An assessment of a stream-based methane monitoring technique for small streams in southern New Brunswick

Abstract

The goal of this study was to examine the suitability of a stream methane monitoring method, recently developed by the United States Geological Survey, for application to small New Brunswick streams. Dissolved methane monitoring has been suggested as an approach to assess changes in methane concentrations in areas of shale gas extraction, a topic relevant to southern New Brunswick. The first objective of the study was the establishment of a baseline for stream methane concentrations. Through sampling nineteen streams within the Kennebecasis River and Pollett River watersheds, methane concentrations were found to range from below detection (< 0.001 mg/L) up to 0.018 mg/L. These concentrations were low compared to those found in similar surveys in the United States. Based on the results of the reconnaissance survey, synoptic surveys of three streams were completed, and water temperature and dissolved methane profiles were used to select one stream for a more detailed tracer test. Parsons Brook best suited the criteria, including indications of significant groundwater inflows, and a tracer test using dissolved methane and potassium bromide was performed in September 2016. The stream was found to have an unusually low discharge at that time of year, and although the tracer test produced some useful data, there was a high degree of uncertainty in the results obtained for stream discharge. This caused issues during the subsequent modelling of dissolved methane transport, resulting in generally poor agreement of measured and modelled values. Additional studies would be needed to locate a stream, or streams, in southern New Brunswick within which the proposed methane monitoring technique would be effective. This stream should be large enough to retain dissolved methane for a significant distance, yet small enough to be significantly influenced by groundwater inputs.