A simulation framework for enhancing natural attenuation for the remediation of subsurface organic contaminants using targeted PAT intervention

A remediation approach which uses pump and treatment (PAT) to enhance the biodegradation of organic contaminant plumes in groundwater was evaluated for a phenol-contaminated aquifer using a novel reactive transport model, which simulates kinetic reactions the groundwater. The influence of system design and operation on plume remediation to enhance contaminant mass removal by biodegradation was examined.

Increasing the distance of an extraction or injection well from the plume interior enhances biodegradation by increasing the dispersive mixing of the plume with the groundwater. An extraction well far away from the plume enhances biodegradation to a greater degree than an extraction well on the fringes. In the best performing single well scenario (injection of EAs at the fringes of the plume), biodegradation was enhanced by 128%, compared with no intervention (intrinsic NA) over the same time period.
It was discovered that wells placed too closely together do not promote mixing and often do not enhance biodegradation as much as a single well. A series of 10 increasingly complex multiwell modelling scenarios were designed to conduct a more in-depth investigation. Analysis of this phenomenon discovered a configuration of 4 injection wells which enhanced biodegradation by 520% over no intervention over 10 years.

It was hypothesized that enhancement of in situ NA could potentially reduce of the total operational cost of site remediation. Six other modelling scenarios, with the goal of remediating 90% of the contaminant over 60 years through a combination of mass removal through PAT and enhanced in situ NA. The arguably best performing scenario enhanced biodegradation by 285%, degraded 15% of total phenol mass, and reduced the cost of remediation by $66,000, but incurred $85,000 in electricity costs and $540,000 in treatment costs over 40 years. It was determined that this approach examined in this study was limited by the concentration of the contaminant, which is orders of magnitude higher than the concentration of the oxidants, in addition to the slow biodegradation kinetics. However, this framework may remediate contaminants that are more readily biodegradable under aerobic conditions, such as BTEX.