator organisms and most pathogenic organisms. Treatment with chlorine products, after the well is properly cleaned and pumped, is an inexpensive and effective way to disinfect the test hole or dewatering well and any equipment installed in the well. Although chlorinating the water is a good treatment for a test hole or dewatering well and equipment, its effectiveness depends on a number of factors, including the following:

Form - The most effective form of chlorine solutions for dosing well water is liquid sodium hypochlorite (such as unscented bleach). When used properly, it is the easiest to mix to achieve a concentration of not less than 50 mg/L, and not more than 200 mg/L, of free chlorine throughout the column of water in the well.

Granular calcium hypochlorite is another choice but it is difficult to mix with water. It is best to avoid the use of chlorine puck or tablet products to dose the well as they can become lodged in the well, corrode the equipment and may not provide the proper concentration for the required amount of time. It is also best to avoid the use of chlorine products used for pools as they typically contain other chemicals such as algaecides and surfactants.

Chlorine concentration - To eliminate pathogens in well water, the Ontario Advisory Council on Drinking Water Quality and Testing Standards recommended a dose to create a free chlorine of not less than 50 mg/L (0.007 oz/gal) and not more than 200 mg/L (0.032 oz/gal).

Free chlorine residual - The amount of chlorine available that acts as an oxidizer (kills micro-organisms). The free chlorine is comprised of hypochlorous acid (HOCl) and hypochlorite ion (OCl⁻) that is not combined with ammonia (NH₃) or other compounds in water.

Contact time - The longer the microorganisms are in contact with the free chlorine, the more effective the disinfection. When a test hole or dewatering well is disinfected, a minimum contact time of 12 hours, but not more than 24 hours^{footnote 3[3]} should be observed.

Agitation - Dosing a well by pouring a chlorine solution into a well is not enough to ensure it is completely mixed to the required concentration. To ensure the free chlorine residual is at the correct concentration throughout the entire water column, the well water should be agitated while avoiding the suspension of sediment from the bottom of the well into the water column.

pH of water - The effectiveness of free chlorine is maximized at pH levels between 6.0 and 7.0^{footnote 4[4]}. As chlorine solutions are highly alkaline (i.e., high pH), the dose of chlorine solution in the well increases the pH of the well water and can diminish the effectiveness of the free chlorine. Therefore, it is important to maintain a concentration range for free chlorine of 50 mg/L to 200 mg/L.

Temperature - The effectiveness of free chlorine can change with temperature. Free chlorine is more effective at higher temperatures.

Interfering substances - Available chlorine will be used up by any inorganic and organic compounds in the well water which will reduce the concentration of free chlorine.

Biofilm - Biofilm is a slimy substance that attaches to the sides of wells and pumping equipment. The slime consists primarily of nuisance microbes (e.g., iron oxidizing bacteria and sulphate-reducing bacteria) that can shield pathogens from the oxidizing action of the free chlorine and reduce the amount of available chlorine. Therefore, it is necessary that biofilm be removed before treating the well water with free chlorine.

Initial Steps for New Wells if a Person Chooses to Disinfect

Sanitary Practices

The initial step for disinfection begins with adopting sanitary practices to prevent contaminants from entering the test hole or dewatering well during construction. This is done by following sanitary practices during storage, transportation, handling and installation of test hole or dewatering well components and equipment. Essentially, anything that comes into contact with the water in the well can potentially introduce contaminants in the well.

Each of the scenarios listed below presents a potential cause of contamination to a test hole or dewatering well:

• Construction equipment has been dragged through a waste disposal site.
• Contaminated sand, gravel or filter pack has been installed around a well screen.
• A storage tank has recently held contaminated water.
• A faulty well cap can act as a direct pathway for foreign materials to enter the well.
• Pumping equipment has been laid on the ground.
• Unsealed annular space outside the casing can provide a pathway for surface water runoff to enter the well.
• Improper use of grease, lubricants and drilling additives during construction can promote bacterial growth^{footnote 5[5]}
• Contaminated water from ponds, rivers and lakes has been used in the construction process.

Disinfection for Sand, Gravel and the Filter Pack

In addition to keeping materials clean during storage and transportation, a person installing sand or gravel (filter pack) during well construction should:^{footnote 10[10]}

• avoid, if possible, buying the material in bulk and storing it on-site to reduce the risk of exposing the material to sources of contamination such as soil bacteria, insects and animal feces,
• ensure the sand and gravel are free of all organic materials to reduce the potential for bacterial growth, and
• saturate the sand or gravel (filter pack) using chlorinated water with a free chlorine residual of at least 50 mg/L, or mix calcium hypochlorite tablets at a ratio of 113 g to 227 g ( ¼ lb to ½ lb) to a 22.7 kg (50 lb) bag of sand or gravel.

Reminder: The use of calcium hypochlorite tablets in hard water environments (hardness in excess of 100 mg/L) should be discouraged as this form is very slow to dissolve in the water. The condition will result in low levels of free chlorine over extended periods of time which may account for low levels of disinfection by-product formation. The situation becomes more critical in test holes that are subject to limited pumping and long periods of inactivity.

Reminder: See Chapter 6: Constructing the Hole, Casing & Covering the Test Hole or Dewatering Well for details on installing sand, gravel and the sand and/or gravel (filter) pack in a test hole or dewatering well.

