This section is to offer appropriate guidance to the public
for basic water and sewer design criteria and reference to current
construction specifications, which shall include those contained within
this chapter, the Charles County Standard Specifications for Construction
Manual, the Charles County Water and Sewer Detail Manual, the Charles
County Plan Preparation Package, the Maryland State Plumbing Code,
the Maryland Department of the Environment, the Code of Maryland Regulations
(COMAR), Pipeline Design for Water and Wastewater, Recommended Standards
for Wastewater Facilities (commonly known as the "Ten States Standards"),
Recommended Standards for Water Works (commonly known as the "Ten
States Standards") and any other local, state or federal agency governing
water and sewer design and/or construction.
A.
General requirements.
(1)
Water plans submitted for review and approval to the County will
not be required to include the standard details on the plans. The
plans, however, must include a table, on the cover sheet, listing
by detail number and name all water details which are applicable to
the project. In cases where the County has no adopted standard detail
for a specific construction method, the engineer must submit a special
detail to the County Water and Sewer Engineer for review and approval.
Once approved, the special detail shall be placed within the plans
with notes in plan and profile on all applicable sheets referring
to the special detail.
(2)
Lines that serve two or more properties will be dedicated to the
County.
B.
Demands. The design engineer who is responsible for the extensions of the distribution mains shall follow the guidelines in this manual for the derivation of design flows. The calculation of water demands will usually require extension of the average daily rate for the facility, application of a peaking factor to derive the maximum daily rate, then addition of the fire flow requirement. System losses have been accounted for in the peaking factors. (See Appendix O.[1])
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
C.
Hydraulic computations.
(1)
General. The hydraulic design of water mains shall be in accordance
with Pipeline Design for Water and Wastewater, ASCE, 1992 (or latest
edition), and the additional guidelines and criteria in this chapter.
Computations shall be submitted for all water designs and shall include
average and peak demands, fire demand, and future requirements. Design
computations for all components of the water system shall be submitted.
(2)
Design flows and residual pressures.
(a)
Service connections, distribution mains and transmission mains
shall be sized based on the following design flow rates and residual
pressures:
(b)
In some locations, the main size will be determined by the flow rate required to refill a storage facility which may be more critical than the above requirements or by main sizes shown in the Comprehensive Water and Sewer Plan. (See Appendix O.[2])
[2]
Editor's Note: Said appendix is included as an attachment to this chapter.
(3)
Flow velocities. Although the flow velocities and direction may vary
considerably in distribution mains, there are upper and lower velocity
bounds that indicate to the design engineer that design weaknesses
may exist.
(a)
The following is a useful guideline. Peak flow velocities shall
not be greater than seven feet per second.
(4)
Hazen-Williams "C" and minor losses.
(a)
The total head loss at the point of discharge for design flows
shall be the sum of both frictional and minor losses. The elevation
difference between the source and discharge point shall be algebraically
added to the total head losses.
(b)
Head losses for new pipes shall be computed using the nomograph in Appendix P[3] and the following coefficients:
Type
|
Pipe Diameter
(inches)
|
Hazen-Williams "C"
| ||
---|---|---|---|---|
Service Connections
| ||||
Copper
|
3/4 – 3
|
130
| ||
PVC
|
3/4 – 4
|
130
| ||
DIP
|
3
|
100
| ||
Distribution Mains
| ||||
PVC
|
4 – 8
|
120
| ||
PVC
|
8 – 12
|
130
| ||
DIP
|
4 – 8
|
100
| ||
DIP
|
10 – 12
|
110
| ||
DIP
|
16 – 24
|
120
| ||
Transmission Mains
| ||||
All material
|
16 – 20
|
120
| ||
All material
|
24 and larger
|
130
|
[3]
Editor's Note: Said appendix is included as an attachment to this chapter.
(c)
Minor losses due to fittings and valves shall be included as equivalent lengths of pipe as shown in Appendix Q[4] or as fractional losses in velocity head as described
in Pipeline Design for Water and Wastewater, ASCE, 1992 (or latest
edition) or other hydraulics texts.
[4]
Editor's Note: Said appendix is included as an attachment to this chapter.
D.
Distribution mains.
(1)
General.
(a)
Extensions to distribution mains will normally be on a grid
basis with interconnecting nodes at street intersections. Lines are
to be "looped" to the maximum extent possible to provide redundancy
and to avoid dead ends in the system. If looping cannot be provided
in accordance with the County request, then written justification
shall be provided to the County for review and approval. Approval
of the justification shall be determined on a case-by-case basis.
(b)
Ductile iron pipe and restrained joints, in accordance with
the County Standard Specifications for Construction Manual and Standard
Detail Manual, shall be used for jack and bore carrier pipe.
(c)
Water mains terminated for future extension shall have a fire hydrant and valve provided as specified in § 291-62D(8)(b)[3] such valves must be anchored to allow removal of the fire hydrant for extension upon closing.
(d)
Flag lot water utilities.
[1]
For a two flag lot maximum, service laterals will be provided
off of the main and include a curb stop and box or meter vault at
the right-of-way or easement line. Water service for each lot shall
be located on each side of the driveway. Adequate easements are to
be provided on both sides of the water service and must extend outside
of the common access easement if necessary. The water service must
be constructed in conjunction with the main from the curb stop and
box to the building lot and capped closed for future connection. The
end of the service should be marked in accordance with the County
Standard Detail Manual. Extension of the service as indicated above
will prevent problems associated with the construction of the driveway
prior to the construction of all water services.
[2]
For three or more flag lots, provide an extension of the water
main to the last lot and terminate with a valve and fire hydrant.
Provide service connections to all adjacent lots, with curb stop and
boxes or meter vault located at the easement line. Adequate easements
are to be provided on both sides of the water main and services and
must extend outside of the common access easement if necessary.
(e)
Where water distribution mains are extended to accommodate future
development, they shall be extended across the full frontage of the
property being served or constructed to the property line of all adjacent
properties for future looping or extension.
(2)
Residential subdivision (new and existing). The water distribution
system for residential areas where fire protection is to be provided
shall meet the following criteria:
(3)
Commercial and industrial. The water distribution mains for commercial
and industrial areas where fire protection is to be provided shall
meet the following criteria:
(a)
Minimum size shall be eight-inch, except for fire hydrant leads
of less than 200 feet and service connections.
(b)
Maximum length of dead end eight-inch main shall be 800 feet.
(c)
Maximum length of dead end ten-inch main shall be 1,200 feet
or as approved by County Engineer.
(d)
Dead ends shall be minimized by providing looping wherever practical.
(e)
Where design flow rates exceed 1,500 gpm, hydraulic computations
shall be provided for dead end mains.
(4)
Location.
(a)
New subdivisions. In new subdivisions, distribution mains shall
be located five feet from the centerline of the street right-of-way,
generally on the side of the street toward high ground. Distribution
mains shall be located within the pavement area wherever possible,
no less than two feet from the edge of the existing or proposed gutter
pan.
(b)
Existing developments (closed section roads). In existing developments
with curbs, distribution main location shall generally be the same
as in new subdivisions. The location of other existing and proposed
utilities shall be fully considered.
(c)
Existing developments (open section roads). In existing developments
without curbs, distribution mains shall generally be located four
feet outside of the edge of pavement, except that the distribution
main shall not be located under a future curb. The location of other
existing and proposed utilities shall be considered.
(d)
Parks and public rights-of-way. Where location of distribution
mains would require the removal of or damage to trees within parks
or public rights-of-way, design engineers shall obtain approval from
the appropriate state or federal agencies for distribution main alignment
and trees to be removed.
(e)
Easements. All distribution main utility easements widths shall
be in accordance with latest plan preparation package. No other utilities
or structures will be allowed in the distribution main utility easement
without written County approval.
(f)
Distribution mains may be designed on a curved alignment to
reduce the number of bends. Along curves, the water main may be deflected
at each joint within 1/2 the limits established by the manufacturer.
(5)
Sizing.
(6)
Cover.
(a)
Normal cover over distribution mains shall be three feet six
inches, except at crossings over utilities where a minimum cover of
three feet zero inches or a maximum cover of nine feet zero inches,
may be allowed.
(b)
In new subdivisions, cover shall be measured from the final
grade of the street.
(c)
In existing roads or unpaved streets, a future profile grade
shall be obtained from the County. If such a profile grade is not
available, the design engineer shall submit a proposed profile grade
for approval by the County. If the future profile grade is at or below
the existing grade, cover shall be measured from the future profile
grade; if the future profile grade is above the existing grade, cover
shall be measured from the existing grade.
(d)
In areas outside of existing or planned streets, cover shall
be measured from existing grade. The design engineer shall thoroughly
investigate, and make suitable allowances for likely changes to existing
topography. Such changes include future erosion of stream beds or
grading of lots.
(7)
Clearance. Clearances between water mains and other utilities shall
be measured from outside of pipe to outside of pipe.
(a)
General. The following design factors must be considered in
providing adequate separation:
[1]
Materials and types of joints for water and sewer pipe.
[2]
Soil conditions.
[3]
Service and branch connection into the water main and sewer
line.
[4]
Compensating variations in horizontal and vertical separations.
[5]
Space for repair and alterations of water and sewer pipes.
[6]
Location of manholes.
[7]
Disturbance of the bedding of the water mains or other utilities.
(b)
Parallel installation. A horizontal distance of at least 10
feet shall separate water mains and sewers mains. The distance shall
be measured outside of pipe to outside of pipe. In cases where a ten-foot
separation is not practical, deviation may be allowed on a case-by-case
basis subject to County and/or state approval, if supported by data
from the design engineer. Such deviation may allow a horizontal separation
of a minimum of five feet with at least a six-foot vertical clearance
or closer installation provided that the sewer main be encased in
concrete 10 feet each side of the water main. If horizontal separation
is less than 10 feet, then compaction requirements shall conform to
the same as with the road right-of-way. This is to protect the interest
of the other utility's bedding.
(c)
Crossings. Where water mains and sanitary sewers must cross,
there shall be a vertical separation of 18 inches between the bottom
of the water main and the top of the sanitary sewer. This vertical
separation must be maintained horizontally for a distance of 10 feet.
The ten-foot distance is to be measured as a perpendicular distance
from the sewer to the water line.
(d)
Exceptions. When it is impossible to obtain the proper horizontal
or vertical separation as stipulated above, both the water and sewer
mains shall be constructed of ductile iron pipe. Other types of pipe
with equal or greater integrity may be used at the discretion of the
County. These installations shall be pressure tested to assure water
tightness before backfilling. Where a water main must cross under
a sewer pipe, additional protection of the water main shall be provided.
The County shall be consulted to discuss the use of double casing
or concrete encasement of the sewer and/or water main.
(e)
Utilities other than Sanitary Sewer. Water mains shall have
a minimum clearance of one foot where crossing utilities other than
sanitary sewers.
(8)
Appurtenances. Where it is not feasible for distribution mains to
be located within the pavements, they shall be located wholly within
the grass plot or wholly within the grass plot between the curb and
sidewalk. On private roads and parking areas valve boxes are to be
located outside of parking areas. Valves boxes will not be allowed
in sidewalk.
(a)
Valves and vaults. Mains of four inches to 16 inches shall have
valves of the same size as the main. All valves larger than 16 inches
shall have bevel gears and enclosed gear case and be constructed within
a valve vault. The valve vault or valve road box type and size to
be used with any size or type of valve shall be as shown in the standard
detail manual.
(b)
Provide valves for isolation at:
[1]
Two-thousand-foot intervals (maximum) on straight/non-intersecting
runs. Valves shall be provided on water mains between intersecting
runs for isolation purposes.
[2]
A maximum of 75 services/dwellings units isolated at once.
[3]
After the last service. Also prior to the terminus of the line
excludes permanent settings allowing future extension without service
disruption to users.
[4]
Provide valves on all sides of tees and crosses, with the exception
of hydrant tees which will require one.
[5]
On water mains at any arterial and major collector road crossings,
creek crossings, railroad crossings, and transmission pressure gas
mains, valves to be on each side of the crossing.
[6]
Existing water mains where there are no isolation valves between
two proposed extensions. The isolation valve is needed on the water
main between the extensions to allow for maintenance on the main while
providing water supply to the development.
(c)
Fire hydrants.
[1]
General.
[a]
Fire hydrants on private property (example: shopping
centers, industrial complexes, commercial sites, townhouse or apartment
complexes) shall be dedicated to the County with the water lines serving
the fire hydrants and the water system being dedicated to the County.
[b]
Fire hydrants shall be installed as shown in the
Standard Detail Manual. Hydrants shall not be located within 10 feet
of sanitary sewers or storm drains.
[c]
All hydrants not meeting substantial completion
acceptance will have an "out of service" disk placed on one or more
of the nozzles most visible to traffic.
[2]
Hydrant spacing.
[a]
Commercial and industrial areas.
[i]
Spacing 300 feet as supply hose is laid from motorized
fire apparatus.
[b]
Multifamily residential areas including but not
be limited to townhouses, duplexes and other multiplex dwellings,
condominiums, apartments, etc.
[i]
Maximum spacing: 300 feet as supply hose is laid
from motorized fire apparatus.
[c]
Single-family detached residential and flag lots:
[i]
Maximum hydrant spacing shall be 400 feet as measured
along an improved roadway.
[d]
Fire hydrants on roadways divided by an island
separator shall alternate from side to side and meet the spacing requirements
described in section § 291-62D(8)(C)[2][c].
[e]
General locations.
[i]
In all areas not specified in § 291-62D(8)(c)[2][a],
[b] and [c] above, the maximum fire hydrant spacing shall be 800 feet.
For divided highways every other hydrant shall be located on opposite
sides of the divided highway and maintain 800 feet on each side of
the highways. If divided highways are abut to commercial or residential
buildings, the spacing must comply with the above § 291-62D(8)(c)[2][a],
[b] and [c].
[3]
Hydrant location.
[a]
Commercial and industrial areas.
[i]
Building sprinkler/standpipe connections must be
shown on plans and not more than 100 feet from the nearest hydrant
as hose is laid from a motorized fire apparatus. The route to the
hydrant shall not be obstructed by fencing, trees and shrubs, significant
elevation changes, or other obstacles that would delay fire department
operations.
[ii]
The sprinkler/standpipe connection for use by
the fire department shall be located within 20 feet of the primary
entrance to the building or a location approved by the first due fire
department. Should a building have multiple entrances on the primary
entrance side (e.g., a one-story building with multiple business entrances),
the connection shall be centered on the primary entrance side of the
building. The primary entrance of a building is defined as that entrance
used by the majority of a building's occupants and/or the public.
[iii]
The fire department sprinkler/standpipe connection
will be labeled with a white reflective sign. The reflective sign
will have eight-inch red reflective letters reading "FDC." Below the
"FDC" lettering, a reflective six-inch icon of a siamese connection
(Y) for sprinklered building, or a six-inch reflective hose reel icon
for buildings with a standpipe system shall be placed. Buildings with
both sprinklers and a standpipe system will have both icons on the
reflective sign. The sign shall be located directly above the FDC
and be clearly visible as the building is approached from the street.
It should be located at least eight feet above the ground and clear
of all vegetation and other obstructions.
[iv]
Locate pumper connections outside of fenced areas.
[v]
No portion of the building shall be more than 300
feet away from the nearest hydrant, or as approved by the County in
cooperation with the local fire department.
[vi]
No portion of a commercial building shall be located
further than 300 feet from a hydrant unless a variance is granted
by the County engineer. One consideration for the variance approval
will be the support of the local fire chief for this request.
[vii]
Building "Fire Department Connection" (FDC) must
be shown on plans and not more than 100 feet from the nearest hydrant.
The location of the FDC shall be on the front of the building within
50 feet of the main entrance. If the building has several entrances
(i.e., strip business malls) the FDC shall be in the middle of the
building. Also, the FDC shall be labeled with a reflective sign with
the letters "FDC" and an icon of a Siamese Connection (Y). This sign
shall be located directly above the FDC and be clearly visible as
the building is approached from the street. It should be at least
eight feet above the ground and clear of all vegetation and other
obstructions.
[viii]
When water mains and hydrants are installed
prior to the buildings being designed it may require additional fire
hydrants and main upsizing to meet the required spacing, flow, or
pressure requirements.
[b]
Multifamily residential areas including but not
be limited to townhouses, duplexes and other multiplex dwellings,
condominiums, apartments, etc.
[i]
No portion of the building shall be more than 300
feet away from the nearest hydrant.
[c]
General locations:
[i]
Locate hydrants at all intersections to provide
easier access and fire fighting capabilities for the fire department.
[ii]
Locate hydrants adjacent to property lines (where
applicable) to avoid conflicts with driveways.
[iii]
Locate hydrants at the terminus of all lines.
