“(1) Subject to paragraphs (2), (3) and (9), a public authority may refuse to disclose environmental information requested if— (a) an exception to disclosure applies under paragraphs (4) or (5); and (b) in all the circumstances of the case, the public interest in maintaining the exception outweighs the public interest in disclosing the information. … (4) For the purposes of paragraph (1)(a), a public authority may refuse to disclose information to the extent that— … (e) the request involves the disclosure of internal communications.”