SECTION 317.2. Sewage 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.

(9) Active geologic faults. For systems to be located in areas of known active geologic faults, the design engineer shall locate any faults within the area of the collection system and the system shall be laid out to minimize the number of sewers crossing faults. Where crossings are unavoidable, the engineering report shall specify design features to protect the integrity of the sewer. Consideration should be given to joints providing maximum deflection and to providing manholes on each side of the fault so that a portable pump may be used in the event of sewer failures. Service connections within 50 feet of an active fault should be avoided.

(10) Erosion control. Erosion or sedimentation control that minimizes the effects of runoff shall be provided during the construction phase of a project. This requirement will be reviewed on a case-by-case basis.

(b) Capacities.

(1) Sources. The peak flow of domestic sewage, peak flow of waste from industrial plants, and maximum infiltration rates shall be considered in determining the hydraulic capacity of sanitary sewers.

(2) Existing systems. The design of extensions to sanitary sewers should be based on the data from the existing system. If this is not possible, the design shall be based on data from similar systems or paragraph (3) of this subsection, new systems.

(3) New systems. New sewers shall be sized using an appropriate engineering analysis of existing and future flow data. The executive director shall have the authority to determine the reliability and appropriateness of the data utilized for sizing the system. In the absence of local reliable flow data and engineering analysis, new sewer systems shall be designed on the basis of an estimated daily sewage flow contribution as shown in the table in §317.4(a) of this title (relating to Wastewater Treatment Facilities). Minor sewers shall be designed such that when flowing full they will transport wastewater at a rate approximately four times the system design daily average flow. Main trunk, interceptor, and outfall sewers shall be designed to convey the contributed minor sewer flows.

(c) Design details.

(1) Minimum size. No sewer other than service laterals and force mains shall be less than six inches in diameter.

(2) Slope. All sewers shall be designed and constructed with slopes sufficient to give a velocity when flowing full of not less than 2.0 feet per second. The grades shown in the following table are based on Manning's formula with an assumed "n factor" of 0.013 and constitute minimum acceptable slopes. The minimum acceptable "n" for design and construction shall be 0.013. The "n" used takes into consideration the slime, grit, and grease layers that will affect hydraulics or hinder flow as the pipe matures.

Attached Graphic

(3) High velocity protection. Where velocities greater than ten feet per second will occur when the pipe is flowing full, at slopes greater than those listed in paragraph (2) of this subsection, special provisions shall be made to protect against pipe displacement by erosion of the bedding and/or shock.

(4) Alignment. Sewers shall be laid in straight alignment with uniform grade between manholes unless slight deviations from straight alignment and uniform grade are justified to the satisfaction of the executive director.

(5) Manhole use. Manholes shall be placed at all points of change in alignment, grade, or size of sewer, at the intersection of all sewers and the end of all sewer lines that will be extended at a future date. Any proposal which deviates from this requirement shall be justified to the satisfaction of the executive director. Clean-outs with watertight plugs may be installed in lieu of manholes at the end of sewers which are not anticipated to be extended. Such installations must pass a leakage test and a deflection test for all flexible lines.

(A) Type. Manholes shall be monolithic, cast-in-place concrete, fiberglass, precast concrete, high-density polyethylene (HDPE), or of equivalent construction. Brick manholes shall not be used, nor shall brick be used to adjust manhole covers to grade.

(B) Spacing. The maximum required manhole spacing for sewers with straight alignment and uniform grades are in the following table. Reduced manhole spacing may be necessary depending on the utility's ability to maintain its sewer lines. Areas subject to flooding require special consideration to minimize inflow.

Attached Graphic

(C) Inflow and infiltration control. Watertight, size-on-size resilient connectors allowing for differential settlement shall be used to connect pipe to manholes. Pipe to manhole connectors shall conform to ASTM C-923. Other types of connectors may be used when approved by the commission. Manholes should not allow surface water to drain into them. If manholes are located within the 100-year flood plain, the manhole covers shall have gaskets and be bolted or have another means of preventing inflow. Where gasketed manhole covers are required for more than three manholes in sequence, an alternate means of venting shall be provided at less than 1,500 foot intervals. Vents should be designed to minimize inflow. Impervious material should be utilized for manhole construction in these areas in order to minimize infiltration.

(D) Manhole diameter. Manholes shall be of sufficient inside diameters to allow personnel to work within them and to allow proper joining of the sewer pipes in the manhole wall. The inside diameter of manholes shall be not less than 48 inches.

