Shapiro, A.M., C.R. Tiedeman, T.E. Imbrigiotta, D.J. Goode, P.A. Hsieh, P.J. Lacombe, et al.
Groundwater 56(2):317-336(2018)

A mass balance formulated to evaluate the mobilization of chlorinated ethane (CE) compounds from the rock matrix of a fractured mudstone aquifer under pre- and postbioremediation conditions relied on a limited number of monitoring locations and was constrained by a detailed description of the groundwater flow regime. Groundwater flow modeling developed under the site characterization identified groundwater fluxes to formulate the CE mass balance in the rock volume exposed to the injected remediation amendments. The initial CE mass in the rock matrix prior to remediation was estimated using analyses of CE in rock core. Differences in the CE fluxes into and out of the rock volume identified total CE mobilized from diffusion, desorption, and NAPL dissolution under pre- and postinjection conditions. The CE mass mobilized per year under preinjection conditions is small relative to the total CE mass in the rock, indicating that current pump and treat and natural attenuation conditions likely will require hundreds of years to achieve groundwater concentrations that meet regulatory guidelines. During 5 years of monitoring postinjection, the CE mobilization rate increased by roughly an order of magnitude.