METAL CONTAMINATION IN SOILS RECEIVING ACID MINE DRAINAGE AT BULLION MINE (MONTANA)

Globally, acid mine drainage can arise as a result of mining activities that expose mineralized zones to oxygen and water, oxidizing pyrite and other acid-producing metals. Remediation practices are designed to stop the contamination of waterways and impacts to biodiversity, but aren’t always 100% successful. Bullion Mine, located in the Boulder River watershed near Basin in southwestern Montana is one such site. Prior to mining this area, acid produced from polymetallic quartz-vein deposits was partially neutralized from the rocks through which it flowed (Church et al., 2004). After development, mine tailings with a high concentration of iron sulfide minerals produced acid mine drainage, resulting in the release of elevated concentrations of potentially toxic metals (such as zinc, chromium and cadmium) and trace elements to the local watershed (USEPA, 2013). Depending on conditions, the metals may remain mobile or can accumulate in soils and sediment over time.

The goal of this research is to determine concentrations and associations of arsenic, copper, iron, lead, and zinc in soil samples collected at areas directly impacted by acid drainage and compare them to soils in an un-impacted wetland. Eight samples were collected from soil trenches dug at each site. A sequential extraction procedure (modified Community Bureau of Reference (BCR)) was used to determine elemental associations in the soil samples. Organic matter content was determined on separate splits of the samples using a loss on ignition (LOI) procedure. Soil organic matter ranged from 1.9-7.0% (with the exception of several outliers) for both sites. Results of the sequential extraction procedure and comparison of metal associations between the two sites will be presented.