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RULE §285.33Criteria for Effluent Disposal Systems

(a) General requirements.

  (1) All disposal systems in this section shall have an approved treatment system as specified in §285.32(b) - (d) of this title (relating to Criteria for Sewage Treatment Systems).

  (2) All criteria in this section shall be met before the permitting authority issues an authorization to construct.

  (3) The pipe between all treatment tanks and the pipe from the final treatment tank to a gravity disposal system shall be a minimum of three inches in diameter and be American Society for Testing and Materials (ASTM) 3034, Standard dimension ratio (SDR) 35 polyvinyl chloride (PVC) pipe or a pipe with an equivalent or stronger pipe stiffness at a 5% deflection. The pipe must maintain a continuous fall to the disposal system.

  (4) The pipe from the final treatment tank to a gravity disposal system shall be a minimum of five feet in length.

  (5) Except for drip irrigation tubing, pipe under internal pressure within any part of an on-site sewage facility system shall meet the minimum requirements of ASTM Schedule 40.

  (6) Pipe that crosses drainage easements shall be sleeved with ASTM Schedule 40 pipe; the pipes shall be buried at least one foot below the surface, or buried less than one foot and encased in concrete; the outside pipe shall have locater tape attached to the pipe; and markers shall be placed at the easement boundaries to indicate the location of the pipe crossing. Crossings shall be designed and constructed in a manner that protects the pipe and the drainage way from erosion.

(b) Standard disposal systems. Acceptable standard disposal methods shall consist of a drainfield to disperse the effluent either into adjacent soil (absorptive) or into the surrounding air through evapotranspiration (evaporation and transpiration).

  (1) Absorptive drainfield. An absorptive drainfield shall only be used in suitable soil. There shall be two feet of suitable soil from the bottom of the excavation to either a restrictive horizon or to groundwater.

    (A) Excavation. The excavation must be made in suitable soils as described in §285.31(b) of this title (relating to Selection Criteria for Treatment and Disposal Systems).

      (i) The excavation shall be at least 18 inches deep but shall not exceed a depth of either three feet or six inches below the soil freeze depth, whichever is deeper. Single excavations shall not exceed 150 feet.

      (ii) In areas of the state where annual precipitation is less than 26 inches per year (as identified in the Climatic Atlas of Texas, (1983) published by the Texas Department of Water Resources or other standards approved by the executive director), the maximum permissible excavation depth shall be five feet.

      (iii) Multiple excavations must be separated horizontally by at least three feet of undisturbed soil. The sidewalls and bottom of the excavation must be scarified as needed. When there are multiple excavations, it is recommended that the ends be looped together.

      (iv) The bottom of the excavation shall be not less than 18 inches in width.

      (v) The bottom of the excavation shall be level to within one inch over each 25 feet of excavation or within three inches over the entire excavation, whichever is less.

      (vi) If the borings or backhoe pits excavated during the site evaluation encounter a rock horizon and the site evaluation shows that there is both suitable soil from the bottom of the rock horizon to two feet below the bottom of the proposed excavation and no groundwater anywhere within two feet of the bottom of the proposed excavation, a standard subsurface disposal system may be used, providing the following are met.

        (I) The depth of the excavation shall comply with clause (i) of this subparagraph.

        (II) The rock horizon shall be at least six inches above the bottom of the excavation.

        (III) Surface runoff shall be prevented from flowing over the disposal area.

        (IV) Subsurface flow along the top of the rock horizon shall be prevented from flowing into the excavation.

        (V) The sidewall area will not be counted toward the required absorptive area.

        (VI) The formulas in clause (vii)(I) - (III) of this subparagraph shall be adjusted so that no credit is given for sidewall area.

        (VII) No single pipe drainfields on sloping ground as shown in §285.90(5) of this title (relating to Figures) or no systems using serial loading shall be used.

      (vii) The size of the excavation shall be calculated using data from §285.91(1) and (3) of this title (relating to Tables). The soil application rate is based on the most restrictive horizon along the media, or within two feet below the bottom of the excavation. The formula A = Q/Ra shall be used to determine the total absorptive area where:

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        (I) The absorptive area shall be calculated by adding the bottom area (L x W) of the excavation to the total absorptive area along the excavated perimeter 2(L+W), (in feet) multiplied by one foot.

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        (II) The length of the excavation may be determined as follows when the area and width are known.

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        (III) For excavations three feet wide or less, use the following formula, or §285.91(8) of this title to determine L.

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    (B) Media. The media shall consist of clean, washed and graded gravel, broken concrete, rock, crushed stone, chipped tires, or similar aggregate that is generally one uniform size and approved by the executive director. The size of the media must range from 0.75 - 2.0 inches as measured along its greatest dimension except as noted in clause (i) of this subparagraph.

      (i) If chipped tires are used:

        (I) a geotextile fabric heavier than specified in subparagraph (E) of this paragraph must be used; and

        (II) the size of the chipped tires must not exceed three inches as measured along their greatest dimension.

      (ii) Soft media such as oyster shell and soft limestone shall not be used.

    (C) Drainline. The drainline shall be constructed of perforated distribution pipe and fittings in compliance with any one of the following specifications:

      (i) three- or four-inch diameter PVC pipe with an SDR of 35 or stronger;

      (ii) four-inch diameter corrugated polyethylene, ASTM F405 in rigid ten foot joints;

      (iii) three- or four-inch diameter polyethylene smoothwall, ASTM F810;

      (iv) three- or four-inch diameter PVC ASTM D2729 pipe;

      (v) three- or four-inch diameter polyethylene ASTM F892 corrugated pipe with a smoothwall interior and fittings; or

      (vi) any other pipe approved by the executive director.

    (D) Drainline installation requirements. The drainline shall be placed in the media with at least six inches of media between the bottom of the excavation and the bottom of the drainline. The drainline shall be completely covered by the media and the drainline perforations shall be below the horizontal center line of the pipe. For typical drainfield configurations, see §285.90(5) of this title. For excavations greater than four feet in width, the maximum distance between parallel drainlines shall be four feet (center to center). Multiple drainlines shall be manifolded together with solid or perforated pipe. Additionally, the ends of the multiple drainlines opposite the manifolded end shall either be manifolded together with a solid line, looped together using a perforated pipe and media, or capped.

    (E) Permeable soil barrier. Geotextile fabric shall be used as the permeable soil barrier and shall be placed between the top of the media and the excavation backfill. Geotextile fabric shall conform to the following specifications for unwoven, spun-bounded polypropylene, polyester, or nylon filter wrap.

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    (F) Backfilling. Only Class Ib, II, or III soils as described in §285.30 of this title (relating to Site Evaluation) shall be used for backfill. Class Ia and IV soils are specifically prohibited for use as a backfill material. The backfill material shall be mounded over the excavated area so that the center of the backfilled area slopes down to the outer perimeter of the excavated area to allow for settling. Surface runoff impacting the disposal area is not permitted and the diversion method shall be addressed during development of the planning materials.


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