Natural wetlands treating mine drainage

Woodcutters Mine, Northern Territory, Australia


Since mining began in 1984, excess water from the Woodcutters lead-zinc mine has been discharged into a small, intermittent creek (Woods and Noller, 1995). Mine dewatering initially produced in excess of 35 ML/day (ca. 25,000 L/min), but now produces up to 10 ML/day (ca. 7000 L/min). The mine drainage is discharged into a 150 x 2,000 m channel. This constant inflow caused large stands of cattails (Typha orientalis) and sedges (Eleocharis spp.) to develop naturally (see Photo 1).

Woodcutters Creek, Northern Territory, Australia

Photo 1. J. Milne, Northern Territory Dept. Mines & Energy, Australia.

The saline, carbonate-rich discharge is buffered against acidification from the oxidation of sulphides in the ore and the waste rock. However, it contains elevated concentrations of cadmium, manganese, lead and zinc. Soon after the wetland developed, mine workers noticed that concentrations (and total loads) of these metals were reduced in the wetland by 95% or better, to below acceptable environmental standards (Noller et al., 1994). Data from the mine are shown in below. Ammonia and nitrate are also reduced as water flows through the wetland.

Metal concentrations (ppb) in discharge from Woodcutters Mine.
Sampling point
As
Cd
Cu
Mn
Pb
Zn
Wetland inflow (0.0 km)
5
63
1.4
600
12
6,900
Mid-point (0.8 km)
3
63
1.7
580
7.3
5,600
Wetland discharge (2.0 km)
1
7.8
0.6
17
<0.2
1,700

ChartObject Sulphate Load (t)

Annual loads of sulphate in and out of the natural wetland in Woodcutters Creek

ChartObject Cadmium Load (t)

Annual loads of cadmium in and out of the natural wetland in Woodcutters Creek

ChartObject Lead Load (t)

Annual loads of lead in and out of the natural wetland in Woodcutters Creek

ChartObject Zinc Load (t)

Annual loads of zinc in and out of the natural wetland in Woodcutters Creek


I'd like to thank my colleague Peter Woods, Senior Environmental Scientist at ERA Ranger Mine, for providing me with the photograph of Woodcutters Creek and much information on wetlands in Australia

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