Well Development

If the person constructing the well makes the decision to disinfect the test hole or dewatering well, proper well development should be conducted to remove fine soils, drilling fluids and drill cuttings from the well and surrounding formation. See Chapter 9: Completing the Test Hole or Dewatering Well Structure, for further details on well development.

Initial Steps for Existing Test Holes or Dewatering Wells if a Person Chooses to Disinfect

During the alteration of an existing test hole or dewatering well, the installation of a pump, or the installation of other equipment, there is the potential for pathogens to be introduced into the well. Where appropriate, disinfection should occur to remove pathogens from the test hole or dewatering well.

Scaling, biofilm and other debris are commonly present on the side of the hole, casing or the equipment and in the well water. This organic and inorganic matter can reduce the available free chlorine. Biofilm can also shield pathogens from the oxidizing action of the free chlorine. To remove this matter and prepare the well before the well is dosed with a chlorinated solution, the person disinfecting the well should follow the next best management practice.

Reminder: It is important that water and debris be collected and disposed of in an approved manner or discharged to waste in an approved manner.

Thorough Flushing of the Test Hole or Dewatering Well (New & Existing) if a Person Chooses to Disinfect

Flushing is the process of pumping out the water to help rid the well of debris. The scouring action of the moving water assists in removing scaling and biofilm from the sides of the hole and casing. Flushing is used:

• before the well is dosed with a chlorinated solution to prepare the well, and
• after the treatment period to remove the chlorine residual from the well^{footnote 13[13]}.

This section discusses flushing prior to dosing the well with a chlorinated solution. For flushing of the well after chlorination see the “Handling Heavily Chlorinated Water Discharge” section in this chapter.

Treatment Using “Shock” Chlorination if a Person Chooses to Disinfect

The simplest and one of the more effective ways to disinfect well equipment and the well water is to use a chlorine solution. The oxidizing action of the chlorine solution kills bacteria, viruses, protozoa and some protozoal cysts.

“Shock” chlorination is an effective treatment method that can be done after the initial steps of developing, cleaning and flushing the well to eliminate pathogens.

Free chlorine also degrades rapidly in the natural environment. As such, an approval from the Ministry of the Environment and Climate Change is not required to disinfect a well with certain chlorine-based products (e.g., hypochlorite).

Forms of Chlorine for Disinfection

1. Sodium Hypochlorite (Such as Typical Household Bleach)

Sodium hypochlorite is commonly found in products like household bleach and swimming pool disinfection products. It has a yellow colour and a chlorine smell. Household bleaches typically contain 3 to 6 % available chlorine. Industrial strength commercial bleach and swimming pool products can contain 10 to12 % available chlorine. However, the use of swimming pool products is not recommended because they typically contain additives that may impair the quality of the well water.

Household bleaches containing sodium hypochlorite are routinely used in wells and are recommended in “shock” chlorination treatment because:

• they are familiar and common household products,
• calculating, measuring and mixing the required volume of liquid to achieve the required dose is less complicated than for other products (e.g., powders, tablets or pucks), and
• they are safer to use than liquid chlorine, chlorine gas or calcium hypochlorite.

However, only regular major brand bleach products should be used as the greater percentage of bleach products on the household market contain silicates, surfactants, silicon and/or thickeners. All of these additives will harm both the water quality and the performance of the well, and bias sample results.

Reminder: A person who is going to use a bleach product for chlorinating well water should check the product’s label to verify that additives such as surfactants or fragrances have not been added.

Reminder: The unstable nature of sodium hypochlorite makes it sensitive to temperature and light, and therefore it has a limited shelf life. For example, sodium hypochlorite degrades extremely rapidly in the hot, sunlit cab of a truck. Purchasing and carrying small containers ensure a fresh supply for each well construction project.

Reminder: Sodium hypochlorite products are described as weight % of available chorine, weight % of sodium hypochlorite and trade %. To convert to weight % of available chlorine from trade % and sodium hypochlorite use the following:
Trade Percent = grams per litre (gpl) of available chlorine ⁄ 10
Weight % of available chlorine = gpl ⁄ 10 × specific gravity of solution
Weight % of available chlorine = Weight % of sodium hypochlorite ⁄ 1.05

Reminder: To minimize impacts to groundwater, it is important that all chlorine products used be approved for potable water use and be either fresh unscented bleach or meet the NSF International Standard 60 for Drinking Water Treatment Chemicals – Health Effects, or an equivalent standard.

Reminder: Scented bleach or products such as swimming pool chlorine should be avoided as they typically contain additives such as surfactants, thickeners, stabilizers, perfumes, UV inhibitors, algaecides or other additives. These additives can impair the quality of the water and aquifer after disinfection and are not designed for potable water use.

Reminder: It is important to always check product labels to verify product contents and manufacturer’s suggested usage as well as Material Safety Data Sheets (MSDS). See the “Safe Handling of Chlorine,” section in this chapter.

Reminder: Chlorine products should always be stored in a cool, dry and dark environment.

2. Calcium Hypochlorite (Dry – Powder, Granules or Tablets)

Calcium hypochlorite is a white granular compound containing about 60 to 70 % available chlorine, which is fairly stable when stored in a cool dry place. Calcium hypochlorite is available as granules, powders, tablets and pucks.

