NEW CAMERA KEEPS AN EYE ON OCEAN FLOOR
BY BENJAMIN MINNICK
It sounds like a job for an ostrich -- getting paid to stick your head in the sand -- but sediment profile imaging is strictly for scientists.
Sediment profile imaging, or SPI, involves sending a camera down to the bottom floor of a water body. When the camera hits the bottom, it digs into the sediment layer and takes a picture.
The images, which measure 15 by 20 centimeters, provide a unique view of the seafloor's biologically active zone. That information can be useful for monitoring underwater disposal sites and as part of remedial investigation and due diligence studies for areas targeted for cleanup or property transfer.
The cameras cost between $35,000 and $65,000. They are designed to penetrate soft sand and mud bottoms, but will not work in rocky or hard surfaces. Two versions of the camera are made; one rated for ocean depths of up to 4,000 meters and another for depths of up to 500 meters.
Locally, the 500-meter model is the choice because it can easily cover the depths of Puget Sound, where the deepest disposal site is about 120 meters and most other study sites are
SPI applications include:
Sediment profile imaging is being used locally to map deposit layers in five Puget Sound open water confined disposal sites, where spoils from maintenance dredging of rivers, channels and harbors typically go.
Olympia-based Striplin Environmental Associates (SEA) is using the system for ongoing studies of the Hylebos Waterway in Tacoma, where over $1.5 million in work has been performed so far for the Hylebos Cleanup Committee, a consortium of potentially responsible parties tied into the Superfund site.
Gene Revelas, senior scientist with SEA, said using sediment profile imaging along with traditional sampling techniques has helped develop a better understanding of what is going on underwater at the site.
With the aid of the camera, Revelas found that log debris and excess organic material had built up at the head of the waterway, stressing the bottom habitat. He also discovered that bottom scour from passing ships had created turbulence in the area of the 11th Street Bridge, disturbing bottom-dwelling life.
SEA President Betsy Striplin said SPI doesn't take the place of traditional surface sediment or "grab" samples, which are chunks of ocean floor that are hauled to the surface and evaluated at a laboratory. However, SPI can serve as a reconnaissance tool to help narrow the focus of where samples are taken. "It's not going to replace data from a chemistry lab," she said.
Narrowing the survey area for traditional sampling is where SPI can be cost effective. Although it costs about $25,000 to map 100 stations with SPI, eliminating the need for just a few traditional sample stations can make up the cost since they run between $8,000 and $10,000 per station.
"On a big program, it will pay for itself quickly," Striplin said.
Using SPI for reconnaissance is a new market Striplin hopes to develop. About 10 percent of SEA's business is now from preliminary SPI sampling and Striplin hopes to expand it to 20 percent within three years.
"It's a tool that's had a very defined niche for the last decade," she said. "We feel it has other capabilities."
Striplin does admit preliminary SPI work is a tough sell because you don't know how much it will save until it is actually used. And there is a downside; a reduction in the sampling effort may not be possible if the entire site needs traditional sampling.
Much of SEA's other work with the camera includes mapping deposit layers in disposal sites along the West Coast, a more traditional use for SPI.
Striplin said sediment profile imaging can only be properly evaluated by trained professionals, like Revelas and Dave Browning, another SEA scientist. Interpretations are developed based on geological, ecological and geochemical principles of how sediments look in profile. "It's finesse ... it's an art," Striplin said.
SPI was first developed in the early 1970s as a research tool by Yale professor Dr. Donald C. Rhoads. Along with former student Dr. Joseph D. Germano, Rhoads established SPI in the 1980s as a tool for designating and monitoring dredged material disposal sites. It has since become used around the world.