Hydrogeology of the Nakhon Luang Aquifer in Bangkok Metropolitan Area and its Vicinity

Abstract

This hydrogeological study is concentrated in the Nakorn Luang aquifer, one of the Bangkok aquifers systems. The study area is situated in the southern part of the Lower Central Plain. The area displays as the depression filled with unconsolidated and semi-consolidated sediment ranging in age from Tertiary to quaternary. Cuttings, lithologic logs, E-logs, water quality and hydraulic properties data of the water wells depict that the depth of the aquifer is at 125-180 m. from ground surface. The aquifer shows the deposition under fluviatile-deltaic environment. The aquifer consists of the alternative layers of sand, gravel and clay with thickness ranging from 2-15 meters capped on the top and bottom of the aquifer. Thickness of aquifer ranges from about 15-75 meters and shows thickening westwards and northwards. The hydrochemical facies are Na-K-CI-So₄ type and Na-K-HCO₃-CO₃ type that occur in the south, southwest up to the central north along the Chao Phraya River and the middle east further to the northeastern part of the study area respectively. Hydraulic properties including hydraulic conductivity, transmissivity and specific capacity are computed from the pumping test data. As a result, they range from 3-196 m/day, from 40-2,200 m2/day and from 0.3-40 m3/hr/m respectively. The hydraulic properties indicate that the Nakhon Luang aquifer is the high potential both in quantity and quality aquifer. The maximum production groundwater yield, from flow net analysis is approximately 1,295,000 m3/day or 57% comparison to the total groundwater extracted while the minimum production of groundwater yield is 435,000 m3/day covering the area 8,000 square kilometer. The heavily pumpage the rapidly lowering of potentiometric surface, salt water encroachment and also subsidence of the land. The Department of Mineral Resources by its Ground Water Division has conducted groundwater management in Bangkok Metropolitan area and its vicinity.