Electrical Resistivity Tomography And Induced Polarization Study For Groundwater Exploration In The Agricultural Development Areas of Brunei Darussalam

Electrical Resistivity Tomography And Induced Polarization Study For Groundwater Exploration In The Agricultural Development Areas of Brunei Darussalam | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Electrical Resistivity Tomography And Induced Polarization Study For Groundwater Exploration In The Agricultural Development Areas of Brunei Darussalam Lieyana Azffri, Stefan Herwig Gödeke, Mohammad Faizan Ibrahim This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-657012/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 01 Apr, 2022 Read the published version in Environmental Earth Sciences → Version 1 posted 4 You are reading this latest preprint version Abstract Electrical Resistivity Tomography (ERT) and Induced Polarization (IP) study was carried out for groundwater exploration at eight agricultural development areas in Brunei Darussalam. The study was undertaken to meet the growing demands of water supply in the Brunei agricultural sector, particularly for paddy field irrigation. A total of nineteen survey lines with survey lengths of up to 800 m and investigation depths of up to 150 m below ground level were conducted to delineate subsurface geological structures, formations and aquifer zones in the study area. Aquifer zones with resistivity values ranging from 1 to 100 ohm-m and chargeability values of less than 1 mV/V were detected in all surveyed locations. New groundwater well drilling was conducted at two of the surveyed sites based on interpretations of 2D resistivity and chargeability inversion models. Water well drilling encountered aquifer zones, which were primarily in sandy layers. Hydraulic tests revealed groundwater yields of 4.3 and 288 m³/day. Estimated transmissivity values of the aquifer units based on pumping tests are 0.53 and 109 m²/day, while their hydraulic conductivity values are 0.05 and 2.75 m/day. Estimated parameters of the aquifer units indicate weak to moderate groundwater yield for withdrawal and distribution for irrigation purposes at the investigated sites. The present study helped decision-makers take suitable measures for placing future irrigation wells and achieve significant groundwater exploration results in the study area. Geology Environmental Chemistry Electrical Resistivity Tomography Induced Polarization Groundwater Agricultural Areas Brunei Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction Groundwater is an essential source of freshwater that is used globally for domestic, industrial and agricultural purposes. In particular, groundwater use for agricultural development has grown exponentially over the past decade, especially in heavily populated areas such as South Asia, Africa and China (Shah et al. 2006 ; Giordano and Villholth 2007 ). However, competing demands and water scarcity often resulted in mismanagement of the water resources (Tamas 2003 ). In countries like China and India, concerns over groundwater quality are rising due to improper disposal of urban wastewater into natural streams or its reuse for irrigation, which ultimately seeps into groundwater (Watto et al. 2018 ). On the other hand, microbiological processes can break down even recalcitrant contaminants (Gӧdeke et al. 2008). Possible complex contamination scenarios may need a range of remediation and assessment measures (Marshall et al. 2019 ). In Brunei, the government relies almost entirely on surface water resources, given the relatively sparse population of around 500,000 (DEPS 2020 ). However, industrialization and urbanization put more pressure on its surface and groundwater resources (Suhip et al. 2020 ). Furthermore, concern over the increase in water demand was highlighted through the Brunei Vision 2035, where the vision calls attention to the public utilities regarding continuous, adequate, and quality water (DEPS 2020 ). Moreover, climate variability causes greater unpredictability in precipitation, including periods of heavier rainfall as well as drought (Thornton et al. 2014 ). Groundwater recharge is also highly dependent on climate (Moeck et al. 2020 ). One study in Brunei found that climate changes were evident from increased rainfall intensity, pointing to the need for careful water management under a changing climate (Gödeke et al. 2020). Groundwater abstraction in Brunei is currently limited to the local bottled water industry found within the Sungai Liang area of the Belait District (FAO 2011 ). This industry has been supplying bottled mineral water from its original artesian well for almost three decades. A previous study in Brunei investigated subsurface layers and groundwater levels using the seismic refraction method at the Berakas area in the Brunei-Muara District (Azhar et al. 2019 ). The study presented velocity profiles and seismic tomography for groundwater system evaluation. Furthermore, water samples from nearby springs revealed low pH values and high sulphate concentrations, likely due to localised acid sulphate soils present in the investigated area. Grealish and Fitzpatrick ( 2013 ) found that acid sulphate soils occur in Brunei within flat inland areas important for agricultural land. A resistivity study in Brunei by Azffri et al. (in press) found that the interpreted groundwater zone yields low resistivity values ranging from 5 to 100 ohm-m at the Labi agricultural site in the Belait District. Furthermore, a borehole drilling encountered sandy aquifer units in the investigated area. Further groundwater pumping revealed a moderate groundwater yield of 288 m³/day and estimated aquifer transmissivity of 109 m²/day. In this study, groundwater exploration was conducted at eight agricultural development areas in Brunei (Fig. 1 ), Electrical Resistivity Tomography (ERT) and Induced Polarization (IP). The ERT and IP surveys helped delineate subsurface geological structures, formations and aquifer zones. The study revealed subsurface resistivity and chargeability variations in the study area. Interpreted 2D subsurface resistivity and chargeability inversion models delineated potential aquifer zones and subsequently identified suitable prospects for groundwater well drilling and construction of groundwater pumping wells in two of the surveyed areas. Hydraulic test results of the newly drilled groundwater pumping wells helped estimate the aquifer transmissivity and hydraulic conductivity for aquifer characteristics. Geological Settings And Survey Locations Brunei lies on the north coast of Borneo Island in Southeast Asia, with a total land area of 5,765 km². It is divided into four main districts: Brunei-Muara, Tutong, Belait and Temburong. Brunei’s climate is typical of the equatorial tropics, characterized by high rainfall and temperatures throughout the year. Rainfall shows a seasonal pattern with wet and dry seasons throughout the year. The wet seasons are from September to January and May to June, and the drier seasons are from February to March and July to August. The average annual rainfall from 2019 was 2909 mm. The temperature is relatively uniform throughout the year, ranging from 23.8 to 32.1°C (BDMD, 2021 ). Brunei is drained by four main river basins, namely the Brunei, Tutong, Belait and Temburong Rivers ( Chuan 1992 ) . The Belait river basin (Fig. 1 ) is the largest, with an area of 2,700 km². Peat swamp forests dominate the lower catchment areas. Some areas in the upper catchment have been cleared for agricultural development areas. The Tutong river basin has an area of about 1,300 km² (Chuan 1992 ). The basin comprises a floodplain in the lower catchment areas, with the upper catchment is forested with few areas cleared for agricultural development areas. The Brunei river basin flows into the Brunei Bay. The upper parts of the river are a major freshwater source for urban water. The Temburong basin is the smallest river basin in the study area, with 430 km². Brunei's geology is closely linked to its neighbouring Malaysian states of Sarawak and Sabah, and many regional geological studies have been conducted (Liechti et al. 1960 ; Wilford 1961 ; Sandal 1996 ; Hutchison 2005 ). Tectonic events govern the geological setting in this region since the Cenozoic era (Hall 1997 ; Hall and Nichols 2002 ; Baillie et al. 2004). Overall compressional tectonics in the northwest Borneo margin formed deformation zones of mountainous terrains extending through central Borneo. Subsequent uplift and erosion of this mountainous range in the hinterland during the Early and Middle Miocene resulted in rapid sedimentation into basin depocenters, forming major deltaic systems in the region (Sandal 1996 ; Hutchison 2005 ). The Champion and Baram delta systems have been major siliciclastic sedimentation locations in both onshore and offshore Brunei areas since the Miocene period (Saller and Blake 2003; Torres et al. 2011 ; Lambiase and Cullen 2013 ). Most sediments are gently deformed due to occasional compressional tectonics during the Miocene to Pliocene (Sandal 1996 ; Morley et al. 2003 ). Stratigraphic formations occur within depositional environments, from the coastal plain to deep marine (Tate 1974 ; Sandal 1996 ). In the study area, quaternary rock formations overlay older bedrocks of the Liang, Miri, Seria, Lambir, Belait, Setap and Meligan Formations (Fig. 2 and Fig. 3 ). The lithologies of the formations are mainly made up of alternating sand and shales. Coal occurrences have been recorded in the Liang and Belait Formations (Fig. 3 ; Osli et al. 2021 ). In the present study, the survey locations were specifically situated within flat-lying or lowland areas with no significant geological structure outcrop seen on the surface. Topographical elevations of the survey locations range from 2 to 5 m above mean sea level. All the survey locations are situated within recent sediments deposited in sub-aerial alluvial floodplain environment (Tate, 1974 ). Methodology Theory Geoelectrical resistivity methods have been widely used in groundwater exploration, engineering and environmental applications (Dahlin 1996 ; Keller and Frischknecht 1996; Sudha et al. 2009 ; Galazoulas et al. 2015 ; Lech et al. 2020 ). Electrical resistivity tomography (ERT) is one of the most commonly used geoelectrical resistivity methods to map subsurface electrical resistivity (Griffiths and Barker, 1993 ; Dahlin, 2001 ), which subsequently can be interpreted from a hydrological perspective (e.g., Saad et al. 2012 ; Ashraf et al. 2018 ; Aziman et al. 2018 ; Riwayat et al. 2018 ; Thiagarajan et al. 2018 ; Kumar et al. 2020a , b ). The electrical resistivity method estimates the variation in the ground's resistivity by injecting direct current into the ground (Fig. 4 ) through a set of current electrodes (C1 and C2) and measuring the resulting voltage differences at the potential electrodes (P1 and P2). The resistivity is determined from Ohm’s law using the voltage differences for a known current and correcting the current geometrical pathway through the earth. From the current ( I ), voltage ( V ) and geometric factor ( k ), the apparent resistivity ( pa ) was calculated using the following Eq. 1 (Telford et al. 1990 ; Dahlin 2001 ; Binley et al. 2015): (1) Resistivity interpretations have proved helpful for detecting geological units of unconsolidated sediments and groundwater prospects (e.g., Saad et al. 2012 ; Ashraf et al. 2018 ; Aziman et al. 2018 ; Riwayat et al. 2018 ; Thiagarajan et al. 2018 ; Kumar et al. 2020a , b ). Igneous and metamorphic rocks, depending on the degree of fracturing and the percentage of the fractures filled with groundwater, generally have higher resistivities than sedimentary rocks, which are usually more porous and have higher water content. For example, the resistivity of granite ranges between 5,000 to 10,000 ohm-m depending on the degree of fracturing and moisture content (e.g., Kumar et al. 2020a , b ), whereas the resistivity of sand and clay materials ranges within 1 to 1,000 ohm-m (e.g., Saad et al. 2012 ; Ashraf et al. 2018 ). Furthermore, clay has significantly lower resistivity values than sand. The resistivity values of clay range between 1 to 100 ohm-m, whereas the resistivity values of sand range between 60 to 1000 ohm-m (Keller and Frischknecht, 1996). The degree of overlap in different resistivities of different types of materials and waters is dependent on several factors such as porosity, degree of water saturation