ANALISIS KERENTANAN INTRINSIK AIR TANAH DAN RISIKO PENCEMARAN DI KARST RENGEL KABUPATEN TUBAN

TRI RAFIKA DIYAH I, Dr. Suprapto Dibyosaputro, M.Sc.

2015 | Tesis | S2 Ilmu Lingkungan

Air tanah pada akuifer karst lebih rentan terhadap pencemaran dibandingkan dengan akuifer lain. Hal ini dikarenakan karakteristik hidrogeologi karst yang unik yaitu lapisan tanah tipis, konsentrasi aliran pada epikarst, dan resapan air melalui ponor sehingga kontaminan secara mudah dan cepat mencapai air tanah. Penelitian ini ditujukan untuk menganalisis kerentanan, bahaya, dan risiko pencemaran air tanah yang merupakan upaya dalam perlindungan kualitas air tanah di kawasan karst. Penilaian kerentanan air tanah dilakukan dengan metode COP yang merupakan metode berbasis Sistem Informasi Geografis (SIG) dengan teknik pembobotan dan overlay setiap faktor. Faktor yang mempengaruhi kerentanan air tanah dikelompokkan dalam 3 faktor yaitu concentration of flow (C), overlying layers (O), dan precipitation (P). Peta risiko pencemaran diperoleh melalui overlay peta kerentanan dengan peta bahaya pencemaran. Peta bahaya pencemaran disusun berdasarkan identifikasi dan pembobotan penggunaan lahan. Hasil penelitian menunjukkan bahwa: 1) Faktor yang mempengaruhi kerentanan air tanah terhadap pencemaran di Karst Rengel adalah faktor C dan faktor O. Tingkat kerentanan air tanah di Karst Rengel didominasi oleh kerentanan sedang dan tinggi, masing-masing sekitar 46,53% dan 33,52% dari luas daerah penelitian. Kerentanan rendah hanya sekitar 4.69%. Kondisi tersebut dipengaruhi oleh ketebalan tanah yang tipis dan konsentrasi aliran melalui ponor 2) Sebagian besar daerah penelitian (82,26%) memiliki bahaya pencemaran rendah, sedangkan bahaya pencemaran tinggi sekitar 6,93%. Kondisi tersebut dipengaruhi oleh dominasi pengunaan lahan ladang dan sawah tadah hujan. 3) Tingkat risiko pencemaran di Karst Rengel didominasi oleh risiko rendah dan sedang, masing-masing sekitar 48,66% dan 32,77%. Sementara itu, daerah dengan risiko pencemaran tinggi sekitar 17,72%. Kondisi ini dipengaruhi oleh dominasi tingkat bahaya pencemaran air tanah yang relatif rendah. Sampel air dari 17 mataair dan 1 sumur menunjukkan bahwa sebagian besar sampel air memiliki kadar total koliform dan nitrat diatas kadar maksimum yang diperbolehkan menurut standar kualitas air bersih. Uji korelasi Sperman menunjukkan bahwa terdapat hubungan yang signifikan antara kadar total koliform dan tingkat risiko pencemaran air tanah dengan level kepercayaan 99%. Kata kunci: Kerentanan Air tanah; Risiko Pencemaran; Karst

Groundwater from karst aquifer is known particularly for its vulnerability to contamination compared to other groundwater systems. This is due to their hydrogeological properties, like thin soils, flow concentration in the epikarst, and point recharge via swallow holes. Such characteristics result in contaminants easily and quickly reach the groundwater. This research is purposed to analyze the degree of groundwater vulnerability, hazard and contamination risk as a basis for protection zoning of groundwater quality in karst aquifer. This research used COP method to assess groundwater intrinsic vulnerability. It is a Geographic Information System (GIS) based method that has been developed by weighting, quantification and overlaying techniques for each factors. It considers three factors; concentration of flow (C factor), overlying layers (O factor) and precipitation (P factor). Contamination risk map was obtained by overlying the groundwater vulnerability and hazard maps. Contamination hazard map was created by ranking and weighting procedure of land use map. The results of the research are: (1) Groundwater vulnerability to contamination in Rengel Karst was determined by C factor and O factor. Groundwater vulnerability was dominated as “moderate” and “high”. The percentages of each class were 46.53% and 33.52%. “Low” vulnerability covered about 4.69% of the research area. It was influenced by the domination of thin soil and flow concentration via swallow holes. (2) In large parts of the area (83,26%), contamination hazard categorized as “low”. “High” degree of hazard was only about 6.93%. It was affected by domination of fields and non irrigated paddy fields in land use types. (3) Contamination risk map showed that a large part of Rengel Karst was classified as “low” and “moderate”. The each class covered about 48.66% and 32.77%. Meanwhile, “high” risk was about 17.72% of the area. It was due to the domination of “low” hazard that covered large parts of research area. Water samples collected from 17 springs and 1 pipe well showed that almost of water samples contain high level of total coliform and nitrate. These exceed the maximum level permitted of clean water standard. Based on Spearman’s correlation, it was known that there was a significant correlation between the total coliform level and the contamination risk degree in Rengel Karst at the confidence level of 99%. Keywords: Groundwater vulnerability; Contamination risk; Karst

Kata Kunci : Kerentanan Air tanah; Risiko Pencemaran; Karst;