TREATMENTS FOR FARMLAND CONTAMINATED WITH RADIOACTIVE MATERIAL 



ness resulted from the fact that tlie root mat 

 and some soil was remo\-ed with tlie sod. A road 

 grader was also effective in removing contami- 

 nated sod. Similar tests with sod-cutting ma- 

 chines have been conducted by the U.S. Depart- 

 ment of Defense, witli equally effective results 

 (3.9). 



The effectiveness of decontamination by remov- 

 ing mulches differed greatly according to the 

 type of mulch and method of contaminating it. 

 "Wheat-straw and bermudagrass mulches were 

 spread evenly on the ground surface at rates 

 of 2 to 5 tons per acre. Then they were contami- 

 nated and afterward removed from the plots 

 with a side-delivery rake. When radioactive solu- 

 tion was sprayed onto wheat-straw mulch, more 

 than 90 percent of the contamination was re- 

 moved with the mulch {31). With di-y simu- 

 lated fallout applied on bermudagrass mulch, 

 about 30 percent of the contamination was re- 

 moved with a mulch of 2 tons per acre and 

 60 percent with a mulch of 5 tons per acre. The 

 poorer decontamination with dry fallout was at- 

 tributed partly to inefficient raking of the fine, 

 short grass and partly to sifting of dry fallout 

 through the mulch. 



Removal of Surface Soil 



Many common types of earth-moving equip- 

 ment have been used in decontamination tests. 

 These include graders, bulldozers, and rotary, 

 elevating, and pan-type scrapers. In tests re- 

 ported by the Agricultural Research Service (18. 

 21, 22), from 80 to 90 percent of radioactive 

 surface contamination was usually removed when 

 2 inches of soil was removed. Although these 

 tests were conducted at different times, there ap- 

 l^eared to be little diffei-ence in the effectiveness 

 of different kinds of scraping equipment. 



Roughness of the soil surface apparently had 

 some influence on the depth of cut necessary to 

 achieve this degree of decontamination. However, 

 the use of rollers to smooth the surface after 

 contamination and before scraping did not in- 

 crease the effectiveness of decontamination. The 

 lack of significant results in this regard may 

 have been due to difficulties in controlling the 

 depth of cut, which varied with moisture con- 

 tent and looseness of the surface soil. The depth 



of cut was more easily controlled witli the rotary 

 and elevating scrapers and graders than with 

 bulldozers and large pan-type scrapers. 



Similar tests have been reported l\v the IT.S. 

 Department of Defense (29). Tilled, hard, or 

 turf-covered soils in moist or dry condition were 

 scraped with a pan-type scraper or with a grader 

 followed by the scraper to pick up windrows 

 left by the grader. The first grader cut, 2 inches 

 deep, removed about 90 percent of the surface 

 contamination from tilled soil, and after a sec- 

 ond cut more than 99 percent of the initial con- 

 tamination had been removed. Decontamination 

 was even more effective with hard or turf-covered 

 soil, or when the scraping was done with the pan- 

 type scraper making a cut from 2 to 4 inches 

 deep. 



Street sweepers using vacuum or rotary brooms 

 have been studied for removal of fallout con- 

 tamination from soil surfaces. A small vacuum 

 street sweeper was used to remove contamination 

 from a clipped meadow of Kentucky .SI fescue 

 and Ladino clover (18). About half of the con- 

 tamination could be removed by sweeping the 

 meadow twice, but little decontamination could 

 be effected by further sweeping. In later experi- 

 ments at Beltsville, a rotating broom sweeper 

 with steel bristles removed about 75 percent of 

 the contamination from a moist soil with a thin 

 cover of fescue. A second sweeping gave almost 

 90 percent remo^'al of contamination. A sweeper 

 with plastic bristles was less effective, apparently 

 because the plastic bristles did not cut as well 

 through vegetation. 



Some attempts have been made to bind con- 

 tamination in a coating of asphalt allowed to 

 harden on the contaminated surface. By peeling 

 off the asphalt coating, Schulz and others (3-3) re- 

 moved 97 percent of a radioactive tracer that 

 had been sprinkled on the surface of small plots. 

 Wlien used on a field scale (21) the asphalt emul- 

 sion did not improve decontamination because 

 mechanical scraping methods broke up the as- 

 phalt coating instead of peeling it from the 

 surface. 



Decontamination in Cold Weather 



The U.S. Army Nuclear Defense Laboratoiy 

 has tested methods for decontaminating various 

 surfaces under cold weather conditions (23). 



