that the thermal water forms a shallow reservoir within the weathered, fractured granite and in the sedimentary basin and seeps to the surface through the Mae Chan Fault (Fig. 2). To further investigate the reservoir, vertical electrical sounding and seismic refraction surveys including drilled holes were conducted in the Mae Chan valley just near the hot springs (Y2 of Fig. 2). These studies indicated that the subsurface geology near Y2 consisted of a 10–20 m thick clay and sand layer above a 100 m thick weather and fracture granite layer. At greater depths granite bedrock was encountered
Even though spring temperatures can reach 99.5◦C, the maximum temperature