Questions and Concerns Regarding Direct Exchange Systems
Heat Transfer Media
Geothermal systems can serve as a direct conduit for contaminants to enter the groundwater, either by leaking of the heat transfer media or as a direct opening to the water table from the surface. DX systems use refrigerants, of which there is limited toxicity data. While the refrigerants are typically gaseous at ambient temperature, they can be soluble in water and as a result dissolve into groundwater and migrate fairly rapidly into the aquifer. As an example we can cite the use of ethylene dibromide (EDB) as a pesticide used in tobacco fields in
DX systems commonly use copper tubing. While copper has excellent corrosion resistance in certain applications, it is susceptible to corrosion over time when buried in the ground. As such it is not improbable that a DX system will develop a leak over time and cause leakage of the refrigerant into the soil or water table. In developing the initial proposed regulations for geothermal systems the Agencies involved specified heat transfer fluids that were food grade and non-toxic as well as construction materials that the Agencies felt were durable and unlikely to fail. As a safeguard, the underground loops were required to be encased in grout, which would contain any leaks of the fluids. DX systems should address how the borehole will be constructed so as not to serve as a conduit for surface pollution to enter the aquifer and address the Agencies’ concern that their systems provide the same degree of safeguards to the environment that were stated in the initial proposed regulations. This could be in the form of proposed regulations or best management practices for DX installations.
Additionally, it is known that a rust inhibitor can be used to prevent copper from corroding, however the effectiveness of these rust inhibitors needs to be determined. Please detail the types of corrosion-prevention chemicals or methods employed when using copper piping and document their effectiveness.
Permitting and Licensing Issues
Drilling any type of borehole can cause a problem if the drill strikes an underground structure, such as a buried pipe or sewer line. Inadequately grouted boreholes may cause a preferential flow path along the bore hole for contamination to travel through the subsurface, impacting ground water resources. Therefore, consideration must be given to requiring borehole systems to be permitted to: 1) Establish a record of the underground system and 2) Eliminate the possibility of drilling into a buried pipe, sewer line, subsurface sewage disposal system, etc., and 3) considering that DX system boreholes can be installed at a horizontal angle, setbacks may have to be established at the point where the borehole is terminated, not just where the borehole enters the ground.
The State must be satisfied that DX system installers are knowledgeable in their trade and are drilling boreholes responsibly. As such, DX systems should respond regarding what type of training and experience would be required to license such individuals. In this response DX systems should also address what type of information should be supplied to the local director of health in order to ensure the proposed boreholes are installed appropriately and not damage any existing underground structures or devices. Further, in the event of an "accident" made during installation, how will DX installers make the homeowner "whole"?