Many aquifers are hydrogeologically classified as two types of soil and rock.
The pore and permeability of fractured rocks are larger than those of soil. In permeable zones of fractured rock, ground water is very easy to flow, and water level rises rapidly under rainfall.
The lava-flows in Fuji region with cooling joints, fractures, tubes, vesicles have the highest transmissivity. According to the observation data of wells in the lava-flows, the cyclic fluctuations of the water level reflect recharge from seasonal rainfall. The serious salt-water intrusion into the lava-flows since 1960 occurred as the result of overdraft in the region.
The management of ground-water resources was started in 1967, and the net effect of the regulation of pumping is the rapid rising of the regional water level and the recovery of fresh water in the salt-water contaminated lava-flows after several years.