Sediment Assessment and Remediation

Contaminated sediment projects are complex, requiring multi-disciplinary teams to identify potential contaminant sources, to understand contaminant fate and transport, to assess human health and ecological risks, and to support risk-based remedial decisions that are protective of human health and the environment. Understanding the fate and transport of chemicals in sediment requires core skills in chemistry, geochemistry, hydraulics, and geomorphology, with the added complexity of spatial and temporal variability and a changing climate. Accurate assessments of human health and ecological risks to support risk-based decision making depend on the identification and assessment of important exposure pathways, the sensitivity of receptors, the toxicity of contaminants of concern, and the impacts of other environmental stressors. These complexities place even greater importance on building multi-disciplinary teams to develop holistic conceptual approaches to contaminated sediment projects.

Strong leadership, resilient management, and strategic vision are needed to move multi-disciplinary teams forward efficiently. EHS Support is known for its strategic vision, management, advocacy, and ability to conceptualize complex problems. These skills are necessary to ensuring highly technical teams are focused on the project goals and ensuring these efforts do not take on a “research project” perspective. Through the use of our internal resources and partners, EHS Support provides a comprehensive array of services to meet our client needs, focusing first on effective scoping and a strategic vision from which teams of technical specialists can be efficiently directed and best advocate for our clients.

Sediment projects amplify the need for strong client-focused teams with exceptional strategic, communication, and advocacy skills. The complexity of regulations, legal requirements, and public, trustee, and agency interest exacerbate the potential cost implications of poorly conceived and executed strategies. At EHS Support, success is measured not by agency approval of the final remedy, but by a combination of factors, including the financial impact to the parties involved.

  • Source Identification and Allocation

    A variety of tools can be applied to source identification and allocation; EHS Support focuses initially on historical research, leveraging our due diligence expertise with strong chemical and process engineering backgrounds to develop a robust understanding of site, the industrial operations, and other potential local and regional sources. Key to this knowledge is an understanding of feedstocks, intermediates, impurities, finish products and wastes that may be produced, the time period of which process was in production, their volumes, molar weights, and associated storage and management locations at facilities. Through a well-grounded understanding of processes and chemistry, site investigations can be effectively scoped and tools selected for identifying sources and evaluating relative contribution to impacts and risk.

  • Investigation Design

    Development of a robust conceptual site model and data quality objectives is critical to an efficient site investigation program that reduces uncertainty to allow for confident decision-making. While many explain the goal of the investigation being sound and cost effective solutions for contaminated sediment – the scope is broader than this and must:

    • Identify and assess risk drivers
    • Provide information of relative contributions to risk (and potential allocation) based on site operations and the contributions of other parties
    • Develop a framework against which remedial goals and objectives can be defined including identifying challenges and limitations and ultimately the performance goals against which remedial success will be evaluated
    • Develop a weight-of-evidence approach in the assessment of human health and ecological risks and develop a cost effective remedial approach to manage unacceptable risks
    • Understand the regional and state agency precedents and politics – a successful endpoint on projects of these magnitude rarely result from purely a good technical solution – rather is a combined political and technical outcome
  • Human and Ecological Risk Assessments

    Exposures to contaminated sediments may pose short- and long-term risk to human health and the environment; unacceptable risks associated with these exposures drive the scope of contaminated sediment remedies. Therefore, the accurate assessment of risk is fundamental to the development of remedies that are protective of human health and the environment, but are appropriately scaled to the level of unacceptable risk.

    EHS Support specializes in the development of risk assessments to identify unacceptable human health or ecological risks based on site-specific conditions that influence the bioavailability and toxicity of sediment-associated contaminants. The primary human health concerns from contaminated sediment are associated with fish consumption; ecological concerns may include direct contact and ingestion exposures at multiple trophic levels and the potential mobility of contaminants from the sediment environment to riparian food webs. EHS Support develops risk assessments to evaluate exposures along these pathways based on weight-of-evidence approaches that incorporate site-specific data, including but not limited to, measurements of contaminants in relevant exposure media (e.g., pore water, biological tissues), sediment and pore water toxicity studies, and benthic community analysis. EHS Support risk assessors have a history of working with the assessment of industrial chemicals, mixtures, and by-products including chemicals associated with plant operations through specialist industrial mixtures or process mixtures used in the petroleum and chemical industries. The development of appropriate site-specific data to assess human health and ecological risks is critical in building consensus with regulatory agencies to support risk-based decision making and to avoid the agency defaulting to conservative exposure assumptions due to a lack of information.

