137. In addition to the limits prescribed by sections 132 to 135, an aluminum smelter must not emit total fluorides into the environment in such manner that the fluoride concentration in forage for feeding animals measured in samples taken off the property of the contamination source exceeds the following limits:
(1) an annual average of 40 ppm;
(2) a monthly average of 60 ppm over 2 consecutive months; and
(3) a monthly average of 80 ppm.
The monthly average fluoride concentration may once a year exceed the limit of 80 ppm prescribed by subparagraph 3 of the first paragraph. It may also exceed the limit of 60 ppm prescribed by subparagraph 2 as long as the limit is not exceeded for more than 2 consecutive months.