To disinfect a new well, a chlorine dosage of at least ______ mg/L of chlorine is required.

To disinfect a new well, a chlorine dosage of at least ______ mg/L of chlorine is required.

• A. 10
• B. 25
• C. 50
• D. 100

Answer: (C)

Shock chlorination of a new well relies on using a high chlorine dose to overcome chlorine demand and ensure disinfection throughout the well and any connected piping. A minimum concentration of about 50 mg/L provides a strong, effective residual that can inactivate bacteria and other contaminants during the contact period, typically 12–24 hours, before flushing and retesting. This level is recommended because it reliably treats the well components, allows chlorine to penetrate sediments and biofilm, and gives a clear indication of whether the system is free of pathogens once flushing is complete. Lower dosages, such as 10 or 25 mg/L, may not consistently achieve the necessary disinfection throughout the entire system, especially in the presence of organic matter or minerals that consume chlorine. A much higher dose, like 100 mg/L, is generally more than required for a standard shock and can cause taste/odor issues and potential corrosion without additional disinfection benefits. Therefore, 50 mg/L is considered the appropriate minimum for disinfecting a new well.

Shock chlorination of a new well relies on using a high chlorine dose to overcome chlorine demand and ensure disinfection throughout the well and any connected piping. A minimum concentration of about 50 mg/L provides a strong, effective residual that can inactivate bacteria and other contaminants during the contact period, typically 12–24 hours, before flushing and retesting. This level is recommended because it reliably treats the well components, allows chlorine to penetrate sediments and biofilm, and gives a clear indication of whether the system is free of pathogens once flushing is complete.

Lower dosages, such as 10 or 25 mg/L, may not consistently achieve the necessary disinfection throughout the entire system, especially in the presence of organic matter or minerals that consume chlorine. A much higher dose, like 100 mg/L, is generally more than required for a standard shock and can cause taste/odor issues and potential corrosion without additional disinfection benefits. Therefore, 50 mg/L is considered the appropriate minimum for disinfecting a new well.