Hydrostratigraphy and geochemistry at a coastal sandfill in Singapore |
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| Authors: | Lloyd H C Chua Edmond Y M Lo David L Freyberg E B Shuy T T Lim S K Tan Mzila Ngonidzashe |
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| Institution: | (1) Division of Environmental and Water Resources Engineering, School of Civil and Environmental Engineering, Nanyang Technological University, Singapore, 639798, Singapore;(2) Department of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305-4020, USA |
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| Abstract: | A characterization study was carried out in a 10-m-thick sandfill, formed by hydraulic filling with marine sand, in Singapore. Placement methods and compaction were found to influence hydrostratigraphy. The deepest part of the sandfill consists of a loose sand layer and is overlain by a medium sand layer extending to mean sea level (MSL). At certain locations, a thin silty-sand layer was found. The different layers within the saturated zone were found to have different values for hydraulic conductivity (K) and groundwater flow velocity. Estimates for K increase according to the following sequence of methods: repacked sand column, step-pumping test, grain-size analysis and slug test. Slug tests and grain-size analysis yielded comparable estimates of K. The freshwater lens in the older part of the sandfill is about 2 m thicker than in a recently completed area. Comparisons of Ca2+/Cl?, Mg2+/Cl?, K +/Cl? and \({\text{Cl}}^{{\text{ - }}} {\text{/}}{\left( {{\text{Cl}}^{{\text{ - }}} {\text{ + HCO}}^{{\text{ - }}}_{{\text{3}}} } \right)}\) ratios indicate that the chemical composition of the groundwater at shallower depths has probably been altered by mineral dissolution. Weathering of carbonate minerals was found to be a major contributor to the major ions at these depths. The molar ratios approach the value for seawater at greater depths. The groundwater is close to equilibrium with calcite. |
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| Keywords: | Sandfill Hydrostratigraphy Heterogeneity Mineral dissolution Hydraulic properties |
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