After concrete has been placed at a construction site, the chutes of ready mixed concrete trucks and hoppers must be washed out to remove the remaining concrete before it hardens. This washout water can be extremely damaging to aquatic life if allowed to reach surface waters. Not only does it contain various toxic metals, it's also extremely caustic (pH ~12) and corrosive. The best best management practice objective is to collect and retain all washout water in leak proof containers and allow to evaporate, leaving only the hardened solids to be recycled. There are many different types of washout containers that can either be attached to individual trucks or located on the construction site for communal use. If a communal container is chosen, it must be sized and maintained to have adequate capacity at all times and should be placed in locations that provide convenient access to concrete trucks.

The site superintendent should make ready mixed truck drivers aware of washout facility locations and include concrete washout requirements in contracts with concrete delivery companies. Improper dumping of cementitious material is considered an illicit discharge and subject to enforcement through Chapter 50.

A chute washout box is mounted on the back of the ready mixed truck and is used to capture all washwater and solids. A filter basket is collects coarse agrregates for reuse on the construction site, while everything captured in the box is returned to the ready mixed plant for recycling.

Trucks can also attach a bucket to the end of their chute and pump their washout back into the truck's drum to be returned to the ready mixed plant. A removable screen at the bottom of the washout bucket prevents coarse aggregate from entering the pump.

Concrete washout facilities, such as washout pits and vinyl or metal washout containers, should be placed in locations that provide convenient access to concrete trucks, preferably near the area where concrete is being poured. However they should not be placed within 50 feet of storm drains, open ditches, or waterbodies. Appropriate gravel or rock should cover approaches to concrete washout facilities when they are located on undeveloped property. On large sites with extensive concrete work, washouts should be placed at multiple locations for ease of use by ready mixed truck drivers. If the washout facility is not within view from the pour location, signage will be needed to direct the truck drivers.

Concrete washout facilities should be inspected daily and after heavy rains to check for leaks or damage from construction activities. If a washout container is filled to over 75 percent of its capacity, the washwater should be vacuumed off or allowed to evaporate to avoid overflows. Then when the remaining cementitious solids have hardened, they should be removed and recycled. Damages to the container should be repaired promptly. Before heavy rains, the washout container’s liquid level should be lowered or the container should be covered to avoid an overflow during the rain storm.

• EPA Stormwater Best Management Practice - Concrete Washout