and concentration of dissolved salts (Samouëlian et al. 2005 ; Hazreek et al. 2015 ; Annuar and Nordiana 2018). Keller and Frischknecht (1996) found that groundwater yields low resistivity values ranging from 10 to 100 ohm-m depending on the concentration of dissolved salts. Due to the ambiguity of resistivity values with overlapping resistivity ranges, several researchers have used an integrated geophysical approach combining resistivity with the induced polarization (IP) technique to solve complicated geological and hydrological problems (e.g., Goldman and Neubauer 1994 ; Amaya et al. 2016 ; Kumar et al. 2016a , b ; Rehman et al. 2016 ). The IP method uses the voltage decay characteristics to study the soil’s induced polarization, also known as the chargeability (Telford et al. 1990 ; Keller and Frischknecht 1996; Kearey et al. 2002 ). Subsurface chargeability measurements have been used to determine high clay content in sedimentary settings. The clay particles have a negative charge that can attract positive ions from the electrolyte contained in the cavities of rocks (Telford et al. 1990 ). High chargeability measurements have been observed for fine-grained sediments such as clay, while deposits with larger particle size like sand and gravel typically yield lower chargeability values (Keller and Frischknecht 1996; Slater and Lesmes 2002 ; Alabi et al. 2010 ; Amaya et al. 2016 ). Hydraulic tests of groundwater wells are crucial for understanding the aquifer potential in any hydrogeological setting (Ashraf et al. 2018 ; Aziman et al. 2018 ; Kumar et al. 2020b ). Transmissivity and hydraulic conductivity are two key hydraulic parameters that can help determine the aquifer characteristics (e.g., Mogaji et al. 2011 ; Shen et al. 2015 ; Wu et al. 2017 ). Furthermore, the records of time-drawdown data have been used to evaluate the aquifer transmissivity and hydraulic conductivity. The Cooper-Jacob solution assumes that the aquifer is confined, homogenous, isotropic and of uniform thickness over the area of pumping. The assumption discussed in Fetter ( 2001 ) for determining aquifer parameters from time-drawdown data is that the pumping well is screened throughout the entire thickness of the aquifer being tested. Using the Cooper-Jacob straight-line time-drawdown method, the aquifer transmissivity was calculated using Eq. 2 (Cooper and Jacob 1946 ): (2) Where Q is the pumping rate and ho - h is the calculated change in drawdown between initial and final drawdown. From the calculated transmissivity (T) and the aquifer thickness ( b ), the hydraulic conductivity ( K ) was calculated using Eq. 3 : (3) Data acquisition and processing Data acquisition was conducted with a combined measurement of resistivity and chargeability. A total of 19 survey lines from eight agricultural sites were carried out in the study area (Table 1 ). Information such as aerial, topographical and geological maps is required when considering resistivity surveying suitability (to select profile lines). The selection of survey locations was predominantly planned based on area availability and accessibility. The survey locations were generally free from obstacles, such as houses, crops or fences. In some areas, permission from landowners was needed to perform the surveys on their land. Table 1 Survey parameters for each resistivity survey line (sites 1-8). Survey location Survey line Electrode configuration Electrode spacing (m) Survey length (m) Site 1 1 - 3 Gradient 10 800 12 Pole-dipole 5, 10 400 19 Pole-dipole 5, 10 400 Site 2 4 - 8 Gradient 10 800 13 Pole-dipole 5, 10 400 Site 3 14 Pole-dipole 5, 10 400 Site 4 15 Pole-dipole 5, 10 400 Site 5 16 Pole-dipole 5, 10 400 Site 6 9 Gradient 10 800 Site 7 10 - 11 Gradient 10 800 Site 8 17 - 18 Pole-dipole 5, 10 400 Two sets of data were acquired between the years 2018 and 2020. The first set of data acquisition was carried out in 2018 using the ABEM Terrameter LS2 resistivity meter covering a lateral distance of 800 m with eighty stainless-steel electrodes arranged at an equal length of 10 m (Line 1–11). This set of data acquisition was conducted using the gradient array configuration. The gradient array configuration uses two current electrodes and two potential electrodes, placed with equal spacings (Fig. 4 ). The gradient method is suitable for multichannel acquisition due to dense and fast data point collection (Dahlin and Zhou 2006 ; Loke 2012 ; Aizebeokhai and Oyeyemi 2014 ). With the multichannel acquisition, resistivity measurements continue down the row of electrodes until the whole survey line is measured. The second set of data acquisition was conducted from 2019 through to 2020 using the ABEM SAS4000 resistivity meter covering a lateral distance of 400 m (Line 12–19). The line uses sixty-one electrodes with 5 m spacings for the inner cables and 10 m spacings for the outer cables. This set of data acquisition was conducted using the pole-dipole array configuration. For the pole-dipole array configuration, one transmitting current electrode, also known as the infinity electrode, was moved to an effective infinity distance, approximately five times the survey depth (Fig. 4 ). Simultaneously, the other current electrode is placed in the vicinity of the two potential electrodes. The pole-dipole method is suitable for deep earth investigation, making it a popular option among researchers (Saad et al. 2012 ; Annuar and Nordiana 2018; Ashraf et al. 2018 ; Kumar et al. 2020a ). Raw data were processed and inverted using the ZONDRES2D software (in DAT format). Resistivity and chargeability inversion models were obtained from the inversion process (Loke and Barker 1996 ). The inversion process averaged the resistance measurements to apparent resistivity values and the apparent chargeability time window measurements to integral chargeability values. The Gauss-Newton inversion method was used to determine the appropriate resistivity values (Griffith and Barker 1993; Loke and Barker 1996 ; Dahlin 2001 ; Loke and Dahlin 2002 ). 2D pseudo-sections were generated to help delineate subsurface geological structures, formations and aquifer zones in the surveyed areas. All the pseudo-sections displayed present RMS errors of not more than 5%, which indicates the measured data are fitted with the computed apparent resistivity; the number of iterations for each survey was ten. Groundwater well drilling and hydraulic tests Groundwater wells were drilled at site-1 in the Brunei-Muara District (Well-B1) and site-5 in the Belait District (Well-L1) through the aquifer zones inferred from resistivity and chargeability interpretations. Borehole drilling was conducted using a straight rotary method. The hole was advanced by rotating a drill string consisting of a series of hollow drill rods to the bottom attached to a 10-inch drill bit. Water-based drilling fluid under pressure was introduced into the bottom of the hole through the hollow drill rods and passages into the bit. The drilling fluid served the dual function of cooling the rotating bit as it entered the borehole and removing the rock cuttings from the bottom of the hole. The rock cuttings move through the annular space between the drill rods and the walls of the hole as they returned to the surface. Rock cuttings were collected at an interval of 3 m, primarily for soil identification purposes. 6-inch diameter UPVC casings and screens with 1.5 mm openings were used to construct the groundwater pumping wells. A gravel pack filter was installed between the aquifer and UPVC screens. A 4-inch submersible pump was installed inside the well to continuously pump water out from the well through a 2-inch riser pipe for hydraulic testing. The pumping well responses in terms of the water discharge and changes in water depth were recorded using a volume meter connected at the outlet pipe on the surface and a water depth meter installed inside the well annulus. None of the newly drilled water wells had yet a nearby observation well that could have been used for time-drawdown observation due to pumping. Hydraulic tests of the newly drilled wells were investigated using time-drawdown data gathered from the pumping well. A five-step drawdown test with different flow rates, constant discharge test and recovery test was carried out in this investigation. Results Interpretations of 2D resistivity and chargeability inversion models Electrical resistivity tomography and induced polarization revealed subsurface resistivity and chargeability variations in the study area with resistivity values from 1 to 500 ohm-m and chargeability values from 0 to 10 mV/V to a depth of about 150 m from the surface. Aquifer zones were also detected at varying depths in all surveyed locations with resistivity values ranging from 1 to 100 ohm-m (Table 2 ). Few shallow boreholes (< 30 m) with lithology information exist within the study area. Lithology correlations with resistivity models were possible. However, they are limited to shallow depths. Two new boreholes were drilled in two selected sites to investigate the deeper rock strata and groundwater availability. The two pilot wells, namely Well-B1 and Well-L1, were placed explicitly in water-scarce agricultural areas used for paddy plantation. The two sites are Bebuloh (site-1) and Lot Sengkuang (site-5). These two sites were found to have favourable groundwater prospects based on resistivity and chargeability interpretations. The detailed interpretation and results of two ERT and IP profiles are presented in this paper, delineating subsurface geological structure, formations and aquifer zones of the area. Line 12 (Site-1) Table 2 Resistivity surveys of sites 1-8 with depth and resistivity of aquifer zone. Survey location Survey line Depth of aquifer zone from the surface (m) Resistivity of aquifer zone (ohm-m) Site-1 ERT 1-3 20-30 1 - 100 ERT 12 10 1 - 100 ERT 19 20 1 - 50 Site-2 ERT 4-8 20-40 1 - 100 ERT 13 50 5 - 100 Site-3 ERT 14 20-30 1 - 100 Site-4 ERT 15 20 1 - 50 Site-5 ERT 16 20-40 5 - 100 Site-6 ERT 9 20 1 - 100 Site-7 ERT 10-11 10-20 1 - 100 Site-8 ERT 17-18 10-20 1 - 100 Inverse model resistivity of ERT 12 revealed resistivity variations to a depth of 110 m from the surface (Fig. 5 ). Two subsurface layers differentiated by resistivity values were deduced. The first layer is interpreted as the topsoil and is distinctive of resistivities ranging from 1 to 140 ohm-m. A second layer distinct of resistivities ranging from 1 to 100 ohm-m is interpreted as the aquifer zone. The saturated zone is about 10 m below ground level. Inverse model chargeability of IP 12 revealed low chargeability values of the aquifer zone of less than 1 mV/V. High chargeability values ranging from 5–10 mV/V were observed in the topsoil layer and are assumed to be composed of fine-grained materials such as clay. Groundwater Well-B1 was drilled to about 96 m from the surface at site-1 (line 12) based on the resistivity and chargeability interpretations. Line 16 (Site-5) Inverse model resistivity of ERT 16 revealed resistivity variations to a depth of 100 m from the surface (Fig. 6 ). Two subsurface layers were deduced based on resistivity values. The first layer is interpreted as topsoil with resistivities ranging from 100 to 500 ohm-m. The second layer with resistivities ranging from 1 to 100 ohm-m was observed at a depth of about 20 to 40 m below ground level. This layer is interpreted as the aquifer zone. Inverse model chargeability of IP 16 indicated chargeability values at line 16. High chargeability values ranging from 5–10 mV/V were observed at a depth of about 40 to 50 m from the surface, possibly extending towards greater depths and are assumed to be composed of fine-grained materials such as clay. Groundwater Well-L1 was drilled to 80 m from the surface at site-5 (line 16) based on the resistivity and chargeability interpretations. Borehole lithology correlation with resistivity datasets Two pilot wells were drilled at site-1 and site-5 based on the resistivity and chargeability data interpretations (line 12 and 16). Borehole lithology of Well-B1 and Well-L1 were correlated with resistivity models and are shown in Fig. 7 . Both the newly drilled wells encountered aquifer zones while drilling, which was primarily in sandy layers. The borehole lithology information revealed the inhomogeneity of the soil materials in the study area, mainly composed of multiple alternating sand and clay layers. Furthermore, the layers cannot be clearly distinguished in terms of their resistivities. However, it