Current through Bulletin 2024-06, March 15, 2024
2.1. General. Construction of a new sewer
system project may not begin unless the applicant has submitted an engineering
report detailing the design, and construction plans to the Director for review
and approval evidenced by a construction permit. The Director will not normally
review construction plans for extensions of the existing sewer systems to new
areas or replacement of sanitary sewers in the existing sewer systems unless
requested or required by state or federal funding programs. Rain water from
roofs, streets, and other areas, and ground water from foundation drains must
not be allowed to enter the sewer system through planning, design and
construction quality assurance and control measures.
2.2. Basis of Design
A. Planning Period. Sewers should be designed
for the estimated ultimate tributary population or the 50-year planning period,
whichever requires a larger capacity. The Director may approve the design for
reduced capacities provided the capacity of the system can be readily increased
when required. The maximum anticipated capacity required by institutions,
industrial parks, etc. must be considered in the design.
B. Sewer Capacity. The required sewer
capacity shall be determined on the basis of maximum hourly domestic sewage
flow; additional maximum flow from industrial plants; inflow; ground water
infiltration; potential for sulfide generation; topography of area; location of
sewage treatment plant; depth of excavation; and pumping requirements.
1. Per Capita Flow. New sewer systems shall
be designed on the basis of an annual average daily rate of flow of 100 gallons
per capita per day (0.38 cubic meter per capita per day) unless there are data
to indicate otherwise. The per capita rate of flow includes an allowance for
infiltration/inflow. The per capita rate of flow may be higher than 100 gallons
per day (0.38 cubic meter per day) if there is a probability of large amounts
of infiltration/inflow entering the system.
2. Design Flow
a. Laterals and collector sewers shall be
designed for 400 gallons per capita per day (1.51 cubic meters per capita per
day).
b. Interceptors and outfall
sewers shall be designed for 250 gallons per capita per day (0.95 cubic meter
per capita per day), or rates of flow established from an approved
infiltration/inflow study.
c. The
Director will consider other rates of flow for the design if such basis is
justified on the basis of supporting documentation.
C. Design Calculations. Detailed
computations, such as the basis of design and hydraulic calculations showing
depth of flow, velocity, water surface profiles, and gradients shall be
submitted with plans.
2.3. Design and Construction Details
A. Minimum Size
1. No gravity sewer shall be of less than
eight inches (20 centimeters) in diameter.
2. A 6-inch (15 centimeters) diameter pipe
may be permitted when the sewer is serving only one connection, or if the
applicant justifies the need for such diameter on the basis of supporting
documentation.
B. Depth.
Sewers should be sufficiently deep to receive sewage from basements and to
prevent freezing. Insulation shall be provided for sewers that cannot be placed
at a depth sufficient to prevent freezing.
C. Odor and Sulfide Generation. The design
shall incorporate features to control and mitigate odor and sulfide generation
in sewers. Such features may include steeper slope to achieve higher velocity,
reaeration through induced turbulence, etc.
D. Slope
1.
The pipe diameter and slope shall be selected to obtain velocities to minimize
settling problems.
2. All sewers
shall be designed and constructed to give mean velocities of not less than 2
feet per second (0.61 meter per second), when flowing full, based on Manning's
formula using an n value of 0.013.
3. Sewers shall be laid with uniform slope
between manholes.
4. Table
R317-3-2.3(D)(4) shows the minimum slopes which shall be provided; however,
slopes greater than these are desirable.
E. Flatter Slopes. Slopes flatter than those
required for the 2-feet-per-second (0.61 meter per second)-velocity criterion
when flowing full, may be permitted by the Director provided that:
1. there is no other practical
alternative;
2. the depth of flow
is not less than 30 percent of the diameter at the average design rate of
flow;
3. the design engineer has
furnished with the report the computations showing velocity and depth of flow
corresponding to the minimum, average and peak rates of flow for the present
and design conditions in support of the request for variance; and
4. the operating authority of the sewer
system submits a written acknowledgement of the ability to provide any
additional sewer maintenance required by flatter slopes.
F. Steep Slopes
1. Where velocities greater than 15 feet per
second (4.6 meters per second) are attained, special provision shall be made to
protect against displacement by erosion and shock.
