1. (1) All wastes shall be treated to remove practically all suspended solids and shall receive such additional treatment as determined by the commission upon consideration of the waste assimilative capacity of the receiving stream and as required to meet the limitations of Part 860 of this Title.
2. (2) Wastes containing biodegradable matter shall receive a minimum of secondary treatment as defined in the standards.

3. (3) Biodegradable and other waste matter to be treated or reduced shall not include that incorporated in influent waters, unless special circumstances as determined by the commission require such inclusion.

   (b) BOD reduction.

4. (1) The 85 percent minimum BOD reduction for secondary treatment will be determined by an average of samples taken over each period of 30 consecutive days of the year.
5. (2) It is recognized that optimum efficiency may not be achieved with certain secondary treatment facilities during the colder months. A slight deviation may be permitted by the commission when it results from reduced plant efficiency caused by temperatures below 59°F (15°C).
6. (3) For dilute industrial process wastewater, the percent BOD reduction may be modified, upon application, provided it has been demonstrated that the best management practices and the highest degree of waste treatment determined to be practicable will be applied.

(a) General.