[iv]
Hydrants shall be located so that parking is not
allowed within 15 feet on either side of the hydrant.
[v]
Locate hydrant such that the 4.5 inch connection
to face the roadway or drive aisle.
[vi]
Locate hydrants no further than 10 feet from a
roadway curb line or shoulder edge.
[vii]
The location of additional hydrants utilized
to meet the fire flow requirement cannot be such that hose will be
laid across a minor arterial or higher classification roadway.
[viii]
Locating the hydrant in pinch point where roadways
will be blocked by a pumper connection to the hydrant shall be avoided.
[ix]
Fire hydrants located within public parking lot
areas shall be placed on island outcrops that separate parking spaces
so that they are fully visible to approaching fire apparatus.
[x]
Fire hydrants located on roadways and within parking
lots shall be accessible by an allweather road surface capable of
supporting the weight of fire apparatus.
[d]
Single-family flag lots detached residential. All
flag lots of single-family residents shall be within 400 feet of a
hydrant.
[4]
Hydrant color coding.
[a]
The following color designations are based on National
Fire Protection Association (NFPA) Standard 291 as well as a local
amendment to NFPA standard. These color designations shall be based
on the available fire flow measured at 20 psi residual pressure under
normal conditions.
Fire Flow
(gpm)
|
Color
|
Reflective tape on
| |
---|---|---|---|
1,500 or greater
|
Blue
|
Around bonnet flange
| |
1,000 to 1,499
|
Green
|
Around bonnet flange
| |
500 to 999
|
Orange
|
Around bonnet flange
| |
All hydrant barrels shall be painted yellow
|
[b]
When the fire flow is less than 500 gpm, the hydrant
bonnet and all nozzle caps shall be painted red.
[c]
At the time the system becomes substantially completed,
the developer/contractor shall install white reflective tape on around
bonnet flange.
[d]
During inventory process, the Department of Public
Works will test the fire flow and color code the hydrant according
to the above table. Note that it is not County responsibility for
the painting of all hydrant barrels. Also the County is not responsible
for painting all bonnet and nozzle caps for hydrant fire flow less
than 500 gpm.
(d)
Tapping sleeve and valves. Tapping sleeves and valves on ductile
iron pipe mains to serve as line valves shall be used for all connections
eight inches and larger in size to any existing main where more than
10 domestic services would be shut off during installation of a standard
tee. The main being tapped may be the same size as the proposed main
or tapping valve, but the tapping cutter shall be 1/4 inch or more
undersized. Use of mechanical joint sleeves may be permitted only
upon written consent of the County and will be considered only where
the pipe being tapped is ductile iron pipe. Valve boxes or vaults
for tapping sleeves shall be sized in accordance with the County Standard
Detail Manual.
(e)
Blow-offs and air release valves. A blow-off shall be installed
at the low point of mains in accordance with the Standard Detail Manual.
Hydrants will serve as blow-offs at the end of mains. Hydrants shall
be installed at the end of mains to be extended in the future. Air
release valves shall be installed at prominent peaks on long distribution
mains where there are no service connections. Air release valves will
generally not be required for distribution mains. Where required,
air release valves shall be installed in accordance with the Standard
Detail Manual.
(9)
Materials. All distribution mains and fittings shall be in accordance
with the Standard Specifications for Construction Manual.
(10)
Installation. Installation of all distribution mains and appurtenances
shall be in accordance with the Standard Specifications for Construction
Manual. Such requirements shall be noted in the specifications and
on the drawings.
(11)
Existing hydrant relocation and reuse will only be allowed if
the hydrant is less than seven years old. If hydrant is greater than
seven years old, the hydrant shall be replaced and the existing hydrant
conveyed to the County.
E.
Transmission mains.
(1)
Location. The approximate location of transmission mains shall be
based on a computerized network analysis by the design engineer, which
meets with County approval. This analysis shall indicate the beginning
and ending points of the main and the major distribution system intersecting
nodes. The design engineer shall select an alignment which satisfies
the approximate location as determined in the analysis while taking
into consideration length of pipe, number and type of fittings, public
or private property, construction and maintenance access, future road
widening, horizontal and vertical alignment changes, flood prone areas,
subsurface conditions, and existing and future utility interferences.
All water utility easements shall be 20 feet minimum width. No other
utilities or structures will be allowed in the water easement without
the County's written approval.
(2)
Sizing. The sizing of transmission mains shall be based on the computerized
network analysis by the design engineer or any previously approved
studies, as to be determined by the County.
(3)
Cover. Normal cover for transmission mains shall be 3.5 feet, except
where existing utilities are crossed, where the minimum will be three
feet. Maximum cover will be nine feet, except where authorized by
the County.
(4)
Clearances. See distribution mains in § 291-62D(7).
(5)
Hydraulics. System hydraulic gradient, static and residual pressures,
velocities, and flow direction will be provided by the County if established.
If not established the design engineer shall submit a proposal to
the County for review and approval. The design engineer will analyze
transient pressures in transmission mains and provide written results
to the County for review. In most cases, the transient pressure analysis
will be limited to pipelines of finite length for line rupture and
sudden valve closure. The computation methodology is detailed in Pipeline
Design for Water and Wastewater, ASCE, 1992 or later edition; see
also Pumping Station Design, 3rd Edition (or later), 2006, by Garr
M. Jones.
(6)
Appurtenances.
(a)
Valves and vaults. All valves larger than 16 inches shall be
placed in a standard concrete vault in accordance with the Standard
Detail Manual and Standard Specifications for Construction Manual.
(b)
Air and vacuum release valves. The proper ventilation of transmission
mains is very important. Trapped air pockets can significantly reduce
the capacity of the mains as well as cause increased pumping heads
and corresponding higher pumping costs. Valve sizing and location
shall be evaluated during design and coordinated with valve manufacturer.
The following guidelines shall be used to locate air and vacuum release
valves:
[1]
Peaks in profiles.
[2]
Abrupt increase in downward slope.
[3]
Abrupt decrease in upward slope.
[4]
Long ascents: 1,500 foot to 3,000 foot intervals.
[5]
Long descents: 1,500 foot to 3,000 foot intervals.
[6]
Long horizontals: 1,500 foot to 3,000 foot intervals.
[7]
Pumps: On the discharge pipe as close as possible to the check
valve.
[8]
System side of the check valve.
[9]
Valves: high point of large valves or bypass piping and downstream
of large pressure reducing valves.
[10]
Shop drawings of manufacturer shall be provided
to County for acceptance prior to installation.
(7)
Materials. The pipe material class of transmission mains shall be
selected based on its corrosion resistance, strength against internal
and external pressures, hydraulic characteristics, installation conditions,
and economics and be in accordance with the Standard Specifications
for Construction Manual.
(8)
Installation. Installation of all service connections and appurtenances
shall be in accordance with the Standard Specifications for Construction
Manual. Such requirement shall be noted in the specifications and
on the drawings.
F.
Service connections.
(1)
Location.
(a)
Water house or building connections shall be constructed with
a curb stop and/or meter vault box to the right-of-way/property/easement
line for all lots within a proposed development unless otherwise approved
by the County Engineer. All adjacent lots which are not part of the
proposed development, but are to be served by the water line shall
be shown on the plans. Water service laterals, including curb stops
and boxes or meter vault, are to be provided to the right-of-way/property/easement
lines for all existing dwellings fronting a new water main. Twin services
may be placed on the property line separating the two houses in single-family,
detached house subdivisions.
(b)
All piping shall be arranged in accordance with the County Standard
Detail Manual.
(2)
Sizing.
(a)
The minimum sizing for any service connections shall be one inch. For larger homes and other buildings, larger connections are required. Provide water meter sizing computations for meter sizing per Appendix R.[5]
[5]
Editor's Note: Said appendix is included as an attachment to this chapter.
(b)
Sizing for commercial, industrial and institutional meters shall be based on Appendix R.[6]
[6]
Editor's Note: Said appendix is included as an attachment to this chapter.
(3)
Cover. Cover over service lines shall be as indicated in the Standard
Details Manual and measured from finished grade.
(4)
Clearances.
(a)
Parallel to sewer house connections. Water house services shall
ordinarily be placed 10 feet horizontally and one foot vertically
over and from the sewer house connections. In cases where this is
not achievable, deviation may be allowed on a case-by-case basis subject
to County and/or state approval. Such deviation may allow a horizontal
separation of 1.5 feet with at least a six-foot vertical clearance
(sewer being placed on the bottom). If schedule 40 PVC solvent weld
pipe is utilized for the sewer house connection a 1.5 foot horizontal
separation with at least a one-foot vertical clearance (sewer being
placed on the bottom) may be allowed if a passing pressure test with
10 feet of head of water or equivalent taken in the presence of a
County representative is achieved.
(b)
Crossing storm drains or other utilities. Water house and building
connections crossing storm drains and other utilities (existing or
future) shall have a minimum clearance of 12 inches from these utilities.
(5)
Cross-connections. Cross-connections shall not be permitted or allowed
to continue. No cooling water or condensate may be returned to the
potable water supply line. All interconnections shall be approved
by the County and other appropriate reviewing authorities. On-site
private wells must be properly abandoned (per MDE guidelines) prior
to public service activation.
(6)
Appurtenances. Backflow prevention devices shall be located in accordance with § 291-29 and Res. No. 2005-20 and the Standard Detail Manual.
(7)
Installation. Installation of all service connections and appurtenances
shall be in accordance with the latest County Standard Specifications
for Construction and Detail Manuals. Such requirement shall be noted
in the specifications on the drawings.
(8)
Booster pumps. Booster pumps are not permitted for any individual
service, without prior County approval. If a booster pump is installed
on any individual service, the service will require protection with
a reduced pressure principle backflow preventer.
(9)
PRVS. When pressure in the water main exceeds 80 psi, an approved
pressure reducing valve at the customer's expense, complying
with ANSI/ASSE 1003, shall be installed to limit pressures on fixtures
to less than 80 psi. Pressure reducing valves may cause a closed system
requiring thermal expansion devices. Where pressure reducing valves
are installed and the downstream piping is not rated for the maximum
upstream pressure, a pressure relief valve shall be installed downstream
of the pressure reducing valve at the customer's expense.
G.
Structural considerations.
(1)
Buttresses and anchors.
(a)
At all fittings which achieve a change in pipeline direction,
such as tees, fire hydrants, valves (as needed) bends and dead ends,
thrust restraint is necessary. Restrained joints and/or anchorage
blocks are two means of achieving thrust restraint. The design engineer
shall decide what is appropriate for each particular situation based
on an analysis of such factors as soil conditions, clearance requirements,
constructability, future expansion and cost.
(b)
Under normal soil conditions, fittings up to thirty-six-inch
diameter shall be buttressed or anchored as provided for in the Standard
Details Manual. In the event the soils will not bear 3,000 pounds
per square foot, the design engineer shall design buttresses or anchorages
appropriate to the situation.
(2)
Restrained joints. If the soils at the project site are unusually
poor, or other factors such as cost, space limitations, or future
construction so indicate, restrained pipe joints shall be designed.
The joint restraint may be either Field Lock Gaskets harnesses or
mechanical joints with retainer glands for mains and valves up to
sixteen-inch diameter. Restrained joint types for larger mains and
valves shall be approved by the County prior to proceeding with design.
The design shall account for test pressures, surge from sudden valve
closures, poly encasement (wrap) soil frictional resistance and effect
of groundwater as a minimum.
(3)
Jacking and tunneling.
(a)
Where mains are being designed to cross railroads, state highways,
County roads, or other roads on which service cannot be interrupted,
the water main shall be installed in a sleeve, tunneled or jacked
under the road. The sleeve size, material, and method of tunneling
or jacking shall be approved by the owner of the road or the railroad
being crossed.
(b)
The sleeve diameter shall be sufficient to permit the proper
positioning of the water main within the sleeve. Water mains installed
in sleeves shall have restrained joints throughout the length of the
sleeve. The annular void between the main and the sleeve shall be
completely filled with grout or County-approved casing spacers with
end caps at the ends of the casing.
(c)
Water mains installed in sleeves shall be equipped with sufficient
valves to isolate the sleeved section. A valve at each end is required.
(4)
Design loads and piping design.
(a)
The design engineer shall submit calculations necessary to support
the selection of the type and class of pipe indicated on the drawings.
(5)
Corrosion protection. If soil tests or inspection of existing utilities
in the project area reveals evidence of, or potential for, corrosion,
the County shall be notified of the condition. Should the County deem
it necessary, the design engineer shall design suitable galvanic and/or
cathodic corrosion protection measures using AWWA Controlling Corrosion
within Water Systems, 1978 or latest edition.
(6)
Curves and deflections. Gradual changes in pipeline direction may
be achieved by joint deflection in accordance with the manufacturer's
recommendations. Curvature shall only be allowed for lines constructed
of ductile iron pipe. The joint deflection for DIP sizes three inches
through 12 inches shall not exceed 3.5°. The joint deflection
for DIP size 14 inches through 20 inches shall not exceed 1.5°.
The joint deflection for DIP sizes 24 inches through 48 inches shall
not exceed 1.0°.
H.
Testing and disinfection. The contract documents shall provide for
hydrostatic testing of newly laid mains as described in the County's
Standard Specifications for Construction Manual. Hydrostatic tests
shall be performed for pressure retention and leakage. Disinfection
shall be done in accordance with the Standard Specification for Construction
Manual.
I.
Abandonment procedures. Abandoned service connections shall be cut
and plugged at the service main, and the meters removed and provided
(delivered) to the County to salvage, if their condition permits reuse.
Distribution mains that are to be abandoned shall be plugged at the
point of abandonment and on each side of any existing valves, and
the valves and hydrants removed and salvaged if their reuse appears
practical. Any necessary buttresses or anchorage required shall be
designed in accordance with the Standard Detail Manual and this chapter.
J.
Water pumping, treatment and storage. A detailed presentation of design criteria for pumping, treatment, and storage facilities shall be in accordance with the requirements of § 291-63, the needs of the County, and the recommendations in Pumping Station Design, 3rd edition (or latest), 2006, by Garr M. Jones. The sizing of water pumping and storage facilities will be in accordance with Appendix O.[7]
[7]
Editor's Note: Said appendix is included as an attachment to this chapter.
A.
General.
(1)
In addition to the criterion contained herein, the design of water
pumping facilities, well houses, and water towers shall meet the requirements
of all relevant guidelines issued by the Maryland Department of the
Environment (MDE) or shall be exceeded where specified by the County.
The following additional manuals shall be consulted and applied to
the design with the approval of the County:
(2)
All aspects of the facility shall maximize operator safety. The facility
shall be designed to operate reliably and efficiently with a minimum
of attention and have provisions for easy access and maintenance.
Equipment shall be selected on the basis of durability, availability
of replacement parts, standardization, efficiency, and ease of maintenance
and repair.
(3)
The pumping/storage facility shall be designed for the maximum build
out conditions of the service area as approved by the County using
flows approved by the County.
B.
Design.
(1)
Planning period. Water pumping/storage facility design conditions
shall, at minimum, accommodate twenty-year planning horizon. For all
pumping/storage facilities, consideration shall be given to future
upgrade flexibility necessary to accommodate design conditions beyond
the normal planning horizon. This is especially important for larger
facilities.
(2)
Hydraulic analysis.
(a)
Refer to § 291-62 and Appendix O[1] for water pumping/storage facility sizing requirements.
A service area map and tabulation of the design flow shall appear
on the plans. The map and tabulations shall show initial and ultimate
service areas.
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
(b)
Water facilities must satisfy the hydraulic conditions of the
system. A complete hydraulic analysis of each water pumping and storage
facility is required. During the study phase, the designer shall consult
with the County for the requirements of the hydraulic analysis. At
a minimum, the designer shall perform twenty-four- and forty-eight-hour
extended period computer simulations using average day demand, maximum
day demand and peak hour demand for both current and full development
conditions. Fire flows shall be analyzed during maximum day rate for
both initial and full development conditions.
(c)
The hydraulic analysis shall be presented in a clear, logical
and easy to understand format and shall relate to the proposed construction
drawings. If construction drawings are not available at the time of
the analysis then scale drawings shall be prepared with street names
to locate the proposed system.
(3)
Pump and system curves.
(a)
The designer shall show pump and system curves on the plans
to scale. System curve characteristics for each design condition shall
be determined by the Hazen Williams formula for piping head loss in
conjunction with the County water model.
(b)
The pump selection shall be reviewed for both the initial and
maximum design year conditions.
(c)
The following pump and system curves shall be shown on the plans:
[1]
System curve for peak hour demand for the design year.
[2]
System curve for maximum day demand plus fire flow for the design
year.
[3]
System curve for average day demand for the design year.
[4]
System curve for average day demand for the initial year of
station operation.
