3.9. POTENTIAL WATER QUALITY PROBLEMS 

In general, the risk of groundwater contamination from closed-loop GSHP systems is very low. However, with an antifreeze fluid that is circulated through the pipes, the potential exists for a leak or rupture to occur that allows the antifreeze to escape. If the fluid is a polluting substance such as a methanol or ethylene glycol, the system owner can be liable for cleanup of the soil and/or aquifer. For this reason, the biodegradable mixtures such as potassium acetate or food grade propylene glycol are recommended. 

Thermal pollution by most closed-loop GSHP systems is likely to be negligible. Although some larger systems could locally affect subsurface temperatures, use throughout the year will tend to offset the effects of heating and cooling (See Chapter 5). 

Pump motors on the heat pumps typically operate on vegetable or mineral oil; most heat pumps have an automatic shutoff device that activates if the system loses pressure. Although there also is a slight chance that pump motors and the actual heat pump system could rupture, the result will most likely be of little consequence to the environment. The refrigerant is also non-toxic. However, all systems should be equipped with pressure shutdown switches. 

3.10. ENVIRONMENTAL CONSIDERATIONS AND RECOMMENDATIONS 

The International Ground Source Heat Pump Association (IGSHPA) has established standards for GSHP systems. They are included in Appendix 1 - IGSHPA Design and Installation Standards. It is recommended that IGSHPA standards be followed. 

Closed-loop pipes should be made of polyethylene or polybutylene, and all joints should be sealed by the heat fusion process. The system should be flushed and pressure checked before the borings are sealed or the trenches are filled. Even though the pipes may last decades without problems, in time the pipes may develop leaks. For this reason, it is strongly recommended that potassium acetate or other non-toxic fluids be used. It is also recommended that the subsurface loops be isolated at least 100 feet from any drinking water wells. 

General recommendations are presented in Chapter 5. The following recommendations are specific to closed-loop GSHP systems. 

3.10.1. Horizontal Loops 

The loop of pipe should not be installed beneath any part of a septic system. Disturbance of the soil underneath a septic bed can lead to inadequate treatment of sewage. Also, heat from the pipes can increase biological growth in the septic tanks, which could lead to costly septic system repairs. Repair of one system would require the excavation of the other. 

3.10.2. Vertical Loops 

Vertical loops that use borings or wells should be grouted with a low permeability material to prevent the following from occurring: 

•contamination of groundwater from surface sources •intermixing of aquifers by flow via the borehole •disruption of aquifer hydraulics 



The driller can prevent these situations by maintaining the conditions of the aquifer that existed before the boring was installed. An impermeable barrier placed around the piping can prevent water from moving vertically in the boring.