CRD Installation Standards & Environmental Compliance 5 — Questions and Answers
Question 1: When drilling vertical boreholes for a geothermal system, what drilling fluid is most commonly used and what is its primary environmental concern?
- Synthetic polymer mud — risk of borehole collapse
- Bentonite-based drilling mud — risk of wellbore sealing interference (Correct answer)
- Potable water — risk of aquifer dilution
- Air rotary — risk of dust inhalation
Correct answer: Bentonite-based drilling mud — risk of wellbore sealing interference
Bentonite drilling mud is most commonly used, but excess bentonite in the borehole can interfere with the thermal grouting process and potentially form a barrier reducing heat exchange.
Question 2: Which condition would trigger a requirement for Enhanced Geothermal System (EGS) environmental review that would NOT be required for a standard residential geothermal installation?
- Borehole depth exceeding 500 feet
- Use of high-pressure hydraulic stimulation of rock formations (Correct answer)
- Installation of more than 5 vertical boreholes
- Use of antifreeze in loop fluid
Correct answer: Use of high-pressure hydraulic stimulation of rock formations
Hydraulic stimulation (fracking) used in EGS triggers additional environmental review under federal and state regulations including induced seismicity risk assessment, unlike standard closed-loop drilling.
Question 3: What is the correct procedure when a geothermal driller encounters an artesian zone (flowing water under pressure) during borehole installation?
- Continue drilling to the planned depth and grout afterward
- Stop drilling, control the flow, and contact the state water resources agency (Correct answer)
- Install a check valve at the surface and resume drilling
- Increase drilling fluid weight to suppress the flow and continue
Correct answer: Stop drilling, control the flow, and contact the state water resources agency
Encountering an artesian zone requires stopping work, controlling the flow to prevent land surface flooding and contamination, and notifying the state water resources agency as required by law.
Question 4: For a geothermal installation near agricultural land, which environmental concern about antifreeze is most critical to address with the property owner?
- Methanol toxicity to soil bacteria
- Propylene glycol impact on crop irrigation water if a loop leak occurs (Correct answer)
- Ethylene glycol vapor pressure affecting greenhouse crops
- Antifreeze pH effects on soil alkalinity
Correct answer: Propylene glycol impact on crop irrigation water if a loop leak occurs
A loop leak could release antifreeze solution into soil or groundwater used for irrigation; propylene glycol is preferred near agriculture because it is non-toxic and biodegradable.
Question 5: What is the industry standard minimum borehole diameter for a residential vertical geothermal installation using 1-inch diameter U-tube loop pipe?
- 2 inches
- 3 inches
- 4 inches (Correct answer)
- 6 inches
Correct answer: 4 inches
IGSHPA standards specify a minimum 4-inch borehole diameter when installing 1-inch U-tube loops to allow proper insertion and adequate space for thermally enhanced grout placement.
Question 6: Which installation practice is prohibited near a drinking water wellhead protection zone in most U.S. states?
- Using thermally enhanced grout containing silica sand
- Using ethylene glycol as a loop antifreeze solution (Correct answer)
- Installing a horizontal loop at depths greater than 6 feet
- Running multiple loop circuits in a parallel manifold configuration
Correct answer: Using ethylene glycol as a loop antifreeze solution
Ethylene glycol is toxic and its use as loop antifreeze is often prohibited or restricted near wellhead protection zones; propylene glycol must be substituted in these areas.
Question 7: A CRD designer is documenting loop field installation for a permit close-out package. Which record is NOT typically required in a state geothermal installation completion package?
- Pressure test report with pass/fail results
- Heat pump manufacturer's efficiency ratings (EER/COP) (Correct answer)
- Borehole log with grouting depths and materials
- Loop fluid type and antifreeze concentration as-installed
Correct answer: Heat pump manufacturer's efficiency ratings (EER/COP)
Heat pump efficiency ratings are product specifications, not installation records; state completion packages focus on installation compliance records like pressure tests, borehole logs, and fluid documentation.
CRD Installation Standards & Environmental Compliance 5
When drilling vertical boreholes for a geothermal system, what drilling fluid is most commonly used and what is its primary environmental concern?