Evaluating Sources of Groundwater Quality Variability in Residential Water Wells for Pre-Drill Sampling

Abstract

Significant concern has been expressed regarding the potential impact of shale gas extraction on surrounding drinking water resources. However, determining whether changes in groundwater chemistry (e.g., methane, salts, etc.) are natural in origin or caused by drilling operations can be difficult, particularly when a) different sampling and analytical methodologies are employed and b) water quality can vary naturally over time due to various factors (e.g., intensity of residential water use). To better understand the sources of variability in water quality in residential water wells in NE Pennsylvania, an area of active Marcellus shale gas extraction, two field studies were completed at nine residential water wells to evaluate the significance of sampling methodology and temporal variability on water quality results. For the sampling variability study, the effect of different sample collection methods and sampling containers on dissolved gas concentrations, as well as the effect of purge volume on dissolved gas concentrations, general water quality (e.g., sodium), and the isotopic signature of dissolved gases, water, and dissolved inorganic carbon was assessed. For the temporal variability study, water quality results from monthly sampling, as well as real-time data from a weather station and down-hole data loggers, were evaluated over an 18 month period to quantify the variability observed in measured parameters, identify relationships between parameters, and assess potential drivers of variability. Findings from these field programs improve our understanding of the inherent variability in pre- and post-drill results and offer insight into methods for improving sample collection protocols and data interpretation.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015