Hydrogeochemistry of the Chiang Mai Basin, northern Thailand

Chemical composition of groundwater samples collected from 247 boreholes throughout the Chiang Mai Basin was determined in order to describe the background ion concentrations and to identify the major hydrogeochemical processes that control the observed water chemistry. The investigation results indicate that the groundwater is generally free from heavy metals although exceptionally high Fe, Mn, F and Na are found locally. The groundwater of the Chiang Mai Basin has evolved chemically through water-rock interactions from low TDI and low pH meteoric water recharges principally at basin rims towards higher TDI and pH groundwaters discharges mainly along the through-flowing Mae Ping River. The average groundwater has hydrochemical facies either of Ca-Na or Na-Ca bicarbonate type with neutral pH and total dissolved ions (TDI) of about 10 meg/l. (C) 1997 Published by Elsevier Science Ltd.