can be inferred that the overall higher clay content at Well-B1 yields lower resistivity values ranging from 1 to 30 ohm-m, whereas higher sand content at Well-L1 yields higher resistivity values ranging from 5 to 200 ohm-m. Well-B1 is mainly composed of clay and sand with traces of decomposed peat at the top layer. The predominance of clay deposits with resistivity values of 3 to 30 ohm-m may be explained by the deposition of fine-grained materials in an alluvial floodplain, specifically a lacustrine environment. Well-L1 is mainly composed of fine to medium sand, clay, sandstone and mudstone. The top part of the lithology log mainly consists of fluvial deposits (clay, sand and gravel) with resistivity values between 60 to 200 ohm-m. The lower part of the lithology log with resistivities ranging between 5–60 ohm-m appears to be associated with alluvial deposits (mix of clay and sand). Hydraulic tests for aquifer characteristics At Well-B1, the UPVC screens were installed at the saturated clayey sand layer at depths of 84 to 95 m below ground level (Fig. 7 ). The constant rate pumping test at Well-B1 was carried out for 4 hours with a steady pumping rate of 4.3 m³/day and a maximum drawdown of 3.63 m. At Well-L1, the UPVC screens were installed be at sand and sandstone layers at depths of 18 to 28 m and 48 to 78 m below ground level (Fig. 7 ). The constant rate pumping test at Well-L1 was carried out for 24 hours with a steady pumping rate of 288 m³/day and a maximum drawdown of 1.52 m. The time-drawdown cross-plot of Well-B1 and Well-L1 are shown in Fig. 8 . Their calculated hydraulic parameters are shown in Table 3 . The unsteady Cooper-Jacob time-drawdown analysis revealed the estimated aquifer transmissivity values of 0.53 and 109.8 m²/day at Well-B1 and Well-L1, respectively. The estimated hydraulic conductivity of the clayey sand unit (with an estimated aquifer thickness of 11 m) at Well-B1 is 0.05 m/day. Lower hydraulic conductivity values are typically associated with fine-grained materials such as clay deposits (Spitz and Moreno 1996 ). The hydraulic conductivity for the sandy units (with an estimated aquifer thickness of 40 m) at Well-L1 is 2.75 m/day. Based on the time-drawdown data and estimated hydraulic parameters of the aquifer, weak to moderate groundwater yield is expected for withdrawal and distribution in the investigated agricultural areas for irrigation purposes. Table 3 Aquifer characteristics estimated through hydraulic tests of newly drilled groundwater wells. Well Pumping duration (mins) Initial and final water depth (m) Discharge rate (m³/day) Transmissivity (m²/day) Hydraulic conductivity (m/day) B1 240 44.5 / 48.2 4.3 0.53 0.05 L1 1440 21.4 / 22.9 288 109.8 2.75 Discussion Geophysical study and results of the 2D inverted resistivity model at eight agricultural development areas and their interpretations of hydrogeology revealed aquifer zones in all the surveyed locations found at varying depths with variation in apparent resistivities. The 2D inverted resistivity models delineated the subsurface geological formations and structures in the study area, showing resistivity contrasts between topsoil and aquifer zones. The resistivity of the topsoil layer ranges from 1 to 500 ohm-m, and the chargeability values range from 0 to 10 mV/V. High chargeability values were assumed to be composed of fine-grained materials such as clay. The resistivity of the aquifer zone ranges from 1 to 100 ohm-m, and the chargeability values are less than 1 mV/V. Based on the resistivity and chargeability interpretations, two new groundwater wells were drilled at site-1 (line 12) and site-5 (line 16). Based on the 2D resistivity and chargeability data interpretation and the yields of the newly drilled boreholes, it was found that site-5 has a higher potentiality for groundwater exploitation compared to site-1. Borehole drilling of groundwater Well-L1 encountered multiple saturated sand layers with a moderate groundwater yield of 288 m³/day. Well-L1 is currently used for groundwater withdrawal and distribution for irrigation purposes at site-5. Borehole drilling of groundwater Well-B1 encountered a saturated clayey sand layer with a poor groundwater yield of 4.3 m³/day. Therefore, Well-B1 was not used for groundwater withdrawal for irrigation at site-1. Our findings indicate that due to the inhomogeneous properties of the soil materials comprising mainly alternating sand and clay, the resistivity and chargeability values often overlap, resulting in ambiguous interpretations. Future studies should include drilling groundwater test wells to determine the soil properties and aquifer potential further. Conclusion Electrical resistivity tomography and induced polarization methods were successfully applied to detect groundwater at eight agricultural development areas in Brunei targeted for irrigation. Resistivity datasets showed subsurface resistivity variations ranging from about 1 to 500 ohm-m in the study area. This suggested variations in geological formations and aquifer systems. 2D inverted resistivity model helped mapped aquifer zones in all the surveyed locations, mainly at shallower depths (< 100 m). Resistivities ranging from 1 to 100 ohm-m and chargeability values of less than 1 mV/V signify favourable groundwater prospects underneath the topsoil layer and correlated with borehole lithology data and drilling results and site-5. New groundwater well drilling was conducted to 96 m depth at site-1 and 80 m depth at site-5 with groundwater yields of 4.3 and 288 m³/day, respectively. The estimated aquifer transmissivity values are 0.53 and 109.8 m²/day, while their hydraulic conductivity values are 0.05 and 2.75 m/day, respectively. Estimated parameters of the aquifer units indicate significant variation in the amount of groundwater availability for withdrawal and distribution for irrigation purposes in the study area. The combination of IP and ERT significantly helped to identify the suitable drilling for Well-L1. The study presented the resistivity and chargeability characteristics, as well as the results of two newly drilled groundwater pumping wells of the studied area, and evaluated groundwater availability for groundwater use for irrigation. Future studies are necessary to locate irrigation wells with significant groundwater potential. Future drilling is planned to install groundwater monitoring wells next to the groundwater pumping well. Declarations Acknowledgements This project was supported by research grant UBD/RSCH/URC//RG(b)/2020/017 from Universiti Brunei Darussalam. The authors thank the Ministry of Primary Resources and Tourism, Department of Agriculture and Agrifood, Brunei Darussalam for the supplied data and for allowing the publication of this study. The authors thank Preston Geocem Brunei for valuable interactions and discussions on the resistivity surveys and groundwater well drilling results. Conflict of Interest The authors declare no conflict of interest. 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J Appl Geophy 29:211–226 Hall R (1997) Cenozoic tectonics of SE Asia and Australasia. In: Howes JVC, Noble RA (eds) Petroleum systems of SE Asia and Australasia. Indonesian Petroleum Association, Jakarta, pp 47–62 Hall R, Nichols G (2002) Cenozoic sedimentation and tectonics in Borneo: climatic influences on orogenesis. In Jones SJ, Frostick L, Sediment flux to basins: causes, controls and consequences, pp 5–22. Geological Society London, Special Publications Hazreek ZAM, Rosli S, Chitral WD, Fauziah A, Azhar ATS, Aziman M, Ismail B (2015) Soil Identification using Field Electrical Resistivity Method. J Phys: Conference Series, Vol 622, Issue 1:012030 Hutchison CS (2005) Geology of North-West Borneo: Sarawak, Brunei and Sabah. Elsevier, Amsterdam, 421p Kearey P, Brooks M, Hill I (2002) An Introduction to Geophysical Exploration. Third Edition. Blackwell Science Ltd Keller GV, Frischknect FC (1996) Electrical methods in geophysical prospecting. Pergamon Press Inc., Oxford Kumar D, Mondal S, Nanda MJ, Harini P, Soma Sekhar BMV, Sen MK (2016a) Two-dimensional electrical resistivity tomography (ERT) and time-domain-induced polarization (TDIP) study in hard rock for groundwater investigation: a case study at Choutuppal Telangana, India. Arab J Geosci 9(5):1–15. https://doi.org/10.1007/s12517-016-2382-1 Kumar D, Mondal S, Soma Sekhar BMV, Balaji T, Nanda MJ, Rangarajan R (2016b) Full waveform inversion of 2D resistivity and IP data for groundwater exploration in granite aquifers: Implications for complex tectonic setting. J Appl Hydrol XXIX (1–4) 9–19 Kumar D, Mondal S, Warsi T (2020a) Deep insight into the complex aquifer and its characteristics from high-resolution electrical resistivity tomography and borehole studies for groundwater exploration and development. J Earth System Sciences 129:68. https://doi.org/10.1007/s12040-019-1336-x Kumar D, Rajesh K, Mondal S, Warsh T, Rangarajan R (2020b) Groundwater exploration in limestone-shale-quartzite terrain through 2D electrical resistivity tomography in Tadipatri, Anantapur district, Andhra Pradesh. J Earth System Sciences, 129(1). https://doi.org/10.1007/s12040-020-1341-0 Lambiase JJ, Cullen AB (2013) Sediment supply systems of the Champion “Delta” of NW Borneo: Implications for deepwater reservoir sandstones. J Asian Earth Sciences 76:356–371 Lech M, Skutnik Z, Bajda M, Markowska-Lech K (2020) Applications of electrical resistivity surveys in solving selected geotechnical and environmental problems. Applied Sciences 10:2263 Liechti P, Roe FN, Hailie NS, Kirk HJC (1960) The geology of Sarawak, Brunei and the Western part of North Borneo. Bulletin 3, Vol 1&2. Geological Survey Department British Territories in Borneo. Government Printing Office, Kuching, Sarawak, 360p Loke MH (2012) Tutorial: 2D and 3D electrical imaging surveys. 172p Loke MH, Barker RD (1996) Rapid least-squares inversion of apparent resistivity pseudosections by quasi-Newton Method. Geophys Prospect 44(1):131–152 Loke MH, Dahlin (2002) A comparison of the Gauss-Newton and quasi-Newton methods in resistivity imaging inversion. J Appl Geophy 49:149–162 Marshall DJ, Abdelhady AA, Wah DTT, Mustapha N, GÓ§deke SH, De Silva LC, Hall-Spencer JM (2019) Biomonitoring acidification using marine gastropods. Sci Total Environ 692:833–843. https://doi.org/10.1016/J.SCITOTENV.2019.07.041 Moeck C, Grech-Cumbo N, Podgorski J, Bretzler A, Gurdak JJ, Berg M, Schirmer M (2020) A global-scale dataset of direct natural groundwater recharge rates: A review of variables, processes and relationships. Sci Total Environ 717:137042. https://doi.org/10.1016/j.scitotenv.2020.137042 Mogaji KA, Olayanju GM, Oladapo MI (2011) Geophysical evaluation of rock type impact on aquifer characterization in the basement complex areas of Ondo state, Southern Nigeria: Geo-electric assessment and Geographic Information Systems (GIS) approach. International Journal of Water Resources Environmental Engineering Vol 3(4):77–86. ISSN 1991-637X Morley C, Back S, Van Rensbergen P, Cravello P, Lambiase J (2003) Characteristics of repeated, detached Miocene-Pliocene tectonic inversion events in a large delta province on an active margin, Brunei Darussalam, Borneo. J Structural Geology 25:1147–1169 Osli LN, Shalaby MR, Islam MA (2021) Source rock characteristics and hydrocarbon generation potential in Brunei-Muara district, Brunei Darussalam: a comparative case study from selected Miocene-Quaternary formations. J of Petroleum Exploration Production. https://doi.org/10.1007/s13202-021-01142-0 Rehman F, Abuelnaga HSO, Harbi HM, Cheema T, Atef AH (2016) Using a combined electrical resistivity imaging and induced polarization techniques with the chemical analysis in determining groundwater pollution at Al Misk Lake, Eastern Jeddah, Saudi Arabia. Arab J Geosci 9:286. https://doi10.1007/s12517-016-2423-9 Riwayat AI, Ahmad Nazri MA, Zainul MH (2018) Application of Electrical Resistivity Method (ERM) in Groundwater Exploration. Journal of Physics: Conference Series, Vol 995 Saad R, Nawawi MN, Mohamad ET (2012) Groundwater detection in alluvium using 2-D Electrical Resistivity Tomography (ERT). J Geotechnical Engineering, pp 369–376 Saller A, Blake G (2003) Sequence stratigraphy and syndepositional tectonics of upper Miocene and Pliocene deltaic sediments, offshore Brunei Darussalam. In: Hasan Sidi et al. (Eds.) SEPM Special Publication – Tropical deltas of Southeast Asia – Sedimentology, stratigraphy and petroleum geology 76:219–234 Samouëlian A, Cousin