that the thermal water forms a shallow reservoir within the weath-ered, fractured granite and in the sedimentary basin and seeps tothe surface through the Mae Chan Fault (Fig. 2). To further investi-gate the reservoir, vertical electrical sounding andseismic refraction surveys including drilledholes were conducted in the MaeChan valley just near the hot springs (Y2 of Fig. 2). These stud-ies indicated that the subsurface geology near Y2 consisted of a10–20 m thick clay and sand layer above a 100 m thick weatheredand fractured granite layer. At greater depths granite bedrock wasencountered.Even though spring temperatures can reach 99.5◦C the maximum temperatureFig