Yes, you can install a trench drain if you already have concrete in your yard or garden. While it can complicate some aspects of the job and slightly run up the cost, it is doable. Residential trench drains can be easily retrofitted to outdoor areas with concrete without having to remove excessive amounts of your patio, pool area, or decorative walkways.

There are several different factors that influence how long it takes to excavate. For a foundation, it could take anywhere from three days to three weeks. It can take even longer if you face weather-related delays or an inaccessible site that’s riddled with boulders and rough terrain. It may also take longer if you have clay soil, which is more difficult to dig.

How deep your septic system needs to be into the ground depends on several factors. In extremely cold environments, the tank needs to rest below the maximum frost line, which can be up to six or eight feet deep. The standard burying depth for most systems is between a few inches and four feet below ground level. Depth can also depend on the slope of the landscaping and other property variables. 

In most areas, you will need a permit for excavation work, even for projects that only involve grading or yard leveling. Permit requirements depend on your local government and the scope of the project, but they are especially common for significant digging or work that could affect utilities or public property. These permits help protect the local topography and prevent drainage issues. An experienced excavation company will typically know whether permits are needed and can often handle the process of pulling and closing them for you. You can also verify permit requirements by contacting your local building department and describing your project.