Digging a Sewer Trench

Large Underground Pipe
George Clerk/Getty Images

A failed sewer line always strikes fear in the hearts of homeowners, because the cost of replacement can easily run into five figures. It is possible, however, to significantly reduce the cost if you're up to the task of hand-digging the trench required to access the old sewer line and install the new one. A big part of the cost of replacement is the contractor who operates large earthmoving equipment to dig out your lawn to reach the sewer line, and tacking the trenching work yourself can cut the cost dramatically. 

This can be a daunting task, though, so ask yourself some serious questions before you tackle the job. 

Am I Able to Do This Work?

By hand, a single adult who is in reasonably good shape can dig a sewer trench 4 feet deep, 8 feet long, and 3 feet wide in about 8 hours of continuous work. This estimate is based on sandy but heavily rooted soil, but a number of factors can change that estimate:  soil composition, seasons and the number of people who can help you dig. If you need to dig 16 feet of trench or more, you are talking about a few days of very hard work to do this. 

A cold climate offers several complications. In cold climates, the depth of the sewer pipe can be quite deep because the frost line can be 4 feet or more below the surface. And if your sewer line fails in winter, you are faced with the very difficult task of breaking through frozen ground in freezing temperatures. It is not a pleasant working environment. 

But if you have the luxury of lots of time, are in relatively good physical condition and enjoy working outside, this is a task you can do. Saving several thousand dollars may well be worth the effort. 

  • WARNING: Working in a deep trench can be dangerous. Every year, people die when the earthen walls of trenches collapse on them while they are working in the bottom. An open trench also poses a distinct hazard to children and pets. Make sure to take precautions if your trench needs to be a deep one. 

Let's look at the general steps involved in digging your own trench for replacing a sewer line.

Phase 1: Locate Your Dig Location and Pull Permits

  1. Locate your sewer line. If you have no idea where your sewer line runs, a video camera inspection can tell you. The technician will run the camera down the line and can stop at various points. The camera has a radio transmitter that signals its location. At each point, the technician will sweep a locator over the ground until it reads the strongest signal. Your sewer clean-out may also give you a visual clue as to the line's location.
  2.  Mark the dig point. Get this point as accurate as possible. You will pay a high price in useless labor for hand-digging at the wrong spot. Work with the inspector until he/she feels you've found an accurate location, then hit it with a spot of marking paint.
  3.  Locate utility lines. Call your local "miss utilities" number. This is usually a free service to residents, supported by utility companies. They will mark your yard for electrical, water, gas, etc. Don't forget that there are other homeowner-installed "utilities" (sprinkler, landscape lights, etc.) in your yard, outside the purview of utility companies.
  1. Apply for a permit. Your community requires a permit as a safety measure to ensure that the work is done correctly. At defined points during the work, a building inspector will visit the work site to make sure the work has been done in compliance with code. In the case of a sewer line replacement, this is normally done after the new sewer line has been installed, but before the trench has been filled in. 

Phase 2: Break Up or Remove Obstructions (Optional)

Before you can get to the soil, you may have to remove obstructions such as concrete or brick sidewalks, driveways or slabs. Use an 8-lb. sledgehammer to break up concrete, starting on the edge. Electric or pneumatic jackhammers can also be leased at tool rental centers.  

Phase 3: Dig, Dig, Dig

Dig straight down, minimizing side digging as much as possible--for right now. Later, you will need to extend the trench sideways so that you can stand in the pit and and create access to the sewer line,  but do as little of this as you possible until you have located the sewer line. As you dig, you may well need to clip or saw off the roots of trees and bushes as you encounter them. Some small roots can be severed with your shovel blade; others you will need to clip with pruning shears or a hand saw. Heavier roots will require a chainsaw.

  • Tip: Do You Need a Trench Shield? Trench shields prevent the walls of the trench from collapse. OSHA regulations require the use of trench shields for trenches 5 feet deep or more (OSHA 29 CFR Part 1926.650 - .652 Subpart P-Excavations). As a homeowner, you are not bound by OSHA regulations, but it's wise to follow OSHA guidelines for your own safety. 

Phase 4: Reaching the Sewer Line

The depth at which you reach the sewer line will vary. It can be as shallow as 18" to 30," or as much as 5 or 6 ft. Often this is a matter of climate--in colder climates, the pipe is often deeper to prevent the pipe from freezing in winter. But this is not always the case; even in warm climates, the pipe is sometimes rather deep. This may depend on how deep your community's sewer mains are located. 

If your sewer problem is an emergency, you'll probably find that the soil is saturated with waste water; you may smell it before you see it. If the sewer line has been well laid, the appearance of a gravel layer will alert you that you're close to the sewer line. Now is the time to dig rather carefully as you excavate space around the pipe, which may be plastic pipe, clay pipe or cast-iron pipe. You might even find all three tied together, as shown here. Clear away a good amount of soil all around the pipe to allow the plumber easy access to replace the pipe. 

After the sewer replacement is complete, make sure to have the work inspected before filling in the trench again.

Then congratulate yourself on saving a lot of money by doing this labor-intensive work yourself.