An Investigation of the Pressure Pulsing Reagent Delivery Approach

Abstract

Pressure pulsing technology is an innovative method that has been developed with the aim of overcoming preferred flow paths associated with remediation techniques that rely on the injection of reagents. Numerical and field experiments were conducted to assess how pressure pulsing affects groundwater flow and solute transport during reagent injection. A series of field experiments were performed at two field sites where a monitoring network designed to capture the breakthrough of solutes delivered from an injection well was installed. Pressure pulsing and conventional injection methods were used at each site. One site was comprised of fine sand with low heterogeneity, while the other was moderately heterogeneous with discrete layers varying from fine sand to silt. The data suggest that breakthrough was more uniform for the pressure pulsing injections; however, this difference was minor and complicated by sorption of some of the tracers employed. The groundwater flow and solute transport modeling exercise simulated the rapid boundary pressure modulation that occurs in association with pressure pulsing. Two‐dimensional (2D) simulations revealed that repeated sudden onset of injection cessation produces brief periods of gradient reversal and the development of a mixing zone near the injection well. The spatial extents of this mixing zone were found to be highly dependent upon the hydraulic diffusivity of the medium, with medium heterogeneity and pulsing frequency playing secondary roles. Three‐dimensional (3D) numerical simulations were used to benchmark the observations from one of the field sites. The results from the modeling effort showed that solute breakthrough from a pressure pulsing injection is more dispersed relative to a conventional injection as a result of the mixing zone phenomenon; however, we were unable to directly observe this mixing zone using the instrumentation deployed at the two field sites.

Field Trials of Chaotic Advection to Enhance Reagent Delivery

“…The remaining contaminant mass exists as immobilized, disconnected pockets/blobs that remain trapped in diffusion‐controlled zones (Conrad et al ), or in lower permeability zones where contact with the injected reagent is hindered by heterogeneity (Parker et al ). In these zones, molecular diffusion ( D* ~10 −9 m 2 /s) is likely the primary transport mechanism responsible for bringing the injected reagent and contaminant together (Jose and Cirpka ; Gale et al ); however, diffusion is a slow process and contributes to inefficient mixing (Kitanidis and McCarty ). The remaining contaminant mass becomes a long‐term source that can lead to eventual rebound and persistence of dissolved plumes downgradient of the source zone (Thomson et al ).…”

The Hidden Potential of Mass-based Treatment: A Method for Preventing Rebound

“…Gale et al. () also noted the potential capacity to overcome variations in hydraulic conductivity and a numerical simulation suggested that flow could be induced into lower permeability zones. These findings are consistent with the observations at the treatment site.…”

“…In a three‐and‐a‐half‐hour field test at the Canadian Forces Base Borden Site, Gale et al. () noted lower formation pressurization using pressure pulse technology compared with conventional injection, suggesting that a greater volume of treatment amendment can be added for a given bulk formation pressure. This occurred while yielding a more uniform advective profile.…”

Methods for Delivery and Distribution of Amendments for Subsurface Remediation: A Critical Review

“…Pressure pulsing technology (PPT) injects an aqueous solution via quick releases of a pressurized solution (Gale et al 2015). In theory, pressure perturbations create a sudden increase in fluid pressure (for fluids with low compressibility), momentarily dilating porous media pores in response to the pressure wave, thereby enhancing movement of the injected solution.…”