Abstract
ABSTRACT −Investigation of saltwater intrusion in Nusawungu Coastal area of Cilacap Regency based on the 2D-resistivity data has been done in April – Juni 2018. The resistivity data acquisition has been carried out using Wenner's configuration on four locations covering of the NWT-01, NWT-02, NWT-03, and NWT-04 with a length as 200 meters. The obtained result is the 2D-resistivity profile of subsurface rocks for each trajectory with a depth of about 30 meters. The rock resistivity values which obtained for each trajectory consists of the NWT-01 is 2.30 – 103.00 Ωm; the NWT-02 is 3.65 – 54.30 Ωm; the NWT-03 is 0.96 – 43.20 Ωm; and the NWT-04 is 2.33 – 70.80 Ωm. Based on the interpretation results, the deep aquifer in each trajectory with a resistivity value of 0.96 - 6.81 Ωm are estimated to be intruded by saltwater, while the shallow aquifers have not been significantly intruded by saltwater. Based on the testing results of the electrical conductivity (DHL) of several water samples taken from some wells around the NWT-01 to NWT-04 trajectory, it is known that all of the water is freshwater. Some well water samples have a rather high electrical conductivity value, such as the well A on the NWT-01 with a value of 740.0 μSi/cm and the well C on the NWT-03 with a value of 894.67 μSi/cm. This is thought to be due to the relatively high salt mineral content in the aquifer rocks.
Highlights
Permasalahan kualitas air bersih sering terjadi di kawasan pesisir
−Investigation of saltwater intrusion in Nusawungu Coastal area of Cilacap Regency based on the 2D-resistivity data has been done in
The resistivity data acquisition has been carried out using Wenner's configuration on four locations covering of the
Summary
Permasalahan kualitas air bersih sering terjadi di kawasan pesisir. Di daerah pesisir, penurunan muka air tanah atau kenaikan air laut dapat menyebabkan intrusi atau infiltrasi air laut (asin) ke darat akibat tekanan air tanah menjadi lebih kecil dibandingkan tekanan air laut (Nainggolan dkk. 2016). Berdasarkan hasil penelitian, kawasan ini memiliki nilai resistivitas batuan bawah permukaan yang sangat kecil,sehingga mengindikasikan potensi intrusi air laut (asin) ke dalam akuifer cukup besar (Nisa 2017). Untuk menginvestigasi potensi intrusi air laut di kawasan Pesisir Nusawungu, maka dilakukan survei geofisika.Metode geofisika yang cocok diterapkan untuk tujuan tersebut adalah metode resistivitas dua dimensi (2D).Metode resistivitas merupakan suatu metode eksplorasi geofisika yang mempelajari sifat kelistrikan batuan bawah permukaan dengan mengalirkan arus listrik searah (DC) ke dalam bumi.Metode ini memanfaatkan resistivitas batuan untuk mengidentifikasi sifat-sifat fisis bawah permukaan, sehingga cocok digunakan untuk eksplorasi bawah permukaan. Proses akuisisi data ini dilakukan menggunakan konfigurasi Wenner dengan teknik lateral mapping untuk mendapat profil resistivitas batuan bawah permukaan. Beda potensial, dan jarak antar elektroda diolah sehingga bisa diperoleh nilai resistivitas semu ( a) masing-masing lapisan batuan. Butiran bijih besi banyak dijumpai pada kedua formasi batuan tersebut, khususnya pada permukaan (Hilman 2014)
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