Kesetimbangan Massa Klorida untuk Menentukan Transfer Airtanah Cat Ciater - Cat Subang di Kabupaten Subang Provinsi Jawa Barat

Abstract

Abstract. According to the Minister of Energy and Mineral Resources Regulation Number 2 of 2017 that CAT Subang borders the NonCAT zone, the division of these boundaries is based on the existence of the Baribis Fault which is considered a barrier to groundwater flow. However, based on Wahi et al (2008) research a fault can act as a barrier or channel for groundwater flow. Quoting from Wahi et al (2008) as the concept of groundwater flow and its recharge mechanism in the Mountain Recharge System (MSR), it can be distinguished from flow infiltration in the mountain-front zone or Mountain Front Recharge (MFR) and subsurface flow from mountains to basins or mountains. Block Recharge (MBR), the presence of the Baribis Fault can affect the control of groundwater flow to become MFR or MBR, even a combination of the two. This research is intended to examine the effect of faults on the groundwater recharge mechanism and flow, including knowing the effect of the Baribis Fault and other faults in the vicinity (Talagasari Fault and Wanareja Fault) on the absorption of rainwater into groundwater through macropore media (fractures) in the fault zone area ( CAT Ciater, Non-CAT, and CAT Subang); knowing the effect of the Baribis Fault on groundwater flow control in the concept of Mountain Recharge System; and estimate the value of groundwater supplied from CAT Ciater, Non-CAT and to CAT Subang. The approach uses the CMB method locally to estimate the value of macropore recharge and the regional CMB method to determine inter-basin flow transferred through the Baribis Fault and estimate its volumetric value. The existence of the Baribis Fault and other faults simultaneously affects the absorption of rainwater into groundwater through macropore media in the CAT Ciater and Non-CAT fault zones. Estimation using the CMB method shows that the duality of groundwater recharge through interstitial and macropore media occurs in CAT Ciater, 29.75% of groundwater in CAT Ciater comes from recharge through macropore media and the rest mostly through interstitial media (rock pores). Meanwhile, Non-CAT is considered unable to escape and store groundwater but can store groundwater through macropore media with a value of 53% and the rest through interstitial media. In CAT Subang there is no groundwater recharge through macropore media, recharge only through interstitial media. Based on the regional CMB method approach with estimation parameters involving the three zones (CAT Ciater, Non-CAT, and CAT Subang) which shows the implications between the sample in the South of the Baribis Fault with the North of the Baribis Fault. Regional groundwater transfer shows the Baribis Fault ability to pass groundwater in the concept of Mountain Recharge System (MSR).

Keywords:  Mountain Recharge System, Mountain Front Recharge, Mountain Block Recharge, Chloride Mass Balance.

Abstrak. Mengacu pada Permen ESDM Nomor 2 Tahun 2017 bahwasanya CAT Subang berbatasan dengan zona NonCAT, pembagian batas tersebut berdasarkan keberadaan Sesar Baribis yang dianggap penghalang aliran airtanah. Tetapi, berdasarkan penelitian yang dilakukan oleh Wahi et al (2008) menyatakan bahwa suatu sesar dapat bertindak sebagai penghalang atau penyalur aliran airtanah. Mengutip dari Wahi et al (2008) sebagaimana konsep aliran airtanah dan mekanisme imbuhannya pada Mountain Recharge System (MSR), dapat dibedakan dengan infiltrasi aliran di zona depan-gunung atau Mountain Front Recharge (MFR) dan aliran bawah permukaan dari gunung menuju cekungan atau Mountain Block Recharge (MBR), keberadaan Sesar Baribis dapat mempengaruhi kontrol aliran airtanah menjadi MFR atau MBR, bahkan gabungan dari keduanya. Penelitian ini dimaksudkan untuk mengkaji pengaruh sesar terhadap mekanisme imbuhan dan aliran airtanah, di antaranya seperti mengetahui pengaruh Sesar Baribis dan sesar lain di sekitarnya (Sesar Talagasari dan Sesar Wanareja) terhadap kemampuresapan air hujan menjadi airtanah melalui media makropori (rekahan) di daerah zona sesar (CAT Ciater, Non-CAT, dan CAT Subang); mengetahui pengaruh Sesar Baribis terhadap kontrol aliran airtanah pada konsep Mountain Recharge System; dan mengestimasi nilai airtanah yang disuplai dari CAT Ciater, Non-CAT dan ke CAT Subang. Pendekatan menggunakan metode CMB secara lokal untuk mengestimasi adanya nilai imbuhan makropori dan metode CMB secara regional untuk mengetahui keberadaan aliran antarcekungan yang ditransfer melewati Sesar Baribis, serta mengestimasi nilai volumetrinya. Keberadaan Sesar Baribis dan sesar lain di sekitarnya secara simultan mempengaruhi kemampuresapan air hujan menjadi airtanah melalui media makropori di daerah zona sesar CAT Ciater dan NonCAT. Estimasi dengan metode CMB menunjukkan bahwa dualitas imbuhan airtanah melalui media interstitial dan makropori terjadi di CAT Ciater, 29,75% airtanah di CAT Ciater berasal dari imbuhan melalui media makropori dan sisanya sebagian besar melalui media interstitial (pori batuan). Sedangkan Non-CAT yang dianggap tidak dapat meloloskan dan menyimpan airtanah, tetapi dapat menyimpan airtanah melalui media makropori dengan nilai 53% dan sisanya melalui media interstitial. Di CAT Subang tidak terdapat imbuhan airtanah melalui media makropori, imbuhan hanya melalui media interstitial. Berdasarkan pendekatan metode CMB secara regional dengan parameter estimasi melibatkan ketiga zona (CAT Ciater, Non-CAT, dan CAT Subang), menunjukkan adanya implikasi antara sampel di Selatan Sesar Baribis dengan Utara Sesar Baribis. Transfer airtanah secara regional menunjukkan kemampuan Sesar Baribis untuk dapat meloloskan airtanah pada konsep Mountain Recharge System (MSR).

Kata Kunci :  Mountain Recharge System, Mountain Front Recharge, Mountain Block Recharge, Kesetimbangan Massa Klorida.