The determination of the characteristics of a wastewater stream for purposes of this division (relating to Industrial Wastewater) shall be made as follows.
  (1) The characteristics shall be determined at a location between the point of generation and before the wastewater stream is exposed to the atmosphere, treated for volatile organic compounds (VOC) removal, or mixed with another wastewater stream. For wastewater streams which, prior to November 15, 1993, were either actually being mixed or construction had commenced which would result in the wastewater streams being mixed, this mixing shall not establish a limit on where the characteristics may be determined.
  (2) The flow rate of a wastewater stream shall be determined on the basis of an annual average by one of the following methods:
    (A) the highest annual quantity of wastewater managed, based on historical records for the most recent five years of operation, or for the entire time the wastewater stream has existed if less than five years but at least one year;
    (B) the maximum design capacity of the wastewater component;
    (C) the maximum design capacity to generate wastewater of the process unit generating the wastewater stream;
    (D) measurements that are representative of the actual, normal wastewater generation rates.
  (3) The VOC concentration of a wastewater stream shall be determined on the basis of a flow-weighted annual average by one of the following methods, or by a combination of the methods. If the executive director determines that the VOC concentration cannot be adequately determined by knowledge of the wastewater, or by bench-scale or pilot-scale test data, the VOC concentration shall be determined in accordance with subparagraph (C) of this paragraph, or by a combination of the methods in subparagraphs (A), (B), and (C) of this paragraph. VOC with a Henry's Law Constant less than 7.5x10-5 atm-m3/mole at 25 degrees Celsius shall not be included in the determination of VOC concentration.
    (A) Knowledge of the wastewater. Sufficient information to document the VOC concentration. Examples of information include material balances, records of chemical purchases, or previous test results.
    (B) Bench-scale or pilot-scale test data. Sufficient information to demonstrate that the bench-scale or pilot-scale test concentration data are representative of the actual VOC concentration.
    (C) Measurements. Collect a minimum of three representative samples from the wastewater stream and determine the VOC concentration for each sample in accordance with §115.145 of this title (relating to Approved Test Methods). The VOC concentration of the wastewater stream shall be the flow-weighted average of the individual samples.
  (4) The annual VOC loading in wastewater for a wastewater stream shall be the annual average flow rate determined in paragraph (2) of this section multiplied by the annual average VOC concentration determined in paragraph (3) of this section.
  (5) The annual VOC loading in wastewater for a plant shall be the sum of the annual VOC loading in wastewater for each affected VOC wastewater stream.

Source Note: The provisions of this §115.148 adopted to be effective May 27, 1994, 19 TexReg 3703; amended to be effective November 18, 1999, 24 TexReg 10095