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How Deep Are Septic Tanks Buried? (And How Do You Find It?)

How Deep Are Septic Tanks Buried? (And How Do You Find It?)

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In more rural areas where certain services aren’t easily accessible or available, things such as septic tanks can become a necessity. After all, we need modern amenities such as proper plumbing to live our lives conveniently.

There is the question, however, of just how deep septic tanks are buried. Knowing where your septic tank is and what can be planted near or on top of it can give you a better idea of just how much of your yard is available for regular gardening.

You May Not Know

While it seems like something a homeowner should be aware of, knowing how deep the septic tank is buried can be a question. Perhaps you forgot after the installation years ago or you are moving into a home that already has the septic tank built in.

Whatever the case may be, knowing the depth of your septic tank can be a difficult thing given the circumstances, especially if you don’t know where the lids are.

The general rule of thumb is that most septic tanks can be buried anywhere from four inches to four feet underground.

How to Locate Your Septic Tank

Septic Tank Cover

Maybe you’re not quite sure where the septic tank on your property is and you’re trying to locate it. There are actually quite a few easy ways to figure out where your tank is without having to go through comprehensive steps.

The first way is to let your sewer pipes lead you. Normally, the tank and your drain field will be installed parallel to the sewer line that extends out from your home.

In the crawl space or basement of your house, you might even be able to locate a four-inch sewer pipe that leaves the house. If you find it, this should lead you to the septic tank.

Follow the pipe all the way across the yard, probing every couple of feet to ensure that you are still following it. As outlined above, septic tanks have to be at least five feet from the house, but most are generally in the 10- to 25-foot range.

When you don’t feel like probing around your yard, you can always check out the county records for your house. Most counties will have records of any building permits; this will include the installation of any septic systems on your property.

This should contain diagrams that have dimensions and even the specific location for where the septic tank is sitting. Not only is this a good idea for locating your septic tank, but it can give you a much better idea about the layout of your specific plot of land, too.

You can also opt to dig up your lid. Call your municipality to find the as-built drawing. This is what will indicate how many lids are on your septic tank. Depending on the setup, it can be either two or three lids. Most septic tanks are rectangular and will measure something in the neighborhood of 5’ x 8’.

Use a metal probe to locate the edges and then mark off the perimeter. If you aren’t able to find the location of your septic tank using a probe, you’ll have to create a shallow excavation using a shovel along the perimeter to eventually locate the lid.

If you have just purchased a property and know that there is a septic tank but don’t know precisely where the tank is located, you will need to locate it.

Look for visual clues first. You should see either septic tank risers or clean-out ports that will be poking above the ground. This will tell you right away where the tank is located underground.

But if you can’t find any visual clues, there are some intelligent guesses that can be made. Take a look at your building’s piping as well as the conditions of the property to get a reasonable idea of where the tank is located.

Should you be able to visually locate the cleanout or the risers, you will need to inspect them to ensure that everything is working properly. If your tank is full to its normal level, it will be full up to just a few inches underneath the underside of your tank lid.

If it is made of plastic, fiberglass, or steel, there can be some variation to the upper surface of the lid.

Where Should the Septic Tank Be Located?

Septic System Diagram

Should your property not currently have a septic tank, but you are interested in the prospect of adding one, it is important to know where it should go. Generally speaking, most septic tanks will be located in a range of 10 to 25 feet from the home.

Please keep in mind that septic tanks cannot and should not be closer than five feet to your home. If you are trying to locate a tank that has already been installed on a property you just bought, you can use a probe to strike for flat concrete. This will indicate to you where the tank is.

Planting Above a Septic Tank

While it may not seem like the best idea in the world, planting over a septic tank can actually be totally fine so long as you grow the right vegetation. Not only is it alright to do, but it can also be quite beneficial depending on what you grow.

The right type of vegetation can help prevent erosion in your tank and can even suck up some of the extra moisture that can get trapped in your drain field. You can even simply grow tall grass over that patch of ground if you so desire to indicate and cover the space where the tank is located.

Grasses (as mentioned) and perennials are the best type of things to plant around your drain field and septic tank. This is because they have shallow root systems that won’t impede the underground system of the tank or cause it any damage.

For much the same reason, you can go with non-woody ground covers as well. Since there are a ton of different options out there for non-woody ground covers, you can check that out on your own. Just consider the growing conditions.

