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PPA/PR/10 REPORT ON THE ENVIRONMENTAL ISOTOPIC INVESTIGATIONS IN KEDAH AND PERLIS AREA, MALAYSIA - PART I IAEA Regional Cooperative Agreement (MAL2623/R1/AG) PPA/PR/10 REPORT ON THE ENVIRONMENTAL ISOTOPIC INVESTIGATIONS IN KEDAH AND PERLIS AREA, MALAYSIA (PART I) IAEA REGIONAL COOPERATIVE AGREEMENT (MAL 2623/R1/AG) DAUD BIN MOHAMAD Tun Ismail Atomic Research Centre (PUSPATI) November, 1982. Contents Page 1.0 Introduction. 1 2.0 The Study Area. 1 2.1 Geography and Climate. 1 2.2 Geology. 1 2.3 Hydrology. 2 3.0 Sampling and Field Procedure 2 4.0 Laboratory Procedure 3 5.0 Results and Discussion 3 5.1 Geochemical Investigations. 3 5.2 Isotopes Investigations. 4 List of Table 1. Chemical and Isotopic Results of Kedah/Perlis Groundwater. 6 2. Isotopic Results of Rainwater Samples, Alor Star, Kedah/Perlis. 10 List of Figure 1. Location of the Study Area, Kedah/Perlis. 11 2. Geological Map of the Study Area. 12 3. Location of Sampling Sites, Kedah/Perlis. 13 4. Triangular Diagram of Cations in Groundwater, Kedah/Perlis Area. 14 5. § D Vs & 0 of Groundwater, Kedah/Perlis. 15 6. Isotopic Composition of Groundwater, Kedah/Perlis. 16 7. Graph Showing Tritium Vs h 0 of Groundwater, Kedah/Perlis. 17 APPLICATION OF ENVIRONMENTAL ISOTOPES TO HYDROLOGY IN KEDAH AND PERLIS AREA 1.0 Introduction Followings the previous RCA meeting held in Seoule, Republic of Korea ir. October 'i960, it has been accepted that a similar project en isotope hydrology undertaken in Kelantan Basin be extended to Kedah and Perlis area, Malaysia. This project was commenced in April, 1981. 2.0 The Study Area The study area is located in the north-west of the Peninsular, between the parallels of 5 and 7 degrees north. The land boundaries of the study area are the frontier with Thailand in the north and east and the states of Perak and Penang in the south-west, see Figure 1. 2.1 Geography and Climates •> The area of the two states combined is 10340 km of which Kedah 2 accounts for 9420 km . Host of the land is less than 77m above mean sea level find a major part of this area consists of alluvial coastal plain. Highland is found to the north and west of Perlis (limestone) and in the eastern half of Kedah (granite) extents from Thailand. The study arer- experiences a typical equatorial maritime climate that is hot and wet, but moderated by insularity. Annual precipita­ tion diminishes northwards and ranges from 2800 - 3500 mm in south Kedah to less than 1800 mm in northern Perlis. The annual rainfall in the region is high (2300 mm) but they mainly fall during certain months of the year i.e May - convectional rains, August/September - south-west monsoon and October - convectional rains. Much of the rain­ falls are convective in origin and are therefore localised in distri­ bution. 2.2 Geology The regional geology of the area is fairly well known although not all of the area has been mapped in detail. A simplified geological map of the study area is given in Figure 2. The main geological forma- - 2 - tions encountered in the study area (i) The limestone hill araa (ii) The Silurian Shales and Quartzites (iii) The Carbonaceous Shales, Sandstones and Quartzites (iv) The Triassic Shales and Sandstones, and (v) The ''•-lU-viura from granitic origin. Hydrology There are two main catchments in Kedah, that of the Sungai Kedah (2600 km2") in the northern half of the state, and that of Sungai Huda, 2 the larger of the two (4150 km ) in the eastern and central part^, see Figure 3. Of the total surface area of Kedah and Perlis, a relatively small part only is presently under total or partial control, mainly to the benifit of agricultural sectors. In regard to groundwater investigation in the area, the main aquifers v/hich have heart identified are as follows. i) Limestones - these are the best potential aquifers of the 3 study area which yields up to 110 m per hour per well (25000 gph). ii) Triassic formations - contain important sandstone strata 3 are also good aquifer with yields of 10 to 40 m per hour per well (2200 to 8800 gph). iii) The Alluvium deposits - originated from weathered granite, are a mixture of medium to coarse sand and clayey materials. 