Calcium hypochlorite is not typically recommended for “shock” chlorination for the following reasons:

• Calculations can be difficult with such a high concentration.
• The high potency and required agitation can cause difficulties in obtaining the recommended free chlorine residual concentration range in the Wells Regulation (not less than 50 mg/L and not more than 200 mg/L).
• Greater safety precautions are needed when handling and using the product.
• Tablets should be avoided as they are slow to dissolve and may become lodged within the parts of the well. If tablets are used, they should first be broken up and dissolved into a 20-litre (4-gallon) pail or tank.
• In limestone, marble and other calcium-rich environments, calcium hypochlorite can increase the concentration of calcium in groundwater that is already hard, causing partial plugging of well intakes, screens and water-bearing fractures.^{footnote 15[15]}

Reminder: When a calcium hypochlorite product is selected, it is important that it be approved for use in potable water and meets all applicable standards such, as ANSI/AWWA B300 titled: AWWA Standard for Hypochlorites and the NSF International Standard 60 for Drinking Water Treatment Chemicals – Health Effects.

Effectiveness of Chlorine if a Person Chooses to Disinfect

Free Chlorine Residual

When a chlorine solution is first added to water (i.e., when the test hole or dewatering well is dosed) the available chlorine will react with substances in the water, and on the surfaces inside the well. During this reaction, some of the available chlorine is used up by organic and inorganic matter and can no longer kill pathogens and disinfect the well. The remaining available chlorine is the free chlorine residual that can effectively react to any pathogens. Free chlorine residual consists of two main compounds: hypochlorous acid (HOCl) and hypochlorite ion (OCl⁻). Hypochlorous acid is much more effective (80 to 200 times better) at killing pathogens than the hypochlorite ion.

Substances that Interfere with the Effectiveness of Free Chlorine Residual

As indicated above, available chlorine will be used up by any inorganic and organic compounds in the well water which will reduce the concentration of free chlorine. Examples of common materials or properties that reduce the free chlorine concentration are:

• alkalinity,
• hydrogen sulphide (H₂S),
• methane (CH₄),
• iron,
• manganese,
• biofilm (e.g., iron-oxidizing bacteria and sulphate-reducing bacteria),
• silt, and
• clay.

Therefore, additional cleaning of the well or additional chlorine solution may be needed to achieve the recommended free chlorine residual concentration range in the Wells Regulation (not less than 50 mg/L and not more than 200 mg/L).

Test Hole or Dewatering Well Structure

In some cases, the geologic environment and test hole or dewatering well structure play a role in the amount and placement of the chlorine dose. For example, injecting and mixing of the dose by a surge block is more appropriate in a well with a well screen, whereas a jetting tool may be more appropriate in an open bedrock hole. Also, large open fractures in open bedrock wells may allow the calculated chlorine solution to move further away from the well. This may require more chlorine solution to maintain the required free chlorine residual in the bedrock well.

pH Levels

Sodium hypochlorite (bleach) and calcium hypochlorite products are alkaline (caustic). It is important to note that when a person adds these chlorine products to water, the pH will increase. The form of free chlorine residual is pH-dependent. High pH environments create more hypochlorite ions and significantly reduce the effectiveness of the treatment. Therefore, it is important not to use too high of a concentration of these chlorine products. Hypochlorous acid production, and thus the effectiveness of free chlorine, is maximized at pH levels between 6.0 and 7.0.^{footnote 16[16]}

Measuring pH

During the mixing of the water with the chemicals, the pH should be tested frequently to identify any risk of chlorine gas production, for other health and safety reasons and to verify that the correct pH (6.0 to 7.0) of the free chlorine residual solution has been achieved. Test papers and comparison charts, calibrated field test kits or calibrated meters should be used to test the mixtures for pH.

Figure 10-2: Measuring pH

Figure 10-2 shows a pH test strip being checked against a comparison chart. The test strip is placed into the solution and changes colour. The test strip’s colour is matched to the colour on the comparison chart, which has the corresponding pH value. In this example, the test solution has a high pH.

Temperature

The effectiveness of free chlorine can change with temperature. Higher temperatures increase the amount of hypochlorous acid in the free chlorine making the treatment more effective. However, as groundwater is typically between 6 and 12°C, increasing the temperature of the well water is cost prohibitive, impractical and could impair the quality of the water.

Safe Handling of Chlorine and Other Chemicals

Proper transportation, storage and use of chemicals must be observed during all phases of well construction. In accordance with the Occupational Health and Safety Act and regulations made under this Act, safe practices must be followed when dealing with chlorine products and solutions, acids and other chemicals used in the “shock” chlorination process. Extra caution should be used when working with acids and calcium hypochlorite tablets or powder as they can cause chemical burns, fire, or explosion. Chlorine gas can be released if the water used to make the chlorine solution is acidified below a pH of 5.0 and hypochlorite is then added to the water. Therefore, proper precautions should be in place to protect workers from any possible release of chlorine gas during the treatment process.