2. Sewers on 20 percent slopes or greater
shall be anchored securely against lateral and axial displacement with suitable
thrust blocks, concrete anchors or other equivalent restraints, spaced as
follows:
a. Not over 36 feet (11 meters)
center to center on grades 20 percent and up to 35 percent;
b. Not over 24 feet (7.3 meters) center to
center on grades 35 percent and up to 50 percent;
c. Not over 16 feet (4.9 meters) center to
center on grades 50 percent and over.
G. Alignment. Sewers 24 inches (61
centimeters) in diameter or less shall be laid with a straight alignment
between manholes. The alignment shall be checked by either using a laser beam
or lamping.
H. Changes in Pipe
Size. When a smaller sewer joins a large one, the invert of the larger sewer
should be lowered sufficiently to maintain the same energy gradient. An
approximate method for securing these results is to place the 0.8 depth point
of both sewers at the same elevation.
I. Materials
1. The material of pipe selected should be
suitable for local conditions. The material of sewer pipe should be compatible
with factors such as industrial wastewater characteristics, putrecibility,
physical and chemical properties of adjacent soil, heavy external loading,
etc.
2. The material of pipe must
withstand superimposed loads without any damage. The design of trench widths
and depths should allow for loads. Special bedding, concrete cradle or
encasement, or other special construction may be used to withstand
extraordinary superimposed loading.
2.4. Curved Sewers. Curved sewers are
permitted only under circumstances where conventional sewer construction is not
feasible. A conceptual approval must be obtained before beginning the design.
A. Design
1. The minimum radius of curvature shall be
greater than 200 feet or one-half of the maximum deflection angle for the
material of pipe allowed by the manufacturer.
2. The design n value for the sewer pipe
shall be 0.018.
3. Only one
horizontal curve in the sewer alignment will be allowed between manholes. No
vertical curves shall be permitted.
4. Manhole spacing shall not exceed 400 feet
(122 meters).
5. Manholes must be
provided at the beginning and the end of a curved alignment (i.e. change in
radius of curvature).
6. The design
should consider increased erosion potential due to high velocities.
B. Other Requirements
1. Maintenance equipment shall be available
at all times for inspection and cleaning.
2. Horizontal and vertical alignment of the
sewer after the construction must be verified and certified by a registered
professional engineer.
a. Accurate record or
as-built drawings must be prepared showing the physical location of the pipe in
the ground, and submitted to the division in accordance with the requirements
of
R317-3-1.
2.5. Installation Requirements
A. Standards
1. The technical specifications shall require
that installation be in accordance with the requirements based on the criteria,
standards and procedures established by:
a.
this rule;
b. recognized industry
standards and practices as published in their technical publications;
c. the product manufacturer's recommendations
and guidance;
d. Uniform Building
Code, Uniform Plumbing Code, Uniform Mechanical Code and National Electrical
Code;
e. American Society of
Testing Materials;
f. American
National Standards Institute; and
g. Occupational Safety and Health
Administration (OSHA), US Department of Labor or its succeeding
agencies.
2. Requirements
shall be set forth in the specifications for the pipe and methods of bedding
and backfilling thereof so as not to damage the pipe or its joints, impede
cleaning operations and future tapping, nor create excessive side fill
pressures or ovalation of the pipe, nor seriously impair flow
capacity.
B.
Identification of Sewer Lines. A clearly labelled tracer location tape shall be
placed two feet above the top of sewer lines less than or equal to 24 inch (61
centimeters) in diameter, along its entire length.
C. Deflection Test
1. Deflection test shall be performed on all
flexible pipes. The test shall be conducted after the final backfill has been
in place at least 30 days.
2. No
pipe shall show a deflection in excess of 5 percent.
3. If the deflection test is run using a
rigid ball or mandrel, it shall have a diameter equal to 95 percent of the
inside diameter of the pipe. The test shall be performed without mechanical
pulling devices.
D.
Joints and Infiltration
1. Joints. The
installation procedures of joints and the materials to be used shall be
included in the specifications. Sewer joints shall be designed to minimize
infiltration and to prevent the entrance of roots throughout the life of the
system.