[5]
Pump curve for single pump operation and multiple pump operation
where station has three or more pumps.
(d)
In addition, the designer shall list next to the curves the pump design criteria including pump motor horsepower, efficiency, npsh at design points and rpm. Pump and system curves shall be shown for new water main conditions. Hazen-Williams "C" factors used in evaluating pump and system curves shall be in accordance with the guidelines given in § 291-62 regarding hydraulic calculations.
(4)
Number of pumps. Water pumping facilities shall be capable of pumping
the maximum day demand with the largest single pump out of service.
(5)
Pump selection criteria. Avoid applications where pumps must operate
in an adverse area of their performance curve. Design for maximum
efficiency at the operating point. Examples would be pumps operating
at very low flows and high heads, near shutoff heads or "runout" conditions.
These conditions can result in excessive hydraulic loading or cavitation
damage to impellers, casings and shafts, rapid bearing and mechanical
seal wear and high vibration. Under no circumstances shall a pump
be specified operating outside of its recommended range.
(6)
Variable frequency drives (VFDs). The use of VFDs or other methods
to achieve minimum flow conditions below the full speed operating
range of the pumps shall be approved by the County. If VFDs are used,
multiple speed performance curves shall be shown.
(7)
Water hammer. The potential impact of water hammer under usual and
unusual circumstances (power outages, etc.) shall be evaluated. If
the combined effects of static head and water hammer (using a safety
factor of 1.1) do not exceed the weakest piping system component working
pressure, no special provisions need to be included to control water
hammer. Where the maximum water hammer pressure (using a safety factor
of 1.1) exceeds the weakest piping system component working pressure,
the designer shall strengthen those elements affected, reevaluate
pipe size and velocities or select an appropriate device to control
water hammer. No pressure vessel/surge tank type devices will be acceptable.
C.
Design criteria for water facilities.
(1)
Site design.
(a)
Location. Water facilities shall be located near the areas to
be served. Natural screening and remoteness of the site shall be primary
elements of site selection wherever possible. Where pump stations
are sited in proximity to developed areas, the architecture shall
be compatible with the surrounding area. Building aspects such as
generator exhaust and ventilation fan noises shall be considered.
Similarly, building setbacks shall be considered to provide minimal
impact to neighboring properties.
(b)
Land acquisition. Land required for facilities, including necessary
vehicular access routes to an existing or proposed public roadway
shall be owned in fee simple by the County. As part of this process,
a boundary survey of the property is required together with a record
plat and a metes and bounds description of the parcel unless otherwise
approved by the County Attorney. In determining the space requirements
for the facility, particular attention should be given to the width
provided for the access road to insure adequate space for grading
and drainage within the access road right-of-way. Sufficient room
shall be provided for future maintenance of wells, tanks, towers,
and generators. Vehicle access shall be provided with adequate turning
radii for well rigs, truck-mounted cranes and other large equipment
that might be expected to be on site.
(c)
Topography. Adjacent areas potentially served by the water facility
must also be considered. Water facility site selection shall also
be compatible with suitable site access and soil capability with respect
to land grading in conjunction with site development. Existing contours
and other topography shall be shown for the entire site including
a one-hundred-foot minimum width outside of the proposed property
boundary on all sides. Contour interval shall be two-foot, unless
otherwise approved by the County engineer.
(d)
Floodplain. Water facilities shall be sited to remain operational
and permit access during a one-hundred-year return frequency flood.
Building top slab elevation shall be set a minimum of two feet above
the one-hundred-year floodplain elevation. The access road shall be
above the one-hundred-year floodplain elevation.
(e)
Wetlands. Avoid direct impacts wherever possible and minimize
impacts to wetland buffer areas. Buffer areas include 25 feet beyond
non-tidal wetlands.
(f)
Grading. Water facility grades shall prevent local ponding and
provide positive drainage away from all structures and site. The site
shall be a minimum of one foot above the surrounding area. Slopes
on site shall be generally limited to no less than 1% and no greater
than 4%. Stone surfaces around paved areas shall provide proper site
drainage at slopes 10% or less. Land grading outside of the water
facility perimeter fence shall not exceed three to one slopes; four
to one slope maximums are desirable. Lesser slopes wherever possible
are preferred. Site grading design shall be compatible with slope
stability for the soils encountered. Slope stabilization shall be
appropriate for the degree of slope and soil conditions. The use of
retaining walls on or immediately adjacent to the water facility site
is not permitted. Provide for adequate drainage and conveyance for
the discharges of the control valves, blow-offs, roof drains, and
condensers as well. There shall never be a situation where roof drains
flow across walkways, roadways, or parking areas.
(g)
Site security. Water facility sites shall be fenced with black
vinyl coated chainlink fencing eight feet tall, black vinyl coated
post and black hardware, and a sixteen-foot wide locking gate for
vehicle access. The fence is to include three strands of barbed wire
around the top. Additional property line fencing may be required as
determined by the County Engineer. Buildings shall have exterior lighting
controlled by motion detectors and provided with an entry alarm connected
to the station SCADA.
(h)
The area within the fencing, and two feet beyond the fence is
to be covered with a minimum of six inches of No. 57 crushed stone
over a weed barrier film. No proposed grassed areas are allowed.
(i)
Paving. Water facility sites shall have P-4 paving section in
accordance with Table 2.07 of the road ordinance[2] and include a minimum of two parking spaces. The site
shall have sufficient room to allow AASHTO WB-40 access to equipment
by maintenance trucks. An access road to the water facility site shall
have P-2 paving section in accordance with Table 2.07 of the road
ordinance.[3] The width of the pavement shall be 20 feet wide with two-foot
gravel shoulders. The maximum grade for the access road shall not
exceed 5%. The cross slope shall be in accordance with standard detail
R/2.16.
[1]
The access road and site shall support a minimum AASHTO WB-40
turning radius. The site shall also include a WB-40 turn-around area.
Access roads shall be used exclusively for facility maintenance and
access.
(j)
Sidewalks. Four feet wide, in accordance with the road ordinance/detail
manual, are to be provided between buildings and/or structures and
from paved areas to buildings and structures for access of equipment,
dollies, etc.
(k)
Sediment control, a sediment control plan shall be provided
and approval obtained from the Charles Soil Conservation District
(SCD).
(l)
At least two test borings shall be taken at the building location
to determine soil types, rock, water table elevations, soil bearing
values, etc., standard penetration tests shall be taken at intervals
not to exceed five feet. Borings shall be taken to a depth of not
less than 15 feet below the bottom of the proposed structure. Borings
shall be taken deeper as necessary, depending on soil conditions.
(m)
Station sign. A permanent sign shall be provided at each facility
stating the station name, street address and emergency telephone number.
The sign must meet Charles County 911 addressing system.
(n)
Yard hydrants and hose bibs shall be provided for wash down,
maintenance, and sanitation purposes.
(2)
Structures.
(a)
Design/architectural standards. Water facilities shall be architecturally
compatible with surrounding structures and shall not have slate roofs.
Water facility buildings shall be precast concrete and shall be designed
to be vandal-proof. Roof shall be precast concrete gable type. There
shall be no exposed woodwork on the outside of the building. All exterior
woodwork shall have a vinyl or aluminum coating. The facility shall
have a lightning protection system. Provisions shall be made in the
structure for traversing bridge cranes of adequate capacity to facilitate
the removal of pumps, motors, valves and all other related heavy equipment.
Doors shall be sixteen-guage steel with deadbolts and locks keyed
to the County standard. Doors shall be located and/or situated so
that they are not affected by rain runoff from the roof. Exterior
lights shall be vandal proof, wall-mounted, energy-efficient, controlled
by motion detectors and an on-off switch. Facilities shall be provided
with outside non-freeze hose bibbs. Ventilation openings shall be
protected with aluminum louvers with birdscreens. The building shall
conform to all Charles County building codes and zoning regulations.
[1]
Pump room. Pumps and piping shall be located above pump room
floor at a height sufficient to connect to suction/discharge piping.
Parallel suction and discharge headers shall be provided. Pumps shall
be of the horizontal style placed on individual concrete bases. Floors
shall be sloped to floor drains piped to a sump. The minimum floor
slope toward the sump shall be 1/4 inch per foot. Water shall not
pool in any areas of the floor. Each water pump shall have a floor
drain located next to it. Pump baseplate drains shall be piped to
adjacent floor drains. A building sump with sump pump and piping shall
be provided. The pump room shall be furnished with a service sink
with both hot and cold water, and inside hose bibb.
[a]
Adequate room is required for working around and
above equipment. A minimum of three feet of clearance between equipment
and walls shall be provided.
[b]
All electrical and control equipment shall be located
at least three feet above the floor.
[c]
Locate all auxiliary equipment above ground in
an appropriate building which allows safe and efficient all-weather,
all-hour, electrical and mechanical maintenance, including but not
limited to motor controls, blowers, meters, etc.
[d]
A restroom shall be provided with toilet, lavatory,
on-demand hot water heater, towel dispenser, soap dispenser and mirror
onsite as determined on a case-by-case basis based on the anticipated
number of man-hours of operation and the remoteness of the site.
[2]
Water service. A minimum of one-inch-diameter metered potable
water source shall be provided for wash down, maintenance, and sanitation
purposes. The service shall include a backflow preventer. The water
service line shall provide a minimum of 30 gallons per minute to the
emergency shower with a minimum residual pressure of 35 psi.
[3]
Control room. Electrical equipment shall be located above grade
in a control room that is designed with adequate space to accommodate
future upgrades.
[4]
Generator area.
[a]
A separate generator area shall be provided for
housing the emergency generator and fuel tank. The generator slab/floor
shall be located a minimum of two feet above the one-hundred-year
flood elevation. If the generator is in a room, it shall have a roll-up
metal garage door for access and shall be equipped with a floor drain
located outside the fuel spillage containment area, piped to the building
sump. The generator area shall be supplied with hose bibb, hose rack
and 50 feet of rubber hose.
[b]
Alternatively, the generator may be installed outdoors
in a separate, self-contained, sound attenuated enclosure on a concrete
pad of sufficient size for the generator and maintenance access.
[5]
Heating and ventilation.
[a]
The building shall be heated by electric unit heaters
with integral thermostats sized to maintain a minimum inside temperature
of 40° F. Provide cooling as necessary to maintain air temperatures
below 95° F. inside electrical devices. Ventilation shall be by
means of wall-mounted exhaust fans with backdraft dampers operated
by thermostats and freezestats and intake louvers with motor operated
dampers.
[b]
Ventilation shall be designed for a minimum of
six air changes per hour. Each room shall have a dedicated exhaust
fan(s). Ventilation shall be sufficient to remove heat generated by
the pump motors and controls. Provisions shall be made to ensure against
condensation forming on controls and other major items of equipment.
(3)
Equipment.
(a)
Yard valves. Yard valves shall be buried resilient seat gate
valves complying with the standard specifications with operating nut
and roadway valve box at grade.
(b)
Station bypass. Water facilities shall be provided with bypass
connections in the form of two fire hydrants, one on each side of
the suction and discharge lines of the station. Hydrants shall be
labeled "suction" and "discharge," respectively. The hydrants shall
be located adjacent to the parking area and shall be no more than
50 feet apart for easy setup of temporary pumps for pump around capability.
(c)
Interior piping. All interior water piping shall be DIP, Class
53, with flanged fittings. Flanges shall be integrally cast on pipe
or factory assembled screwed-on with proper bonding compound. Manifolds
shall include flexible couplings for make-up and for expansion and
contraction of the piping system. Flexible couplings shall be provided
on the suction and discharge of each pump. Arrangement of piping and
equipment within the station shall be made with adequate space for
maintenance, repair, removal or replacement of equipment, as well
as to safeguard personnel working in the station. A minimum of three
feet of clearance between equipment and walls shall be provided. Depending
on the size of the equipment and piping, greater clearances may be
needed. Piping shall be adequately supported. Control and instrumentation
piping shall be copper or stainless steel. Chemical feed piping shall
be clear PVC. Provide color coding for piping in accordance with the
standard specifications for construction manual.
(d)
Interior valves. Each water pump shall have isolation valves
to permit the removal or maintenance of the pumps without affecting
the operation of the remaining pumps. Isolation valves shall be resilient
seated gate valves. Valves larger than sixteen-inch shall have geared
operators with handwheels. Handwheels shall be marked with an open
arrow. Each pump shall have a hydraulically operated, time adjustable
pump check service valve to prevent backflow through inoperative pumps.
In accordance with the criteria for water hammer control, pump check
service valves shall be of the type and strength required to eliminate
water hammer damage. Surge relief valves shall also be provided on
the suction and discharge headers of the station and piped to the
nearest storm drain system.
(e)
Pressure gauges. Pressure gauges for direct reading of line
conditions shall be placed on both the suction and discharge of each
pump, on the main discharge header piping after the last pump, and
on the suction header as it enters the building. Pressure gauges shall
be oil-filled type, have a minimum 3 1/2-inch diameter face and
be equipped with snubbers. Pressure gauges shall be installed and
configured such that the gauge can be isolated and the gauge piping
be drained. Accuracy shall be to within 0.5% of pressure. Pressure
gauges shall have a range such that the normal operating pressure
is near the middle of the gauge.
(f)
Flow metering. All water pumping facilities shall have a County
approved water meter. A seven-day chart recorder and 4-20 MA output
to the SCADA system, with totalizer, and indicator recorder in units
of gpm shall also be provided.
(g)
Transfer pumping units.
[1]
All water pumps shall rotate clockwise as viewed from the motor
end. Pump bearings shall have a minimum 100,000 hours abma-10 bearing
life. Pump motors shall operate on three-phase, sixty-cycle electrical
service and at a speed no higher than 1,780 rpm. Pump discharge velocities
shall be between five and 15 feet per second. Pump inlet pressure
shall be maintained at a sufficient level to avoid cavitation. Pump
motor horsepower shall be sufficient to prevent motor overload under
all possible conditions. Water pumps and motors shall be suitable
for continuous duty. All pumps shall be factory witness tested and
approved prior to shipment. Water pumps shall meet the requirements
of the hydraulic institute for vibration. Pumps shall be one of the
following types:
[2]
The pump casing/volute, impeller, seal housing and motor housing
shall be of cast iron construction. Impeller shall be cast iron or
bronze. The pump's casing and impeller shall be fitted with replaceable
hardened bronze or stainless steel wear rings to maintain sealing
efficiency between the volute and the impeller. At the County's
option, other pump materials may be required to suit a particular
application.
[3]
Pumps shall have the following additional features:
[a]
Stainless steel shaft.
[b]
NSF approved fusion bonded epoxy coating (interior).
[c]
Flexible shaft coupling and removable OSHA-compliant
shaft guard.
[d]
Mechanical shaft seals cooled and lubricated by
the pumped fluid.
[e]
Premium efficiency motors shall be specified (where
commercially available) for all three-phase pump motors.
(4)
Electrical and controls.
(a)
Electrical design. All electrical designs and components shall
be in strict accordance with all applicable national and County Code
requirements. Electrical design shall be such that phase out protection
shall be provided so that the power will automatically switch off
in the event of a loss of any one phase. Incoming electrical service
shall be underground with electric meters installed outside the building.
The electrical plans shall include, but not be limited to, the following:
[1]
Design report shall provide the correspondence with the Charles
County local power company showing the consultant's load breakdown
along with the local power company's assessment of the voltage
available, their ability to serve the project, and the availability
of a second independent source of power. Specific local power company
permission to use across-the-line starters or requirement for reduced
voltage starters is required.
[2]
In addition to the proposed wiring diagrams, provide a narrative
of the control sequence scenario which clearly explains the operational
intent.
[3]
Complete plan layout indicating all conduit, wire sizes and
equipment locations including lighting and other appurtenances. Incoming
electrical service on the site shall be underground and within concrete-encased
conduits.
[4]
Installation details of equipment that are wall-mounted, or
suspended from the ceiling or otherwise required for clarity.
[5]
Single line diagrams incorporating all electrical components
required for operation of the facility.
[6]
Complete lighting schedule noting model, size, location and
installation data as well as appurtenances. Vandal proof exterior
lighting shall be provided. Interior and exterior quartz lighting,
separately switched, for maintenance purposes including auxiliary
dc safety lighting is to be provided. Minimum lighting levels shall
be 15 footcandles for stairways, 50 footcandles for operation, and
100 footcandles for electrical and mechanical maintenance.
[7]
Complete control and SCADA diagrams.
[8]
Elevation of control panels with equipment and mounting dimensions
and notes identifying each component.
[9]
Complete circuit breaker schedule indicating size and identifying
each circuit.
[10]
Ventilation schedule noting fan size, operating
conditions, location, model, installation data, etc. The ventilation
schedule shall also outline louver data including size, material,
fixed or motorized.
