NATURE OF PROJECT: GROUNDWATER FLOW & TRANSPORT MODELLING FOR LANDFILL DESIGN / ENVIRONMENT IMPACT ASSESSMENT
CLIENT: LYNAS MALAYSIA SDN BHD
DURATION: FEB – MAR 2019
BACKGROUND AND METHODOLOGY
Numerical Groundwater flow and solute transport modelling was used to establish the (i) groundwater flow characteristics, (ii) migration of contaminants (Pb, Cr, Zn, Ba and Hg) from the proposed onsite secured Landfill (Prescribed Premise) for Neutralized Underflow (NUF) solids at Kuantan Malaysia.
(i) Numerical Modelling Approach – The study applies the advanced method of using computer modelling technique, numerical code Modular finite-differential flow (MODFLOW) for assessment. The transient-state model was used to simulate a worst-case scenario under various assumptions: (i) secured landfills at the site are unlined (non -engineered type), (ii) contaminant are non-reactive i.e. adsorption process is negligible and contaminants are expected to migrate at maximum concentration to groundwater.
(ii) Model Development – Six hydrostratigraphic layers were modelled comprising of two aquifer systems:
Table 1: Hydrostratigraphic layers of the area.
RESULT & DISCUSSION
Figure 1: Six (6) layers of hydrostratigraphic unit at LAMP site that was used in the model
(i) Groundwater movement is northeast –southwest, and north-south towards the earthen waste water retention pond at the site. The flow is outwardly discharging to the South China Sea at the southern part of LAMP site.
Figure 2: groundwater movement towards the waste water retention pond at the site. The pond is hydraulically connected with the aquifers..
(ii) Contaminant (Pb, Cr, Ba, Hg) will reach the upper aquifer after 3650 days (10 yrs.) of migration and Zn will reach after 730 days (2yrs) under assumptions of unlined landfill (no liner systems).
Figure 3: Pb migration after 10950 days (30 years) in (Model 2).
CONCLUSION
The model demonstrates that there is minimal negative impact associated with the landfill design to the environment and surrounding rivers due to double liners, moderate permeability of the aquifer and clay layer absorptive properties to retard the contaminants.
