Modelling of surface water quality in old mining area contaminated with arsenic

Abstract

Tin mining activities in some Southern Provinces of Thailand have lasted for more than 100 years. However, arsenic contamination from the old mines is still posing health problems in some areas along the water pathway connecting the mines and the sea. The area under this study is in Ronphiboon district, Nakhon Srithammarat province where the incidents have been most severe. It has caused arsenic to spread in surface water and environment depending on the runoff by natural rainfall as well as other physical and chemical factors along the passageway. This study aimed to understand the dynamics of arsenic dissolution, its binding with ferrous and aluminium oxides to form colloids and sediments, and its dispersion in aqueous and colloidal phases. Other objectives are to develop basic mathermatical models used to explain the historical arsenic-contamination data in the past 10 years (2005-2014), as well as to predict the future trends. The tota length of 20 km, starting from the mine to the area closed to sea was in focus. The 10-year data were collected from 3 sub-basins which include Huay Ronna, Huay Huawmeang, and Huay Namkhun basins. The parameters analysed for surface water quality were the levels of As, Cu, Fe, Mn, Zn, pH, T, conductivity and salinity in conjunction with waterway flow rate, rainfall intensity. It was found that in general, arsenic concentration had gradually decreased over time and distance, but fluctuated during different seasons of any particulat year, as well as various geographical factors. Currently, the developed dispersion models can only predicy general pattern of arsenic concentration as a function of geography, runoff, waterway flow rate, time and distance. It was found that pH in the area varied between 4.4-9.5 which was significantly wide and must be considered in more realistic model formulation together with dynamics of colloid and sediment dislocation. This was not yet incorporated into the current models.