Time-lapse resistivity investigation of salinity changes at an ex-promontory land: a case study of Carey Island, Selangor, Malaysia

Abstract

Time-lapse resistivity measurements and groundwater geochemistry were used to study salinity effect on groundwater aquifer at the ex-promontory-land of Carey Island in Malaysia. Resistivity was measured by ABEM Terrameter SAS4000 and ES10-64 electrode selector. Relationship between earth resistivity and total dissolved solids (TDS) was derived, and with resistivity images, used to identify water types: fresh (ρ e > 6.5 m), brackish (3 m < ρ e < 6.5 m), or saline (ρ e < 3 m). Long-term monitoring of the studied area's groundwater quality via measurements of its time-lapse resistivity showed salinity changes in the island's groundwater aquifers not conforming to seawater-freshwater hydraulic gradient. In some aquifers far from the coast, saline water was dominant, while in some others, freshwater 30 m thick showed groundwater potential. Land transformation is believed to have changed the island's hydrogeology, which receives saltwater pressure all the time, limiting freshwater recharge to the groundwater system. The time-lapse resistivity measurements showed active salinity changes at resistivity-image bottom moving up the image for two seasons' (wet and dry) conditions. The salinity changes are believed to have been caused by incremental tide passing through highly porous material in the active-salinity-change area. The study's results were used to plan a strategy for sustainable groundwater exploration of the island.

Effects of long-term mixed land use of human settlement and oil palm plantation on the groundwater quality of ex-promontory land

“…As expected, ammonium-nitrogen (NH 4 -N) is found quite high in groundwater and exceed the Malaysian NWQS of Class V which is more than 2.7 mg/L (Fig. 4) Generally, in unpolluted waters NH 3 and NH 4 compounds occur in relatively small quantities, usually on the order of 1 mgL -1 or less [27]. Nitrate (NO 3 -) causes the most concern in terms of pollutant in the freshwater source.…”

“…Construction and exploration of deep wells at Carey Island andKelanang village in the district were also conducted to seek groundwater resources [2].Recently, a further study has been carried out to determine the occurrence of freshwater lens and seawater intrusion in the island [3][4][5]. Other studies on contamination of aquifers and water sources have also been conducted [6][7][8][9].…”

Soil Moisture Content and Density Prediction Using Laboratory Resistivity Experiment

“…The basis of geophysics is the study of earth using a quantitative physical scence approach. In Malaysia, most ongoing geophysical methods are effectively used for field exploration purposes relating to the engineering, environmental and archeological studies such as subsurface profile mapping in order to locate bedrock [2], boulder and cavity [3], groundwater resources [4] - [7] and contamination [8], [9], leachate migration [10], mining [11] and archeology [12]. Geophysical techniques are an indirect or surface method which consists of seismic, geoelectrical and induced polarization, ground penetrating radar, gravity, magnet and electromagnetic.…”

Geophysical Assessment of Groundwater Potential: A Case Study from Mian Channu Area, Pakistan

“…Electrical resistivity methods are the most successful geophysical techniques for the assessment of aquifer potential. These techniques are extensively used to apply on both high and low resistive formations and are useful tools to study the groundwater vulnerability (Hubbard and Rubin ; Sørensen et al ) and salinity effect on the aquifer system (Mondal et al ; Baharuddin et al ; Son ). Specifically, electrical resistivity methods are commonly used to deal with the solutions of different geological and environmental problems.…”