I, Tabbagh A, Bruand A, Richard G (2005) Electrical resistivity survey in soil science: a review. Soil Tillage Research 83:173–193 Sandal ST (1996) The geology and hydrocarbon resources of Negara Brunei Darussalam. Brunei Shell Petroleum Company, Bandar Seri Begawan, 243p Shah T, Villholth KG, Burke JJ (2006) Groundwater Use in Agriculture: A Global Assessment of Scale and Significance for Food, Livelihoods and Nature. Comprehensive Assessment, IWMI, International Water Management Institute Shen SL, Wu YX, Xu YS, Hino T, Wu HN (2015) Evaluation of hydraulic parameters from pumping tests in multi-aquifers with vertical leakage in Tianjin. Comput Geotech 68:196–207. doi 10.1016/j.compgeo.2015.03.011. Slater LD, Lesmes D (2002) IP interpretation in environmental investigations. Geophys 67:77–88 Spitz K, Moreno J (1996) A practical guide to groundwater and solute transport modelling. Wiley, New York Sudha K, Israil M, Mittal S, Rai J (2009) Soil characterisation using electrical resistivity tomography and geotechnical investigation. J Applied Geophysics 67:74–79 Suhip MAABH, GÓ§deke SH, Cobb AR, Sukri RS (2020) Seismic refraction study, single well test and physical core analysis of anthropogenic degraded peat at the Badas Peat Dome, Brunei Darussalam. Eng Geol 273:105689 Tamas P (2003) Water resource scarcity and conflict: Review of applicable indicators and systems of reference. Technical documents in Hydrology, Report No 21. UNESCO-IHP, Paris Tate RB (1974) Paleo-environmental studies in Brunei. Brunei Museum J 3:285–305 Telford WM, Geldart LP, Sheriff RE (1990) Applied Geophysics. Cambridge University Press, Cambridge, 770p Thiagarajan S, Rai SN, Kumar D, Manglik A (2018) Delineation of groundwater resources using electrical resistivity tomography. Arab J Geosci 11(9):1–16. https://doi.org/10.1007/s12517-018-3562-y Thornton PK, Ericksen PJ, Herrero M, Challinor AJ (2014) Climate variability and vulnerability to climate change: a review. Global Change Biology. Wiley-Blackwell Online Open. https://doi.org/10.1111/gcb.12581 Torres J, Gartrell A, Hoggmascal N (2011) Redefining a sequence stratigraphic framework for the Miocene to present in Brunei Darussalam: roles of local tectonics, eustacy and sediment supply. International Petroleum Technology Conference, Bangkok, pp 15–17 Watto MA, Bashir S, Khan N (2018) Pakistan heading for groundwater crisis. In: Springer Nature, Vol 554, Macmillan Publishers Limited Wilford GE (1961) The geology and mineral resources of Brunei and adjacent parts of Sarawak: with descriptions of Seria and Miri oil fields. British Borneo Geological Survey, Memoirs 10. Brunei Press Limited, Brunei Darussalam Wu YX, Shen JS, Cheng WC, Hino T (2017) Semi-analytical solution to pumping test data with barriers, wellbore storage, and partial penetration effects. Eng Geol. https://dx.doi.org/10.1016/j.enggeo.2017.05.011 Cite Share Download PDF Status: Published Journal Publication published 01 Apr, 2022 Read the published version in Environmental Earth Sciences → Version 1 posted Reviewers invited by journal 16 Sep, 2021 Reviews received at journal 26 Jul, 2021 Editor assigned by journal 27 Jun, 2021 First submitted to journal 24 Jun, 2021 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-657012","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":42087270,"identity":"876971cc-41fc-496c-8f21-c15ca714c967","order_by":0,"name":"Lieyana Azffri","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2klEQVRIiWNgGAWjYBACNvYexsc/KiTkGCQYDIBcBhCJH/DxnGE2ZjhjY0y8FjmJHDZpxra0xAaitbBJ5B42LmA7nL7hdvMGhg9lhxnMpRsIaOF5l/h4Bs/h3A13jhUwzjh3mMFyzgECWthzjA14JIBabuQYMPO2HWYwuJFAQAtDjpkEj8HhdAOQlr9EaeHIMZPmSUhLAGthJEoLzxljwxkHbAxnAv1ysOdcOo/lDAJa5Nt7DB98/Cchz3e7eeODH2XWcuYSBLSggANAzEOC+lEwCkbBKBgFuAAA35FF+DtUNVsAAAAASUVORK5CYII=","orcid":"","institution":"Universiti Brunei Darussalam Faculty of Science","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Lieyana","middleName":"","lastName":"Azffri","suffix":""},{"id":42087271,"identity":"a308c7e7-3bb2-48a3-95e8-4de2ed0173a9","order_by":1,"name":"Stefan Herwig Gödeke","email":"","orcid":"","institution":"Universiti Brunei Darussalam","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Stefan","middleName":"Herwig","lastName":"Gödeke","suffix":""},{"id":42087272,"identity":"756f2266-aa83-477c-a924-00b74c457682","order_by":2,"name":"Mohammad Faizan Ibrahim","email":"","orcid":"","institution":"Department of Agriculture","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Mohammad","middleName":"Faizan","lastName":"Ibrahim","suffix":""}],"badges":[],"createdAt":"2021-06-25 05:25:59","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-657012/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-657012/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s12665-022-10284-1","type":"published","date":"2022-04-01T06:29:47+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":11922857,"identity":"1ba90671-3a3d-4eda-9aee-c3f6e40c7d12","added_by":"auto","created_at":"2021-07-29 15:21:07","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":286305,"visible":true,"origin":"","legend":"Map of Brunei showing the four major districts, rivers and survey locations (sites 1-8); Inset map of Southeast Asia showing the location of Brunei.","description":"","filename":"fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-657012/v1/b7560047ab9e1410574df08a.png"},{"id":11922856,"identity":"68c40416-cb39-46cc-b581-18750399007f","added_by":"auto","created_at":"2021-07-29 15:21:07","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":342443,"visible":true,"origin":"","legend":"Geological map of Brunei (after Sandal, 1996).","description":"","filename":"fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-657012/v1/656f0748e5f9bcb22b135be9.png"},{"id":11922738,"identity":"a6b09df2-bf96-444f-a591-07858b2c75bf","added_by":"auto","created_at":"2021-07-29 15:18:07","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":410824,"visible":true,"origin":"","legend":"Chrono-lithostratigraphy of central onshore Brunei (after Osli, 2020).","description":"","filename":"fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-657012/v1/4bd520141bec8291ed618b08.png"},{"id":11922733,"identity":"1890b828-8377-460b-b4ed-d9b475b336b9","added_by":"auto","created_at":"2021-07-29 15:18:07","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":33105,"visible":true,"origin":"","legend":"Schematic representation of gradient and pole-dipole array configurations; ‘a’ represents the distance between the electrodes (Loke, 2012).","description":"","filename":"fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-657012/v1/fb142e29756621f54d89dd81.png"},{"id":11922855,"identity":"3e9d5d2b-a09e-4a7f-8625-3505783145f9","added_by":"auto","created_at":"2021-07-29 15:21:07","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":194026,"visible":true,"origin":"","legend":"Inverse model resistivity and chargeability sections of Line 12.","description":"","filename":"fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-657012/v1/e573e10a5cdf25b1afab83cf.png"},{"id":11922734,"identity":"8e6f2a40-06cc-4545-ac26-651d5db32e53","added_by":"auto","created_at":"2021-07-29 15:18:07","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":457916,"visible":true,"origin":"","legend":"Inverse model resistivity and chargeability sections of Line 16.","description":"","filename":"fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-657012/v1/5d9084ef3d9f040a66d91f7e.png"},{"id":11922731,"identity":"28bebd38-d952-49e2-b047-f08a00fb02f2","added_by":"auto","created_at":"2021-07-29 15:18:07","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":80624,"visible":true,"origin":"","legend":"Borehole lithology of groundwater Well-B1 and Well-L1 showing correlation with resistivity values and groundwater yield.","description":"","filename":"fig7.png","url":"https://assets-eu.researchsquare.com/files/rs-657012/v1/365c9ff32f56784a64216e36.png"},{"id":11922736,"identity":"21ed96fd-e16b-424b-ad44-29a8d985d4d4","added_by":"auto","created_at":"2021-07-29 15:18:07","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":70657,"visible":true,"origin":"","legend":"Drawdown of pumping and recovery curves of groundwater Well-B1 and Well-L1.","description":"","filename":"fig8.png","url":"https://assets-eu.researchsquare.com/files/rs-657012/v1/91bc395ee193f315ed9c30dc.png"},{"id":19961295,"identity":"150b8f29-720f-4bdf-9b57-07cea0307860","added_by":"auto","created_at":"2022-04-05 06:29:51","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2027826,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-657012/v1/2b3cdf84-cc6d-4a50-97a1-0dd45f3b7442.pdf"}],"financialInterests":"","formattedTitle":"\u003cp\u003eElectrical Resistivity Tomography And Induced Polarization Study For Groundwater Exploration In The Agricultural Development Areas of Brunei Darussalam\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eGroundwater is an essential source of freshwater that is used globally for domestic, industrial and agricultural purposes. In particular, groundwater use for agricultural development has grown exponentially over the past decade, especially in heavily populated areas such as South Asia, Africa and China (Shah et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Giordano and Villholth \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). However, competing demands and water scarcity often resulted in mismanagement of the water resources (Tamas \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). In countries like China and India, concerns over groundwater quality are rising due to improper disposal of urban wastewater into natural streams or its reuse for irrigation, which ultimately seeps into groundwater (Watto et al. \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). On the other hand, microbiological processes can break down even recalcitrant contaminants (Gӧdeke et al. 2008). Possible complex contamination scenarios may need a range of remediation and assessment measures (Marshall et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn Brunei, the government relies almost entirely on surface water resources, given the relatively sparse population of around 500,000 (DEPS \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). However, industrialization and urbanization put more pressure on its surface and groundwater resources (Suhip et al. \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Furthermore, concern over the increase in water demand was highlighted through the Brunei Vision 2035, where the vision calls attention to the public utilities regarding continuous, adequate, and quality water (DEPS \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Moreover, climate variability causes greater unpredictability in precipitation, including periods of heavier rainfall as well as drought (Thornton et al. \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Groundwater recharge is also highly dependent on climate (Moeck et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). One study in Brunei found that climate changes were evident from increased rainfall intensity, pointing to the need for careful water management under a changing climate (G\u0026ouml;deke et al. 2020).\u003c/p\u003e \u003cp\u003eGroundwater abstraction in Brunei is currently limited to the local bottled water industry found within the Sungai Liang area of the Belait District (FAO \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). This industry has been supplying bottled mineral water from its original artesian well for almost three decades. A previous study in Brunei investigated subsurface layers and groundwater levels using the seismic refraction method at the Berakas area in the Brunei-Muara District (Azhar et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The study presented velocity profiles and seismic tomography for groundwater system evaluation. Furthermore, water samples from nearby springs revealed low pH values and high sulphate concentrations, likely due to localised acid sulphate soils present in the investigated area. Grealish and Fitzpatrick (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) found that acid sulphate soils occur in Brunei within flat inland areas important for agricultural land. A resistivity study in Brunei by Azffri et al. (in press) found that the interpreted groundwater zone yields low resistivity values ranging from 5 to 100 ohm-m at the Labi agricultural site in the Belait District. Furthermore, a borehole drilling encountered sandy aquifer units in the investigated area. Further groundwater pumping revealed a moderate groundwater yield of 288 m\u0026sup3;/day and estimated aquifer transmissivity of 109 m\u0026sup2;/day.