Pengaruh Karakteristik Kimia Lindi Terhadap Sifat Kelistrikan Endapan dan Lapukan Batuan Vulkanik (Studi Kasus TPA Piyungan Yogyakarta)
JAINGOT PARHUSIP, Dr. Agung Harijoko, S.T., M.Eng; Dr.rer.nat. Doni Prakasa Eka Putra, S.T., M.T.;Dr.rer.nat. Wiwit Suryanto, S.Si., M.Si.
2018 | Disertasi | S3 Teknik GeologiUntuk mengetahui distribusi pergerakan lindi di sekitar TPA Piyungan perlu dilakukan penelitian dan pemantauan berkelanjutan. Penelitian ini menggunakan metoda geofisika geolistrik resistivitas listrik dengan tujuan untuk mengetahui distribusi pergerakan lindi disekitar TPA serta untuk meningkatkan akurasi pengukuran geolistrik resistivitas dalam pengukuran perlapisan endapan vulkanik dan lapisan lapukan batuan vulkanik. Melalui pengukuran konduktivitas airtanah sebagai fluida pori diperoleh grafik hubungan tingkat resistivitas listrik sampel sebagai fungsi dari tingkat konduktivitas fluida pori. Metode penelitian terdiri dari lima tahapan, yaitu pendahuluan, penelitian lapangan, pengukuran laboratorium, pengolahan data, dan analisis hasil pengolahan data. Penelitian lapangan meliputi pengukuran topografi, kedalaman muka airtanah, pengambilan sampel airtanah, sampel lindi, sampel lapukan batuan, serta pengukuran nilai resistivitas listrik perlapisan tanah dengan metode geolistrik resistivitas. Analisis laboratorium meliputi pengujian sifat fisis dan sifat kimia airtanah, lindi dan lapukan batuan. Metode yang digunakan adalah dengan metode XRD dan pengukuran resistivitas listrik sampel endapan dan lapukan batuan vulkanik tersaturasi fluida. Dari pengukuran ini diperoleh suatu grafik hubungan nilai resistivitas listrik endapan dan lapukan batuan vulkanik tersaturasi fluida, terhadap tingkat konduktivitas fluida pori. Grafik ini digunakan untuk melakukan interpretasi nilai perlapisan resistivitas listrik yang telah di proses dengan piranti lunak RES2Dinv. Selanjutnya dengan menggunakan piranti lunak Rokwork dilakukan pemodelan penyebaran lindi secara tiga dinesi. Berdasarkan hasil pengukuran laboratorium dan pengukuran lapangan, diperoleh suatu hubungan antara kontaminasi lindi terhadap nilai resistivitas listrik endapan dan lapukan batuan vulkanik. Perlapisan endapan dan lapukan vulkanik dengan nilai resistivitas listrik < 10�m, merupakan perlapisan lanau pasiran yang sudah terkontaminasi lindi yang berasal dari TPA Piyungan. Perlapisan dengan nilai resistivitas listrik antara 10 - 20 �m , merupakan material lanau lempung pasiran yang tersaturasi airtanah. Kondisi penyebaran kontaminan lindi dari TPA Piyungan secara vertikal pada daerah hulu (sekitar pembuangan pengolahan lindi TPA Piyungan) sudah mencapai kedalaman 10 - 15 m, sedangkan di daerah hilir (Desa Banyakan) mencapai kedalaman lebih dari 35 m. Secara horizontal kontaminasi lindi telah mencapai lebih 1100 m dari tapak TPA Piyungan. Kontaminasi ini diperkirakan bersumber dari lindi yang masuk ke dalam aliran aliran sungai Banyak, bukan kontaminasi lindi yang turun dari tapak TPA dan masuk ke dalam sistim aliran airtanah.
A continuous investigation and monitoring was conducted to disclose a leachate dispersion in TPA Piyungan and surrounding. This research used a geophysical method of electrical resistivity geoelectrics with intention not only on finding out the leachate transport distribution around TPA but also to improve the acuracy of a geoelectrical resistivity mesurement related to measuring the layers of vulcanic rocks either deposit and wethered. Measuring the conductivity of groundwater as pore fluid relates to the electrical resistivity rates between samples and pore fluid conductivity as graphs having an understandeable function. Method of this research comprises of 5 steps, i.e. preliminary, field study, laboratory gauging, data processing, and interpretation. Field studies consist of plotting a position, measuring the watertable depth, groundwater and leachate sampling, weathered rock sampling, as well as the electrical resistivity values of ground layering by relying on a resistivity geoelectric method. Several laboratory tests including physical and chemical properties of the groundwater, leachate, and weathered rocks was also carried out. XRD test was aimed at designating the samples of volcanic rock either deposits or weathering having been saturated by the sort of leachate in which the electrical resistivity data had been well documented. A graph depicting the relation between the electrical resistivity values of deposited and weathered volcanic rock saturated with fluid to the conductivity rate resulted in pore fluid; was usable for interpreting the cross-section of electrical resistivity layers based on software RES2Dinv. The electrical resistivity data of a datum which was gained was used for creating a 3D leachate dispersion model by using a software RockWork. Based on measuring both laboratory and field, there was an understandeable relation between leachate contaminant vs electrical resistivity values of a volcanic rock. That the layers of deposit and weathering of such volcanic rocks existing around TPA Piyungan having electrical resistivity values lesser than 10 �m is a sendish silt layering that have been contaminated by leachate emanating from TPA Piyungan. Whereas layering with an electrical resistivity value of 10 -20 �m is a material of groundwater-saturated sandish shale silt. The dispersion of the leachate contaminant from TPA Piyungan in the upstream area (around the leachate processing disposal of TPA Piyungan) have reached 10 - 15 m vertically, while in the downstream area (Bayakan village) the leachate contaminant have disseminate till more than 35 m depth. Horizontally, the leachate contaminant have widely disseminated till more than 1100 m from center of TPA Piyungan. These contaminations approximately originate from leachate flowing into Banyak river flow, neither a leachate contaminant flow down from TPA site into groundwater flow systems.
Kata Kunci : endapan vulkanik, lapukan batuan vulkanik, kontaminasi lindi, resistivitas listrik fluida pori, TPA Piyungan
