Poster Title

H2SO4 Contamination of Freeman Branch Creek, Alabama from Disturbance of Geologic Materials During Highway Construction [Hybrid Poster 1-B]

Grade Level at Time of Presentation

Senior

Institution

Western Kentucky University

KY House District #

20

KY Senate District #

32

Department

Geography and Geology

Abstract

Pennsylvanian-aged clastic and coal-bearing rocks of the southeastern US often contain sulfide minerals, especially pyrite (FeS2). When these rocks are disturbed through mining or other activities the pyrite can be exposed to weathering by water and oxygen, resulting in pyrite oxidation that in turn produces sulfuric acid and ferric iron in solution. Since iron and other metals that may also be present have strongly pH-dependent solubilities, such low pH H2SO4 solutions, called “acid mine drainage” (AMD), can have relatively high metal concentrations. As pH is buffered these metals can precipitate in various forms along streambeds. In 2012 residents along Freeman Branch Creek near Eldridge Alabama observed orange and black discoloration along the stream which had not previously been seen. Inspection of geological maps showed that the Pennsylvanian Pottsville Formation underlying the area contains coal and as surface mining has taken place nearby this appeared to be a likely source of the contamination, although it was not clear what might have changed. Subsequent field investigation to understand relations between landscape disturbance and water quality in the creek instead suggested that blasting of units within the Pottsville Formation associated with recent highway construction about one kilometer upstream from where the discoloration had been observed may have enhanced pyrite weathering, along with buffering by limestone bedrock used as fill material. This highlights how construction activities in sulfide-bearing geologic materials can influence local water quality. Understanding of associated geochemical processes in such settings can be informed by the extensive existing literature on AMD.

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H2SO4 Contamination of Freeman Branch Creek, Alabama from Disturbance of Geologic Materials During Highway Construction [Hybrid Poster 1-B]

Pennsylvanian-aged clastic and coal-bearing rocks of the southeastern US often contain sulfide minerals, especially pyrite (FeS2). When these rocks are disturbed through mining or other activities the pyrite can be exposed to weathering by water and oxygen, resulting in pyrite oxidation that in turn produces sulfuric acid and ferric iron in solution. Since iron and other metals that may also be present have strongly pH-dependent solubilities, such low pH H2SO4 solutions, called “acid mine drainage” (AMD), can have relatively high metal concentrations. As pH is buffered these metals can precipitate in various forms along streambeds. In 2012 residents along Freeman Branch Creek near Eldridge Alabama observed orange and black discoloration along the stream which had not previously been seen. Inspection of geological maps showed that the Pennsylvanian Pottsville Formation underlying the area contains coal and as surface mining has taken place nearby this appeared to be a likely source of the contamination, although it was not clear what might have changed. Subsequent field investigation to understand relations between landscape disturbance and water quality in the creek instead suggested that blasting of units within the Pottsville Formation associated with recent highway construction about one kilometer upstream from where the discoloration had been observed may have enhanced pyrite weathering, along with buffering by limestone bedrock used as fill material. This highlights how construction activities in sulfide-bearing geologic materials can influence local water quality. Understanding of associated geochemical processes in such settings can be informed by the extensive existing literature on AMD.