(E) Manhole inverts. The bottom of the manhole shall be provided with a "U" shaped channel that is as much as possible a smooth continuation of the inlet and outlet pipes. For manholes connected to pipes less than 15 inches in diameter the channel depth shall be at least half the largest pipe diameter. For manholes connected to pipes 15 to 24 inches in diameter the channel depth shall be at least three-fourths the largest pipe diameter. For manholes connected to pipes greater than 24 inches in diameter the channel depth shall be at least equal to the largest pipe diameter. In manholes with pipes of different sizes, the tops of the pipes shall be placed at the same elevation and flow channels in the invert sloped on an even slope from pipe to pipe. The bench provided above the channel shall be sloped at a minimum of 0.5 inch per foot. Where sewer lines enter the manhole higher than 24 inches above the manhole invert, the invert shall be filleted to prevent solids deposition. A drop pipe should be provided for a sewer entering a manhole more than 30 inches above the invert.

(F) Manhole covers. Manhole covers of nominal 24-inch or larger diameter are to be used for all sewer manholes.

(G) Manhole access. Design of features for entering manholes shall be guided by the following criteria.

(i) It is suggested that entrance into manholes in excess of four feet deep be accomplished by means of a portable ladder. Other designs for ingress and egress should be given careful evaluation considering the safety hazards associated with the use of manhole steps under certain conditions.

(ii) Where steps are used, they shall be made of a noncorrosive material and be in accordance with applicable OSHA specifications as published by the United States Department of Labor.

(H) Testing. Manholes shall be tested for leakage separately and independently of the wastewater lines by hydrostatic exfiltration testing, vacuum testing, or other methods acceptable to the commission. If a manhole fails a leakage test, the manhole must be made watertight and retested. The maximum leakage for hydrostatic testing shall be 0.025 gallons per foot diameter per foot of manhole depth per hour. Alternative test methods must ensure compliance with the above allowable leakage. Hydrostatic exfiltration testing shall be performed as follows: all wastewater lines coming into the manhole shall be sealed with an internal pipe plug, then the manhole shall be filled with water and maintained full for at least one hour. For concrete manholes a wetting period of 24 hours may be used prior to testing in order to allow saturation of the concrete.

(6) Sag pipes (inverted siphons). Sag pipes shall have two or more barrels, a minimum pipe diameter of six inches and shall be provided with necessary appurtenances for convenient flushing and maintenance. The manholes shall have adequate clearances for rodding, and in general, sufficient head shall be provided and pipe sizes selected to assure velocities of at least three feet per second at design flows. The inlet and outlet details shall be arranged so that the normal flow is diverted to one barrel. Provisions shall be made such that either barrel may be taken out of service for cleaning.

(d) Alternative wastewater collection systems. Use of alternative wastewater collection systems may be considered when justified by unusual terrain or geological formations, low population density, difficult construction, or other circumstances where an alternative wastewater collection system would offer an advantage over a conventional gravity system. An alternative wastewater collection system will be considered for approval only when conditions make a conventional gravity collection system impractical. Alternative wastewater collection system types include pressure sewers (septic tank effluent pumping or grinder pump systems), small diameter gravity sewers (minimum grade effluent sewers or variable grade effluent sewers), vacuum sewers, and combinations thereof. Alternative wastewater collection systems are comprised of both on-site (interceptor tanks, pumps, pump tanks, valves, service laterals) and off-site components (collector mains, force mains, vacuum stations, clean-outs, manholes, vents, and lift stations). Pressure sewer systems, small diameter gravity sewers, and vacuum sewers will be approved on a case-by-case basis. The engineering report must justify the design of alternative wastewater collection systems to the satisfaction of the executive director. The EPA's Manual of Alternative Wastewater Collection Systems (EPA/625/1-91/024), the WEF's Alternative Sewer Systems (MOP FD-12), or other appropriate engineering literature should be used as the basis for design.

(1) Management. A responsible management structure under the regulatory jurisdiction of the Texas Commission on Environmental Quality shall be established, to the satisfaction of the executive director, to be in charge of the operation and maintenance of an alternative wastewater collection system. A legally binding service agreement shall be required to insure the alternative wastewater collection system is properly constructed and maintained. The required elements of the service agreement are as follows.

(A) The document must be legally binding.

(B) Existing septic and pump tanks that are to be used as interceptor tanks for primary treatment, wastewater storage, or pump tanks prior to the discharge into an alternative sewer system must be cleaned, inspected, repaired, modified, or replaced if necessary, to minimize inflow and infiltration into the collection system prior to connection.

