predicting model of arsenic transport and transformation in soil columns and ground water contamination (case study: gorgan plain, iran)

Soil and water resources quality is affected by various pollutants because of human direct interventions in recent decades. arsenic is recognized as one of the toxic heavy metals in environment. arsenic is a metalloid whose unauthorized amounts in soil and ground water tables is a serious threat to human life. soil and ground water of golestan province, iran is contaminated with arsenic in some areas such as gorgan plain area. in this study arsenic transport in soil columns and ground water tables of gorgan is investigated. a mathematical computer model, leachm is applied which is based on mass balance equation, including dispersive and convective transport, surface adsorption, oxidation and reduction, and also volatilization, chemical and biological transformation. this model simulates different species of arsenic such as arsenite, arsenate, and organic arsenic. validation of model is by comparison of simulation results to sampling data under transient states. the simulation results by leachm model are in good agreement with measured values. variation between measured data and the simulation results is highly affected by the absorption coefficient with a coefficient of 0.07 with a mean error of 4.43%. results of this study indicate that the distribution of arsenic in soil column to the ground water table is predictable. the simulation results represents that by increase of total time from beginning to end of the simulation, the concentration of arsenic compounds approaches the measured values.