“Shock” Chlorination Procedures if a Person Chooses to Disinfect

Calculating Chlorine Solution Dose Amounts Using Bleach

It is recommended that water and equipment in the well be chlorinated by dosing the well water to a concentration of not less than 50 mg/L (0.008 oz/Imp gal) and not more than 200 mg/L (0.032 oz/Imp gal) of free chlorine.

To determine the dose that will create a free chlorine residual between 50 mg/L and 200 mg/L, a person constructing a well or installing a pump should calculate the volume of water in the well and then the amount of chlorine product needed to dose the well water.

The following calculations and tables in this section are provided to assist the person in calculating the correct dose for the well.

To Calculate the Volume of Well Water in a Test Hole and Dewatering Well

1. Well depth elevation and static water level elevation are measured.
2. Height of water column in well is calculated:
   = well depth elevation − static water level elevation
3. If the well opening is circular, the inner diameter of the well is measured.
4. The radius of the well is calculated:
   = diameter of well ⁄ 2
5. The radius is converted to the same units as the length of the water column.
6. The area of the well casing opening is calculated:
   = Π × radius²
   or
   = 3.14 × radius × radius
7. The volume of well water in the well is calculated:
   = area of well casing opening × height of water column in the well

Reminder: To prevent calculation errors and incorrect doses, it is important to use consistent units (e.g., metric or Imperial).

Example

The well depth is 35 m below the ground surface and the static water level is 5 m below the ground surface.

Therefore, the water well column height is 35 m − 5 m = 30 m (100ft).

The inner diameter of the well casing is 16 cm (6 ¼ inches).

The inner radius of the well casing = (diameter of well) ⁄ 2 = 16 cm ⁄ 2 = 8 cm

All units are converted to metres.

Therefore, the inner radius = 8 cm ⁄ 100 = 0.08 m

The area of the well casing opening = Π × radius²

= 3.14 × 0.08 m × 0.08 m = 0.02 m²

The volume of the water well column = area of well casing opening × water column in the well
= 0.02 m² × 30 m
= 0.6 m³
*1 m³ = 1,000 L
0.6 × 1,000 = 600 L

Percent Volume of Bleach Required

Typical available chlorine concentrations of unscented bleach by weight (as noted on the product label) are as follows:

0.005% = 50 mg/L

0.02% = 200 mg/L

1% = 10,000 mg/L

5% = 50,000 mg/L

12% = 120,000 mg/L

To Dose 1 L of Water to 50 mg/L of Free Chlorine

Using typical fresh unscented bleach (5.25% available sodium hypochlorite) with 5% (or 50,000 mg/L)available chlorine

(1 L × 50 mg/L) ⁄ (50,000 mg/L) = 0.0010 L of bleach

An alternative formula using percentages

(1 L × 0.005%) ⁄ 5% = 0.0010 L of bleach
= 1 mL (0.035 fl oz) of typical fresh unscented bleach is needed to create a concentration of 50 mg/L of free chlorine in 1 L of water

Using typical fresh unscented bleach (6% available sodium hypochlorite) with 5.7% (or 57,000 mg/L) available chlorine

(1 L × 50 mg/L) ⁄ (57,000 mg/L) = 0.00088 L of bleach

An alternative formula using percentages

(1 L × 0.005%) ⁄ 5.7% = 0.00088 L of bleach
= 0.88 mL (0.031 fl oz) of typical fresh unscented bleach is needed to create a concentration of 50 mg/L of free chlorine in 1 L of water

Using industrial sodium hypochlorite (12.5% available sodium hypochlorite) with 12% (or 120,000 mg/L) available chlorine

(1 L × 50 mg/L) ⁄ (120,000 mg/L) = 0.00042 L of bleach

An alternative formula using percentages

(1 L × 0.005%) ⁄ 12% = 0.00042 L of bleach
= 0.42 millilitres (0.015 fluid ounces) of industrial sodium hypochlorite at 12% available chlorine is needed to create a concentration of 50 mg/L of free chlorine in 1 L of water

Reminder: There are about 227 mL in one Imperial cup. There are about 4.7 mL in one Imperial teaspoon and 28.4 mL in one Imperial fluid ounce.

To Dose 1 L of Water to 200 mg/L of Free Chlorine

Using typical fresh unscented bleach (5.25% available sodium hypochlorite) with 5% (or 50,000 mg/L) available chlorine

(1 L × 200 mg/L) ⁄ (50,000 mg/L) = 0.0040 L of bleach

An alternative formula using percentages

(1 L × 0.02%) ⁄ 5% = 0.0040 L of bleach
= 4 mL (0.14 fl oz) of typical fresh unscented bleach is needed to create a concentration of 200 mg/L of free chlorine in 1 L of water

Using typical fresh unscented bleach (6% available sodium hypochlorite) with 5.7% (or 57,000 mg/L) available chlorine

(1 L × 200 mg/L) ⁄ (57,000 mg/L) = 0.0035 L of bleach

An alternative formula using percentages

(1 L × 0.02%) ⁄ 5.7% = 0.0035 L of bleach
= 3.5 mL (0.12 fl oz) of typical fresh unscented bleach is needed to create a concentration of 200 mg/L of free chlorine in 1 L of water

Using industrial sodium hypochlorite (12.5% available sodium hypochlorite) with 12% (or 120,000 mg/L) available chlorine

(1 L × 200 mg/L) ⁄ 120,000 mg/L = 0.0017 L of bleach

An alternative formula using percentages

(1 L × 0.02%) ⁄ 12% = 0.0017 L of bleach
= 1.7 mL (0.06 fl oz) of industrial sodium hypochlorite at 12% available chlorine is needed to create a concentration of 200 mg/L of free chlorine in 1 L of water

To Calculate the Dose for the Column of Well Water

Dose = volume of water in well × dose for 1 L of water

Reminder: Dose is dependent on what free chlorine concentration is being targeted (i.e., from not less than 50 mg/L to not more than 200 mg/L per litre), and is also dependent on the % of available chlorine (e.g., 5, 5.25 or 12%).

