Hydraulic performance analysis of a multiple injection–extraction well system

Abstract

Investigating the hydraulic performance of the flow field created by a multiple injection extraction well system for groundwater remediation requires the design of novel strategies for tracer testing and efficient modeling. In this work, we report on tracer tests conducted in a well system comprising two injection and two extraction wells designed for an in situ bioremediation of uranium at Oak Ridge, TN, about 2 years after the start of operation. The domain of the flow field can be divided into an inner cell, an outer cell, and transition zones. To characterize advective dispersive transport, two tracer tests were performed with the injection of bromide solution. The system was operated as during groundwater remediation, and the tracer was partially recirculated. Breakthrough curves (BTCs) were measured in the extraction wells and the multi-level sampling (MLS) ports. The methods of transfer function and temporal moments were implemented to analyze the BTCs. By jointly evaluating the temporal moments of the BTCs in the extraction wells, we can conveniently estimate the recirculating flow fractions in different zones. This approach does not require the detailed characterization of the flow field. The parameters of transfer functions fitted at the MLS wells indicate the flow field maymore » have changed over the tracer test period. This observation indicates that bioremediation influences the flow field even when the well pumping rates are kept constant, which suggests that aquifer characterization may need to be repeated during bioremediation. The methods of transfer functions and temporal moments with tracer tests are flexible, economical, and well-suited to evaluate the performance of the system during long periods of remediation.« less