Formatted Title
Design and Management Insights at ERH Sites Addressing Variable Geology, Groundwater Flux, and Resistivity
Background/Objectives
Electrical resistance heating (ERH) has proven to be a highly effective in situ thermal remediation (ISTR) technology at removing target contaminants from the subsurface. As the most used ISTR technology in the marketplace, it has many examples of successfully achieving the remediation goals. That popularity has also revealed some subsurface conditions and design approaches that can challenge the effectiveness of ERH. Site subsurface conditions affect all remediation technologies uniquely, ERH performance can be affected by variable geology, groundwater flux and electrical resistivity. Some of these conditions such as electrical resistivity, also vary throughout application due to changes in temperature, saturation and contaminant degradation. Having a good site conceptual model including good data on site geology, hydrogeology, and electrical properties, both at ambient and target temperature is important for selection of the correct technical approach and specification of design parameters such as electrode spacing, diameter, lengths and installation intervals, water injection rates, voltage and current ranges, sizing of electrical supply and control equipment, heating rates and durations, and power usage.
Approach/Activities
This presentation will present lessons learned from applying ERH at over 100 sites and discuss subsurface conditions that must be evaluated and addressed during the design phase to ensure performance and prevent difficultly in management of an ERH system during application. Key site data will be discussed as well as a review of the primary strategies and design approaches that can be utilized to address sites with variable geometries, depths, geologies (including groundwater flux rates and soil resistivities), and treatment zones that extend beneath buildings and infrastructure. Case studies will be presented illustrating how these variations impacted the design and performance of the ERH systems at different sites. Thermal models will be used to illustrate how these variations can impact heating both vertically and across a site. Evaluating the performance of a system based on averages can cloud some of the details that are preventing the system from achieving its goals.
Results/Lessons Learned
Electrical resistance of the soil and groundwater is the primary property governing the effectiveness of ERH. During heating, changes in temperature, saturation or newly formed electrolytes, can change the electrical resistance within a matter of weeks or hours. The resistance throughout the vertical profile can also vary due to changes in soil or rock type which can impact heating and remediation within portions of the treatment volume. This presentation will highlight successful strategies to mitigate these impacts within the design process and monitor their effects during implementation to ensure an effective remediation. Examples of sites and design approaches that have had poor ERH performance will also be shared. The technology has matured from the early days of pushing technical or application boundaries, the results of a shared understanding of the primary heating mechanisms within the subsurface that dictate performance and proper design approaches to address site variability can improve the application of ERH at future sites.