Water-quality comparisons in the Greater Mooses Tooth unit of the National Petroleum Reserve in Alaska, 2010 and 2023

The United States has long held oil reserves in the National Petroleum Reserve in Alaska (NPR–A), but oil production did not begin until 2015. The waters of the NPR–A are generally considered “pristine,” but water quality has not been characterized temporally or spatially in a rigorous manner. In 2010 and 2023, the U.S. Geological Survey, in cooperation with the Bureau of Land Management, collected water-quality samples from four small, beaded streams in the NPR–A, three of which currently (2024) have oil and gas infrastructure within their drainage. Samples collected preconstruction and postconstruction were analyzed and compared to determine concentration changes in nutrients, major ions, trace elements, and volatile organic compounds to evaluate the effectiveness of required operating procedures designed to minimize potential effects to water quality from oil and gas activities.

The four small streams in the Greater Mooses Tooth unit of the NPR–A had similar water-quality characteristics in the 2010 and 2023 samples. Most analytes were measured at low concentrations or below the reporting level for both samples. For analytes that were detected, variability between the two samples was generally low and mostly showed lower concentrations in the 2023 samples, possibly partially because of recent rainfall that led to streamflow being much higher at the time of the 2023 sample. Trichloromethane was present in the sample at one site in both years and at a second site in the 2023 sample. All three detections of trichloromethane were within the expected natural background range for the area. The few increases in analyte concentrations in the watersheds with oil and gas facilities were all within the range of predevelopment concentrations or background concentrations for the area.