(a) Separate
sewers. Separate sewers shall be provided for collection of stormwater and
wastewater. Roof, areaway, drive or foundation drains shall not be connected to
sanitary sewers.
(b) Pipe
materials.
(i) Wastewater characteristics.
Pipe materials shall resist acid and alkaline solutions, organic solvents, and
other wastewater constituents and environmental conditions
encountered.
(ii) Pipe loadings.
Pipe materials shall be chosen and the pipeline shall be designed to withstand
all trench and superimposed surface live loads with a minimum factor of safety.
Rigid pipes shall have a minimum factor of safety of 1.5, and flexible pipes
shall have a minimum factor of safety of 1.25.
(iii) Soil characteristics. Pipe materials
shall be chosen to resist corrosion due to aggressive soil characteristics by
the soil it contacts. Iron or steel pipe shall be protected from corrosion with
polyethylene encasement or cathodic protection.
(iv) Joints. Pipe joints shall be flexible,
durable and designed to minimize infiltration/exfiltration and exclude
roots.
(v) Performance tests.
Piping shall be subjected to leakage tests. Leakage tests shall be
infiltration, exfiltration, or air tests.
(A)
Infiltration. Maximum of 200 gallons per inch diameter per mile per day (1200
liters/cm/km/day) with a minimum of two feet (0.6 m) of head over the top of
the pipe.
(B) Exfiltration. Maximum
of 200 gallons per inch diameter per mile per day (1200 liters/cm/km/day) with
a minimum of two feet (0.6 m) of head over the top of the pipe.
(C) Air. Air tests shall conform to ASTM
C-828-80. (D) Deflection. Maximum five percent deflection after flexible pipe
is backfilled for thirty (30) days. A mandrel of 95 percent of pipe diameter
shall be used. No mechanical pulling of mandrel is permitted.
(vi) Approved pipe material
specifications. Type of commercial pipe approved for gravity sanitary systems
include:
(A) Extra strength and standard
strength vitrified clay pipe: ASTM C700-78a.
(B) PVC sewer pipe and fittings: ASTM
D3034-80, SDR35, ASTM F679-81, or ASTM F794-83.
(C) ABS composite sewer pipe: ASTM
D2680-80.
(D) Reinforced plastic
mortar pipe: ASTM D3262-81.
(E)
Asbestos cement nonpressure sewer pipe: ASTM C428-80.
(F) Reinforced concrete sewer pipe: ASTM
C76-82.
(G) Concrete Sewer Pipe:
ASTM C-14.
(H) Ductile iron sewer
pipe: ASTM A746-77.
Types of commercial pipe approved for pressure sanitary
sewer systems include:
(I)
PVC water pipe: ASTM D2241-80, or AWWA C900.
(J) Asbestos cement pressure pipe: AWWA
C400-80.
(K) Ductile iron pipe:
AWWA C151-81.
(L) Glass
Fiber-Reinforced Thermo-setting-Resin Pressure Pipe: AWWA C950-81.
(c) Collection piping
design, construction and testing. A sewage collection line is any conduit that
carries wastewater that originates from two (2) or more separate buildings or
from a single building that generates more than 2,000 gpd (7.6
m
3/d) of average daily flow.
(i) Gravity system.
(A) Depth. Sewers shall be located to protect
them from freezing and frost heave as prudently possible.
(B) Size. Sewers to be aligned straight shall
be 8-inch (20.3 cm) diameter or larger except 6-inch (15.2 cm) sewers may be
used in cul-de-sacs, or other dead end locations where the sewer cannot be
extended in the future. 18-inch (45.7 cm) or larger sewers may be laid on
curves. Lines shall be sized for 200 percent of maximum daily flow or more. In
the absence of data deriving maximum daily flow, the chart on Figure 1-1 shall
be used to determine maximum daily flow.
