Ground Heat Exchanger Construction
Ground Heat Exchanger Construction
Ground Heat Exchanger Construction covers vertical and other closed-loop boreholes used for geothermal heating and cooling. On the Colorado exam, expect questions on how a GHX borehole is both a construction project and a regulated well: permit and licensing, borehole sealing, loop integrity, separation distances, reporting, and abandonment.
Licensing, permit, and siting
GHX boreholes are regulated under the state well construction program. A ground heat exchanger contractor license is required for the work, and the borehole must be authorized by DWR before drilling. Locate utilities and verify setbacks from water wells, septic systems, property lines, and other specified features. The approved plan controls the borehole location and depth; field changes that affect the seal or spacing need review.
Borehole construction and grout
A GHX borehole must be drilled and sealed so it does not create a vertical pathway for groundwater movement between aquifers. The loop pipe is installed with centralizers and pressure-tested, then the annular space is grouted continuously from the bottom upward by tremie. Drill cuttings, washed sand, or a surface seal alone are not acceptable substitutes for continuous grout. The grout must be compatible with the borehole and loop and must fill the annulus without voids.
Loop integrity, reporting, and abandonment
Pressure-test the loop before and after grouting and record the results. A failed test means the loop is not ready to be sealed or placed in service. Submit the required GHX construction report to DWR and provide the owner with as-built information. If a borehole or loop is abandoned, it must be sealed according to rule; pulling the loop and leaving an open hole is a violation.
Worked example
A vertical loop is pressurized to 100 psi and isolated. After one hour the gauge reads 85 psi. Reasoning: a 15 psi drop is a failed integrity test, not normal gauge drift. The crew must locate the leak, repair or replace the loop, and repeat the test before grouting. Grouting a leaking loop would seal a defect in place and make correction more expensive.
Traps that cost marks
- Treating a closed loop as “not a well” and skipping the permit or licensed contractor requirement.
- Grouting only the top of the borehole.
- Using drill cuttings as backfill instead of specified grout.
- Pressure-testing only before installation or only after grouting.
- Failing to file the GHX report or to seal an abandoned borehole.