4. Water Table: is the level at which the groundwater pressure is equal to atmospheric pressure.
Aquitard: is a zone within the earth that restricts the flow of groundwater from one aquifer to another. Aquitards comprise layers of either clay or non-porous rock with low hydraulic conductivity.
Unconfined aquifer: It is an aquifer with the water table as its upper boundary. Because the aquifer is not under pressure the water level in a well is the same as the water table outside the well.
Confined aquifer: It is an aquifer found between two relatively impermeable layers.

5. Borehole: It is a narrow shaft drilled in the ground as part of a groundwater site assessment.
Groundwater Recharge: The natural or intentional infiltration of surface water into the groundwater system.

36. Tutorial
1)An extensive aquifer is known to have a groundwater flow in N 30o E direction. Three wells A,B and C are drilled to tap this aquifer. The well B is to East of A and the well C is to North of A. the following are the data regarding these wells: Estimate the elevation of water table at well C

37. 2) A confined aquifer is 25 m thick and 2 km wide
2) A confined aquifer is 25 m thick and 2 km wide. Two observation wells located 2 km a part in the direction of flow indicate heads of 45 and 39.5 m. if the coefficient of permeability of the aquifer is 30 m/day, calculate (a) the total daily flow through the aquifer and (b) the piezometric head at the observation well located 300 m from the upstream well.