This action continues approval of an alternative monitoring method to the Portland Cement Industry direct final rule.  In July 2016, when this alternative monitoring method was first published, it was believed that HCl calibration gases would become available within a period of 1 year. The calibration gases are needed for compliance demonstrations relative to the hydrogen chloride (HCl) continuous monitoring requirements of the Portland Cement Industry final rule. However, as the 1-year deadline approaches, it is apparent that the calibration gases will not be widely available for operators, and the date when they will be readily available is uncertain. For this reason, we are developing a direct final rule/parallel proposal to extend the alternative monitoring method until such time when the calibration gases become available. (Note that this change will affect only kilns that do not have HCl controls, which are required to continuously monitor for HCl.) The direct final rule/parallel proposal will include: An alternative method for HCl compliance that requires a yearly stack test along with the HCl monitors performing as parametric monitors instead of direct continuous monitoring.