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Published: 2004-06-28 00:00:00

Environment Waikato is warning concrete companies to watch what they do with wastewater following the fining of a Waikato company for allowing concrete wash water to flow into stormwater.

A Waikato company was fined $750 for allowing water from washing an exposed aggregate driveway to enter stormwater which led to a waterway at a Raglan subdivision development. The wash water killed a large number of native fish.

Resource Officer Brett Moore said the lime content of concrete raised the pH of water, making it toxic to most aquatic life. In Auckland a firm was fined $11,000 for discharging concrete wash water and the offence carries a maximum penalty of $200,000 and two years’ imprisonment.

“The primary issue is the washing of concrete to expose the aggregate, a technique which has been made popular by many home improvement television programmes in recent years, although washing concrete mixers, wheelbarrows and other tools contributes to the problem too.

“Firms are washing down exposed aggregate or concrete chutes without thinking about the consequences. Many don’t have management plans for dealing with concrete wash water.

“There is a considerable volume of concrete-contaminated water generated when laying exposed aggregate concrete. Any water contaminated with concrete washings is toxic when it gets to our streams and lakes. People need to be aware that the stormwater grates on the roadside and downpipes off roof gutter systems lead straight to natural waterways with no treatment,” he said.

He said firms needed to think about what they were going to do with wash water to keep it out of stormwater, such as diverting it onto land or blocking off stormwater outlets and pumping it onto land. Water could also be collected and discharged into a sewer with permission from the local council.

Some contractors use water blasters to reduce the volume of water that is generated, making it easier to soak the water away into the soil.

“We are approaching concrete firms warning them of the consequences of allowing toxic wash water to flow into waterways and we will be forced to take a hard stance on offences.”
Water used for cooling concrete cutting blades also had a high pH from concrete finings, and contractors were liable for making sure this water did not flow into stormwater drains and into waterways.

“There is a great deal of new development going on around the Region, particularly in Raglan and all these properties have driveways and other constructions that use concrete. Firms should ensure they have management plans to deal with the wastewater,” he said.