Which of the following can cause a well screen to become clogged?

The presence of iron bacteria and calcium hardness can lead to the clogging of a well screen. Iron bacteria are microorganisms that thrive in iron-rich water and can create a gel-like substance that accumulates and obstructs the well screen openings. As this material builds up, it not only inhibits water flow but can also create an environment that allows more sediment and bacterial growth, further compounding the clogging issue.

Calcium hardness refers to the concentration of calcium ions in water. High levels of calcium can lead to scale formation, where minerals precipitate out of the water and adhere to the surfaces of the well screen. This scaling can effectively block water flow into the well, resulting in reduced water yield and potentially requiring maintenance or rehabilitation of the well.

While the options regarding silt and sand, excessive pumping, and temperature variations can also affect a well screen, they do not specifically address the biological and chemical processes at work with the clogging caused by iron bacteria and calcium hardness. These processes illustrate the complex interactions that can occur within a well environment, leading to eventual clogging right at the well screen where water entry occurs.