Example

This example uses the above calculations and the previous well example where the 35 metre deep well has 600 L of water.

To obtain a concentration of 50 mg/L free chlorine using typical fresh unscented bleach with 5% available chlorine, the 600 L is multiplied by 1 mL/L = 600 mL (21 fl. Oz.) of typical fresh unscented bleach.

An alternative formula using percentages

(600 L × 0.005%) ⁄ 5% = 600 mL of bleach

To obtain a concentration of 200 mg/L free chlorine using typical fresh unscented bleach with 5% available chlorine, the 600 L is multiplied by 4 mL/L = 2.4 L (84 fl oz) of typical fresh unscented bleach.

An alternative formula using percentages

(600 L × 0.02%) ⁄ 5% = 2.4 L of bleach

Figure 10-3: Common Measuring Cup to Assist in Calculating Amount of Bleach

Tables to Calculate Dose Using Bleach

Tables 10-1 to 10-4 provide the amount of bleach needed to dose various diameters of wells that will create 50, 100, 150 or 200 mg/L of free chlorine per metre of water column. The calculations previously shown were used to derive Tables 10-1 to 10-4.

If a different concentration of bleach is used, the calculations shown on the previous examples can be used to determine the amount required to dose the well.

Notes regarding Tables 10-1 to 10-4

Reminder: The volume of bleach provided by the tables will have to be multiplied by the depth of the column of well water to determine the dose for the well. The calculations consider well volumes only and do not include the water used for mixing. For additional information see the final note below.

Reminder: To dose the entire well column, the volume of bleach needed in millilitres is obtained from the appropriate Table (Table 10-1 or Table 10-3) and multiplied by the water well column height in metres.

Reminder: If the height of the water well column is measured in feet, the height of the water well column is divided by 5 and multiplied by the volume of bleach in fluid ounces obtained from Table 10-2 or Table 10-4.

Reminder: The tables provide the amounts of bleach required to achieve the target concentrations under the ideal conditions of neutral pH (i.e., 7 pH units), no turbidity and no total dissolved solids. Additional bleach may be needed if these conditions are not met. Test strips or other methods are used to verify that the free chlorine residual achieved is no less than 50 mg/L and no more than 200 mg/L. Not meeting the recommended range can reduce the effectiveness of the treatment.

Reminder: The values in the tables do not account for the volume of any mixing water (typically 25 L or up to 4 to 5 times the volume of the well water column). It is important to consider this factor prior to putting the well into use because additional bleach will be needed to achieve the recommended range (see Table 10-7 or Table 10-8).

Reminder: See Table 10-2 for the equivalent information provided in Imperial measurements.

Reminder: The formula used to calculate this table is based on common well casing diameters in inches. The formula calculates the metric equivalent for diameter, litres per metre and then millilitres based on the initial industry standard diameter. The calculated numbers have then been rounded.

Reminder: See Table 10-1 for the equivalent information provided in metric measurements.

Reminder: When using feet and Imperial fluid ounces, a person needs to divide the entire water column height in the well in feet by 5 and then multiply the result by the corresponding concentration found in the table to obtain the required dose.

Reminder: The formula used to calculate this table is based on common well casing diameters in inches. The calculated numbers have then been rounded.

Reminder: See Table 10-4 for the equivalent information provided in Imperial measurements.

Reminder: The formula used to calculate this table is based on common well casing diameters in inches. The formula calculates the metric equivalent for diameter, litres per metre and then millilitres based on the initial industry standard diameter. The calculated numbers have then been rounded.

Reminder: See Table 10-3 for the equivalent information provided in metric measurements.

Reminder: When using feet and Imperial fluid ounces, a person needs to divide the entire water column height in the well in feet by 5 and then multiply the result by the corresponding concentration found in the table to obtain the required dose.

Reminder: The formula used to calculate this table is based on common well casing diameters in inches. The calculated numbers have then been rounded.

Calculating Chlorine Solution Dose Amounts Using Calcium Hypochlorite Powder

The following calculations are provided to be used in conjunction with Table 10-5 and Table 10-6 to assist the person in calculating the correct dose for the well.

