SPI-Cost-effective Tool for Investigations and Cleanup of Contaminated Sediment
SPI refers to Sediment Profile Imaging – a specialized imaging technology that provides photographic documentation of environmental conditions in surficial sediments. Gene Revelas, of our Olympia, Washington office, is a nationally recognized expert on the use of SPI as a sediment reconnaissance tool at contaminated sediment sites, where it is used to streamline and focus site investigations and clean-up.
How SPI is Used
SPI allows us to map near-surface sediment textures and features by lowering a specially-designed camera system to the seafloor, river, or lake bottom and imaging a cross section (or profile) of the top 20 cm of sediment. (Figure 1) This profile of the upper sediment column allows a broad range of physical, geochemical, and ecological characteristics to be viewed directly, or interpreted based on the imaged structures. (Figure 2)
Physical features observed in the sediment-profile images include:
Grain size.
Range of depositional (e.g., dredged material deposits) structures.
Range of erosional structures.
Key geochemical features include:
Depth of the apparent Redox Potential Discontinuity, or RPD.
Presence of methane gas pockets indicative of organic enrichment.
The ecological interpretation of SPI images is based on a fully ground-truthed benthic infauna successional paradigm for marine sediments. (Figure 3) The benthic successional stage can be identified in profile images gained from observations of the infauna themselves, as well as the biogenic structures they create in the substrate.
SPI provides a unique view of benthic systems because it preserves in situ sedimentological features and animal-sediment relationships. This perspective allows us to infer benthic system functions (physical, chemical, and biological) from the imaged structures.
How SPI Can Help You
Three important factors make SPI an ideal reconnaissance tool at contaminated sediment sites:
The in situ perspective it provides.
The complexities of the benthic environmental data that can be obtained using it.
The rapidity of the data collection.
Collectively, the distribution of SPI parameters – such as the apparent RPD depth, the presence of sedimentary methane or surface bacteria mats, and the infauna successional stage across a surveyed area – allows identification of benthic disturbance gradients.
When images are collected over a broad region or area of concern, these rapidly mapped disturbance gradients can be used to focus and limit more expensive and time-consuming sediment assessment techniques such as sediment chemical analyses or toxicity testing. *The result is faster, cheaper, and targeted benthic investigation and clean up.*
Applying Our Expertise
Our recent experience includes the use of SPI technology at two large, complex sediment cleanup sites in the northwest – the Hylebos Waterway in Tacoma, WA and Portland Harbor in Portland, OR. At both sites, we used SPI surveys to define areas and gradients of benthic disturbance and to identify potential stressors to the systems. This information, in turn, was used to focus the overall site assessments and clean-up.
For More Information
For more information on SPI in general, or on its specific applications in contaminated sediment site assessments, contact Gene Revelas at Integral’s Olympia, WA office at 360-705-3534 or grevelas@integral-corp.com