How must all gravel used in gravel packed wells be treated before placement?

Gravel used in gravel packed wells must be disinfected in at least 50 ppm chlorine before placement to ensure that it is free from harmful microorganisms that could contaminate the well water. This step is crucial for maintaining the safety and quality of drinking water because the gravel acts as a filter that can harbor bacteria or other pathogens. Proper disinfection not only protects the integrity of the water supply but also adheres to best practices in well construction, promoting public health.

In contrast, heating gravel or mixing it with sand does not address the potential for microbial contamination. Similarly, while packing the gravel tightly against the screen might be necessary for structural stability and filtration efficiency, it does not ensure that the gravel itself is safe for use in water extraction. Thus, disinfection prior to placement is the most critical step in preparing gravel for use in well construction.