|(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:
(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.
(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.