§ 7.5-93. Design criteria and materials for sewers.

(1)

Generally. The criteria listed herein is not intended to cover all aspects of design, but rather to mention the basic guidelines and those particulars that are required by the city water department. For more detailed criteria, the reader should refer to standard references such as "Ten States Standards," Georgia EPD rules, Water Pollution Environment Federation Manual of Practice No. FD-5, and other available literature.

(2)

Types of sewers. All sewers for the conveyance of wastewater shall be designed as separate sanitary sewers in which groundwater, stormwater or other runoff from roofs, streets, parking lots, foundation drains and any source other than wastewater are excluded. Overflows from sewers shall not be permitted.

(3)

Design period. Gravity sewer pipelines should, as a minimum, be designed with capacity sufficient to handle the estimated tributary population. Tributary population is considered to be all areas upstream of the discharge point of the system being designed as well as any anticipated pumped flow from other basins. Sewers will be designed and installed along the entire road frontage of the property where gravity service is feasible and to the uppermost property line of the development being served.

(4)

Capacity and size determinations. In determining the required capacities of sanitary sewers, the following factors should be considered:

(1)

Maximum hourly sewage flow.

(2)

Additional maximum sewage or waste flow from industrial plants.

(3)

Ground water infiltration.

(4)

Topography of the area.

(5)

Depth of excavation.

New sewer systems shall be designed on the basis of an average daily flow of sewage of not less than four hundred (400) gallons per household per day. Normally, all sewers shall be designed for a peak flow of not less than two and one-half (2½) times the average flow; this peak factor will be higher for smaller basins (see design guides). Sewers should be designed to carry the peak flow when flowing at a depth of two-thirds ( 2/3 ) pipe diameter.

The city land use plan should be consulted and special consideration given to commercial and industrial areas. Where developers are installing major trunk lines or interceptor sewers, the city's long range plan should be consulted as a guide and the sewer should as a minimum be of the size called for in the long range plan. If proposed land use conditions have changed subsequent to the plan, these changes should be factored into the determination.

(5)

Special city requirements.

(a)

Distance between manholes. Maximum distance between manholes shall be four hundred (400) feet.

(b)

Depth. Any sewers installed in the street shall, topography permitting, be sufficiently deep to provide five (5) feet of cover over service laterals at the street right-of-way, and over any part of the main or service within the street right-of-way. The maximum depth for PVC pipe shall be fifteen (15) feet, depths in excess of this shall be ductile iron. Sewers installed in streets shall have maximum depth of twelve (12) feet unless otherwise approved. Any sewers on off-street easements shall have a minimum of three (3) feet of cover unless ductile iron pipe is used. Filling over the pipe to obtain minimum cover is not allowed.

(c)

Drop across manholes. All manholes shall be provided with, a minimum vertical drop across the manhole (between in and out pipes) of one-fourth (0.25) feet.

(d)

Detection tape. Detection tape shall be installed over all sewer pipe. Bury tape eighteen (18) to twenty-four (24) inches below grade. Use detection wire on all service laterals.

(6)

Slope. All sewers shall be so designed and constructed to give mean velocities, when flowing full, of not less than two (2.0) feet per second based on Manning's formula using an "n" value of 0.013. The following are the minimum slopes which should be provided; however, slopes greater than these are desirable:

Minimum Slope in Feet

Sewer Size (in inches)	Per 100 Feet
8	0.40
10	0.29
12	0.22
14	0.17
15	0.15
16	0.14
18	0.12
21	0.10
24	0.08

 

 

These minimum slopes will be used only when sufficient flows are expected to maintain a velocity of two (2.0) feet per second and maintain a cleaning action in the line. Sewers shall be laid with uniform slope between manholes. Sewers on ten (10) percent slope or greater shall be ductile iron pipe and shall be anchored securely with concrete anchors (See standard details) to prevent displacement by erosion or shock. Maximum slope of sewers shall be twenty (20) percent and sewers shall be designed at less than ten (10) percent whenever possible unless otherwise approved.

