Sains Malaysiana 41(7)(2012): 829–840

Kajian Migrasi Bahan Larut Resap di Tapak Pelupusan Sampah Sungai Sedu, Telok Datuk dengan Kaedah Geofizik dan Geokimia

(Study of Leachate Migration at Sungai Sedu, Telok Datuk Waste Disposal Site by

Geophysical and Geochemical Methods)

Mark Jeeva & Umar Hamzah*

Program Geologi, Pusat Pengajian Sains Sekitaran & Alam Sekitar, Fakulti Sains & Teknologi

Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor D.E. Malaysia

Diserahkan:  29 September 2010 / Diterima: 15 Julai 2011

ABSTRAK

Pemantauan air dan tanah tercemar di sekitar tapak pelupusan sampah selalunya dilakukan dengan analisis kimia air permukaan, bahan larut resap dan tanah serta pengukuran geofizik. Air larut resap merupakan cecair yang berasal daripada hasil larutan air hujan terhadap sisa-sisa buangan di tapak pelupusan, yang terkumpul dan meresap masuk ke dalam liang-liang tanah. Satu kajian untuk mengesan pergerakan cecair larut resap telah dilakukan di tapak pelupusan sampah Sungai Sedu yang terletak atas tanah seluas 10 ekar berhampiran pekan Banting. Geologi kawasan kajian dibahagikan kepada formasi Beruas dan Gula iaitu aluvium berusia Kuaterner terdiri daripada lempung samudera yang terendap di atas batuan dasar metasedimen Formasi Bukit Kenny. Survei geofizik dengan teknik pengimejan keberintangan geoelektrik 2D, keberintangan profil menegak (VRP) dan analisis geokimia terhadap sampel tanah dan air telah dijalankan untuk mengetahui tahap migrasi bahan larut resap di sekitar tapak pelupusan tersebut. Tahap migrasi bahan pencemaran akan dikaji melalui hasil analisis seperti nilai model keberintangan elektrik dan kepekatan logam berat berbanding dengan nilai latar belakang. Dalam kajian ini, survei pengimejan elektrik 2D telah dilakukan di sepanjang 8 garis rentasan dan pengukuran VRP telah dilakukan di dalam 6 lubang gerudi. Analisis geokimia untuk mengetahui kepekatan unsur-unsur tertentu telah dilakukan ke atas 33 sampel tanah dan 7 sampel air. Keratan rentas keberintangan menunjukkan bahawa bahan larut resap telah meresap sehingga kedalaman 3-5 m berdasarkan nilai keberintangan elektrik yang rendah secara relatif iaitu kurang daripada 1 ohm m. Kepekatan unsur-unsur yang disukat pula menunjukkan bahan larut resap telah bergerak ke arah sungai yang terletak di sebelah kawasan kajian. Kepekatan logam berat dalam sampel-sampel air sungai dan tanah adalah tinggi dan melebihi nilai latar belakang terutama bagi unsur Ni, Mn, Cr, Zn dan As. Konduktiviti elektrik sampel tanah tebing sungai, air sungai dan air larut resap yang diukur di lapangan adalah masing-masing 6600 μS/cm, dan 20000-50000 μS/cm manakala julat pH bagi semua sampel tersebut adalah di antara 3-5. Nilai konduktiviti dan kepekatan logam berat yang tinggi membuktikan bahawa bahan larut resap telah bergerak dari tapak pelupusan untuk mencemari air sungai, air tanah dan tanah di kawasan sekitar.

Kata kunci: Analisis geokimia; migrasi air larut resap; pengimejan elektrik 2D; tapak pelupusan sampah.

ABSTRACT

Monitoring of contaminated water and soil in waste disposal sites is normally carried out by chemical analysis of surface water, leachate and soils as well as by geophysical measurements. Leachate is defined as any contaminated liquid or wastewater generated from rain water percolating through solid waste materials, accumulating contaminants, and moving into subsurface and surrounding areas. A study was carried out to detect the leachate movement at Sungai Sedu landfill located on ten square acres near Banting town. Geologically, the study area is underlined by Holocene marine clay of Gula and Beruas formations sitting on top of metasedimentary rocks of Kenny Hill Formation. Geophysical surveys using techniques 2D electrical resistivity imaging, vertical resistivity profiling (VRP) as well as geochemical analysis on soil and water samples were used in this study to investigate the level of leachate migration from the dumping spot into the surrounding areas. This was based on characterizing the measured electrical resistivities and analyzing the heavy metal concentrations. The 2D electrical imaging surveys were carried out on 8 profiles while the VRP surveys were conducted in 6 boreholes. Based on resistivity imaging sections, the leachate was detected to migrate at about 3-5 m depth. Basically the electrical resistivity of leachate was less than 1 ohm m. The concentration of heavy metals also showed that the leachate has migrated into the nearby river. The concentration of heavy metals in river bank soil, leachate and surface water samples were high and exceeded the background values especially Ni, Mn, Zn, Cr and As. The electrical conductivity of the river bank soil, leachate, surface water and the surrounding soil samples were approximately 6600 μS/cm and 20000-50000 μS/cm, respectively with pH values of 3-5. The high concentrations of heavy metals and soil conductivities indicated the possibility of leachate migration from the dumping site to contaminate the nearby river, soil and groundwater of the study area.

Keywords: 2D resistivity imaging;geochemical analysis; leachate migration; waste disposal site

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*Pengarang untuk surat-menyurat; email: umar@ukm.my