GROUNDWATER QUALITY ASSESSMENT AROUND ORPHANED AND UNCONVENTIONAL OIL AND GAS WELLS IN THE UNITED STATES

The United States has approximately 1 million producing oil and gas wells, with 18.1% of them being unconventional as of 2021. Many of these active wells coexist with documented orphaned and abandoned wells. This study aims to evaluate the influence of both active and orphaned oil and gas wells on groundwater quality across the United States by compiling groundwater data from national and state-level databases.

The Water Quality Portal (http://waterqualitydata.us) provided a dataset of 1,110,065 specific conductance measurements collected from 276,755 groundwater sampling sites. We carefully verified the accuracy of the reported units and sampling locations for these specific conductance measurements. To determine the geospatial relationship between groundwater quality samples and orphaned wells, we calculated the Euclidean distances between the water samples and the locations of orphaned wells. Preliminary findings show that more than 90% (n = 72,230) of orphaned wells have no specific conductance measurements reported within a 1 km radius, and only 33 orphaned wells have more than 10 specific conductance measurements available. The data availability is even scarcer for groundwater quality measurements collected post-2000, and the presence of specific conductance measurements varies significantly by state.

To focus on regions with extensive unconventional oil and gas development, we narrowed our analysis to three states: Pennsylvania, Colorado, and Texas. In these states, we compiled specific conductance, strontium, and barium concentrations from the national and various state-level databases. The preliminary results indicate that in Pennsylvania, the concentrations of all three analytes in groundwater samples tend to increase as the distance between the water sample and the nearest unconventional well decreases. Moreover, their concentrations also rise with an increasing number of unconventional wells within 3 km of the water sample. In Colorado and Texas, the correlation between specific conductance and unconventional well indices differs from those observed in Pennsylvania.