A groundwater table, also known as a water table, is the underground boundary between the soil surface and the area where the groundwater sits in spaces between sediments and rocks.
Groundwater is the best reserve of freshwater that the United States has.
Thus, we must understand how this resource works and the best ways to care for it.
Here’s what you should know about the groundwater table as a landowner and steward of the planet.
1. What is groundwater?
Groundwater is water found in the cracks and spaces in the soil, sand, and rock.
However, contrary to popular belief, groundwater doesn’t form underground “rivers.”
Instead, it fills all the existing pores and fractures in underground material.
About 30 percent of all readily available freshwater on the planet is groundwater.
Groundwater is a resource we should both protect and harvest when possible.
Compared to surface water, groundwater is more convenient, less expensive, and less vulnerable to pollution.
Of all states, California withdraws the most groundwater.
Globally, over 2 billion people rely on groundwater as their primary water source.
2. What is a groundwater table?
A groundwater table is the upper level of an underground surface in which the soil or rocks are permanently saturated with water.
This water table separates two zones — the groundwater zone (below it) and the capillary fringe (above it).
3. Where does groundwater originate from?
Most groundwater comes from precipitation infiltrating the surface into the soil zone.
Once the soil becomes saturated, the water percolates downward.
4. What factors impact the groundwater table?
Topography is the upward and downward tilts of the land.
In most cases (but not always), groundwater tables follow the topography of the land above them.
In some cases, the water table may intersect with the land surface and features such as a spring, oasis, canyon, cliff, sloping hillside, etc.
The geology of the groundwater table is often responsible for how much water can filter into the zone of saturation.
This is because light, porous rocks can hold more water the heavy, dense rocks.
For example, an area with pumice — a light, porous rock — is more likely to hold a full aquifer than an area that has hard granite or marble.
The weather also greatly affects the groundwater table.
These tables are often higher in rainy seasons, which is when they recharge.
Spring is the season when you’ll find the fullest groundwater table because it has a lot of precipitation and snow melts from the winter.
Ground cover can also contribute to an area’s water storage in the groundwater table.
Areas with spongy and absorbent vegetation like swamps have saturated groundwater almost year-round.
Their water tables are shown to be nearly level or even higher than the surface.
The final factor that affects the water table is land use.
Urban areas have more impervious surfaces like parking lots and roads.
This means that water becomes runoff instead of entering the area’s zone of saturation.
In these cases, the groundwater table will decline.
Additionally, land use can also contribute to the pollution of groundwater in an area.
5. Where does groundwater occur?
Groundwater is everywhere beneath the soil surface.
It exists in most places if it’s allowed to recharge.
Humans can access it through springs, lakes, rivers, streams, and manmade wells.
Groundwater is used for domestic, industrial, commercial, and agricultural purposes.
It’s a limited resource, and thus, we must take care to not pump out too much groundwater at once.
Wells can dry up if groundwater is not recharged faster (or at the same rate) than it is removed.
6. How does groundwater move?
Believe it or not, groundwater is constantly moving due to the force of gravity.
Gravity moves the water from recharge areas to discharge areas.
In most areas, this movement is rather slow at just a few feet per year.
However, in more permeable zones like solution channels in limestone, movement can be several feet per day.
You can see evidence of groundwater moving in rock and soil through road cuts.
This is most visible in winter because the water will freeze when it emerges from the rock.
Sometimes the water will emerge along rock layers, and at other times, it’ll appear along vertical fractures.
7. What are the seasonal patterns for groundwater table recharge and storage?
In areas where the ground commonly freezes, it is less common for the groundwater table to recharge from rain or snowmelt during the winter.
This causes the water table to fall as it’s used as a resource.
Over time, the saturated zone beneath the water table may be recharged by precipitation or the excess water that’s not discharged to streams.
The rising water table increases groundwater storage in the aquifer system.
The decline or recharge in the water storage that occurs largely depends on the season.
Late spring, summer, and early fall – evaporation and transpiration by plants capture most of the water that would help to recharge the aquifer
Winter – freezing of the soil prevents recharge and causes a decline in storage
Early spring – frequent precipitation causes a rapid increase in storage and a rise in the water table
8. What are the effects of long-term climatic trends on groundwater tables?
There are long-term trends that impact the variations in precipitation, and as precipitation is the main source of groundwater, many people wonder what that will mean for the groundwater supply.
During periods of long-term, above-average precipitation, the water table may rise close to the surface and interfere with both home construction and waste disposal.
For instance, some people may see flooding in their basements when the groundwater table rises significantly due to an increase in precipitation.
Conversely, long periods of below-average precipitation will cause the groundwater table to decline and aquifer levels to lower.
9. What types of wells exist?
While there is a huge amount of groundwater below your feet, it can only be pumped for use when it’s found in aquifers.
Aquifers are when a water-bearing rock readily transmits water to wells and springs.
When you drill into an aquifer, you can pump the water out.
The environment then relies on precipitation to refill the porous rock.
Here are the types of wells that can be dug to access groundwater.
Dug wells are constructed in the ground by shovel or backhoe.
Typically, this type of well was excavated below the groundwater table until incoming water exceeded the digger’s bailing rate.
The well was then cased with stones, brick, tile, or another material to prevent the well from collapsing and covered with a cap of wood, stone, or concrete
Dug wells weren’t normally very deep (around 10 to 30 feet) because it is so difficult to dig beneath the groundwater table.