(7)

Increasing size. When a small sewer is connected to a large one (1), the connection shall not be lower than matching the top of both sewers to the same elevation.

(8)

Gravity sewer pipe materials. The city reserves the right to disallow any manufacturer that does not have a consistent, long-term record of quality control and successful product performance. Gravity sanitary sewer pipe up through fifteen-inch diameter will normally be polyvinyl chloride (PVC), solid wall type SDR 35 thickness meeting ASTM D3034. Ductile iron pipe (DIP) will be used where certain conditions exist (see discussion of DIP). For eighteen-inch diameter pipe and above, the contractor may have the option of using either polyvinyl chloride (PVC), reinforced concrete pipe (RCP), or ductile iron pipe. Bedding for sewer pipe shall be as follows (also see city standard details):

For PVC the minimum bedding shall be #57 or #89 crushed stone a minimum of six (6) inches below bottom of pipe extending up to six (6) inches above top of pipe for the full width of the trench.

For ductile iron pipe the minimum bedding shall be #57 or #89 crushed stone a minimum of six (6) inches below bottom of pipe extending up to the top of pipe.

In wet areas, the minimum bedding requirements will be increased as required to ensure a stable support under the pipe and on the sides of the pipe.

(a)

Ductile iron pipe (DIP).

1.

Scope. Ductile iron sewer pipe shall be required at all utility crossings with less than two (2) feet of clearance, in locations where cover is less than three (3) feet, at stream crossings, where slopes exceed ten (10) percent, and where cover exceeds fifteen (15) feet.

Ductile iron pipe shall be designed in accordance with ANSI Specification A21.50-81. The thickness and class of the pipe shall be governed by ANSI Specification A21.50-81, but shall be no less than class 50 thickness. Pipe shall be manufactured in accordance with ANSI Specification A21.51-81 latest revision.

Pipe shall be coal tar epoxy lined and seal coated with approved bituminous seal coat in accordance with AWWA C151, latest revision. Coal tar epoxy lining shall adhere to the following specifications.

2.

Joints. DIP joints shall be of the bell and spigot type with push-on joints, conforming to ANSI Specification A21.11 or mechanical joints.

(b)

Polyvinyl chloride (PVC) sewer pipe.

1.

Scope. The contractor shall provide unplasticized polyvinyl chloride (PVC) plastic gravity sewer pipe meeting the requirements of ASTM D3034 (latest revision) in the sizes shown unless otherwise indicated on the contract documents.

2.

Materials. Pipe and fittings shall meet the requirements as specified under ASTM D3034 (latest revision) for pipe through fifteen (15) inches and ASTM F679 for pipe eighteen (18) inches through twenty-seven (27) inches. All pipe and fittings shall be suitable for use as a gravity sewer conduit. Bell joints shall consist of an integral wall section with elastomeric gasket joint which provides a watertight seal. The pipe shall be capable of passing all tests which are detailed in this specification. Minimum wall thickness shall be SDR 35.

3.

Fittings. All fittings and accessories shall be manufactured and furnished by the pipe supplier. They shall have bell and/or spigot configurations compatible with that of the pipe and shall have an equivalent wall thickness.

4.

Pipe and fittings tests. Before shipping any pipe, the manufacturer shall submit shop drawings to the city and shall furnish written certification that all pipe through fifteen (15) inches meets ASTM Specification D3034 and that pipe eighteen (18) inches through twenty-four (24) inches meets ASTM F679. The city reserves the right to require additional laboratory testing at the developer's expense to verify minimum quality standards are being met.

5.

Pipe stiffness. Minimum "pipe stiffness" (F/Y) at five (5) percent deflection shall be forty-six (46) psi for all sizes, when tested in accordance with ASTM Standard Method of Test D2412 (latest edition), to determine the "External Loading Properties of Plastic Pipe by Parallel-Plate Loading." There shall be no evidence of splitting, cracking, or breaking at a deflection of up to thirty (30) percent of the original diameter.