(C) Slope. Sewers shall be laid with uniform
slope between manholes. Minimum slopes shall be:
Sewer Size Inch (cm) |
Minimum Slope in Feet
Per 100 Feet (m/100 m) |
6 (15.2) |
0.60 |
8 (20.3) |
0.40 |
10 (25.4) |
0.28 |
12 (30.5) |
0.22 |
14 (35.6) |
0.17 |
15 (38.1) |
0.15 |
16 (40.6) |
0.14 |
18 (45.7) |
0.12 |
20 (50.8) |
0.11 |
21 (53.3) |
0.10 |
24 (61.0) |
0.08 |
27 (68.6) |
0.067 |
30 (76.2) |
0.058 |
33 (83.8) |
0.051 |
36 (91.4) |
0.046 |
Maximum slopes without the use of concrete anchors shall be
20 percent. The following spacing of concrete anchors shall apply to slopes
greater than 20 percent:
Slopes (percent) |
Concrete Anchor |
20-35 |
36 ft (11 m) |
35-50 |
24 ft (7.3 m) |
More than 50 |
16 ft (4.9 m) |
(D) Velocity. Minimum velocities shall be 2
fps (0.6 mps) when flowing full. Velocities greater than 10 fps (3.0 mps)
require special design considerations.
(E) Increasing size. All sewer pipe size
changes shall be at manholes. Pipe size shall not be decreased in the direction
of flow. The energy gradient line should be maintained when a smaller sewer
joins a larger one.
(F) Excavation,
bedding installation, backfill.
(I)
Excavation. Trench width from the trench bottom to a point one foot above the
top of the pipe shall be no less than the outside diameter of the pipe plus 8
(8) inches (20.3 cm) but not more than twenty-four (24) inches (61 cm) plus the
pipe O.D. The trench bottom shall be excavated for the pipe bell. All rock
shall be removed within six (6) inches (15.2 cm) of pipe. The trench shall be
dewatered for all work.
(II)
Bedding. Bedding shall be designed in accordance with:
(1.) Rigid pipe. Types A, B, C (Water
Pollution Control Federation Manual of Practice No. 9) or ASTM
C12-81.
(2.) Flexible pipe. Types
I, II, III, ASTM D2321-74.
(III) Backfill. Backfill shall be performed
without disturbing pipe alignment. Backfill shall not contain debris, frozen
material, unstable material, or large clods. Stones greater than three (3)
inches (7.6 cm) in diameter shall not be placed within two (2) feet (0.6 m) of
pipe. Compaction shall be to a density equal to or greater than the surrounding
soil.
(ii)
Force mains and pressure sewers.
(A) Depth.
Force mains shall be located to protect them from freezing and frost
heave.
(B) Size. Force mains shall
be four (4) inches (10 cm) diameter or greater. Pressure sewer collection
system piping shall be one (1) inch (2.5 cm) minimum.
(C) Velocity. Minimum velocity shall be 2.5
fps (0.76 mps).
(D) Air release.
Air release facilities shall be provided at the high point in the piping
whenever the pipe crown elevation falls below the pipe invert elevation. Access
to air release manholes shall not be in traffic-ways.
(E) Cleanouts. Cleanouts shall be provided at
400-foot (122 m) maximum spacing in pressure piping four-inch diameter or
less.
(F) Pressure sewer systems.
Pressure sewer collection systems shall be preceded by grinder pumps or septic
tanks.
(G) Pressure sewer
collection system pumps. Pumps shall be provided with isolation and check
valves. If a septic tank is not provided before the pump, a grinder pump shall
be required. Pump holding sumps shall not be steel, iron, or coated metal. The
sump chamber shall be fifty (50) gallon (189 liters) volume, minimum.
(iii) Service connections. A
service connection is any conduit that carries wastewater that is not defined
as a sewage collection line. Service connections shall conform to the
requirements for sewage collection lines (Section 9(c)(i) and (ii) ) with the
following modifications:
(A) Size: minimum
size shall be four (4) inches (10.2 cm).
(B) Slope: minimum slope shall be 2 feet/100
feet (2 m/100 m).
(C) Flow: flow
shall be determined from a fixture unit count and the sewage size based on
flowing full.
