Groundwater Characteristics in Nickel Laterite Deposits in the Pomalaa Region, Kolaka Regency, Southeast Sulawesi Insights from Resistivity, Pumping Test, and Water Chemistry

Abstract

This study describes the groundwater characteristics including aquifer layer identification, hydraulic parameters, and water chemistry in nickel laterite deposits. The research area is located in Pomalaa, Southeast Sulawesi that is covered by ultramafic rocks. Electrical Resistivity Tomography was used to interpret subsurface layers into schematic laterite profile and hydrostratigraphic unit, correlated with borehole drilling data. Electrical Resistivity Tomography uses resistivity value as a physical property response to differentiate rock types. Moreover, the direction of groundwater flow was determined through groundwater level mapping in 38 observed wells. Pumping test is conducted to obtain hydraulic conductivity and transmissivity of the identified aquifer, while groundwater sample is also taken to be tested for chemical content identification. The resistivity data processing identified that limonite zone has 144–604 ohm.m as aquitard, saprolite has 5–144 ohm.m as aquifer, and bedrock (ultramafic rock) has 144 – 1200 ohm.m as aquifuge. The saprolite layer is at a depth of 14,18–36 m and has good porosity and permeability. The groundwater flow direction is illustrated towards the north of the study area. The aquifer potential can indeed supply water needs locally based on the hydraulic conductivity and transmissivity value of the aquifer. However, the groundwater quality index calculation shows that the groundwater in the study area has poor quality (groundwater quality index value 63,7), thus requiring water treatment to be utilized by the community. In summary, Electrical Resistivity Tomography is an effective tool for categorizing aquifer and non-aquifer layers in nickel laterite deposits, combined with flow analysis, pumping tests, and chemical analysis for groundwater characterization.