Concrete Washout: What It Is, Site Rules & Best Practices for Managing Wash Water
- Kelly Bryant
- Mar 20
- 10 min read
In this article, Kelly Tanks shares over 10 years of industry experience to highlight best practices for concrete washout and wash water management. We explore the environmental risks and operational challenges associated with washout and concrete wash water, as well as the regulations construction sites must follow to remain compliant.
Contents
What Is Concrete Washout?
Concrete washout is the process of washing out concrete trucks, pumps, or equipment on construction sites. During this process, highly alkaline wash water is produced. Because concrete contains alkaline materials such as cement, the wash water can reach high pH and must be properly contained to ensure regulatory compliance and prevent environmental contamination.
Concrete washout typically takes place on construction sites after concrete deliveries or pumping operations, when trucks and equipment must be cleaned before leaving the site.
Why Concrete Washout Is a Problem
The issues with concrete washout aren't in the washout itself, but with the wash water produced as a by-product. The three main challenges are environmental, operational, and regulatory.
Environmental risks
Concrete washout can pose several environmental risks due to the highly alkaline nature of concrete wash water. The most significant risks include:
High alkalinity (pH 11+)
Pollution of rivers and streams
Harm to aquatic life
The high alkalinity of concrete wash water is the primary cause of environmental harm.
At high pH levels, wash water can cause direct harm to the gills and skin of fish and other aquatic life, impairing their ability to regulate salt and water intake and absorb oxygen.
This can lead to mass fish deaths and long-term impacts on aquatic populations, including reduced growth rates and reproductive success.
The less toxic ammonium ion shifts to the highly toxic, unionised ammonia form. This greatly increases the risk of ammonia poisoning, which is lethal to many fish species such as salmon.
When algae die and decompose, the process depletes dissolved oxygen levels, creating hypoxic conditions (dissolved oxygen levels too low to support aquatic life).
Soil contamination and vegetation damage
A high pH causes essential nutrients to become less soluble and harder for plants to absorb. It can also cause the soil to harden, making it difficult for roots to penetrate the surface and reducing drainage.
The lack of essential nutrients available to plants can lead to problems such as chlorosis (yellowing leaves caused by an iron deficiency), stunted growth, unhealthy roots, necrosis (leaf edges appear burnt and brown), and a reduced crop yield and quality.
Groundwater pollution
Sediment pollution in waterways
One of the main issues with high-pH runoff contaminating groundwater is the high levels of dissolved calcium and magnesium found in highly alkaline wash water. These mineral ions precipitate as solid deposits that encrust pipes and valves, reducing water flow. Additionally, they reduce the effectiveness of chlorine disinfectants that would commonly be used to treat groundwater for consumption, leaving the water more vulnerable to microbial contamination as higher chlorine levels are required for effective treatment.
Sediment pollution in waterways can occur when hardened concrete particles enter water systems, reducing sunlight penetration and hindering photosynthesis for aquatic plants. Furthermore, high turbidity and suspended solid levels decrease oxygen production and hinder fish from finding food.
Operational Risks
Concrete washout can also create a number of operational challenges on construction sites, particularly when wash water is not properly managed. These include:
Blockages in onsite drainage systems
Hardened concrete build-up in pipes and equipment
Limited space on construction sites
Because concrete contains cement, sand, and aggregates, wash water can cause severe blockages in drainage systems when not properly treated. This is because when wash water enters pipes, the suspended solids settle, with the cement curing to create solid obstructions that restrict water flow, often referred to as "concretebergs".
Limited space can also pose challenges on construction sites in urban areas, making it difficult to find a suitable location for a concrete washout station.
Construction delays
Increased maintenance requirements
Worker safety hazards
Concrete washout without the proper equipment and systems for managing wash water can cause significant delays on construction sites, as setting up impermeable containment areas is time-consuming and requires regular monitoring.
The chemical treatment of wash water using either acidic reducers or CO₂ is also an ongoing cost in both time and budget, as these chemicals need contact time to be effective.
The safety of workers throughout the concrete washout process is vital, as wash water can cause severe skin burns and poses a significant health risk. Spills can lead to health and safety incidents on-site, which will cause work stoppages for inspections or clean-up.
