Technology:
Segmented Gate System (SGS)
- SGS is a combination of conveyor systems, radiation detectors (primarily gamma radiation), and computer control
- Contaminated soil on conveyor belt was diverted by segmented gates into stockpiles
- Detectors monitored radioactivity content of soil traveling on belt and computer opened specified gates to separate portions of soil based on radioactivity criteria
- Operating parameters included a belt speed of 30 ft/min, belt length of 16 18 ft, soil layer thickness of 2 in by width of 30.75 in, and soil density of 1.0 g/cm3
- Average daily processing time was 4.7 hrs, less than the target of 7 hrs
- Oversize debris and rock pre-screened using a field grizzly (vertical bar grate) and hammermill
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Cleanup Authority:
RCRA Corrective Action - Part B permit issued 8/93
Site Contact:
Tom Burford
Sandia Corporation
DOE/AL
(505) 845-9893
Technical Support:
Sue Collins
Sandia National Laboratories
(505) 284-2546 | Regulatory Authority:
New Mexico Environment Department |
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Contaminants:
Depleted Uranium (DU)
- Concentrations reported as high as 4,100 pCi/g |
Waste Source:
Dump Site |
Type/Quantity of Media Treated:
Soil
- 661.8 yds3 of soil were processed
- Soil identified as silty sands, containing 35-45% silt and clay; moisture content estimated as 10% |
Purpose/Significance of Application:
Use of a gate system to reduce soil volume requiring off-site disposal |
Regulatory Requirements/Cleanup Goals:
- Reduce the volume of contaminated soil by separating soil that was above the specified criteria and that would require off-site storage and disposal, from soil that was below the criteria
- The sorting criterion was 54 pCi/g |
Results:
- Overall volume reduction of contaminated soil was 99.9%; 358 kg of above-criteria soil required off-site disposal
- After first pass, average activity of above-criteria soil was 406.5 pCi/g and below-criteria soil 4.2 pCi/g |
Cost Factors:
- Actual cost was $164,109, including $59,326 for mobilization, $57,770 for operations, and $47,013 for demobilization
- Overall unit cost was $236/yd3 of soil processed ($80/yd3 for operations), reflecting the relatively small amount of soil processed
- Additional activities included site preparation, operation of crane, excavation, oversight labor, health physics support, water supply, sample analysis, and waste disposal |
Description:
Sandia National Laboratories' Environmental Restoration (ER) Site 16 is located northeast of the Technical Area III/V complex, within Kirtland Air Force Base. The site covers 25 acres and was an open dumping ground for concrete and other rubble. The concrete and rubble was presumed to be the source on contamination. Approximately 1/3 acre was excavated for the project from the side and bottom of an arroyo, after the removal of larger debris.
A Segmented Gate System (SGS) was used to reduce the volume of contaminated soil that required off-site disposal. SGS is a combination of conveyor systems, radiation detectors, and computer control, where contaminated soil on a conveyor belt is diverted by segmented gates into stockpiles. Detectors monitor the radioactivity content of the soil traveling on the belt and a computer opens specified gates to separate portions of the soil based on radioactivity criteria. At this site, the overall volume reduction was measured as 99.9%. The actual cost for the application was $164,109, including $59,326 for mobilization, $57,700 for operations, and $47,013 for demobilization. This corresponded to an overall unit cost of $236/yd3, including $80/yd3 for operations. Lessons learned included impacts from startup requirements, jams in the screen/hammermill caused by larger rocks, and soil buildup in the gas chutes. |
