(b) It is the underlying principle of these regulations that each class and subclass of waters within the Interstate Environmental District is to be suitable for its best intended uses and that all waters are to be protected, maintained, and improved to the end that they will afford as satisfactory conditions as possible for the maintenance and restoration of the natural ecosystems. It is also recognized that different classifications of waters are appropriate for different areas because of varying activities such as are associated with industry, commerce (including waterborne transportation), recreation, and aesthetic enjoyment. All waters should be aesthetic assets and should, at a minimum, be available for those recreational uses which do not bring the human body into direct contact with the water.

1. (1) Streams and other waterbodies shall have a minimum dissolved oxygen content in accordance with their respective classifications as follows:

   1. (i) A: Dissolved Oxygen: 5 milligrams per liter;
   2. (ii) B-1: Dissolved Oxygen: 4 milligrams per liter;
   3. (iii) B-2: Dissolved Oxygen: 3 milligrams per liter.

2. (2) In addition to meeting the requirements set forth in paragraph (1) of this subdivision, waters shall in all respects be suitable for their best intended uses as follows:

   1. (i) A: Suitable for all forms of primary and secondary contact recreation and for fish propagation. In designated areas, they also shall be suitable for shellfish harvesting.
   2. (ii) B-1: Suitable for fishing and secondary contact recreation. They shall be suitable for the growth and maintenance of fish life and other forms of marine life naturally occurring therein, but may not be suitable for fish propagation.
   3. (iii) B-2: Suitable for passage of anadromous fish and for the maintenance of fish life in a manner consistent with the criteria established in section 550.1(a)-(b) of this Part.

(c)

(d) As used in this Part:

1. (1) Primary contact recreation means recreational activity that involves significant ingestion risk, including but not limited to wading, swimming, diving, surfing and water skiing.
2. (2) Secondary contact recreation means recreational activity in which the probability of significant contact with the water or water ingestion is minimal, including but not limited to boating, fishing, and shoreline recreational activity involving limited contact with surface waters.

(e) Effluents discharged or flowing into waters of any class shall meet the requirements provided in this Part. The effluent limitation values contained in paragraph (2) of this subdivision are geometric means, and in paragraphs (3) and (4) of this subdivision are arithmetic means. Industrial effluent limitation values are for process water volume. Any contaminants taken into the discharger's plant or process from the waters of the Interstate Environmental District shall not be charged against the effluent quality in computing the values for compliance with these regulations.

1. (1) pH within the range from 6.0 to 9.0 may be required if the receiving waters are outside this range.
2. (2) Fecal coliform content shall not exceed 200 per 100 ml on a 30-consecutive-day average; 400 per 100 ml on a 7-consecutive-day average; and 800 per 100 ml on a 6-consecutive-hour average, but no sample may contain more than 2,400 per 100 ml. The only portion of the Interstate Environmental District to which this provision shall not apply at all times is that referred to in section 550.3(a)(2) of this Part. For the aforementioned portion of the district, these disinfection requirements shall apply when disinfection is required to protect the best intended uses of the waters in question. For example, in the case of discharge into waters used primarily for bathing, this bacterial standard need not be required except during the bathing season.
3. (3) Biochemical oxygen demand shall not exceed 30 mg/l on a 30-consecutive-day average, 45 mg/l on a 7-consecutive-day average, and 50 mg/l on a 6-consecutive-hour average. Further, all sewage or other polluting matter discharged or permitted to flow into waters of the district shall first have been so treated as to effect a reduction in the oxygen demand of the effluent sufficient to maintain the dissolved oxygen content in the waters of the district, and in the general vicinity of the point of discharge of the sewage or other polluting matter into those waters, at a depth of about five feet below the surface, of not less than the dissolved oxygen concentration set forth in subdivision (c) of this section.
4. (4) Total suspended solids content shall not exceed 30 mg/l on a 30-consecutive-day average, 45 mg/l on a 7-consecutive-day average, and 50 mg/l on a 6-consecutive-hour average.
5. (5) Effluents shall contain no floating solids.
6. (6) All wastes shall be of a character that will not violate or cause violation of the requirements contained in section 550.1 of this Part.
7. (7) An effluent discharge which does not satisfy the requirements of the commission shall not be considered to be in violation thereof if caused by temporary excess flows due to storm water conveyed to treatment plants through combined sewer systems, provided that the discharger is operating the facility with reasonable care, maintenance and efficiency, and has acted and continues to act with due diligence and speed to correct the condition resulting from the storm water flow.