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Care, therefore, must be taken in building the barrier because if it breaks, it will release the contaminants. A depression in the waterway may be dug to trap the spilled material. Generally, however, a natural pool is used for this purpose. An overflow or confinement dam works best on slow moving and relatively narrow waterways. The faster the waterway, the less likely this method will work. A floating boom is a second confinement measure for a spilled material that floats and is insoluble or slightly soluble in water. Once the spilled material has been contained, it can be herded to a collection point. There it can be skimmed from the surface using several different types of skimmers . Alternatively, the spilled material can be collected for disposal by sorbents, which can be loose or in sheets or pads. In the case of a viscous liquid, straw may be used. There are several different types of booms on the market, including some which absorb the spill instead of confining it. Booms are not usually effective in rough water. Rather, booms are usually the fastest method of containment in small, slow-moving streams . DEFLECTION BOOMS Material that is highly soluble in water is very difficult to confine and contain. This is especially true in a stream that is fairly wide, deep and has a moderate to fast flow rate. In fact, even floating material is difficult to control in such a stream. For pollutants that are lighter than water (specific gravity < 1) , it is possible to confine and contain the material by discharging clean water into the stream while retaining the floating material. This method only works if the material is not soluble in water. Another confinement option for water discharges is the use of a siphon or underflow dam. An underflow dam is a dike constructed with a pipe placed lower on the upstream side and higher on the downstream side. This creates a waterway through the piping and traps the contaminants on the upstream side. As with the overflow dam, it is necessary to have additional manpower and supplies downstream, just in case the dam breaks. Hay can be used as a temporary measure to create a fixed barrier. An underflow dam is generally limited to smaller waterways, and is particularly useful for controlling and confining hazardous material that floats on the surface of the stream of water. 60 site Safety 4 Health Plan Rev./1. 0 October 20, 1997