Table 1. Summary of Site Characterization Needs for Contaminated Sediment
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 recovery if cleaner material is being deposited | Sedflume measurement;
sediment trap;
bathymetric survey
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Sediment deposition rate | Sediment deposition rates may be estimated using sediment trap and geochronology cores. Requiring dredge record, historical bathymetry survey, sediment dating | Monitored natural recovery requires deposition of clean material over contaminated material | sediment trap;
core sampler
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Erosion potential of bedded sediments | Estimated using combined Sedflume measurement, flow measurement, and hydrodynamic evaluations | Contaminated sediment with high resuspension potential may represent source of downstream and water column contamination | flow(hydrodynamic) measurement device;
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Water depth and site bathymetry | Bathymetric features including water depth estimation; it helps delineation of contaminant extent | Important for removal method selection | water measurement device
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In-water and shoreline infrastructure | Physical and geophysical site survey for identifying location of structure | The presence of structure has impact on feasibility of various sediment remediation options | ||
Presence of hard bottom | Hard bottom (bedrock, hard pan, coarse sediment, large cobbles, boulders) maybe identified | The presence of hard bottom may limit the effectiveness of dredging. | sediment core (for hard bottom);
geophysical survey
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Presence of debris | Debris survey performed in urban waterway should include geophysical survey, diver survey | The presence of debris has significant impact on feasibility and effectiveness of removal based sediment remedies | side scan sonar;
sub bottom profiler; underwater photograph;
metal detector
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Hydrodynamics | The evaluation should include assessment of wave action, tidal force, wind-driven seiche potential | Hydrodynamics have direct bearing on the evaluation of contaminant mobility, and therefore capping-based remedies and MNR remedies | doppler profile;
water stage data;
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Groundwater/ surface water interaction |
Evaluation of the potential of groundwater movement to transport subsurface sediment and groundwater contaminant to surface sediment layer and water column. | Useful for understanding groundwater source control, contaminant fate and transport, and bioavailability. Areas with high advective groundwater flux may limit the effectiveness of sediment remedies. | water level log;
Piezometer;
Geochemical measurement
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Sediment and pore-water geochemistry (TOC, DOC, POC) | Characterizing sediment and pore water for a range of constituents may be useful for understanding contaminant fate and transport processes, biodegradation and contaminant bioavailability. | Useful for evaluation of MNR, in-situ treatment and capping technologies | ||
Sediment characteristics | ||||
Geotechnical properties | including bulk density, shear strength, specific gravity, water content, cohesiveness, organic content, Atterberg limits | Geotechnical parameters have direct effect on feasibility of all remedial technologies; also useful in evaluation of dewaterability of dredged sediment | core sampler;
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Potential for resuspension/ residual |
Elutriate testing such as dredged residual elutriate test (DRET) can inform assessment of short term water quality impacts | Data maybe used to evaluate releases during dredging and to estimate potential short term and long term impact
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Sediment consolidation (pore-water extraction) | Provide engineering properties needed to calculate settlement or pore-water extraction, followed by chemical testing | Influence extent to which dissolved contaminant may move into cap during placement and settling. | ||
Benthic community structure and bioturbation potential | Characterization of benthic community through diversity and abundance survey may be performed to determine habitat characteristics | The presence of a healthy benthic community should be considered when evaluating invasive sediment remedies such as dredging | core sampler;
benthic sampler
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Contaminant transformation of degradation | Literature surveys should be performed to develop an initial understanding of the potential for contaminant transformation and degradation. | Support capping models and evaluate MNR (Monitored natural recovery ) | ||
Source identification and control | Develop CSM that considers sources of contaminants; identify regulatory program and framework in place to control sources of contaminant | Effective source control is a critical components of all successful sediment remedies | ||
Ebullition | identify areas with significant ebullition | Affect contaminant mobility and transport and may impede capping success | ||
Background | Characterization of natural and anthropogenic background is critical for bioaccumulative chemicals such as PCBs; testing may be bulk sediment, surface water, biota tissue, and pore water | characterization of background is critical to the evaluation of MNR and the establishment of achievable site cleanup levels and effectiveness of any remedial technology’ | ||
Contaminant characteristics | ||||
Horizontal and vertical distribution of contamination | The area and volume of sediment contamination that is useful for identifying area of diffuse, widespread, low level contamination and localized area of high concentration | Critical element for evaluation of all sediment remedial technologies. | XRF for metals;
UVF for PAH;
Immunoassay(PCB, PAH, pesticide, dioxin)
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Contaminant type (Inorganic, UXO, size fraction) | Most contaminant are associated with the fine-grained sediment fraction (silt and clay), some contaminant area sand-sized and larger (lead shot, UXO) | Direct effect on risk and exporesure potential as well as removal strategies | ||
Contaminant concentration | Bulk sediment, surface water, pore-water, and biota tissue may be analyzed to determine contaminant concentration distribution and bioavailability | Critical element for evaluation of all sediment remedial technologies. | ||
Exposure pathway | Exposure pathway contributing to risk at the site and the degree of risk throughout the site | Direct impact on the RAOs and evaluation of remedial technologies | ||
Presence of source material (NAPL) | Sediment core should be evaluated to determine presence/absence of NAPL | Direct effect on releases during dredging and the effectiveness of capping, MNR. | sediment core sampler
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Contaminant mobility | NAPL and soluble contaminants should be identified | Critical element for evaluation of all sediment remedial technologies. | ||
Contaminant bioavailability and toxicity | Measures needed to fully assess risk at sediment sites | Critical element for assessing risk and developing site cleanup level and to identify areas that may contribute disproportionately to potential site risk | Bioassay for toxicity;
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Contaminant transformation of degradation | Literature surveys should be performed to develop an initial understanding of the potential for contaminant transformation and degradation. | Support capping models and evaluate MNR | ||
Source identification and control | Develop CSM that considers sources of contaminants; identify regulatory program and framework in place to control sources of contaminant | Effective source control is a critical components of all successful sediment remedies | ||
Ebullition | identify areas with significant ebullition | Affect contaminant mobility and transport and may impede capping success | ||
Background | Characterization of natural and anthropogenic background is critical for bioaccumulative chemicals such as PCBs; testing may be bulk sediment, surface water, biota tissue, and pore water | Characterization of background is critical to the evaluation of MNR and the establishment of achievable site cleanup levels and effectiveness of any remedial technology’ | ||