[11]
Secondary power facilities and alarm equipment
shall be designed so that they may be manually activated for periodic
maintenance checks to ensure proper operation.
[12]
Provide a legend of all symbols used for the above.
[13]
Power for the station shall be 480 volts, three-phase.
[14]
IEC electrical components shall not be utilized.
For replacement compatibility and availability, only full-sized NEMA
UL listed electrical devices shall be used regardless of any equivalent
UL ratings of IEC devices.
[15]
Lockable safety disconnect switches are to be
provided for all rotating equipment. Use lockable knife-switches rather
than remote lockable start/stop button stations.
[16]
Provide "push-to-test" type indicator lamps with
screw-in type bulbs. Use of 120 mb type bulbs is prohibited.
[17]
Permanent, in-place, volt/amp meters are required
for each pump or major piece of equipment.
[18]
Due to compatibility and standardization needs,
provide only "Square-D," "Furnas," or "Cutler-Hammer" electrical equipment;
no alternatives allowed.
[19]
Use "Square-D," or County-approved equal, Class
8501 Type "K" plug-in style relays to the maximum extent possible
where appropriate. Provide integral power indicating lamps in the
relays. The only exception to this should be where current requirements
exceed contact ratings. Use plug-in style relays for timers, alternators,
and latching as well. Octal or square relays are equally acceptable,
although eight-pin octal relays are preferred. Use "Square-D" Type
KP12P14 or KP13P14 or County-approved for DPDT or 3PDT respectively.
[20]
Provide non-resettable elapsed time meters for
all rotating equipment. Meters are to be in hours and tenths of an
hour, not minutes. Provide an elapsed time meter for parallel operation
of main pumps; e.g., a meter for Pump No. 1, Pump No. 2, and Pump
Nos. 1 and 2 together.
[21]
A weatherproof red exterior "trouble light" for
visual indication of equipment failures/problems is to be provided.
A horn is not to be provided.
(b)
Lightning and surge protection: the designer shall provide lightning
and surge protection at the water facility. The lightning and surge
protection shall comply with the latest editions of all applicable
codes and standards. Provide phase failure and phase reversal protection
for all equipment. A single phase condition shall not destroy motors,
transformers, relays, etc., should the second source of power fail
to take over.
(c)
Backup power. All water pumping facilities shall be provided
with emergency generators with automatic transfer switches as described
in MDE guidelines. Emergency generators shall be sized to maintain
full station operation. Emergency generators shall be diesel driven
with fuel storage on the underside of the generator in a belly tank
or outside the building in an aboveground storage tank. Fuel spillage
protection shall be provided. Tank size shall be suitable for a minimum
of 24 hours of generator operation at full load. Generators shall
be mounted on vibration spring isolators. When emergency generators
are located inside a building, they shall be mounted with a fuel tank
fill connection to the outside. Generator engine exhaust shall be
provided with a critical grade silencer and piped to the outside of
the control building. Generator exhaust shall face away from nearby
neighbors. If this is not possible, a baffle wall shall be constructed
in front of the generator exhaust to deflect the noise.
(d)
Control/SCADA system: a complete and operable control/SCADA
system shall be provided per County standard specifications for construction.
(5)
Painting and coating. All exposed piping, pump equipment and appurtenances,
including all structures, shall be painted per County standard specifications
for construction.
(6)
Disinfection. All piping, pumps and appurtenances shall be disinfected
prior to placing in service in accordance with applicable AWWA standards.
(7)
Safety.
(a)
Appropriate emergency eyewash facilities shall be provided whenever
chemical handling is proposed. The need for emergency fountains and
showers, the design/configuration thereof, and their locations shall
be in accordance with the most current edition of the 10 states standards
and the applicable requirements of MOSH and the County Safety Officer.
As a minimum, the eyewash fountains shall be supplied with water of
moderate temperature, 50° F. to 90° F., suitable to provide
15 to 30 minutes of continuous irrigation to the eyes. As a minimum,
the emergency showers shall be capable of discharging 30 gallons per
minute of water at moderate temperature and at a minimum pressure
of 35 psi.
(b)
Appropriately designed dielectric rubber floor mats are to be
provided for insulation at all motor controls for personnel safety.
If water on the floor is a possibility, the design must eliminate
such water. A situation of motor control maintenance in wet or unsafe
conditions is unacceptable.
D.
Production wells.
(1)
General. The design professional is directed to Section 02555, Production
wells, of Charles County's Standard Specifications for Construction,
and the following:
(a)
General well appurtenances. The following well appurtenances
are required:
[1]
A pitless adapter shall be provided.
[2]
A sampling tap shall be provided for raw water sampling within
the well house piping.
[3]
Adequate control switches, etc., for the pumping equipment shall
be provided.
[4]
A water meter is required to determine water production for
each well and the meter shall be located upstream of the well blow-off.
[5]
The well casing shall extend at least 12 inches above the concrete
floor or apron surrounding the well and above the one-hundred-year
floodplain elevation.
[6]
Adequate support for the well pump and drop pipe shall be provided.
[7]
Each well casing shall be equipped with a drawdown gauge, airline,
and appurtenances for measuring the change in the elevation of the
water level in the well and a conduit for level transducer from the
well to the well house.
[8]
Wellhead protection shall be provided.
(b)
Submersible pumps. Where a submersible pump is used, the top
of the casing shall be effectively sealed against entrance of water
under all conditions of vibration or movement of conductors or cables.
(c)
Discharge piping. The discharge piping shall be provided with
separate means to pump (blowoff) water of unsatisfactory quality to
a point away from the groundwater source and toward the stormwater
management system, but shall not be directly connected to a sewer.
The discharge line shall:
(d)
Well apron surrounding the well shall meet the following requirements:
[1]
Be minimum 3,500 psi concrete with adequate reinforcement meeting
standard specs for construction.
[2]
Be a minimum of six inches in thickness.
[3]
Extend a minimum of three feet in all directions from the well.
[4]
Slope at least 1/4 inch per foot towards a screened four-inch
floor drain to atmosphere.
E.
Potable water storage facilities.
(1)
General. The materials and designs used for finished water storage
structures shall provide stability and durability as well as protect
the quality of the stored water. Steel and concrete structures shall
follow the most current available American Water Works Association
(AWWA) standards concerning steel and concrete tanks, standpipes,
reservoirs, and elevated tanks except as may be modified herein.
(a)
Location of finished water storage facilities.
[1]
The bottom of ground-level reservoirs, storage tanks and standpipes
should be placed a minimum of two feet above the one-hundred-year
flood elevation.
[2]
Buried tanks are not permitted.
[3]
The site shall be large enough to permit construction of the
facility, maintenance for painting and have a right-of-way to the
nearest public road.
[4]
All sites shall have electrical service providing a minimum
of 480 volts/three-phase power.
(b)
Obstructions to air navigation.
[1]
For structures within a four-nautical-mile radius of a public-use
airport, the design professional shall be governed by the latest revision
of COMAR; shall contact the Maryland Aviation Administration (MAA)
office of regional aviation assistance; and shall complete the appropriate
Federal Aviation Administration (FAA) form as required by the Federal
air regulations and deliver the completed form to the MAA.
[2]
For structures within a four-nautical-mile radius of a military
airport, submit to the FAA.
(c)
Safety. The safety of employees shall be considered in the design
of the storage structure. As a minimum, such matters shall conform
to pertinent building codes, laws, and regulations of the area where
the storage structure is constructed.
[1]
Ladders, ladder guards, balcony railings, and safe location
of entrance hatches shall be provided.
[2]
Elevated tanks with riser pipes over eight inches in diameter
shall have protective bars over the riser opening inside the tank.
[3]
Ladders must meet the minimum requirements of OSHA, 29 CFR 1910.
[4]
Requirements for safety belts and harnesses shall be included
in the specifications.
[5]
Lighting, pumps and cathodic protection system equipment shall
meet the requirements of the national electric code. Lights shall
be LED.
(d)
Drains.
[1]
No drain on a water storage structure shall have a direct connection
to a sewer or storm drain.
[2]
All finished water storage structures shall be equipped with
separate drains discharging to the atmosphere. Drainage of finished
water storage structures to the distribution system through inlet/outlet
piping shall not be allowed.
(e)
Freezing. All finished water storage structures and their appurtenances,
especially the riser pipes, overflows, and vents, shall be designed
to prevent freezing which will interfere with proper functioning.
(f)
Internal catwalk. Every catwalk over finished water in a storage
structure shall have a solid floor with raised edges so designed that
shoe scrapings and dirt will not fall into the water.
(2)
Storage tanks.
(a)
Types of tanks permitted.
[1]
Ground level shall be glass-lined steel bolted tanks.
[2]
Welded steel, single pedestal spheroid elevated tanks shall
be used for up to 1,000,000 gallons.
[3]
Composite concrete/steel tanks shall be used for any tank 1,000,000
gallons and greater.
[4]
All tanks must meet the latest AWWA standards.
[5]
All tanks shall provide a mounting system for cellular antennas
and County SCADA equipment.
[6]
Exceptions to the above must be given in writing by the County
Engineer.
(b)
Welded steel tanks. Design shall follow the provisions of AWWA
Standard D100, "Welded Steel Tanks for Water Storage," modified as
follows:
[1]
Tanks should be designed for Seismic Zone Zero.
[2]
All permanent attachments to the tank shall be made prior to
the hydrotest.
[3]
The alternative design basis presented in AWWA D100 will not
be used unless approved by the County Engineer.
[4]
Aluminum dome roofs shall be used only by approval of the County
Engineer.
[5]
Tanks shall be provided with remote level sensing and recording
equipment with telemetry to the Mattawoman WRF control building.
[6]
The design professional will specify that the contractor will
furnish at a minimum, the information listed in AWWA D100, forward,
Paragraph iii.b.1 or iii.b.2, as appropriate.
[7]
Silt stops are not required for welded steel tanks.
[8]
Disinfection shall be performed by the contractor in accordance with § 291-63E(5)(a) of this chapter.
(c)
Factory-coated bolted steel tanks. Design shall follow the provisions
of AWWA Standard D103, "Factory-Coated Bolted Steel Tanks," modified
as follows:
[1]
Tanks shall be designed for Seismic Zone Zero.
[2]
Coatings for bolted tanks are usually proprietary, and each
tank manufacturer is different. The coating shall, therefore, be a
consideration in the selection of a manufacturer.
[3]
Foundations shall be installed by the contractor.
[4]
Foundation selection in AWWA D103, Section 11.4, shall be based
on site soil conditions.
[5]
Aluminum dome roofs shall be used only by approval of the County
Engineer.
[6]
Silt stops are not required for factory-coated bolted steel
tanks.
[7]
Tanks shall be provided with remote level sensing and recording
equipment with telemetry to the Mattawoman WRF control building.
[8]
Disinfection will be performed by the contractor in accordance with § 291-63E(5)(a) of this chapter.
[9]
The design professional will specify that the contractor will
furnish, at a minimum, the information listed in AWWA D103, forward,
Paragraph iv.
(3)
Coatings and linings for steel tanks. Selection of coating and lining
systems for steel tanks shall follow the provisions of AWWA Standard
D102, "Coating Steel Water Storage Tanks," modified as follows:
(a)
Use Outside Coating System No. 6 except the Dry Film Thickness
(DFT) of the system selected should be a minimum of nine mils.
(b)
Use Inside Coating System No. 2, Paint 2, except the dry film
thickness (DFT) of the system selected should be a minimum of 13 mils.
(c)
Roller application is the preferred method of application.
(d)
Dry film thickness (DFT) is the preferred method to determine
acceptability.
(e)
The design professional shall specify that the contractor submit
an affidavit of compliance that all materials and work comply with
the applicable requirements of AWWA Standard D102.
(f)
The design professional shall list in the project specifications
all federal, state and local regulations regarding environmental issues.
(g)
The design professional shall specify that the contractor will
furnish for approval submittals for the coatings manufacturer to include,
but not be limited to, application method, materials, and material
safety data sheets.
(4)
Cleaning. All finished water storage facilities shall be cleaned
to remove all dirt and loose materials prior to disinfection of the
structure. Only potable water shall be used to clean and rinse the
water storage facilities. All equipment including brooms, brushes,
spray equipment, and workmen's boots shall be disinfected before
they are used to clean the storage facilities.
(5)
Disinfecting and testing.
(a)
Disinfection. All potable water storage facilities shall be
satisfactorily disinfected in accordance with AWWA Standard C652,
Chlorination Method 1, using calcium hypochlorite, prior to being
placed in operation. The disinfection of the storage facilities shall
be repeated until it is determined, by bacteriological testing, that
the water is free of coliform bacteria.
(b)
Testing. Testing of the water following disinfection shall be
performed in accordance with AWWA Standard C652.
(6)
Cathodic protection. If, at the direction of the County Engineer,
cathodic protection is required the design shall follow the provisions
of AWWA Standard D104, "Automatically controlled, impressed current
cathodic protection for the interior of steel water tanks," modified
as follows:
(a)
The design professional shall retain the services of a NACE
International (National Association of Corrosion Engineers) certified
corrosion engineer to design the cathodic protection system.
(b)
The design professional shall specify that the contractor shall
furnish an affidavit of compliance for all applicable provisions of
AWWA D104.
(c)
The design professional shall use the Type A - IR drop-free
potential measurement system.
(d)
Long life anodes with a minimum life of 20 years shall be specified.
(e)
The anode suspension system shall be a buoyant spider-type rope
system with a design life of 20 years, minimum.
(7)
Flexible membrane lining and floating cover materials.
(8)
Distribution storage.
(a)
Pressure variation. The maximum variation between high and low
water levels in finished water storage structures which float on a
distribution system should not exceed 30 feet or as approved by County
Engineer. Large diameter, shallow depth reservoirs are preferable
over small diameter, deep depth reservoirs.
(b)
Level controls. Adequate controls shall be provided to maintain
levels in distribution system storage structures at all times.
(c)
A telemetering system and recording equipment shall be provided,
to Mattawoman WRF control building, for the transmission and recording
of storage levels in the distribution system.
(d)
Pressure tanks. Pressure tanks shall not be used for distribution
storage systems. Pressure tanks may be used for small community systems
if approved by the County.
A.
General.
(1)
Sewer plans submitted for review and approval to the County will
not be required to include the standard detail on the plan. The plans
however must include a table, on the cover sheet, listing by detail
number and name all sewer details which are applicable to the project.
In cases where the County has no adopted standard detail for a specific
construction method, the engineer must submit a special detail to
the County Water and Sewer Engineer for review and approval. Once
approved, the special detail shall be placed within the plans with
notes in plan and profile on all applicable sheets referring to the
special detail.
(2)
Lines that serve two or more properties will be dedicated to the
County.
(3)
Lines terminated for future shall end with a manhole and a one-foot
temporary capped stub.
(4)
Computations shall be shown on the plans in accordance with Chapter
2, Subsection 1.J, Technical Bulletin: M-DHMH-EHA-S-001 Edition "Design
Guidelines for Sewer Facilities," State of Maryland.
(5)
Provide concrete encasement for protection of sewer mains per State
Health Standards/Maryland Department of the Environment requirements
as they relate to the vicinity of other utilities. Concrete encasement
is also to be provided where SDR-PVC mains have less than a two-foot
clearance under storm drains, C-900-PVC and ductile iron mains have
less than a one-foot clearance under storm drains, under stream crossings,
and on a case-by-case basis as determined by the County.
(6)
Ductile iron pipe and restrained joints, in accordance with the County
Standard Specifications for Construction Manual and Standard Detail
Manual, shall be used for jack and bore carrier pipe.
(7)
Ductile iron pipe with VITON or NBR rubber gaskets is required if
gasoline storage is within 100 feet of the lines or if there is the
presence of petroleum products within the soil.
(8)
Sewer mains are to be constructed to the property line of all adjacent
properties for future extension. If the adjacent property is designated
as commercial, industrial or subdivided, the main extension should
be sized appropriately.
(9)
The repaving of roads shall be in accordance with the County Standard
Specifications for Construction Manual and Standard Detail Manual.
B.
Collector sewers.
(1)
Design basis. A sewage collection system shall be designed, to service
the potential development of the sewerage service area at full build
out based on the Zoning Ordinance permitted densities and current
design criteria.[1] Systems shall also be designed to connect with existing
trunk lines or sub-interceptors at existing stub-outs wherever feasible.
Whenever cost-effectiveness permits, the construction may be programmed
in stages to accommodate both present and future needs. Special attention
shall be paid to the depth of sewers adjacent to drainage ways such
that the sewer is deep enough to accept flow from both sides of the
drainage way. Sufficient cover over the sewer is required to prevent
adverse affect on the drainage way.
