of relatively steep hills in the upper reaches of the Dee River catchment – factors which have facilitated
its oxidisation and transport offsite.
Sulphide minerals have been exposed to weathering for more than 100 years in some parts of the mine.
Inadequate past mine management practices have left the Dee River in a poor state, where pH is as
low as 2.8. High metal concentrations have been recorded in the Dee River next to the mine site during
periods of low flow (Wels et al., 2007). While there is no recent evidence of acidic flows extending
beyond the Dee River catchment into the Don, Dawson or Fitzroy rivers, there are anecdotal reports of
acidic flows extending into the Dawson River when the mine was still working (GreenGold, 2021).
Water quality in the Dee River network deteriorated over time due to ARD seepage from the OCP,
known as one of the main source points (Markham et al., 2003). In 2000, as a part of rehabilitation
planning for this site, the former Department of Natural Resources and Mines (DNRM) engaged EWL
Sciences Pty Ltd (Jones, 2001) to undertake a contaminant source study in which the Dee River was
monitored. Rehabilitation plans aimed to improve water quality downstream and enable greater usage
of water resources by preventing overflows from the OCP (Markham et al., 2003).
River water quality monitoring indicates impacts from the Mount Morgan mine site are most prevalent
in the first 20 km downstream (AARC, 2017a). The diversity of species in this section of the river is
greatly reduced, however some species do exist there. The water quality in the Dee River continues to
improve with distance downstream as it is diluted by other freshwater catchment inflows. Although
contaminated water seepage from the Mount Morgan Mine has a high level of sulphates (salts), the
water quality at the lower end of the Dee River is suitable for irrigation and livestock. The water quality
in the Dee River improves with distance downstream as it is diluted by large freshwater inputs further
down the catchment. Water quality at Duaringa (140 km downstream of Mount Morgan) is suitable for
potable use (GreenGold, 2021).
The DSITI Guidelines for draft environmental values and Water quality guidelines for Fitzroy Basin
fresh, estuarine and marine waters, including Keppel Bay (Newham et al. 2017) identify the Dee River
as a highly disturbed ecosystem with modified environmental values and water quality objectives.
In January 2013, ex-cyclone Oswald caused unusually intense rainfall over the Mount Morgan Mine
that resulted in the first-ever overtopping of the spillway of the OCP. The impacts of this runoff extended
down the Dee River for approximately 50 km. Despite this, monitoring on the Don River at Rannes
(approximately 70 km downstream of the mine) showed only very minor changes to water quality
(AARC, 2017a). Sampling of the Dee, Don and Dawson rivers after the January 2013 event showed
that water quality returned to pre-flood conditions shortly after the event.
Contaminated water seepage and runoff from the Mount Morgan Mine is currently managed by the
State via the seepage interception system. While this has reduced contamination loads, the system
cannot collect all contaminated water and water quality values in the Dee River remain adversely
affected. The effects of this can be observed in monitoring data downstream from the Mount Morgan
Mine in the Dee River.
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Wulguru Technical Services Pty Ltd – Supporting Information to Amend an Environmental Authority
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