Underground coal mining and subsidence, channel fracturing and water pollution : a five-year investigation

![CDATA[Subsidence from underground coal mining can be a problematic issue. Our study investigated a waterway that had been disturbed by a coal longwall that made multiple passes directly under it. The most obvious impact was loss of stream flow through sections of fractured bedrock channel. Water quality of the stream was monitored over a 5-year period, where the creek had flow. Ochre-coloured water appeared in some sections of the creek. Salinity increased by four times from <250 (upstream) to 1195 μS/cm in subsidence affected zones. The concentration of metals such as zinc and nickel increased by many times to levels in exceedance of the ANZECC water quality guidelines for aquatic ecosystems. The macroinvertebrate composition of sections of the creek was strongly impaired and mosquitos were abundant. One sampling site was conducted where upwelling groundwater entered the creek through recent subsidence fractures, and below that point the creek flowed continuously during the most recent six months of the study. Mean electrical conductivity increased due to that upwelling, rising 6.8 times from (230 μS/cm) at upstream/reference sites to 1806 μS/cm below the upwelling. Dissolved oxygen of the upwelling groundwater was extremely low (2.7 %) and was also acidic (5.8 pH).]]