Additional waste management and disposal costs
Increased transport requirements for waste disposal
Difficulty managing large volumes of concrete wash water
If concrete wash water is not treated, it is classed as hazardous waste, which is very costly to have treated externally. Furthermore, landfill disposal costs for sediment and hardened concrete can quickly increase if not properly separated from the water.
On-site storage may also be a problem if your site is using a lot of concrete, as containing large volumes of wash water without spills requires skips, trays, or tanks. If wash water volumes are not properly planned for, it can easily escalate to the point that you require expensive tanker removal.
Concrete Washout Regulations in the UK
The main enforcer's of regulations on Concrete Washout in the UK is Environment Agency, who released the Regulatory Position Statement for concrete wash water (RPS 287).
The primary objective of RPS 287 is to outline conditions under which construction sites can treat and use water that has come into contact with concrete without requiring an environmental permit. The intent is to prevent pollution while still facilitating necessary construction activities.
Conditions for Treatment and Use of Water
1. Treatment Process
Neutralisation:
Water must undergo a treatment process to neutralise its pH. This is typically achieved by adding acids or carbon dioxide. The aim is to ensure that the water is safe for release into the environment or for reuse on the construction site.
Sediment Removal:
Before discharging or reusing water, it's crucial to remove any sediments or solids. This step is essential to maintain the quality of the water.
2. Use of Treated Water
On-Site Reuse:
Once treated, water can be reused on the same construction site as long as it meets the required safety standards. This can be an efficient way to minimize water usage during construction.
Discharge to Surface Water or Sewer:
If the intention is to discharge treated water, it must meet specific environmental standards. This helps prevent any potential pollution that could harm local ecosystems.
For more information on these regulations, please visit our article breaking them down in detail:
For more information regarding the effects of wastewater onsite, please visit our article on water management:
Concrete Washout Best Practices
There are 4 key steps to ensure an efficient and compliant concrete washout and wash water management while minimising the chance of environmental harm.
1. Designated washout area
When deciding on a designated washout area, you should first look at location. A strategically placed washout area should be a minimum of 10m from any watercourses or drains but ideally as far as logistically possible to limit damage.
The washout area needs to be accessible by concrete trucks but also need enough space to operate safely. Ensuring the area chosen is on stable, level ground is the best way to avoid tipping or accidental spills leading to pollution.
2. Secure containment
Whatever you decide to use for containment must be impermeable, waterproof and durable to prevent any runoff seeping into the ground. Ensure you are adequately prepared for the volume of wash water you will need to contain during treatment. Allowing for a minimum of 10% empty space prevents overflow in the case of unforeseen heavy rain.
3. Separation
Concrete washout water contains a number of suspended solid particles such as cement particles, sand, and aggregates. These need to be settled or filtered or out before discharge to remain compliant
4. pH treatment and monitoring
After separating the solids, you need to treat the pH of the highly alkaline wash water before discharge. This can be done using an acidic reducer or C0₂, ensuring they have enough contact time to reduce the pH to a compliant method.
Concrete Washout Solutions and Systems
At Kelly Tanks we have developed a number of solutions and systems to tackle every problem in concrete washout. We not only offer the largest fleet of concrete washout systems in the UK, but also the widest range of solutions available.
CWS Concrete Washout System
The CWS concrete washout system is a closed-loop system which means it only needs to be filled once as it recycles concrete wash water indefinitely to continue to use for future washouts. This provides a significant benefit, as it leaves you with considerably less concrete wash water to treat.
It works by allowing operators to wash off concrete trucks using a hose supplied by a built-in water tank, retaining the solids in an adsorption sack specially designed to allow the fast flow of water whilst capturing solids and oil residue. The filtered effluent can then drain while contaminants are adsorbed by the sack.
Manual pH neutralisation is easily carried out using KT liquid reducer, however, the pH of the concrete wash water must always be checked before discharge. If you're looking for automatic pH control, the CWS Ultra may be the solution for you.
CWS Ultra and Double Washout
The CWS Ultra builds on the CWS with several additional features and improvements, including automatic pH neutralisation of the wash water using CO₂. It also has a higher volume pump for optimum hose pressure, and an increased capacity of 1000 L.
