KAJIAN HIDROKIMIA AIRTANAH BEBAS DI KECAMATAN KALIORI, KABUPATEN REMBANG

RENDY KURNIA, Prof. Dr. Setyawan Purnama, M.Si

2017 | Skripsi | S1 GEOGRAFI DAN ILMU LINGKUNGAN

Kecamatan Kaliori, Kabupaten Rembang mengalami kelangkaan air bersih. Sebagian besar airtanahnya bersifat payau karena lokasinya di bentuklahan kepesisiran. Penelitian ini bertujuan untuk (1) mengkaji persebaran dan karakteristik hidrokimia airtanah; dan (2) menganalisis faktor-faktor penyebab variasi hidrokimia airtanah. Data utama yang dikumpulkan meliputi kandungan ion mayor, Daya Hantar Listrik (DHL), dan tinggi muka airtanah. Kandungan ion mayor airtanah, terdiri dari kalsium, magnesium, natrium, kalium, bikarbonat, sulfat serta klorida, didapatkan dari sampel air sumur yang diuji laboratorium. Lokasi sampelnya ditentukan secara stratified DHL airtanah pada bentuklahan. DHL dan tinggi muka airtanah diukur langsung pada saat kerja lapangan. Lokasi sampelnya ditentukan secara systematic sampling setiap 1 km dan keterdapatan sumur. Metode pengolahan data berupa jaringan arah aliran, klasifikasi DHL, serta tipe hidrokimia airtanah Diagram Stiff, Ion Dominan, dan Diagram Kloosterman. Data kemudian disajikan dalam bentuk tabel, grafik, dan peta. Analisis data dilakukan secara spasial dan deskriptif. Hasil penelitian menunjukkan adanya airtanah bertipe semi bikarbonat, evaporit, sulfat, dan pencampuran. Airtanah semi bikarbonat dengan ion dominan Ca(HCO3)2 dan NaHCO3 berasa tawar dan payau terdapat pada seluruh bentuklahan. Airtanah ini dipengaruhi oleh air hujan. Airtanah evaporit (CaCl2) berasa payau terbentuk karena pelarutan kristal garam yang berasal dari penguapan air laut masa lampau. Airtanah evaporit ditemukan di fluviomarin bagian selatan. Airtanah sulfat (NaCl) yang berasa payau di fluviomarin bagian utara terbentuk karena proses reduksi bahan organik dan pertukaran kation. Airtanah pencampuran (NaCl juga) yang berasa asin dan ditemukan di gisik berasal dari proses pencampuran dengan air laut.

Kaliori Subdistrict, Rembang District experiences fresh water scarcity. Most of the groundwater is brackish because of its location at coastal landform. This research aims (1) to study the distribution and characteristics of groundwater hydrochemistry; and (2) to analyze factors affecting groundwater hydrochemistry variation. The primary data collected are major ions contents, electric-conductivity, and depth of groundwater. Major ion contents from well water samples, consisting of calcium, magnesium, sodium, potassium, bicarbonate, sulphate, and chloride, are tested in laboratory. The sample location is decided by stratified sampling based on groundwater electric-conductivity in each landform. Electric-conductivity and depth of groundwater are measured directly in fieldwork. The sample location is decided by systematic sampling for every 1 km and well availability. Processing data methods consist of flow net, electrical-conductivity classification, and hydrochemistry of groundwater with Stiff Diagram, Dominant Ions, and Kloosterman Diagram. The data are showed in table, graph, and map. The data are then analyzed spatially and descriptively. Result shows that groundwater types found are semi bicarbonate, evaporite, sulphate, and mixing. Semi bicarbonate groundwater with dominant ions of Ca(HCO3)2 and NaHCO3 can be fresh and brackish is found in all of the landforms. The groundwater is affected by rain water recharge. Evaporite brackish groundwater (CaCl2) formed by salt crystal dissolution derives from evaporation of past sea water. Evaporite groundwater is found in south part of fluviomarine. Sulphte groundwater (NaCl) which tastes brackish in north part of fluviomarine is formed by organic matter reduction and cation exchange. Mixing groundwater (also NaCl) which tastes salty and is found in beach derives from mixing process with sea water.

Kata Kunci : hidrokimia airtanah, salinitas airtanah, bentuklahan kepesisiran, Kaliori-Rembang