Drainage without polluting waterways

By - , Build 160

Take care that pollutants such as clay and concrete waste don’t get into stormwater drains. The consequences can be severe, and resource consent inspectors visiting your site will be checking.

Never let concrete slurry or wastewater enter stormwater drains on your site or on the road.
Never let concrete slurry or wastewater enter stormwater drains on your site or on the road.
Figure 1: Installing a silt fence on sloping sites captures sediment run-off.

UNLIKE the wastewater system, water that goes down stormwater drains flows straight into local streams and the sea without being treated.

Only want rainwater down stormwater drains

Anything else going down such as mud, concrete and paint pollutes waterways and everything that lives in them.

For example, concrete and cement products are extremely toxic and can raise the pH levels of streams, killing wildlife. It takes 100,000 litres of freshwater to dilute just 1 litre of concrete slurry to safe levels.

The consequences aren’t only severe for wildlife. Discharging contaminants to stormwater drains can result in a $750 fine under the Resource Management Act and the possibility of further court action.

One of the things resource consent inspectors look for on site is the environmental controls you have in place to prevent contaminants such as sediments, clays and concrete products entering the stormwater network.

Put controls in place to do it right

Here are some easy, inexpensive tips to ensure clean rainwater is the only thing that goes down stormwater drains at your site:

  • Create a stabilised entranceway for your site by putting down GAP 65 aggregate. This gives tradespeople a place to park and stops them driving over exposed clay or dirt and tracking it onto the road.
  • Install a silt fence on the downhill side of sloping sites to capture sediment run-off (see Figure 1).
  • Keep stockpiles of sediment or soil behind your silt fence, or cover them with plastic sheeting or hay mulch.
  • Keep as much grass coverage on site as possible.
  • Before pouring concrete, de-water pile holes and footings to stop slurry spilling out and into drains.
  • Never wash concrete equipment where run-off may enter a stormwater drain – wash on unsealed ground such as grass or gravel.
  • Remember, you are responsible for your subcontractors, so ensure delivery companies or pumpers don’t wash concrete slurry to the stormwater drains.
Figure 1: Installing a silt fence on sloping sites captures sediment run-off.

Quiz

1. Outside stormwater drains flow:

a. to a treatment plant

b. to local streams and the sea

c. nowhere.

2. How deep should a sediment fence be dug into the ground?

a. 500 mm

b. 200 mm

c. It should sit on top of the ground.

3. How many litres of freshwater does it take to dilute one litre of concrete slurry?

a. 10 litres.

b. 1,000 litres.

c. 10,000 litres.

d. 100,000 litres.

4. A stabilised entrance way with GAP 65 aggregate should be installed to:

a. park on

b. keep the road clean

c. gain better access to your site

d. all of the above.

5. How much is an RMA fine for discharging pollutants to the stormwater system?

a. $300.

b. $500.

c. $750.

d. $1,000.

Answers

1. b   2. b   3. d   4. d   5. c

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Never let concrete slurry or wastewater enter stormwater drains on your site or on the road.
Never let concrete slurry or wastewater enter stormwater drains on your site or on the road.
Figure 1: Installing a silt fence on sloping sites captures sediment run-off.

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