The Supreme Court has declined to halt a Biden administration rule that seeks to prevent legacy toxic waste from now-shuttered coal plants from leaking out and contaminating nearby groundwater.  In a brief order, the high court said it would deny an emergency request from the East Kentucky Power Cooperative to temporarily block the rule from taking effect while underlying litigation against it plays out.  The Supreme Court did not offer an explanation for its rejection of the power cooperative’s petition. No dissents were noted.  The court’s move does not necessarily mean that the Supreme Court's justices believe the rule is permissible; it just means they are not ready to block it at this stage — before lower courts hear challenges to it.  The rule in question applies to waste that’s also known as “coal ash” — which contains dangerous substances like mercury and arsenic.  It requires coal plants that closed before October 19, 2015, to take steps to prevent coal ash from leaking out of “ponds” where it is stored.  Asking the court to halt the rule, the East Kentucky co-op argued that it would suffer from  “unrecoverable compliance costs” if the rule is not halted. Zach Schonfeld contributed.