Groundwater origin investigation with isotopic compositions for evaluation of high-productive deep aquifers in Khon Kaen area: Hydrogeology and isotope technique

Groundwater and surface water are analyzed for stable and radioactive isotopes, including 2H, 18O, and 3H, 14C respectively. The results show that the shallow groundwater of the depth less than 50 meters is originated by direct recharge of rainfall between 180-6,820 years of age. The groundwater flow is relatively rapid from West to East and North-West to South-East, excepts the high productive deep aquifers of Phu Tok flow radiate from recharging area to all direction. However, the groundwater flow rate is based on 14C analysis of Phu Tok is 2-3 meters a year. Within some area the flow is about 8 meters a year, while the unconsolidated aquifers along the Phong river give flow rate about 4 meters a year, where this flow rates compared to Bangkok aquifers are higher. The deeper aquifers have a source as direct rain recharge the same as the above aquifers but the flow rates are lower, especially the deepest aquifers at the depth of nearly 200 meters indicate no direct rain recharge with age of more than 20,000 years, which is confirmed with the amount of tritium less than 1.0 TU. Recharge area covers ca. 60 percent of western and southeastern parts of the study area, while the rest 40 percent of the area along the Chi and the Phong Rivers acts as discharge area. The Phu Tok aquifers is, therefore, underneath the recharge area, and could be subdivided in to three layers, i.e. the Upper, the middle and the lower layers lying respectively at the depth of 15-50, 50-150, and 150-250 meters. The aquifers are contaminated at some degree indicating by their nitrate contents. The result of this study indicates high potential of groundwater in many regions of Khon Kaen, especially from the Phu Tok aquifer. The aquifers compose of both modern and ancient water of rapid and very slow flow respectively. Though some aquifers show some degree of nitrate pollution, but 2 of the test wells have proved on their high yield for domestic, agricultural and industrial uses. However, aquifers of high salt content should be deal with very good care and should also be further studied in details.