Final answer:
The recommended residual of free chlorine for newly completed wells is a vital safety measure to ensure water quality by effectively disinfecting the water supply, but the exact recommended amount may vary.
Step-by-step explanation:
When a new well is completed, it is necessary to disinfect the well, pump, and screen; a specific residual of free chlorine is recommended.
Disinfection is important to ensure the safety of the water supply by killing harmful bacteria and other pathogens. The efficiency of chlorination depends on the form of the chlorinating species, predominantly free chlorine, which includes forms such as Cl2, HOCl and OCl-. These forms of chlorine are available for disinfecting the water supply and contribute to the free chlorine residual. This residual is what remains after the chlorine demand has been met — the amount of chlorine that has reacted with contaminants but still maintains levels sufficient for disinfection.
It's necessary to establish the correct amount of chlorine to achieve the desired disinfection levels — too much chlorine can be harmful to humans, while too little may not effectively eliminate harmful organisms from drinking water. The recommended residual of free chlorine, as set by various health and safety guidelines, is typically specified in parts per million (ppm), but the exact amount can vary depending on several factors, including water quality and local regulations.