ISSN: 0852-0682, EISSN: 2460-3945 Forum Geograf, Vol 33 (2) December 2019: 140-152 DOI: 10.23917/forgeo.v33i2.7672 © Author(s) 2019. CC BY-NC-ND Attribution 4.0 License. Groundwater Vulnerability to Pollution in Kasihan District, Bantul Regency, Indonesia Setyawan Purnama * , Ahmad Cahyadi Departement of Environmental Geography, Faculty of Geography, Universitas Gadjah Mada, Indonesia *) Corresponding Author (e-mail: setyapurna@geo.ugm.ac.id) Received: 31 January 2019 / Accepted: 19 September 2019 / Published: 27 December 2019 Abstract. The groundwater vulnerability to pollution refers to the ease with which pollutants reach groundwater and, by extension, the risk of potential contamination. This concept shows the probability of pollution, based on the assumption that the physical environment has varying capacities to prevent the fow of pollutants into the aquifer. This study was designed to predict groundwater vulnerability in Bantul Regency, Special Region of Yogyakarta, Indonesia. Besides processing secondary data, it measured the depth of the phreatic surface and slope, and analyzed groundwater samples. The measurement and sampling points were determined by considering the location of previous infltration measurements conducted by Purnama in 2017. The groundwater vulnerability to pollution in the study area was analyzed using the SINTACS method, which operates on a numerical system of weights and rating scores. Each research parameter was assigned with a weight value according to the signifcance of its effect on groundwater contamination; each of its variables was then rated or ranked based on its intrinsic vulnerability to pollution. As a result, the groundwater vulnerability index ranged from 117.0 to 189.9, which according to the criteria of the SINTACS method, fell into the categories of medium to fairly high vulnerability. Areas with medium vulnerability were located in the Sentolo Formation (consisting of limestone and grumusol soil), while those with fairly high vulnerability were identi fed in the Yogyakarta Formation (volcanic rock and regosol soil). These fndings indicate that geological aspects and soil type greatly affect the groundwater vulnerability to pollution in the research area. Keywords: vulnerability, groundwater, Bantul Regency Abstrak. Kerentanan airtanah terhadap pencemaran merujuk pada kemudahan zat pencemar mencapai airtanah, sehingga airtanah akan tercemar. Konsep ini menunjukkan suatu probabilitas bahwa pencemaran akan terjadi, yang pada prinsipnya mendasarkan pada anggapan bahwa lingkungan fsik dapat mencegah aliran zat pencemar ke dalam akui fer. Tujuan dari penelitian ini adalah untuk memprediksi kerentanan airtanah di daerah penelitian terhadap pencemaran. Untuk mencapai tujuan tersebut, selain mendasarkan dari data sekunder juga dilakukan pengukuran kedalaman muka freatik, kemiringan lereng dan pengambilan sampel airtanah dari sumur observasi. Penentuan lokasi pengukuran dan pengambilan sampel dilakukan dengan mempertimbangkan lokasi pengukuran infltrasi yang pernah dilakukan oleh Purnama pada Tahun 2017. Untuk melakukan analisis kerentanan airtanah terhadap pencemaran di daerah penelitian dilakukan dengan Metode SINTACS, yang mendasarkan pada sistem numerik berupa bobot dan rating. Bobot ditentukan berdasarkan signifkansi pengaruh parameter terhadap pencemaran airtanah, sedangkan rating ditentukan berdasarkan signifkansi pengaruh variabel dalam masing-masing parameter terhadap pencemaran airtanah. Hasil penelitian menunjukkan bahwa nilai indeks kerentanan airtanah di daerah penelitian berkisar dari 117,0 hingga 189,9, yang dalam kriteria Indeks SINTACS tergolong pada tingkat kerentanan sedang dan agak tinggi. Wilayah yang termasuk tingkat kerentanan sedang umumnya terletak pada Formasi Sentolo yang berbatuan gamping dan