Guidelines for Managing Concrete Wash Water

Introduction

Under the Environmental Permitting (England and Wales) Regulations 2010 (as amended in 2012) and the Water Resources Act 1991 (as amended), it is on offence to discharge polluting substances to controlled waters (surface water and groundwater) without prior approval from the Regulators (Environment Agency (EA) England or National Resources Wales (NRW).

Therefore, measures to control, store and treat concrete wash water prior to discharge will need to be implemented.  Failure to implement control measures may cause a significant pollutant to be released into the environment, having the potential to pollute both land and the aquatic environment.

It is therefore necessary to develop control over the washing down of any plant or equipment that has come into contact with fresh concrete.

Why Control of Concrete Wash Water is Important?

The chemical processes (chemical reactions) that cause fresh concrete to slowly stiffen and harden (set) are very complex.  A by-product of these reactions is the production of calcium hydroxide, a highly alkaline chemical that has a natural pH in excess of 12.

For comparison purposes drinking water has a pH of circa 6.5 to 7 and a strong acid a pH of circa 2 to 3.  Typical pH limits stated with a discharge permit stipulate pH limits of between 6 and 9 for discharges into the aquatic environment.  The environmental risk can be measured by far away the pH is from pH 7.

The release of untreated highly alkaline concrete wash water into the aquatic environmental (surface water or ground water) can have devastating effects on the health and bio-diversity of the receiving waterbody.

To make it even worse, the pH scale is non-linear, it is in  fact a logarithmic scale.  This means that every single unit change in pH for example pH 6 to 7 represents a tenfold increase in strength.

pH

Quantity of pH7 water required to dilute 1 litre of each pH level to pH 7 (Neutral).

Neutral

0 litres

Common pH Range of Concrete Washwater.

10 1,000 litres
11 10,000 litres
12 100,000 litres
13 1,000,000 litres

 

Even the release of relatively small volumes of concrete washwater can have devastating long lasting effects on the health of the receiving watercourse.  Small volume of alkaline concrete wash water can be a significant source of pollution.

Why Dilution can’t be the solution?

Because the pH Scale is a logarithmic scale, a huge dilution factor is needed to dilute concrete water to a safe level.  For example to dilute 1 litre of pH 12 concrete waste water, would need approximately 100,000 litres of tap water.

If these large dilution rates are not accurately achieved, then are actions would simply just have increased the problem on a massive scale rather than fix it.

Concrete Wash Water Can Harm the Environment

September 2007

Council and Contractor in court following pollution resulting from bridge strengthening works

What Happened

The Damage

A contractor was employed by the Council to make repairs to a bridge.

As part of these works, a new concrete structure was needed to strengthen the bridge.

Strengthening works should have been carried out in dry conditions

When interviewed the Contractor admitted that some water had passed across the area where the concrete had been poured.

The Court heard that cement is highly alkaline and can be fatal to fish.

The stream turned milky white in colours and had an elevated pH.

Dead fish were reported over a 1.5 km stretch downstream of the bridge.

Some 4,000 fish were killed

 

Concrete Wash Water Can Harm the Financial Health of a Company

On the 1st July 2014, new guidance was issued to the Courts setting out the level (size) of the fines that are to be handed out by the Courts for Environmental Offence (Environmental Sentencing Guidelines).

A Category 1 (most severe) pollution incident such as that described above would now see a company facing fines of between £300,000 to £1,000,000 (Assuming that the polluting Company has an annual turnover of £50 million).

In addition to having an detrimental impact on the health of a water body, a pollution incident can, if you are found guilty have a detrimental impact on the financial health of the offending company

 

Managing Concrete Washwater

Effective concrete washout area serve two functions.  These are:

  • Containment of slurry and solids.
  • Containment of liquids generated during the washing down of chutes, concrete mixers, hoppers of concrete pumps or other equipment which has come into contact with fresh concrete.

Concrete wash water has a highly alkaline pH (circa pH 12) which if released has the potential to pollute land and leach into the ground and contaminate groundwater.  The release of concrete wash water can also increase the pH of surrounding waters and has the potential to harm aquatic life and cause pollution of waters, including storm water.

