Preliminary Laboratory-Scaled Characterization of 2-Nitrophenol Transport Parameters for Groundwater Contamination Risk Assessment

Groundwater is one of the important sources of water supply in Thailand especially in non-irrigated areas during dry season. Numerous groundwater contaminated sites have been reported from both natural and anthropogenic (i.e., man-made) activities with extent of plume migration, leading to a degrading quality of groundwater which is unacceptable for human consumption. Determination of contaminant transport parameters in the saturated zone is of great importance for groundwater risk assessment. For our study, a series of column experiments were conducted to obtain the transport parameters of 2-nitrophenol in natural soil which are collected from a contaminated site in Thailand. 26 porous media samples were randomly collected from the site from 1.5 m depth below ground surface and further analyzed for their grain size distribution using ASTM D422-63 standard method (standard test method for particle-size analysis of soils) to cluster the sample. Upward flow direction column setup was employed with 23.7 mM phosphate buffer containing 10 mg/L NaCl solution (as a conservative tracer) influent for at least five pore volumes (PV) at 30 mL/h constant rate injection, then switched to 10 mg/L of 2-nitrophenol in 23.7 mM phosphate buffer solution and the column was consecutively flushed for another 5 PVs. Effluents were systematically collected in every 0.25 PV and further analyzed for their Cl- and 2-nitrophenol contents by using a well-calibrated conductivity meter and gas chromatograph (GC), respectively. Natural soil from the study area could be clustered into three groups based on their D₅₀ values of 0.16 mm, 0.27 mm, and 1.08 mm, respectively. Cl- and 2-nitrophenol breakthrough curves were plotted and compared to assess the contaminant transport parameters, including its dispersivity and retardation factor in comparison to the conservative tracer. The dispersivity of 2-nitrophenol for three groups of sample is 0.41 cm, 0.34 cm, and 0.35 cm, respectively. For retardation factor, they were equal to 1.127, 1.086, and 1.086, respectively.