ScienceDirect. Identification of saltwater intrusion/assessment scheme in groundwater using the role of empirical knowledge

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1 Available online at ScienceDirect Procedia Environmental Sciences 30 (2015 ) International Conference on Environmental Forensics 2015 (ienforce2015) Identification of saltwater intrusion/assessment scheme in groundwater using the role of empirical knowledge Noorain Mohd Isa a,b, Ahmad Zaharin Aris a,b * a Environmental Forensics Research Centre, Faculty of Environmental Studies, Universiti Putra Malaysia, UPM Serdang, Malaysia b Department of Environmental Sciences, Faculty of Environmental Studies, Universiti Putra Malaysia, UPM Serdang, Malaysia Abstract Kapas Island depends solely on groundwater as the major source of freshwater supply for the drinking and domestic purposes. High consumption of fresh groundwater leads to deterioration of its quality. In order to overcome this issue, a monitoring of groundwater sampling was conducted. A total of 216 groundwater samples were collected in different monsoon and were tested for physic-chemical parameters. Pre-monsoon was recorded Na-rich type while post-monsoon was dominated by Ca-rich type. The level of saline interferences was identified using ionic strength and Cl concentrations where it reveals the fresh to moderate groundwater condition The The Authors. Published by Elsevier by Elsevier B.V This B.V. is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of organizing committee of Environmental Forensics Research Centre, Faculty of Peer-review Environmental under Studies, responsibility Universiti of organizing Putra Malaysia. committee of Environmental Forensics Research Centre, Faculty of Environmental Studies, Universiti Putra Malaysia. Keywords: small island; ionic strength; Kapas Island; hydrochemistry; groundwater quality 1. Introduction It has been acknowledged that intensive development activities in small islands specifically in Kapas Island usually increase the risk of groundwater quality degradation through over-exploitation of fresh groundwater [1]. The uncontrolled of groundwater extraction leads to modification of natural flow system and induces contamination of seawater from the coast [2]. Seawater disturbance could alter the groundwater compositions that are subjects to * Corresponding author. Tel.: ; fax: address: zaharin@upm.edu.my The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of organizing committee of Environmental Forensics Research Centre, Faculty of Environmental Studies, Universiti Putra Malaysia. doi: /j.proenv

2 292 Noorain Mohd Isa and Ahmad Zaharin Aris / Procedia Environmental Sciences 30 ( 2015 ) water-rock interaction and chemical reactions [3]. The Kapas Island aquifer is a shallow aquifer which is more sensitive to deteriorate. In addition, temporal and spatial changes have to be considered because its affects the recharge and discharge of groundwater. This therefore requires a fundamental understanding on the spatial and temporal variability of groundwater hydrochemistry as to identify the controlling factors for groundwater constituents [4]. The principal aims of this study are to characterize the groundwater hydrochemistry in different monsoon seasons and to determine the extents of saltwater intrusion in Kapas Island aquifer based on the ionic strength of selected ions. 2. Methods 2.1. Study site Present study was done in Kapas Island which is located at 'N, 'E, with an area about 2 km² [5]. It is situated in the tropical region with average annual rainfall of 1000 mm and experiences constant temperature at 30 C. The monitoring boreholes were scattered in low-lying coastal area which frequently experience pumping activities. Fig. 1 shows the location of the monitoring boreholes at Kapas Island. A total of 216 groundwater samples were collected based on spatial (six monitoring boreholes) and temporal scales (pre- and postmonsoon). The dry season is pronounced as pre-monsoon, given that the highest water demand usually coincides with the drought season while post-monsoon related to wet season where the aquifer is being recharged by precipitation (rainfall). Kapas Island A B KW 6 KW 5 KW 4 KW 3 KW 2 KW Fig. 1. The location of the monitoring boreholes at Kapas Island

3 Noorain Mohd Isa and Ahmad Zaharin Aris / Procedia Environmental Sciences 30 ( 2015 ) The groundwater samples were tested for physicochemical parameters. In-situ parameters, namely temperature, DO, ph, Eh, TDS, EC and salinity as well as the anions variables of HCO 3, Cl and SO 4 were tested on-site as to collect a representative data. Groundwater samples for cation measurements (Ca, Mg, Na, K) were filtered and stored in a cool box for transportation to the designated laboratory in Faculty of Environmental Studies, UPM. The quality control and quality assurance of the sampling methods including calibration of probes and instruments were scrutinized in order to obtain minimize or zero error in data collection Data analyses Simple statistical analyses of descriptive analysis and correlation coefficient were calculated to gather meaningful information from a large dataset. These analyses were done using PASW Statistics 18 software. The inferential statistics can make judgments of the probability that the difference between groups is a dependable one or independent of each other. The data collected from this study were simplified in a graphical of bar chart and piper diagram as to illustrate the differences which can explains the evolution of groundwater hydrochemistry between seasons. For this study, the ionic strength for the selected minerals was calculated to gain a better understanding of the hydrochemical processes that take place in the aquifer during the mixing of freshwater and seawater. PHREEQC software was used to set up the hydrogeochemical components of the groundwater, especially the ionic strength. 3. Results and discussion Most hydrochemical parameters showed very wide ranges of concentrations and shows significant correlation between seasons. In particular, pre-monsoon were controlled by Na and Cl which recognized as seawater elements while post-monsoon dominated by Ca and Mg which describes the contribution of mineral elements. The correlations of each ion are shown in Table 1. Fig. 2 shows the high concentration of Na and Cl during pre-monsoon while increasing of Ca and Mg during post-monsoon. The ion domination were explains by the groundwater type. As pre-monsoon has higher Na concentrations, Na-HCO 3 type was dominant. The groundwater showed paths of hydrochemical evolution, from Na to Ca-rich during post-monsoon as the Ca-HCO 3 type take place. These patterns indicate that the groundwater chemistry is experiences changes by the cation exchanges reaction and simple mixing process (Fig. 3) Concentration (mg/l) Ca Mg Na K HCO Cl SO Major ions Pre-monsoon Post-monsoon Fig. 2. The concentration of major ions for the two different monsoon seasons

