DETERMINING SOURCES OF SALINITY IN PRE-HYDRAULIC FRACTURING BASELINE WATER QUALITY DATA USING MULTIVARIATE STATISTICAL METHODS

Environmental risks of hydraulic fracturing include introduction of highly saline formation water into shallow groundwater. It is challenging to determine if elevated salinity in groundwater is due to anthropogenic introduction of formation water because there is evidence formation water is present naturally in shallow groundwater aquifers and there are several other potential sources of salinity, including road salt, septic effluent, landfill leachate, or animal waste. We used new and published data on shallow groundwater quality in southern New York State, which currently has a moratorium on hydraulic fracturing, and to explore the sources of salinity in groundwater pre-hydraulic fracturing. We compared shallow groundwater chemistry data from Project SWIFT (n=60), the USGS 305(b) program (n=21), and the NURE program (n=1092) with published data for several potential sources of salinity, including Appalachian Basin formation water, road salt runoff, septic effluent, landfill leachate, animal waste, and water softeners. Observed means and covariance of log-transformed solute concentrations in low salinity groundwater (< 20 mg/L Cl) were used to create a random, synthetic low salinity groundwater data set (n=1000) we then contaminated with variable amounts of different sources of salinity. We then used the synthetic contaminated groundwater to train a discriminant analysis model to classify high salinity samples (> 20 mg/L Cl) as affected by formation water, road salt, septic effluent, landfill leachate, animal waste, or water softeners. Overlapping distributions of Cl, Na, Br, I, Ca, Mg, Ba, SO4, and Sr show that no single element uniquely differentiated formation water from other sources of salinity. Discriminant analysis classified most accurately samples affected by formation water and landfill leachate, whereas those contaminated by road salt, animal waste, and water softeners were more likely to be discriminated as contaminated by a different source. Using our approach, no shallow groundwater samples from New York appear to be affected by formation water, suggesting the source of salinity pre-hydraulic fracturing is primarily a combination of road salt, septic effluent, landfill leachate, and animal waste.