(a) Flow Design Basis. An owner must use the requirements of this section to design a gravity collection system.
  (1) A collection system must be designed to transport the peak flow from the service area, plus infiltration and inflow. The design must minimize inflow and infiltration. Flow calculations must be included in the engineering report.
  (2) The flow calculations must include the details of the average flow, the flow peaking factor, and the infiltration and inflow.
  (3) The flow calculations must include the flow expected in the wastewater treatment facility immediately upon completion of construction and at the end of a 50-year period following construction.
(b) Gravity Pipe Materials.
  (1) An owner must identify in the engineering report the proposed gravity collection system pipe with its appropriate American Society for Testing and Materials (ASTM), American National Standards Institute (ANSI), or American Water Works Association (AWWA) standard numbers for both quality control (dimensions, tolerances, pipe stiffness, dimensional ratio, etc.) and installation (bedding, backfill, etc.).
  (2) The selection of gravity collection system pipes must be based on:
    (A) the characteristics of the wastewater conveyed;
    (B) the possibility of septic conditions;
    (C) the ability to minimize inflow and infiltration;
    (D) any external forces;
    (E) any groundwater conditions;
    (F) the internal pressures; and
    (G) the abrasion and corrosion resistance of the pipe material.
(c) Joints for Gravity Pipes.
  (1) The specifications for joints for gravity pipes must include the materials and methods used in making joints.
  (2) Materials used for gravity pipe joints must prevent inflow, infiltration, and root entrance. A joint must:
    (A) include rubber gaskets;
    (B) include polyvinyl chloride (PVC) compression joints;
    (C) include high density polyethylene compression joints;
    (D) be welded; or
    (E) be heat fused.
  (3) The specifications must include ASTM, AWWA, ANSI, or other appropriate national reference standards for the pipe joints.
(d) Separation Distances.
  (1) Collection system pipes must be installed in trenches separate from water supply trenches.
  (2) Wherever possible, a collection system pipe must be located below a water supply pipe. If a collection system pipe cannot be located below a water supply pipe, the owner must justify in the engineering report why it is not possible to locate the collection system pipe below the public water supply pipe.
  (3) Wherever possible, collection system pipes and manholes must be located at least nine feet from all water supply pipes. If a collection system pipe or manhole cannot be located at least nine feet away from a water supply pipe, the owner must justify in the engineering report why it is not possible to provide at least nine feet of separation. Table C.1. in Figure: 30 TAC §217.53(d)(3) provides a reference to paragraphs in this subsection that apply if a collection system pipe or manhole cannot be located at least nine feet away from a water supply pipe.
Attached Graphic
  (4) If a collection system pipe is located above a water supply pipe and runs parallel to the water supply pipe, each portion of the collection system pipe within nine feet of the water supply pipe must be encased. The casing pipe must be constructed of at least 150 per square inch (psi) pressure class pipe that:
    (A) encases the entire length of collection system pipe that is within nine feet of the water supply pipe;
    (B) is sealed at both ends with cement grout or a manufactured seal;
    (C) is at least two nominal sizes larger than the wastewater collection pipe; and
    (D) is supported by spacers between the collection system pipe and the encasing pipe at a maximum of five-foot intervals.
  (5) If a collection system pipe crosses above a water supply pipe, each portion of the collection system pipe within nine feet of the water supply pipe must either be encased in a casing pipe according to subparagraph (A) of this paragraph, or must be constructed using at least 150 psi pressure class pipe according to subparagraph (B) of this paragraph.
    (A) A casing pipe for a collection system pipe that crosses above a water supply pipe must be constructed of at least 150 psi pressure class pipe that is:
      (i) sealed at both ends with cement grout or a manufactured seal;
      (ii) at least two nominal sizes larger than the wastewater collection pipe; and
      (iii) supported by spacers between the collection system pipe and the encasing pipe at a maximum of five-foot intervals.
    (B) A collection system pipe that crosses above a water supply pipe must be constructed of at least 150 psi pressure class, corrosion-resistant, non-brittle pipe and must use manufacturer-approved adapters. Gasketed joints, compression joints, and other non-bonded joints must be designed to seal at atmospheric pressure.
  (6) If a collection system pipe is located below a water supply pipe and runs parallel to the water supply pipe, each portion of the collection system pipe within nine feet of the water supply pipe must either be constructed using at least 150 psi pressure class pipe according to subparagraph (A) of this paragraph, or must be encased in a casing pipe according to subparagraph (B) of this paragraph.
    (A) A collection system pipe that runs parallel to and below a water supply pipe must be constructed of at least 150 psi pressure class, corrosion-resistant, non-brittle pipe that:
      (i) is located at least two vertical feet below the water supply pipe;
      (ii) is located at least four horizontal feet away from the water supply pipe; and
      (iii) includes joints that are designed to seal at atmospheric pressure.
    (B) A casing pipe for a collection system pipe that runs parallel below a water supply pipe must be constructed of at least 150 psi pressure class pipe that:
      (i) is sealed at both ends with cement grout or a manufactured seal;
      (ii) is at least two nominal sizes larger than the wastewater collection pipe; and
      (iii) is supported by spacers between the collection system pipe and the encasing pipe at a maximum of five-foot intervals.
  (7) If a collection system pipe crosses below a water supply pipe, each portion of the collection system pipe within nine feet of the water supply pipe must either be constructed using at least 150 psi pressure class pipe according to subparagraph (A) of this paragraph, or must be encased in cement-stabilized sand according to subparagraph (B) of this paragraph, or must be encased in a casing pipe according to subparagraph (C) of this paragraph.
    (A) A collection system that crosses below a water supply pipe and is constructed of at least 150 psi pressure class, corrosion-resistant, non-brittle pipe must:
      (i) have at least six inches of separation between the outsides of the pipes;
      (ii) be centered on the crossing;
      (iii) be at least 18 feet long; and
      (iv) terminate at joints that are designed to seal at atmospheric pressure.
    (B) A collection system pipe that crosses below a water supply pipe and is constructed of any material other than at least 150 psi pressure class, corrosion-resistant, non-brittle pipe must:
      (i) have at least two feet of separation between the outsides of the pipes; and
      (iii) be encased in cement-stabilized sand backfill that meets the requirements of subparagraph (D) of this paragraph.
    (C) A casing pipe for a collection system pipe that crosses below a water supply pipe must be constructed of at least 150 psi pressure class pipe that is:
      (i) sealed at both ends with cement grout or a manufactured seal;
      (ii) at least two nominal sizes larger than the wastewater collection pipe; and
      (iii) supported by spacers between the collection system pipe and the encasing pipe at a maximum of five-foot intervals.
    (D) Cement-stabilized sand for encasing collection system pipes must:
      (i) include at least 160 pounds of cement for every cubic yard of sand;
      (ii) be installed beginning one-quarter pipe diameter below the centerline of the collection system pipe;
Cont'd...