4 294 Noorain Mohd Isa and Ahmad Zaharin Aris / Procedia Environmental Sciences 30 ( 2015 ) Fig. 3. The changes of groundwater type in Kapas Island aquifer during two different monsoon seasons The impact of ongoing salinization found during pre-monsoon can be evaluated by the ionic strength variation in the groundwater. Fig. 4 shows the water type classification based on ionic strength and Cl concentrations. The Cl was chosen because it is the most abundant ion in seawater along with good relationship between other major ions (p<0.01; Table 1). The scheme of ionic strength plotted against Cl on log-log scales produce of five major classes; AA (fresh), BB (slightly fresh), CC (moderate), DD (slightly saline) and EE (saline). Apart from these, there are other minor groups involved; e.g. AB (fresh-slightly fresh), BC (slightly fresh-moderate), CD (moderate-slightly saline) and DE (slightly saline-saline). Samples with circle shape represent data for pre-monsoon, scattered diversely in group A, group B and some in group C. From here, it can be concluded that samples in pre-monsoon were under fresh to moderate type. Differ from post-monsoon, samples in triangle (represent post-monsoon) were concentrated in group A but with higher I values because of increasing other elements such as Ca and Mg.

5 Noorain Mohd Isa and Ahmad Zaharin Aris / Procedia Environmental Sciences 30 ( 2015 ) A B C D E saline slightly saline moderate slightly fresh fresh Ionic strength (I) AE AD AC AB AA EB EC ED DB DC DD CB CC CD BD BB BC AB AC AD EE DE CE BE AE E D C B A saline slightly moderate slightly fresh saline fresh Cl (mg/l) KW 1 KW 2 KW 3 KW 4 KW 5 KW 6 Pre-monsoon KW 1 KW 2 KW 3 KW 4 KW 5 KW 6 Post-monsoon Fig. 4. Assessment scheme for seawater intrusion based on ionic strength (I) against Cl concentration 4. Conclusion Table 1 Correlation analyses of major ions (n = 216) Ca Mg Na K HCO₃ Cl SO₄ Ca ** ** ** ** ** ** Mg Na ** ** ** ** K ** ** HCO₃ ** ** Cl ** SO₄ 1 -Upper triangle; p<0.01**, p<0.05* The major groundwater type in Kapas Island was Na-HCO 3 and Ca-HCO 3. Each water type is defined by the concentration of ions in the groundwater. The scheme to assess the extent of seawater intrusion has been proposed using the chart of ionic strength (I) variation against Cl concentrations. Pre-monsoon recorded to have fresh to moderate types of water while post-monsoon solely have fresh water type. Although it shows a significant contribution of saltwater intrusion, groundwater in Kapas Island was only slightly affected. The significant of

6 296 Noorain Mohd Isa and Ahmad Zaharin Aris / Procedia Environmental Sciences 30 ( 2015 ) salinization in groundwater is attributed from the other chemical mechanism, such as cation exchanges process and simple mixing process as the values of contamination was too small (Cl concentration < 150 mg/l). Acknowledgements This study was supported by the Exploratory Research Grant Scheme (ERGS) Project No: ERGS/1/2013/STWN01/UPM/02/2. Allowance and scholarship from Universiti Putra Malaysia is gratefully acknowledged. Special thanks to the Faculty of Engineering and Nuclear Agency Malaysia for the valuable help in the completing this research. References 1. Dragon, K. The Influence of Anthropogenic Contamination on the Groundwater Chemistry of a Semi-confined Aquifer (The Wielkopolska Buried Valley Aquifer, Poland). Water Resources Management 2008; 22(3), Dehghanzadeh, R., Safavy Hir, N., Shamsy Sis, J. and Taghipour, H. Integrated Assessment of Spatial and Temporal Variations of Groundwater Quality in the Eastern Area of Urmia Salt Lake Basin Using Multivariate Statistical Analysis. Water Resources Management 2015; 29(4), Edet, A. and Okereke, C. A regional study of saltwater intrusion in southeastern Nigeria based on the analysis of geoelectrical and hydrochemical data. Environmental Geology 2001; 40(10), Masoud, A.A. Groundwater quality assessment of the shallow aquifers west of the Nile Delta (Egypt) using multivariate statistical and geostatistical techniques. Journal of African Earth Sciences 2014; 95, Shuib, M.K. Transpression in the Strata of Pulau Kapas, Terengganu. Geological Society of Malaysia, Buletin 2003; 46,