A.
Location.
(1)
Within street right-of-way. The sewer shall generally be located
on the same side of the road as the sanitary sewer.
(2)
Within easements. Sewer easements shall generally be centered on the sewer and have a minimum width of 20 feet. Permanent structures which will restrict the maintenance of the sewer shall not be located within the easement area. Sewers to be located within easements which are established at the time land is platted shall be located and sized in accordance with the requirements of Chapter 152, Subdivision Control, and/or the Plat Act. Easements for possible extensions shall be provided as required by the Director.
(3)
General. Sewer shall be constructed no closer than 10 feet to any
building structure.
B.
Size. The minimum pipe diameter size for all storm sewers shall be
12 inches.
C.
Sewer capacity.
(1)
Tributary drainage areas. The sewers shall be designed to accommodate
off-site tributary drainage. The upstream topography with existing
and proposed developments and conformance with the Master Utility
Plan shall be considered.
(2)
Hydrologic consideration.
(a)
The sewers shall be designed for a ten-year storm by means of
the rational method formula: Q = CIA, where "Q" is the peak rate of
runoff in cubic feet per second, "A" is the area in acres, "C" is
the runoff coefficient for the drainage area and "I" is the average
rainfall intensity in inches per hour for a given time of concentration.
The rainfall intensity and runoff coefficients shall be determined
in accordance with the Wayne County Storm Water Management Program.
(3)
Hydraulics.
(a)
Allowable pipe/slopes (n = 0.013). Generally, all catch basin
and inlet leads shall be laid on a slope not less than 1%.
|
Pipe Diameter
(inches)
|
Minimum Slope
(feet per 100 feet)
|
Maximum Slope
(feet per 100 feet)
| |
|---|---|---|---|
|
12
|
0.32
|
3.9
| |
|
15
|
0.24
|
2.8
| |
|
18
|
0.18
|
2.1
| |
|
21
|
0.14
|
1.7
| |
|
24
|
0.12
|
1.4
| |
|
27
|
0.10
|
1.2
| |
|
30
|
0.09
|
1.05
| |
|
36
|
0.067
|
0.80
| |
|
42
|
0.054
|
0.65
| |
|
48
|
0.045
|
054
| |
|
54
|
0.038
|
0.46
| |
|
60
|
0.034
|
0.40
|
(b)
Design velocities. Minimum design velocity shall be 2 1/2
feet per second with pipe flowing full. Maximum design velocity shall
be eight feet per second.
(c)
Calculations. Manning's formulas shall be used for hydraulic
calculations.
[1]
Allowances for changes in pipe size. The hydraulic gradient
shall generally be maintained by matching the 0.80 diameter depth
above invert for pipe size increases.
[2]
Allowance for direction changes. A drop of 0.10 foot shall be
provided in the downstream sewer invert for direction changes in excess
of 30° to compensate for the hydraulic head losses.
(d)
Hydraulic grade line. The hydraulic grade line must be calculated
based on ten-year storm flows, starting with the crown elevation at
the outlet. The hydraulic grade lines of closed conduits must meet
both of the following requirements:
[1]
The hydraulic grade line must not be higher than 2.5 feet below
the rim elevation at any upstream manhole location. However, exceptions
may be granted in special circumstances such as for managing stormwater
in and around truck docks.
[2]
The rim elevation at any manhole location along the closed conduit
upstream of a detention system must be at least one foot above the
design water level of the detention system.
A stub with a watertight bulkhead of brick and mortar shall
be provided at all manholes and catch basins where future connections
are anticipated.
A minimum cover of three feet shall be provided for all storm
sewer pipe, unless otherwise approved by the Director.
Whenever differences in manhole pipe invert elevations exceed
two feet, a plunge pool (sump) two feet in depth shall be provided
to prevent channel erosion.
Manholes shall be provided at every change of pipe size, change
in grade, change in direction, or at all junction points. The maximum
distance between manholes, catch basin, and inlets may not exceed
300 feet plus 100 additional feet for every 12 inches of diameter
for closed conduits over 36 inches in diameter.
The following design criteria shall be used when establishing
catch basin and inlet locations:
A.
Low points in gutters and in swales and ditches, where applicable.
B.
Upstream curb return, if more than 200 feet downstream of high point
in gutter or of intercepting structure.
C.
