ENTACT & GEI CONSULTANTS PUBLISH NEW RESOURCE ON SUBAQUEOUS ISS

A team of the industry’s leading sediment remediation specialists—including Rory Kilkenny, PE; Ben Gezon; Tony Moran, PE; and Jule Carr, PE of ENTACT and Paul C. Jansen; Michael W. Sabulis, LSP; Ryan S. Sheaffer, PG; Grant Wallace; and Julia Farr, EIT, of GEI Consultants—has released a new manuscript titled State of the Practice: Subaqueous In-Situ Solidification for Contaminated Sediment Remediation.

This comprehensive manuscript captures the most current knowledge, lessons learned, and implementation strategies for subaqueous in-situ solidification (ISS), an increasingly essential technology for managing complex, deep, or infrastructure-constrained sediment sites.

Contaminated sediment sites are becoming more challenging as projects face deeper impacts, aging shoreline infrastructure, and increasing urban access constraints. In parallel, evolving regulatory expectations and rising transportation and disposal costs are leading project teams across the country to evaluate ISS as a practical alternative or complement to dredging and capping.

EXPERT INSIGHTS SHARED AT 2025 SMWG FALL FORUM

Content from this landmark manuscript was also featured during a panel presentation at the 2025 Sediment Management Work Group (SMWG) Fall Membership Forum, where Rory Kilkenny (ENTACT), Ben Gezon (ENTACT), Mike Sabulis (GEI Consultants), and Trea Deri (Geo-Solutions) presented findings and discussed real-world applications of subaqueous ISS in today’s regulatory and construction environment. Their discussion highlighted the growing demand for reliable, cost-effective sediment remedies that minimize disruption to communities, protect surrounding infrastructure, and deliver long-term environmental stability.

PREMIER EXPERTS DRIVING INDUSTRY ADVANCEMENT

What distinguishes this work is not only the technical depth contributed by the authors, but also the breadth of experience it reflects. While the authors are recognized experts with extensive project experience, the paper draws on the collective knowledge of the wider sediment remediation community, including approaches, challenges, and observations documented across many firms and project teams.

The authors bring:

• Decades of field experience in sediment remediation
• Expertise in remediation and geotechnical construction
• Advanced understanding of sediment chemistry, hydrodynamics, and structural interactions
• Direct lessons from pilot-scale evaluations and full-scale subaqueous ISS projects
• Cross-disciplinary perspective spanning engineering, design, and specialty construction

Rather than representing a single organization’s viewpoint, this work compiles knowledge, lessons learned, and approaches emerging from real-world projects throughout the industry.

A LANDMARK RESOURCE SUPPORTING SMARTER, MORE SUSTAINABLE REMEDIATION

As sediment sites grow more complex and as project teams work to balance performance, cost, and community considerations, the guidance in this new subaqueous ISS publication offers a clearer understanding of when and how the technology can be applied effectively. The insights are intended to support owners, designers, regulators, and contractors in making well-informed decisions at sites where traditional approaches may face limitations.

With this publication, the authors establish a clear and practical technical reference that supports science-based decision making for sediment remediation projects amid evolving regulatory, technical, and site constraints.

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We are pleased to provide a summary of several key points from the manuscript below.

ADDRESSING REAL-WORLD CHALLENGES FACING SEDIMENT REMEDIATION TODAY

The environmental remediation industry is confronting a convergence of pressures: deeper contamination profiles, aging bulkheads and waterfront infrastructure, limited upland staging areas, rising disposal costs, and increasingly stringent community and regulatory expectations. The authors directly address these issues, grounding their guidance in real-world constructability, cost, risk, and long-term performance factors.

