Significant Aspect

No, it is not in the standard that any aspect/impact that has a legal requirement is automatically significant.

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If an environmental aspect has compliance obligations and they do not comply the aspect is significant, but if they are satisfied then it is up to your evaluation criteria to determine if they are or not significant.
 
Please check this information below with more detailed answers:

• Environmental aspect identification and classification - https://advisera.com/14001academy/blog/2019/08/27/key-iso-14001-benefits-to-customers/nowledgebase/environmental-aspect-identification-and-classification/
• ISO 14001 document template: Procedure for Identification and Evaluation of Environmental Aspects and Risks - https://advisera.com/14001academy/documentation/procedure-for-identification-and-evaluation-of-environmental-aspects/
• Enroll for free in this course – ISO 14001:2015 Lead Auditor Course - https://advisera.com/training/iso-14001-lead-auditor-course/
• Book – The ISO 14001:2015 Companion - https://advisera.com/books/the-iso-14001-2015-companion/