6.

Fusion quality. There shall be no evidence of flaking, swelling, or disintegration when the pipe material is tested in accordance with ASTM D2152, "Quality of Extruded Poly (Vinyl Chloride) pipe by Acetone Immersion."

7.

Joint tightness. Pipe and fitting joints shall comply with ASTM D3212 (latest edition) for "Joints for drain and Sewer Plastic Pipes Using Flexible Elastomeric Seals." Joint assemblies shall not leak when subjected to both an internal and external hydrostatic test at equivalent pressures of ten and eight-tenths (10.8) psi gauge for a period of one (1) hour. Pipes shall be tested in straight alignment, axially deflected position, and by shear load test as otherwise defined in Paragraphs 7.2, 7.3, and 7.4 of ASTM D3212.

8.

Installation. PVC pipe will be installed in accordance with ASTM D2321 (latest revision). Initial backfill shall be compacted to the densities outlined in D2321. The city may require random compaction tests at the developer's expense to insure compliance with D2321.

9.

Deflection limit. Vertical deflection of installed pipe shall not exceed five (5) percent of the undeflected diameter as defined in ASTM D3034.

Upon completion of the pipe laying, the pipe will be tested for conditional acceptance. The test shall be performed by the contractor pulling a mandrel of specified dimensions through the pipeline.

(c)

Reinforced concrete pipe (RCP).

1.

General. The use of reinforced concrete pipe for sewers will be subject to approval on a case-by-case basis depending upon size of the sewer and site conditions. When approved for use, concrete gravity sewer pipe shall meet all materials and testing requirements of ASTM C-76, ASTM C-443, and ASTM C-497 (except where modified herein).

2.

Quality assurance. The contractor must submit to the owner and engineer the concrete pipe manufacturer's evidence of a working quality control program for approval, prior to any pipe being manufactured. The program and standards of manufacturing must be established and well defined. The program must include the minimum following requirements:

a.

A full time quality control technician.

b.

A complete and working quality control laboratory capable of testing and recording the requirements set forth in these specifications for concrete pipe.

c.

A zero (0) defect program for daily material testing and finished product testing to assure quality control as the pipe is being manufactured and shipped for this particular project.

3.

Guarantee. The contractor shall provide a guarantee against defective materials and workmanship in accordance with the requirements of these specifications.

4.

Material.

a.

All concrete pipe and fittings twelve (12) inches in diameter and larger shall be reinforced concrete sewer pipe conforming to the latest requirements of ASTM C-76 with the following modifications: All concrete pipe with zero (0)—twenty (20) feet of fill shall be a minimum of Class III with four thousand five hundred (4,500) psi concrete. All pipe with twenty (20)—thirty (30) feet of fill shall be Class IV with four thousand five hundred (4,500) psi concrete. All pipe with thirty (30) feet of fill and over shall be Class V with five thousand five hundred (5,500) psi concrete.

b.

Pipe shall have circumferential reinforcement as required for the particular class of pipe furnished. The bell and spigot of the joint shall contain circumferential and longitudinal reinforcement. Reinforced concrete pipe shall be centrifugally cast or vibrated, horizontally or vertically cast or made on a Packerhead machine and shall be furnished in lengths not more than twenty (20) feet and not less than eight (8) feet, except where short lengths are required for construction conditions. Reinforced concrete pipe shall have bell and spigot joints suitable for the use of a rubber gasket to be provided as a part of this item.

c.

Concrete pipe for sanitary sewers shall have bell and spigot joints consisting of self-centering steel joint rings securely attached to the pipe reinforcing steel. The steel joint rings shall be suitable for use with a rubber O-ring type gasket to be provided as part of this item.

d.

