Formatted Title
Multi-Phase Extraction (MPE)'s Role in Hydraulic Control in Three Unique ISTR Projects
Background/Objectives
In situ thermal remediation (ISTR) stands out as an effective method for addressing contaminants within low-permeability zones, largely due to its unique operational mechanics. Unlike traditional remediation approaches that rely on fluid flow through soil permeability, ISTR is primarily driven by the thermal conductivity of the soil. This means that even in zones of low permeability, effective heat propagation can be achieved. Achieving hydraulic control, however, remains a cornerstone for the success of ISTR. Within this context, this presentation delves into three distinct ISTR projects. Each underscores the crucial role of multi-phase extraction (MPE) not for the delivery of heat but for the efficient extraction of steam and vapor produced during the heating process, thereby establishing optimal hydraulic control.
Approach/Activities
The first project, a pilot test adjacent to a coastal region, faced the unique challenge of consistent thermal treatment amidst the unpredictable tidal influences. The project had temperature monitors strategically placed at varying distances from the heating wells, intending to understand the potential influences before determining any remedies.
California's second project revolved around a dry cleaner site. Initially confronting drought conditions, the site's dynamics changed dramatically due to unforeseen rainfall, leading to an increase in groundwater levels. This scenario necessitated quick adaptations from the initial vadose zone design to one which addressed the newly saturated conditions and the accompanying hydrological changes.
In the third project, located in an expansive contaminated NAPLs zone, the priority was clear: establish an impenetrable hydraulic barrier. The vastness of the area, coupled with its contamination levels, demanded a strategy that would efficiently use reinjection wells. To optimize energy, the project also introduced the technique of preheating reinjected water using residual heat from the remediation process.
MPE, in all these projects, stood out as a dynamic tool for ensuring and maintaining hydraulic control.
Results/Lessons Learned
The coastal pilot test uncovered surprising insights. The observed lags in temperature rise near the coastline suggested an intriguing interplay between the coastal tides and the heating process. This led to innovations, post-insights, like the consideration of deploying sheet piling or tweaking the heating configuration. Furthermore, the consistent temperature gradients across varying distances from heating wells highlighted the profound impact of groundwater flow on the heating process.
The dry cleaner project in California underscored the vitality of flexibility in remediation strategies. With the unexpected groundwater level rise due to sudden rainfalls, there was an evident need to pivot quickly and effectively.
The NAPL zone project further accentuated the significance of establishing a robust hydraulic control in expansive contamination zones. With MPE and optimized reinjection strategies, the project aimed to protect against external NAPL and groundwater intrusions.
Collectively, these projects underscore MPE's unmatched value in addressing the challenges of hydraulic control across varied ISTR settings. Its adaptability and effectiveness solidify its central role in ISTR.