To Dose 1 Litre of Water to 50 mg/L of Free Chlorine

1 L = 1 Kg or 1,000 g of water

To obtain the weight of a calcium hypochlorite powder at 65% available chlorine to create a dose of 50 mg/L (0.005%)

(1 kg × 0.005%) ⁄ 65% = 0.00008 Kg

= 0.00008 kg (0.003 ounces) of calcium hypochlorite powder is needed to create a concentration of 50 mg/L of free chlorine in 1 L of water

To Dose 1 L of Water to 200 mg/L of Free Chlorine

To obtain the weight of a calcium hypochlorite powder at 65% available chlorine to create a dose of 200 mg/L (0.02%):

(1 kg × 0.02%) ⁄ 65% = 0.0003 kg

= 0.0003 kg = 0.3 g (0.01 oz) of calcium hypochlorite powder is needed to create a concentration of 200 mg/L of free chlorine in 1 L of water

To Calculate Dose for the Column of Well Water

Volume of Water in well = Weight of Water in Well × free chlorine residual desired [e.g., 50 mg/L (0.005%) or 200 mg/L (0.02%)] divided by % of available chlorine (65%).

Example

Use the above calculations and the previous well example where the 35-metre deep well has 600 L of water (600 L of water = 600 kg of water).

To obtain a concentration of 50 mg/L free chlorine using calcium hypochlorite powder with 65% available chlorine

(600 kg × 0.005%) ⁄ 65% = 0.046 kg = 46 g (1.62 oz)

To obtain a concentration of 200 mg/L free chlorine using calcium hypochlorite powder with 65% available chlorine

(600 kg × 0.02%) ⁄ 65% = 0.185 kg = 185 g (6.52 oz)

Tables To Calculate Dose Using Calcium Hypochlorite Powder

Table 10-5 and Table 10-6 provide the amount of calcium hypochlorite powder (at 65% available chlorine) needed to dose various diameters of wells that will create 50, 100, 150 or 200 mg/L of free chlorine per metre of water column. The calculations shown previously were used to derive Table 10-5 and Table 10-6.

If a different concentration of calcium hypochlorite powder is used, the calculations shown previously can be used to determine the amount required to dose the well.

Notes Regarding Table 10-5 and Table 10-6

Reminder: The volume of calcium hypochlorite powder provided by the tables will have to be multiplied by the depth of the column of well water to determine the dose for the well. The calculations consider well volumes only and do not include the water used for mixing. For additional information, see the final note below.

Reminder: To dose the entire well column, the volume of calcium hypochlorite required in grams is obtained from Table 10-5 and multiplied by the water well column height in metres.

Reminder: If the height of the water well column is measured in feet, the height of the water well column is divided by 5 and multiplied by the volume of calcium hypochlorite in ounces obtained from Table 10-6.

Reminder: The tables provide the amounts of calcium hypochlorite needed to achieve the target concentrations under the ideal conditions of neutral pH (i.e., 7 pH units), no turbidity and no total dissolved solids. Additional calcium hypochlorite may be needed if these conditions are not met. Test strips or other methods can be used to verify that the free chlorine residual achieved is no less than 50 mg/L and no more than 200 mg/L. Not meeting the recommended range can reduce the effectiveness of the treatment.

Reminder: The values in the tables do not account for the volume of any mixing water (typically 25 L or up to four to five times the volume of the well water column). It is important to consider this factor prior to putting the well into use because additional calcium hypochlorite will be needed to achieve the recommended range (see Table 10-7 or Table 10-8).

Reminder: See Table 10-6 for the equivalent information provided in Imperial measurements.

Reminder: The formula used to calculate this table is based on common well casing diameters in inches. The formula calculates the metric equivalent for diameter, litres per metre and then millilitres based on the initial industry standard diameter. The calculated numbers have then been rounded.

Reminder: See Table 10-5 for the equivalent information provided in metric measurements.

Reminder: When using feet and imperial fluid ounces, a person needs to divide the entire water column height in the well in feet by 5 ft and then multiply the result by the corresponding concentration found in the table to obtain the required dose.

Reminder: The formula used to calculate this table is based on common well casing diameters in inches. The calculated numbers have then been rounded.

Preparing Mixing Dose Above Ground Surface

Adding bleach or calcium hypochlorite powder directly to the well typically does not allow for a uniform dose of the well water column and makes it almost impossible to control the pH. To properly mix and, if necessary, control the pH, it is important to create the mixing dose above the ground surface. Therefore, extra water used to create the mixing dose has to be added to the water well column volume to provide the total water needed to be dosed.

If 25 L of water is used to mix the solution above the ground surface, then Table 10-7 or Table 10-8 provides the amount of unscented bleach and weight of calcium hypochlorite powder required to dose the 25 L (or 5 gal) of extra water used to mix the chlorine solution at 50, 100, 150 and 200 mg/L.

Reminder: See Table 10-8 for the equivalent information provided in Imperial measurements.

Reminder: See Table 10-7 for the equivalent information provided in metric measurements.

Formula for pH Control During Chlorination

Mixing hypochlorite solutions will raise the pH and decrease the amount of effective hypochlorous acid available for disinfection. To control the pH, acids such as white vinegar can be added to the mixing water prior to adding the bleach. If the alkalinity of the water is measured or known then the following formula can be used:

Litres of White Vinegar = (Mixing Water Alkalinity ⁄ 100) × (Chlorine Dose ⁄ 500) × (Mixing Water Volume (Litres) ⁄ 100 )
or
Gallons of White Vinegar = (Mixing Water Alkalinity ⁄ 100) × (Chlorine Dose ⁄ 500) × (Mixing Water Volume (Gallons) ⁄ 100 )

Reminder: Alkalinity and chlorine dose are in milligrams per litre and volume is in litres and Imperial gallons.