In addition to the environmental harm that the solids can cause by: affecting the turbidity of the water, blocking gills of fish and smothering the bed of the water body; the improper disposal of the solids can cause blockages of streams, drains and pipes and increase the risk of flooding.

The use of a properly design, installed and operated wash out facility not only assists in preventing pollution but is also a matter of good housekeeping.

Planning and Design

The details of the designated concrete wash out facilities should be determined during establishment on site and should be clearly identifiable on site plans.

Site documentation should show:

  • The location of the concrete washout facility.
  • How the concrete wastes are going to be stored.
  • How the concrete wastes will be collected from these storage points.
  • Where the wastes will be taken to and/or how they will be treated and disposed.
  • How any treatment systems to treat the liquid phase and/or recover the solids will be operated and maintained.

As a minimum the concrete wash out system must securely capture, contain and store the concrete solids and washwater in an impervious bund.  Whenever possible the liquid phase should be treated to ensure it’s safe disposal or to allow it to be safely reused (recycled).  That is the washwater system is operated on a closed loop basis reducing the demand for water, minimising the amount of waste which is produced.

Site personnel, particularly those responsible for concrete delivery and pumping, should be made aware (via induction, toolbox talks, pre-starts etc.) that a wash-down area is available on-site and when and how it is to be used.

Location and Management of Washout Areas

The following management measures should be considered as a means of minimising the potential impacts of concrete washout areas on the environment:

  • The washout area should be located away from drainage gullies, surface water drains and water bodies.
  • The concrete washout area should be conveniently located for washing out equipment and clearly signposted.
  • All wash down water should be contained within an imperious bund, treated to  enable re-use or disposal.Alternatively the wash water should consigned correctly for off-site disposal at a suitably licenced waste management facility, in accordance with the Duty of Care for Waste Management.
  • Concrete washout areas are generally not designed for the collection and treatment of excess concrete.Excess concrete waste should be returned to the local batching plant for treatment and re-use, or placed in a site receptacle designated for concrete masonry, and allowed to set.
  • To minimise the amount of washout water generated, excess concrete should be scraped off the equipment before it is washed.  These excess solids should be placed in a designated site storage container.
  • A high pressure, low volume water spray nozzle reduces water use.

Monitoring

All concrete washout areas should be monitored and maintained to ensure that they are functioning correctly and have adequate storage capacity.  As a minimum monitoring should be undertaken at a minimum frequency of:

  • Weekly during dry weather.
  • Prior to forecast rainfall events.
  • During rainfall events.
  • As soon as practical following rainfall events.

Set concrete and wash water should be removed as required to ensure that the facility has sufficient capacity and prevent overtopping.

Reporting

An environmental incident occurs if:

  • Concrete is washed out in an area other than the designated concrete washout area.
  • Mismanagement of the concrete washout leads to a release of concrete washout to land, surface water or the drainage network.
  • Excessive volumes of washwater are stored in the washout facility causing it to overtop (soak into the ground).
  • The lining of the washdown facility is punctured allowing the washwater to escape into the environment.
  • Records should be maintained detailing the off-site waste management facility used to dispose of the liquid or solids.

In the event that an environmental incident occurs then this occurrence should be reported in accordance with the sites reporting procedure.

Developing an Action Plan

  1. Plan and implement your wastewater control measures before starting your job.  Also plan and prepare for a spill should it occur.
  2. Control the volume of water used when washing down concrete surfaces, or cleaning mixers, wheelbarrows or tools (Minimise the size of the problem).
  3. Spilt or surplus cement products (mortar and concrete) should be allowed to harden and disposed off to landfill or recycled to allow beneficial re-use.
  4. Contain the wash water and slurry.  Direct any run-off into a waterproof sump or secure thank, monitor to ensure that overtopping does not occur and identify any deterioration in the integrity (waterproofness) of the structure does not occur.
  5. Identify any deterioration in the integrity (waterproofness) of the structure, prior to a leakage (breach) occurring.  Repair as necessary.
  6. Do not try to dilute the run-off and dispose of it into the surface drainage system; this will only make it worse.
  7. Ensure that you clean up after yourself once the job has been completed.

Source:  Watery News  20th July 2016