This study examined the effects of subsurface contaminants on installed subsurface utilities (pipes) commonly used by the Department. The focus was on quantifying and modeling the effect of benzene and tetrachloroethylene (PCE) on the durability of PVC and concrete pipes as well as a variety of pipe gaskets. In addition, the migration of contaminants through utility installation areas was investigated using several saturated and unsaturated flow scenarios to provide a better understanding of the alternation of the contaminant transport regime with the installation of pipes in contaminated subsurface media. Modeling included the effect of several mitigation measures on the migration of contaminants into concrete pipes with an assumed level of damage. Benzene and PCE were chosen as contaminants due to their prevalence within the Right of Way and also represent petroleum-based and dry-cleaning solvents. The experimental results were used to develop a degradation model with a proposed approach to account for the effect of contaminant concentration on the degradation rate.
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The experimental results also included data on the effect of benzene and PCE on the compressive strength of concrete material. Conclusions and recommendations are included in the report. Highlights include that compared to PCE, benzene has a more detrimental effect on the durability of plastic and rubber materials, the reduction of neoprene tensile strength was highest among all gasket materials, the breakthrough of benzene concentrations into the subsurface pipe is dependent on the saturated hydraulic conductivity of the native soil and the highest potential of benzene breaking through the pipe was when the pipe was damaged rather than a damaged gasket. Mitigation strategies included the use of a clay barrier as an effective method to protect the trench and subsurface pipe, the use of flowable fill leads to a 99% reduction of benzene permeation through the pipe and the natural hydraulic gradient affects the level of contamination breaking through the pipe.