  • Persistent, Bioaccumulative, and Toxic (PBT) Chemicals

    Sediments are both a sink and reservoir for persistent, bioaccumulative, and toxic (PBT) chemicals, including mercury, pesticides, polychlorinated biphenyls (PCBs), and dioxins. PBT chemicals are resistant to abiotic and biotic degradation, resulting in their widespread distribution and persistence in sediment. These chemicals bioaccumulate in biological tissues and may biomagnify between trophic levels within the food web. Based on their persistence, toxicological properties, and ability to bioaccumulate/biomagnify in food webs, PBT chemicals may pose long-term risks to human health and the environment.

    EHS Support has expertise in assessing the fate, transport, and risks of PBT chemicals in sediment. EHS Support has designed investigations to evaluate the environmental fate of PBT chemicals and to assess human health and ecological risks based on the site-specific bioavailability, toxicity, and mobility of PBT chemicals into food webs. In particular, EHS Support has experience on multiple large-scale mercury-impacted sediment sites investigating the fate, transport, and risks associated with mercury and methylmercury. For further discussion of EHS Support’s mercury expertise, click on the Mercury tab below.

  • Mercury

    EHS Support has expertise in the fate, transport, and ecological risk assessment of mercury, a persistent bioaccumulative toxin that presents special challenges for sediment sites. The challenges posed by mercury are driven by mercury methylation and biomagnification and the gap between sediment quality guidelines and mercury levels that present potential ecological effects.

    Mercury methylation is biological process where certain types of bacteria convert inorganic mercury into the more toxic methylmercury, which is efficiently bioaccumulated by organisms and biomagnified in aquatic food webs. The availability of inorganic mercury to bacteria is dependent on the geochemical speciation of mercury in sediment, pore water, and overlying water, which may vary greatly horizontally and vertically in sediment. As a result, some environments may be sensitive to additional mercury loading. EHS Support leverages itsexpertise in mercury biogeochemistry to design cost-effective investigations and select protective and effective risk-based remedial solutions.

    Investigations of mercury-impacted sediment are challenged by the potentially wide difference between accepted sediment quality guidelines and levels that may cause potential ecological effects. EHS Support’s experience in conducting ecological risk assessments on large-scale mercury-impacted sediment sites translates into a cost-effective approach built on transparency and good science.

  • Sediment Sampling

    Sediment sampling is a complex and challenging endeavor, especially in estuarine and marine environments. These activities require specialized equipment and highly trained staff. EHS Support consistently retains the right resource for the project and leverages qualified contractors (under our oversight) to complete sample collection. Numerous tools and specialized collection techniques and field strategies are required in order to successfully plan and collect sediment samples and EHS Support leverages the experience of our team to ensure data quality objectives are met at the lowest cost.

  • Remedy Selection, Design, and Implementation Oversight

    Our scientists and engineers are focused on development of risk-based criteria which can be integrated into practical remedial strategies, leading to final regulatory closure. However, sediment remediation is costly, has frequent challenges and the remedial approaches developed must include sufficient flexibility that inherent uncertainties can be addressed in the implementation phase. All these strategies should be considered not only for management of risk, but also mitigate of constituent and project related risks and impacts. The definition of remedial goals based on chemistry, bioavailability, and impacts observed in aquatic biota is critical to defining a successful program.


Contact Gary Long today to learn more about how we can be your advocate for contaminated sediment assessment needs by providing effective scoping and strategic vision.

 

Sediment Assessment and Remediation Team: