Recent advances in in-situ remediation technologies

Full text: Introduction - In-situ remediation techniques have been utilised by the North American and European environmental industry to remediate contaminants in subsurface environments for more than 20 years. Many early uncertainties inherent in these technologies were overcome and refined through years of development, implementation and persistence. Best-in-class implementers have tamed aggressive chemistries, developed focused injection methods and enhanced approaches by combined or sequenced delivery. Understanding the underlying chemical processes enables engineers to evaluate good conceptual site models and build focused designs that approach treatment goals with improved certainty. Reagent delivery methods have substantially developed with many options now available. A myriad of fixed well designs and screen types are routinely used as are many proprietary pumps, direct push tooling and screens. These approaches are sometimes stymied by low conductive subsurface obstructions and lenses. More recently the industry has focused on soil mixing delivery options for many reagents, including binding agents for contaminant stabilisation within the soil matrix. Common methods used include bucket mixing to specially designed soil mixing tools to deep soil mixing with large diameter augers attached to large rotary drill rigs. These delivery tools have unique abilities, but they all are able to eliminate the reagent delivery problems inherent with injection technologies. Limitations such as soil stability after mixing and potential overland sheeting flow of what was groundwater prior to mixing are lessons learned that assist when considering these aggressive reagent delivery options. In-situ thermal remediation was developed by the oil industry to help recover previously uneconomic oil reserves. Electrical thermal techniques were further developed and utilised for remediation of mostly organic contaminants. These techniques, coupled with appropriate vapour treatment systems, have become widely accepted as the best-available-technology by the environmental community over the last 5 years or so. Thermal remediation has often been considered too costly for many projects requiring timelines and site accessibility-type drivers for client consideration. More recent fuel-based thermal delivery options have started to change the high cost paradigm. Additionally, vendors are developing additional capabilities and new smaller vendor companies are forcing the industry to be more competitive. Conclusion - This presentation will provide an overview of each of these in-situ remediation technologies including recent advances and lessons learned from direct implementation. (author)