Section 25-128-39b - Closed-loop geothermal system fluid(a) All chemicals used or added to fluids circulating through a closed-loop geothermal system for heat exchange, and the amount of chemicals used or added, shall be those specified by the manufacturer and shall be subject to industry approved standards for geothermal system efficiency.(b) A well contractor shall only use the following closed-loop geothermal system fluids in closed-loop geothermal systems:(1) The refrigerants commonly referred to as R-134A, R-407C, and R-410A;(2) Drinking water, as defined in section 19-13-B102 of the Regulations of Connecticut State Agencies;(3) Heat transfer fluids containing potable water combined with a maximum of twenty-five (25) per cent propylene glycol that has been approved by the federal Food and Drug Administration; and(4) Other geothermal system fluids or additives approved by the department and the Department of Public Health.Conn. Agencies Regs. § 25-128-39b