Managing Concrete Wash Water On Construction Sites

Where concreting operations, producing less than 1,000 litres of wash water, extend longer than 12 consecutive weeks (or involve an intermittent discharge over a longer period), advice needs to be sought from the EA regarding permitting. Sites generating more than 1,000 litres of high pH water per week may require an environmental permit prior to commencing discharge to either surface or ground water. Those generating more than 2,000 litres per week will require both a bespoke environmental permit and a full treatment system before any treated concrete wash water can be discharged into the environment. However, given that the permitting process will take at least 12 weeks, contractors operating larger sites may prefer to seek approval from their water utility company to discharge the water to sewer or simply tanker it off site.

The new guidance by the Environment Agency (EA) on the treatment and disposal of concrete wash water is a welcome step forward in reducing pollution from building sites, according to Dr Richard Coulton of Siltbuster, the wastewater solutions provider to the construction industry. The clarification is set out in a regulatory position statement (RPS) entitled “Managing concrete wash water on construction sites: good practice and temporary discharges to ground or to surface waters”.

While the RPS provides clear guidance on the environmental permitting and treatment needs for the disposal of wash water generated from rinsing truck mixer chutes, Dr Coulton is concerned that time-pressured site managers may be tempted to ignore the advice and risk fines or prosecution. “Construction managers need to understand how this affects their sites and plan ahead to ensure the treatment and disposal of concrete wash water is managed professionally,” he comments.

Different environmental permitting and treatment needs are based on the number of truck mixer movements and, hence, the estimated volume of high pH wash water generated. Under the RPS, sites are classified as small, medium, large or very large depending on the number of concrete deliveries received per week and the resultant amount of high pH water generated. Sites receiving fewer than ten truck loads of concrete per week are categorised as small, whilst those receiving more than 100 loads per week are categorised as very large.

However, the RPS does not address the issue of high pH water generated from washing other equipment used to handle wet concrete, such as concrete pumps and batch plant. Consequently, categorising a site solely on the number of mixer truck movements can significantly underestimate the risk posed to the surrounding environment. To counter this, Dr Coulton suggests categorising each site on the total volume of high pH water generated, rather than the number of concrete trucks movement. On this basis, a site generating less than 200 litres per week of high pH wash water would be classified as small, whereas one generating in excess of 2,000 litres per week would be deemed to be very large.