| (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... |
