(a) The design of a new wastewater treatment facility must be based on the flows and loadings in paragraphs (1) - (3) of this subsection, unless subsection (b) of this section applies.
  (1) Design flow.
    (A) If the flow is greater than or equal to 1.0 million gallons per day, as determined by multiplying the per capita flow in Table B.1. in paragraph (3) of this subsection by the number of individuals in the service area, then the design flow is the flow calculated from the table.
    (B) If the flow is less than 1.0 million gallons per day as determined by multiplying the per capita flow in Table B.1. in paragraph (3) of this subsection by the number of individuals in the service area, then the design flow is determined by multiplying the average annual flow calculated from the table by a factor of at least 1.5.
    (C) The design flow must be based on the flow authorized in the wastewater treatment facility's wastewater permit.
  (2) Peak flow. When site-specific data is unavailable, the peak flow must be determined by multiplying the design flow by a factor of at least 4.0. If site-specific data or projections are available, the peak flow must be based on the site-specific data.
    (A) If the average daily peaking factor at a wastewater treatment facility exceeds 4.0, the actual daily peaking factor must be used to calculate the peak flow, unless flow equalization is provided.
    (B) If a wastewater treatment facility experiences occasional peak events with a peaking factor that exceeds 5.0, the event-based peaking factor must be used to calculate the peak flow, unless flow equalization is provided.
    (C) In a wastewater treatment facility with flow equalization, the subsequent treatment units may be designed for a lower estimated peak flow. The engineering report shall include data that supports the lower estimated peak flow.
    (D) A treatment unit, pipe, weir, flume, disinfection unit, or any other treatment unit that is flow limited must be sized to transport or treat the peak flow.
  (3) Design organic loading. If available, actual organic loading data must be used as the basis for the design of the wastewater treatment facility. If actual organic loading data is not available, the design organic load must be determined by using the following table. The design organic load is determined by multiplying the annual average flow from the projected uses by the corresponding influent concentrations:
Attached Graphic
(b) An owner designing a new wastewater treatment facility that will serve the same service area as an existing wastewater treatment facility must use historical data from the existing wastewater treatment facility to design the new wastewater treatment facility, if there is enough historical data to meet the needs of §217.34 of this title (relating to Organic Loadings and Flows for Existing Wastewater Treatment Facilities, Re-Ratings, and Alterations). The engineering report must justify the design conclusions that are based on existing data.

Source Note: The provisions of this §217.32 adopted to be effective August 28, 2008, 33 TexReg 6843; amended to be effective December 4, 2015, 40 TexReg 8254