Highlighting the implications of selenium dispersion from disposal of Kahota Industrial Triangle area, Islamabad, Pakistan using three-dimension solute transport model

摘要

This study highlights the implications of selenium (Se) dispersion in groundwater flow regimes of Kahota Industrial Triangle area located adjacent to the Soan River, Islamabad. Initially, a regional groundwater 3-D flow model has been developed, calibrated to the known observed heads of 24 water wells, verified, and confirmed that convergence has actually arrived to satisfy the steady state condition. Later, the transient simulation was carried out adding in the known recharge, storage factor, porosity, and observed drawdown matched with the simulated drawdown that appears to fall in close agreement with a difference of 0.25 m. As such the steady state groundwater model has facilitated to understand the mechanism of groundwater flow regimes inrnreference to the implications of selenium dispersion from disposal of Kahota Industrial Triangle area. Thirty-five water samples were collected mainly from the industrial water wells for the evaluation of heavy metals. Selenium being the major contributor of pollution has been short listed to monitor its dispersion using a solute transport model modular three-dimensional transport model (MT3D). Chemical parameters related to selenium characteristics including horizontal and vertical transverse dispersivity/longitudinal dispersivity, effective molecular diffusion coefficient and bulk density of the porous medium of aquifers have been used in MT3D contaminant transport model. MT3D is run for 30 years in steady state condition. As usual first run did not produce the exact field conditions. Therefore, the contaminant transport model is calibrated against the 32 values of observed selenium concentrations in boreholes by minor adjustments in the chemical parameter values. The final calibration has been achieved with residual value of 3.88 × 10~(-5) Kg/m~3. Seven hypothetical observation wells are used to monitor the selenium concentrations over a long-term period of time.