WORK ON OVERPASS IS HALTED

CHAFFEE -- Work on the Highway 77 Cotton Belt railroad bridge overpass north of here was halted last week until the Missouri Highway and Transportation Department determines if a compound mixed into the soil to stop soil subsidence at the bridge is environmentally safe.

"We shut the project down on Wednesday until we can get this thing resolved," said Bob Sfreddo, District 10 highway engineer at Sikeston. He said the project was about 10 to 15 percent complete when the work stopped.

Sfreddo said the compound, crystalline silica, is contained in a lime-based product known commercially as Codel. It is manufactured by Mississippi Lime Co. of Ste. Genevieve.

Sfreddo said about three or four tanker loads of Codel already had been mixed in with the clay soil when it was discovered crystalline silica is a toxic corrosive that may in sufficient amounts be a carcinogen to animals and humans.

Sfreddo said a nearby property owner was notified of the discovery. "We assured him that we will meet with him before any work resumes," Sfreddo said.

Crystalline silica is not listed as a carcinogen by the Occupational Safety and Health Administration (OSHA), but it is on other safety lists that describe it as a possible carcinogen, Sfreddo said.

"That was enough to send up a very big red flag and stop work on the project until we can get more information on the product," he said. "Right now we have this cloud that it may or may not be a hazard to humans or the environment. We're going to check this out thoroughly to make sure we're not doing anything here that would be harmful."

Sfreddo said he has been in contact with officials at Mississippi Lime and the Missouri Department of Natural Resources in Jefferson City to find out more about Codel. "The people I talked to at DNR did not seem to be very concerned about it," he said.

Sfreddo said he hopes to be able to make a decision before the end of the week on whether to continue with the Codel or switch to hydrated lime. He said the decision will be made as soon as all of the data is received and questions about the safety issue to humans and the environment have been resolved.

Sfreddo said both Codel and hydrated lime are dangerous when wet.

"Both products are toxic corrosives that can cause burns or skin irritation when wet, and they require protective clothing," he said. "But Codel has the extra warning of being a possible carcinogen to animals and humans in certain amounts. It is my understanding that we are about .2 of a percent over this threshold limit."

Sfreddo said Codel is less expensive than hydrated lime.

He said hydrated lime is commonly used by contractors and bricklayers, and by municipal water departments in treating drinking water.

"We have used hydrated lime many times for this type of work," he said. "I have worked with the stuff for over 30 years and have never suffered any ill effects.

"What we may have to do is eliminate the Codel and go to hydrated lime," Sfreddo said. "But for the economics of it, we'd like to be able to stay with Codel if we can be assured that it will be safe to use."

The highway department has been trying to stop subsidence of earthen slopes at the railroad overpass for about seven years. Since 1984, nearly $500,000 has been spent to try to resolve the subsidence problem.

After a rain, as the clay soil slopes on each side of the bridge dry, wide, deep cracks at the surface develop that allow moisture to penetrate deep into the soil. Eventually, the clay soil becomes saturated with water, causing earth slides on the four slopes.

In separate projects in 1984 and 1986, a slurry mixture of lime fly-ash was injected into each slope; however, the slurry did not penetrate deep into the soil, Sfreddo said.

This time the soil from the slopes has been stripped away and stored in a nearby field where it was being mixed with the Codel before being reapplied.

Sfreddo said while the slopes are cut back, drain tiles are being installed and an 18-inch blanket of sand will be laid on top of the subsoil before the upper layer of clay mixed with lime is reapplied to the slope.

"This top layer of lime and clay should make the soil impervious to water. What water does get through will drain through the sand into the drain pipes and into a nearby ditch," Sfreddo said. "We hope this will take care of the problem."

Work on the $857,431 project got under way last month.

Sfreddo explained when the overpass was built in the mid-1960s, highway engineers were not aware of the unstable characteristics of the clay soil when it is exposed to excessive moisture and dry weather. Since then, the state has specified a different type of soil be used when building earthen bridge approaches such as the Route N railroad overpass at nearby Rockview.

While the overpass work is going on, the speed limit over the bridge has been reduced to 30 mph. Sfreddo said the slopes on the east side of the overpass have been cut back to nearly a vertical level.

There is a concrete barrier on the edge of the northbound lane, but Sfreddo said if a vehicle should hit one of the barriers at a high rate of speed it could crash through the barrier or flip over the top.

"If a vehicle goes through or over the barrier it is nearly a straight drop over the side," Sfreddo said. "We urge motorists to use extreme caution when crossing the bridge even while there is no work going on."