TREATING ACIDITY IN COAL PIT LAKES USING SEWAGE AND ...

3 Introduction
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McCullough, Lund and May (2008)
Environmental legacies of open cut mining operations are the large voids created. Too large
to backfill and typically requiring extensive dewatering operations to keep dry, many are
destined to become large, deep lakes. In Australia, these new lakes have few natural
counterparts in size (especially depth) and are a potentially valuable new asset to rural
Australia. Despite considerable improvements in mining practices, acid mine drainage
(AMD) resulting from exposed overburden and void walls can result in these new lakes
becoming highly acidic. Worldwide AMD is potentially the largest negative environmental
impact resulting from coal mining (Robertson, 1987; Ryan & Joyce, 1991; Lowson et al.,
1993; Harries, 1998a, b). In Australia there are many well publicised examples of the
consequences of AMD from coal and other mineral mines including Rum Jungle (Northern
Territory), Captains Flat (New South Wales), Brukunga (South Australia), Mount Lyell
(Tasmania), and Mount Morgan (Queensland) (Zhou, 1994; Lawton, 1996).
Extremely elevated aluminium, iron and sulfate concentrations, combined with extremely low
dissolved carbon and other nutrients, are typical of AMD (Castro et al., 1999; Peiffer et al.,
1999; Fyson, 2000; Woelfl, 2000; Taylor & Waters, 2003). Dissolved metal concentrations
may be so high as to be toxic to most aquatic biota (Spry & Wiener, 1991; Bowell, 2000).
Although literature is sparse for sulfate toxicity (ANZECC/ARMCANZ, 2000a),
concentrations can also reach potentially toxic levels in these lakes. However, acid mine
drainage (AMD) waters also differ greatly between regions and geologies (Robb & Robinson,
1995; Johnson & Hallberg, 2003).
Australian data on remediation techniques specific to our pit lakes is sparse. The expensive
and high-maintenance operations of active remediation strategies (e.g. liming, anoxic
limestone drains) are often not appropriate to the remoteness, high dissolved metal
concentrations and high acidity of many Australian mine lakes (Brown et al., 2003; Taylor &
Waters, 2003). Furthermore, although dealing with low pH issues of AMD waters, active
remediation strategies are often not efficient at removing high dissolved concentrations of
metals such as iron and aluminium, or sulfate.