Formatted Title
High-Energy Injection of Activated Carbon Slurry for In Situ Remediation: A Case Study from Australia
Background/Objectives
In situ remediation of organic contaminants is often challenging due to the heterogeneous nature of the subsurface, which results in complex contaminant distributions and conditions impeding adequate delivery of remedial amendments using conventional, low-pressure systems. This work presents a case study using a high-energy injection system in a site located 1-2 h north of Sydney. A leak of petroleum hydrocarbons (PHCs) from an up-gradient neighboring underground storage system impacted the subject site. The geology of the site comprises a shallow layer of clayey material overlying sandstone of various levels of weathering. The groundwater level varies between 1.5 m below ground level (mBGL) upgradient and 3 mBGL downgradient. Light non-aqueous phase liquid (LNAPL) and dissolved PHC plues were observed on site since 2017.
Approach/Activities
The Trap & Treat ® BOS 200 ® technology developed by Remediation Products, Inc. (RPI) was selected for the project. Historical and contemporary environmental data were used to estimate the mass of PHC present in the subsurface. The load of injectates (activated carbon, electron terminal acceptors and specialized microorganism consortium) was calculated considering the targeted remediation goals. The injection design comprised 36 injection points distributed with a triangular grid spacing of 5 m across the treatment area and 190 vertically staggered injection intervals. Due to the geological constraints (injection in fractured rock/sandstone), each injection location was pre-drilled using AST Environmental’s proprietary methodology. The injection was conducted using direct push technology to drive the injection probe to the specified interval depths. The geometry of the probe built for this program was selected to achieve the velocity of injection recommended for adequate distribution of the solid particles of carbon in the formation.
Results/Lessons Learned
Following the injection program in July 2023, a vacuum truck was used to redevelop all monitoring wells across the area of treatment, purge them of the accumulated injectates and pump out any LNAPL mobilized during the injection. Being a solid, the activated carbon remained immobile in the soil profile as soon as the injection pressure receded. Biofilms develop over time at the water/activated carbon interface biodegrading the sorbed PHC and freeing sorption sites. Through this process, the installed BOS 200® continues to trap and treat the contamination. A first comparison of pre-injection (March 2023) and post-injection (August 2023) groundwater samples showed a drop in total recoverable hydrocarbons in all wells, with the concentration reductions ranging from 45.3% to 99.9%. Following the successful results of this injection program, a second round will be conducted to treat other areas of the site.