This webpage is intended to address the most common questions asked regarding trenching for utilities.

Multiple Utilities in a Shared Trench

The only potential required separation for residential utilities is between the sanitary sewer and water service. This is required when the sanitary sewer is constructed of materials not allowed to be in the building. Most modern installations use schedule 40 ABS or PVC for sewer and PEX for water supply. These are allowed to be side by side in the same trench.

Nothing prohibits electrical and gas from being installed in the same trench as the water supply and sanitary sewer lines.

Trench Depth

• The required trench depth for water supply lines is 12” below the frost depth (OPSC 609.1). Frost depth in Lane County is 12” (ORSC Table 301.2) which means the trench depth for the water supply line at 24” below grade.
• The depth for sanitary sewer will depend on the distance from the beginning of the sanitary sewer line to the septic tank with the sewer line sloping a ¼” per foot, but not have less than 12” of ground cover (OPSC 718.1).
• Trench depth for gas piping must be a minimum of 18” (ORSC G2415.12) except for individual outdoor appliances such as lights, grills, and heaters which may be buried at a minimum of 8” below grade (ORSC G2415.12.1). Gas pipping to generators must be buried at 18” below grade.

Materials for Water Supply and Sanitary Sewer

• The plumbing code allows for a variety of material to be used for water supply lines. All lines must be listed to ASTM standards. Refer to Table 604.1 OPSC for materials and their required listing.
• Please note, there are two materials that are allowed to be used as supply lines but must transition to an approved material before entering the building (PE and PVC).
• The plumbing code allows for a variety of materials to be used for sanitary sewer lines. If using materials that are not approved for use within a building, there must be separation between your water supply and sanitary sewer line. For sanitary sewer materials, see Table 701.2 OPSC.
• Separation, if required is as follows: the bottom of the water pipe shall not be less than 12” above the top of the sewer line and shall be placed on a solid shelf excavated horizontally 12” from the sewer line. Water pipes crossing sewer lines shall be laid not less than 12” above the sewer line (OPSC 720.1).

Tracer Wires

Tracer wires must be laid in the trench on the pipe they are serving for the entire length with one end terminated above ground. Tracer wires must be colored and sized as follows:

• Tracer wires for water lines must be blue 14 AWG
• Tracer wires for sanitary sewer lines must be green 14 AWG
• Tracer wires for gas piping must be yellow 18 AWG

Other Considerations

• When digging trenches adjacent to foundations, take care to not undermine the footing. The depth of the trench determines how far away from the footing the trench must be.
• For example: If the trench is 24” deep, it must be at least 24” away from the bottom of the footing.
• Plumbing pipe materials such as PVC and ABS are made of different types of materials and as a result must be assembled using the appropriate glue type. Be sure to verify what materials you are using and use the correct type of glue accordingly. You cannot use ABS glue on PVC or vice versa. Using the incorrect type of glue will cause degradation of materials and is a code violation. When transitioning from ABS to PVC, transition glue must be used. Transition glue can only be used at this one location. The type of glue should be clearly marked on the can which should be on site in case your inspector has questions.
• For electrical utility questions, please contact your electrical inspector.