(2)
Existing development. In developed areas, the basis for the flow
projection shall be the actual number of single or multifamily homes,
apartments units, various types of businesses, etc., present in the
drainage area as determined by field count. An allowance shall be
made for undeveloped areas as described below. Unless field investigations
give reason to choose a different number, it shall be assumed that
2.83 persons reside in each dwelling unit. If there is strong evidence
from field investigations that sufficiently less than 2.83 persons
reside in each dwelling unit in the drainage area and that this condition
will persist throughout the design period, the County will consider
using a smaller number for design.
(3)
Future development.
(a)
In small undeveloped areas, the basis for flow projection shall
be the maximum number of residential units per acre according to current
zoning regulations. This applies to residential or mixed residential/commercial
zones. It shall be assumed that 2.74 persons will reside in each dwelling
unit. In the case of small undeveloped portions of commercial or industrial
zones, design flows shall be based on the land use consistent with
current zoning regulations which would provide the most likely maximum
sewage flow.
(b)
In large, undeveloped areas, the average daily flow for a given zoning classification shall be as given in Appendix S, regarding flow generation rates by zoning classification.[2]
[2]
Editor's Note: Said appendix is included as an attachment to this chapter.
(4)
Average daily flow.
(a)
The average daily flow for collector sewers is based on the
population and land use inventories and projections described above.
Appendices T and U are compilations of average daily flow generation
rates for various types of establishments.[3] The flow from each existing establishment shall be based on Appendix T when the number of persons using the facility can be determined or on Appendix U when only the gross area of the facility can be determined. The average daily flow shall be the sum of the flows projected for the existing or ultimate land use of each lot or parcel in the service area. In the case of largely undeveloped service areas, the average daily flow shall be based on Appendix S, as described in § 291-64B(3).
[3]
Editor's Note: Said appendixes are included as attachments to this chapter.
(b)
Average daily flows given in the appendices for industrial facilities
are for domestic-type flows only. Flows generated by industrial processes
must be determined on a case-by-case basis.
(5)
Peak domestic flow.
(a)
The peak domestic flow is the average daily domestic flow peaked in accordance with the curve entitled "Diagram for Converting Average Daily Domestic Flow to Peak Flow" (Appendix V).[4]
[4]
Editor's Note: Said appendix is included as an attachment to this chapter.
(b)
Peak commercial or industrial flow is the average daily commercial or industrial flow peaked in accordance with a factor determined by evaluation of historical data for the commercial or industrial facilities and the periods in which these flows are generated. If historic peaking data for these facilities is unavailable, the average daily domestic flow, average daily commercial flow, and average daily industrial flow may be combined and then peaked using the curve in Appendix V.[5]
[5]
Editor's Note: Said appendix is included as an attachment to this chapter.
(c)
When evaluating and designing sewers that convey flow discharged
from pump stations, the peak flow calculation for each downstream
sewer section from the point of discharge, shall include the design
pumping rate of the pump station within the calculation.
(6)
Infiltration and inflow.
(a)
In the evaluation and design of sewers both future and existing,
a minimum infiltration rate of 400 gallons/acre of service area per
day shall be used. A higher rate of infiltration may be justified
if there is evidence of poor soil conditions, high groundwater table,
or deteriorated SHCs.
(b)
New nonsanitary connections to sanitary sewers are strictly
prohibited.
(7)
Design hydraulic flow. The design hydraulic flow shall be the sum of the peak flows determined as described in § 291-64B(5), the infiltration rate determined as described in § 291-64B(6), and any industrial flows.
C.
Interceptor sewers. Determination of design hydraulic flows for interceptor
sewers shall be generally as outlined for collector sewers. Interceptors
which carry flows from a significant number of older collectors may
have infiltration rates far in excess of 400 gallons/acre/day. ASCE
manuals on Engineering Practice No. 37 (WPCF MOP-9) and No. 60 (WPCF
MOP FD-5) should be consulted for further information on computation
of design flows for interceptor sewers. In all cases, the design hydraulic
flows shall be approved by the County prior to proceeding with sewer
design.
D.
Hydraulic criteria.
(1)
Collector sewers.
(a)
Size. The size of the sewer shall be sufficient to carry the
previously discussed design hydraulic flow with the hydraulic gradient
coincident with or slightly below the crown of pipe. Size shall be
determined by the relationship Q = VA, where:
Q
|
=
|
Quantity of sewage in cubic feet per second (design flow). All
flow calculations shall be expressed in GPM, GPD, MGD and CFS.
| |
V
|
=
|
Velocity in feet per second
| |
A
|
=
|
Required cross section area of conduit in square feet
|
(b)
Velocity.
[1]
Velocity shall be determined by the manning formula:
V
|
=
|
1.486 R2/3S1/2
| |
n
| |||
n
|
=
|
Coefficient of roughness as indicated in Appendix W[6]
| |
S
|
=
|
Slope in feet per foot
| |
R
|
=
|
Hydraulic radius-area divided by wetted perimeter
|
[6]
Editor's Note: Said appendix is included as an attachment to this chapter.
[2]
Minimum velocities of 2.5 feet per second shall be provided. Minimum velocities shall be determined based upon present average sewage flow. Appendix X (Mannings Formula Solutions) shows required slopes for various velocities with pipes flowing full. Appendix Y (Hydraulic Elements of Circular Section) indicates hydraulic elements of pipes flowing partially full.[7]
[7]
Editor's Note: Said appendixes are included as attachments to this chapter.
[3]
Where velocities greater than 15 feet per second are attained,
provisions shall be made to protect against erosion and displacement
by shock. If practical, suitable drop manholes shall be provided to
reduce steep slopes so as to thereby limit the velocities in pipes
and manholes. When drop manholes are impractical for reduction of
velocities, the sewer shall be ductile iron or other abrasion resistant
material as approved by the County.
(2)
Interceptor sewers.
(a)
Size. Interceptor sewers shall be sized to carry the design hydraulic flow when two-thirds full (i.e., the maximum hydraulic grade line will be at [D/d -] d/D = 0.67 per Appendix Y.
(b)
Velocity. Velocities in interceptor sewers shall be as presented in § 291-64D(1)(b).
(3)
Force mains.
(a)
General.
[1]
The design of a wastewater force main must be coordinated with
the design of the wastewater pumping station. The proposed alignment
and profile of the force main shall depict the changes in force main
elevations and strive to achieve a vertical profile that rises continuously
from the pumping station toward the transition manhole. The need for
air and vacuum relief valves shall be evaluated and minimized as much
as possible by adjusting the force main profile to minimize high points.
The system curve for the force main, showing the total energy losses
associated with the range of possible pumping rates, shall be developed
and provided on the plans.
[2]
HGL profiles shall be developed for the various flow scenarios
planned for the pumping station using the system curve for the force
main. All HGL profiles shall be provided on the plans separately from
the standard force main design profiles and shall indicate hydraulic
gradients, flows, force main velocities, design friction coefficients,
existing ground, proposed pipe invert elevations and all other pertinent
data.
(b)
Size.
[1]
Force main size shall be based on the required pipe's maximum carrying capacity to convey the design flow rate within the required velocities per § 291-64D(3)(c), while minimizing life cycle, construction, maintenance, and operational costs. The minimum force main size shall be four inches.
[2]
The Hazen-Williams (HW) equation shall be used for calculating
friction losses in force mains. Minor losses at transitions and bends
shall also be added in the determination of the total energy losses,
the hw coefficient of roughness ("C" factors) for force mains shall
be as follows:
Material
|
"C" factor
| |
---|---|---|
DIP (new)
|
140
| |
DIP (design)
|
120
| |
DIP (old)
|
100
|
[a]
The Hazen-Williams factors indicated are representative
of long-term design values for the system. The designer shall check
all pump station and force main selections for the anticipated lower
headlosses (higher C value representing new conditions) and higher
headlosses (lower C value representing old conditions) to ensure the
satisfactory operation throughout the design life of the system.
[3]
The static head shall be based on the difference in vertical
elevations between the lowest "normal pump stop" level in the wet
well and the point the force main discharges to the gravity sewer
or at the highest point along the system, whichever is higher.
(c)
Velocity. Forcemain design velocities shall be a minimum of
2.5 feet per second and a maximum of 5.0 feet per second.
(d)
Water hammer. The design professional shall prepare a complete
study of each force main design in conjunction with the related pumping
station. A written detailed analysis along with supporting plans and
calculations shall be submitted to the County for approval prior to
completion of the design and the contract drawings. This analysis
shall include, but is not necessarily limited to the following:
[1]
Transient pressures due to water hammer and the effect of these
pressures on the entire system.
[2]
Investigation of the pipeline profile to determine the possibility
of water column separation.
[3]
Reverse rotation characteristics of the pumps.
[4]
Shut-off characteristics of the proposed pump control valves.
[5]
A graphic solution of the transient pressures combined with
the total system characteristics.
[6]
Substantiation for the use of surge valves, when necessary,
listing recommended size and computed discharge pressures. The maximum
transient pressure plus the static head shall not be greater than
the working pressure strength of the pipe and associated appurtenances.
(e)
Hydrogen sulfide control. The design at a minimum, shall address
hydrogen sulfide control as follows:
[1]
In areas where hydrogen sulfide is a concern the designer shall
minimize the number of drop manholes to the maximum extent possible
(i.e., drops downstream of force main discharge).
[2]
All interior surfaces and inverts of sanitary sewer manholes
including the transition manhole shall be coated with a hydrogen sulfide
resistant material per County specifications. The coverage of protection
shall be from either a force main or grinder pump discharge to the
first downstream manhole or within 400 feet, whichever is greater.
In addition, hydrogen sulfide protection shall be provided where turbulence
may be caused due to a drop manhole, severe pipeline slopes or any
other sources of turbulence within a sewer system. Protection must
be provided to all surfaces exposed to the sulfides. All applications
of specialized coatings and liners are subject to the review and approval
of the County engineer. See the standard specifications for all coating
and lining material requirements.
[3]
The design shall also address odor control and may warrant additional
corrosion control measures if high concentrations of hydrogen sulfide
are expected. The designer shall provide an evaluation of the system
and indicate the measures proposed to address odor and corrosion control.
E.
System layout criteria.
(1)
Collector sewers.
(a)
Horizontal layout.
[1]
General. Collector sewers shall be laid on tangents only. All
changes of direction and connections to other collector sewers shall
be accomplished at manholes. In laying out the sewer, the design engineer
shall take into full account such factors as environmental impact,
maintenance of traffic, maintenance of existing utility services,
constructability, and system maintenance, and shall produce the overall
most cost-effective design.
[2]
New subdivisions. In new subdivisions, collector sewers shall
be located five feet from the centerline of the street right-of-way,
generally on the side of the street toward low ground. Collector sewers
shall be located within the pavement area wherever possible, no less
than five feet from the face of existing or proposed curb. Where it
is not feasible for manholes to be located within the pavements, they
shall be located wholly within the grass plot or wholly within the
grass plot between the curb and sidewalk. On private roads and parking
areas manholes are to be located outside of parking areas. Manholes
will not be allowed in sidewalk.
[3]
Existing developments (closed section roads). In existing developments
with curbs, sewer location shall generally be the same as in new subdivisions.
The location of other existing and proposed utilities shall be fully
considered.
[4]
Existing developments (open section roads). In existing developments
without curbs, collector sewers shall generally be located four feet
outside of the edge of pavement, except that the sewer shall not be
located under a future curb. The location of other existing and proposed
utilities shall be considered.
[5]
Parks and public rights-of-way. Where location of sewer would
require the removal of or damage to trees within parks or public rights-of-way,
design engineers shall obtain approval of the state department of
forestry for sewer alignment and trees to be removed.
[6]
Easements. All sewer utility easement widths shall be in accordance
with latest plan preparation package. No other utilities or structures
will be allowed in the sewer utility easement without written County
approval.
(b)
Profile layout.
[1]
Grades. Grades shall be such as to require the least excavation
while satisfying minimum and maximum velocity requirements, clearances,
and depth requirements discussed hereinafter. All collector sewers
shall be on tangent grades with required breaks in grade accomplished
in manholes.
[2]
Depth. In developed areas, sewer inverts shall be a minimum
of [two feet + H] below the basement elevations, where H = length
of house lateral connection between the sewer and the point of connection
to the existing house sewage system, or stack, multiplied by the required
house connection slope. For houses without basements, sewers shall
be a minimum of [two feet + H] below the first floor elevations. In
all cases, sewer depth shall be sufficient to meet criteria established
for house connection, depth, grade, and clearance.
[a]
Sewers at stream crossings shall be constructed
with a minimum of three feet of cover between the pipe and stream
invert. At all stream crossings, the design engineer shall consider
such items as flotation, stream meandering and scouring, and infiltration;
and shall include protective measures for such in the design.
[3]
Upstream of pumping stations.
[a]
Protection of private property from collection
system surcharges where a plumbing drainage system is subject to backflow
of sewage from the public sewer or private disposal system, suitable
provision shall be made to prevent overflow in the building.
[b]
In order to insure that surcharges in the collection
system and/or pumping station failures will not result in sewage backing
up into basement and first floor plumbing fixtures of nearby residences,
the design of all pumping station collection systems shall:
[i]
Determine the rim elevation of the next upstream
manhole in the public sewer from the building.
[ii]
For projects having basement service, all basement
elevations lower than the manhole frame and cover established in § 291-64E(1)(b)[3][a][i]
above shall be identified, fixtures and/or drain inlets subject to
backflow and flooding from blocked or restricted public sewers shall
be protected by a backwater valve. Such situations include those where
fixtures and/or drains are located above the crown level of the public
sewer at the point of connection thereto but are below the overflow
level of the public sewer.
[iii]
For projects or portions of projects having first
floor service only, first floor elevations lower than the manhole
frame and cover established in § 291-64E(1)(b)[3][a][i]
above shall be identified and protected by a backwater valve.
[iv]
All vacant lots having a ground elevation lower
than the manhole frame and cover established in § 291-64E(1)(b)[3][a][i]
above shall be identified.
[4]
Gravity service not to be provided. Sewer project plans shall
clearly label any improved lots for which gravity service is not to
be provided. Any recommendation for not providing gravity service
is to be documented, with the reasons therefore, by the design engineer
to the County for approval. For lots where it is determined that gravity
service is not available, a note shall be placed on the drawings as
follows:
"A grinder pump is required for sewer service to this lot. The
grinder pump and associated low pressure sewer system shall be owned,
operated, maintained, and replaced by the property owner."
(c)
Clearances of other utilities.
[1]
Interactive considerations. In general, existing utilities have
prior right to maintain their location. The existence and location
of such utilities must be considered when designing new sewers. Clearance
shall be measured between outside of pipes. Design engineers shall
investigate clearance between sewer and other utilities, both existing
and future.
[a]
General. The following design factors must be considered
in providing adequate separation:
[i]
Materials and type of joints for water and sewer
pipes.
[ii]
Soil conditions.
[iii]
Service and branch connection into the water
main and sewer line.
[iv]
Compensating variations in horizontal and vertical
separations.
[v]
Space for repair and alterations of water and sewer
pipes.
[vi]
Location of manholes.
[b]
Parallel installation. A horizontal distance of
at least 10 feet shall separate water mains and sewers. The distance
shall be measured edge to edge. In cases where a ten-foot separation
is not practical, deviation may be allowed on a case-by-case basis
subject to County and state approval if supported by data from the
design engineer. Such deviation may allow closer installation provided
that the water main is laid in a separate trench or on an undisturbed
earth shelf located on one side of the sewer at such an elevation
that the bottom of the water main is at least 18 inches above the
top of the sewer.
[c]
Crossings. Where water mains must cross sanitary
sewers, building drains or storm drains cross, there shall be a vertical
separation of 18 inches between the bottom of the water main and the
top of the sanitary sewer, building or storm drain. This vertical
separation must be maintained horizontally for a distance of 10 feet.
The ten-foot distance is to be measured as a perpendicular distance
from the sewer, building or storm drain to the water line.
[d]
Exceptions. When it is impossible to obtain the
proper horizontal or vertical separation as stipulated above, both
the water and sewer lines shall be constructed of ductile iron with
mechanical joints. Other types of pipe and joints with equal or greater
integrity may be used at the discretion of the County. Thermoplastic
pipe may be used with mechanical or solvent weld joints. These installations
shall be pressure tested to assure water tightness before backfilling.
Where a water main must cross under a sewer, additional protection
of the water main shall be provided. The County shall be consulted
to discuss the use of double casing or concrete encasement of the
sewer and/or water main.
[2]
Separation of utilities and sewer manholes. No utilities shall
pass through any part of a sewer manhole.
[3]
Clearances at other utilities. Sewers shall have a minimum of
12 inches of clearance from drains, gas mains, and other unspecified
utilities. If 12 inches cannot be maintained at crossings, provide
encasement of sewer for the width of the utility trench.
