Publication Details

IMPACT OF GROUNDWATER ABSTRACTION TO THE SURFACE WATER OF TOP GLOVE PLANT AREA, OLAK LEMPIT, SELANGOR

National Water Research Institute of Malaysia (NAHRIM) was appointed to conduct a study on the impact of groundwater abstraction on surface water in the surrounding area of the Top Glove Plant area, Olak Lempit, Selangor. The objectives of the study include: (i) to investigate the impact of groundwater abstraction to the surface water flow of the Langat river (ii) to investigate the impact of groundwater abstraction on groundwater level in surrounding area of Top Glove Factory Plant and (iii) to obtain the total availability of groundwater resources and water balance. The study is simulated as a three layered, three-dimensional (3D) numerical groundwater flow model using MODFLOW-2005, MODPATH (modular finite differential pathlines), and ZONEBUDGET for sub regional water budgets. Modelling was carried out on the platform of Visual MODFLOW Flex software and was calibrated in steady-state and run as a transientstate model. Three hydrostratigraphic unit-were considered for the study area; (i) Layer 1 (top soil), (ii) Layer 2 (aquitard) and (iii) Layer 3 (aquifer). Layer 1 is the topmost layer comprises of peat or completely weathered soil (sandy clay /sandy silt) with an estimated average thickness of 3 m. Layer 2 is less permeable of aquitard layer that comprises of clay or silty clay material with an average thickness of 14.2 m. Layer 3 is confined aquifer and comprises of gravelly sand with average thickness of 20 m. The regional trend of groundwater flow is from northeast-southwest towards the lower area around Banting. The rainfall recharge is 156 mm mm/year or equivalent to 7.5% of the average annual rainfall of 2,092 mm/year. Evapotranspiration account 65.1% or 1,361 mm/year of average annual rainfall (2,092 mm/year. Groundwater inflows is mainly from the north eastern area of Paya Indah and Bukit Changgang area. The overall inflow from outside sources (including the river and its environs) is 470,230 m3 /day (470.2 MLD), which is virtually equal to the total discharges at 471,293 m3 /day (471.2 MLD). Of the total inflows in the study area, groundwater discharge to the Langat River (as base flows of gaining river) makes up 24% (-113,049 m3/day). According to the findings of the water balance analysis in the study area, the quantity of water resources in the downstream area, particularly the raw water intake in the Labohan Dagang water treatment plant area, is unaffected by the groundwater abstraction. This is because the groundwater abstracted is only about 4.8 MLD (200 m3 /h or 4,800 m3 /d) compared to the full ii operational capacity of the Labohan Dagang plant, which is 400 MLD. Groundwater abstraction by Top Glove will cause a drop in the water table in the surrounding area. However, groundwater still continues to discharge into the Langat River, which supports the river base flow (gaining river). The groundwater abstracted from the tube well aquifer is not a river bank filtration (RBF) concept due to the abstraction area is located quite far from Langat river (around 1.5 km). In addition, the river bed is covered by fine sediment with a low permeability rate and underlain by clay layer (14 m thick), which reduces river water infiltration into the groundwater aquifer. The impact of the Top Glove plant's effluent discharge on water quality is negligible because the water intake area (water treatment plant) is approximately 4 km upstream from the Top Glove plant's effluent discharge point. Furthermore, the influence of the Langat river tides is minimal and has no effect on the transport of effluent to the upstream (intake area).