Procedure For “Shock” Chlorination

To “shock” chlorinate a new or altered well after the initial disinfection steps have taken place, it is recommended that the person constructing the well dose the well to obtain a free chlorine concentration of not less than 50 mg/L and not more than 200 mg/L.

The following is only one suggested method of dosing the well with best practices that achieve a free chlorine concentration of not less than 50 mg/L and not more than 200 mg/L.

Suggested Method of Dosing the Well Water

The steps for this recommended treatment approach are to:

Step 1: Calculate the volume of the well water in the well column. Also, mixing water should be added to the calculated volume of the well water in the well column (e.g., an additional 25 L of water).For example, the well has 375 L of water in the well column and the person will use 25 L of water to mix. The actual volume of water that needs to be dosed to not less than 50 and not more than 200 mg/L free chlorine is 375 + 25 = 400 L. These additional 25 L of clean water are the typical volume of water used in the mixing of the chlorine solution at the site. In other cases where the well and the aquifer space around the well need to be treated, the additional water may be five times the volume of the water well column.

Step 2: Determine the free chlorine concentration (e.g., 50, 100, 150 or 200 mg/L) within the required range needed to achieve the most effective treatment. It is also necessary to determine the type of hypochlorite product (e.g., bleach or calcium hypochlorite powder) that will be used in the treatment process. For better mixing results use fresh, unscented bleach.

Step 3: Calculate the amount of chlorine solution required to achieve the most effective treatment determined in Step 2. To determine the dose needed to achieve 50, 100, 150 or 200 mg/L free chlorine in the well refer to Table 10-1 to Table 10-6. To determine an alternate concentration of free chlorine within the required range of 50 to 200 mg/L see the formulas on “Percent Volume of Bleach Required” section of this chapter.

Step 4: Place the calculated mixing water (e.g., 25 L) in a clean container set on the ground surface. The mixing water should be clean and potable. Combine the mixing water with the calculated amount of chlorine product in the container. When placed into the well, the calculated amount of chlorine product should be able to create the desired concentration of free chlorine in a single well volume.

Reminder: See “Best Management Practice – Mixing Large Volume of Clean and Potable Water, Vinegar and Chlorine Products Prior to Dosing the Well to Achieve Higher Concentrations of Hypochlorous Acid,” below.

Step 5: Prepare the chlorine solution by adding the calculated amount of liquid bleach or calcium hypochlorite powder to the mixing water into the container, taking into account pH levels and other factors that will impact the effectiveness of the dose.

Step 6: Pour this solution in the well and adequately mix to distribute the dose throughout the well column and let it stay undisturbed in the well for a minimum of twelve (12) hours. Pouring should be done at a rate where the solution will not overflow out of the well. Pouring options to ensure the mixture is distributed throughout the entire well column include the following:

• The chlorine dose is poured into the test hole or dewatering well. A clean and spray-chlorinated drill string with a surge block or other development tool is moved up and down in the well column. Surge blocks are very effective in wells with well screens.
• Using an injection pump on a rig, the chlorine dose is pumped into the well. Then, the rig is used to surge the well with air. The surging technique lifts the column of water without discharging the water out of the well and drops it back down. The technique will mix the solution in the well column.
• The chlorine dose is poured into a larger diameter test hole or dewatering well while the well water is re-circulated with a pump, other than the water supply pump (i.e., discharging pumped water back into the well).
• The chlorine dose is placed into the bailer. The bailer is raised and lowered to agitate the well water.
• A clean and spray-chlorinated tremie pipe is installed near the bottom of the well. Then, the chlorine dose is injected into the well through the tremie pipe and allowed to discharge into the well. The tremie pipe is raised during the injection process to mix the dose throughout the entire well water column. This method can be used for both drilled and driven-point wells.
• A jetting tool is installed into the well. Then the chlorine dose is injected throughout the well water column using the jetting tool.

Reminder: It is important to conduct a free chlorine residual test shortly after dosing the well to ensure the free chlorine residual is within the recommended range and will likely be in the same range during a recommended treatment period of at least 12 hours to not more than 24 hours after dosing the well. If the testing shortly after dosing shows a problem (< 50 or > 200 mg/L free chlorine) the person constructing the well can immediately:

• discharge or dispose of the chlorinated water in an approved manner (See “Handling Heavily Chlorinated Water Discharge” section of this chapter) and re-dose the well with another chlorine solution, or
• adjust the concentration of the free chlorine accordingly by either adding water or adding additional chlorine solution.

Reminder: In highly fractured bedrock environments or highly permeable overburden environments, there is a potential for heavily chlorinated water to migrate from the well off-site to receptors (e.g., wells, rivers, streams). The person constructing the well should carefully calculate the volume and concentration of the chlorinated water to reduce the risk of off-site impacts and take all reasonable care to prevent the movement of chlorinated water off-site. It may be advisable to monitor off-site wells for free chlorine and have a contingency plan in case chlorinated water impairs off-site wells or other receptors.

