TREATMENTS FOR FARMLAND CONTAMINATED WITH RADIOACTIVE MATERIAL 



11 



mipht sift through the straw, resulting in poor 

 decontamination as was achieved with the ber- 

 mudagrass hay mulch. 



In view of the rather poor removal of radio- 

 activity, crop removal would probably be used 

 only as a necessary preliminary to some soil treat- 

 ment that would be more effective. For example, 

 a bulky crop would interfere with tlie loading of 

 scrapers, and cause excessive spillage from the 

 blades of graders or bulldozers. Such crops would 

 have to be removed before the land could be 

 decontaminated by scraping. Even then, roots 

 that could not be cut might decrease the effec- 

 tiveness of scraping. Areas with trees probably 

 could not be decontaminated effectively. 



Crop removal requires considerable time. The 

 most rapid methods will clear little more than 

 one acre per hour. 



Tlie problem of disposal of contaminated plant 

 material has received little attention. It consists 

 of reducing bulk of the material, hauling it, and 

 storing it in a safe manner. For the ratings in 

 table 1, it was considered that crop disposal 

 would be easier than disposal of surface soil, 

 since the weight of material to be hauled would 

 be much less. Methods that remove and load the 

 plant material for hauling in one operation are 

 generally less time consuming than those that 

 do not. Disposal might be in pits or isolated 

 stacks or buildings. 



The removal of crops and mulches would have 

 no detrimental effect on soil productivity. 



Removal of Surface Soil 



Decontamination of farmland is easier if the 

 contaminated surface soil can be removed before 

 the soil has been cultivated. Penetration of sur- 

 face contamination into soil by leaching or ero- 

 sion is minor compared to that in cultivation. 

 Thus, removal of a few centimeters of surface 

 soil will give a high degree of decontamination 

 unless the soil has been disturbed by cultivation 

 or the surface is so rough that some of the ex- 

 posed soil is not removed by shallow scraping. 



Feasibility ratings are summarized in table 2 

 for various methods of removing unfrozen con- 

 taminated surface soil. The equipment ranges 

 from sweepers, which would remove a minimal 

 thickness of soil, to heavy earth-moving equip- 



ment. Soil conditions vary from a rough plowed 

 surface to light vegetative covers, wliich are not 

 expected to interfere with soil removal. 



Scraping operations usually remove more than 

 75 percent of the radioactive contamination on a 

 soil surface. The removal of radioactivity is 

 likely to be better from a smooth seedbed than 

 from a corn stubble or other rough soil surface. 



Decontamination with scrapers is ineffective 

 on stony soils. Scrapers cannot cut at shallow 

 depths when large stones lie at the soil surface. 

 Even small stones, a few centimeters in diam- 

 eter, may cause the scraper blade to roll over 

 considerable quantities of fine soil containing the 

 radioactive material. Thus, it would be neces- 

 sary to scrape repeatedly, or to greater depth, 

 to achieve a high degree of decontamination. 



Rough soil surfaces are common in pastures 

 and cultivated fields. Freshly plowed surfaces 

 and row-crop ridges often have differences in 

 elevation of several inches between the highest 

 and lowest surface. Land that has been bedded 

 for furrow irrigation presents even greater ex- 

 tremes. Since a greater amount of soil would have 

 to be removed for effective decontamination, 

 rough surface areas would require extra effort 

 for soil removal and disposal. 



Measurements of the time required for soil re- 

 moval and disposal were made in the U.S. De- 

 partment of Defense tests (29) and in some of 

 our unpublished studies. Bulldozers, road grad- 

 ers, and scrapers required more than one hour 

 of equipment time per acre of surface soil re- 

 moved. It usually required more time to haul the 

 soil to a disposal pit or pile than it did to scrape 

 the surface. 



Feasibility ratings for disposal (table 2) are 

 based on the mass of soil to be moved and the 

 loading effort required after decontamination. 

 After scraping with a motor grader or bulldozer, 

 the removed soil must be loaded for hauling to a 

 disposal area. The sweepers and other scrapers 

 are loaded during decontamination. The mass 

 of soil to be hauled is much greater with the 

 scrapers than with sweepers. 



Studies on removal of surface soil have often 

 shown some loss in soil productivity (3, 34) • 

 The loss in productivity will vary according to 

 the depth of fertile soil originally present, and 

 the amount of soil removed. Restoring the pro- 



