Migration of Aqueous Benzene through a Subsurface Concrete Utility Pipe under Saturated Soil Conditions

The objective of this study was to evaluate the potential of contamination by the aqueous benzene through transport in a saturated soil domain supporting subsurface concrete pipe. The focus of the study was on assessing the potential for benzene to migrate through concrete pipe and/or its joints (gaskets) for both intact and damaged conditions. A three-dimensional finite difference method (FDM), implemented through Visual MODFLOW Flex, was utilized to simulate groundwater flow and contaminant transport phenomena. Site conditions and soil parameters were selected on the basis of the average range of hydrologic parameters representative of regions in the coastal area of North Carolina. The study was conducted by varying the following parameters: i. hydraulic conductivity (k), and ii. longitudinal dispersivity (α_L). Damaged pipe and damaged gaskets scenarios were considered, as represented by k-values. No benzene broke through the pipe, even under damaged gaskets scenarios, when the saturated k_soil was 10^-5 cm/s. In this case, benzene was transported upward into the backfill soil with a higher k_backfill of 10^-3 cm/s. For damaged pipe scenarios and k_soil =10^-5 cm/s, benzene concentrations inside of the pipe remained below 5 μg/L, the maximum contaminant level (MCL) for drinking water. In the case of the saturated k_soil=10^-3 cm/s, benzene concentrations reached the MCL for the case of damaged pipe. The highest potential for aqueous benzene migration into water flowing in the pipe was when pipe damage was assumed.