Of all types of wells, these have the highest risk of becoming contaminated.
Certain features can help prevent contamination, such as:
- Casing the well with watertight material like tongue-and-groove precast concrete and a cement grout or bentonite clay sealant poured along the outside of the casing to the top of the well
- Covering the well with a concrete curb and cap that stands about a foot above the ground
- Mounding the land surface around the well so that the surface water runs away from the well and doesn’t pool around the outside of the wellhead
- Placing the pump for your well inside your home or in a separate pump home rather than in a pit next to the well
- Avoiding any activities that may contaminate a dug well
This type of well pulls water from the water-saturated zone above the bedrock just like dug wells.
However, driven wells can be deeper than dug wells at 30 to 50 feet deep.
It’s best to dig driven wells in areas with thick sand and gravel deposits where the groundwater table is within 15 feet of the surface.
When placed properly, these wells are often easy and inexpensive to install.
Although less risky than dug wells, these wells are still shallow which means they can be contaminated by nearby land activities.
The following construction features can improve them.
- Driving assembled lengths of two inch to three inch diameter metal pipes into the ground
- Creating a screened “well point” located at the end of the pipe to help drive the pipe through the sand and gravel (this screen also filters out the sediment)
- Capping the well and pit with the same large-diameter concrete tile used for a dug well
- Use a tight-fitting concrete curb and cap with no cracks that sit about a foot above the ground
- Slope the ground away from the well so that the surface water will not enter the pond
- Casing the access pit with pre-cast concrete
- Placing the pump of the well either on top of the well or in the house
Drilled wells are the deepest of all types.
They penetrate about 100 to 400 feet into the bedrock.
When bedrock is found at the surface, it’s commonly called a ledge.
A drilled well intersects bedrock fractures containing groundwater to find a water supply.
Here are the best well-construction features that minimize contamination.
- Casing the well in metal or plastic pipe as this will help prevent shallow water from entering the well
- Laws will often dictate how much this casing must extend into the ground (for example, at least 18 feet) as well as the bedrock
- Installing submersible pumps near the bottom of the well (sometimes drilled wells with shallow water tables may feature jet pumps located inside the home)
- Incorporating a pitless adapter to provide a sanitary seal at the point where the discharge water line leaves the well to enter your home
10. How can you find the depth of the groundwater water table in a specific location?
The depth of a water table isn’t an exact science.
It can rise or fall depending on the time of year.
The water table is generally most plentiful in the late winter or early spring when the accumulated snow starts to melt and spring precipitation is most robust.
The summer is the opposite.
During this time, it’s typically the hottest and driest period of the entire year.
Additionally, water-loving plants normally begin to grow again in the spring and require a lot of water to maintain their growth.
If you want to find the depth of the water table at any given time, it’s best to measure the water level in a shallow well with a measuring tape.
If no wells are available, then surface geophysical methods can sometimes be used.
However, these methods often rely on surface accessibility for electric or acoustic probes.
You can also consider checking a database with depth-to-water measurements; although, these aren’t always up to date.
The USGS National Water Information System – NWIS Mapper
The National Groundwater Monitoring Network’s data portal
Your state government’s database of drillers’ logs
11. How does groundwater get polluted?
Unfortunately, while it’s less vulnerable to pollution, groundwater is still heavily susceptible to environmental issues.
One big reason for this is that groundwater is less visible than surface water, which means when it becomes polluted it’s more difficult to see and diagnose the issue.
It’s also more complicated to clean up than pollution in rivers and lakes.
Additionally, while groundwater will typically look clean and clear because the ground filters out particulate matter, looks can be deceiving.
Both natural and human-induced chemicals have been found in groundwater that appears “clean.”
Here’s a list of the contaminants found in groundwater (typically collected as it flows through the ground).
- Dissolved solids
- Volatile organic compounds
- Plasticizers, chlorinated solvents, benzo[a]pyrene, and dioxin
- Coliform bacteria
Visit here to learn more about the Contamination of Groundwater.
12. How do you protect and conserve groundwater?
If you’re a landowner looking for ways to protect and conserve groundwater, here are a few ideas that can keep you mindful of the groundwater table beneath your feet.
Choose native plants for your landscaping to avoid extensive watering or chemical applications
Reduce chemical use in your home and around your yard
Manage your waste properly, especially when it comes to toxic substances
Don’t let your water run when you’re shaving or brushing your teeth
Fix any dripping faucets, fixtures, toilets, or taps in your home
Limit yourself to just a short (5-minute) shower and only run full loads of dishes or laundry
Water your lawn and plants wisely — only during the cool hours of the day and when your vegetation truly needs it
Reduce the amount of stuff you use and reuse what you can
Swap in natural and nontoxic household cleaners whenever possible
13. Do you need to obtain water rights before using groundwater?
In some states, you must obtain a water right before you can use groundwater on your land.
A water right is the right of a user to use water from a water source like a river, stream, or pond.
If you’re planning to become a landowner and you’re wondering whether you’ll have a water right, check your deed and speak directly with a state official.
This is the only way you’ll know for sure.
For example, if you’re in Utah, visit the Office of Public Record for Water Right Ownership.
This is the county recorder’s office for the county or counties in which water is diverted.
You can access all official water rights records either in the Salt Lake City office or online.
It’s everyone’s job to protect the planet.
Groundwater is a primary water source for billions of people.
As a landowner, learn how you can use your water most responsibly and recharge your groundwater table as quickly as possible.
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