Final answer:
High likelihood aquifers include unconsolidated gravel and sand, conglomerate, and sandstone due to their high porosity and permeability. Low likelihood aquifers tend to be granite and gneiss owing to low porosity and lack of fractures. The depth of a new well is determined by the depth at which permeable layers are located.
Step-by-step explanation:
The likelihood of a rock formation being a good aquifer largely depends on its porosity and permeability. Materials with high porosity and interconnected pore spaces, like unconsolidated gravel and sand, sandstone, and conglomerate, offer a high likelihood of being good aquifers. Such materials allow for significant water movement and storage. On the other hand, rocks with low porosity and lacking in fractures or cracks, such as granite and gneiss which are igneous and metamorphic rocks respectively, are low likelihood candidates for aquifers due to their poor ability to transmit water.
In the field of hydrogeology, a good approach to locating potential groundwater supplies is by studying the stratigraphy of rock layers and looking for laterally continuous sand layers that would likely serve as the best aquifers. The minimum depth for a new well would depend on the local geology and the depth at which these permeable layers are found.