Sec. 26.08.04.02-1. Discharge Permit Limits

A. General.

(1) Each discharge permit, unless inappropriate, shall specify average and maximum daily quantitative limits, in terms of weight, for the discharge of pollutants in the authorized discharge.

(2) Other discharge limits, such as minimum, average, or maximum concentration limits, may be imposed.

(3) If a schedule of compliance is included as a discharge permit condition, quantitative limits shall be set for the interim period as well as for the period following the final compliance date.

B. Net Credits. The discharge permit limits for the discharge of noncontact cooling water shall be based on the water quality standard unless the discharger applies to have the permit limits based on the concentration in the intake water. A discharger may make this application if:

(1) The intake water is the receiving water;

(2) The pollutant concentration in the intake water exceeds the water quality standard;

(3) Except for the additional provisions of a compliance schedule for corrosion and erosion in §C of this regulation, the discharger demonstrates to the Department's satisfaction, using a statistically rigorous demonstration, that no significant difference exists, at the edge of the appropriate mixing zone, between the intake concentration or loading and the effluent concentration or loading of the pollutant which exceeds the water quality standard; and

(4) The discharger demonstrates to the Department's satisfaction that no other activity, condition, method of operation, or materials used or produced at the facility which results in the introduction of wastewater into the facility's discharge (including entrainment of pollutants previously discharged or disposed of by the facility), significantly contributes to the exceedance of surface water quality standards.

C. Corrosion and Erosion.

(1) Reasonable Potential. A discharger will not be found to cause, have the reasonable potential to cause, or contribute to an exceedance of a numerical water quality standard for a pollutant caused by normal corrosion and erosion from a facility’s water distribution piping and appurtenances or associated with intake water from a municipal drinking water supply, if:

(a) The facility is an existing facility as of the effective date of this section;

(b) The permitted dry-weather discharge from the facility consists of a combination of drinking fountain drainage, fire protection system drainage, and interior atmosphere control equipment drainage;

(c) The total annual estimated dry-weight mass loading for the pollutant of concern of the permitted dry-weather discharge from the facility does not exceed 5 pounds;

(d) The annual average effluent concentration of the permitted dry-weather discharge at the facility does not exceed the ambient concentration of the pollutant of concern in the facility's receiving water body; and

(e) The discharger’s receiving water body for the discharge is not a Class III or Class III-P water.

(2) Compliance Schedule for Noncontact Cooling Water Discharges.

(a) For purposes of this section, normal corrosion and erosion shall be determined through site-specific calculations that are performed in accordance with scientifically defensible methodology approved by the Department and are based, where appropriate, on annual average intake concentrations.

(b) In establishing discharge permit limits on the basis of either water quality standards or intake water pollutant concentrations, the Department may grant a credit for normal corrosion and erosion associated with the discharging facility's noncontact cooling water condenser tubes, if the discharger:

(i) Demonstrates that, in the absence of the pollutant corroded and eroded from the facility's piping and appurtenances or noncontact cooling water condenser tubes, the discharger would not exceed the otherwise applicable permit limit;

(ii) Demonstrates that the normal corrosion and erosion associated with the intake water used by the facility for noncontact cooling water is sufficient to cause an exceedance of the otherwise applicable permit limit; and

(iii) Has entered into a consent order requiring that, within 5 years after the promulgation of this regulation or the permit expiration date at the time of promulgation, whichever is later, sufficient noncontact cooling water condenser tubes or other piping and appurtenances for noncontact cooling water will be modified, replaced, or repaired, to consist of noneroding and noncorroding materials, until the need for the corrosion/erosion credit is eliminated.

(c) The Department may reduce or deny the credit if any other activity, condition, method of operation, or material used or produced at the facility results in the increase of the erosion and corrosion-based pollutant in the facility's discharge (including entrainment of a pollutant previously discharged or disposed of by the facility) and significantly contributes to the exceedance of the water quality standard for that pollutant in the receiving water.

D. Mixing Zones.

(1) When any effluent meets water quality criteria at the end of the discharge pipe, the Department may not require the discharger to submit mixing zone calculations.

(2) When mixing zones are used to establish discharge permit limits, the discharger, at the time of application for permit issuance or renewal, or at a later time stipulated by the Department, shall select the mixing zone technique appropriate for each discharge and submit actual mixing zone calculations. All calculations and supporting studies should be based on established criteria and protocols or otherwise performed in accordance with scientifically defensible methodology approved by the Department. Supporting documentation may include one or more of the following:

(a) Tracer studies;

(b) Receiving water and discharge flow measurements;

(c) Surface water bathymetry;

(d) Diffuser design and performance data; and

(e) Effluent modeling results.

(3) When a mixing zone has been previously used to establish permit limits, the Department may, in its discretion, waive the requirement for full mixing zone development if the discharger demonstrates that:

(a) Discharge conditions have not changed; and

(b) No surface water impacts attributable to the facility have been identified.