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 1.29 g/cm3
- Average daily processing time was 4.47 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:
Not identified
Site Contact:
Sandia Corporation
DOE/AL | Technical Support:
Sue Collins
Sandia National Laboratories
(505) 284-2546 |
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Contaminants:
Depleted Uranium (DU)
- Concentration not provided |
Waste Source:
Burial pits |
Type/Quantity of Media Treated:
Soil
- 1,352 yds3 of soil were processed
- Extended 0.4 acres at a depth of 2 ft
- Soil identified as sandy, 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 27 pCi/g |
Results:
- Overall volume reduction was measured as 99.56%; 21 55-gallons drums of above-criteria soil required off-site disposal
- Average activity of above-criteria soil was 223 pCi/g and below-criteria soil 14.77 pCi/g
- 5.2 yds3 of soil from Burn Site showed volume reduction of 99.4% |
Cost Factors:
- Actual cost was $220,040, including $29,000 for excavation and pre-screening, $41,300 for mobilization, $117,000 for operations, and $32,340 for demobilization
- Overall unit cost was $154/yd3, including $82/yd3 for operations, reflecting the relatively small quantity of soil processed
- Project contracted as a lump sum fixed price; did not include excavation, oversight labor, health physics support, water supply, fuel services, generator support, sample analysis, and waste disposal |
Description:
Environmental Restoration (ER) Site 228A, the Centrifuge Dump Area and Tijeras Arroyo Operative Unit-ADS 1309, is located 500 ft east of Technical Area II, within Kirtland Air Force Base. In July 1997, heavy rains eroded a portion of a depleted uranium burial from the Tijeras Arroyo rim. Depleted uranium mixed with soil and debris washed down the slope.
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 99.56%. The actual cost for the application was $220,040, including $29,000 for excavation and pre-screening, $41,300 for mobilization, $117,000 for operations, and $32,340 for demobilization. This corresponded to an overall unit cost of $154/yd3, including $82/yd3 for operations. Lessons learned included impacts from weather delays and equipment concerns, and difficulties with rocks that were 3 inches in diameter. |
