Kerentanan Intrinsik dan Spesifik Airtanah terhadap Pencemaran di Kecamatan Banjarnegara dan Sekitarnya

Airtanah merupakan sumber air bersih yang penting bagi manusia. Keberadaan airtanah saat ini mulai terancam akibat aktivitas manusia, khususnya terkait dengan kegiatan yang menghasilkan limbah. Tujuan penelitian kerentanan airtanah terhadap pencemaran adalah untuk mengetahui persebaran tingkat kerentanan airtanah intrinsik dan spesifik di Kecamatan Banjarnegara dan Sekitarnya. Tujuan kedua mengetahui kondisi kualitas airtanah berdasarkan parameter nitrat. Metode yang digunakan dalam mengkaji kerentanan airtanah bebas untuk tercemar adalah Susceptibikity Index (SI). Parameter SI yang digunakan untuk proses pengolahan adalah kedalaman muka airtanah, imbuhan airtanah , media akuifer, kemiringan lereng, dan penggunaan lahan. Kerentanan airtanah intrinsik di lokasi kajian terdiri atas tiga klasifikasi yaitu rendah, sedang, dan tinggi dengan luasan kerentanan rendah 2.063 Ha, sedang 187 Ha, dan tinggi 4.700 Ha. Kerentanan airtanah spesifik metode SI diperoleh tiga klasifikasi yaitu rendah, sedang, dan tinggi dengan klasifikasi rendah memiliki luasan 1.965,49 Ha, sedang 2.357,34 Ha, dan tinggi 2.631,87 Ha. Sebaran kualitas airtanah berdasarkan parameter nitrat dilokasi kajian terdiri atas tiga kelas rendah (0-5 mg/liter), sedang (5-10 mg/liter), dan tinggi (> 10 mg/liter). Dominasi kelas tinggi dan sedang berada pada morfologi datar. Validasi kerentanan intrinsik diperoleh keakuratan sebesar 53,65% dan spesfik 56%

Petrogenesa Endapan Pasir Besi di Pantai Panggul, Trenggalek

Endapan pasir besi di Pantai Panggul Trenggalek didominasi oleh mineral-mineral berat yang terdiri dari magnetit (> 70 %), ilmenit, piroksen, horenblenda, zirkon, apatit dan feldspar. Batuan sumber diduga berasal dari batupasir magnetit bagian dari Formasi Jaten serta batuan gunung api Tersier yang banyak tersebar di daerah Trenggalek. Terbentuknya magnetit diduga berasal dari mineralisasi magnetit dari batuan gunung api Formasi Mandalika, seperti yang dijumpai di Ngadipuro, Kecamatan Munjungan. Batuan gunung api Tersier daerah Trenggalek, Jawa-Timur umumnya dibentuk oleh batuan berkomposisi andesitik hingga dasitik, yang berbentuk dyke, stock dan sill, serta berstruktur lava bantal. Analisis petrografi umumnya memperlihatkan tekstur porfiritik, berstruktur aliran dan teralterasi pada tingkatan yang rendah menjadi klorit, karbonat serisit dan epidot. Kata kunci: pasir besi, batuan gunung api, mineralisasi, pantai Panggul Trenggalek. Iron sand deposit in Panggul coast Trenggalek is dominated by heavy minerals, consist of magnetite (> 70 %), ilmenite, pyroxene, hornblende, zircon, apatite and feldspar. The source rock is estimated from magnetite sandstone of Jaten Formation and Tertiary volcanic rocks which are widely distribute in Trenggalek area. The formation of magnetite is interpreted from volcanic rock of Mandalika Formation, which crop out in Ngadipuro, Munjungan. Tertiary volcanic rocks in The Trenggalek area, East Java are mainly formed by andesitic to dacitic composition which are in the form of dyke, stock, sill and pillow lava structures. Petrographic analysis generally shows porphiritic, flow structure in textures and low alteration to chlorite, carbonate, sericite and epidot minerals. Keywords: iron sand, volcanic rocks, mineralization, Panggul coast Trenggalek

Asal-usul Pembentukan Gunung Batur Di Daerah Wediombo, Gunungkidul, YOGYAKARTA

Http://dx.doi.org/10.17014/ijog.vol2no3.20073Physiographically, the Gunung Sewu Subzone is predominantly composed of limestone of the Wonosari Formation, but in Wediombo area volcanic rocks of the Wuni Formation is exposed. The Wediombo volcanic rocks contain lava flows and volcanic breccias associated with Batur intrusive rock, in which all the rocks have andesitic composition. The problem is whether the Wedi- ombo volcanic rocks originated from far distance area which then was intruded by local magma after its deposition, or it is an association of the Wediombo volcanic and the Batur intrusive rocks which both are the remnants of a paleovolcano in the area. To identify the central facies of the paleovolcano, the geological principle that “the present is the key the past” is used as a geological approach.Wediombo area forms a high landscape showing an elevation of about 280 m above sea level with dips of the outer slopes 20 - 40%. The drainage pattern developing in the area fol- lows the existing circular structure to form subradial - radial patterns. The high landscape shows a circular structure with a diameter of less than 2 km and it opens to the Indian Ocean. Besides the Mount Batur intrusive rock, there are some other dikes which have been already hidrothermally altered, with some mineralization in the circular structure. Meanwhile, the outer slopes are composed of alternating lava flows and fragmental volcanic rocks of 22 - 25o in dip forming a concentric pattern. Petrologically, the Batur intrusive rock is light to dark grey in color, hypocrystalline porphyritic texture, with phenocryst ranges from 1.2 - 2.2 mm in size, subhedral-euhedral crystals, fine vesicular structures. The rock comprises plagioclase, pyroxene, hornblende and opaque minerals. Geochemically, the rock indicates an island arc tholeitic magma (SiO = 60.38 – 64.53 wt%, K O = 0.63 – 0.85 wt%). Those data indicate that the circular structure was the central facies and the outer slope was the proximal facies of the Wediombo paleovolcano in Gunungkidul Yogyakarta

