Groundwater is the water that soaks into the ground from rain or melting ice and snow that then moves downward to fill in the cracks and spaces in soil, sand and rock until it reaches the saturated zone where the groundwater is freely flowing. Groundwater accounts for up to 20% of all the fresh water on earth.
The top of this saturated layer is called the water table. The height of this water table also effects the local surface water. If the water table drops too low, creeks and rivers on the surface will start to run dry, which frequently happens in late August. A prime example of this can be seen in Arizona where due to excessive groundwater pumping the water table has dropped and the Santa Cruz River has stopped flowing for several years.
When a well is drilled to supply water to a home, community or for some other use, it must be seated in the water table. This is referred to as a production well. When the installed pump is turned on a cone of depression will be formed, caused by the recharge rate of the aquifer being less than the pumping rate of the well. It is important to install monitoring wells in the water table beyond the cone of depression in order to accurately monitor any changes to the water table. Conversely, if you are using reclaimed water to recharge your groundwater, you will get what is known as “mounding” until the water can evenly distribute through the water table.
If the amount of groundwater extracted causes the water table to drop permanently, your well can become a “dry well” and a new deeper well will have to be installed. This is why monitoring of the groundwater levels is so vital. Over-pumping will de-water the area, reducing well yield and even leading to the well no longer producing.
The underground area where Groundwater is collected is referred to as an aquifer. Some materials are more porous and the water can travel more easily through these layers. Sand, gravel, sandstone, and fractured limestone are very porous and can conduct water easily making them ideal aquifers. Clay and granite on the other hand are not as water permeable and are considered aquitards, an area that does not transmit water easily and will comprise the walls of the aquifer. An aquifer surrounded by aquitards is considered a confined aquifer, while an unconfined aquifer is only partially limited in motion. The water table is considered the top of the first unconfined aquifer. While the water comprising the unconfined aquifer water table is usually very fresh, consisting of recent rain or snowfall, the deeper confined aquifer can be made up of much older water that collected years or centuries ago. These deeper aquifers recharge much more slowly and if used as a water source can be over-pumped and depleted. While they are more resistant to surface contamination they can also be more briny or salty.
Heron Instruments has a variety of ways to simplify your groundwater monitoring projects. Our dipper-T will give you an immediate accurate groundwater level while our dipperLog can be deployed to track seasonal and demand based water level fluctuations over a period of time. With these tools in your arsenal you will be ahead of any major groundwater changes.