\u003c/p\u003e \u003cp\u003eIn this study, groundwater exploration was conducted at eight agricultural development areas in Brunei (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), Electrical Resistivity Tomography (ERT) and Induced Polarization (IP). The ERT and IP surveys helped delineate subsurface geological structures, formations and aquifer zones. The study revealed subsurface resistivity and chargeability variations in the study area. Interpreted 2D subsurface resistivity and chargeability inversion models delineated potential aquifer zones and subsequently identified suitable prospects for groundwater well drilling and construction of groundwater pumping wells in two of the surveyed areas. Hydraulic test results of the newly drilled groundwater pumping wells helped estimate the aquifer transmissivity and hydraulic conductivity for aquifer characteristics.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Geological Settings And Survey Locations","content":"\u003cp\u003eBrunei lies on the north coast of Borneo Island in Southeast Asia, with a total land area of 5,765 km\u0026sup2;. It is divided into four main districts: Brunei-Muara, Tutong, Belait and Temburong. Brunei\u0026rsquo;s climate is typical of the equatorial tropics, characterized by high rainfall and temperatures throughout the year. Rainfall shows a seasonal pattern with wet and dry seasons throughout the year. The wet seasons are from September to January and May to June, and the drier seasons are from February to March and July to August. The average annual rainfall from 2019 was 2909 mm. The temperature is relatively uniform throughout the year, ranging from 23.8 to 32.1\u0026deg;C (BDMD, \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eBrunei is drained by four main river basins, namely the Brunei, Tutong, Belait and Temburong Rivers \u003cstrong\u003e(\u003c/strong\u003eChuan \u003cspan class=\"CitationRef\"\u003e1992\u003c/span\u003e\u003cstrong\u003e)\u003c/strong\u003e. The Belait river basin (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e) is the largest, with an area of 2,700 km\u0026sup2;. Peat swamp forests dominate the lower catchment areas. Some areas in the upper catchment have been cleared for agricultural development areas. The Tutong river basin has an area of about 1,300 km\u0026sup2; (Chuan \u003cspan class=\"CitationRef\"\u003e1992\u003c/span\u003e). The basin comprises a floodplain in the lower catchment areas, with the upper catchment is forested with few areas cleared for agricultural development areas. The Brunei river basin flows into the Brunei Bay. The upper parts of the river are a major freshwater source for urban water. The Temburong basin is the smallest river basin in the study area, with 430 km\u0026sup2;.\u003c/p\u003e\n\u003cp\u003eBrunei\u0026apos;s geology is closely linked to its neighbouring Malaysian states of Sarawak and Sabah, and many regional geological studies have been conducted (Liechti et al. \u003cspan class=\"CitationRef\"\u003e1960\u003c/span\u003e; Wilford \u003cspan class=\"CitationRef\"\u003e1961\u003c/span\u003e; Sandal \u003cspan class=\"CitationRef\"\u003e1996\u003c/span\u003e; Hutchison \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e). Tectonic events govern the geological setting in this region since the Cenozoic era (Hall \u003cspan class=\"CitationRef\"\u003e1997\u003c/span\u003e; Hall and Nichols \u003cspan class=\"CitationRef\"\u003e2002\u003c/span\u003e; Baillie et al. 2004). Overall compressional tectonics in the northwest Borneo margin formed deformation zones of mountainous terrains extending through central Borneo. Subsequent uplift and erosion of this mountainous range in the hinterland during the Early and Middle Miocene resulted in rapid sedimentation into basin depocenters, forming major deltaic systems in the region (Sandal \u003cspan class=\"CitationRef\"\u003e1996\u003c/span\u003e; Hutchison \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eThe Champion and Baram delta systems have been major siliciclastic sedimentation locations in both onshore and offshore Brunei areas since the Miocene period (Saller and Blake 2003; Torres et al. \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e; Lambiase and Cullen \u003cspan class=\"CitationRef\"\u003e2013\u003c/span\u003e). Most sediments are gently deformed due to occasional compressional tectonics during the Miocene to Pliocene (Sandal \u003cspan class=\"CitationRef\"\u003e1996\u003c/span\u003e; Morley et al. \u003cspan class=\"CitationRef\"\u003e2003\u003c/span\u003e). Stratigraphic formations occur within depositional environments, from the coastal plain to deep marine (Tate \u003cspan class=\"CitationRef\"\u003e1974\u003c/span\u003e; Sandal \u003cspan class=\"CitationRef\"\u003e1996\u003c/span\u003e). In the study area, quaternary rock formations overlay older bedrocks of the Liang, Miri, Seria, Lambir, Belait, Setap and Meligan Formations (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). The lithologies of the formations are mainly made up of alternating sand and shales. Coal occurrences have been recorded in the Liang and Belait Formations (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e; Osli et al. \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eIn the present study, the survey locations were specifically situated within flat-lying or lowland areas with no significant geological structure outcrop seen on the surface. Topographical elevations of the survey locations range from 2 to 5 m above mean sea level. All the survey locations are situated within recent sediments deposited in sub-aerial alluvial floodplain environment (Tate, \u003cspan class=\"CitationRef\"\u003e1974\u003c/span\u003e).\u003c/p\u003e"},{"header":"Methodology","content":"\u003cdiv class=\"Section2\" id=\"Sec4\"\u003e\n \u003ch2\u003eTheory\u003c/h2\u003e\n \u003cp\u003eGeoelectrical resistivity methods have been widely used in groundwater exploration, engineering and environmental applications (Dahlin \u003cspan class=\"CitationRef\"\u003e1996\u003c/span\u003e; Keller and Frischknecht 1996; Sudha et al. \u003cspan class=\"CitationRef\"\u003e2009\u003c/span\u003e; Galazoulas et al. \u003cspan class=\"CitationRef\"\u003e2015\u003c/span\u003e; Lech et al. \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e). Electrical resistivity tomography (ERT) is one of the most commonly used geoelectrical resistivity methods to map subsurface electrical resistivity (Griffiths and Barker, \u003cspan class=\"CitationRef\"\u003e1993\u003c/span\u003e; Dahlin, \u003cspan class=\"CitationRef\"\u003e2001\u003c/span\u003e), which subsequently can be interpreted from a hydrological perspective (e.g., Saad et al. \u003cspan class=\"CitationRef\"\u003e2012\u003c/span\u003e; Ashraf et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e; Aziman et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e; Riwayat et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e; Thiagarajan et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e; Kumar et al. \u003cspan class=\"CitationRef\"\u003e2020a\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003eb\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eThe electrical resistivity method estimates the variation in the ground\u0026apos;s resistivity by injecting direct current into the ground (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) through a set of current electrodes (C1 and C2) and measuring the resulting voltage differences at the potential electrodes (P1 and P2). The resistivity is determined from Ohm\u0026rsquo;s law using the voltage differences for a known current and correcting the current geometrical pathway through the earth. From the current (\u003cem\u003eI\u003c/em\u003e), voltage (\u003cem\u003eV\u003c/em\u003e) and geometric factor (\u003cem\u003ek\u003c/em\u003e), the apparent resistivity (\u003cem\u003epa\u003c/em\u003e) was calculated using the following Eq. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e (Telford et al. \u003cspan class=\"CitationRef\"\u003e1990\u003c/span\u003e; Dahlin \u003cspan class=\"CitationRef\"\u003e2001\u003c/span\u003e; Binley et al. 2015):\u003c/p\u003e\n \u003cp\u003e\u003cimg src=\"https://myfiles.space/user_files/83064_0857a92044b57365/83064_custom_files/img1627531434.png\"\u003e\u0026nbsp; (1)\u003c/p\u003e\n \u003cp\u003eResistivity interpretations have proved helpful for detecting geological units of unconsolidated sediments and groundwater prospects (e.g., Saad et al. \u003cspan class=\"CitationRef\"\u003e2012\u003c/span\u003e; Ashraf et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e; Aziman et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e; Riwayat et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e; Thiagarajan et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e; Kumar et al. \u003cspan class=\"CitationRef\"\u003e2020a\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003eb\u003c/span\u003e). Igneous and metamorphic rocks, depending on the degree of fracturing and the percentage of the fractures filled with groundwater, generally have higher resistivities than sedimentary rocks, which are usually more porous and have higher water content. For example, the resistivity of granite ranges between 5,000 to 10,000 ohm-m depending on the degree of fracturing and moisture content (e.g., Kumar et al. \u003cspan class=\"CitationRef\"\u003e2020a\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003eb\u003c/span\u003e), whereas the resistivity of sand and clay materials ranges within 1 to 1,000 ohm-m (e.g., Saad et al. \u003cspan class=\"CitationRef\"\u003e2012\u003c/span\u003e; Ashraf et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e). Furthermore, clay has significantly lower resistivity values than sand. The resistivity values of clay range between 1 to 100 ohm-m, whereas the resistivity values of sand range between 60 to 1000 ohm-m (Keller and Frischknecht, 1996). The degree of overlap in different resistivities of different types of materials and waters is dependent on several factors such as porosity, degree of water saturation and concentration of dissolved salts (Samou\u0026euml;lian et al. \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e; Hazreek et al. \u003cspan class=\"CitationRef\"\u003e2015\u003c/span\u003e; Annuar and Nordiana 2018). Keller and Frischknecht (1996) found that groundwater yields low resistivity values ranging from 10 to 100 ohm-m depending on the concentration of dissolved salts.\u003c/p\u003e\n \u003cp\u003eDue to the ambiguity of resistivity values with overlapping resistivity ranges, several researchers have used an integrated geophysical approach combining resistivity with the induced polarization (IP) technique to solve complicated geological and hydrological problems (e.g., Goldman and Neubauer \u003cspan class=\"CitationRef\"\u003e1994\u003c/span\u003e; Amaya et al. \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e; Kumar et al. \u003cspan class=\"CitationRef\"\u003e2016a\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003eb\u003c/span\u003e; Rehman et al. \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e). The IP method uses the voltage decay characteristics to study the soil\u0026rsquo;s induced polarization, also known as the chargeability (Telford et al. \u003cspan class=\"CitationRef\"\u003e1990\u003c/span\u003e; Keller and Frischknecht 1996; Kearey et al. \u003cspan class=\"CitationRef\"\u003e2002\u003c/span\u003e). Subsurface chargeability measurements have been used to determine high clay content in sedimentary settings. The clay particles have a negative charge that can attract positive ions from the electrolyte contained in the cavities of rocks (Telford et al. \u003cspan class=\"CitationRef\"\u003e1990\u003c/span\u003e). High chargeability measurements have been observed for fine-grained sediments such as clay, while deposits with larger particle size like sand and gravel typically yield lower chargeability values (Keller and Frischknecht 1996; Slater and Lesmes \u003cspan class=\"CitationRef\"\u003e2002\u003c/span\u003e; Alabi et al. \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e; Amaya et al. \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eHydraulic tests of groundwater wells are crucial for understanding the aquifer potential in any hydrogeological setting (Ashraf et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e; Aziman et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e; Kumar et al. \u003cspan class=\"CitationRef\"\u003e2020b\u003c/span\u003e). Transmissivity and hydraulic conductivity are two key hydraulic parameters that can help determine the aquifer characteristics (e.g., Mogaji et al. \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e; Shen et al. \u003cspan class=\"CitationRef\"\u003e2015\u003c/span\u003e; Wu et al. \u003cspan class=\"CitationRef\"\u003e2017\u003c/span\u003e). Furthermore, the records of time-drawdown data have been used to evaluate the aquifer transmissivity and hydraulic conductivity. The Cooper-Jacob solution assumes that the aquifer is confined, homogenous, isotropic and of uniform thickness over the area of pumping. The assumption discussed in Fetter (\u003cspan class=\"CitationRef\"\u003e2001\u003c/span\u003e) for determining aquifer parameters from time-drawdown data is that the pumping well is screened throughout the entire thickness of the aquifer being tested. Using the Cooper-Jacob straight-line time-drawdown method, the aquifer transmissivity was calculated using Eq. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e (Cooper and Jacob \u003cspan class=\"CitationRef\"\u003e1946\u003c/span\u003e):\u003c/p\u003e\n \u003cdiv class=\"Equation\" id=\"Equ2\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\u003cimg src=\"https://myfiles.space/user_files/83064_0857a92044b57365/83064_custom_files/img1627531468.png\"\u003e\u0026nbsp; (2)\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eWhere \u003cem\u003eQ\u003c/em\u003e is the pumping rate and \u003cem\u003eho - h\u003c/em\u003e is the calculated change in drawdown between initial and final drawdown.\u003c/p\u003e\n \u003cp\u003eFrom the calculated transmissivity \u003cem\u003e(T)\u003c/em\u003e and the aquifer thickness (\u003cem\u003eb\u003c/em\u003e), the hydraulic conductivity (\u003cem\u003eK\u003c/em\u003e) was calculated using Eq. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e:\u003c/p\u003e\n \u003cdiv class=\"Equation\" id=\"Equ3\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\u003cimg src=\"https://myfiles.space/user_files/83064_0857a92044b57365/83064_custom_files/img1627531542.png\"\u003e\u0026nbsp; (3)\u003c/div\u003e\n \u003c/div\u003e\n \u003ch2\u003eData acquisition and processing\u003c/h2\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec5\"\u003e\n \u003cp\u003eData acquisition was conducted with a combined measurement of resistivity and chargeability. A total of 19 survey lines from eight agricultural sites were carried out in the study area (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). Information such as aerial, topographical and geological maps is required when considering resistivity surveying suitability (to select profile lines). The selection of survey locations was predominantly planned based on area availability and accessibility. The survey locations were generally free from obstacles, such as houses, crops or fences. In some areas, permission from landowners was needed to perform the surveys on their land.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eTable 1\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eSurvey parameters for each resistivity survey line (sites 1-8).\u0026nbsp;\u003c/p\u003e\n \u003ctable border=\"1\" cellpadding=\"0\" cellspacing=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.181818181818183%\"\u003e\n \u003cp\u003eSurvey location\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.19191919191919%\"\u003e\n \u003cp\u003eSurvey line\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.22222222222222%\"\u003e\n \u003cp\u003eElectrode\u003c/p\u003e\n \u003cp\u003econfiguration\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.2020202020202%\"\u003e\n \u003cp\u003eElectrode spacing (m)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.2020202020202%\"\u003e\n \u003cp\u003eSurvey length\u003c/p\u003e\n \u003cp\u003e(m)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" width=\"18.181818181818183%\"\u003e\n \u003cp\u003eSite 1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.19191919191919%\"\u003e\n \u003cp\u003e1 - 3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.22222222222222%\"\u003e\n \u003cp\u003eGradient\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.2020202020202%\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.2020202020202%\"\u003e\n \u003cp\u003e800\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.45679012345679%\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"27.160493827160494%\"\u003e\n \u003cp\u003ePole-dipole\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.691358024691358%\"\u003e\n \u003cp\u003e5, 10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.691358024691358%\"\u003e\n \u003cp\u003e400\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.45679012345679%\"\u003e\n \u003cp\u003e19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"27.160493827160494%\"\u003e\n \u003cp\u003ePole-dipole\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.691358024691358%\"\u003e\n \u003cp\u003e5, 10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.691358024691358%\"\u003e\n \u003cp\u003e400\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" width=\"18.181818181818183%\"\u003e\n \u003cp\u003eSite 2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.19191919191919%\"\u003e\n \u003cp\u003e4 - 8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.22222222222222%\"\u003e\n \u003cp\u003eGradient\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.2020202020202%\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.2020202020202%\"\u003e\n \u003cp\u003e800\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.45679012345679%\"\u003e\n \u003cp\u003e13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"27.160493827160494%\"\u003e\n \u003cp\u003ePole-dipole\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"24.691358024691358%\"\u003e\n \u003cp\u003e5, 10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.691358024691358%\"\u003e\n \u003cp\u003e400\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.181818181818183%\"\u003e\n \u003cp\u003eSite 3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.19191919191919%\"\u003e\n \u003cp\u003e14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.22222222222222%\"\u003e\n \u003cp\u003ePole-dipole\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"20.2020202020202%\"\u003e\n \u003cp\u003e5, 10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.2020202020202%\"\u003e\n \u003cp\u003e400\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.181818181818183%\"\u003e\n \u003cp\u003eSite 4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.19191919191919%\"\u003e\n \u003cp\u003e15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.22222222222222%\"\u003e\n \u003cp\u003ePole-dipole\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"20.2020202020202%\"\u003e\n \u003cp\u003e5, 10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.2020202020202%\"\u003e\n \u003cp\u003e400\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.181818181818183%\"\u003e\n \u003cp\u003eSite 5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.19191919191919%\"\u003e\n \u003cp\u003e16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.22222222222222%\"\u003e\n \u003cp\u003ePole-dipole\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"20.2020202020202%\"\u003e\n \u003cp\u003e5, 10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.2020202020202%\"\u003e\n \u003cp\u003e400\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"18.181818181818183%\"\u003e\n \u003cp\u003eSite 6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"19.19191919191919%\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"22.22222222222222%\"\u003e\n \u003cp\u003eGradient\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.2020202020202%\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"20.2020202020202%\"\u003e\n \u003cp\u003e800\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"18.181818181818183%\"\u003e\n \u003cp\u003eSite 7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"19.19191919191919%\"\u003e\n \u003cp\u003e10 - 11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"22.22222222222222%\"\u003e\n \u003cp\u003eGradient\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"20.2020202020202%\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"20.2020202020202%\"\u003e\n \u003cp\u003e800\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"18.181818181818183%\"\u003e\n \u003cp\u003eSite 8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"19.19191919191919%\"\u003e\n \u003cp\u003e17 - 18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"22.22222222222222%\"\u003e\n \u003cp\u003ePole-dipole\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.2020202020202%\"\u003e\n \u003cp\u003e5, 10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"20.2020202020202%\"\u003e\n \u003cp\u003e400\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003eTwo sets of data were acquired between the years 2018 and 2020. The first set of data acquisition was carried out in 2018 using the ABEM Terrameter LS2 resistivity meter covering a lateral distance of 800 m with eighty stainless-steel electrodes arranged at an equal length of 10 m (Line 1\u0026ndash;11). This set of data acquisition was conducted using the gradient array configuration. The gradient array configuration uses two current electrodes and two potential electrodes, placed with equal spacings (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). The gradient method is suitable for multichannel acquisition due to dense and fast data point collection (Dahlin and Zhou \u003cspan class=\"CitationRef\"\u003e2006\u003c/span\u003e; Loke \u003cspan class=\"CitationRef\"\u003e2012\u003c/span\u003e; Aizebeokhai and Oyeyemi \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e). With the multichannel acquisition, resistivity measurements continue down the row of electrodes until the whole survey line is measured. The second set of data acquisition was conducted from 2019 through to 2020 using the ABEM SAS4000 resistivity meter covering a lateral distance of 400 m (Line 12\u0026ndash;19). The line uses sixty-one electrodes with 5 m spacings for the inner cables and 10 m spacings for the outer cables. This set of data acquisition was conducted using the pole-dipole array configuration. For the pole-dipole array configuration, one transmitting current electrode, also known as the infinity electrode, was moved to an effective infinity distance, approximately five times the survey depth (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). Simultaneously, the other current electrode is placed in the vicinity of the two potential electrodes. The pole-dipole method is suitable for deep earth investigation, making it a popular option among researchers (Saad et al. \u003cspan class=\"CitationRef\"\u003e2012\u003c/span\u003e; Annuar and Nordiana 2018; Ashraf et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e; Kumar et al. \u003cspan class=\"CitationRef\"\u003e2020a\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eRaw data were processed and inverted using the ZONDRES2D software (in DAT format). Resistivity and chargeability inversion models were obtained from the inversion process (Loke and Barker \u003cspan class=\"CitationRef\"\u003e1996\u003c/span\u003e). The inversion process averaged the resistance measurements to apparent resistivity values and the apparent chargeability time window measurements to integral chargeability values. The Gauss-Newton inversion method was used to determine the appropriate resistivity values (Griffith and Barker 1993; Loke and Barker \u003cspan class=\"CitationRef\"\u003e1996\u003c/span\u003e; Dahlin \u003cspan class=\"CitationRef\"\u003e2001\u003c/span\u003e; Loke and Dahlin \u003cspan class=\"CitationRef\"\u003e2002\u003c/span\u003e). 2D pseudo-sections were generated to help delineate subsurface geological structures, formations and aquifer zones in the surveyed areas. All the pseudo-sections displayed present RMS errors of not more than 5%, which indicates the measured data are fitted with the computed apparent resistivity; the number of iterations for each survey was ten.