Journal of Applied Geology, vol. 5(1), 2020, pp. 13–24 DOI: http://dx.doi.org/10.22146/jag.51627 Determination of Groundwater System by Using Hydroisotope Method of Sei Bingei and Surrounding Areas, Langkat Regency, North Sumatra Azmin Nuha1, Heru Hendrayana*1, Agus Budhie Wiyatna2, Doni Prakasa Eka Putra1, and Azwar Satrya Muhammad3 1Department of Geological Engineering, Faculty of Engineering, Universitas Gadjah Mada, Yogyakarta, Indonesia 2Department of Nuclear Engineering and Engineering Physics, Universitas Gadjah Mada, Indonesia 3Water Resources and Process Department, Aqua Danone, Indonesia ABSTRACT. Groundwater plays an essential role in the supply of water for various pur- poses, so the use of groundwater must also pay attention to the balance and preservation of the resource itself. The formation of springs can be used as a reference to evaluate the quantity, quality, and continuity of the flow of water coming out of the spring. The shape and size of the spring recharge area are significant for determining the spring protection area, both in quantity and quality. Comprehensive research into the hydrogeological sys- tem is carried out through geological, hydrogeological, and hydroisotope studies. The purposes of this study are (1) to determine the LMWL (Local Meteoric Water Line) of the Sei Bingei Region, (2) to determine the recharge area for the Sei Bingei area and (3) to de- termine the genesis or origin of groundwater that appears in the Sei Bingei area. To answer the objectives, the campaign of water sampling of 23 groundwater and 15 rainwater sam- ples were taken during different months and measure for the 2H/1H(dD) and 18O/16O (d18O) isotope ratios. Isotopic ratios are used to assess the origin and recharge elevation of water. The results of the study are (1) the LMWL (Local Meteoric Water Line) equa- tion in the Langkat area is dD = 8.052 × d18O + 14.162, (2) the main groundwater recharge area is located above 883 masl and (3) based on its isotopic ratios, groundwater in the study area can be differentiated into 3 genesis group: (a) Genesis-A Groundwater Group representing shallow-local groundwater system originated from local direct rainfall, (b) Genesis-B Groundwater Group is the main deep groundwater system in the research with the lowest value of the isotopic ratio of d18O and dD, and (c) Genesis-C Groundwater Group is groundwater which it may come from the intermediate system between shallow and deeper groundwater system. Keywords: Groundwater genesis · Hydroisotope · Groundwater recharge area. 1B ACKGROUND concrete steps to minimize the negative impacts Groundwater is a resource that has an essen- caused by groundwater exploitation activities. tial role in providing water needs for various Research on springs is fundamental to explain purposes, so the use of groundwater must pay the origin of groundwater formation in springs. attention to the balance and its preservation. The genesis of a spring can be used as a refer- Groundwater is one of the water resources that ence to evaluate the quantity, quality, and conti- has now become a national problem, so it needs nuity of water flow at a spring. Besides, know- ing the shape and extent of the recharge area *Corresponding author: H. HENDRAYANA, Depart- of spring is essential to determine the conserva- ment of Geological Engineering, Universitas Gadjah tion area for the spring. Mada. Jl. Grafika 2 Yogyakarta, Indonesia. E-mail: The application of hydroisotope technology [email protected] 2502-2822/© 2020 The Authors. Open Access and published under the CC-BY license. NUHA et al. has been used to determine groundwater con- tion of surface water. While the infiltrated wa- servation areas with high accuracy for the bene- ter is shielded by the aquifer from evaporation, fit of environmental protection at the Wonosobo thus preserving the isotopic composition of the Region (Wijatna et al., 2017). Hendrayana et al. rainwater. The Groundwater flows in aquifers (2019) used a similar technique to determine the as shallow groundwater and deep groundwa- origin of groundwater in springs for spring pro- ter. Shallow groundwater has the short cir- tection at Mambal Region. The Sei Bingei area culating with a near exit through a locally-fed is a new area for the development of residential groundwater system. and industrial areas. The food and beverage in- Meanwhile, the deeply-circulating ground- dustry is developing in this area, it is necessary water system has exit points in regionally-fed to protect water resources to ensure the conti- spring (Mazor, 2004). The isotopic composition nuity of the industrial activities. Comprehen- of the deep groundwater type is typically cal- sive research on the hydrogeological system of culated using the rainwater data. The derived