“Strategic” is a term often used when discussing military campaigns or geopolitical affairs and when describing business initiatives. But you might wonder how the term applies to the characterization and remediation of environmental contaminants. In this piece, “strategic” highlights the need to be mindful of the desired endpoint — risk reduction, resource restoration, regulatory closure — when deploying resources to obtain new data.
There are many tools that have been developed to assist remediation professionals in characterizing the subsurface and analyzing environmental media. Using the geologic model and process-based conceptual site model (CSM) as foundations, focused characterization and advanced analytical techniques are used to support and optimize remedy selection and design while providing a baseline for measuring predictable results.
High-resolution or advanced site characterization strategies and techniques use scale-appropriate measurement and sample density to define contaminant distributions with greater certainty, supporting faster and more effective site remediation. They also are used to obtain depth-discrete physical subsurface data — such as permeability, grain size, flow velocity and direction — that is critical for quantifying the processes that govern contaminant movement and the viability of various remediation technologies. These strategies and techniques focus on heterogeneities in the subsurface that are often too small, whether a few feet or just a few inches, for conventional investigation tools and approaches to adequately characterize.
These heterogeneities often exert the primary control over contaminant distribution, transport and fate at complex remediation sites. Strategic characterization and analysis are highly effective in obtaining the detailed geologic, hydrogeologic and contaminant information necessary to select and design remedies matched to the scale of the spatial attributes of the subsurface. The use of these methods also provides the high-density datasets needed to prepare representative 3D visualization and contaminant fate and transport models for analyzing and calibrating data, assessing uncertainties, and communicating characterization results and potential remediation strategies to stakeholders.
Technologies commonly associated with advanced site characterization include real-time, direct sensing equipment and other field-based data generation technologies that provide high quantities of discrete data that form the basis for evaluating a site in high resolution. This data can be used by project teams and stakeholders to efficiently resolve decision questions in a dynamic characterization environment. High-resolution site characterization strategies can be implemented adaptively using various sampling approaches including, but not limited to, discrete sample intervals, vertical subsurface profiling, and transect-based and media-sequenced characterization strategies.
Here are a few examples of tools used for specific sites and contaminant classes:
- Membrane interface probe delineates volatile organic carbons at sites impacted by chlorinated solvents.
- Ultraviolet light induced fluorescence detects nonaqueous phase liquid (NAPL) containing polycyclic aromatic hydrocarbons.
- Laser-induced fluorescence detects NAPLs of varying composition, depending on the sensor used — ultraviolet optical screening tool (UVOST), TarGOST and DyeLIF.
The UVOST system is commonly used to delineate light nonaqueous phase liquids at petroleum contaminated sites, while TarGOST has proven effective in mapping heavy NAPLs such as coal tar at former manufactured gas plant sites. The hydraulic profiling tool is used to collect continuous vertical profiles of subsurface hydraulic properties and, when equipped with a groundwater sampling tool, can even collect multiple depth-discrete groundwater samples from the same boring. This tool has recently proven valuable in characterizing complex subsurface conditions at coal combustion residuals units located at coal-fired power plants.
In addition to direct sensing tools, there also are multiple geophysical, sampling and remote sensing technologies that can be used to collect high-resolution characterization data. Recently published by the Interstate Technology & Regulatory Council, the Implementing Advanced Site Characterization Tools document provides detailed descriptions of many high-resolution site characterization methods as well guidance for selecting tools for specific sites and investigation objectives.
Advanced analytical methods also are critical components in understanding the mechanisms that control the degradation of contaminants and performance of remediation methods. For inorganic contaminants, understanding the mechanisms and rates of attenuation as well as the capacity and stability of the reactions in the subsurface are critical. Specialized chemical extraction techniques to identify the speciation of target constituents and the use of spectroscopic and electron microscopy to examine aquifer solids are often needed to fully characterize the geochemical reactions. Isotope analysis can help differentiate between inorganics originating from potential manmade contaminant sources and those that occur naturally.
Similarly, advanced analytical methods, including molecular biological tools (MBTs), are used to characterize the biological and biogeochemical degradation of organic contaminants. MBTs such as polymerase chain reaction analysis identify and quantify microbial species and strains that support complete biodegradation. A compound-specific isotope analysis can be used to gain information about potential contaminant sources, the extent of degradation, comingling of contaminant plumes and the origins of some chemicals. These and other advanced analytical methods are used to develop chemical fingerprinting used for environmental forensic analyses.
Selection and proper use of strategic characterization and analysis methods are fundamental to developing a process-based CSM and successful remediation approach. Data collection planning must include a thorough understanding of the process-based CSM and key drivers for successful remediation and align with the desired project endpoint.
Advanced techniques can be perceived as expensive to use; however, the amount, precision and accuracy of data generated are often greater than traditional sampling and analysis techniques and can result in significant cost savings throughout the project life cycle. Before collecting data, a cost-benefit analysis should be conducted to consider monetary costs, the value added, and the ability of the data collection approach to reduce the cloud of uncertainty and enable the delivery of precise, predictable remediation results.
Strategic characterization and analysis use new technology and analytical tools to cost-effectively extract information critical to defining site complexities and achieving remediation success. But this is only one critical component of PROGRESS and its comprehensive, next-generation approach to remediating complex sites.