This study is an integrated analysis of the Buayan-Malungon watershed’s hydrogeochemistry based on several groundwater datasets (i.e., General Santos City, Municipality of Alabel, Malungon, and Tupi) from the Mines and Geosciences Bureau XII. This research aims to characterize the groundwater quality in terms of drinking usage, classify groundwater sources in terms of dominant ions, and investigate the hydrogeochemical processes.
Hydrogeological analyses were done by comparing different groundwater parameters to the Philippine National Standard for Drinking Water (PNSDW), generating spatial maps to visualize the distribution of water quality results using ArcMap 10.7, and producing different hydrogeochemical diagrams using the AqQa software and Microsoft Excel. Correlational statistics were also employed to identify the correlation coefficient of various parameters using Microsoft excel. Statistical Package for Social Sciences (SPSS) was used to identify the significant difference between the water quality parameters and type of water sources through Analysis of Variance (ANOVA).
The results show that most of the water samples are within the PNSDW’s allowable limit. However, some samples exceed in terms of TDS, nitrates, turbidity, Cr, Ni, Zn, and Mn. The spatial distribution of the different water quality parameters represented areas with higher or anomalous values/concentrations. Towards west are pH and nitrates; South are conductivity, salinity, and TDS; Central to south, HCO3, K, Na, SO4, Cl; Northwest/Southeast, Ca; North/Southeast, Mg; Northwest, Zn, Ni, Cr; South, Mn.
The Piper Diagram identified two (2) dominant types of facies, (1) the fresh-recharge water type, (Ca-HCO3) comprising 44% of the total samples, and (2) the deep-source, alkaline water type (Na-HCO3) comprising 8.88%. The mixed water types such as (3) CaMgHCO3, (4) MgCaHCO3, (5) NaMgHCO3, (6) MgNaHCO3, (7) NaCaHCO3, (8) CaNaHCO3, and (9) CaMgHCO3SO4 comprise almost 46.6%. The Durov plot identifies major hydrogeological processes such as (1) ion exchange (2) weathering of silicate and carbonate dissolution, and (3) mixing as dominant processes affecting the dissolved constituents in the area. Gibb’s plot showed that the groundwater quality is dominantly influenced by lithology and secondarily by environmental and anthropogenic factors. Pearson correlation analysis of the various parameters revealed a strong to moderate relationship. ANOVA analysis showed various water quality parameters having significant differences in the type of water sources.
Keywords: hydrogeochemistry, water quality, dominant ions, spatial distribution