(d)
Appurtenances.
[1]
Manholes.
[a]
Details are shown in the Standard Details Manual.
The designer shall use these standards as required to meet the design
situation and shall designate the type of each manhole on the drawings.
[b]
Manholes and vaults are to be constructed two feet
above finished grade in flood plains and nonmaintained areas.
[c]
Maximum spacing for manholes on sewers less than
18 inches in diameter shall be 400 feet; 500 feet for sewers 18 inches
to 27 inches in diameter; and 600 feet for sewers larger than 27 inches.
[d]
Line manholes shall be used at all changes of pipe
size, grade, alignment, or connections of two or more sewers. A minimum
drop of 0.10 feet between influent and effluent inverts shall be used
at line manholes.
[e]
Interior coating of manholes shall be as specified
in the Charles County Standard Specifications for Construction Manual.
[2]
Frames and covers.
[a]
Provide a bolt-down frame and cover for all manholes
in flood plains and nonmaintained areas in accordance with the County
Standard Detail Manual.
[b]
Watertight frames and covers are to be provided
for manholes within flood plains, ditches or other areas of collecting
or passing water.
[c]
All manhole frames and covers that are not bolt-downs
shall be fitted with manhole cover inserts/liners to minimize the
amount of inflow and sediment that enters the sewer system. The inserts
shall be installed upon "substantial completion."
(e)
Structural considerations.
[1]
Soil conditions/foundations. Where extremely poor soil conditions,
such as running sand, material with high organic content, etc., are
anticipated, design engineers shall secure soil samples and discuss
the analysis of the samples with the County. In all cases, a proper
foundation shall be provided for pipes. Where pipes are to be placed
on fill, ductile iron pipe shall be placed on timber pile bents unless
special measures satisfactory to the County are taken to consolidate
the fill.
[2]
Grades/anchors. Sewers designed on slopes of 20% or greater
shall have anchorages in accordance with the Standard Details Manual
as follows:
[3]
Under drains. Where there is evidence of spring heads or a high
groundwater table in the area of the proposed sewer, under drains
shall be provided and shown on the drawings.
[4]
Depth and loading. Minimum and maximum permissible depths and
loadings for pipes of the various types and classes shall be in accordance
with the Standard Specifications for Construction Manual and the manufacturers'
recommendations and bedding requirements. Manufacturers' data
shall be submitted as part of the plan submittal.
(f)
Venting. The design engineer shall indicate the method of proposed
ventilation of gravity sewers if other than manhole top openings.
(2)
Interceptor sewers. There shall be no service connections made directly
to interceptor sewers. All service connections shall be made at manholes.
Once the interceptor has been installed, no new manholes may be constructed
over interceptor sewers.
(a)
Horizontal layout.
[1]
Interceptor sewers generally follow streams or the valley of
a drainage area. They shall be located so as to best serve the drainage
area. Special caution is required to insure the proper location of
manholes for future connection of collecting sewers.
[2]
All sewers, especially interceptor sewers shall be laid with
straight horizontal and vertical alignment between manholes. Horizontal
and/or vertical curves shall not be employed on gravity sewer mains.
(b)
Profile layout.
[1]
Grade requirements shall generally be as described for collector sewers in § 291-64E(1)(b)[1]. The depth of interceptor sewers is not directly controlled by lot and house elevations. The depth of interceptor sewers shall be sufficient to allow connection of all existing and foreseeable future collector sewers within the service area served. In general, the top of the sewer elevation should be a minimum 3 1/2 feet (42 inches) lower than the stream bed and have six feet of cover where possible.
[2]
Sewers at stream crossings shall be constructed with a minimum
of 3 1/2 feet (42 inches) of cover between the pipe and stream
invert. At all stream crossings, the design engineer shall consider
such items as flotation, stream meandering and scouring, and infiltration;
and shall include protective measures for such in the design.
(c)
Clearances at other utilities. The requirements for horizontal and vertical clearances between interceptor sewers and other utilities shall be the same as those for collector sewers. See § 291-64E(1)(c).
(d)
Appurtenances.
[1]
Manholes. Manhole requirements for interceptor sewers shall be the same as those for collector sewers, § 291-64E(1)(d)[1], with the following modifications:
[2]
Frames and covers. Frame and cover requirements for interceptor sewers shall be the same as those for collector sewers, § 291-64E(1)(d)[2].
(e)
Structural considerations. Structural considerations shall be the same as for collector sewers. See § 291-64E(1)(e).
(3)
Force mains.
(a)
Layout. Force mains shall be located within public rights-of-way
or easements.
(b)
Material. Force main material shall be ductile iron.
(c)
Profile.
[1]
Ideally, the force main shall be designed without intermediate
high points and with the top of the force main being below the hydraulic
grade line at the minimum pumping rate so that air release valves
will not be needed. If the elimination of high points is not feasible
or if the design requires long, relatively flat vertical alignments,
the design may require air release and air and vacuum valves.
[2]
Blowoffs along four-inch and larger force mains are required
where the force main contains a depressed section between two high
points.
[3]
Continuous uphill pumping is preferred for a force main, where
the force main discharge point to the gravity sewer is at a higher
elevation than the rest of the system, so as to keep the force main
full.
[4]
Force mains with intermediate high points above the gravity
sewer discharge point can create partial vacuum conditions in the
force main under circumstances such as draining conditions that occur
due to intermittent pumping or when the HGL profile drops below the
pipeline profile. The designer shall provide appropriate air release
and air vacuum valves to protect the force main against damage under
these conditions.
[5]
Downhill pumping is prohibited.
[6]
All force mains shall have a minimum 3.5-foot depth of cover.
In street rights-of-way cover shall be measured from the top of the
force main to the proposed grade, or in cases when the proposed grade
is above the existing ground surface, the depth of cover shall be
measured from the existing ground line. In easements across private
property, future development in the area shall be given consideration
when developing the force main profile and possible future development
grades shall be evaluated to ensure that the minimum depth of cover
is met.
[7]
The top of the force main and its appurtenances shall generally
be designed to be lower than the HGL. If the top of the force main
is above the HGL, then the fm should be lined with Protecto 401 or
better for a sufficient distance to eliminate H2S corrosion.
(d)
Clearance.
[1]
Sanitary force mains paralleling water mains shall have a minimum
clearance of 10 feet horizontally and shall be a minimum of 1.5 feet
below water main.
[2]
Sanitary force mains shall have a minimum of one foot vertical
clearance when parallel to or crossing other utilities.
[3]
Clearance shall be measured from the outside diameter of the
pipes.
(e)
Appurtenances.
[1]
Pipe deflections. Force mains may be curved by deflecting the
alignment at the joints. Deflection at the joints shall not exceed
1/2 the maximum as set forth by the manufacturer of the pipe used.
[2]
Air release and air/vacuum release valves.
[a]
Valves shall be constructed per County specifications
and details. The following guidelines shall be used to locate air
and vacuum release valves:
[i]
Peaks in profile.
[ii]
Abrupt increases in downward slopes.
[iii]
Abrupt decreases in upward slopes.
[iv]
Long ascents: 1,500 feet to 3,000 feet intervals.
[v]
Long horizontal: 1,500 feet to 3,000 feet intervals.
[vi]
At pumps: on the discharge pipe as close as possible
to the check valve.
[vii]
At large valves or bypass piping.
[b]
The air and vacuum release valve vault will be
vented above ground as shown on the standard details. Odor control
measures, such as soil odor filters, may be required by the department
if air release valves are located near populated areas. Air release
valve bypasses may be required at the County's option. Intakes
for vacuum valves shall be above the one-hundred-year flood elevation
to allow proper operation of the valve during flood conditions.
[3]
Blowoff valves shall be located at all low points along the
force main per County standard details manual.
[4]
Isolation valves shall be located at intervals and crossings as stated under section § 291-62D(8)(b)[1] and [5] and at air/vacuum/blowoff valve locations.
(f)
Structural considerations.
[1]
Pipe loading. Minimum and maximum permissible depths and loadings
for pipes of the various types and classes shall be in accordance
with County standard details and the manufacturers' recommendations
and bedding requirements. Manufacturers' data shall be submitted
as part of the plan submittal.
[2]
Anchorages. Force main design shall have anchorages in accordance
with the standard details manual.
(g)
Test. Leakage tests shall be in accordance with the procedures
outlined in the latest County specifications.
F.
Grinder pumps/pressure sewer systems/step systems. Alternative wastewater
systems will be reviewed on a case-by-case basis, but will not be
considered as a method of providing sewer service that could otherwise
be furnished by conventional gravity systems (including pumping stations).
Unless otherwise agreed to, grinder pumps are to be privately operated
and maintained and must adhere to the County Standard Specifications
for Construction Manual.
G.
Sewer house connections.
(1)
Location. The County-owned portion of house connections shall be
built to the right-of-way/property/easement line for all lots within
proposed developments. All adjacent improved lots which are not a
part of the proposed development, but which front and may be served
by the service line, shall have the sewer service laterals, including
cleanouts, constructed to the right-of-way/property/easement lines.
Twin sewer house connections shall be allowed and encouraged. Service
lines for house connections shall not be connected directly to interceptor
sewers.
(2)
Size. Connections to large buildings such as apartments or factories
shall be designed and sized in accordance with the criteria previously
presented for collector sewers. The minimum connection size for buildings
shall be six-inch diameter from the main to the clean-out and four-inch
from the clean-out to the building.
(3)
Materials. House and building connections shall be in accordance
with the latest County Standard Specifications for Construction Manual.
(4)
Appurtenances. Clean-outs shall be provided on all house and building
connections at the right-of-way/property/easement line. Clean-outs
shall be shown and constructed in accordance with the latest County
Standard Specifications for Construction Manual and Standard Detail
Manual.
(5)
Grades. House and building connections shall be designed such that
service is provided for all lots to the mid-point of the lot at a
two-percent minimum grade, unless otherwise approved by the County.
The maximum grade shall be 6%. House and building connections may
have a one-percent minimum grade as determined by the County on a
case-by-case basis. Minimum cover at the right-of-way/property/easement
line shall be 42 inches. Where storm drains have been designed, or
have not been installed, house connections shall have a minimum cover
within the street right-of-way of 6.5 feet.
(6)
Clearance.
(a)
Parallel to water house service. Sewer house services shall
ordinarily be placed 10 feet horizontally and one foot vertically
under and from the water house connections. In cases where this is
not achievable, deviation may be allowed on a case-by-case basis subject
to County and/or state approval. Such deviation may allow a horizontal
separation of 1.5 feet with at least a six-foot vertical clearance
(sewer being placed on the bottom). If schedule 40 PVC solvent weld
pipe is utilized for the sewer house connection a 1.5 foot horizontal
separation with at least a one-foot vertical clearance (sewer being
placed on the bottom) may be allowed if a passing pressure test with
10 feet of head of water or equivalent taken in the presence of a
County representative is achieved.
(b)
Crossing storm drains or other utilities. Sewer house and building
connections crossing storm drains and other utilities (existing or
future) shall have a minimum clearance of 12 inches from these utilities.
(7)
Structural considerations. Structural considerations shall be the same as for collector sewers. See § 291-64E(1)(e).
H.
Grease interceptors.
I.
Oil and flammable liquids separators. Oil and flammable liquids separators
are required in accordance with COMAR requirements.
J.
Flag lot sewer utilities.
(1)
For a two flag lot maximum, service laterals will be provided off
of the main and include a clean-out at the right-of-way or easement
line. Sewer service for each lot shall be located on each side of
the driveway. Adequate easements are to be provided outside of the
common access easement if necessary. The sewer service must be constructed
in conjunction with the main from the clean-out to the building lot
and capped for future connection. The end of the service should be
marked in accordance with the County Standard Detail Manual. Clean-outs
are to be provided every 75 feet and at the end of the lateral. Extension
of the service as indicated above will prevent problems associated
with the construction of the driveway prior to the construction of
all sewer services.
(2)
For three or more flag lots, provide an extension of the sewer main
to the last lot and terminate with a manhole. Provide service connections
to all adjacent lots, with clean-outs located at the easement line.
Adequate easements are to be provided on both sides of the sewer main
and services and must extend outside of the common access easement
if necessary.
A.
General.
(1)
In addition to the criterion contained herein, the design of wastewater
pumping stations and related facilities shall meet the requirements
of the 1978 edition of the State of Maryland "Design Guidelines for
Sewage Facilities" or shall be exceeded where specified by the County.
The following additional manuals shall be consulted and applied to
the design with the approval of the County:
(a)
Water Environment Federation Manuals of Practice.
(b)
Recommended Standards for Sewage Works, (latest edition) also
known as the "Ten State Standards."
(c)
"Pumping Station Design," 3rd Edition (or latest), 2006, by
Garr M. Jones.
(d)
"Design and Construction of Sanitary and Storm Sewers," 1969
by ASCE (MOP NO. 37) and WPCF (MOP NO. 9).
(e)
"Odor Control in Wastewater Treatment Plants," 1995, WEF (MOP
NO. 22) AND ASCE (MOP NO. 82).
(2)
All aspects of the facility shall maximize operator safety. The facility
shall be designed to operate reliably and efficiently with a minimum
of attention and have provisions for easy access and maintenance.
Equipment shall be selected on the basis of durability, availability
of replacement parts, standardization, efficiency, and ease of maintenance
and repair.
(3)
The pumping station shall be designed for the maximum build out conditions
of the wastewater pumping station service area as approved by the
County using flows approved by the County.
B.
Hydraulic computations.
(1)
Design hydraulic flow rate.
(2)
Wastewater composition. Wastewater composition can vary widely depending
upon the proportion of design flow generated by nondomestic users.
Nondomestic user wastewater composition shall be investigated and
the results included in the Engineering Report provided to the County
Engineer. Adequate consideration and all necessary provisions shall
be taken to ensure that wastewater pumping station equipment and materials
are suitable for the anticipated composition of the wastewater. Consultation
with the County Engineer is required in the event that the wastewater
composition affects standard material and equipment requirements.
(3)
Number of pumps. Wastewater pumping stations shall be capable of
pumping the design hydraulic flow rate with the largest single pump
out of service.
(4)
Wetwell sizing. A minimum cycle time of 15 minutes is to be provided.
Wet well capacity (in gallons) from pump on to pump off shall be of
four times the capacity of the largest pump (in gallons per minute)
for pumping stations with a three-pump arrangement or greater, the
minimum cycle time of 15 minutes shall be provided for each pump.
Larger pumps may require cycle times greater than 15 minutes to satisfy
motor manufacturer requirements.
(5)
Hydraulic analysis.
(a)
Wastewater pumping stations must satisfy the hydraulic conditions of the system. The designer shall perform a complete hydraulic analysis of each wastewater pumping station, the hydraulic analysis shall consider potential impacts on existing force mains, gravity sewers and pumping stations when the new pumping station is added to the system. See § 291-64, Sewer mains, for force main design requirements and analyses that must be performed in conjunction with the pumping station design.
(b)
Wastewater pumping stations shall be designed to operate at
the appropriate discharge head and flow rate without the need for
throttling valves or flow restriction devices.
(6)
Pump and system curves.
(a)
System curve (head versus flow) characteristics shall be determined
by the Hazen-Williams formula for piping head loss. The pump/system
curve shall be shown on the plans to scale. The pump/system curve
shall show the following information at a minimum:
[1]
Static head.
[2]
System curves for both new, design, and existing system conditions.
[3]
Pump curve: include single and multiple pump performance curves.
If VFDS are used, multiple speed performance curves shall be shown.
[4]
Pump horsepower, efficiency and rpm.
[5]
Pump manufacturer's published recommended range of operation.
(b)
Pump/system curves shall be shown for single pump operation, as well as for multiple pump operation in stations having three or more pumps. Hazen-Williams "C" factors used in evaluating pump and system curves shall be in accordance with the guidelines given in § 291-64, regarding hydraulic calculations, of this chapter for various pipe materials.
(7)
Water hammer. The potential impact of water hammer under usual and
unusual circumstances (power outages, etc.) shall be evaluated. If
the combined effects of static head and water hammer (using a safety
factor of 1.1) do not exceed the weakest piping system component working
pressure, no special provisions need to be included to control water
hammer. Where the maximum water hammer pressure (using a safety factor
of 1.1) exceeds the weakest piping system component (all piping, fittings,
thrust blocks, and other appurtenances) working pressure, strengthen
those elements affected, reevaluate pipe size and velocities or select
an appropriate device to control water hammer. No pressure vessel/surge
tank type devices will be acceptable.
(8)
Pump selection criteria.
