The extend of subsurface flow and recharge areas of thermal groundwater systems are dificult to estimate. Two simple methods for making such estimates are described.
The methods are based on heat flow and on tha 14C age of thermal groundwater discharge. The two methods were applied to thermal groundwater systems in the southern Idaho Batholith and the results suggest that although thermal groundwater only accounts for about 1,5% of the drainage basin base flow, about one-third of the drainage basin surface area is involved in thermal grounwater system recharge.