Inlets shall only be allowed in pavement areas, and, then only as
a high-end structure and when followed by a catch basin within 50
feet of inlet.
D.
Generally, the flows to be accommodated shall not exceed the intake
capacity of the cover. Catch basin cover capacities shall be determined
by assuming a value of 0.011 cfs per square inch of opening.
E.
Catch basin and inlet leads may be tapped directly into storm sewer
pipes larger than 42 inches.
F.
Catch basins shall be located within 50 feet of all ditch inflow
devices.
A.
Pipe.
(1)
Storm sewer pipe shall be reinforced concrete or ductile iron.
(2)
Ductile iron (pipe) shall meet current requirements of ANSI.50.
(3)
All pipe shall have class, lot number and date of manufacture marked
on each length by the manufacturer.
(4)
Concrete pipe under paved areas shall have premium joints in all
pipe from structure to structure.
B.
Sewer joints. Sewer joints for reinforced concrete pipe shall be
tongue-and-groove joints secured with rubber gaskets, mastic, or concrete
mortar.
(1)
All storm sewer under paved areas shall have synthetic rubber gasket
joints from structure to structure conforming to ASTM C 361. Natural
rubber gaskets are not allowed.
(2)
Joints for storm sewer with diameters 30 inches or greater shall
have concrete mortar applied on the inside.
(3)
Mastic material for joints shall be of DeWitts No. 10, or approved
equal.
C.
Structures. Storm structures shall be constructed of precast concrete
pipe, brick or block.
(1)
Precast concrete. Reinforced concrete structures and grade rings
shall conform to the current ASTM Specifications for Precast Reinforced
Concrete Manhole Sections, Serial Designation C478. Manhole section
joints shall be made with mortar. Dome sections shall be straight
side type.
D.
Brick and block.
(1)
Brick for brick and mortar structures shall conform to the current
ASTM Specification C135. Mortar for plastering drainage structures
shall be made of one part portland cement and two parts of fine aggregate.
(2)
The block shall not exceed 18 inches in length or eight inches in
depth (height). No block shall be less than six inches in width (thickness).
All blocks in one structure shall be of the same height dimension.
The blocks shall be designed for length so that only full-length or
half-length blocks are required to lay the circular wall of any one
course.
(3)
Blocks intended for use in the cones or tops of manholes and catch
basins shall have such shape as may be required to from the structure
as shown on the plans with inside and outside joint not to exceed
1/4 inch in thickness.
E.
Castings.
(1)
Castings shall conform to the latest revision of the ASTM Specification
A48, Gray Iron Castings, and be coated by the manufacturer with coal
tar pitch, varnish or other asphaltum coating reviewed by the Director.
(2)
Frames and covers shall be as follows:
(a)
For use on drainage structures in paved areas: East Jordan Frame
5105 with Type M1 grate, or equal.
(b)
For use in curb and gutter line: East Jordan Frame 7045 with
Type M1 grate, or equal.
(c)
For use on drainage structures in grassed areas: East Jordan
Frame 1040 with Type 02 Beehive Grate, or equal.
(d)
For use on drainage structure manholes: East Jordan 1040 with
Type B perforated cover, or equal.
F.
Headwalls. Headwalls shall be constructed of concrete in accordance
with the latest revision of MDOT specifications.
Sewers for footing drains shall be provided in all subdivision
developments. All lots shall be provided with a house lead connecting
to the storm sewers, or a sewer constructed for the sole purpose of
collecting waters discharged from footing drains. Connection to a
storm sewer within the road right-of-way is not permitted.
A.
Footing drain collector sewer.
(1)
Minimum pipe diameter shall be eight inches with a cleanout provided
at the upstream end with a manhole or catch basin at all changes in
size and/or any change in horizontal or vertical alignment.
(3)
Surface water drainage will not be permitted to enter into the footing
drain collector pipe.
(4)
Minimum slope shall be 0.50%.
All construction plans shall be submitted to the Township for
storm sewer approval and shall contain, but not be limited to, the
following information:
A.
Certification. The plans and specification shall be prepared under
the supervision of a civil engineer registered in the State of Michigan.
The title sheet of the plans shall contain the signature and seal
of that engineer.
B.
Plan contents. Plans shall consist of a title sheet showing a plan
view of the complete job, split plan and profile sheets, design calculation
sheets, and standard detail sheets. Sheet sizes shall be 24 inches
by 36 inches.