(a)
Provide proper wet well design and suction line design per hydraulic
institute standards to avoid cavitations. The designer shall perform
a Net Positive Suction Head Available (NPSHA) analysis and include
this information in the pump specification.
(b)
The NPSHA shall be calculated for the expected design flows
and shall exceed the pump manufacturer's requirements by an added
margin of safety of not less than five feet. Pumps shall be selected
to have their maximum efficiency at the operating design point. Under
no circumstances shall a pump be specified to operate outside of its
published recommended range under new through old system operating
conditions. Examples would be pumps operating at very low flows and
high heads, near shutoff heads, or "runout" conditions (maximum possible
flow rate of the pump). These conditions can result in excessive hydraulic
loading or cavitation damage to impellers, casings and shafts, rapid
bearing and mechanical seal wear, and high vibration. The designer
shall avoid the selection of pumps whose curves are flat (i.e., small
changes in head resulting in large changes in flow rate).
C.
Types of wastewater pumping stations and selection. Charles County
wastewater pumping stations are divided into two categories, large
(500 gpm and greater) and small (less than 500 gpm). The types of
stations allowed are described below along with acceptable selection
criteria. Station selection shall be determined by the County.
(1)
Large pumping stations. Conventional: This type of pumping station
is defined here as pumping stations in which the wet well and dry
well structures are assembled or constructed on site and are typically
used for flows 500 gpm and greater. The preferred method of construction
is for the contractor to use precast concrete sections. However, if
the configuration or sizes would make this unfeasible then cast-in-place
concrete sections will be permitted with the approval of the County.
To help prevent overflows and maintain continuous operation during
maintenance procedures, pumping stations shall have divided wetwells.
Dry wells, including their superstructure, shall be completely separated
from the wet wells. To facilitate differential settling or unforeseen
movement, flexible joints shall be placed in the piping between all
structures. All of the piping, valves, wiring and controls are assembled
on-site by the contractor. Conventional wastewater pumping stations
shall be engineered to meet the requirements of these guidelines,
as well as any supplemental guidelines imposed by the County Engineer
on a case-by-case basis. These stations will have a wet well/dry well
configuration and be of precast or cast-in-place concrete construction.
Conventional pumping stations shall be designed as long-term (greater
than 30 years) facilities. The design of conventional stations shall
include room for anticipated expansion. The following guidelines and
features shall be incorporated in the design of these stations:
(a)
Site design.
[1]
Location: wastewater pumping stations shall be located as far
as possible from populated areas. Natural screening and remoteness
of the site shall be primary elements of site selection wherever possible.
Where pumping stations are sited in proximity to developed areas,
the architecture of the station shall be compatible with the surrounding
area. Predominant wind direction for potential odor dispersion and
building aspects such as generator exhaust and ventilation fan noises
shall be considered. Similarly, building setbacks shall be considered
to provide minimal impact to neighboring properties.
[2]
Land acquisition: land required for pumping stations, including
necessary vehicular access routes to an existing or proposed public
roadway shall be owned in fee simple by the County. As part of this
process, a boundary survey of the property is required together with
a record plat and a metes and bounds description of the parcel. In
determining the space requirements for the facility, particular attention
shall be given to the width provided for the access road to ensure
adequate space for grading and drainage within the access road right-of-way
and easy access for maintenance and delivery trucks.
[3]
Topography: sewers tributary to wastewater pumping stations
commonly dominate site selection. Adjacent drainage areas potentially
served by the wastewater pumping station must also be considered.
Wastewater pumping station site selection shall also be compatible
with suitable site access, drainage, and soil capability with respect
to land grading in conjunction with site development. Existing contours
and other topography shall be shown for the entire site including
a one-hundred-foot minimum width outside of the proposed property
boundary on all sides.
[a]
Contour interval shall be two-foot, unless otherwise
approved by the County Engineer.
[4]
Floodplain: wastewater pumping stations shall be sited to remain
operational and permit access during a one-hundred-year return frequency
flood. All top slab elevations of structures shall be set a minimum
of two feet above the one-hundred-year floodplain elevation. The access
road shall be above the one-hundred-year floodplain elevation.
[5]
Wetlands: avoid direct impacts wherever possible and minimize
impacts to wetland buffer areas. Buffer areas include the first 25
feet beyond non-tidal wetlands.
[6]
Grading: wastewater pumping station site grades shall prevent
local ponding and provide positive drainage away from all structures
and site. The site shall be a minimum of one foot above the surrounding
area. Slopes on site shall be generally limited to no less than 1%
and no greater than 4%. Stone surfaces around paved areas shall provide
proper site drainage at slopes 10% or less. Land grading outside of
the wastewater pumping station perimeter fence shall not exceed three
to one slopes; four to one slope maximums are desirable. Lesser slopes
wherever possible are preferred. Site grading design shall be compatible
with slope stability for the soils encountered. Slope stabilization
shall be appropriate for the degree of slope and soil conditions,
the use of retaining walls on or immediately adjacent to the wastewater
pumping station site is not permitted. There shall never be a situation
where roof drains flow across walkways, roadways, or parking areas.
[7]
Pump-around connection: a pump-around configuration shall be
provided for the use of portable pumps to prevent overflows during
maintenance or repair of the pumping station. A manhole shall be provided
within the fenced area of the station immediately upstream of the
wet well. A device for isolation purposes (stainless steel sluice
gate) shall be provided in the upstream manhole or on the influent
sewer within the wet well. The force main will be provided with a
connection on the outside of the pumping station for portable pumping
from the upstream manhole directly to the force main. As an alternative,
a partitioned wet well can be utilized such that the wastewater can
be directed to either of the pump intakes while allowing safe maintenance
of the opposite side of the wet well or intake. Enough room shall
be provided on the pump site to park the portable pump while allowing
vehicle access to the wet well and dry well. The pump-around connection
shall provide the capability to launch PIGS pipe cleaning devices,
which shall require the pump-around diameter to be the same size as
the force main and with an "increaser" to the next nominal size of
pipe and a spool-piece whose length is two times the diameter of the
force main. (Example: a six-inch force main needs a six-inch pump-around
line with a six-by-eight increaser and a twelve-inch long spool-piece.).
[8]
Pumping stations shall not be located directly downstream of
any stormwater management facility discharge. Grading shall direct
stormwater away and around the access road and site to an area downstream
for treatment and/or further conveyance.
[9]
Sediment control: A sediment control plan shall be provided
and approval obtained from the Charles Soil Conservation District
(SCD).
[10]
At least two test borings shall be taken, one
at the proposed wetwell location and one at the proposed drywell/building
structure to determine soil types, rock, water table elevations, soil
bearing values, etc. Standard penetration tests shall be taken at
intervals not to exceed five feet. Borings shall be taken to a depth
of not less than 15 feet below the bottom of the proposed structure.
Borings shall be taken deeper as necessary, depending on soil conditions.
[11]
Site security: Pumping station sites shall be
fenced with black vinyl coated chainlink fencing eight feet tall,
black vinyl coated post and black hardware, and a sixteen-foot wide
locking gate for vehicle access. The fence is to include three strands
of barbed wire around the top. Additional property line fencing may
be required as determined by the County Engineer. The pumping station
building shall have exterior lighting controlled by motion detectors.
The building shall be provided with an entry alarm connected to the
station SCADA.
[12]
Paving: Pumping station sites shall have P-4 paving
section in accordance with Table 2.07 of the road ordinance[1] and include a minimum of two parking spaces. The site
shall have sufficient room to allow AASHTO WB-40 access to equipment
by maintenance trucks (boom and vacuum trucks). An access road to
the pumping station site shall have P-2 paving section in accordance
with Table 2.07 of the road ordinance. The width of the pavement shall
be 20 feet wide with two-foot gravel shoulders. The maximum grade
for the access road shall not exceed 5%. The cross slope shall be
in accordance with Standard Detail R/2.16.
[a]
The access road and site shall support a minimum
AASHTO WB-40 turning radius. The site shall also include a WB-40 turn-around
area. Pumping station access roads shall be used exclusively for pumping
station maintenance and access.
[13]
Sidewalks, four feet wide in accordance with the
road ordinance/detail manual, are to be provided between buildings
and/or structures and from paved areas to buildings and structures
for access of equipment, dollies, etc.
[14]
Station sign: A permanent sign shall be provided
at each pumping station stating the station name, street address and
emergency telephone number. The sign must meet Charles County 911
addressing system.
[15]
Yard hydrants and hose bibs shall be provided
for wash down, maintenance, and sanitation purposes.
(b)
Structures. All structures shall be set such that the top slab
elevation is a minimum of one foot above finished grade.
[1]
Wet well design: wet wells shall be considered a hazardous environment,
classified as NEC Class I, Division I for explosive gases. Wet wells
shall be designed and constructed to be as hazard free as possible,
and corrosion resistant materials shall be used throughout. All materials
and equipment used in wet wells shall meet NEC Class I, Division I
standards, with the exception of control floats. Wet wells shall not
exceed 25 feet in depth.
[a]
Structure: Wastewater pumping station wet wells
shall be constructed of precast concrete. Wastewater pumping station
wet wells shall consist of reinforced concrete base slabs, riser sections/walls
and top slabs. Wet wells shall have an interior epoxy coating and
exterior elastomeric membrane waterproofing. The bottom of the wet
well shall be grouted to a minimum slope of one to one to the hopper
bottom and pump suction inlet. The horizontal area of the hopper bottom
shall not be greater than necessary for proper installation and function
of the inlet. Slope the hopper bottom between the inlets if necessary
to prevent deposition of material between the inlets. Wet wells for
pumping stations greater than 1.5 MGD design hydraulic flow shall
be of the self-cleaning trench type design. Wet wells shall be adequately
designed to prevent flotation. The wet well size and depth shall be
as required to accommodate the influent sewer, as well as pump suction
submergence as recommended by hydraulic institute standards and manufacturer
requirements. The required working volume and preferred intervals
between influent sewer and control elevations shall be determined
as follows:
[i]
Wet wells shall be designed for a minimum pump
cycle time of 15 minutes as defined by the following formula:
T = 4V/Q
| ||||
Where:
| ||||
T
|
=
|
pump cycle time (time between pump starts) in minutes
| ||
V
|
=
|
volume of wet well between the lead pump start and pump stop
elevations, in gallons
| ||
Q
|
=
|
pump rate of the lead pump, in gallons per minute
|
[ii]
The detention period for wastewater in the wet
well shall not exceed 30 minutes at the average flow rate for the
initial, intermediate and ultimate design years. When initial average
flows are insufficient to actuate the pumps within a thirty-minute
period, temporary removable appurtenances shall be placed in the wet
well or the adjustable floats for pump start shall be lowered. Wet
wells shall be deep enough to accommodate the control elevation points.
[b]
Access: Wet well access shall be through a top
slab opening with aluminum hatch cover and frame. Hatch shall be sized
to utilize the top slab area to the maximum extent possible to facilitate
removal of equipment and cleaning/maintenance of wetwell. The hatch
shall also be designed to the same loading as the top slab. In no
instance, shall the access hatch be less than thirty-six-inch by thirty-six-inch.
[c]
Ventilation: wet wells shall be provided with a
separate ventilation system and shall be sized to provide a minimum
of 30 complete air changes per hour. In addition to manual control,
time clock operation of fans shall be provided to allow a minimum
of two complete air changes per hour.
[i]
Ventilation shall be accomplished by the introduction
of fresh air into the wet well under positive pressure. The fan shall
be installed outdoors. The fan assembly and housing shall be corrosion-resistant
and weatherproofed. The entrance hatch to the wet well shall be provided
with a limit switch to energize the fan whenever the hatch is open.
The fan shall be direct drive.
[2]
Dry well design: Dry wells shall consist of precast concrete
construction. Dry wells shall have exterior elastomeric membrane waterproofing.
The dry well floor shall be sloped to a sump. A sump pump with piping
to the wet well shall be provided and sump pump alarms are required.
Sump pump piping shall contain a check valve to prevent siphoning
from the wet well. The pump suction isolation valve shall have a hand
wheel with an operating stem extending up to the control room. The
hand wheels shall be marked with an open arrow, a surge relief valve,
if required, shall be placed on the discharge header before the pipe
leaves the station. Surge relief piping shall be piped to the wet
well.
[a]
Access: dry well access shall be via a staircase
with all necessary landings and handrails per OSHA requirements. Stairs
are to be provided with appropriate landings in lieu of ladders with
cages. Hatch and ladder access and circular stairs are prohibited.
Equipment hatches for the pumps shall be located in the top slab and
directly above the pumps. Traversing monorails with cranes of adequate
capacity shall be provided above the dry well to facilitate removal
of the pumps, motors, valves and all other related equipment. Grating
(catwalks) shall be provided in the dry well to facilitate access
to all piping without climbing over pipes, equipment, etc. Grating,
where used shall be structurally sound for the loads to be applied
during maintenance and removal of equipment.
[b]
Ventilation: Dry wells shall be provided with a
separate ventilating system and shall be sized to provide a minimum
of 10 complete air changes per hour. In addition to manual control,
time clock operation of fans shall be provided to allow a minimum
of four complete air changes per hour.
[i]
Ventilation shall be accomplished by the introduction
of fresh air into the dry well under positive pressure. The dry well
ventilation system shall under no circumstances be connected to the
wet well ventilation system and shall be away from any source of contamination.
[ii]
Ventilation shall be automatically activated whenever
the dry well lighting is energized and/or the access door is opened
and the station is occupied by personnel.
[c]
Dual sump pumps shall be provided for redundancy.
Alternation shall be accomplished by means of a manual H-O-A selector
switch rather than electrical alternators.
[d]
To facilitate pump draining without flooding the
building, pump intakes shall be drainable directly to the sump through
piping or a channel drain.
[3]
Influent manhole: One influent manhole collecting all of the gravity sewers that flow to the pumping station shall be provided. The influent manhole shall be located on the pumping station site. A gravity sewer shall carry wastewater from the influent manhole to the wet well. The influent manhole shall be capable of being isolated from the pumping station wet well by a sluice gate as required in § 291-65C(1)(a)[7].
[4]
Pumping station design.
[a]
Pumping station building design/architectural standards:
pumping stations shall be architecturally compatible with surrounding
structures and shall not have slate roofs. Pumping station buildings
shall be of precast concrete and shall be designed to be vandal-proof.
Roof shall be precast concrete gable type. Wood or asphalt shingles
are not permitted. There shall be no exposed woodwork on the outside
of the building. All exterior woodwork shall have a vinyl or aluminum
coating. The pumping station shall have a lightning protection system.
Provisions shall be made in the structure for traversing bridge cranes
of adequate capacity to facilitate the removal of pumps, motors, valves
and all other related heavy equipment. The pumping station doors shall
be sixteen-gauge steel with deadbolts and locks keyed to the County
standard. Doors shall be located and/or situated so that they are
not affected by rain runoff from the roof.
[b]
The building shall be a minimum of 10 feet by 12
feet and shall include a work bench and wall cabinets for storage.
[c]
The finished floor and all electrical equipment
shall be located at least two feet above the one-hundred-year flood
elevation. Ventilation openings shall be protected with aluminum louvers
with bird screens. Floors shall be sloped (minimum slope shall be
1/4 inch per foot) to floor drains piped to the influent manhole or
wet well. The building floor shall be higher than the top elevation
of the wet well. The building shall be furnished with a service sink
with both hot and cold water, on-demand hot water heater, outside
non-freeze hose bibb, and small desk with chair, a restroom shall
be provided onsite as determined on a case-by-case basis based on
the anticipated number of man-hours of operation and the remoteness
of the site. The building shall conform to all Charles County building
codes and zoning regulations.
[i]
Control room. Electrical equipment shall be located
above grade in a control room above the dry well. The control room
shall be designed with adequate space to accommodate future upgrades.
[ii]
Toilet room. In some instances, a toilet room
shall be provided with toilet, lavatory, on-demand hot water heater,
towel dispenser, soap dispenser and mirror.
[iii]
Water service. A one-inch diameter metered potable
water source shall be provided for wash down, maintenance, and sanitation
purposes. The service shall include a backflow preventer. The water
service line shall provide a minimum of 30 gallons per minute to the
emergency shower with a minimum residual pressure of 35 psi.
[iv]
Heating and ventilation. The building shall be
heated by electric unit heaters with integral thermostats sized to
maintain a minimum inside temperature of 40° F. Provide cooling
as necessary to maintain air temperatures below 95° F. inside
electrical devices. Ventilation shall be by means of wall mounted
exhaust fans with backdraft dampers operated by thermostats and freezestats
and intake louvers with motor-operated dampers. Ventilation shall
be designed for a minimum of six air changes per hour. Provisions
shall also be made, if applicable, to ensure against condensation
forming on controls and other major items of equipment.
(c)
Equipment.
