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There is no standard depth for burying a septic tank; they are typically buried anywhere from 4 inches to 4 feet underground. The final depth depends on several factors, including the depth of your main sewer line, the height of the bedrock, soil type, local regulations, and the property's landscape. If you plan to grow grass or plants over the tank, a depth of at least 4 to 6 inches is recommended. Deeper tanks can be more difficult to locate, but a septic professional can help find it for you.

Most residential basements are 8 to 10 feet deep. You can dig deeper depending on building codes, but it does become more difficult. You’ll likely need to install stronger foundation walls and additional supports to handle the increased load. Depending on the water table, you may also need a water management system. Clay soil can support a deeper foundation than sandy soil. A structural engineer will be able to tell you the maximum, feasible depth.

Depth is not a qualifying component of evacuation. Any human-made cut, cavity, or depression in the earth’s surface is considered excavation. The hole from excavation can be any size, shape, or depth. Excavation is used to create foundations, reservoirs, drainage ditches, and roads. Long, narrow excavations are called trenches and are often used for underground utilities.

Because decomposed granite is a durable material, a crushed rock or gravel base is optional as long as the DG is properly installed and compacted. However, installing a base is a good idea because it will ensure proper drainage and stability and act as a weed suppressant (although you may still occasionally have to pull weeds). Installing an adequate base can also increase the durability of driveways and walkways. If you forego the paver base or gravel underneath, line the area with landscaping fabric to avoid weeds.