Hidrokimia dan Indikasi Kontaminasi pada Air Tanah di Lereng Selatan Gunung Merapi, Mlati dan Sekitarnya, Sleman, D.I.Yogyakarta

Rahmat Satya Nugraha, Doni Prakasa Eka Putra

Abstract


Daerah Mlati - Sleman di Daerah Istimewa Yogyakarta secara hidrogeologi regional terletak pada sistem Cekungan Air Tanah (CAT) Yogyakarta-Sleman, yang secara stratigrafi terdiri dari Formasi Sleman dan Formasi Yogyakarta. Kedua formasi batuan ini membentuk sistem akuifer multilayer. Penelitian ini bertujuan untuk mengetahui karakteristik hidrokimia serta indikasi kontaminasi di Daerah Mlati. Penelitian dilakukan dalam beberapa tahapan yaitu observasi hidrogeologi lapangan, penentuan titik pengambilan sampel, pengambilan sampel air tanah dan analisis laboratorium. Hasil analisis laboratorium menunjukkan tipe air tanah pada sumur gali yang mewakili akuifer bebas didominasi oleh tipe Ca2+-Na+-HCO3- . Pada air tanah dari sumur bor dalam, tipe air didominasi oleh tipe Ca2+-Na+-HCO3--Cl-. Selain itu, diketahui bahwa kandungan besi dan mangan pada sumur bor dalam umumnya lebih tinggi daripada sumur dangkal. Indikasi kontaminasi ditunjukkan dengan adanya kandungan  nitrat pada sumur gali dengan kadar nitrat rata-rata 15 mg/l, sedangkan pada sumur bor dalam tidak dijumpai unsur nitrat. Dapat disimpulkan bahwa kedua akuifer memiliki karakteristik kimia air yang didominasi oleh unsur Ca2+-Na+-HCO3-, hanya saja pada akuifer dalam terdapat  ion klorida turut mendominasi. Adanya nitrat pada sumur gali dengan kadar nitrat rata-rata diatas 10 mg/l, menandakan bahwa sumur gali atau akuifer bebas dangkal rentan terhadap pencemaran yang bersumber dari aktivitas manusia di permukaan.

The area of Mlati - Sleman is hydrogeologically located in the Yogyakarta-Sleman Groundwater Basin (GB) system, which stratigraphically consists of the Sleman Formation and the Yogyakarta Formation. The purpose of this study is to determine the hydrochemical characteristics and indications of contamination in the Mlati Region. The research was started with the field hydrogeological observation, determination of sampling points, groundwater sampling and laboratory analysis. Based on laboratory analysis, the groundwater types in the dug wells (unconfined aquifers) were dominated by type Ca2+-Na+-HCO3- . The groundwater from deep wells was dominated by type Ca2+-Na+-HCO3--Cl-. In addition, it is known that the iron and manganese content in deep bore wells is generally higher than shallow wells. The contamination is indicated by the presence of nitrate in the dug wells with an average nitrate level of 15 mg/l, while in the deep well bore there is no element of nitrate. Therefore, we concluded that the two aquifers are dominated by the elements Ca2+-Na+-HCO3-. In the deep aquifer, the chloride ion is also dominating. The presence of nitrates in dug wells with an average nitrate level above 10 mg/l indicates that shallow wells or shallow unconfined aquifers are susceptible to pollution from human activities.


Keywords


Groundwater chemistry, Merapi Mountain, Daerah Istimewa Yogyakarta

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DOI: http://dx.doi.org/10.14203/risetgeotam2019.v29.1027

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