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec6\"\u003e\n \u003ch2\u003eGroundwater well drilling and hydraulic tests\u003c/h2\u003e\n \u003cp\u003eGroundwater wells were drilled at site-1 in the Brunei-Muara District (Well-B1) and site-5 in the Belait District (Well-L1) through the aquifer zones inferred from resistivity and chargeability interpretations. Borehole drilling was conducted using a straight rotary method. The hole was advanced by rotating a drill string consisting of a series of hollow drill rods to the bottom attached to a 10-inch drill bit. Water-based drilling fluid under pressure was introduced into the bottom of the hole through the hollow drill rods and passages into the bit. The drilling fluid served the dual function of cooling the rotating bit as it entered the borehole and removing the rock cuttings from the bottom of the hole. The rock cuttings move through the annular space between the drill rods and the walls of the hole as they returned to the surface. Rock cuttings were collected at an interval of 3 m, primarily for soil identification purposes. 6-inch diameter UPVC casings and screens with 1.5 mm openings were used to construct the groundwater pumping wells. A gravel pack filter was installed between the aquifer and UPVC screens.\u003c/p\u003e\n \u003cp\u003eA 4-inch submersible pump was installed inside the well to continuously pump water out from the well through a 2-inch riser pipe for hydraulic testing. The pumping well responses in terms of the water discharge and changes in water depth were recorded using a volume meter connected at the outlet pipe on the surface and a water depth meter installed inside the well annulus. None of the newly drilled water wells had yet a nearby observation well that could have been used for time-drawdown observation due to pumping. Hydraulic tests of the newly drilled wells were investigated using time-drawdown data gathered from the pumping well. A five-step drawdown test with different flow rates, constant discharge test and recovery test was carried out in this investigation.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Results","content":"\u003cdiv class=\"Section2\" id=\"Sec8\"\u003e\n \u003ch2\u003eInterpretations of 2D resistivity and chargeability inversion models\u003c/h2\u003e\n \u003cp\u003eElectrical resistivity tomography and induced polarization revealed subsurface resistivity and chargeability variations in the study area with resistivity values from 1 to 500 ohm-m and chargeability values from 0 to 10 mV/V to a depth of about 150 m from the surface. Aquifer zones were also detected at varying depths in all surveyed locations with resistivity values ranging from 1 to 100 ohm-m (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). Few shallow boreholes (\u0026lt;\u0026thinsp;30 m) with lithology information exist within the study area. Lithology correlations with resistivity models were possible. However, they are limited to shallow depths. Two new boreholes were drilled in two selected sites to investigate the deeper rock strata and groundwater availability. The two pilot wells, namely Well-B1 and Well-L1, were placed explicitly in water-scarce agricultural areas used for paddy plantation. The two sites are Bebuloh (site-1) and Lot Sengkuang (site-5). These two sites were found to have favourable groundwater prospects based on resistivity and chargeability interpretations. The detailed interpretation and results of two ERT and IP profiles are presented in this paper, delineating subsurface geological structure, formations and aquifer zones of the area.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eLine 12 (Site-1)\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eTable 2\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eResistivity surveys of sites 1-8 with depth and resistivity of aquifer zone.\u003c/p\u003e\n \u003ctable border=\"1\" cellpadding=\"0\" cellspacing=\"0\" width=\"90%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003eSurvey location\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003eSurvey line\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"28.571428571428573%\"\u003e\n \u003cp\u003eDepth of aquifer zone from the surface (m)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"28.571428571428573%\"\u003e\n \u003cp\u003eResistivity of aquifer zone (ohm-m)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" width=\"21.428571428571427%\"\u003e\n \u003cp\u003eSite-1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003eERT 1-3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"28.571428571428573%\"\u003e\n \u003cp\u003e20-30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"28.571428571428573%\"\u003e\n \u003cp\u003e1 - 100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"27.272727272727273%\"\u003e\n \u003cp\u003eERT 12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"36.36363636363637%\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"36.36363636363637%\"\u003e\n \u003cp\u003e1 - 100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"27.272727272727273%\"\u003e\n \u003cp\u003eERT 19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"36.36363636363637%\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"36.36363636363637%\"\u003e\n \u003cp\u003e1 - 50\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" width=\"21.428571428571427%\"\u003e\n \u003cp\u003eSite-2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003eERT 4-8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"28.571428571428573%\"\u003e\n \u003cp\u003e20-40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.571428571428573%\"\u003e\n \u003cp\u003e1 - 100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"27.272727272727273%\"\u003e\n \u003cp\u003eERT 13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"36.36363636363637%\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"36.36363636363637%\"\u003e\n \u003cp\u003e5 - 100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003eSite-3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003eERT 14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"28.571428571428573%\"\u003e\n \u003cp\u003e20-30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"28.571428571428573%\"\u003e\n \u003cp\u003e1 - 100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003eSite-4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003eERT 15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"28.571428571428573%\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"28.571428571428573%\"\u003e\n \u003cp\u003e1 - 50\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003eSite-5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003eERT 16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"28.571428571428573%\"\u003e\n \u003cp\u003e20-40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"28.571428571428573%\"\u003e\n \u003cp\u003e5 - 100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003eSite-6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003eERT 9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"28.571428571428573%\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.571428571428573%\"\u003e\n \u003cp\u003e1 - 100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003eSite-7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003eERT 10-11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"28.571428571428573%\"\u003e\n \u003cp\u003e10-20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.571428571428573%\"\u003e\n \u003cp\u003e1 - 100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003eSite-8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003eERT 17-18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"28.571428571428573%\"\u003e\n \u003cp\u003e10-20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"28.571428571428573%\"\u003e\n \u003cp\u003e1 - 100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cdiv class=\"Section3\" id=\"Sec9\"\u003e\n \u003cp\u003eInverse model resistivity of ERT 12 revealed resistivity variations to a depth of 110 m from the surface (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e). Two subsurface layers differentiated by resistivity values were deduced. The first layer is interpreted as the topsoil and is distinctive of resistivities ranging from 1 to 140 ohm-m. A second layer distinct of resistivities ranging from 1 to 100 ohm-m is interpreted as the aquifer zone. The saturated zone is about 10 m below ground level. Inverse model chargeability of IP 12 revealed low chargeability values of the aquifer zone of less than 1 mV/V. High chargeability values ranging from 5\u0026ndash;10 mV/V were observed in the topsoil layer and are assumed to be composed of fine-grained materials such as clay. Groundwater Well-B1 was drilled to about 96 m from the surface at site-1 (line 12) based on the resistivity and chargeability interpretations.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eLine 16 (Site-5)\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv class=\"Section3\" id=\"Sec10\"\u003e\n \u003cp\u003eInverse model resistivity of ERT 16 revealed resistivity variations to a depth of 100 m from the surface (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e). Two subsurface layers were deduced based on resistivity values. The first layer is interpreted as topsoil with resistivities ranging from 100 to 500 ohm-m. The second layer with resistivities ranging from 1 to 100 ohm-m was observed at a depth of about 20 to 40 m below ground level. This layer is interpreted as the aquifer zone. Inverse model chargeability of IP 16 indicated chargeability values at line 16. High chargeability values ranging from 5\u0026ndash;10 mV/V were observed at a depth of about 40 to 50 m from the surface, possibly extending towards greater depths and are assumed to be composed of fine-grained materials such as clay. Groundwater Well-L1 was drilled to 80 m from the surface at site-5 (line 16) based on the resistivity and chargeability interpretations.\u003c/p\u003e\n \u003ch2\u003eBorehole lithology correlation with resistivity datasets\u003c/h2\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eTwo pilot wells were drilled at site-1 and site-5 based on the resistivity and chargeability data interpretations (line 12 and 16). Borehole lithology of Well-B1 and Well-L1 were correlated with resistivity models and are shown in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e. Both the newly drilled wells encountered aquifer zones while drilling, which was primarily in sandy layers. The borehole lithology information revealed the inhomogeneity of the soil materials in the study area, mainly composed of multiple alternating sand and clay layers. Furthermore, the layers cannot be clearly distinguished in terms of their resistivities. However, it can be inferred that the overall higher clay content at Well-B1 yields lower resistivity values ranging from 1 to 30 ohm-m, whereas higher sand content at Well-L1 yields higher resistivity values ranging from 5 to 200 ohm-m.\u003c/p\u003e\n\u003cp\u003eWell-B1 is mainly composed of clay and sand with traces of decomposed peat at the top layer. The predominance of clay deposits with resistivity values of 3 to 30 ohm-m may be explained by the deposition of fine-grained materials in an alluvial floodplain, specifically a lacustrine environment. Well-L1 is mainly composed of fine to medium sand, clay, sandstone and mudstone. The top part of the lithology log mainly consists of fluvial deposits (clay, sand and gravel) with resistivity values between 60 to 200 ohm-m. The lower part of the lithology log with resistivities ranging between 5\u0026ndash;60 ohm-m appears to be associated with alluvial deposits (mix of clay and sand).\u003c/p\u003e\n\u003ch2\u003eHydraulic tests for aquifer characteristics\u003c/h2\u003e\n\u003cp\u003eAt Well-B1, the UPVC screens were installed at the saturated clayey sand layer at depths of 84 to 95 m below ground level (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e). The constant rate pumping test at Well-B1 was carried out for 4 hours with a steady pumping rate of 4.3 m\u0026sup3;/day and a maximum drawdown of 3.63 m. At Well-L1, the UPVC screens were installed be at sand and sandstone layers at depths of 18 to 28 m and 48 to 78 m below ground level (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e). The constant rate pumping test at Well-L1 was carried out for 24 hours with a steady pumping rate of 288 m\u0026sup3;/day and a maximum drawdown of 1.52 m.