LEGACY OF COAL MINING ON ISLANDS IN THE SUSQUEHANNA RIVER: SELINSGROVE, PA

Uninhabited alluvial bar islands in the Mainstem of the Susquehanna River near Selinsgrove, PA contain evidence of anthropogenic activity from coal mining. These islands and other floodplain sediments are mapped as Recent to Late Illinoian stratified drift and glacial outwash. The islands are overlain by Udifluvent soils composed of coal overwash. They are composed of flood alluvium consisting of loam to sand size grains and some layers contain iron nodules and abundant coal sand (up to 20 cm thick). Exchangeable cations like MgO, Na₂O, CaO, K₂O and TiO₂ decrease in abundance with depth as coal abundance increases. Layers with abundant coal sand contain elevated levels of Fe₂O₃, MnO, SO₃, Zn, Pb, Cu, and Ni. The coal overwash consists of coal, quartz, orthoclase, muscovite, illite, kaolinite and chlorite. Sand from underlying glacial deposits contain heavy minerals like garnet, zircon, tourmaline, and magnetite, as well as quartz, muscovite, and orthoclase. Island elevation and density of midstream islands influences the composition of island sediments. Higher elevation islands contain finer sediments and less concentrated coal sand. Low elevation islands may have up to 2.7 m of anthropogenic sediment from mining.

Sediment cores were drilled (up to 2.7 m) from the top of four islands (Byers, Cherry Upstream, Fisher, and an unnamed island) and sampled every decimeter. Grain size was determined using a gravity settling method and hydrometer. Samples were pressed into pellets and analyzed using WDXRF. Mineralogy was determined using XRD and standard petrographic methods.

The legacy of coal mining in the Susquehanna River Valley is significant. In addition to thick layers of coal representing floods, Pb values reach 165 ppm. Though coal deposits become less abundant in high elevation islands, the potential of erosion of alluvial bar islands with climate change involving high energy rain storms and more frequent flood events may wash more of this toxic sediment downstream to the Chesapeake Bay.