A characteristic disadvantage of bored wells is:

Bored wells are typically dug using a large-diameter drill and can be vulnerable to surface contamination. Their design means that they often do not produce a protective seal against pollutants that can seep down through the soil and groundwater. The large diameter allows for more surface water and contaminants to enter the well, significantly increasing the risk of pollution compared to deeper wells that have better geological barriers. This susceptibility to pollution is a major concern for public health and safety regarding drinking water supplies.

In contrast, while factors like a large diameter (which allows for easier access to water) and excessive depth might seem to raise concerns, they are not characteristic disadvantages. The high yield of water can also be advantageous rather than detrimental; many well designs aim to maximize water yield for efficiency. Hence, the primary drawback remains the potential for contamination, which makes option B the most fitting answer.