\u003c/p\u003e\n\u003cp\u003eThe time-drawdown cross-plot of Well-B1 and Well-L1 are shown in Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e. Their calculated hydraulic parameters are shown in Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. The unsteady Cooper-Jacob time-drawdown analysis revealed the estimated aquifer transmissivity values of 0.53 and 109.8 m\u0026sup2;/day at Well-B1 and Well-L1, respectively. The estimated hydraulic conductivity of the clayey sand unit (with an estimated aquifer thickness of 11 m) at Well-B1 is 0.05 m/day. Lower hydraulic conductivity values are typically associated with fine-grained materials such as clay deposits (Spitz and Moreno \u003cspan class=\"CitationRef\"\u003e1996\u003c/span\u003e). The hydraulic conductivity for the sandy units (with an estimated aquifer thickness of 40 m) at Well-L1 is 2.75 m/day. Based on the time-drawdown data and estimated hydraulic parameters of the aquifer, weak to moderate groundwater yield is expected for withdrawal and distribution in the investigated agricultural areas for irrigation purposes.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3\u003c/strong\u003e Aquifer characteristics estimated through hydraulic tests of newly drilled groundwater wells.\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"1\" cellpadding=\"0\" cellspacing=\"0\" width=\"101%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"10.309278350515465%\"\u003e\n \u003cp\u003eWell\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003ePumping duration (mins)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003eInitial and final water depth (m)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.43298969072165%\"\u003e\n \u003cp\u003eDischarge rate (m\u0026sup3;/day)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.587628865979383%\"\u003e\n \u003cp\u003eTransmissivity (m\u0026sup2;/day)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.68041237113402%\"\u003e\n \u003cp\u003eHydraulic conductivity (m/day)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"10.309278350515465%\"\u003e\n \u003cp\u003eB1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003e240\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003e44.5 / 48.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.43298969072165%\"\u003e\n \u003cp\u003e4.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.587628865979383%\"\u003e\n \u003cp\u003e0.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.68041237113402%\"\u003e\n \u003cp\u003e0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"10.309278350515465%\"\u003e\n \u003cp\u003eL1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003e1440\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003e21.4 / 22.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.43298969072165%\"\u003e\n \u003cp\u003e288\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.587628865979383%\"\u003e\n \u003cp\u003e109.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.68041237113402%\"\u003e\n \u003cp\u003e2.75\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"},{"header":"Discussion","content":"\u003cp\u003eGeophysical study and results of the 2D inverted resistivity model at eight agricultural development areas and their interpretations of hydrogeology revealed aquifer zones in all the surveyed locations found at varying depths with variation in apparent resistivities. The 2D inverted resistivity models delineated the subsurface geological formations and structures in the study area, showing resistivity contrasts between topsoil and aquifer zones. The resistivity of the topsoil layer ranges from 1 to 500 ohm-m, and the chargeability values range from 0 to 10 mV/V. High chargeability values were assumed to be composed of fine-grained materials such as clay. The resistivity of the aquifer zone ranges from 1 to 100 ohm-m, and the chargeability values are less than 1 mV/V. Based on the resistivity and chargeability interpretations, two new groundwater wells were drilled at site-1 (line 12) and site-5 (line 16). Based on the 2D resistivity and chargeability data interpretation and the yields of the newly drilled boreholes, it was found that site-5 has a higher potentiality for groundwater exploitation compared to site-1. Borehole drilling of groundwater Well-L1 encountered multiple saturated sand layers with a moderate groundwater yield of 288 m\u0026sup3;/day. Well-L1 is currently used for groundwater withdrawal and distribution for irrigation purposes at site-5. Borehole drilling of groundwater Well-B1 encountered a saturated clayey sand layer with a poor groundwater yield of 4.3 m\u0026sup3;/day. Therefore, Well-B1 was not used for groundwater withdrawal for irrigation at site-1. Our findings indicate that due to the inhomogeneous properties of the soil materials comprising mainly alternating sand and clay, the resistivity and chargeability values often overlap, resulting in ambiguous interpretations. Future studies should include drilling groundwater test wells to determine the soil properties and aquifer potential further.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eElectrical resistivity tomography and induced polarization methods were successfully applied to detect groundwater at eight agricultural development areas in Brunei targeted for irrigation. Resistivity datasets showed subsurface resistivity variations ranging from about 1 to 500 ohm-m in the study area. This suggested variations in geological formations and aquifer systems. 2D inverted resistivity model helped mapped aquifer zones in all the surveyed locations, mainly at shallower depths (\u0026lt;\u0026thinsp;100 m). Resistivities ranging from 1 to 100 ohm-m and chargeability values of less than 1 mV/V signify favourable groundwater prospects underneath the topsoil layer and correlated with borehole lithology data and drilling results and site-5. New groundwater well drilling was conducted to 96 m depth at site-1 and 80 m depth at site-5 with groundwater yields of 4.3 and 288 m\u0026sup3;/day, respectively. The estimated aquifer transmissivity values are 0.53 and 109.8 m\u0026sup2;/day, while their hydraulic conductivity values are 0.05 and 2.75 m/day, respectively. Estimated parameters of the aquifer units indicate significant variation in the amount of groundwater availability for withdrawal and distribution for irrigation purposes in the study area. The combination of IP and ERT significantly helped to identify the suitable drilling for Well-L1. The study presented the resistivity and chargeability characteristics, as well as the results of two newly drilled groundwater pumping wells of the studied area, and evaluated groundwater availability for groundwater use for irrigation. Future studies are necessary to locate irrigation wells with significant groundwater potential. Future drilling is planned to install groundwater monitoring wells next to the groundwater pumping well.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis project was supported by research grant UBD/RSCH/URC//RG(b)/2020/017 from Universiti Brunei Darussalam. The authors thank the Ministry of Primary Resources and Tourism, Department of Agriculture and Agrifood, Brunei Darussalam for the supplied data and for allowing the publication of this study. The authors thank Preston Geocem Brunei for valuable interactions and discussions on the resistivity surveys and groundwater well drilling results.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u0026nbsp; The authors declare no conflict of interest.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAizebeokhai AP, Oyeyemi KD (2014) The use of the multiple-gradient array for geoelectrical resistivity and induced polarization imaging. J Appl Geophy 111:364\u0026ndash;375\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlabi AA, Ogungbe AS, Adebo B, Lamina O (2010) Induced polarization interpretation for subsurface characterization: A case study of Obadore, Lagos state. 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Brunei Press Limited, Brunei Darussalam\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWu YX, Shen JS, Cheng WC, Hino T (2017) Semi-analytical solution to pumping test data with barriers, wellbore storage, and partial penetration effects. Eng Geol. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://dx.doi.org/10.1016/j.enggeo.2017.05.011\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"environmental-earth-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"enge","sideBox":"Learn more about [Environmental Earth Sciences](https://www.springer.com/journal/12665)","snPcode":"12665","submissionUrl":"https://submission.nature.com/new-submission/12665/3","title":"Environmental Earth Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Electrical Resistivity Tomography, Induced Polarization, Groundwater, Agricultural Areas, Brunei","lastPublishedDoi":"10.21203/rs.3.rs-657012/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-657012/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eElectrical Resistivity Tomography (ERT) and Induced Polarization (IP) study was carried out for groundwater exploration at eight agricultural development areas in Brunei Darussalam. The study was undertaken to meet the growing demands of water supply in the Brunei agricultural sector, particularly for paddy field irrigation. A total of nineteen survey lines with survey lengths of up to 800 m and investigation depths of up to 150 m below ground level were conducted to delineate subsurface geological structures, formations and aquifer zones in the study area. Aquifer zones with resistivity values ranging from 1 to 100 ohm-m and chargeability values of less than 1 mV/V were detected in all surveyed locations. New groundwater well drilling was conducted at two of the surveyed sites based on interpretations of 2D resistivity and chargeability inversion models. Water well drilling encountered aquifer zones, which were primarily in sandy layers. Hydraulic tests revealed groundwater yields of 4.3 and 288 m³/day. Estimated transmissivity values of the aquifer units based on pumping tests are 0.53 and 109 m²/day, while their hydraulic conductivity values are 0.05 and 2.75 m/day. Estimated parameters of the aquifer units indicate weak to moderate groundwater yield for withdrawal and distribution for irrigation purposes at the investigated sites. The present study helped decision-makers take suitable measures for placing future irrigation wells and achieve significant groundwater exploration results in the study area.\u003c/p\u003e","manuscriptTitle":"Electrical Resistivity Tomography And Induced Polarization Study For Groundwater Exploration In The Agricultural Development Areas of Brunei Darussalam","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2021-07-29 15:18:05","doi":"10.21203/rs.3.rs-657012/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewersInvited","content":"","date":"2021-09-16T22:33:04+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2021-07-26T13:26:41+00:00","index":0,"fulltext":""},{"type":"editorAssigned","content":"","date":"2021-06-28T00:00:00+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Earth Sciences","date":"2021-06-24T10:19:05+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-earth-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"enge","sideBox":"Learn more about [Environmental Earth Sciences](https://www.springer.com/journal/12665)","snPcode":"12665","submissionUrl":"https://submission.nature.com/new-submission/12665/3","title":"Environmental Earth Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"3e511d07-a775-4fcd-a7ae-76bd9c78b732","owner":[],"postedDate":"July 29th, 2021","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":6063975,"name":"Geology"},{"id":6063976,"name":"Environmental Chemistry"}],"tags":[],"updatedAt":"2022-04-05T06:29:47+00:00","versionOfRecord":{"articleIdentity":"rs-657012","link":"https://doi.org/10.1007/s12665-022-10284-1","journal":{"identity":"environmental-earth-sciences","isVorOnly":false,"title":"Environmental Earth Sciences"},"publishedOn":"2022-04-01 06:29:47","publishedOnDateReadable":"April 1st, 2022"},"versionCreatedAt":"2021-07-29 15:18:05","video":"","vorDoi":"10.1007/s12665-022-10284-1","vorDoiUrl":"https://doi.org/10.1007/s12665-022-10284-1","workflowStages":[]},"version":"v1","identity":"rs-657012","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-657012","identity":"rs-657012","version":["v1"]},"buildId":"WrCJVZZCHTDjtuVLN7oU0","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}