Bell and spigot joints consisting of self-centering steel joint rings shall have the joint rings securely attached to the pipe reinforcing steel. The rings which form the joint shall be made so that they will join with a close, sliding fit. The joint surfaces shall be such that the rubber gasket shall be confined on all sides and shall not support the weight of the pipe.

The spigot ring shall have an external groove accurately sized to receive the gasket. Special section steel for spigot rings shall conform to ASTM A-283, Grade A, or ASTM A-306, Grade 50.

The bell ring shall be flared to permit gradual deformation of the gasket when the joint is assembled. Minimum thickness of bell rings shall be three-sixteenths ( 3/16 ) inch. Bell rings one-fourth (¼) inch or thicker shall conform to ASTM A-283, Grade A, or ASTM A-306, Grade 50. Bells less than one-fourth (¼) inch thick shall conform to ASTM A-570, Grade A.

Each ring shall be precisely sized by expansion beyond the elastic limit of the steel and then gauged on an accurate template. All exposed surfaces of both rings shall be protected by a corrosion-resistant coating of zinc applied by an approved metalizing process after proper cleaning.

5.

Lining. The coal tar epoxy system shall be Koppers 300 M, Porter Tarset, Wise Chem CTE 200, Amercoat 78, Protecto 101 or equal.

The interior concrete or mortar surfaces of pipe and fittings are to be sandblasted and painted with one (1) coat of a high-build, coal tar epoxy system or two (2) coats of a standard coal tar epoxy system. The dry film thickness of the total system shall be sixteen (16) mils minimum on concrete or mortar surfaces and on steel joint ring surfaces.

Sandblasting shall result in a clean dry surface free of oil, grease, or other contaminants. Any air pockets over one-fourth (¼) inch in diameter and one-eighth ( 1/8 ) inch deep appearing on the concrete surface after sandblasting will be filled with an epoxy sand patching material such as those sold by Sherwin-Williams, Glidden, or Moran. The epoxy sand patch should be troweled prior to the application of the coal tar epoxy.

Any steel surfaces to be painted should be sandblasted, solvent cleaned, or wire brushed prior to painting. Application of the coal tar epoxy shall be by brush, roller, or spray system using equipment recommended by the manufacturer of the coal tar epoxy system. The temperature during application and curing of coal tar epoxy shall be as recommended by the manufacturer of the coal tar epoxy. Time between coats (if applicable) shall be as recommended by the manufacturer of the coal tar epoxy.

If the inside joint recess will be mortared and painted with coal tar epoxy in the field, the pipe supplier shall not paint the inside vertical surfaces at the ends of the pipe. When the inside joints will not be mortared in the field, the pipe supplier shall paint the inside vertical concrete or mortar surfaces at each end of the pipe.

The paint shall be extended continuously over the front lip of the steel spigot ring and a minimum of two (2) inches onto the sealing surface of unrestrained bell rings so that all interior joint surfaces which can be exposed to the fluid inside the pipe are coated.

(9)

Precast concrete manholes.

(a)

Manholes. Sewer manholes shall consist of precast reinforced concrete sections with eccentric top section, or flat slab for shallow manholes, and a base section conforming to the typical manhole details as shown on the standard detail drawings. Flat top manholes will be approved only if a need for such can be demonstrated by the design engineer.

(b)

Manhole sections. Precast manhole sections shall be manufactured, tested, and marked in accordance with the latest provisions of ASTM Standard Specifications, Serial Designation C 478.

(c)

Manhole section joints. Joints of the manhole sections shall be of the tongue-and-groove type with the inside tongue in the up position, sections shall be joined using a double strand seal of butyl mastic sealant (Kent Seal, Ram-Nech or equal). The inside and outside of all joints, lift holes and any bricks or precast adjusting rings shall be covered with non-shrink grout.

(d)

Lift holes. Each section of the precast manhole shall have not more than two (2) holes for the purpose of handling and laying. These holes shall be sealed before backfilling using either rubber plugs specially designed for this purpose or with quick-setting cement mortar.