If your septic tank is located in a sunny area, this is probably the best for perennials that enjoy sunlit spaces. Without the proper sunlight, you may want to go with a shade garden plant instead. Remember, you need optimal conditions for these plants to grow.

Keep in mind that the soil that surrounds the septic tank drain field will generally be wetter than average. It can even be saltier, or both in some instances.

Make sure that when you plant, you cover both of those bases by going with a perennial such as a hollyhock, wild violet, or bee balm as all of them are more tolerant to salty, wet ground.

Just because you have a septic system underneath these plants, it doesn’t mean that deer will avoid the area. So, if you don’t want deer to permeate your yard, consider growing perennials that are deer resistant. Something such as a spring bulb or ornamental grass that the deer don’t normally consume.

Plants That You Don’t Want to Grow

Planting a Small Shrub

Just because you can plant over your septic tank doesn’t mean that everything is applicable. There are some plants that you definitely want to avoid planting over your septic tank, primarily large trees that are fast-growing.

On the same note, some of the worst plants are the shrubs and trees that have aggressive root systems. These roots will sprout out in search of water and don’t care where they find it. That can mean finding a source of water in the pipes of your septic tank drain field.

When those roots start to intrude on your septic drain field, it can wind up doing serious damage to your septic tank. Repairs are a pain to deal with and even then, it might not do the job. You could be looking at a total replacement.

Trees to avoid are pussywillow shrubs, weeping willow shrubs, birch, beech, elm, maple, American sweetgum, tulip, and ash trees. There are plenty of others with aggressive root systems that you would want to avoid planting anywhere near your septic tank or drain field.

How Your Septic System Works

How Septic Systems Work

Knowing how your septic system works can give you a greater appreciation for how to manage, maintain, and care for it. Otherwise, it is just a big tank in the ground that collects your waste (which is true, but still).

In rural areas, there may be a lack of sewer systems. Not every rural area is the same, so it isn’t a guarantee that your local rural area will require septic systems. In any event, when there are no sewer systems present, the septic tank works as a wastewater treatment facility of sorts.

There is a pipe that brings all of the wastewater from your showers, toilets, sinks, and washing machine out of your home and puts it all in that underground septic tank. The tank is created to be watertight so that your wastewater doesn’t leach out into the ground.

The tank is actually intricate enough that it can separate your solids (or sludge) and scum from the liquid waste. The solids sink to the bottom, the scum rises up to the top, and the liquids sit in the middle between the aforementioned layers.

The liquids eventually will leave the septic tank through a baffle pipe in the shape of a T. The reason for the exit is the wastewater coming from your house.

The baffle is designed so that only the liquids, none of the solids, can exit through this specific pipe. This liquid gets transferred out through the pipe and into a larger part of your septic system. This is the leach field or drain field.

Your drain is generally made up of a series of perforated PVC pipes that are laid underground in trench form. These trenches get filled up with gravel or crushed stone for durability and longevity, though you can cover those drains using a drain field fabric to keep the dirt from getting into your drains.

A Stack of PVC Pipes

Since the drains are perforated, they let the wastewater seep out into the crush gravel or stone and then finally into the soil. The wastewater will begin to slowly drift throughout the soil, removing most of the harmful bacteria that is present in waste before it gets to the groundwater.

Any excess moisture in the soil is then taken care of by natural evaporation unless you do something to block the flow out of the pipes.

Every three years or so, you will want to pay a septic service to come out and pump the scum and sludge out of your septic tank, essentially cleaning it and resetting it back to its original state.

How to Plan a Septic Field

The tank is just one part of the equation. You also need to have a drain field where all that liquid waste can seep. Your drain pipes are the primary cause for concern when you plant around your septic tank.

The last thing that you want is for those aggressive roots to permeate your septic drain and damage the pipes. When this happens, it can keep your septic tank from draining properly and can even compromise the groundwater.

A good rule of thumb is the less gardening work you have to do near your septic tank, the better. Go with annuals such as impatiens that have shallow roots and need less care. The only thing is that they need to be planted each year, so keep that in mind.

There are three things that you want to avoid when planting near your septic tank. The first is adding soil to the septic drain field. The second is adding too much mulch to that area. The third is potentially watering the plants more than you should.

All three of these can compromise the ability of your drain field to evaporate normally.


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