Sorption and transport of arsenic in shallow aquifer: a case study of Laem Chabang sanitary landfill, Changwat Chonburi

Abstract

This study mainly aims to describe sorption and mobility behavior of arsenic (As) in shallow aquifer in Laem Chabang sanitary landfill Changwat Chonburi. The study was divided into 3 parts as follows: 1) Field survey of groundwater level measurement as well as soils and groundwater sampling in rainy and dry seasons, 2) column experiments and 3) ground water flow and As transport modeling. In first part. The sixteen shallow groundwater samples from domestic wells were collected in the study area and were then analyzed for As concentration and other water quality parameters (i.e., pH, EC, ORP, Ca, Mg, K, HCO₃, Cl, SO₄, Fe, Mn, Zn and Al). A relatively high As concentration was founded in dry season at the monitoring well no. WB02 where located in the north of the landfill, about 0.107 mg/L. Also Fe and Mn were found in some shallow wells where located in th west of the study area, exceeding the drinking water standards of the World Health Organization (WHO). Most shallow groundwater samples mainly are the mixed type, calcium bicarbonate type and sodium chloride type. The soil samples were collected around landfill, at 0-200 cm depth below ground surface and analyzed the physic-chemical properties of sand and sandy loam, which are the major medias of shallow aquifer, were determined by column tests under saturated condition. By fitting with HYDRUS-1D, the dispersion coefficient of sand and sandy loam are 18.68 and 13.65 cm²/mg, respectively. According to microwave digestion followed EPA 6-8 cm³/mg and 20 cm³/mg, respectively. According to microwave digestion followed EPA 3051A, As amount remained in sandy loam is 6 times higher than that remained in sand. Groundwater levels and such sorption and transport parameters from part 1 and 2 were further applied in mathematical model, so-called GMS-MODFLOW, to simulate groundwater flow and As migration in the real world. In the last past, with calibration and validation procedures, the groundwater movement, derived from the model, which conforms to the southwest but As transport migrate from the landfill site to the river, in the north-westward direction due to the local groundwater flow effect.