[1]
Screening and grit removal: Coarse bar screens are to be provided
ahead of the pumps to protect equipment from rags, cans, bottles,
sticks, etc. Grit removal will be required in areas where the County
has experienced or expects a collection of grit and debris as determined
by the County Engineer. The pumping station shall include provisions
for the installation of a grinder/macerator that may be installed
at a later time by the County. This includes determining the correct
size unit, and ensuring that sufficient electric service is provided
to operate the grinder/macerator. This shall also include the furnishing
and installation of lifting hoist, access hatch, sliding guide rails,
and associated mounting hardware.
[2]
Provide built-in lifting equipment rated for the expected loads.
The equipment should be capable of transporting the equipment to the
exterior of the building for loading onto service trucks.
[3]
Yard valves: Yard valves shall be buried gate valves complying
with the County's standard specifications and details for construction
with operating nut and roadway valve box at grade.
[4]
Interior piping: All interior wastewater piping shall be DIP,
Class 53, with flanged fittings. Flanges shall be integrally cast
on pipe or factory assembled screwed-on with proper bonding compound.
Manifolds shall include flexible couplings for make-up and for expansion
and contraction of the piping system.
[a]
Flexible couplings shall be provided on the suction
and discharge of each pump.
[5]
Arrangement of piping and equipment within the station shall
be made with adequate space for maintenance, repair, removal or replacement
of equipment, as well as to safeguard personnel working in the station.
A minimum of three feet of clearance between equipment and walls shall
be provided. Depending on the size of the equipment and piping, greater
clearances may be needed. Piping shall be adequately supported. Control
and instrumentation piping shall be copper or stainless steel.
[a]
Provide color coding for piping in accordance with
the Standard Specifications for Construction Manual.
[6]
Valves: each wastewater pump shall have isolation valves on
the suction and discharge to permit the removal or maintenance of
the pumps without affecting the operation of the remaining pumps.
Valves shall be gate type per County standard specifications for construction.
To prevent valve fouling, locate the suction gate valve a minimum
three feet ahead of the reducers. In addition to the valving normally
utilized within the pumping station provide an additional exterior
isolation valve on each pump suction line between the wet well and
dry well. The pumping station isolation valve shall be provided with
a handwheel, extension stem and operating nut to allow access from
the control room floor. The handwheel shall be marked with an open
arrow. Each pump shall have a hydraulically operated, time adjustable
pump check service valve or a swing check valve to prevent backflow
through inoperative pumps. In accordance with the criteria for water
hammer control, pump check service valves shall be of the type and
strength required to eliminate water hammer damage. Pump isolation
or check valves shall not be located in the wet well. Spring type,
oil cushioned surge relief valves, when required, shall be provided
on the discharge header of the station and be piped to the wet well.
[7]
Pressure gauges: Pressure gauges for direct reading of line
conditions shall be placed on both the suction and discharge of each
pump and on the main discharge header piping after the last pump.
Pressure gauges shall be oil-filled type, have a minimum 3 1/2-inch
diameter face and be equipped with snubbers and diaphragms. Pressure
gauges shall be installed and configured such that the gauge can be
isolated and the gauge piping be drained.
[a]
Accuracy shall be to within 0.5% of pressure. Pressure
gauges shall have a range such that the normal operating pressure
is near the middle of the gauge.
[8]
Flow metering: all wastewater pumping stations shall have polyurethane
lined magnetic type flow meters with a replacement spool piece or
bypass line provided to enable the pumping station to operate when
the meter is being serviced.
[a]
Magnetic flow meters shall be provided with grounding
rings and isolation valves. Accuracy shall be to within 1% of flow.
All flow meters shall have an adequate straight run of pipe both upstream
and downstream of the meter in accordance with the manufacturer's
recommendations. A seven-day circular chart recorder with totalizer
and indicator recorder in units of gpm shall also be provided.
[9]
Pumping units: wastewater pump suction and discharge shall be
four-inch minimum diameter. All wastewater pumps shall rotate clockwise
as viewed from the motor end. Wastewater pumps shall be centrifugal
non-clog solids handling pumps capable of passing a hard three-inch
sphere as well as stringy material and meet all requirements of MDE.
[a]
The pump bearings shall have a minimum 100,000
hours ABMA-10 bearing life. The pump motors shall operate on 480 volt,
three-phase, 60 cycle electrical service and at a speed no higher
than 1,780 rpm. The pump motor horsepower shall be sufficient to prevent
motor overload under all possible conditions. The pumps shall meet
the vibration performance specifications of the Hydraulic Institute
(HI). All wastewater pumps shall be factory witness tested and approved
prior to shipment. All wastewater pumps must pass an on-site vibration
test performed by an independent vibration testing company prior to
acceptance. Wastewater pumps and motors shall be suitable for continuous
duty, pumps shall be of the types listed below.
[i]
Dry well wastewater pumps (conventional and package
stations only): pumps shall be of the dry pit submersible design.
The pump casing/volute, impeller, support base, suction elbow, seal
housing/motor adapter and motor housing shall be of cast iron construction.
The pump's casing and impeller shall be fitted with replaceable
hardened stainless steel wear rings to maintain sealing efficiency
between the volute and the impeller. At the option of the County Engineer,
other pump materials may be required to suit a particular application.
Each pump discharge volute casing and suction elbow shall be provided
with an inspection and clean out opening.
[ii]
Dry pit submersible wastewater pumps shall have
the following additional features:
[A]
One piece backhead and motor adapter with impeller
adjustment cap screws.
[B]
Solid full diameter stainless steel shaft with
no shaft sleeve or solid large diameter high strength alloy steel
shaft with stainless steel shaft sleeve having a tapered end with
a keyway to receive the impeller.
[C]
Double mechanical shaft seals cooled and lubricated
by potable water through a cleanable seal filter assembly and provided
with a mechanical seal vent with petcock. Oil cooled may be provided
with the approval of the County Engineer.
[D]
Premium efficiency motors shall be specified (where
commercially available) for all three-phase pump motors dry pit submersible
wastewater pumps shall be designed for continuous operation in air
for application in a dry well. The motors for dry pit applications
shall be capable of a minimum of eight starts per hour in air.
[iii]
The pumps/motors shall also be designed to function
continuously in a submerged condition should the dry well become flooded.
Motor cooling shall be via cooling water jacket, submersible-rated
air-over motor cooling fan or positively forced oil cooling. Variable
drive units shall be provided when feasible.
(d)
Electrical and controls.
[1]
Electrical design: All electrical designs and components shall
be in strict accordance with all applicable national and County code
requirements. Electrical design shall be such that phase out protection
shall be provided so that the power will automatically switch off
in the event of a loss of any one phase. Incoming electrical service
shall be underground with electric meters installed outside the pumping
station building. The electrical plans shall include, but not be limited
to, the following:
[a]
Design report shall provide the correspondence
with the Charles County local power company showing the consultant's
load breakdown along with the local power company's assessment
of the voltage available, their ability to serve the project, and
the availability of a second independent source of power. Specific
local power company permission to use across-the-line starters or
requirement for reduced voltage starters is required.
[b]
In addition to the proposed wiring diagrams, provide
a narrative of the control sequence scenario which clearly explains
the operational intent.
[c]
Complete plan layout indicating all conduit, wire
sizes and equipment locations including lighting and other appurtenances.
Incoming electrical service on the pumping station site shall be underground
and within concrete encased conduits.
[d]
Installation details of equipment that are wall
mounted, or suspended from the ceiling or otherwise required for clarity.
[e]
Single line diagrams incorporating all electrical
components required for operation of the facility.
[f]
Complete lighting schedule noting model, size,
location and installation data as well as appurtenances. Vandalproof
exterior lighting shall be provided. Interior and exterior quartz
lighting, separately switched, for maintenance purposes including
auxiliary DC safety lighting is to be provided. Minimum lighting levels
shall be 15 footcandles for stairways, and 100 footcandles for operations
and maintenance.
[g]
Complete control and SCADA diagrams, including
panel and instrument diagrams.
[h]
Elevation of control panels with equipment and
mounting dimensions and notes identifying each component.
[i]
Complete circuit breaker schedule indicating size
and identifying each circuit.
[j]
Ventilation schedule noting fan size, operating
conditions, location, model, installation data, etc. The ventilation
schedule shall also outline louver data including size, material,
fixed or motorized.
[k]
Secondary power facilities and alarm equipment
shall be designed so that they may be manually activated for periodic
maintenance checks to ensure proper operation.
[l]
Provide a legend of all symbols used for the above.
[m]
Power for the station shall be 480 volts, three-phase.
[n]
IEC electrical components shall not be utilized.
For replacement compatibility and availability, only full-sized NEMA
UL listed electrical devices shall be used regardless of any equivalent
UL ratings of IEC devices.
[o]
Lockable safety disconnect switches are to be provided
for all rotating equipment. Use lockable knife-switches rather than
remote lockable start/stop button stations.
[p]
Provide "push-to-test" type indicator lamps with
screw-in type bulbs. Use of 120 mb type bulbs is prohibited.
[q]
Permanent, in-place, volt/amp meters are required
for each pump or major piece of equipment.
[r]
Due to compatibility and standardization needs,
provide only "Square-D," "Furnas," or "Cutler-Hammer" electrical equipment;
no alternatives allowed.
[s]
Use "Square-D," or County-approved equal, Class
8501 Type "K" plug-in style relays to the maximum extent possible
where appropriate. Provide integral power indicating lamps in the
relays. The only exception to this should be where current requirements
exceed contact ratings. Use plug-in style relays for timers, alternators,
and latching as well. Octal or square relays are equally acceptable,
although eight-pin octal relays are preferred. Use "Square-D" Type
KP12P14 or KP13P14 or County-approved for DPDT or 3PDT respectively.
[t]
Provide non-resettable elapsed time meters for
all rotating equipment. Meters are to be in hours and tenths of an
hour, not minutes. Provide an elapsed time meter for parallel operation
of main wastewater pumps; e.g., a meter for Pump No. 1, Pump No. 2,
and Pump Nos. 1 and 2 together.
[u]
A weatherproof red exterior "trouble light" for
visual indication of equipment failures/problems is to be provided.
A horn is not to be provided.
[v]
Provide a junction pedestal(s) near, but outside,
the wet well for power, lighting, and control cables leading to the
wet well. Provide gas tight connections. No junction boxes are allowed
inside the wet well. Gas tight lighting is to be provided inside the
wet well.
[2]
Lightning and surge protection: The designer shall provide lightning
and surge protection at the wastewater pumping station. The lightning
and surge protection shall comply with the latest editions of all
applicable codes and standards. Provide phase failure and phase reversal
protection for all equipment. A single phase condition shall not destroy
motors, transformers, relays, etc. should the second source of power
fail to take over.
[3]
Backup power: All pumping stations shall be provided with emergency
generators with automatic transfer switches as described in MDE guidelines.
At the discretion of the County, a diesel driven permanent standby
pumping system may be required in lieu of an emergency generator.
The generator area shall be located a minimum of two feet above the
one-hundred-year flood elevation. Emergency generators shall be sized
to maintain full station operation. Emergency generators shall be
diesel driven with fuel storage on the underside of the generator
in a belly tank or outside the building in an aboveground storage
tank. Fuel spillage protection shall be provided. Tank size shall
be suitable for a minimum of 24 hours of generator operation at full
load. Generators shall be mounted on vibration spring isolators. When
emergency generators are located inside the pumping station building,
they shall be mounted with a fuel tank fill connection to the outside.
Generator engine exhaust shall be provided with a critical grade silencer
and piped to the outside of the control building. Generator exhaust
shall face away from nearby neighbors. If this is not possible, a
baffle wall shall be constructed in front of the generator exhaust
to deflect the noise. If the generator is located outside, its enclosure
shall be acoustically lined.
[4]
Control/SCADA: A complete and operable control/SCADA system
shall be provided per County standard specifications for construction.
(e)
Painting and coating. All exposed piping, pump equipment and
appurtenances including all structures shall be painted per County
standard specifications for construction.
(f)
Miscellaneous.
[1]
Odor control.
[a]
An odor-control system shall be provided when required
by the County Engineer. The type of odor-control system to be used
at a particular station must be approved by the County Engineer prior
to design. Odor-control systems shall be designed to mitigate odors
from the wet well and influent manhole.
[b]
Acceptable methods include, but are not limited
to: Carbon adsorption (air scrubbing), chemical addition at the wet
well or influent manhole, and soil odor filters.
[c]
Wastewater pumping stations should be designed
to minimize the possible formation of odors by limiting wet well detention
times and avoiding turbulence in manholes and wet wells which cause
odors to be released.
[2]
Hydrogen sulfide control: See § 291-64D(3)(e).
(g)
Safety.
[1]
Gas detection and annunciation shall be provided for the dry
well in the form of low explosive levels, and oxygen level as a minimum.
[2]
Appropriate emergency eye wash facilities shall be provided
whenever chemical handling is proposed for the pumping station. The
need for emergency fountains and showers, the design/configuration
thereof, and their locations shall be in accordance with Section 57.29
of the most current edition of the Ten States Standards for wastewater
facilities and the applicable requirements of MOSH and the County
Safety Officer. As a minimum, the eyewash fountains shall be supplied
with water of moderate temperature, 50° F. to 90° F., suitable
to provide 15 to 30 minutes of continuous irrigation to the eyes.
As a minimum, the emergency showers shall be capable of discharging
30 gallons per minute of water at moderate temperature and at a minimum
pressure of 35 psi.
[3]
Appropriately designed dielectric rubber floor mats are to be
provided for insulation at all motor controls for personnel safety.
If water on the floor is a possibility, the design must eliminate
such water. A situation of motor control maintenance in wet or unsafe
conditions is unacceptable.
(2)
Small pumping stations. Design criteria for small wastewater pumping
stations shall be the same as for conventional stations described
above except where specifically stated otherwise.
(a)
Submersible: Submersible stations are defined as stations where
the pumps are "submerged" in the wet well. Because the pumps operate
under water in the wet well, there is no need for a separate pump
room. Guide rails enable the pump to be raised and lowered into place
without requiring entry by personnel under normal circumstances. Submersible
stations shall not be used for wet well depths greater than 25 feet.
[1]
Pumping station configuration: submersible pumping stations
shall be designed with an equipment hatch in the top slab for pump
removal, nonsparking guide rails and manway hatch. Pumps shall be
of the wet pit submersible type. The pumping station building shall
contain all mechanical, electrical, and control equipment and a toilet
room as described in the preceding sections of this chapter. The wet
well and pumps shall be located adjacent to the pumping station building.
The emergency generator shall be located outside of the pumping station
building in a weatherproof, sound insulated enclosure.
[2]
Wet well design: submersible pumping station wet wells shall
be designed for precast concrete construction. Wet well coating and
design features shall be the same as described for conventional pumping
stations.
[3]
Wet pit submersible wastewater pumps: Pump volute, impeller
and motor housing shall be of cast iron construction. Pumps shall
be centrifugal non-clog solids handling pumps capable of passing a
hard three-inch sphere as well as stringy material and meet all requirements
of MDE. The pump volute casing and impeller shall be fitted with replaceable
stainless steel wear rings to maintain sealing efficiency between
the pump volute and impeller. At the County Engineer's option,
other special pump materials may be required for a particular application.
The motor shaft shall be a single piece heat-treated high strength
alloy steel or high strength stainless steel having a tapered end
with keyway to receive the impeller. All nuts, bolts and screws shall
be stainless steel. The motor shall be Class F insulated (minimum)
and sealed from the pump by independent double mechanical seals.
[a]
The upper and lower mechanical seal shall run in
an oil chamber. The upper seal shall be a stationary tungsten-carbide
seal with rotating carbon ring. The lower seal shall be one stationary
and one positively driven rotating tungsten-carbide ring. All mating
surfaces where watertight sealing is required shall be machined and
fitted with a rubber o-ring. The machining of mating surfaces shall
provide metal to metal bearing on sealing surfaces without crushing
the o-ring.
[4]
Influent grinder/macerator: The wetwell or influent manhole
shall be designed to accommodate an influent wastewater grinder/macerator
(grinder) along with a bypass screening mechanism. The influent grinder
shall be of the vertical twin rotor type and be located in either
the influent manhole or in the wet well. The influent grinder shall
be capable of being lifted out of the wet well or manhole by means
of stainless steel guide rails without entering through an adequately
sized access hatch. The pumping station shall include provisions for
the installation of a grinder/macerator that may be installed at a
later time by the County. This includes determining the correct size
unit, and ensuring that sufficient electric service is provided to
operate the grinder/macerator. This shall also include the furnishing
and installation of lifting hoist, access hatch, sliding guide rails,
and associated mounting hardware.
[5]
Electrical and controls: Shall meet the same requirements for
conventional pumping stations.