CHARACTERIZING SOURCES OF TURBIDITY IN STREAM SEDIMENTS IN THE MARCELLUS SHALE GAS-WELL DRILLING REGION IN CENTRAL PENNSYLVANIA

Throughout the development of the Marcellus Shale gas play in Pennsylvania, potential environmental impacts and cost-benefit have been vigorously debated. It is important for the public, as well as the science community, to fully evaluate the influence Marcellus activities can have on local economy and the environment. One such concern was the possibility of an increase in turbidity on receiving streams, resulting from an upswing in Marcellus Shale infrastructure building, as well as modification of existing dirt and gravel roads.

Sediments collected from streambeds, farmlands, stream banks, and gravel roads in the vicinity of Marcellus Shale gas-well activities were analyzed using x-ray fluorescence (XRF) to determine their elemental composition. Sediment samples from two watersheds, namely Marsh Creek and Baker Run, with varied intensities of Marcellus Shale activities were collected and analyzed. Marsh Creek watershed was used as a reference, due to the absence of Marcellus Shale activities; whereas the Baker Run watershed contained 9 gas-well drilling pads. The results were compared using a variety of graphical and statistical methods, such as plotting data on ternary diagrams, XY scatter plots, and the student’s t-test.

A characteristic geochemical signature was created for each landuse type by symbolizing elemental concentrations, such as Ca, Si, Sr, Al, K, Mn, Ni, and Zn. The results of student’s t-test indicated that sediments from various landuses are statistically less discernable from each other in Marsh Creek watershed when compared to those in Baker Run watershed. In the Marsh Creek watershed, on average 28-78% of gravel road samples were characterized by similar elemental composition as stream bed sediments. In Baker Run watershed, depending on elemental compositions plotted on ternary diagrams, on average 11-44% of gravel road samples were characterized by similar elemental composition as the stream bed sediments. When comparing these two watersheds, it can be concluded that gravel roads in Marsh Creek watershed contribute relatively more to stream turbidity as compared to the gravel roads in Baker Run watershed.

Methods used to determine the sources of stream turbidity in this study can be used in other geologic and landuse settings.