An owner who proposes to materially alter, expand, or re-rate an existing facility in order to meet an amended permit condition is required to use the facility's current operating data as the design basis for sizing the proposed wastewater treatment equipment and processes. The compiled data must meet the criteria outlined in paragraphs (1) and (2) of this section.

1. (1) Flows.

   1. (A) The volume of existing flow shall be determined when an existing treatment facility is to be re-rated, expanded, or upgraded.
   2. (B) An existing facility's data for the latest five years must be used to determine the annual average flow, the maximum monthly average flow, the peak flow, the ratio of maximum monthly average flow to annual average flow, and the ratio of the peak flow to the annual average flow. If the facility is less than five years old, all data must be used. All calculations and assumptions must be included in the report.
   3. (C) All flow data for these analyses must be collected by a totalizing meter.
   4. (D) An analysis of the peak flow must be based on a frequency distribution analysis using flow charts for each individual day to determine the maximum sustained flow rate over any two-hour period.
   5. (E) The projected peak flow must be the result of collection system monitoring or modeling based on a two-year, 24-hour storm event for the service area.

2. (2) Organic loadings.

   1. (A) When an owner seeks to have an existing facility re-rated or to expand or upgrade an existing facility, the design organic loading must be calculated based on the average daily organic load that the facility is required to treat during the design life. A calculation of the average daily organic loading must use the facility's actual data plus one standard deviation. The data must conform at a minimum to the following:

      1. (i) The data must document a minimum of one year, consisting of three samples per week taken during days with a representative flow. If a sampling program is for a frequency of less than three times per week or less than a three-part grab sample, an owner shall document how the proposed sampling program is representative of actual conditions at the facility.
      2. (ii) The samples must be representative of the peak loading.
      3. (iii) Sampling data must include a minimum of five-day carbonaceous biochemical oxygen demand or five-day biochemical oxygen demand, total suspended solids, and ammonia-nitrogen, unless justified because of specific treatment requirements.

      4. (iv) An engineering analysis for the minimum sampling period must include:

         1. (I) a summary of the monthly data;
         2. (II) annual-average monthly load; and
         3. (III) the standard deviation of the monthly data.
      5. (v) An analysis may use a linear regression or other appropriate statistical method for predicting the design organic load when significant data exists.
   2. (B) A design must be based future loading and future flow calculated from the anticipated changes from the existing loading and flow.

   3. (C) The report must justify the design organic loading.

      1. (i) A design organic loading must account for both dry weather and wet weather conditions.
      2. (ii) An owner shall use the design organic loading to determine the size of any treatment unit that provides treatment of organic waste.

Source Note:The provisions of this §217.34 adopted to be effective August 28, 2008, 33 TexReg 6843.