3 The sandy layers may provide for yields of 20 to 25 m per hour per well (4400 to 5500 gph). iv) Other formations - consist of hardshales, quartzites or sand­ stones (Carboniferous or Silurian) and have rather low poten- 3 tial output of 2 to 10 m per hour per well (440 to 2200 gph). However, they are generally sufficient, in most cases, for rural water supply. Sampling and Field Procedure Groundwater samples were collected from exploration/production wells in Kedah/Perlis area in four sampling occassions i.e April 1981, - 3 - October 1981, April 1982 and August/September 1982. Sample localities are shown in Figure 3. Groundwater samples were collected in polye­ thylene and glass bottles from each site for tritium (it), chemical (it) and stable isotopes (30 ml) analyses. In addition to groundwater samples, rainwater samples are also collected every month mainly for isotonic analyses. The specific electrical conductance, temperature and pH of ground­ water samples were measured soon after collection. In the last trip, however bicarbonate concentrations were also determined in the field using titration technique. As most groundwaters are of pre-nuclear origin, a few wells were selected for C investigation in the last trip in order to confirm other isotopic findings. Laboratory Procedure Groundwater samples were shipped to IAEA and AAEC laboratories for the analyses of stable isotopes ( H and 0) and T respectively. Whilst major cations ( Na , K , Ca and Mg ) and anions (HC0~ , SO = and cl~) are determined in Malaysia. Results and Discussion 5.1 Geochemical Investigations Standing water level, temperature, pH and specific electrical conductance were measured at the study site in all water samples taken in the test holes, see Table 1. Major cations and anions v/ere analysed by the Department of Geology, National University of Malaysia/Dept. of Chemistry Malaysia (Table 1). pH values, in general varied from 3.7 to 7.9 with most values fall about 6.2. The temperature of the groundwater samples ranges from 27 to 30 C. Standing v/ater levels were observed fluctuating with seasons. The electrical conductance of groundwater samples ranged from 18 to 2660 Ms /cm' with majority of the determinations are below 400^-S/cm. High values are observed for waters near limestone formations i.e wells 480 - Gunong Keriang, 487 - Kodiang Town, 488 - Kodiang Quarry and 519 - - 4 - Tambun Tulang. The high conductivity value at the.-^e locations may be attributed to high dissolution of the limestone formations. Bicarbonate concentrations in the groundwater samples ranged from o mg/6/ to as high as 444 mg/ V UCO~ . This range is very wide which reflects different zones of geologic setting (different litho- logy, structure, topography, etc.) of the study area. The high content of bicarbonate in waters is probably produced from dissolution of carbo­ nate minerals such as dolomite and calcite that are associated with parents rocks/aquifer materials eg. wells 480 - Gunong Keriang» 563 - Arau Pump House, 519 - Tambun Tulang etc. The laboratory analyses of Na+, Ca2+, Mg +, K+, KC©"-, cLT and SO = show the concentrations of these constituents vary considerably over the sites, those sites near the limestones area show remarkably high concentration of HCO^" . In addition to bicarbonate concentration, groundwaters in the area are also Ca-Mg rich waters which may be pro­ duced from dissolution of calcite and dolomite, see Figure 4. It is, however of all the sites, the concentrations of all constituents are most significant at location 519 - Tambun Tulang, see Table 1. The chloride and sulphate contents are generally low, indicating that sea water may not present. Hence, the high salt content in some of the wells may be attributed to leaching of the aquifer matrix. 5.2 Isotopes Investigations All the isotopic results are given in Table 1. The & and o 0 values are linearly correlated as in all-natural waters. The values do not fit well the meteoric water line, see Figures 5. The long term mean isotopic composition of precipitation at Bangkok (<5 O = -6.91 , SD = -45.5 ) and at Singapore ( § o = -7.34 ,§5>- -46.9 )•fall within the range of variation of Kedah/Perlis groundwaters (Figs. 5). The interpretation of stable isotopic results is quite difficult to be made at this stage. However, it seems that in the southern part PIS of the basin more negative O O values are encountered which also have *•*-] Q a low tritium content. Also, the o O values less negative than - 7 A'-*-«- are always coupled with significant tritium content, see Figure 6. The above phenomena indicate the occurrence of two typeu of water; one recharged in the highlands with more negative & 'w0 values and low tritium (due to the time spent in covering the distance between the recharge area and the sampling point) and; a r.<. cond ox local -eoh-jrcjt; with hLjh tri^iu:.. u-I 1-:^.. :. ^'.iv-' <£ ' 0. On the other hand, in the northern part of the basin the results are more confused and there is no correlation at all botv/jen tritium p'iQ and ^ °C, see Figure 7. Results of the tritium assay show that most samples are pre- nuclear in age as indicated from first and second sampling. In the first set of samples, only two samples are modern waters i.e Wells 480 - Gunong Keriang and 475 - Masjid Lama.

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