1. Rising Disposal and Dewatering Costs
   Landfills nationwide continue to tighten acceptance criteria and raise pricing. Transportation and dewatering expenses have also escalated sharply. These realities make traditional dredge-and-haul remedies increasingly challenging (particularly at sites with large volumes or deep impacts). Subaqueous ISS, by contrast, minimizes offsite disposal volumes and reduces reliance on landfills, a shift that can generate major cost and schedule advantages.
2. Urban and Industrial Waterways with Limited Footprints
   Many modern projects are located in dense urban or industrial settings where the space needed to dewater and handle dredged material is simply not available. Subaqueous ISS allows remediation to occur in place, requiring significantly smaller upland support areas. This has become a critical advantage as redevelopment continues to encroach on former industrial corridors.
3. Increasing Focus on Sustainability and Community Impact
   Communities and regulatory agencies are placing greater weight on construction impacts including greenhouse gas emissions, truck traffic, and neighborhood disruption. Subaqueous ISS can reduce these burdens by limiting material handling, avoiding long-distance hauling, and minimizing the number of vehicle trips required for a cleanup. As a result, sustainability and community impact have moved from secondary considerations to central factors in modern remedy evaluation.
4. Aging Shoreline Infrastructure and Geotechnical Sensitivity
   Many contaminated sediment sites are located next to aging or sensitive infrastructure such as unstable slopes, old wharves, sheet pile walls, bridge foundations, and buried utilities. Deep dredging in these areas can create stability concerns or exacerbate existing weaknesses. Subaqueous ISS can mitigate many of these risks by increasing shear strength, reducing liquefaction potential, and providing localized geotechnical support, allowing remediation to proceed in areas where dredging alone may be difficult or impractical.
5. Complex Contaminant Profiles and Deep Impacts
   Dredging becomes increasingly challenging and expensive as contamination extends deeper into the sediment column or spans large volumes. Subaqueous ISS is well suited for deeper impacts, generally greater than five feet, and for projects involving more than roughly 10,000 cubic yards of material. In these situations, ISS can reduce uncertainty associated with deep excavation and provide reliable hydraulic and geotechnical performance within the treated mass.

A PRACTICAL, SCIENCE-BASED FRAMEWORK FOR REMEDY SELECTION

One of the most notable contributions of the manuscript is its clear and balanced decision framework. Rather than presenting subaqueous ISS as a universal solution, the guidance outlines where the technology is appropriate, where it is not, and how it can be effectively combined with dredging and capping. The approach reflects the reality that successful sediment remediation is often hybrid in nature, with different tools applied where they fit best.

The framework is informed by decades of collective project experience within the remediation community and by lessons learned across a wide range of site conditions. The analysis considers:

• Hydrodynamic constraints
• Treatment thickness and geometry
• Debris management and obstructions
• Regulatory acceptance
• Water quality protection
• Geotechnical compatibility
• Construction sequencing and quality control
• Long-term monitoring and performance criteria

The outcome is a guidance document that supports the broader industry by clarifying common misconceptions, defining practical performance expectations, and outlining the steps that contribute to predictable and repeatable project success.

SETTING THE STANDARD FOR DESIGN AND IMPLEMENTATION BEST PRACTICES

Throughout the manuscript, the authors address design, treatability testing, and construction considerations. The guidance is grounded in real-world field experience rather than theoretical assumptions.

Design and Treatability Testing

The manuscript summarizes a practical design process for subaqueous ISS that begins with a strong pre-design investigation and Conceptual Site Model. It emphasizes understanding nature and extent of contamination, nearby structures and utilities, debris and obstructions, geotechnical conditions, hydrodynamics, and sensitive habitats so that ISS zones, offsets, and constraints are defined realistically from the start.

Performance objectives are framed primarily around hydraulic conductivity and unconfined compressive strength, with leachability, durability, and cap performance considered as project- and regulator-specific needs. Treatability studies and mix design are presented as the bridge between site conditions and constructible remedies, including reagent selection, dosage optimization, swell control, and schedule expectations for lab testing.

The design discussion also acknowledges the time and coordination required for permitting and stakeholder engagement, noting that regulatory approvals, riparian rights, and community acceptance are often on the critical path. Together, these elements provide a science-based, stepwise framework for taking subaqueous ISS from concept through a defensible, implementable design.

Field Implementation

The manuscript offers a concise view of how subaqueous ISS is carried out in real project environments. It highlights core implementation elements such as site preparation, staging and batch plant setup, reagent delivery, and debris management to support safe and efficient on-water operations.

Water quality protection is emphasized throughout, with practical guidance on selecting controls such as cofferdams, moon pools, turbidity curtains, and controlled auger advancement to manage turbidity, pH, and sheen. The discussion also underscores how barge layout, spudding systems, and coordinated positioning influence production and access in constrained waterways.

Mixing technologies are summarized with clear distinctions between auger mixing, bucket mixing, and related tools, along with the importance of real-time GPS/RTK positioning, column sequencing, and maintaining verticality to achieve consistent geometry and grout dosing. The manuscript also touches on QA/QC sampling, swell removal to restore bathymetry, and integration with capping and long-term monitoring.

Taken together, the guidance distills field lessons learned across many sediment projects, providing a practical understanding of what drives reliable ISS construction in aquatic settings.

Long-Term Reliability

Subaqueous ISS is ultimately judged by how well it performs over time. The manuscript summarizes the factors that govern long-term effectiveness, including hydraulic containment, structural stability, durability of the treated mass, and the role of restoration caps. It also outlines monitoring approaches that help confirm performance and maintain protectiveness well into the future.