(D) Connections: all
service connections to sewage collection lines shall be made with a wye or tee
for new construction and a tapping saddle for connection to existing collection
lines.
(d)
Manholes and cleanouts.
(i) Location. Manholes
shall be located at all changes in pipe size, vertical or horizontal alignment,
pipe intersections, and the end of lines. Maximum spacing for various line
sizes are as follows:
Line Size (In) |
(cm) |
Maximum M.H.
|
Spacing |
15 or less |
(38 or less) |
400 ft
|
122 m |
16 - 30 |
(40.6 - 76) |
500 ft
|
152 m |
31 or more |
(78 or more) |
600 ft
|
183 m |
Terminal sewer cleanouts may be provided at the end of
sewer lines if they are not more than 150 feet (45.7 m) from the nearest
downstream manhole. The cleanout shall be constructed using 45-degree bends to
the upturned pipe coming to the surface of the ground. The diameter of the
cleanout shall be the same as the pipe size. Lampholes shall not be
used.
(ii) Size. Minimum
manhole interior size is four (4) feet (1.2 m).
(iii) Drop manhole. Drop manholes must be
constructed where the change in elevation between two lines is greater than
twenty-four (24) inches (0.6 m). Concrete encasement shall be provided around
the drop pipe.
(iv) Invert. Manhole
inverts shall be constructed to conform to the shape of the sewer. The bench
shall drain to the invert. Connections to the manhole shall be watertight and
allow differential settlement between the manhole and pipe. Minimum fillet
height shall be one half of the pipe diameter.
(v) Cover. The manhole cover shall be
suitable to withstand all loads, including impact loading without deformation,
slip or rattle. The manhole cover shall be watertight in areas subject to
flooding and a bolt-down type in areas subject to unauthorized dumping or
vandals.
(vi) Steps. Access to
manholes shall be with portable ladders, or with cast iron manhole steps spaced
at sixteen (16) inches (40.6 cm) maximum.
(vii) Materials. Manholes shall be
constructed watertight and durable using cast-in-place concrete, or precast
concrete with gasketed joints. Where precast concrete bases are used, the first
twelve (12) inches (30 cm) of wall will be monolithically cast with the
base.
(viii) Access. A twenty-two
(22) inch (56 cm) minimum diameter clear opening shall be provided on all
manholes. All manholes shall be located to be accessible by motorized equipment
for maintenance.
(e)
Special structures.
(i) Inverted siphons.
Inverted siphons shall have a minimum of two (2) six (6) inch (15.2 cm)
barrels. The inlet and outlet shall be arranged to cause only one (1) pipe to
be used during normal flows. The minimum velocity shall be 3 fps (1 mps) at
average flow, and occur at least daily. The siphon shall be designed for
flushing and maintenance.
(ii)
Aerial crossings. Aerial crossings shall be designed to prevent freezing,
leaking, settlement, lateral movement, and damage from expansion/contraction.
It shall be located with proper vertical clearances for highway vehicles and
the 100-year flood.
(iii) Stream
crossings. Stream crossings shall be within 10° of the perpendicular
direction of the stream. Pipe shall have a minimum cover of one (1) foot in
rock, and three (3) feet under other surfaces. The crossing shall be made with
an inverted siphon or without a grade change. Pipe materials shall be steel,
cast iron, or ductile iron pipe.
(f) Potable water supply protection.
(i) Cross connections. There shall be no
cross-connections between sewer lines and potable water lines.
(ii) Horizontal and vertical separation from
water mains. Minimum horizontal separation shall be ten (10) feet (3 m) where
the water main is less than 1.5 feet (0.46 m) above the elevation of the sewer.
Minimum vertical separation shall be 1.5 feet (0.46 m) at crossing. Joints in
sewers at crossing shall be located at least ten (10) feet (3 m) from water
mains. The upper line of a crossing shall be specially supported. Where
vertical and/or horizontal clearances cannot be maintained, the sewer shall be
placed in a separate conduit pipe.