Spectral Reflectance and Detection of Iron-Oxide Precipitates Associated with Acidic Mine Drainage

The objective of this study is to develop a repeatable technique to spectrally discriminate between acid and neutral streams based on the reflectance characteristics of acid and neutral iron precipitates. Field spectral measurements were conducted in situ on iron-oxide precipitates coating bottom substrates of an acidified stream (pH < 4) in the Virginia Gold-Pyrite Belt. Spectra of two neutral (pH 6 and 7) streams, one with iron precipitates present, were also measured. Acid precipitates were found to have higher spectral reflectance than neutral precipitates in the 650- to 750-nm region. With regard to water quality, the acid stream possessed low pH and high specific conductance. Guided by the field spectral data, a remote sensing technique using bandpass interference filters and a digital multispectral video system was used to detect mine drainage in two Virginia streams. Where acidic discharge was present, false-color composites showed precipitates having high reflectance in both the 650-nm and 750-nm wavebands. In contrast, neutral iron-rich streams were low in reflectance, and streams unimpaired by mine drainage had virtually no detectable reflectance.