Groundwater Reaeration and Hydrocarbon Plume Length: A Modeling Analysis

A series of three-dimensional numerical modeling experiments was conducted to determine the impacts of reaeration on the bioattenuation of petroleum hydrocarbon contaminants in groundwater systems. The influence of reaeration on plume length and mass loss was affected by four mechanisms including the groundwater mass transfer coefficient $K_{L\text{,}\mathrm{GW}}\text{,}$ the concentration on partial pressure of $O_2$ in the overlying soil gas $P_{O_2}\text{,}$ the aquifer vertical dispersivity ${\alpha }_v\text{,}$ and the reaeration zone Z or region of mixing between contaminated ground water and $O_2$ supplied from the vadose zone. Results from this study showed that reaeration may reduce steady-state hydrocarbon plume length and mass by up to 87% as compared to the case in which reaeration is not considered. Among the four mechanisms, ${\alpha }_v$ exerted the greatest influence on plume length followed by $K_{L\text{,}\mathrm{GW}}\text{,}$ $P_{O_2}\text{,}$ and Z. Comparisons between plume length and the ratio of reaeration transport $K_{L\text{,}\mathrm{GW}}$ to hydraulic conductivity K indicated that appreciable reductions in steady-state plume length were possible when $K_{L\text{,}\mathrm{GW}}/K⩾{10}^{-3}\text{.}$