When ready-mix trucks, pumps, chutes and tools are rinsed, the water carries cement fines and is highly alkaline (high pH). Washed into a storm drain or onto the ground, it can harm aquatic life and contaminate soil and groundwater.
What the EPA Construction General Permit requires
Under EPA's 2022 CGP, wastewater from concrete washout is a prohibited discharge unless managed by an appropriate control, and wastewater from washing out stucco, paint, form release oils, curing compounds and other materials is prohibited. For washing applicators and containers of these materials, the permit requires operators to:
- Direct wash water into a leak-proof container or a leak-proof, lined pit designed so no overflows occur from inadequate sizing or rain.
- Not dump liquid wastes into drainage features, storm inlets or receiving waters, and not dispose of them on the ground or by infiltration. Follow state, tribal and local disposal rules.
- Remove and dispose of hardened concrete with other construction waste.
- Locate washout activities as far away as possible from receiving waters, drainage features and storm drain inlets, and use designated areas.
State permits have similar or stricter rules.
Washout options
| Option | How it works | Notes |
|---|---|---|
| Prefabricated washout containers | Rented steel or plastic bins delivered and serviced by a vendor | Leak-proof by design; vendor pumps and hauls |
| Lined pit | Excavated or bermed area lined with heavy plastic sheeting without seams or tears | Must be sized and maintained; liner punctures are common |
| Above-ground lined structure | Straw bales or lumber frame lined with plastic | Quick to build; check liner and walls often |
| Truck-mounted / chute washout systems | Collect washout at the truck for return to the plant | Reduces on-site washout volume |
Setup tips
- Size for the expected number of trucks and pours, plus rain.
- Place it near the pour but away from inlets, ditches and waters, on level ground.
- Post a "Concrete Washout" sign and tell drivers and pump operators where it is.
- Protect it from traffic damage and keep the liner free of tears.
Maintenance and disposal
- Inspect at every SWPPP inspection and during pours.
- Don't let it fill to overflow. Many contractors pump or replace it when it reaches about two-thirds to three-quarters full, before rain does the rest.
- Let water evaporate or have it pumped and hauled per local rules; break up and dispose of hardened concrete with construction waste.
- Replace damaged liners immediately.
See all pollution prevention practices in lesson 7.
Sources and official references
Last reviewed: October 25, 2026 · Free general education based on the Clean Water Act, EPA NPDES rules and the EPA Construction General Permit. Your governing permit (EPA, state, tribal or local) controls. This is not legal advice, not EPA-approved, and not a California QSP/QSD or other state credential, and it does not issue a certificate. Nothing you enter on this page is saved or sent.