The contaminated silt and clay in the washwater settle out and are then separated from the washwater. The washwater, which now also contains contaminants, is treated by wastewater treatment processes so it can be recycled for further use. As mentioned earlier, the washwater may contain additives, some of which may interfere with the wastewater treatment process. If this is the case, the additives must be removed or neutralized by "pretreatment" methods before the washwater goes to wastewater treatment. Once separated from the washwater, the silt and clay are tested for contaminants. If all the contaminants were transferred to the washwater and the silt and clay are clean, they can be used at the site or taken elsewhere for use as backfill. If still contaminated, the material may be run through the soil washing process again, or collected for alternate treatment or off-site disposal in a permitted RCRA or TSCA landfill.