Sains Malaysiana 37(1): 1-13(2008)

Pencirian Hidrokimia Air Tanah dan Air

Bawah Tanah di Kerpan Kedah

(Hydrochemical characterization of soil water and

groundwater of Kerpan Kedah)

Umar Hamzah, Yong Cheng Yeu, Bashillah Baharudin

& abdul Rahim Samsudin

Program Geologi

Pusat Pengajian Sains Sekitaran & Sumber Alam

Fakulti Sains & Teknologi, Universiti Kebangsaan Malaysia

43600 Bangi, Selangor D.E. , Malaysia

Diserahkan:  13 Mac 2007 / Diterima: 12 Mei 2007

ABSTRAK

Analisis kimia air telah dilakukan terhadap larutan yang diekstrak dari 85 sampel tanah yang dipungut di kawasan ternakan udang harimau di Kerpan. Sampel tanah dikorek pada kedalaman 2 m bermula dari garis pantai sehingga 20 km ke arah daratan. Selain daripada tanah, air bawah tanah juga disampel dengan penggerudian yang berkedalaman 10 hingga 25 m untuk dilakukan analisis kimia air. Hasil analisis hidrokimia larutan yang diekstrasi dari sampel tanah yang diambil pada kedalaman 1-2 m menunjukkan kepekatan klorida berjulat dari 12 hingga 6500 mg/L. Berdasarkan kepekatan ion tersebut, kawasan kajian telah dibahagikan kepada beberapa zon-zon iaitu zon masin dan payau. Kepekatan pepejal terlarut yang diukur adalah dalam julat 100 hingga 40,000 mg/L dengan julat ini merangkumi zon berair segar hingga masin. Zon berair masin yang ditafsir berdasarkan kepekatan pepejal terlarut adalah dalam lingkungan 1 km dari pantai manakala berdasarkan kepekatan klorida sempadan ini adalah disekitar 4-5 km. Kehadiran air masin boleh berasal dari penerobosan langsung dari laut ataupun melalui proses air pasang-surut dimana air laut masuk melalui sungai atau terusan berhampiran ke kawasan kajian. Kehadiran air masin juga disokong oleh pertambahan kepekatan unsur-unsur seperti naterium, kalium dan kalsium ke arah laut. Berdasarkan peta taburan spatial kepekatan klorida, pola kontur kemasinan tinggi didapati mengikut bentuk kolam ternakan udang. Oleh itu besar kemungkinan pengaruh air masin adalah dari proses infiltrasi air kolam ke kawasan sekitar. Untuk melihat samada proses penerobosan juga turut memainkan peranan dalam mempengaruhi kemasinan di kawasan kajian, sampel air dari lubang gerudi pada kedalaman 10-25 meter juga turut dibuat. Sampel air yang dipam dari lubang gerudi menunjukkan kepekatan klorida dalam julat 2030 hingga 13,000 mg/L manakala kepekatan pepejal terlarut berjulat 3233 hingga 9280 mg/L. Berdasarkan nilai kepekatan klorida dan pepejal terlarut sampel air lubang gerudi, kawasan di sekitar lubang gerudi khususnya pada jarak hampir 1 km dari pantai telah tercemar dengan kesan penerobosan air laut.

