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

Reported changes in residential water well quality in areas of active shale gas operations have fueled significant concerns regarding the impact of shale gas extraction on surrounding drinking water resources. Given that water quality can vary substantially over time due to factors unrelated to shale gas extraction (e.g., intensity of residential water use, well construction, aquifer geochemistry, precipitation events, temperature, weather patterns, and road salting), the source(s) of observed variability in water quality is often left in question. To further complicate matters, recommended practices for baseline water quality sampling vary considerably between states and organizations, imparting additional variability on water quality analytical results. An improved understanding of the effect of sample methodologies and temporal variability on dissolved gas concentrations, isotopic signature, and other water quality parameters in residential water wells is needed to better differentiate sources of natural variability in residential water wells from induced variations (e.g., stray gas events).

This presentation summarizes the results of two field studies aimed at evaluating sources of variability in pre-drill groundwater data and quantifying their impact on dissolved gas concentrations and other water quality parameters from a series of private residential water supply wells in northeast Pennsylvania. The objectives of the study are twofold: (1) investigate the effects of sampling methodologies on pre-drill water well quality, and (2) quantify the degree of variability in dissolved gas concentration, isotopic signature, and general water quality parameters over an 18-month period. The goal of this work is to form a better understanding of the inherent variability in pre-drill and post-drill analytical results and develop recommendations for improved sample collection methods and data interpretation.