For obvious reasons concrete trucks should never be washed out into the street or into the storm drain. Solids that are washed out of the concrete trucks can clog storm drains, causing flooding and expensive clean-up. However, it is also important to contain the concrete wash water as well. The wash water is very alkaline, which means it has a very high pH. Water must have a pH in the range of 6.5-9.0 in order for aquatic life to survive. Concrete wash water typically has a pH of 12 or above. Furthermore, the pH scale is logarithmic, meaning that a pH of 12 is 10 times greater than a pH of 11, 100 times greater than a pH of 10, and 1000 times greater than a pH of 9.0, which is the highest level of alkalinity that aquatic life can tolerate. If allowed to escape the site, concrete wash water can have a severe effect on our streams and rivers.
Other significant pollutants in concrete wash water are heavy metals such as chromium. If wash water that is high in heavy metals leaches through the soil to the water table, it can contaminate our groundwater, which is where most cities in Nebraska get all of their drinking water.
Concrete washout is also high in suspended and dissolved solids. The average stream or river in the United States typically has a suspended solid count of no more than 60 parts per million (ppm). The average suspended solids in concrete wash water is 27,000 ppm, well above the range at which aquatic life can survive.
Luckily, it is not very difficult to control concrete washout on your construction site. There are several different ways to build a concrete washout facility, the most simple being to dig a pit and line it with plastic sheeting that is at least 10-mil thick. If you don’t have a good location on your site for a facility like this, you can also build a portable facility by building a box with a liner to contain the washout. There are also several products available for purchase that are effective, portable concrete washout containers.
Always locate concrete washouts as far away from storm drains as possible. Make sure they are clearly labeled and that drivers know where they are supposed to wash out. By doing this, we can make sure that one of the biggest pollutants from construction sites does not reach our waterways.