(C) The utility shall have approval authority for the design of the system including all materials and equipment prior to the installation of an interceptor tank, pressure sewer pump tank, or vacuum system appurtenances. The materials shall comply with standard specifications submitted to and approved by the executive director.

(D) The utility must be able to approve the installation of the interceptor tank, pressure sewer pump tank, or vacuum system appurtenances after construction to ensure the installation was as specified.

(E) The utility must be responsible for the operation and maintenance of the system including any interceptor tank, pressure sewer pump tank, or vacuum system appurtenances incorporated.

(F) The utility must be able to stop any discharges from any collection system appurtenances in order to prevent contamination of state waters.

(G) The utility shall submit a maintenance schedule to the executive director which outlines routine service inspections and maintenance for all types of pressure sewers, small diameter gravity sewers, and vacuum sewer system components.

(H) Pumping units, grinder pumps, vacuum sewer appurtenances, interceptor tanks shall be regarded as integral components of the system and not as a part of the home plumbing.

(I) Provision to ensure collection system integrity during a power outage (two-year event) shall be incorporated into the design. Power outage duration will be determined as described in §317.3(e)(1) of this title (relating to Lift Stations).

(2) Pressure sewer system design considerations. The following shall be submitted to and approved by the executive director:

(A) hydraulic calculations for sizing the pressure sewer pumping system shall be based on providing the firm capacity to pump the expected peak flow. These calculations shall include system and pump curves as described in §317.3(c)(4) of this title, wet well capacity calculations based on minimum cycle times as described in §317.3(b)(4)(B) of this title, and emergency and flow equalization storage as necessary. The number of units pumping at any one time may be estimated based on appropriate engineering literature;

(B) flow velocities in the range of three to five feet per second;

(C) the installation of air relief valves;

(D) the provision of means to flush all lines in the system;

(E) the installation of clean-outs; and

(F) development of procedures whereby portions of the pressure system may be rerouted with temporary lines in the event of leaks, construction, or repair.

(3) Pipe selection. Appropriate ASTM, ANSI, or AWWA standards shall be specified for alternative wastewater collection system pipe and joints. Pipe which will be used in pressure sewer systems shall have a minimum sustained working pressure rating of 150 pounds per square inch gauge as per appropriate standard. Pipe selection shall also conform to subsection (a)(1) - (3) and (5) of this section.

(4) Leakage testing. All alternative wastewater collection systems components shall be tested for leakage. Testing procedures for on-site system components, small diameter gravity sewer systems, and vacuum sewer systems will be approved on a case-by-case basis. Pressure sewer installation shall be tested for leakage with a hydrostatic test. Copies of all test results shall be made available to the executive director upon request. Leakage in the pressure sewer hydrostatic test shall be defined as the quantity of water that must be supplied into the pipe or any valved section thereof to maintain pressure within five pounds per square inch of the specified test pressure after the air in the pipeline has been expelled. The test pressure shall be either a minimum of 25 pounds per square inch gauge or 1.5 times the maximum force main design pressure, whichever is larger. The maximum allowable leakage shall be calculated using the formula in this paragraph. If the quantity of leakage exceeds the maximum amount calculated, remedial action shall be taken to reduce the leakage to an amount within the allowable limit as follows.

Attached Graphic

(5) Pumps. Pumping units and grinder pumps used in pressure sewer systems should be reliable, easily maintained, and should have compatible characteristics.

(A) Pumps and grinder pump units shall be provided with two backflow prevention devices (one check valve at tank, to protect against back drainage into tank, second check valve at connection of service line to pressure collection line to protect against leaking sewage in case service line is damaged) and shall be easily accessible for maintenance.

(B) Sufficient holding capacity shall be provided in the pumping compartment to allow for wastewater storage during power outages and equipment failures. Storage volume should be based on power supply outage records and replacement equipment availability.

(C) Pumping units shall not be installed in the settling chamber of an interceptor tank if the interceptor tank is to be used for solids reduction.

(D) Alarms, warning lights, or other suitable indicators of unit malfunction shall be installed at each pumping station.

(E) Whenever any pumping station handles waste from two or more residential housing units or from any public establishment, dual pump units shall be provided to assure continued service in the event of equipment malfunction.

Source Note: The provisions of this §317.2 adopted to be effective November 26, 2015, 40 TexReg 8341