Dr. Mohammed GabrSultan Abdulaziz Alhomair2022-06-012022-06-01https://drepo.sdl.edu.sa/handle/20.500.14154/58233Many subsurface utilities and drainage pipes might be exposed to contamination migration in contaminated soil and groundwater during their service life. The contamination migration through the subsurface concrete pipes has not been investigated with the simulation methods. In the first part of this work, the contamination by the aqueous benzene breaking through the subsurface drainage concrete pipe installed in site initially not contaminated was evaluated. A 3-D finite difference method (FDM), implemented using MODFLOW paired with MT3DMS software, was utilized to simulate groundwater flow and contaminant transport phenomena. Site conditions and soil parameters were selected based on the average range of hydrologic parameters representative of regions in the coastal area of North Carolina. Various scenarios of two native soil types (sandy soils and sandy clay soils), gaskets condition, pipe condition, and pipe size were analyzed. Modeling results indicate that, after 20 years, no benzene breakthrough the pipe in the intact pipe and intact gaskets scenario with two native soil types. Also, no benzene was estimated within the pipe with the damaged gaskets scenarios under sandy clay soils (ksoil = 10-7 m/s). For damaged pipe scenarios with sandy clay soil, the estimated benzene concentrations inside the pipe remained below 5 µg/l, the maximum contaminant level (MCL) for drinking water. In the case of sandy soils (ksoil = 10-5 m/s), benzene concentrations reached the MCL for the same period in the case of the damaged pipe. The highest potential of benzene concentration breaking through the pipe was when the damaged pipe was quantified due to the larger surface area through which breakthrough occurs. The pipe size affects contamination breaking through the pipe with a smaller benzene breakthrough with larger pipe size. In the second part of this work, the efficacy of mitigation measures (i.e., clay barrier, flowable fill, and anti-seep collar) was evaluated to reduce benzene breakthrough the subsurface concrete pipe at the gasoline spill site. The site parameters are developed from data for a site in Jacksonville, North Carolina, where the subsurface contamination occurred in the presence of subsurface concrete drainage pipe. Groundwater flow and solute transport models were developed using MODFLOW paired with MT3DMS software. Modeling results indicate that, after 20 years, the installation of a clay barrier reduces the concentration of benzene within the pipe by 22% compared to no clay barrier case. In comparison, the use of flowable fill leads to a 99.9% reduction in the concentration of benzene breaking through the pipe, and the use of an anti-seep collar leads to a 60% reduction in the concentration of benzene. The natural hydraulic gradient of the site affects the level of contamination breaking through the pipe with a smaller breakthrough mass with lower site hydraulic gradients. In the third part of this work, the factors affecting Tetrachloroethene (PCE) contaminant ingress into the subsurface concrete pipe embedded in the saturated soil profile and the efficacy of the permeable reactive barrier (PRB) were evaluated. Groundwater flow and solute transport models were established using MODFLOW paired with Reactive Transport in 3-Dimension (RT3D) software, which implements a finite-difference numerical scheme. The site parameters are developed from data for a site in Wilson, North Carolina, at which subsurface chlorinated organic solvents from dry cleaning occurred in the presence of a subsurface concrete drainage pipe. Modeling results indicated that, after 10 years, the degradation process taking place in the native soils, for the cases of KPCE-soil=0.00019 d-1 and 0.0033 d-1 reduced the PCE concentrations in the concrete pipe by 30.7% and 34.1%, respectively. The greater percent of the soil sorption (foc=1.4% vs. foc=0.0en