New Frontiers for In Situ Thermal Remediation: Using High Resolution Site Characterization to Improve Conceptual Site Model Accuracy and Lower Project Costs

As a Cascade Company, one of the major benefits TerraTherm is able to extend to our clients is a whole new suite of capabilities that we now have more readily available to us. These capabilities allow us to better define the target treatment zone (TTZ) and Conceptual Site Models (CSM), enabling us to minimize cost for treatment while ensuring that all of the source material is treated. This not only saves our clients money, but it also limits future liability associated with any missed source materials outside of the TTZ.

One of the capabilities we have available to us is an approach called high resolution site characterization (HRSC).  HRSC utilizes a variety of soil and groundwater profiling techniques to define the extent of contamination both vertically and horizontally. The HRSC approach can be used in the early stages of site assessment and/or to fill in data gaps in a pre-design phase.

A thorough understanding of soil properties across a contaminated site such as permeability, VOC concentrations, distribution of coal tar, or other NAPLs etc. is necessary to optimize the cost effectiveness of thermal remediation design. Each soil parameter under investigation is fitted to an appropriate HRSC technology. We can locate non aqueous phase liquids using laser induced fluorescence NAPL detection with technologies such as Ultra-Violet Optical Screening Tool (UVOST®). Some technologies such as Membrane Interface Probe Hydraulic Profiling Tool (MiHPT) and WaterlooAPS Profilers are capable of investigating multiple parameters at once. We also have access to on site analytical chemistry capability through the MobiLab™ service line.  MobiLab™ makes NELAP-accredited and defensible analytical data available in near real time to allow for the use of Dynamic Work Strategies which save time and money in the investigation phase.

 

Figure 1 Example of a HRSC sampling grid showing 65 points at 20ft spacing in the horizontal direction. At this site the HRSC tools were used to determine permeability contrasts and to determine screen depths for extraction and venting.

Figure 1 Example of a HRSC sampling grid showing 65 points at 20ft spacing in the horizontal direction. At this site the HRSC tools were used to determine permeability contrasts and to determine screen depths for extraction and venting. Click to enlarge

 

Figure 2 Example of a HRSC layout designed to prioritize locations that had not been previously been investigated and accurately define the boundaries of previously investigated locations. At this site TG-P locations were primary locations given the highest priority and TG-S were secondary step-in/step-out locations that were explored if the boundary was not sufficiently defined by the TG-P points in any given area. Click to enlarge

How does HRSC benefit our clients?
HRSC is beneficial to our clients because it refines the treatment zone dimensions, often resulting in a smaller treatment volume, which translates directly to dollars saved for our clients. Additionally, it better ensures that the entire source area is characterized and that minimal source mass is left outside of the treatment zone, thus guaranteeing a more successful clean-up. Both of these points reduce treatment costs for our clients and allow for a better thermal design and implementation. The remedy becomes more sustainable – less energy is used and it only has to be attempted once, because the probability of success is maximized by having a solid CSM and TTZ definition.

How Does HRSC Work?
Implementing HRSC requires designing an investigation layout suited to the site-specific data gaps. Investigation layouts may consist of a grid of regularly ordered points (Figure 1), an array of points with step-in and step-out options (Figure 2), or a combination of the two. Resolution is varied according to how many points are sampled in a given area and the vertical sampling interval in the subsurface. Many HRSC technologies are able to measure continuously, meaning the entire length of the soil boring is sampled, giving the greatest vertical resolution possible. Additionally, the data can typically be viewed in real-time, which means that the investigation strategy and implementation can be adjusted and adapted to field conditions. This is referred to as Dynamic Work Strategy. When defining the horizontal and vertical extent of contamination, it is often unknown how far the sampling points should extend laterally or how deep probe(s) should be advanced. Therefore, investigation layouts often include an interior of primary sampling points bordered by secondary sampling points that are profiled only if the contamination boundary is not sufficiently defined by the primary points (Figure 2). To define the vertical extent of contamination, HRSC designers will often choose a depth to advance the probe to at all locations based on prior understanding of the depth of contamination; such as the depth of an impenetrable surface like bedrock or until the probe hits refusal. The ability to view the data in real-time means that operators can immediately see when contamination levels rise and fall as the probe is advanced into the subsurface and make informed decisions regarding how deep to advance the probe and whether to step out to a secondary sampling location. Data is also incorporated into 3D models as it is collected so the conceptual site model can be updated day to day and the investigation strategy can be adjusted according to fill data gaps (Figure 3).

The HRSC technologies TerraTherm has been using at several sites include:

  • Membrane Interface Hydraulic Profiling Tool (MiHPT),
  • WaterlooAPS TM,
  • Ultra-Violet Optical Screening Tool (UVOST®) and
  • High resolution continuous soil core profiling with onsite laboratories (MobiLab™)

Figure 3 Screenshot of 3D model showing results from TarGOST™ and soil sampling from a recent HRSC project. Click to enlarge

Stay tuned for one of our upcoming blog posts where we’ll take a closer look at these HRSC technologies and how they help us deliver accurate, cost-saving solutions to our clients.

About Amber Bonarrigo

Amber is a Data Manager and Subsurface Designer at TerraTherm, Inc. She keeps the project management team informed of projects’ statuses by monitoring and processing real-time operational data that comes in from the field. She was awarded a degree in Geology from Hampshire College, MA in 2015. She has a background in numerical modeling of lake temperatures and groundwater flow. She assists in the subsurface design and numerical modeling of steam and TCH during the early design phases of ISTR projects.
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