Chapter 17 — GEOTHERMAL ENERGY SYSTEMS AND AMBIENT TEMPERATURE LOOPS
1707.18 Trenches, Excavation, and Backfill — 2025 California Mechanical Code
California Mechanical Code (Title 24, Part 4) · 2025 edition · updated 2026-09-25 · California
CBSC: official editions, supplements and errata
Italicized text is a California amendment to the model code, as printed in the official publication.
Cite as: 2025 California Mechanical Code (Title 24, Part 4) § 1707.18 · Effective January 1, 2026 · Official source: Building Standards Commission
Excavation for horizontal piping shall comply with Section 1707.18.1 through Section 1707.18.8, Section 1707.8 through Section 1707.11, and in accordance with the requirements of the Authority Having Jurisdiction. Prior to any excavation, trenching, or drilling, all buried utilities including drainage, and irrigation systems shall be located and flagged by the appropriate utility and ground source heat pump system contractor representative.
1707.18.1 Trenches. Trenches for underground piping or tubing shall be excavated in accordance with the setback requirements in Section 1712.4. 1707.18.2 Buried Systems. Buried open-loop system piping, shall be installed not less than 3.3 feet (1006 mm) below the finished grade.
1707.18.3 Pipe Installation. Piping in horizontal trenches shall be embedded with not less than 6 inches (152 mm) of inert granular material above and below, or in accordance with the Authority Having Jurisdiction and project specifications.
Horizontal piping trenching shall be backfilled with approved material and shall be compacted. 1707.18.4 Separation. The horizontal piping shall be separated from fluid-based onsite service systems to prevent excessive short-circuiting heat transfer between such systems.
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(6) Vertical and horizontal ground-heat exchangers shall maintain the following setbacks:
(a) Ten feet (3048 mm) horizontally from a pressuretested sewer lateral into a building.
(b) Twenty feet (6096 mm) horizontally from a nonpressure tested sewer lateral into a building.
(c) Three feet (914 mm) horizontally from buried utilities such as electrical, gas, or water.
(d) Fifty feet (15 240 mm) from a water well.
(e) Fifty feet (15 240 mm) from a septic tank and 100 feet (30 480 mm) from a subsurface sewage leaching field.
(f) One hundred feet (30 480 mm) from a spring; or at distances specified by the Authority Having Jurisdiction.
(7) Wells and boreholes shall be sealed in accordance with the Authority Having Jurisdiction. Where grout is required, it shall be applied in a continuous operation from the bottom of the borehole by pumping through a tremie pipe.
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