Identifying Critical Watersheds and Streams due to Accidental Spills from Unconventional Drilling Sites

[摘要] The Marcellus Shale is a marine sedimentary rock formation that has attracted many drilling operators to extract natural gas. Hydraulic fracturing is the major gas recovery technique used today, but it produces large amount of fluid wastes that may potentially pollute water bodies. One of the major risks is identified as water contamination by accidental spills of shale gas wastes. Therefore, it is extremely important to understand how contaminants can travel from drilling sites into streams, and to identify and quantify risks of stream contamination. To this end, there are four objectives in this study: (1) delineate surface pathways from drilling sites to nearby streams, (2) quantify pollutant travel time based on the physical characteristic variations across the geography of Pennsylvania, (3) identify critical watersheds that are under high risk for spill occurrence, and (4) carry out environmental monitoring of critical watershed. Geographic Information System (GIS) is utilized for spatial analyses. The Analytic Hierarchy Process (AHP) was applied to introduce weight distribution among influencing factors such as land cover, soil type and slope. The cost path analysis delineates travel pathways and areas around shale gas drilling sites with cheapest pollutant travel cost for the entire Pennsylvania. Travel times are calculated by using these cost paths. Results identify areas where the contaminants can potentially travel in a short time into nearby stream network. Based on this analysis, critical HUC-10 watersheds are identified with potential risk of contaminating water bodies and should be considered for further analysis of their water quality and stream importance. Herein, for the purpose of environmental monitoring of critical watershed, two of them are chosen: (1) South Fork Tenmile in the southwest PA, (2) Tioga River in the northeast PA. Future work will include using the Hydrologic Engineering Center's River Analysis System (HEC-RAS) for modeling contaminant transport and the application of the Baseline Streamflow Estimator (BaSE) and the StreamStats program to obtain water discharges for ungauged streams, typically found in PA. This framework will be able to provide useful information for sensor placement, water surface management and monitoring for critical watersheds and streams.

[发布机构] the University of Pittsburgh