PENELITIAN AIR TANAH DI KOTA SOFIFI HALMAHERA MALUKU UTARA MENGGUNAKAN METODE GEOLISTRIK KOMBINASI RESISTIVITY DIPOLE-DIPOLE, WENNER DAN INDUCED POLARIZATION

MARIYAMA RUSTAM, S. Pd, Dr. Wahyudi

2012 | Tesis | S2 Ilmu Fisika

Sofifi merupakan ibukota definitif Propinsi Maluku Utara, sebagai wilayah pemekaran tentunya membutuhkan upaya pengembangan sarana prasarana dalam berbagai aspek, salah satunya adalah penyediaan air bersih. Dalam memenuhi kebutuhan air bersih, pemerintah telah menyediakan PDAM, namun perusahaan ini belum dapat beroperasi, sehingga masyarakat setempat masih menggunakan sumur galian. Untuk mengetahui keberadaan, kedalaman serta menggambarkan struktur bawah permukaan lapisan air tanah di Wilayah Sofifi dan sekitarnya, maka dilakukan survei geolistrik. Penelitian ini menggunakan Metode Resistivity konfigurasi mapping dipole– dipole, wenner dan Induced Polarization Time Domain hanya menggunakan konfigurasi wenner, yang terdiri dari 10 lintasan meliputi Kel. Guraping, Kel. Sofifi, Desa Somahode, Ampera, Durian, Bukulasa, Barumadoe, dan Hijrah dengan panjang lintasan 120–437 m. Pengukuran Geolistrik menggunakan alat Ares Automatic Sistem. Data yang diperoleh diolah menggunakan Program Res2Dinv. Hasil pengolahan data resistivity dipole–dipole diperoleh nilai resistivitas berkisar 1,4 Ωm – 23,8 Ωm pada kedalaman 0,8 –74,4 m sedangkan wenner terdeteksi pada kedalaman 1,2–75,1 m dengan nilai resistivitas berkisar 2,3 Ωm -30,4Ωm, diduga merupakan air tawar. Nilai resistivitas < 10,1 Ωm diduga air tawar yang dipengaruhi oleh rawa, sedangkan nilai > 10,1 Ωm diduga merupakan lapisan air tawar yang digunakan sebagai sumber air bersih. Selain itu dengan menggunakan metode Induced Polarization dapat mendeteksi intrusi air laut pada lintasan yang berada di pesisir pantai, dengan nilai Chargeability <13 msec. Untuk lintasan yang jauh dari pesisir pantai diperoleh nilai Chargeability <13 msec diduga lapisan homogen (alluvium) yang dipengaruhi oleh air rawa dan lempung. Hasil penelitian ini disimpulkan bahwa Keberadaan akuifer air tanah pada wilayah Sofifi dan sekitarnya adalah lapisan akuifer bebas.

Sofifi is the devinitive capital city of Northem Maluccas Province. It is also as an expansion area where the exspansio of various aspects is needed and required for the development of such infrastructures. One of them is the provision of drinking water. In fulfilingthe needed of drinking water, the govermmnt has provided a provincial water company but the company has not been able to accomplish this task yet; so the local people in this region still continue to use dug wells. In order ti find out the existence, to determine the depth and to describe the structure of ground water’s surface layers in Sofifi region and surrounding, consequently the geoelectrical survey must be done This study used two method, the first Resistivity Mapping method which used dipoledipole, Wenner configuration. The secound is Induced Polarization time domain method, which only used wenner configuration . It consists of 10 tracks including Guraping, Sofifi, Somahode, Ampera, Durian, Bukulasa, Barumadoe and Hijrah with 120-437m path length . Geoelectrical measurements were using Ares Automatic System. The data obtained were processed using Res2Dinv Program. The results of Resistivity Mapping data processing using dipole-dipole configuration were obtained ranging from1.4 to 23.8 Ωm at the depth of 0.8 to 74.4 m, while using Wenner configuration was detected at the depth of 1, 2 to 75.1 m with the value of resistivity ranging from 10.1 to 30.4 Ωm, suspected as freshwater. If the resistivity values had been less than 10,1 (<10.1) Ωm, it would have been affected by swamp water; but if the value had been more than 10.1 ( > 10.1) Ωm, it would have been suspected as the freshwater layer used as the source of clean water.. In addition, by using the Induced Polarization method, it could detect seawater intrusion at tracks resided near coastal area Where the chargeability value obtained are less than 1 are less than 13 (< 13) msec. For the tracks that are far from coastal area, the chargeability values obtained are less than 13 (<13) msec, suspected as a homogeneous layer (alluvium) affected by swamp water and clay. The results of this study concluded that the presence of groundwater in the Sofifi region and surrounding is an unconfined aquifer layer.

Kata Kunci : Air tanah, Resistivity, Induced Polarization.