A survey of selected West Coast Streams was undertaken in Summer 2001,
Summer 2002 and Winter 2002 to establish the degree of arsenic (As)
contamination in waters and sediments downstream of old coal and gold mine
workings on the West Coast. Of the catchments studied, Soldiers/Ford Creek and
Rapid Stream showed the most significant elevated As concentrations,
predominantly in dissolved form, and evidence of AMD or ARD contamination (high
sulfate concentrations and/or acidity). The rate and processes of removal of
dissolved arsenic from the water column (attenuation) have been studied in these
catchments. The Rapid Stream and Soldiers/Ford Creek catchments are directly
affected by adit drainage from the Sullivan and Blackball coal mines
respectively. Both catchments have high As concentrations in the sediments, with
up to 770 mg/kg in Soldiers Creek and 490 mg/kg in Rapid Stream. Dissolved As
concentrations are significantly elevated in the neutral pH waters of Soldiers
Creek; typically as high as 100 - 200 g/kg, up to 500 m downstream of the main
adit discharge (800 g/kg As). Adit inflows to Rapid Stream were acidic and
contained 20 - 30 g/kg dissolved As, with relatively high concentrations of
arsenic in the stream water in winter (up to 18 g/kg), but not in summer.
Analysis of concentration trends and As:SO4 ratios downstream of these obvious
As sources confirmed that dissolved As had been actively removed from the water
column, but varied seasonally with greater removal evident in summer. Adsorption
of arsenic onto iron oxide in the stream sediments is the most likely mechanism
of removal. The Snowy River catchment, on the other hand, has relatively high As
concentrations in both the sediments and the water column, but there was little
evidence of a distinct AMD or ARD input from the Blackwater gold mining area.
Preliminary investigation suggests that dilution rather than attenuation is
responsible for decreasing As concentrations downstream.