When We Are History

Steve McCracken has overseen a 13-year, $800 million cleanup and burial of the radioactive waste at Weldon Spring. Now that the odyssey is nearing its end, one thought haunts him -- how to warn people in the future not to dig it up.

The design for the storage facility, or "cell," is pretty standard, Wesely says. The "footprint" of the cell covers 45 acres, and the height will incline upward to about 75 feet. It sits on top of about 20 feet of naturally occurring clay that, when highly compacted, is nearly impervious to water. But on top of that, the DOE tamped down an additional 128,000 cubic yards of clay brought over from a 200-acre site about a quarter-mile east of the high school. Another special haul road was built for the transfer of the clay.

On top of the clay is a flexible membrane liner made of a high-density polyethylene material. "But we're depending on the clay for the long haul," Wesely notes. Then a layer of "geonet" -- a combination of natural and synthetic materials -- was added, and then another liner. The liners are designed to collect leachate, which will flow toward the north end of the cell, where it will be captured. In between the geonet and the liner, Wesely called for an additional layer of natural material, peat moss -- which, she explains, is decayed organic matter about midway on its evolutionary trip from living plants to coal.

The waste goes basically in the middle; more radioactive trash at the bottom, less radioactive stuff on top.

While Wesely's team designs the facility, Greenwell's team oversees its construction. "The layer of larger stones, called 'rip-rap,' is actually sitting on a bedding of smaller stones, which itself is on top of clay," Greenwell explains. All in all, from the bottom of the cap to the top, there's a barrier of silty clay to capture radon, a geosynthetic liner, sand bedding and the "cap" of large limestone boulders covering it all.

It will not, Wesely admits, be a monument of architectural beauty, but it will stand for an awfully long time, come rain, sleet, snow or earthquakes.

"This containment is the best that we know how to do," Wesely says. "Its biggest components are earthen material that has been around here forever and will continue to be around here forever. We size the rock (on top) so its potential for deterioration is at a minimum. We size it also for the biggest storms we can imagine on this site, which is about 30 inches of rain in 24 hours. We've designed it to last for 1,000 years and actually go a step farther and include maximum precipitation and the maximum earthquake that you can have at this site, taking into consideration the New Madrid (Fault) down below and any other faults near here."

Two-thirds of the "footprint" was built in '97. The remaining third would wait until later, so a more accurate measure of the final waste volume could be estimated. Estimating waste volumes is an almost daily task for Greenwell and Wesely, because the less empty space in the cell when the cap goes on, the better.

"A lot of the material was in stockpiles," Greenwell explains in a matter-of-fact way, "and once it got into stockpiles we were able to do rough calculations and then determine void ratios, and then -- knowing how much soil and solids that was there -- we calculated the approximate volume that we needed."

The soil proved a big problem, though. To estimate how much soil was contaminated and therefore had to be placed in the cell, bores were drilled every 100 feet or so to figure out how far the toxins had penetrated. But as work progressed, the waste spread, so though there wasn't additional waste, more soil was being contaminated by it all the time.

Then last March, workers began putting the stockpiled debris into the cell, starting with a load of contaminated dirt and followed by the rows of drums, steel, concrete and other debris, including 6,000 cubic yards of asbestos stored in 80 SeaLand containers.

But the sludge from the waste pits couldn't be added to the collection in its liquid, unstable form. It was like mush, and the DOE had to find a way to either store it someplace else or to transform it into a solid.

The choice was made to solidify the sludge. It meant building a special treatment plant near the cell, where fly ash and Portland cement -- stored in seven army-green tanks called "pigs" -- were added to the liquid. The resulting mortar was pumped into trucks, then hauled to the cell, where it was poured onto some of the debris, such as piping, that still carried poisonous residues. The process is called "macroencapsulization."

In total, 122,000 cubic yards of sludge was treated between April and November of 1998 and about 186,000 cubic yards of grout was produced and poured into the cell, where it hardened.

That same month, the last of the debris was placed in the cell.
Within the next three years, the quarry will be sealed with caulk and filled with dirt, and the bottoms of the waste pits and the south dump will be purged of their contaminated soil. After that, in the year 2002, the cap will be put on the cell.

So for McCracken, forever begins three years out, when the buildings and workers are gone and the only thing left of the 15-year project is the 75-foot-high storage facility, rising up on the Weldon Spring horizon, a huge concrete mound.

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