Passive Grab Sampling for Dissolved Methane at Depth with the Sealed-In-Situ Snap Sampler Device

Deep groundwater sampling has always been challenging due to difficulties with physical retrieval, high pressure pumping lift, and degassing. A relatively new approach, the Snap Sampler, allows the user to deploy double-end-opening sampling containers to depths of at least 2700 feet, limiting some of the problematic aspects of deep sampling. Sample containers are deployed downhole with both ends in an open position, and an electric or pneumatic triggering system is used to release (i.e., “snap”) an internal Teflon-coated spring that secures end caps on the individual sample containers. The pneumatic system is particularly useful for sampling groundwater with potentially ignitable gases (e.g., methane) since the device is made of plastic components and low air pressure (<50psi) is required to trigger closure. Up to six containers can be deployed simultaneously. Different container sizes (40ml, 125ml and 350ml) and materials (clear or amber borosilicate glass and HDPE) are available for the sample bottles so that multiple analytes can be collected together. The sampler system is reusable with replaceable individual sample bottles.

The Snap Sampler system was used for methane sampling at moderate depth (400-800 feet) at a location in Mississippi. Several rounds of samples were collected from 15 wells to assess the effectiveness of the system and to characterize the deep groundwater. Methane concentrations were measured using the Snap method and closely approximated calculated saturation concentrations. Degassing within the Snap Sampler bottles did occur upon retrieval because the bottles are not pressure sealed; however, because degassed vapor and fluid is contained within the vessel, the methane concentrations measured in the Snap vials appear to be representative of downhole concentrations.