Cement powder, workable concrete and grout are extremely alkaline. You may also hear this referred to as a high pH.

There are several construction processes that risk contaminating water in this way.

Where shafts are to be sunk wet (ie material is removed from below the water level in the shaft), there is a risk of the water in the shaft becoming highly alkaline when the concrete base is poured.

When using dry-mix concrete to set kerbs or paving, water that runs off may be alkaline and, if so, needs to be contained.

Civil engineering works that use workable concrete close to watercourses or groundwater, such as cast in situ piling or bridge works.

Cement powder, workable concrete and grout can be highly polluting to water if released into the environment.

What you must do

If you are using concrete or grout, ensure that they are contained within your working area and do not enter any watercourses or surface water drains.

If you are pumping concrete or grout into the ground, keep records of the quantity that you are using. If you find that you are using larger quantities than you expected it is possible that these materials are escaping into the ground and potentially polluting groundwater.

If you are mixing grout on site, construct a suitable barrier around mixing areas, supply lines and around working areas to prevent its escape.

Run-off from concrete operations and concrete wash out water are highly alkaline, which can cause water pollution.

Concrete also contains chromium, which is potentially polluting not only to watercourses but also to groundwater.

Trucks, hoppers, mixers and concrete pumps that have contained concrete must be washed out in a contained area, see ‘management of concrete wash out areas’ below.

Management of concrete wash out areas

It is important to carefully choose the location of any concrete wash out or batching areas on site. These should be sited away from any watercourses or drainage channels to prevent accidental escapes of liquid or slurries to the water environment.

You should put on place measures to control, store (and treat) concrete wash water and waste arising from the process on site.

Dealing with wash down water

Wash down water arising from the washing of equipment that has come into contact with concrete must be collected in an impervious container and, if possible, treated to enable recycling/re-use within the wash down area or concrete batching process.

Important note: It cannot be used for wheel washes or dust suppression purposes.

Wash water that has been in contact with cement is alkaline in nature. It is not good practice to dispose of this liquid on site.

If disposal on site is necessary then you will require an authosisation from your environmental regulator. This would be classed as a discharge of effluent either to water or to groundwater.

You would have to treat the effluent prior to discharge, which may include pH adjustment, CO2 aeration etc.

Alternatively, wash water can be sent off-site to a licenced facility for treatment and/or disposal, in accordance with the Duty of Care for Waste.

Solid fraction

Excess cement products (mortar and concrete) should be allowed to harden and you can use them as general fill on the site as required.

Alternatively solid material can be sent off-site to a licenced waste management facility in accordance with the Duty of Care for Waste Management.

Good practice

Only order the amount of concrete or grout that you need. Where you have several smaller areas that require concrete, plan your works so that you can pour more than one of these areas at once.

When preparing method statements and risk assessments, include information on:

  • testing the water prior to disposal
  • treating the water if necessary to reduce its alkalinity
  • how the water will be disposed of.

Supply good quality gloves for people working with concrete to reduce the quantity of gloves that you have to order and later dispose of.

Follow the pulverised fuel ash quality protocol in Northern Ireland

The pulverised fuel ash (PFA) and furnace bottom ash (FBA) quality protocol means that PFA and FBA will no longer be classified as waste when used in bound and grout applications, providing you meet the criteria set out in the quality protocol. This means PFA and FBA can be used without waste management controls.

For example, if it is not classed as a waste, you do not need to transport it using a waste carrier or with a waste transfer note.

The quality protocol for PFA applies in Northern Ireland.

GOV.UK: Pulverised fuel ash quality protocol

In Scotland: You can use pulverised fuel ash on construction sites under a Paragraph 19 exemption if you meet certain requirements. 

SEPA: Activities exempt from waste management licensing

SEE ALSO: Settlement tanks, Protecting groundwater during drilling and boring

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