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RULE §317.2Sewage Collection System

(a) General requirements.

  (1) Design. Sewer lines shall be designed for the estimated future population to be served, plus adequate allowance for institutional and commercial flows. The collection system design shall provide a minimum structural life cycle of 50 years. The collection system design shall provide for the minimization of anaerobic conditions. Design procedures for the minimization of anaerobic conditions outlined in the United States Environmental Protection Agency (EPA) Design Manual for Odor and Corrosion Control in Sanitary Sewerage Systems and Treatment Plants (EPA/625/1-85/018), American Society of Continuing Education (ASCE) Manual of Engineering Practice Number 69 (MEP-69), or other appropriate references, should be followed. The owner of the collection system shall provide inspection under the direction of a Texas registered professional engineer during construction and testing phases of the project. All collection systems to be located over the recharge zone of the Edwards Aquifer shall be designed and installed in accordance with Chapter 213 of this title (relating to Edwards Aquifer) in addition to these rules.

  (2) Pipe selection. The choice of sewer pipe shall be based on the chemical characteristics of the water delivered by public and private water suppliers, the character of industrial wastes, the possibilities of septicity, the exclusion of inflow and infiltration, the external forces, internal pressures, abrasion, and corrosion resistance. For all installations, if a pipe as a whole or an integral structural component of the pipe will deteriorate when subjected to corrosive internal conditions, a corrosive resistant coating or liner acceptable to the commission shall be installed at the pipe manufacturing facility unless the final engineering design report, including calculations and data, submitted by the engineer demonstrates that the design and operational characteristics of the system will maintain the structural integrity of the system during the minimum life cycle. The sewer pipe to be used shall be identified in the plans and technical specifications 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, etc.) and installation (bedding, backfill, etc.).

    (A) Flexible pipe. The engineer shall submit an engineering report that includes the method of defining the modulus of soil reaction, (E'), for the bedding material, (E'b ), and the natural soil (E'n ), or other specific information to quantify the effect of the in-situ material on the effective modulus, (E'e ). The report shall also include design calculations for E'e , prism load, live loads, long-term deflection, strain, bending strain, buckling, and wall crushing. The design calculations shall include all information pertinent to the determination of an adequate design including, but not limited to: pipe diameter and material with reference to appropriate standards, modulus of elasticity, tensile strength, pipe stiffness or ring stiffness constant converted to pipe stiffness as described below, Leonhardt's zeta factor or E'e from another acceptable method, the conversion factor used to obtain vertical deflection when using the Modified Iowa Equation, trench width, depth of cover, water table elevation, etc. Pipe stiffness shall be related to Ring Stiffness Constant (RSC), when necessary, by the following equation:

Attached Graphic

    (B) Rigid pipe. The engineer shall submit an engineering report that includes the trench width, water table, and depth of cover, etc. For rigid conduits the minimum strengths for the given class shall be noted in the appropriate standard for the pipe material. For the purpose of this section, rigid pipe is defined as concrete, vitrified clay, or ductile iron pipe.

    (C) Other pipe materials may be considered on a case-by-case basis by the executive director. The design and installation of such materials shall generally follow the guidelines for flexible or rigid pipe with appropriate exceptions.

  (3) Jointing material. The materials used and methods to be applied in making joints shall be included in the technical specifications. Materials used for sewer joints shall have a satisfactory record of preventing infiltration and root entrance. Rubber gaskets, polyvinyl chloride (PVC) compression joints, high compression polyurethane, welded or other types of factory made joints are required.

  (4) Testing of installed pipe. An infiltration, exfiltration, or low-pressure air test shall be specified. Copies of all test results shall be made available to the executive director upon request. Tests shall conform to the following requirements.

    (A) Infiltration or exfiltration tests. The total exfiltration, as determined by a hydrostatic head test, shall not exceed 50 gallons per inch diameter per mile of pipe per 24 hours at a minimum test head of two feet above the crown of the pipe at the upstream manhole. When pipes are installed below the groundwater level an infiltration test shall be used in lieu of the exfiltration test. The total infiltration, as determined by a hydrostatic head test, shall not exceed 50 gallons per inch diameter per mile of pipe per 24 hours at a minimum test head of two feet above the crown of the pipe at the upstream manhole, or at least two feet above existing groundwater level, whichever is greater. For construction within the 25-year flood plain, the infiltration or exfiltration shall not exceed ten gallons per inch diameter per mile of pipe per 24 hours at the same minimum test head. If the quantity of infiltration or exfiltration exceeds the maximum quantity specified, remedial action shall be undertaken in order to reduce the infiltration or exfiltration to an amount within the limits specified.

    (B) Low pressure air test. The procedure for the low pressure air test shall conform to the procedures described in ASTM C-828, ASTM C-924, ASTM F-1417, or other appropriate procedures, except for testing times. The test times shall be as outlined in this section. For sections of pipe less than 36-inch average inside diameter, the following procedure shall apply unless the pipe is to be joint tested. The pipe shall be pressurized to 3.5 per square inch (psi) greater than the pressure exerted by groundwater above the pipe. Once the pressure is stabilized, the minimum time allowable for the pressure to drop from 3.5 pounds per square inch gauge to 2.5 pounds per square inch gauge shall be computed from the following equation. The test may be stopped if no pressure loss has occurred during the first 25% of the calculated testing time. If any pressure loss or leakage has occurred during the first 25% of the testing period, then the test shall continue for the entire test duration as outlined in this subparagraph or until failure. Lines with a 27-inch average inside diameter and larger may be air tested at each joint. Pipe greater than 36-inch diameter must be tested for leakage at each joint. If the joint test is used, a visual inspection of the joint shall be performed immediately after testing. The pipe is to be pressurized to 3.5 psi greater than the pressure exerted by groundwater above the pipe. Once the pressure has stabilized, the minimum time allowable for the pressure to drop from 3.5 pounds per square inch gauge to 2.5 pounds per square inch gauge shall be ten seconds.