Kata kunci: Tanah; air bawah tanah; kemasinan; intrusi air laut 

ABSTRACT

Chemical analysis was carried out on solution extracted from 85 soil samples collected at a prawn aquaculture in Kerpan. These soil samples were taken at depths of about 2 m by using hand auger. Localities of samples were along several parallel lines which are perpendicular to the coast to about 20 km towards inland. Water samples were also collected from boreholes drilled at depths of 10 m to 25 m for chemical analysis. Hydrochemical data of water extracted from soil samples taken from depths of 1-2 m show chloride concentrations ranging from 12 to 6500 mg/L. The wide range of ions concentrations indicates the presence of different type of water which can be classified as fresh to saline. Total dissolved solid values of the water samples also show quite a considerable range of concentrations ranging from 100 to 40,000 mg/L representing fresh to saline type of water. This saline zone is within about 1 km from the coast if interpreted based on total dissolved solid values while the distance is much further towards inland which is 4-5 km based on chloride concentrations. In coastal areas, the presence of salt water can be associated with direct intrusion of sea water into the underground water system or it can be contributed from the infiltration of sea water through the rivers or cannels during high tides into the coastal plain. The presence of salt water is supported by the increase in the concentration of naterium, kalium and calcium towards the sea. Based on spatial distribution map of chloride concentration, high salinity contour seems to follow the shape of the aquaculture ponds in the study area indicating some possibility of infiltration of sea water in the pond into the neighbouring areas. Water samples from boreholes drilled to depths of 10 to 25 m were taken and analysed in order to detect for any influence of sea water intrusion into the salinity of groundwater in the study area. Borehole water samples show chloride concentration ranging from 2030 to 13000 mg/L while the concentration of total dissolved solid ranges from 3233 to 9280 mg/L. The high chloride and total dissolved solid concentrations in the samples indicate the areas near the boreholes or within 1 km from the coast were contaminated due to the intrusion of sea water.  

Keywords: Soil; groundwater; salinity; seawater intrusion

RUJUKAN/REFERENCES

Bashillah Badarudin. 2005. Penggunaan kaedah geofizik dan geokimia dalam kajian penerobosan air masin di Kerpan, Kedah. Tesis SSn, UKM .

Davies, S.N. & DeWiast, R.J.M. 1966. Hydrogeology. New York: J ohn Wiley & Sons, Inc.

Fetter, C.W. 2001. Applied Hydrogeology. New Jersey: Prentice Hall.

Hamzah U., Samsudin A.R. Mohamad I.C., 2002. Salinity mapping of coastal groundwater aquifer by surface geoelectrical methods: Case studies at Kuala Selangor and Nenasi, Pahang. Proceedings of Malaysian Science & Technology Congress, Symposium A, Johor Bharu: 232-243.

Jones, C.R. 1978. Geology and mineral resources of Perlis, North Kedah and Langkawi Islands. Geological Survey Malaysia Memoirs 17.

Kim, J.H., Kim, R.H., Lee, J. & Chang, H.W. 2003. Hydrogeochemical characterization of major factors affecting the quality of shallow groundwater in the coastal area at Kimje in South Korea. Environmental Geology 44:478-489

Mustafa M. 2002. Kajian keberintangan geoelektrik dan geokimia di kawasan Kerpan, Sanglang, Kedah, Disertasi Sarjana Muda, Program Geologi, Universiti Kebangsaan Malaysia.

Philbert, F.J., 1982. Major ions. Dlm. Chemical analysis of inorganic constituents of water. Jon, C.S.N(Ed). pp 69-128. United States of America: CRC Press, Inc.

Samsudin A.R., Hamzah U., Rafek A.G., Haryono. J. 1997. Salinity mapping of coastal groundwater aquifers using hydrogeochemical and geophysical methods: A case study of North Kelantan. Proceedings of International Symposium on Integrated Coastal & marine Resource Management. Malang, Indonesia. 154-160.

Sapari N., & Awang M. N. 1996. Alluvial aquifer: A threatened water resource. Prosiding Seminar Geologi dan Sekitaran: Impak dan Pengauditan,  85-104.

Soed S.B. 2002. Kajian geologi dan keberintangan duga dalam geoelektrik di kawasan Kerpan-Ayer Hitam, Jerlun, Kedah. Disertasi Sarjana Muda Program Geologi, Universiti Kebangsaan Malaysia.

WHO. 1971. International standards for drinking water. Ed. Ke-3. Geneva: WHO.

Yeu, Y. C. 2003. Pemetaan zon air masin, air payau dan air tawar serta pengelasan air tanah dengan kaedah analisis kimia air di kawasan Kerpan, Kedah Darul Aman. Disertasi Sarjana Muda, Program Geologi, Universiti Kebangsaan Malaysia.