Septic tanks and underground storage tanks (USTs) serve somewhat similar purposes, and due to their designs, they are often located using similar methods. Septic tanks collect and store untreated sewage material to be pumped out and collected later, usually found on the property of residential buildings. Underground storage tanks store a variety of materials, from waste oil at automotive garages to gasoline at gas stations, and in many places are no longer in use because of the potential environmental consequences of any leak or puncture. When developing property that contains the potential for either septic tanks or USTs, locating septic tanks and storage tanks is crucial, because the cleanup and environmental damage that they can pose can be very costly if they are damaged during excavation. 

Locating Underground Storage Tanks Using Radio Detection

locating septic tanks

USTs sometimes have secondary lines that feed into them, and these can be used to locate the tank. If a secondary line opening can be found above ground, a conductive line is fed through the feeder line. A technician directly connects to the conductive line with the transmitter, then locates the line using radio detection locating.

Unfortunately, this method has its drawbacks. Sometimes the secondary lines for the UST are clogged with grease, and a conductive line will not push through the accumulated debris. Often the secondary lines take a hard 90-degree turn into the tank, and cannot therefore be pushed all the way into the tank. Furthermore, since these tanks are often several feet long and wide, one small conductive line cannot accurately mark the width or length of the tank.

Sometimes underground storage tanks have metallic vent stacks that are visible above ground, and a technician can also directly connect to the vent stack and transmit a signal to the entire tank. This is a much more effective method of locating a UST with radio detection locating, but vent stacks are few and far between.

How To Locate Septic Tanks Using Radio Detection

locating septic tanks

Septic tanks require underground sanitary sewer lines to feed into them to process the wastewater. By accessing a clean out (an access point for cleaning out the line should it become clogged) and using the conductive line method described above, they can also be located properly.

Some septic tanks also have the same vent stacks, and can therefore be located using the method above. Septic tanks are also typically plastic, so the vent stack method often will not work for this reason when they are plastic.

However, due to the problems associated with both of these methods, it is ALWAYS a good idea to find another way to verify the location and depth of these tanks.




Locating Septic Tanks with Ground Penetrating Radar

Ground-penetrating radar (GPR) has many advantages to radio detection locating when it comes to septic tanks and USTs.

Since it is often difficult or even impossible to access an above-ground indicator of a septic or underground storage tank, locating using GPR allows a technician to scan as much of the property as possible for a potential tank . A septic tank or UST can’t hide from the GPR, unless it is significantly deeper than these tanks are usually found or the dielectric contrast between the ground and the tank material is too similar to be distinguished with GPR.

Additionally, locating septic tanks and underground storage tanks using GPR allows the technician to image the entire outline of the tank. They can then mark the outline for the excavator, so that there is no doubt as to how large the tank is.

A general rule with GPR is that the larger an object is, especially if it is metallic, the easier it is to locate. Since septic tanks and USTs tend to be very large as compared to other underground utilities, ground-penetrating radar locating is typically the preferred method for a technician locating septic and underground storage tanks. Depth of the tank and local soil conditions can vary the final GPR findings. The difficulty of any GPR locate increases with depth. Also wet or mineral-laden soil can make the locate more difficult or impractical.

We’ll Find Your Septic or Underground Storage Tank

Encompass Inspections is an industry leader in locating underground storage tanks and septic tanks. Whether your project is for environmental remediation or repair on a leaky septic tank, let our technicians assure you of the size, depth and location of your septic tank or UST. For more information, visit our website or contact us.