such  as  bulldozers  and  graders.  Hand-  or  power- felling  equipment,  explosives,  and  fire  are  used  when they  make  the  completion  of  these  operations  easier. CAUTION Large-scale   clearing   and   grubbing operations often   produce   damaging environmental effects, such as increased soil erosion,  reduction  of  atmospheric  oxygen,  and destruction of wildlife habitat. Additionally, introduction  of  particulate  matter  into  streams and riverbeds causes increased siltation and algae growth. Federal regulations may require an   environmental   impact   statement   or assessment   prior   to   beginning   clearing operations. To  prevent  these  damaging  effects,  save  as  much vegetation as possible, such as trees, grass, and other plants, to hold the soil in place. Constructing a shallow trench or application of plastic barriers or hay bales around  the  perimeter  of  a  project  will  help  to  contain water  runoff  into  streams  and  rivers,  preventing siltation.  Burning  of  scrubs  and  stumps  should  be  done only when atmospheric conditions are favorable and the material to be burned is dry, However, do NOT use petroleum base fuels to start fires, as fuels do not burn completely and seep into the underground water table. NOTE: A burn permit is required in all burning operations  on  NCF  projects  to  prevent  wild  fires  and production of smog. When  determining  the  methods  of  earthwork operations  needed,  consider  the  following  factors: .  The .  The .  The .  The .  The acreage to be cleared type  and  density  of  vegetation physical  features  of  the  land expected  weather  conditions time available for completion of the job For best results, a combination of methods should be used in a sequence of operations. Use the method most  suitable  and  effective  for  the  job. EQUIPMENT Knowing  your  equipment,  its  limitations,  and  its operating characteristics is part of the knowledge you need to know to be an efficient EO on earthmoving jobs. Equipment  production  must  be  determined  so  that the  correct  amount  and  type  of  equipment  is  selected for  a  project.  Equipment  production  rates  are  available in the Seabee Planner’s and Estimator’s Handbook, NAVFACP-405. The handbook provides information on  estimating  construction  work  elements  and material   quantities,   including   equipment   and manpower requirements. Before you begin earthmoving operations, it is often  necessary  to  remove  overgrowth,  boulders,  and other  obstructions.  Also,  you  often  have  to  build  a drainage system, so the construction site will drain. These  operations  are  carried  out  with  bulldozers, scrapers, graders, and similar equipment. The load, hauled by a scraper, is usually referred to as either  heaped  or struck  (fig.  15-63).  When moving earth, take a full, heaped load and make it Figure 15-63.-Heaped and struck load. 15-38