| (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.
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