The accurate characterization and assessment of marine sediment is an important step for environmental characterization and remediation of marine based contaminated sites. Investigation of marine sediments is commonly completed using a vibracore equipped sampling vessel capable of coring marine sediments. Extracted cores provide data that is related to in-situ sediment depths. The data collected from sediment investigations is integral to delineate sediment contamination and to estimate contaminated sediment volumes for potential dredging remediation.
Typically, vibracore sampling vessels are equipped with GIS navigation systems and depth sounders to provide accurate measurements of sample coordinates and water depth (to mudline). Other measurements and observations are recorded during sediment coring and include drive penetration, headspace measurement, and core recovery. These measurements allow the geoscientist to determine the recovery percentage which is then used to apply a correction factor to the recovered sediment core and determine sampling intervals. Uncertainty with respect to the measurements of core recovery and core corrections can have a large impact on the accuracy of sample intervals and, therefore, estimated remediation volumes. Error and uncertainty in remediation volumes can lead to significant increases in remediation costs.
In recognition of this issue, Coastline Technologies Inc. (Coastline) has developed, with the support of the National Research Council’s (NRC) Industrial Research Assistance Program (IRAP), a new technology to provide measurements of core tube penetration and core recovery. This new technology offers digital data measurements in real time that can be used to improve the efficiency of Coastline’s coring systems. We anticipate that these results, when applied to the selection of sampling intervals, will greatly increase the accuracy and precision of sediment core measurements and sampling intervals and, therefore, the accuracy and precision of all data that are derived from those measurements.
The new measurement system allows the operator to zero the measurement system immediately prior to taking the sample. The core tube penetration measurement is a proxy for depth of sediment. A second measurement system records the level of the sediment as it enters the core tube. Real time measurement in 1.0 cm increments are recorded and compared to provide percent core recovery for each 1.0 cm increment. The operator can adjust vibracore parameters to optimize core recovery. On extraction and retrieval, the measurement system detects any changes (core catcher inversion, washout, etc.) that might affect the data acquired from the core prior to sampling. The results for each core sample are transferred to the core sampling team so that the geoscientists know how the core relates to in-situ sediment depths for each core sampled.
SNC-Lavalin and Coastline will employ this technology in field trials between January and March 2017 to test technology and to compare the data and results to previously used techniques. SNC-Lavalin plans to complete data analysis and comparisons using statistical techniques to demonstrate improvements to sample confidence, remediation volume estimates, and investigation costs.