A technique facilitates monitoring of parameters related to a downhole operation, e.g. a water injection operation. A completion string may be deployed in a borehole with at least one water injection mandrel combined with a side pocket. A sensor tool is constructed for conveyance down through the completion string and into sealing engagement with the interior surface of the side pocket. The sensor tool comprises at least one sensor for sensing a desired parameter or parameters, e.g. pressure and/or temperature. Additionally, the sensor tool comprises a nose which is positioned to mechanically open a check valve coupled to the side pocket so as to enable monitoring of the desired parameter or parameters via the at least one sensor.