(1)
Title sheet. A title sheet, or the first sheet of a set of plans,
shall identify:
(a)
Project title.
(b)
Location map with North arrow and scale, drawn at a scale not
greater than one inch equals 100 feet nor smaller than one inch equals
2,000 feet. Locations of proposed sewers and relationship of general
project area to the surrounding area shall be shown.
(c)
Overall layout of the sewer system with manhole, catch basin
or other structure numbers.
(d)
Sheet index.
(e)
Symbol legend.
(f)
List of quantities.
(g)
Name, address, phone number and e-mail of proprietor.
(h)
Name, address, phone number and e-mail of designer.
(i)
Plan completion date and all revision dates.
(j)
A statement that the work shall conform to the Township's
current standards and specifications.
(2)
Plan and profile sheets.
(a)
Scale of plan portion of sheet shall be one inch equals 50 feet,
or larger, with scale of profile portion of sheet one foot equals
five feet vertical or proportionally larger.
(b)
Plan portion of sheets shall include, at least:
[1]
Two bench marks shall be shown on each plan sheet. Plans shall
be prepared based on the Michigan South State Plane Coordinates, North
American Datum of 1983 (NAD 1983) for the x and y coordinate system,
and based on the North American Vertical Datum of 1988 (NAVD88) for
the z coordinate system.
[2]
Existing topography extending 50 feet past the site boundaries,
including all existing and proposed improvements. Elevation contours
shall be at a minimum of two-foot intervals.
[3]
Street names, street and easement width, subdivision names,
lot numbers and lot dimensions.
[4]
Location, length, and size of each section of proposed sewer
between structures.
[5]
Locations of all structures.
[6]
All proposed connections.
[7]
Dimensions to manholes and sewers from property lines, right-of-way
lines or buildings.
[8]
"Miss Dig" note.
[9]
Limits of special backfill requirements.
(c)
Profile portion of sheets shall appear below the corresponding
plan portion, generally projected vertically, and shall show at least
the following:
[1]
Size, slope, length, type and class of pipe.
[2]
Invert of each pipe and top-of-casting elevations at each structure.
[3]
Limits of special backfill requirements.
[4]
Profiled elevations over center line of proposed sewer of existing
and proposed ground, and pavement surfaces. The existing profile shall
be obtained from actual field survey data.
[5]
All crossings with other utilities (existing or proposed) with
elevations of the top or bottom of the pipe, as appropriate, and shall
have "Warning" notes for all gas main crossings in profile.
[6]
Location, by station, or coordinate, of every proposed structure
with structure number, top-of-casting elevation, and structure type.
[7]
Location of any proposed connections.
(3)
Calculation sheets. Identify engineering data to support the size,
slope and hydraulic grade line for the storm sewers.
(4)
Detail sheets. Provide the Township standard detail sheets consisting
of specifications and drawings. Wayne County details shall also be
provided, where applicable.
All storm sewer construction within the Township shall be in
accordance with these standards and specifications:
A.
Manholes, catch basins and inlets.
(1)
Pipe shall not extend into a manhole beyond the inside face of the
manhole wall.
(2)
All manholes shall be the eccentric cone type.
(3)
Brick and radial block shall be laid in a full bed of mortar and
shall be plastered on the outside with as least 1/2 inch of mortar
to completely seal the structure. Plastering shall be performed in
conjunction with the laying of brick or block.
(5)
All precast sections shall be set in full bed of mortar.
(6)
A minimum of three courses and a maximum of five courses of brick
shall be placed on the cone section of all precast concrete and concrete
block structures.
(7)
All brick, block, mortar and concrete work shall be properly cured
and protected from freezing for a minimum of 48 hours. When the temperature
is 40° F. and falling, brick, block, mortar, and concrete shall
be heated to a minimum temperature of 60° F.
(8)
After the concrete and/or plaster has set up sufficiently, the area
around the structure shall be backfilled with sand.
B.
Acceptance inspection. All sewer systems shall be subjected to a
final inspection prior to acceptance of the system by the Township,
or the issuance of a certificate of occupancy, including a compaction
test.
(1)
Where storm sewer is constructed in pavement areas or where the sewer
is within a one-on-one influence of pavement, compaction testing shall
be performed by an independent testing laboratory.
(2)
Testing shall be performed at intervals or one test per layer per
75 feet of trench or as determined necessary by the Director.