the Sei Bingei area through hydro-isotope stud- isotopic values, in terms of Deuterium (2H) and ies is used to determine the recharge area for Oxygen-18 (18O), are collectively called the Me- water sources, including the shape and extent teoric Water Index (MWI) (Salonga, 2015) or accurately so that the water conservation pro- Meteoric Water Line (Crawford et al., 2014). gram can be optimally achieved. IAEA (2014) defined that the Global Meteoric Based on the above facts, the purpose of this Water Line (GMWL) used to d2H = 8 d18O + study is to determine the groundwater flow sys- 10. The primary source d2H and d18O data for tem and the origin of groundwater in the Sei GMWL is the Global Network of Isotope in Pre- Bingei and surrounding areas. The research ob- cipitation (GNIP) globally. The local precipita- jectives were (1) to determine the LMWL (Local tion data is called Local Meteoric Water Line Meteoric Water Line) of the Sei Bingei Region, (LMWL), (Clark and Fritz,1997). (2) to determine the groundwater recharge area Local Meteoric Water Line (LMWL) is a lin- for the Sei Bingei Region and (3) to determine ear correlation of d2H and d18O contents ob- the genesis or origin of groundwater that ap- served in the specific area. LMWL is useful pears in the Sei Bingei Region. for the evaluation of the origin of waters. If the values of a pair of isotopes ratio determine 2L OCATION from groundwater samples plot in the range of The research area was in the Sei Bingei area, the Meteoric Water Line (MWL), it means that Langkat Regency, North Sumatra Province (Fig- the groundwater was recharged by local pre- ure 1). The delineation of sub-watersheds bor- cipitations and come from meteoric water. Lo- ders the study area by considering local geolog- cal Meteoric Water Line (LMWL) is obtained ical conditions. The study area is volcanic hills from the analysis of monthly rainwater sam- with gentle slopes to steep slopes and in the ples in a specific area. The LMWL is com- form of gently sloping terrain and steep slopes monly used to determine the relationship of in the south. Elevation between 25–2,200 masl. surface/groundwater to a potential precipita- Geologically, the upstream area consists of mas- tion source or to determine the degree of water sive volcanic rocks in the form of andesite and evaporation enrichment (Crawford et al., 2014). dacite intrusion which are covered by autoclas- The determination of the groundwater tic breccia and lava flows, whereas in the down- recharge area is closely related to the calcu- stream areas dominated by lahar deposits in the lation of LMWL because of LMWL as a basis form of pebbly sand and pebbly clay. for whether the water comes from rainwater/ surface water or groundwater. LMWL equation 3T HEORETICAL BACKGROUND can be applied as a reference in natural iso- According to the hydrological cycle, ground- tope research to study groundwater dynamics water comes from the infiltration of rainwater in the hydrology cycle and to determine the towards the subsurface. The surface water is groundwater recharge area (Mook and Rozan- susceptible to be evaporation, which degree of ski, 2000). evaporation will change the isotopic composi- To determine the effect of elevation and rain- 14 Journal of Applied Geology DETERMINATION OF GROUNDWATER SYSTEM BY USING HYDROISOTOPE METHOD OF SEI BINGEI 430000 435000 440000 445000 450000 MAP OF 0 0 0 0 0 TUNGGURONO 0 5 PADANG BRAHRANG PUJI DADI 5 RESEARCH AREA AND 9 LAU MULGAP SUKA MAJU 9 3 KUTA PARIT TANJUNG MERAHE NAMO RUBE JULU 3 WATER SAMPLING POINTS TANAH SERIBU SELESAI SEI MENCIRIM TANAH MERAH EMPLASMEN KWALA MENCIRIM SEI BINGEI, LANGKAT, SUMUT PADANG CERMIN BHAKTI KARYA MA 8 SUKA RAYA BINJAI SELATAN !( BEKIUN PERKEBUNAN BEKIUN SAWIT REJO 0 0 0 BELA RAKYAT NAMBIKI PASAR VI KWALA MENCIRIM 0 0 0 0 PURWO BINANGUN SILEBO LEBO 0 9 9 0 1.25 2.5 5 7.5 10 3 DALAN NAMAN BALAI KASIH 3 AHL-5 Kilometers PEKAN KUALA ").! GUNUNG TINGGI PASAR IV NAMU TERASI SISTEM PROYEKSI.......DECIMAL DEGREE TUNTUNGAN I DATUM..........................WGS 84 SEI PENJARA SG 4 NAMU UKUR UTARA Sumber : - Peta Rupa Bumi Indonesi, BIG !( [ - Survai Lapangan, 2018 SIDO MAKMUR RAJA TENGAH LAU BAKERI 0 MA 11 SB 2 0 0 MA 4 0 PASAR 8 NAMU TERASI 0 !( MA 7 !( 0 LEGEND : 5 SG 2 !( 5 8 BLANKAHAN !( 8 3 !( SUKA RENDE 3 NAMU UKUR SELATAN District Boundary SUKA DAMAI SG 1 SUKA DAMAI !( Village Boundary MEKAR JAYA SAMPE CITA BERUAM DURIAN LINGGA KUTALIMBARU National Road River GUNUNG AMBAT MA 9 SG 3 0 !( 0 Collector Road 0 !( SB 7SB 8 0 0 !( 0 0 !( 0 Local Road Elevation Countour 8 BESADI PARIT BINDU MA 10 8 3 AHL-4 !( !(SG 7 3 ") PEKAN SAWAH Hidrogeology SIMPANG KUTA BULUH PASAR X Sei Bingei Borehole MA 5 PERPANDEN Boundary .! MA 3 !( SB 1 SG 5 !(!( !( ") Rainwater Sampling 0 SUKA DAME 0 0 AHL-3 0 0 MA