A Staff Report from the Straight Dope Science Advisory Board

Why do you see signs saying, "clean fill wanted"?

Dear Straight Dope:

Now and then, I see curbside signs in front of people's homes in rural areas that read "clean fill wanted." Now, what exactly _is_ "fill", how is it judged to be clean, and why can't the people who want it just go out and get some? Is there some other group of people driving around with a van of "fill," hoping desperately to be able to sell it somewhere? Please fill me in.

"Fill" is dirt. Top soil, clay, sand, gravel, rubble, even brick or concrete. "Clean", in this case, means environmentally clean, i.e. free from contaminants, including corrosive, combustible, noxious, zootoxic, reactive, or radioactive materials. The reason some people want it is to raise the elevation of a lot in order to make it more suitable to construction, change the contours of a construction site to improve drainage, replenish soils lost to erosion, or simply to obtain some suitable material for a subfoundation where otherwise a site may not support construction.

The reason for hoping that somebody out there may be driving around, looking for some place to get rid of their fill, is that construction of some types, or on some sites, often entails the removal of such material from a site, and simply dumping it elsewhere on the site may be impractical or illegal. So, if some developer has a few truckloads of dirt, rubble, whatever, the best place for them to put it is on the site of some other builder. Typically, the two will share the transportation costs. The people with excess fill save disposal fees, the people with need save material costs, and the environment benefits because this material is essentially recycled. A pretty example of how a barter system of economy can work. More efficient ways of advertising the supply or demand for fill dirt exist, of course, and in some situations, several different developers will often form a consortium wherein each member gives or receives fill as they need, from their different building sites. Of course, you can just go out and buy some dirt, but what fun is that?

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