This Hot Topic offers a remedy selection framework to help project managers evaluate remedial technologies and develop remedial alternatives (often composed of multiple technologies) based on site-specific data. General categories of contaminated sediment remedial technologies include monitored natural recovery (MNR) and enhanced monitored natural recovery (EMNR); in situ treatment; capping (conventional and amended); and removal (dredging and excavation)… Continue reading
In order to reduce potential risks to human health and the environment dredging or excavation remedies for contaminated sediment are the primary means of remediation. Removal of contaminated sediment is generally effective for source control but can be less effective for overall risk reduction if not done properly because of the potential … Continue reading
Because of the inherent complexity of sediment remediation projects, site characteristics (such as source areas, transport mechanisms, background and upstream areas, and key site features) should be clearly identified in a conceptual site model (CSM) before evaluating and selecting remedial alternatives. The remedy evaluation framework presented here assists in selecting remedial technologies and evaluating … Continue reading
Table 1. Summary of Site Characterization Needs for Contaminated Sediment Data Type Potential Site characterization Approach Implication for remedy selection Tools involved Physical characteristic Sediment stability Require to perform tests including bathymetric survey, grain size analysis, bed pins, scour chains, geochronology cores. Stable sediments require less erosion protection for capping options, conductive to monitored natural … Continue reading
Table 2. Evaluation Factors for the Evaluation of Remedial Technologies Monitored natural recovery In Situ treatment Capping Removal Characteristics MNR EMNR conventional capping amended capping hydraulic dredging mechanical dredging excavation Physical characteristics Sediment stability H H H M M L L L Sediment deposition rate H H H M M L L L Erosional potential … Continue reading
Capping is designed to achieve one or more of the following objectives depending upon the cause of exposure and risk at a site: Cap thickness often determines the effectiveness of the cap. Typically the thicker the cap, the greater the reductions in pore-water concentration in the near surface and the greater the reduction in contaminant … Continue reading
In situ sediment treatment involves applying or mixing of an amendment into sediments. Mixing may be achieved either passively, through natural biological processes such as bioturbation, or actively through mechanical means (using augers, for instance). Treatment amendments may be preferred in areas with higher contaminant concentrations, where MNR/EMNR cannot achieve risk goals in an acceptable … Continue reading
Monitored natural recovery (MNR) is defined as a remediation practice that relies on natural processes to protect the environment and receptors from unacceptable exposures to contaminants. Enhanced MNR (EMNR) applies material or amendments to enhance these natural recovery processes. The success of MNR/EMNR also depends on adequate control of contributing sources of contamination so … Continue reading
Dredging of harbors and rivers for navigational purposes has been practiced for centuries and studied extensively. By comparison, environmental dredging (dredging for the sole purpose of removing contaminated sediment) is a relatively new development. For environmental dredging operations, the removal operation is highly controlled, with efforts focused on minimizing the removal of clean material while, … Continue reading
Monitoring data collected before, during, and after remediation provide an objective basis for evaluating remedy performance and effectiveness. Monitoring data are used for gauging progress towards meeting the RAOs and determining whether further remediation or a change to the current remedy is required. Three basic types of monitoring related to sediment remediation are discussed … Continue reading
