(a) Particulate emissions from any waste heat stack must not exceed 0.050 grains per dry standard cubic foot and the average opacity of emissions from such stack must not exceed 20 percent as measured in accordance with the procedures set forth in subdivision (b) of this section.

(b) For the purpose of determining compliance with subdivision (a) of this section, the observer must stand at a distance sufficient to provide a clear view of the waste heat stack with the sun oriented in the 140° sector of his back. The observer will, as much as possible, make his observations from a position where his line of vision is perpendicular to the plume direction. The opacity of emissions will be computed by averaging the results of 24 consecutive opacity observations made at 15-second intervals.