A 'Wide Protection Zone' (Zone III) serves to protect wells against long-range impairments, notably against contamination by non-degradable or less readily degradable chemical or radioactive substances, and usually covers the entire subsurface catchment area. If the catchment area is very large, with a boundary more than 2 km from the well, it may be subdivided into Zone III A and Zone III B, with different levels of land use restrictions.