This minor event was an overflow of seawater mixed with a small amount of sediment and nodule fragments, which contain no toxic levels of heavy elements and which did not have the potential to cause harm to the marine environment. NORI notified the regulator (ISA) of the event after it occurred. A further update on the event and the mitigation measures implemented to prevent it from occurring again was presented by NORI to the ISA during the ISA’s inspection and audit visit to the Hidden Gem at demobilisation.

In more detail: during the production ramp-up sequence in October a temporary overflow of water occurred. Due to the dynamic behavior of the airlift riser when first switched on, there was a surge in the volume of water flow which briefly exceeded the buffer capacity of the cyclone separator at the top of the riser. As a result, the cyclone experienced a minor overflow of water containing a small amount of sediment and nodule fragments. This occurred intermittently during a 7-8 hour test run, with the overflowing water landing on the deck of the vessel and eventually flowing overboard.

When safe to do so the test run was stopped in a controlled manner. NORI and Allseas conducted an assessment to determine if the overflow had the potential to cause serious harm to the marine environment. Based on the estimated discharge volumes and contents, NORI and Allseas concluded that this incident did not have the potential to cause serious harm. In collaboration with subject matter experts, an assessment was conducted on how to prevent an overflow reoccurring on future runs. Based on this assessment, modifications were made to the cyclone separator. Testing was conducted and the implemented modifications to the cyclone separator proved effective. There were no further overflows during subsequent test runs.

As outlined in the Collector Test Environmental Impact Statement, the purpose of these pilot trials was to test an untried system, at a scale that could not cause serious harm to the marine environment. The trials proceeded as planned with any design flaws identified and corrected immediately, learnings that Allseas will incorporate into the design of the full-scale commercial system.

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