Attached Graphic

    (C) Deflection testing. Deflection tests shall be performed on all flexible pipes. For pipelines with inside diameters less than 27 inches, a rigid mandrel shall be used to measure deflection. For pipelines with an inside diameter 27 inches and greater, a method approved by the executive director shall be used to test for vertical deflections. Other methods shall provide a precision of plus or minus two-tenths of 1.0% (0.2%) deflection. The test shall be conducted after the final backfill has been in place at least 30 days. No pipe shall exceed a deflection of 5.0%. If a pipe should fail to pass the deflection test, the problem shall be corrected and a second test shall be conducted after the final backfill has been in place an additional 30 days. The tests shall be performed without mechanical pulling devices. The design engineer should recognize that this is a maximum deflection criterion for all pipes and a deflection test less than 5.0% may be more appropriate for specific types and sizes of pipe. Upon completion of construction, the design engineer or other Texas registered professional engineer appointed by the owner shall certify to the executive director that the entire installation has passed the deflection test. This certification may be made in conjunction with the notice of completion required in §317.1(e)(1) of this title (relating to General Provisions). This certification shall be provided for the commission to consider the requirements of the approval to have been met.

      (i) Mandrel sizing. The rigid mandrel shall have an outside diameter equal to 95% of the inside diameter of the pipe. The inside diameter of the pipe, for the purpose of determining the outside diameter of the mandrel, shall be the average outside diameter minus two minimum wall thicknesses for outside diameter controlled pipe and the average inside diameter for inside diameter controlled pipe, all dimensions shall be per appropriate standard. Statistical or other "tolerance packages" shall not be considered in mandrel sizing.

      (ii) Mandrel design. The rigid mandrel shall be constructed of a metal or a rigid plastic material that can withstand 200 psi without being deformed. The mandrel shall have nine or more "runners" or "legs" as long as the total number of legs is an odd number. The barrel section of the mandrel shall have a length of at least 75% of the inside diameter of the pipe. A proving ring shall be provided and used for each size mandrel in use.

      (iii) Method options. Adjustable or flexible mandrels are prohibited. A television inspection is not a substitute for the deflection test. A deflectometer may be approved for use on a case-by-case basis. Mandrels with removable legs or runners may be accepted on a case-by-case basis.

  (5) Bedding: trenching, bedding, and backfill. The width of the trench shall be minimized, but shall be ample to allow the pipe to be laid and jointed properly and to allow the backfill to be placed and compacted as needed. The trench sides shall be kept as nearly vertical as possible. As used herein, a trench shall be defined as that open cut portion of the excavation up to one foot above the pipe. The engineer shall specify the maximum trench width. The width of the trench shall be sufficient, but no greater than necessary, to ensure working room to properly and safely place and compact haunching materials. The space must be wider than the compaction equipment used in the pipe zone. A minimum clearance of four inches below and on each side of all pipes to the trench walls and floor shall be provided. Bedding Classes A, B, or C, as described in ASTM C 12 (ANSI A 106.2), Water Environment Federation (WEF) Manual of Practice (MOP) Number 9 or American Society of Civil Engineers (ASCE) MOP 37 shall be used for all rigid pipes, provided that the proper strength pipe is used with the specified bedding to support the anticipated load(s). Embedment Classes IA, IB, II, or III, as described in ASTM D-2321 (ANSI K65.171) shall be used for all flexible pipes, provided the proper strength pipe is used with the specified bedding to support the anticipated load, except that ASTM D-2680 may be used if the pipe stiffness is 200 psi or greater. Secondary backfill shall be of suitable material removed from excavation except where other material is specified. Debris, large clods or stones greater than six inches in diameter, organic matter, or other unstable materials shall not be used for backfill. Backfill shall be placed in such a manner as not to disturb the alignment of the pipe. Where trenching encounters extensive fracture or fault zones, caves, or solutional modification to the rock strata, construction shall be halted and an engineer shall provide direction to accommodate site conditions. Water line crossings shall be governed by special backfill requirements specified in §317.13 of this title (relating to Appendix E--Separation Distances).

  (6) Site inspections. The executive director shall, on a random basis, perform site inspections.

  (7) Protecting public water supply. Water lines and sanitary sewers shall be installed no closer to each other than nine feet between outside diameters. Where this cannot be achieved, the sanitary sewer shall be constructed in accordance with §317.13 of this title and §290.44(e)(1) of this title (relating to Water Distribution). Separation distances between sanitary sewer systems and water wells, springs, surface water sources, and water storage facilities shall be installed in accordance with the requirements of §290.41(c)(1), (d)(1), (e)(1)(C), and (e)(3)(A), and §290.43(b)(3) of this title (relating to Water Sources; and Water Storage, respectively), as appropriate. Where rules governing separation distance are in conflict, the most strict rule shall apply. No physical connection shall be made between a drinking water supply, public or private, and a sewer or any appurtenance. An air gap of a minimum of 18 inches or two pipe diameters, whichever is greater, shall be maintained between all potable water outlets and the maximum water surface elevation of sewer appurtenances. All appurtenances shall be designed and constructed so as to prevent any possibility of sewage entering the potable water system.

  (8) Excluding surface water. Proposals for the construction of combined sewers will not be approved. Roof, street, or other types of drains which will permit entrance of surface water into the sanitary sewer system shall not be acceptable.


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