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Figure F3. Schematic of shipboard tracer injection system during Expedition 327, illustrating pumps, manifolds, mixing points, and rig floor sampling location (not to scale). Mud pumps were used to inject fluid into the formation during the 24 h pumping experiment. Sulfur hexafluoride (SF6) gas was introduced upstream from the mud pumps using an injection manifold (Fig. F4) to control the gas concentration. V = sampling valve, Vs = switching valve, CV = check valve, G = pressure gauge. Fluid exiting the mud pumps was directed to the rig floor, where it entered the drill pipe. For several brief periods, additional tracers were added to this flow using the cement pump system. Seawater was mixed with salt tracers, and seawater or freshwater was mixed with solutions containing fluorescent microspheres or microbes and then added to the flow generated with the mud pump system. A sample port installed on the rig floor allowed collection of injectate samples before they were pumped into the drill pipe.

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