2. Leakage Tests.
Procedures for leakage tests shall be specified. This may include appropriate
water or low pressure air testing. The leakage outward or inward (exfiltration
or infiltration) shall not exceed 200 gallons per inch of pipe diameter per
mile per day (0.19 cubic meter per centimeter of pipe diameter per kilometer
per day) for any section of the system. An exfiltration or infiltration test
shall be performed with a minimum positive head of 2 feet (0.61 meter). The air
test, if used, shall, as a minimum, conform to the test procedure described in
the American Society of Testing Materials standards. The testing methods
selected should take into consideration the range in ground water elevations
projected during the test.
E. Inspection
1. The specifications shall include
requirements for inspection of manholes for water-tightness prior to placing in
service, including television inspection.
2. Records of television inspection shall be
retained for future reference.
2.6. Manholes
A. Location. Manholes shall be installed at:
1. the end of each line exceeding 150 feet
(46 meters) in length;
2. all
changes in grade, size, or alignment;
3. all intersections; and
4. distances not greater than:
a. 400 feet (120 meters) for sewers 15 inches
(38 centimeters) or less; and
b.
500 feet (150 meters) for sewers 18 inches (46 centimeters) to 30 inches (76
centimeters).
5.
Distances up to 600 feet (180 meters) may be approved in cases where adequate
cleaning equipment for such spacing is provided.
6. Greater spacing may be permitted in larger
sewers.
7. Cleanouts shall not be
substituted for manholes nor installed at the end of lines greater than 150
feet (46 meters) in length.
B. Drop Type Manholes
1. A drop pipe should be provided for a sewer
entering a manhole at an elevation of 24 inches (61 centimeters) or more above
the manhole invert. Where the difference in elevation between the incoming
sewer and manhole invert is less than 24 inches (61 centimeters), the invert
should be filleted to prevent solids deposition.
2. Drop manholes should be constructed with
an outside drop connection. If an inside drop connections is necessary, it
shall be secured to the interior wall of the manhole and provide access for
cleaning.
3. Due to the unequal
earth pressures that would result from the backfilling operation in the
vicinity of the manhole, the entire outside drop connection shall be encased in
concrete.
C. Diameter.
The minimum diameter of manholes shall be 48 inches (1.22 meters); larger
diameter manholes are preferable for large diameter sewers. A minimum diameter
of 22 inches (56 centimeters) shall be provided for safe access.
D. Flow Channel. The flow channel through
manholes should be made to conform in shape and slope to that of the sewers.
The depth of flow channels should be up to one-half to three-quarters of the
diameter of the sewer. Adjacent floor area should drain to the channel with the
minimum slope of 1 inch per foot (8.3 centimeters per meter).
E. Watertightness
1. Manholes shall be of the pre-cast concrete
or poured-in-place concrete type. Manholes shall be waterproofed on the
exterior.
2. Inlet and outlet pipes
shall be joined to the manhole with a gasketed flexible watertight connection
arrangement that allows differential settlement of the pipe and manhole wall to
take place.
3. Watertight manhole
covers shall be used wherever the manhole tops may be flooded by street runoff
or high water. Locked manhole covers may be desirable in isolated easement
locations or where vandalism may be a problem.
F. Electrical. Electrical equipment installed
or used in manholes shall conform to appropriate National Electrical Code
requirements.
2.7.
Inverted Siphons. Inverted siphons shall consist of at least two barrels, with
a minimum pipe size of 6 inches (15 centimeters) with an arrangement to exclude
debris and solids. The siphon 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 secure velocities of at least 3.0 feet per second (0.92
meter per second) for average flows. The inlet and outlet details shall be so
arranged that the normal flow is diverted to 1 barrel, and that either barrel
may be cut out of service for cleaning. The vertical alignment should permit
cleaning and maintenance.
2.8.
Sewers In Relation To Streams
A. Location of
Sewers on Streams
1. The top of all sewers
entering or crossing streams shall be at a sufficient depth below the natural
bottom of the stream bed to protect the sewer line. In general, the following
cover requirements must be met:
a. one foot
(30 centimeters) of cover is required where the sewer is located in
bedrock;
b. three feet (90
centimeters) of cover is required in other material;
c. cover in excess of 3 feet (90 centimeters)
may be required in streams having a high erosion potential; and
d. in paved stream channels, the top of the
sewer must be placed below the bottom of the channel pavement.
