Duplin groundwater sampling

Project Goals Expansion of ongoing effort to determine groundwater exchange/inputs to the Duplin from surrounding upland. Methods include time series radon and electrical resistivity measurements. Piezometer and resistivity cable transects will be laid out in several locations for ~24 hours each. Three time-series stations will be established to monitor radon-222 activities in Duplin River waters over the course of the week (to be installed Sunday, April 1 and removed Friday, April 6). The stations will be set up: (1) on the floating dock at Marsh Landing; (2) from a moored john boat near the pilings at Lumber Landing; and (3) on the floating dock at Hunt Camp. Each station will consist of the follow equipment: (1) A submersible bilge pump (10cm x 10cm x 10cm) to be deployed ~1 m below the water surface, suspended from the floating platform. The pump will be powered by an on-site 12-v car battery (which will be housed in a plastic storage box) and will continuously pump water through a short section of garden hose (5/8" diameter) to an air-water exchanger. (2) The air-water exchanger will aerate the water through a spray nozzle(s) to equilibrate the dissolved gases from the water with air in the instrument loop and headspace. The water will immediately overflow from the air-water exchanger and return to the river. (3) A closed air loop will connect the air-water exchanger to a commercial radon-in-air monitor (Durridge Co., Inc.) via a dessicant column, the latter two of which will be housed in the on-site plastic storage box. The air loop will be formed with 3/16" diameter tygon tubing, and an internal air pump within the radon monitor will circulate the air. (4) A Solinst CTD probe will be fastened to the water pump and a water level pressure sensor will be deployed to the river bottom inside a cinder block. The cinder block will be secured to the floating platforms at each site for recovery. Groundwater samples will be acquired through PVC piezometers. At each site, we will insert 4 piezometers (1/2" PVC pipe with a 2" section of slotted 1/2" PVC at the bottom) in a transect across the marsh from the river bank to the upland. The piezometers will remain in the ground for ~24 hours at each site. Water will be pumped from the piezometers via a peristaltic pump to be collected in 250-mL glass bottles for analysis. Finally, subsurface resistivity time-series will be conducted by laying a resistivity cable (100 m) along a transect from the upland through the marsh and into the river. The cable will remain on the ground surface for ~24 hours measuring the subsurface resistivity. We will deploy this cable at each site for 1 day.