For the purpose of computing whether a discharge will violate the classification of any river or stream, the assimilative capacity of such river or stream shall be computed using the minimum seven day low flow which occurs once in ten years. Waste discharges shall be appropriately reduced when flows fall below the seven day-ten year-low flow if the Board determines that such reduction is necessary to maintain such applicable classifications.
06- 096 C.M.R. ch. 581, § 1