just as air and water are susceptible to pollution,soil is often our depository for human wastes such as sewage,garbage,and milling residues-sometime deliberately,sometimes thoughtlessly. depending on the technology employed,application of these wastes can contribute to the quality of soil or it can render them unfit for food crops. the most costly pollution cleanup site in the united states tend to be site with contaminated soil. many such site are military installations with organic fuels or solvents spilled on the ground,threatening surface or groundwater.