(a) The permittee must demonstrate in the engineering report and ensure that the hydraulic application rate for a subsurface area drip dispersal system meets one of the following.
  (1) The hydraulic application rate shall not exceed 0.1 gallons per square foot per day for a subsurface area drip dispersal system located west of the boundary shown in Figure 1 in paragraph (2) of this subsection, and using a vegetative cover of non-native grasses that are over seeded with cool season grasses in the winter months (October - March).
  (2) The hydraulic application rate for a subsurface area drip dispersal system located east of the boundary shown in Figure 1 of this paragraph or in any part of the state when the vegetative cover is any crop other than non-native grasses, the permittee shall use the equations in Figure 2 or 3 of this paragraph to establish the rate.
Attached Graphic
Attached Graphic
Attached Graphic
  (3) The applicant must calculate the hydraulic application rate for each month of the year. A monthly water balance is computed that includes soil moisture storage. Any available soil moisture is carried over to the next month. The maximum application rate is exceeded when the total hydraulic loading (rainfall and irrigation) exceeds the total of the available soil moisture storage, the actual water requirement of crop (inches per month), and leaching.
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  (4) The permittee may use an alternative method to calculate the hydraulic application rate with approval from the executive director.
(b) The nitrogen application rate for a subsurface area drip dispersal system must be calculated using the anticipated nitrogen concentration of wastewater effluent prior to land application.
  (1) The permittee must calculate the allowable annual hydraulic loading rate based on nitrogen limits using the equation in this paragraph.
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  (2) Upon request by the applicant, the executive director may approve other fractions of applied nitrogen removed based upon special conditions relating to a proposed site, if justified in the engineering report.
(c) The result obtained from calculation of the allowable annual hydraulic loading rate that is based upon nitrogen limits must be compared to the hydraulic loading rate that is based on crop need and soil water holding capacity in the figure in subsection (a)(3) of this section. The more restrictive of the two calculations will set the maximum hydraulic application rate.
(d) The volume of wastewater used when calculating the disposal area required based on the hydraulic application rate as described in this section may be reduced by the beneficial reuse credit, as calculated in accordance with Chapter 309, Subchapter D of this title (relating to Beneficial Reuse Credit) and approved by the commission.
(e) The disposal site area required may not be reduced by more than 50% of what the disposal site requirement would be using the permitted flow without the beneficial reuse credit.

Source Note: The provisions of this §222.83 adopted to be effective July 5, 2006, 31 TexReg 5308; amended to be effective January 9, 2020, 45 TexReg 363