Aquifers that are recharged directly by the infiltration of rain or snow melt through the overlying ground surface are called aquifers. these aquifers have a which is the boundary between the saturated zone and zone of aeration. these aquifers are highly susceptible to by activities at the ground surface.
2. aquifers are overlain by or sandwiched between extensive impermeable strata called . these aquifers cannot be directly recharged by through the overlying materials. instead, recharge is delivered slowly from regions where the aquitard is not present or where the aquifer is exposed nearer the ground surface. when wells are drilled into these aquifers, the confining exerted by the accumulation of water in the aquifer and the weight of the overlying strata will force water up into the wells. the force on the water is called pressure. when the groundwater is under a significant amount of artesian pressure the groundwater will flow directly to the surface without the use of pumps. these wells are said to be artesian wells.