The nature of the geology is going to determine what becomes dissolved in the groundwater. For example, calcium bicarbonates are going to dissolve in the water if the formation contains carbonates. Many different types of bacteria that could cause the typical depositions of iron are abundant in subsurface environments. There has been a lot of research which supports how widespread microorganisms are in the subsurface environment. Although rare, there may be some situations when one type of microorganism may be introduced by such things as well-drilling equipment. This can prove to be an essential part of the community of microorganisms which could then cause plugging. Most people are therefore very concerned to determine whether the well is subject to the surface water infiltration because it means that the water treatment process is going to have to be scaled up to surface water standards.