Aquifers are permeable layers of rock that hold enough groundwater to supply wells. The level of an aquifer or height of the water table can be measured by checking the elevation of water in wells dug into the layer.
The level of water in an aquifer changes over time. If the amount of water put into the aquifer (recharge) is higher than the amount taken out of the aquifer (discharge), then the water level in the aquifer goes up. If discharge is greater than recharge, the water level goes down.
! Examine the graph showing water levels in the Arapahoe aquifer over time.