Dredging at weldon spring super fund project Morrison Knudsen - St. Charles, Missouri, USA


Courtesy of Liquid Waste Technology LLC - Mud Cat

Remote controlled Dredging proved to be the best method of removing radioactive sludge from settling ponds of a former uranium processing plant near St. Charles, Missouri. Dredging keeps the material wet and out of contact with the atmosphere throughout the removal and treatment process, eliminating the danger of contaminates becoming airborne.

The Weldon Spring Site Remedial Action Project (WSSRAP) is a Superfund site that was designated a Major Project for control and decontamination in May 1985. Funding of up to $1 billion has been allocated for this site, which consists of four waste (raffinate) pits, a facility for chemical stabilization and solidification of low level radioactive sludge.

In 1984, scientists from Argonne National Laboratory were retained to evaluate the contaminates at the former uranium processing facility and to recommend a way to handle and dispose of the waste. Argonne is a research facility operated by the University of Chicago in the suburbs west of Chicago.

Mary Picel, an environmental health scientist at Argonne, has worked the project since 1993.

'We determined that the best way to move the material was to dredge it, grout it and bury it,' said Picel. The disposal cell is 30 feet deep with clay to prevent migration of contaminants through to the groundwater. A million and a half cubic yards of contaminated materials are being placed in the cell. Besides 186,000 cubic yards of grouted raffinate, this includes wood and metal debris, process equipment, piping and construction materials. About 6,130 drums containing PCB-contaminated oils, asbestos insulation, uranium wastes, magnesium compounds, graphite and sediment were samples, repackaged and placed in storage until final placement in the disposal facility. The pit will be capped with rubble and soil, which will be an effective shield, said Picel. The area will be continuously monitored for radon.

Two Liquid Waste Technology (LWT) Electric Remote Control Lagoon Pumpers, (RCLPE's) custom built at 34 feet long and the standard 101 inches wide for extremely shallow draft, were purchased by project owner, the Department of Energy, in addition to another smaller dredge which was used in a pilot project to test the dredging and processing technique.

The dredging portion of this massive cleanup project consisted of removing 122,000 cubic yards of sludge from the raffinate pits and pumping it to a CSS (chemical stabilization and solidification) facility. More than 75 million gallons of water with an average of eight to 10 percent solids was pumped to move the sludge from the pits to the treatment plan. The sludge was screened for oversize materials, then thickened with a polymer before it was blended with Portland cement and fly ash and transferred as grout to the disposal cell. About 180,000 cubic yards of grout was produced.

More than 25,000 cubic yards of sludge was treated in situ in pit 4, then excavated and transported to the disposal facility.

MK-Ferguson with Jacobs Engineering Group, Inc., as its integrated subcontractor, is the Project Management

Contractor (PMC). MK's responsibilities include procurement and management of remedial construction services; site maintenance, surveillance, security; characterization, analysis, and engineering services; planning, budgeting, and reporting; and integration of cost and schedule for all participants. MK-Ferguson is a major subsidiary of Morrison Knudson Corporation of Boise, Idaho. The company's WSSRAP Project Director is Douglas E. Steffen.

Matt Myers is MK project supervisor. The dredging portion began in April 1998 and was completed by the end of the year, he said. Two dredges were purchased to ensure continued operation should one shut down, said Myers. Dredging continued around the clock, seven days a week from start to finish, with four three-person crews, all members of the AFL-CIO Operating Engineers Union.

All personnel on the project were required to wear Level B protective clothing. No personal clothing was worn on the site. Workers dressed in hospital pants and shirts and disposable cotton coveralls, cotton socks and 16-inch rubber boots, hard hats and safety glasses. Though the dredge was designed for remote operation, the management opted for on-board operation, and the dredge operator wore a disposable Syranex waterproof coverall.

At the end of the shift, the crews would remove all clothing, pass through a personal contamination monitor and into a shower facility before donning their street clothes.

The dredges are 125 hp machines with eight foot, two inch augers. Steel I-beams at the ends of the ponds provide stabilization for winching forward and back, and trolleys move the dredge laterally at the end of a cut. A triple-sheave traverse winch is mounted on deck on an elevated stand, which holds the travel cable well off the water surface. The cable is shrouded along the length of the deck.

An electric motor drives a pressure-compensated hydraulic pump providing constant hydraulic pressure for all functions. A pressure relief valve prevents damage or blown fuses in the event of over-power or junction blockage.

The rubber-lined pump is an eight-inch by eight-inch recessed-impeller centrifugal pump.

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