Scientists test sediment behind dam

Scientists test sediment behind dam

By Mark Freeman
Mail Tribune
July 15, 2009

GOLD HILL — A 7-foot tube of gooey muck stuck for decades behind 105-year-old Gold Ray Dam is splayed out Tuesday before geologist Bill Elliott, and the mud-loving kid inside the Southern Oregon University professor all but takes over.

Elliott’s gloved hands pick and squeeze the clay, mud and silt freshly cored from the Rogue River’s Tolo Slough and exposed to the sun for the first time in 50 years or more.

“Ooooh,” Elliott coos. “Look at that sweet mud. It’s awesome.”

The same mud is one of the largest unknowns remaining for those deciding when, how and even whether the last impediment to 157 miles of free-flowing river is removed from the Rogue.

Elliott and a team of soil specialists have begun the long-awaited sampling to determine whether heavy metals, pesticides or other contaminants are locked in the estimated 400,000 cubic yards of sediment submerged by water backed up by the 38-foot dam.

If the sediment is deemed clean enough to be dissipated naturally, Jackson County could move forward with an environmental study that could result in the dam’s removal next year.

But the presence of contaminants or too much of the wrong silt could mean that some or all of the sediment would have to be dug out of the Rogue before the dam is removed. It also could mean keeping the dam in place makes the most sense for Jackson County, which owns the dam decommissioned as a hydropower plant 37 years ago.

“Up until now, everything’s been 100 percent speculation,” says John Vial, the county’s roads and parks director. “This will answer a big portion of the questions of what removing the dam means environmentally. So far we haven’t been able to assess that.”

The sampling, called “coring,” began Tuesday morning when Washington-based Gravity Environmental launched its custom boat designed to sample muck.

Long, ultra-clean plastic tubes vibrate as they pulsate downward through the various strata, shaking the boat like an on-board earthquake before the tube strikes something hard, like a tree trunk or bedrock, and stalls.

When the first tube is removed and the water drained, Gravity Environmental’s Steve Saugen lays out a 7-foot-long, liquorice-like sample, light and watery near the surface and growing in density farther down the tube.

“I live for this,” says Elliott, who has donated his time for this study to DHR Engineering, which is managing the project for the county.

Out tumbles a handful of rocks that Elliott snatches immediately.

“Ooh, that’s a piece of quartzite,” he says. “This probably washed down Bear Creek. This one’s basalt that probably came down the Rogue.

“That’s good stuff,” he says.

To curb any contamination of the samples, Saugen uses a freshly bought spatula to cut the segment in half. The sample is broken into 4-foot sections, from which Elliott pulls chunks using a mixing spoon.

The chunks are mixed as a unified sample that is jarred in 4-ounce and 8-ounce bottles, then labeled.

Some of the 4-ounce bottles will go to SOU, which will test for the presence of metals and for the sediment’s grain sizes.

The rest will go to Neilson Research Corp. in Medford, where the lab will test for everything from mercury and arsenic to pesticides, hydrocarbons and levels of organic material, DHR’s Steve Mason says.

Those studies are all required by the U.S. Army Corps of Engineers, which oversees sediment issues involving dam-removal projects.

In all, 12 core samples will be taken, Mason says. The sampling, which should conclude today, cost $17,000, he says. The tests were expected to cost about $20,000, with preliminary results expected by the end of July, Mason says.

If the tests show the sediment is benign, the county has the option of pursuing a so-called “blow-and-go” strategy similar to the one currently used in the removal of Savage Rapids Dam 19 miles downstream, where no troublesome levels of contaminants were found in upstream silt.

That approach, along with sediment-transport analysis, could be vetted in an upcoming environmental assessment, funded through the $5 million in federal stimulus money tapped for the dam, Vial says.

“If contaminants are found, then our approach to this project has to be rethought,” Vial says.

Elliott’s enthusiasm for the muck does not wane during his work.

He plies it like Play-Doh, photographs it, stirs his pot like he’s making mud pies and waxes on how field work like this is personal validation for choosing the path of a geologist.

“You’ve probably never seen somebody so excited about sand, mud and silt,” Elliott says.

Read the original story