You can dig 60 to 80 linear feet by hand per day depending on the depth. Digging a 100-foot trench by hand will take you two work days, but it can take longer if you have heavy or rocky soil. If you’re digging a deep trench or one that’s over 100 feet, consider renting a mechanical trencher, such as a walk-behind or ride-on, or calling a pro for help. 

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. 

The average cost of excavation is approximately $3,200, with typical projects ranging from $500 to $15,000. Depending on the contractor, you may be charged between $50 and $200 per cubic yard or an hourly rate of $40 to $180 for an excavation specialist. The total cost is influenced by several factors, including the project size, the amount of soil to be removed, and the soil's condition. Hard soil, tree roots, or excessive rocks and clay can increase the price, potentially adding $200 to $1,200 to the final bill. Other factors that can drive up costs include the presence of nearby structures that complicate the work or tight spaces that require manual excavation instead of heavy machinery.

Downspouts should be buried at least 5 to 10 feet away from your foundation. This can vary depending on your local building codes, soil type, and property slope. The main goal is to ensure water is directed away from your foundation.