An injection vessel for injecting liquid amendment into contaminated subsurface sediment in ecologically sensitive areas such as shallow water salt marshes, tidal flats, or fresh water wetlands is disclosed. The injection vessel described herein includes a shallow-draft floating platform that has an injection system mounted thereon. The injection system includes an injection grid containing a plurality of injection syringes that receive liquid amendment from a metering pump. The injection grid is lowered such that the output of the injection syringes is within the contaminated sediment. The metering pump provides the liquid amendment to the injection syringes and a fluid path is established that injects the liquid amendment into the contaminated sediment. A propulsion system mounted on the floating platform provides for locomotive and maneuvering power. A control system allows the operation of the system either in a semi-autonomous mode in which an on-board controller is programmed to provide the command signals, or in a remote control mode with an operator providing real time command signals through either a wireless or wired controller. The control system provides propulsion commands to the propulsion system and injection commands to the injection system. The propulsion commands include both locomotive commands and maneuvering commands. The injection commands include the lowering and raising of the injection gird and the operation of the metering pump to dispense the predetermined amount of liquid amendment.