(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.
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