IDENTIFIKASI KONDISI FISIK AIR SUMUR DANGKAL DAN POLA ALIRAN AIRTANAH DANGKAL DI KECAMATAN SADANG KEBUMEN

 
 
Penulis: Puguh Dwi Raharjo S.Si., M.Sc., Nandian Mareta S.T, Sueno Winduhutomo S.T., Sueno Winduhutomo S.T.
ABSTRAK Secara geologi kecamatan Sadang termasuk kedalam kompleks melange Luk Ulo yang merupakan percampuran berbagai jenis blok batuan yang tertanam dalam massa dasar lempung hitam bersisik (scaly clay). Percampuran ini diakibatkan oleh proses subduksi lempeng benua Eurasia dan lempeng samudera Indo-Australia pada zaman kapur. Blok-blok batuan yang tertanam dalam massa dasar lempung hitam itu beraneka jenis, baik batuan sedimen, batuan beku dan batuan metamorf. Penelitian ini bertujuan untuk mengetahui kondisi fisik air bersih yang dipergunakan sehari-hari oleh masyarakat kecamatan Sadang dan pola aliran airtanah dangkalnya yang selanjutnya untuk mengidentifikasi konservasi airtanah. Pendekatan survei geologi dan pengamatan hidrogeologi di lapangan menghasilkan data pH, TDS dan suhu air bersih serta kondisi pola aliran airtanah dangkalnya. Hasil identifikasi kondisi fisik air bersih di daerah Sadang memperlihatkan variasi nilai pH, TDS dan suhu. Nilai pH air berkisar antara 6,4 – 8,7, dengan rata-rata pH 7,32. Nilai pH terendah tercatat di sumur penduduk (SP) 19 dan SP 23 dengan nilai 6,4, sementara nilai pH tertinggi tercatat di Bak Penampungan (BP) 3 dan BP 4 dengan nilai 8,7. Berdasarkan standar air baku Permenkes No. 32 tahun 2017, pH air baku berada pada kisaran 6,5 – 8,5. Sehingga di empat lokasi yaitu SP 19, SP 23, BP 3 dan BP 4, dimana nilai pH-nya diluar kisaran perlu menjadi perhatian. Secara keseluruhan daerah Sadang dan sekitarnya yang mempunyai nilai rata-rata pH 7,32 merupakan daerah dengan kondisi air yang baku, sedang variasi nilai TDS berkisar antara 29-190, dengan rata-rata TDS 95,87. Nilai TDS terendah tercatat di SP 9 sebesar 29 dan nilai TDS tertinggi tercatat di SP 26 sebesar 190. Berdasarkan standar air baku Permenkes No. 32 (2017), TDS air baku maksimal 500 mg/L. Nilai TDS tertinggi yang tercatat di daerah telitian sebesar 190 mg/L, tidak melebihi 500 mg/L, sehingga secara keseluruhan kondisi titik pengamatan termasuk kedalam air baku dari segi nilai TDS. Variasi nilai suhu berkisar 270C – 320C, dengan rata-rata suhu 28,750C. Nilai suhu terendah tercatat di SP 1, SP 9, SP 10, SP 12, SP 13 sebesar 270C dan nilai suhu tertinggi tercatat di SP 31 dan BP 4 sebesar 320C. Secara keseluruhan nilai suhu air daerah telitian sesuai dengan standar baku air bersih. Pola aliran airtanah di daerah telitian mengalir dari wilayah utara dan wilayah barat menuju wilayah timur dan wilayah selatan dengan ketinggian MAT di wilayah utara dan wilayah barat pada kisaran 55 mdpl semakin ke wilayah selatan dan wilayah timur ketinggian MAT semakin tinggi mencapai 219 mdpl. Kata kunci : geologi, air bersih, Sadang, pola pengaliran, akuifer, konservasi airtanah ABSTRACT Geologically, Sadang sub-district is included in Luk Ulo melange complex which is a mixture of various types of rock blocks embedded in the base mass of scaly clay. This mixture was caused by the Eurasian continental plate subduction process and the Indo-Australian oceanic plate in the cretaceous era. Rock blocks embedded in the base mass of black clay are of various types, both sedimentary rocks, igneous rocks and metamorphic rocks. This study aims to determine the physical condition of clean water that is used daily by the people of Sadang sub-district and the pattern of shallow groundwater flow which is then to identify groundwater conservation. Geological survey approaches, hydrogeological observations in the field and pH, TDS and clean water temperatures and conditions of the shallow groundwater flow patterns through approaches to measuring wells and springs. The results of the identification of the physical condition of clean water in the Sadang area showed variations in pH, TDS and temperature. The pH value of water ranges from 6.4 - 8.7, with an average pH of 7.32. The lowest pH value was recorded in monitoring wells (SP) 19 and SP 23 with a value of 6.4, while the highest pH values were recorded at monitored well (BP) 3 and BP 4 with a value of 8.7. Based on the raw water standards issued by Permenkes 2 (2017), the pH of raw water is in the range of 6.5 – 8,5. So that in four locations namely SP 19, SP 23, BP 3 and BP 4, where the pH values outside the range need to be a concern. Overall the Sadang and surrounding areas which have an average pH value of 7.32 are areas with standard water conditions, while the variation in TDS values ranges from 29-190, with an average TDS of 95.87. The lowest TDS value was recorded in SP 9 at 29 and the highest TDS value was recorded in SP 26 at 190. Based on the standard of raw water issued by Permenkes (1990), the raw water TDS was a maximum of 500 mg/L. The highest TDS value recorded in the study area is 190 mg/L, not exceeding 500 mg / L, so that the overall condition of the observation point is included into raw water in terms of the TDS value. Variations in temperature values range from 270C - 320C, with an average temperature of 28.750C. The lowest temperature values recorded in SP 1, SP 9, SP 10, SP 12, SP 13 amounted to 270C and the highest temperature values were recorded in SP 31 and BP 4 at 320C. Overall the temperature value of the regional water is in accordance with the standard of clean water. The pattern of groundwater flow in the study area flows from the northern region and the western region to the east and the southern region with the height of the MAT in the northern region and the western region in the range of 55 meters above sea level to the south and the eastern region of the MAT height reaches 219 meters above sea level. Keyword : geology, clean water, Sadang, drainage patterns, aquifera, shallow groundwater

JURNAL LINGKUNGAN DAN BENCANA GEOLOGI (WAITING ASSIGNMENT)

ISSN / ISBN / IBSN : 2086-7794

No. Arsip : LIPI-20190103