After cementitious materials, such as concrete, mortar, plaster, stucco, and grout, have been placed on a construction site, the equipment used must be washed out to remove the material before it hardens. This equipment can include the chutes of ready mixed concrete trucks and hoppers, equipment such as wheelbarrows and hand tools, or mobile cement mixers.

This washout water, or wash 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. Rainwater polluted with concrete wash water can percolate down through the soil and alter the soil chemistry, inhibit plant growth, and contaminate the groundwater. Its high pH can increase the toxicity of other substances in the surface waters and soils.

The best management practice objective is to collect and retain all washout water in leak proof containers and allow it to evaporate, leaving only the hardened solids behind, which can then be recycled.

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 Dane County's Chapter 50 Ordinance.

Management practices for concrete washout must be designed to comply with the following:

1. Temporary concrete washout areas must be designated on all sites that will generate concrete wash water or liquid concrete waste from any onsite concrete mixing, tool washing, concrete delivery, or where mortar-mixing stations exist. Concrete washout activities must be conducted in a manner that does not contribute pollutants to stormwater runoff, surface waters, or groundwater.
2. Concrete washout areas must be constructed and maintained in sufficient quantity and size to contain all liquid and concrete waste generated by storage, handling, and washing operations.
3. The concrete washout area must be installed prior to concrete placement on site.
4. Concrete washout areas may be either a washout container that can be attached to individual trucks, or a facility located on the construction site for communal use. If a communal container is chosen it may be one of the following: a lined or unlined excavated pit in the ground, a commercially manufactured prefabricated washout container, or an aboveground holding area with a plastic liner constructed of berms, sandbags or straw bales.
5. When unlined pits are used for concrete washout, the soil must have adequate buffering capacity to result in protection of state groundwater standards; otherwise, a liner/containment must be used. Unlined concrete washout areas shall not be located in any of the following areas to prevent an impact to water quality:
   1. Within 100 feet of any sensitive resource areas, which includes but is not limited to; storm drains, open ditches, water bodies, springs, and wetlands.
   2. Within 1,000 feet of any wells or drinking water sources.
   3. In areas with high groundwater or soils with inadequate buffering capacity, such as sandy or silty soils.
   4. Sites where the use of a washout area will be longer than 1 year.
6. If site constraints in (5) make these setbacks infeasible or if highly permeable soils exist in the area, pits must have an impermeable liner with a minimum 10 mm thickness. Surface storage alternatives using prefabricated concrete washout devices or a lined aboveground storage area may also be used.
7. Auxiliary concrete truck components (e.g. chutes and hoses) and small concrete handling equipment (e.g. hand tools, screeds, shovels, rakes, floats, trowels, and wheelbarrows) may only be washed in the following locations:
   1. A washout facility, or;
   2. A formed area awaiting concrete pour where grade soils have been sufficiently compacted so as to limit vertical and horizontal drainage until the liquid portion of wash off evaporates, or is covered with surface pavement, or;
   3. A depression on site where the following conditions are met:
      1. Located where wash water cannot leave the site.
      2. Not within 100 feet of any storm drains, open ditches, water bodies, springs, or wetlands
      3. Adequate buffering to prevent infiltration to groundwater (e.g. is not sited on sandy soils).
      4. Adequate volume to contain all washout or harden prior to the next anticipated storm event.
8. At no time shall any concrete be washed off into the footprint of an area where a stormwater management practice will be installed.
9. Concrete washout facilities 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.
10. Concrete washout facilities should be inspected daily and after heavy rains to check for leaks, identify if any plastic linings and sidewalls have been damaged by construction activities, and determine whether they have been filled to over 75 percent capacity. When the washout container is filled to over 75 percent of its capacity, the wash water 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.
11. Upon termination of use of the washout site, accumulated solid waste, including concrete waste and any contaminated soils, must be removed from the site to prevent on-site disposal of solid waste. If the wash water is allowed to evaporate and the concrete hardens, it may be recycled. Holes, depressions, or other ground disturbances caused by the removal of the temporary concrete washout facilities must be backfilled and stabilized.

Different types of washout containers are available for collecting, retaining, and recycling the washwater and solids from washing down mixed truck chutes and pump truck hoppers at construction sites. Some systems attach to the back of the truck for individual use, but more common is to have a pit or large container for communal use located on the construction site. Examples of acceptable washout containers are shown below.

Chute Washout Box	Chute Washout Box with Pump
Hay Bale Washout Pit	Metal Washout Bin
Manufactured Washout Container

• EPA Stormwater Best Management Practice - Concrete Washout