Study of hydrogeochemistry and groundwater flow in Thachin-Mae Klong basin for groundwater quality management

Abstract

The Department of Groundwater Resources has studied and collected a large number of groundwater samples in Tha Chin-Mae Klong Basin to analyze their chemical composition. However, most data are in numerical and table forms representing various parameters which lead to a difficulty for perception and utilization. Thus, this study aimed to obtain hydrogeochemical characteristics of each aquifer by analyzing and interpreting such data. A computer program was employed to conduct Piper diagram, Durov diagram, Stiff diagram, X-Y scatter plot (ion ratio analysis), and Wilcox diagram (Sodium Adsorption Ratio analysis) in order to comprehend the hydrogeochemical characteristics and groundwater evolution. According to the study, it can be concluded that there are four main groups of groundwater including: 1) Ca- HCO3, Ca-Na-HCO3 and Na-HCO3 group which is common in young-age groundwater, high terrain or recharge area, i.e. the western area from Ratchaburi to Chainat and some parts of the centre, 2) Ca-HCO3-Cl, Na-HCO3-Cl and Ca-Na-HCO3-Cl group which is found in groundwater that has migrated far from the recharge area. It is generally freshwater but brackish to salt water in some areas. 3) Ca-Na-Cl, Ca-Cl and Na-Cl group which is found in groundwater with a great distance migration in discharge area such as the southern part of the study area, and 4) SO4 group which is distributed in certain areas, particularly Phra Pradaeng aquifer, assumed to be a result of seawater contamination, dissolution of sulfate or sulfide minerals, or human activities. According to the hydrochemical analysis along the groundwater flow path from West to East, Na+ is primarily a product of Plagioclase weathering. Ca2+ and Mg2+ are products of carbonate minerals' dissolution. There is also mixing of groundwater, ion exchange, and alteration of water types as follows: - Recharge area (West of Lao Khwan) => Discharge area (West of Chao Phraya Basin): Rainwater => Ca-HCO3 => Na-Ca-HCO3 => Ca-Na-HCO3 => Ca-Na-Mg-HCO3 => Ca-Na-Mg-HCO3-Cl-SO4. - Recharge area (Tha Maka) => Discharge area (Sai Noi, Pathum Thani): Rainwater Ca- HCO3 => Ca-Mg-HCO3 => Ca-Mg-Na-HCO3=> Na-HCO3-Cl=>Ca-Na-Mg-Cl. The following three areas of categorized groundwater types were delineated for groundwater quality management: (i) where groundwater quality is high to very high (mostly groundwater types in Group 1). Preventive measures are required for these areas, (ii) where groundwater quality is moderate to high (mostly groundwater types in Group 2). There should be measures taken for groundwater quality monitoring and (iii) in contaminated areas (mostly groundwater types in groups 3 and 4). Remediation measures and groundwater utilization control are necessary. Groundwater quality for agriculture mostly is proper to average, except in the coastal area.