2. If the proposed sewer crossing
will not interfere with the future improvements to the stream channel, then
reduced cover may be permitted.
B. Horizontal Location. Sewers shall be
located along streams outside of the stream bed and sufficiently removed
therefrom to provide for future possible stream widening and to prevent
pollution by siltation during construction.
C. Structures. The sewer outfalls, headwalls,
manholes, gate boxes, or other structures shall be located so they do not
interfere with the free discharge of flood flows of the stream.
D. Alignment
1. Sewers crossing streams should be designed
to cross the stream as nearly at right angles to the stream flow as possible,
and shall be free from change in grade.
2. Sewer systems shall be designed to
minimize the number of stream crossings.
E. Construction
1. Materials. Sewers entering or crossing
streams shall be constructed of cast or ductile iron pipe with mechanical
joints; otherwise they shall be constructed so they will remain watertight and
free from changes in alignment or grade. Material used to backfill the trench
shall be stone, coarse aggregate, washed gravel, or other materials which will
not cause siltation.
2. Siltation
and Erosion. Construction methods that will minimize siltation and erosion
shall be employed. The design engineer shall include in the project
specifications the method(s) to be employed in the construction of sewers in or
near streams to provide adequate control of siltation and erosion.
Specifications shall require that cleanup, grading, seeding, and planting or
restoration of all work areas shall begin immediately. Exposed areas shall not
remain unprotected for more than seven days.
F. Aerial Crossings
1. A carrier pipe shall be provided for all
aerial sewer crossings. Support shall be provided for all joints in pipes
utilized for aerial crossings. The supports shall be designed to prevent frost
heave, overturning and settlement.
2. Precautions against freezing, such as
insulation and increased slope, shall be provided. Expansion jointing shall be
provided between above-ground and below-ground sewers.
3. The design engineer shall consider the
impact of flood waters and debris for aerial stream crossings. The bottom of
the pipe should be placed below the elevation of twenty-five (25) year flood.
Crossings, in no case, shall block the channel.
2.9. Protection of Water Supplies.
The applicant must review the requirements stated in R309-112-2 - Distribution
System Rules, Drinking Water and Sanitation Rules, to assure compliance with
the said rule.
A. Water Supply
Interconnections. There shall be no physical connections between a public or
private potable water supply system and a sewer, or appurtenance thereto which
would permit the passage of any sewage or polluted water into the potable
supply. No water pipe shall pass through or come in contact with any part of a
sewer manhole.
B. Relation to Water
Mains
1. Horizontal Separation
a. Sewers shall be laid at least 10 feet (3.0
meters) horizontally from any existing water main. The distance shall be
measured edge to edge. In cases where it is not practical to maintain a ten
foot separation, a deviation may be allowed based on the supportive data from
the design engineer. Such deviation may allow installation of the sewer closer
to a water main, provided that the sewer is laid:
(1) in a separate trench, or
(2) on an undisturbed earth shelf located on
one side of the sewer trench, or
(3) in the sewer trench which has been
backfilled and compacted to not less than 95 percent of the optimum density as
determined by the ASTM Standard D-690, as amended, and
b. In each of the above cases, the bottom of
the water main shall be at least 18 inches (46 centimeters) above the top of
the sewer.
2. Crossings.
Sewers crossing above water mains shall be laid to provide a minimum vertical
distance of 18 inches (46 centimeters) between the outside of the water main
and the outside of the sewer. The crossing shall be arranged so that the sewer
joints will be equidistant and as far as possible from the water main joints.
Where a water main crosses under a sewer, adequate structural support shall be
provided for the sewer to prevent damage to the water main.
3. Special Conditions. When it is impossible
to obtain proper horizontal and vertical separation as stated above, the sewer
shall be designed and constructed of cast iron, ductile iron, galvanized steel
or protected steel pipe with mechanical joints for the minimum distance of 10
feet on either side of the point of crossing. The design engineer may use other
types of joints if equivalent joint integrity is demonstrated. The lines shall
be pressure tested to assure watertightness before backfilling.