How deep is a drain field?

How deep is a drain field? Ask the agency that issues septic permits where the lot is what depth and separation to groundwater or rock apply there. The drainfield is the soil area that receives the septic tank’s liquid. Oregon and Pennsylvania, below, show two examples of what a state rule can call for.

What do state rules call for?

In Oregon, for example, the minimum depth of a standard trench starts at 18 inches, and a standard trench must have at least 6 inches of drain media, the gravel or similar material around the pipe, under the distribution pipe and at least 2 inches over it (OAR 340-071-0220).¹ Pennsylvania, for example, calls for at least 4 feet between the bottom of the gravel (aggregate) and the top of any limiting zone, such as a water table or bedrock (25 Pa. Code § 73.51).²

What should you check before you dig?

Before you drive, pave or dig over the drainfield area, ask the agency that issues septic permits where the lot is for the permit records showing where it is.

Citations

1. Oregon Department of Environmental Quality, OAR 340-071-0220, official text from the Oregon Secretary of State; Clackamas County, Oregon, Septic System Recommended Standards and Guidelines. ↩

2. Pennsylvania Department of Environmental Protection, 25 Pa. Code § 73.51, official text from the Pennsylvania Code and Bulletin; Penn State Extension, Septic System Basics. ↩