Pengukuran Modulus Elastisitas Dinamis Batuan dengan Metode Seismik Refraksi

The seismic wave velocity in rock formation depends on the elastic modulus and mass density of rock where the wave travels. The velocity measurement of P and S waves on rock formation and the mass density in the laboratory can be used for calculating the elastic modulus of rock formation. The elastic modulus is part of rock mechanical parameter needed in geological engineering researches. The velocity measurement of P and S waves by the seismic refraction method was done on a tunnel with 11 spreads of measurement. From the results of the measurement, three groups of rock formation could be identified. The first is rock formation with Ed=8.890-12.68 MPa and G=3.306-4.830MPa; the second group is rock formation with Ed=8.890-12.68 MPa and G=3.306-4.830MPa; and the third group is with Ed=18.520-21.120MPa and G=6.724-7.744MP. The first group is clay formation while the second and third groups are andesitic stone formation

INTERPRETASI STRUKTUR BAWAH PERMUKAAN DAN IDENTIFIKASI JALUR SESAR DI KECAMATAN BAGELEN KABUPATEN PURWOREJO DENGAN METODE GEOMAGNET

Penelitian ini bertujuan untuk mengetahui pola sebaran anomali medan magnet, mengetahui struktur bawah permukaan serta mengidentifikasi jalur sesar di kawasan jalur sesar Kecamatan Bagelen dengan menggunakan metode geomagnet. Penelitian dilakukan di Desa Kalirejo, Clapar, Hargorejo, Soko, Semagung, Semono, Sokoagung, dan Somorejo Kecamatan Bagelen. Pengambilan data dibatasi pada koordinat 7o46’40,58” – 7o49’23,99” LS dan 110o1’22,65” – 110o3’33,46” BT. Penelitian dilakukan menggunakan satu set alat Proton Precession Magnetometer merek Geometrics tipe G-856. Pengukuran dilakukan pada 75 titik pengukuran di Kecamatan Bagelen dengan jarak antar titik 500m. Tahapan pengolahan data dilakukan dengan koreksi variasi harian, koreksi IGRF, koreksi topografi, reduksi ke kutub, kontinuasi ke atas, SVD, serta pemodelan 2D dan 3D. Nilai anomali medan magnet pada wilayah penelitian berada pada rentang -500 nT sampai 862 nT. Nilai tersebut disumbangkan oleh formasi-formasi batuan penyusun wilayah penelitian yaitu Kebobutak, Andesit, Dasit, dan Aluvium. Berdasarkan hasil pemodelan 2D, 3D maupun analisis SVD, diketahui bahwa keberadaan jalur sesar di kawasan penelitian bukan merupakan suatu jalur sesar yang berkemenerusan melainkan berupa segmen-segmen pada daerah tertentu

Geologi Daerah Dimito dan Sekitarnya Kabupaten Boalemo Provinsi Gorontalo

Administratively, the research area covers two districts, Wonosari Sub-district and Dulupi Sub-district, Boalemo District, Gorontalo Province. Based on the physiography of the Gorontalo region, the research area which is included in the southern mountain zone of Bone-Tilamuta-Modello generally consists of ancient volcano-sedimentary rock formations in Gorontalo, the Eocene-Oligocene. The purpose of this geological research is to discover the geological order that developed in the area of Dimito and surrounding are as covering several aspect such as geomorphology, stratigraphy, geological structure, and geological history. The result shows that the geomorphology of the research area divided into three geomorphic units, namely the units of the Alluvial Plain, Volcanic Hills, and Denudasional Hills. Stratigraphy of the research area divided into five types of units sorted from the early Miocene to the Holocene, i.e., Lava Basal Dimito (Early Eocene), Wackestone Dimito (Early Eocene), Andesit Kalidingin (Middle Miocene), Granodiorite Bualo (Middle Pliocene), and Alluvial Buaolo (Recen). Geological structures that work on the location of the research area relatively trend from northeast-southwest to northwest-southeast. Fault working on the location of the research area from the data processing consists of Normal Left Slip Fault Kalidingin and Lag Left Slip Fault Bualo

Hubungan Kumpulan Mineral Berat Pada Sedimen Pantai Dan Lepas Pantai Dengan Batuan Asal Darat Di Perairan Teluk Pelabuhan Ratu, Jawa Barat

DOI: 10.17014/ijog.v5i1.93Based on the depth contour, the sea bottom morphology in southern part of the researched area is very steep, while in the northern area it is sloped slightly. It shows that sedimentation process is from south to the north and continues to the west. It is supported by the current process in studied area. Rock slope stability of hilly morphology in the Cimandiri River area is related to weathering, erosion, and transportation process in coastal and nearshore areas. The presence of mineral in the studied area caused by those processes, was accumulated in the mouth of Cimandiri River, coastal, and nearshore areas. Those minerals were deposited in Cibelendung to Karangbeureum nearshore area by the longshore current. Magnetite and pyroxene minerals are dominant along the coastal and offshore areas of Pelabuhan Ratu Bay. The presence of augite and diopside shows that the source rock is basic igneous rocks (basalt), while the presence of hornblende and biotite minerals tend to indicate that the source rock is intermediate igneous rocks (andesite)