In this editorial, we introduce the concept of high-resolution site characterization (HRSC) tools and strategies, a recent USEPA focus area that reflects the state of the science for enhanced environmental site characterization (USEPA 2021b). Sites addressed under EPA Superfund (USEPA 2021a) and state-delegated Leaking Underground Storage Tank (LUST) (Dyment and Kady 2018, 2019) programs have documented successful use of HRSC technologies and strategies. Where appropriate, environmental professionals and researchers are encouraged to consider integrating HRSC concepts into their site assessment and remediation projects.HRSC strategies and techniques use scale-appropriate measurements and increased spatial and temporal information density to define contaminant distributions, and the physical context in which they reside, with greater certainty, supporting faster and more effective site cleanup. HRSC is designed and implemented to collect environmental measurements at the appropriate scale of the heterogeneities in the subsurface, which control contaminant distribution, transport, and fate. These heterogeneities occur at scales that are often too small for conventional investigation strategies and technologies to adequately characterize. Conventional technologies originally used to assess water resource availability and subsequently characterize contaminated sites typically assess heterogeneities that are on the scale of tens of meters, while heterogeneities that control contaminant transport are often on the centimeter to meter scale.HRSC is a highly effective strategy to obtain the detailed geologic, hydrogeological, and contaminant distribution information to improve selection, design, and optimization of remedial technologies matched to the scale of the spatial attributes of the subsurface problems. Taking advantage of advances in direct push drilling platforms, direct sensing and downhole tools, field analytical methods, and in situ sensors, HRSC strategies seek to increase spatial and temporal data density reducing uncertainty in the life-cycle conceptual site model (CSM) (USEPA 2011), improving targeted in situ remediation applications and increasing stakeholder collaboration and trust. Superfund optimization reviews commonly identify characterization and CSM needs that can impact remedy performance. A review of the 2020 Superfund Optimization Progress Report (USEPA 2020) highlights CSM and characterization needs because they continue to be the most common recommendations for improvements to remedy effectiveness, comprising more than 50% of overall Superfund optimization review recommendations. HRSC tools and strategies not only offer tremendous project value in early characterization phases but remain applicable and informative to improve remediation performance (USEPA 2020).Whether exploring the use of ex situ pump and treat or in situ treatment technology, cost, and performance, sites characterized using HRSC tools and strategies can improve injection, extraction, and monitoring well placement including targeted screen intervals. HRSC is focused on the scale of subsurface heterogeneities controlling fate and transport at the site, providing more efficient site characterization and enabling more appropriate remedy selection, design, and implementation. Additionally, due to the high-density data sets that are generated during HRSC efforts, modeling software and three-dimensional visualization and analysis can be indispensable tools for managing data and developing or updating a life-cycle CSM. These tools can assist in identifying and assessing CSM uncertainties, performing advanced site analyses, and communicating characterization results as the basis for project decisions to stakeholders and affected communities.HRSC concepts can be applied to sites of any size or regulatory program and provide stakeholders with faster and more effective site characterization and cleanup. Attributes of HRSC include obtaining the data at an appropriate scale and density, utilizing collaborative data sets and multiple lines of evidence, supporting the development and use of a life-cycle CSM, and accounting for matrix heterogeneity. HRSC tools and approaches are included among best management practice (BMPs) and enhance the implementation of other environmental site characterization BMPs, such as systematic project planning, life-cycle CSMs, dynamic work strategies, real-time measurement technologies, and adaptive site strategies. Technologies commonly associated with HRSC include real-time and direct sensing equipment and other field-based data generation technologies that provide high quantities of data, which form the basis for evaluating a site in high resolution. These data can be used by stakeholders to efficiently resolve decision questions in a dynamic characterization environment. HRSC 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.While use of HRSC technologies and strategies can increase overall characterization costs for some projects, it is important to consider life-cycle project costs in the context of using HRSC. Additional characterization costs can be minimized by improved targeting of other more costly drilling and analytical or sampling methods, better placement of monitoring wells and screen intervals, and providing a high-density interpretation of the hydrogeological environment controlling contaminant mass storage, transport, and fate at the site. Additionally, while it can be a challenge to estimate remediation improvement efficiencies derived solely from HRSC activities, anecdotal information and project applications indicate that for many projects HRSC costs can be recouped through efficiencies gained in characterization activities and remedy performance.HRSC technologies are being approved for use at sites by regulators and state trust fund administrators, who see the value in gathering better data up front to potentially shorten the lifetime of a cleanup project, as well as the potential for cost savings. If you need more information about the future development and application of HRSC on site characterization, you can visit the EPA website for HRSC (USEPA 2021b) and consult the references therein.References USEPA. 2011. Environmental cleanup best practices. Effective use of the project life-cycle conceptual site model, office of solid waste and emergency response and office of superfund remediation and technology innovation. EPA-542-F-11-011. Washington, DC: USEPA. USEPA. 2020. Superfund optimization progress report. EPA-542-R-20-002. Washington, DC: Office of Land and Emergency Management, USEPA.

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