Sec.  178.  The Administrator  shall  issue  guidance documents
under   section  108   for  purposes   of  assisting   States  in
implementing requirements  of  this part  respecting  the  lowest
achievable emission  rate. Such a document shall be published not
later than nine months after the  date of enactment of this  part
and shall be revised at least every two years thereafter.
[42 U.S.C. 7508]