Step 7: Obtain a grab sample of the well water using clean sampling equipment and bottles at least 12 hours and not more than 24 hours after dosing the well to verify the concentration of the free chlorine residual. The grab sample should be tested for free chlorine residual. Testing can be done using simple test strips (see Figure 10-4) similar to pH test strips shown in (see Figure 10-2). If the free chlorine residual is within the required range (50 to 200 mg/L), see Step 10. If it is outside the range, see Step 8.

Figure 10-4: Measuring Free Chlorine

Figure 10-4 shows an example of a free chlorine residual test strip (at the top of figure) and a comparison chart for various free chlorine residual concentrations. The test strip is placed into the chlorinated water solution and changes colour. The test strip’s colour is matched to the comparison chart, which has the corresponding free chlorine residual concentration. In this case, a test strip for the 0 to 120 mg/L range shown at the top of Figure 10-4 was placed in the chlorinated water. The blue colour on the test strip matches a free chlorine residual of 30 mg/L on the 0 to 120 mg/L free chlorine residual comparison chart (shown in the middle of Figure 10-4). In this case, it is recommended that additional work be done to bring the free chlorine in the water above 50 mg/L but not more than 200 mg/L. A 0 to 750 mg/L free chlorine residual comparison chart is also shown in the bottom of Figure 10-4. The 0 to 750 mg/L free chlorine residual comparison chart also has similar test strips for testing free chlorine residual in water.

Step 8: Pump the well water out of the well until it has a free chlorine residual concentration of less than 1 mg/L if the test shows a free chlorine residual below 50 mg/L or more than 200 mg/L. A sample of the water should be obtained in a clean sample container and use the test strips and comparison chart shown in Figure 10-4 can be used to determine the free chlorine concentration. See Step 9.

Reminder: See the “Handling Heavily Chlorinated Water Discharge” section in this chapter for details on how to properly discharge or dispose of heavily chlorinated water.

Step 9: Repeat steps 1 to 7 until the test shows the recommended free chlorine residual concentration range is between 50 to 200 mg/L after 12 hours and not more than 24 hours after the water is re-dosed if Step 8 applies (i.e., the free chlorine residual is outside of the recommended range).

Step 10: Pump the well water out of the well until the well water has a free chlorine residual concentration of less than 1 mg/L after a test in accordance with Step 7 shows the free chlorine residual is within the target range (50 to 200 mg/L). The person constructing the well can obtain a sample of the water in a clean sample container and use the test strips and comparison chart shown in Figure 10-4 to determine the free chlorine residual.

Reminder: See the "Handling Heavily Chlorinated Water Discharge," section of this chapter for details on how to properly discharge or dispose of heavily chlorinated water.

Step 11: Indicate on the well record that the well has been disinfected if a well record is to be completed.

Restricting Water Use During “Shock” Chlorination Period

Handling Heavily Chlorinated Water Discharge

Collection and Analysis of Water Samples for Indicator Bacterial Parameters

In cases where test holes and dewatering wells are disinfected, the proper collection and analysis of well water samples after a “shock” chlorination treatment are a good way to determine if the chlorination treatment was successful.

Reminder: See the “When Should Disinfection Not Take Place” section of this chapter for situations when test holes and dewatering wells should not be “shock” chlorinated.

When well water is tested for bacterial (as opposed to chemical) parameters, typically laboratories test for certain bacteria called indicator organisms or indicator bacteria. The indicator bacteria usually show up in a test result if water has become contaminated by surface water runoff, soil bacteria, animal waste, sewage waste or some agricultural activities.

Indicator Bacteria

There are two common indicator organisms that accredited and licensed laboratories will test for in a well water sample. These are total coliform and Escherichia coli (E. coli).

Total Coliform

Total coliform refers to:

• a general family of bacteria that is found in animal and human wastes, surface soils and vegetation,
• the presence of total coliform may indicate contamination of water with disease-causing organisms, and possible evidence of surface water runoff contamination in well water, and
• the presence of total coliform provides an early warning signal that there may be a problem with the test hole or dewatering well.

E. Coli

E. coli are a group of bacteria that live in the intestines of warm-blooded animals. The presence of E. coli:

• indicates fecal contamination from sources such as human sewage or livestock waste.
• may indicate that there may be a problem with the test hole or dewatering well.

Interpretation of Laboratory Analysis

If the three test results, as explained in the “Best Management Practice – Sampling and Analyzing Well Water” in this chapter, report no E. coli and no total coliform present, then the well water has been successfully disinfected.

In cases where test holes and dewatering wells are not intended to encounter such indicator bacteria but if the test results show the presence of indicator organisms, it is important to take further action to protect the groundwater resource and ensure no bias in sampling. Some options include:

• re-sampling the well to verify the initial sample results, and
• sampling for various chemical or bacterial parameters. If the presence of indicator organisms were confirmed, it is important for the Professional Geoscientist or Professional Engineer involved in the construction of the test hole or dewatering well to:
  • assess the hydrogeology and the well,
  • identify the source or sources of contamination, and
  • provide recommendations.

Reminder: In cases where the Professional Geoscientist or Professional Engineer identifies a potential source of off-site contamination, it is important to contact and report the issue to the local Ministry of the Environment and Climate Change office (see resources at the end of this manual for Ministry office locations and telephone numbers) or the Ministry’s Spills Action Centre at 1-800-268-6060.