Natural Attenuation Modelling of Heavy-Metal in Groundwater of Kirkuk City, Iraq

This study deals with the shallow alluvial aquifer situated beneath the urban area of kirkuk city. The ancient part of the city (Shorja) is affected by seepage from local agricultural areas causing relatively high heavy metals concentration in groundwater. The selection of polluted site depended on the highest TDS value (3856 mg/L) associated with the highest heavy metal concentrations (Pb, Ni, Co and Zn) in groundwater. This study focuses on the evaluation of natural attenuation effectivity for long-term protection of groundwater quality using realistic three-dimensional reactive-transport groundwater model. The requirements of 3-dimensional reactive transport model were obtained from field observation and laboratory works, in addition to aquifer stratigraphy, minerology and hydrochemistry. The simulations were achieved by using PHAST program that is depended on the HST3D flow and transport code and the hydrochemical PHREEQC code. The modeling results explained the ability of natural attenuation in consuming the concentration of heavy metals, where Long-term (20 year) simulation results show that heavy metal adsorption on hydrous ferric oxide, effectively capture the movement of heavy metals in groundwater down gradient of source areas, resulting in an basically immobile groundwater plume.