The trust sacked Collins for causing it "harm and embarrassment" by disclosing the report, which warned that the quarry posed a danger to the public.
The report was not sent to the trust for more than a year and the site remained open. A later council report downgraded the risk.
The tribunal said the seriousness of the case was raised by the trust's status as a "well-known and well-respected conservation charity in which the public places special trust".
The trust told Third Sector that it had sought advice from relevant agencies and experts and had never been advised to close the site.