If you are dealing with large volumes of concrete, you may need an even higher capacity.
The Double Washout retains all the improvements of the CWS Ultra, but with the added benefit of an additional adsorption sack. This not only doubles its capacity but also allows for continuous washout, because one adsorption sack can continue to be used while the other is being changed or left to drain, minimising operational delays.
Mini Mobile Washout
Primarily designed for small tools, the Mini Mobile Washout System is a portable concrete washout system fitted with wheels making it easily transportable around construction sites. It is the perfect solution for confined spaces on-site, with an adsorption sack to retain solids and the same closed-loop system design as the CWS. It only needs to be filled once, before being wheeled away to where you're working, saving you a trip across site every time you need to wash your tools off.
Sack Frames for Concrete Washout
No power? No problem. Sack frames provide a cost-effective, robust solution for concrete washout. Available as a single, double, enclosed, or heavy-duty. The frames suspend the adsorption sacks in or out of water, retaining solids and oil residue whilst allowing effluent to filter and drain.
Frequently Asked Questions About Concrete Washout
Below are answers to the most common questions we receive about concrete washout, including best practices for managing concrete wash water on construction sites, it's environmental impact, and UK concrete washout regulations.
What is concrete washout water?
Concrete washout water is the highly alkaline wastewater produced when concrete trucks, pumps, or tools are washed after use. Because concrete is naturally alkaline, this water typically has a pH between 11 and 13 and contains suspended solids such as cement particles, sand, and aggregates.
Why is concrete washout harmful to the environment?
Concrete wash water is harmful to the environment because of its high alkalinity and suspended solids. If discharged without treatment, it can raise the pH of soil and watercourses, damage vegetation, and contribute to sediment pollution. Elevated pH levels can also disrupt aquatic ecosystems by reducing oxygen levels and increasing the toxicity of compounds such as ammonia.
What are the regulations for concrete washout in the UK?
Concrete washout in the UK is regulated by the Environment Agency. Guidance is outlined in Regulatory Position Statement 287 (RPS 287), which sets out the conditions under which concrete wash water should be treated and recycled on construction sites without requiring an environmental permit. To remain compliant, wash water must be treated with the sediment filtered or settled out before it can be re-purposed or discharged.
How is concrete washout water treated?
Concrete wash water is commonly treated by first removing suspended solids such as cement particles, sand, and aggregates through settlement or filtration. The remaining alkaline water is then neutralised by reducing the pH, typically from around 11–13, using acidic reducers or C0₂.
Where should a concrete washout area be located onsite?
Best practices recommend concrete washout area should be located at least 10m away from any watercourses, drainage and on stable, level ground. The location needs to be accessible location for workers and concrete trucks, without disrupting the work flow onsite.
What happens if concrete washout water is not managed properly?
If concrete washout water is not properly managed, it can lead to environmental pollution and compliance breaches. Highly alkaline wash water can damage aquatic ecosystems, contaminate watercourses, and harm vegetation, while untreated solids can block drainage systems. Poor management may also result in regulatory penalties, increased clean-up or remediation costs, and reputational damage for both contractors and site operators.
Is concrete wash water hazardous waste?
Yes, concrete wash water is classed as hazardous waste because of it's high pH due to the alkalinity of concrete. This means that it's illegal to discharge without treatment, and is costly to have removed and treated externally.
Conclusion
But why does all of this matter? Concrete washout is a vital part of construction that is often overlooked. What may seem as a small job in the grand scheme of things, can pose huge problems if not properly managed.
The high alkalinity of wash water makes it a danger to both workers and the environment if left unmanaged. Combined with the operational challenges and potential regulatory penalties for compliance breaches, failing to follow best practices can quickly become costly in terms of both money and reputation.
Establishing a designated washout area away from drains or watercourses and on flat, stable ground, using waterproof and leak-proof containment systems that are not overfilled, separating solids, and neutralising the highly alkaline pH of wash water are the key steps to effective concrete washout management. Following these steps greatly reduces the risk of pollution and compliance breaches.
If you have any more questions about concrete washout or wastewater management, we have a range of related articles linked below. Alternatively, if you have a more specific query, we invite you to contact us at:
Related articles:
Comments