(e)

Manhole steps. Manhole steps conforming to the applicable provisions of ASTM Specification C 478, latest edition, shall be of #4 steel reinforcing bars covered with polypropylene plastic or rubber and shall be supplied with depth rings and other necessary appurtenances. See the standard details for a typical manhole step detail.

(f)

Pipe holes. Holes in precast bases to receive sewer pipe shall be precast at the factory at the required locations and heights. Knocking out of holes in the field will not be permitted on new construction; however, holes can be cored in the field with a coring machine. All manholes shall have Kor-N-Seal by Press Seal Gasket Corporation (or equal) rubber boots for all pipe entries/exits.

(g)

Inverts. Manhole inverts shall be constructed of either concrete or brick in accordance with details on standard detail drawings and the invert (flow channel) shall have the same cross-section as the sewers which it connects. The manhole bench and invert shall be carefully formed to the required size and grade by gradual and even changes in direction. Changes in direction of flow through the invert shall be made to a true curve with as large a radius as the size of the manhole will permit. Inverts shall have a smooth trowel finish. The manhole bench shall be sloped thirty (30) degrees from the manhole wall toward the invert.

(h)

Manhole foundation. The manhole base shall be set upon a twelve-inch minimum thickness compacted mat of size #57 crushed stone graded level. In wet areas the crushed stone mat shall be thickened as needed to provide a non-yielding foundation.

(i)

Brick. Brickwork required to complete the precast concrete manhole shall be constructed using one (1) part portland cement to two (2) parts clean sand, meeting ASTM Specifications, Serial Designation C 144, thoroughly mixed to a workable plastic mixture. Brickwork shall be constructed in a neat and workmanlike manner. Nonshrink grout shall be used to grout interior and exterior exposed brick joints and faces. No more than three (3) courses of brick with nine-inch maximum total depth of bricks may be used to adjust manhole covers.

(j)

Frame and cover. The cast iron frame for the manhole cover shall be set at the required elevation and thoroughly anchored to the masonry in a bed of mortar. Frames and covers shall be city standard casting design by Vulcan Foundry, Standard Model V1327-1-CWD (see standard drawings). Where manholes are constructed in paved areas, the top surface of the frame and cover shall be tilted, if necessary, to conform to the exact slope, crown and grade of the existing adjacent pavement. In areas where manhole tops may be submerged by street runoff or high flood waters, the manhole lid shall be water-tight by Vulcan Foundry, water-tight Model V2327-1-CWD.

(k)

Masonry work. Masonry work shall be allowed to set for a period of not less than twenty-four (24) hours' before being placed under traffic or in operation. All loose or waste material shall be removed from the interior of the manhole.

(l)

Location. Manholes shall be installed at the end of each line; all changes in grade, size, or alignment; at all intersections; and at distances normally not greater than four hundred (400) feet. Cleanouts may be used only for special conditions and shall not be substituted for manholes nor installed at the ends of laterals greater than one hundred fifty (150) feet in length. Manholes in cross-country areas shall be elevated so that the top is twenty-four (24) inches above ground.

(m)

Drop manholes. A drop pipe shall be provided for a sewer entering a manhole at an elevation of more than three (3.0) feet above the manhole invert. The drop pipe shall be of PVC materials with ductile iron mechanical joint fittings. All outside ninety-degree elbows shall have concrete support blocking poured below the elbow to rest on stable undisturbed earth. Outside drop manhole will be noted on the construction plans at any time the drop exceeds three (3.0) feet. Where the difference in elevation between the incoming sewer and the manhole invert is less than three (3.0) feet, the invert shall be sloped from invert to invert to prevent solids deposition. Areas around the pipe will be backfilled with #57 or #89 crushed stone.

(10)

Casings. Steel casing pipe shall be used where boring and jacking of more than twenty (20) feet in length is required for installation. Steel casing pipe shall be standard class thickness with a minimum yield strength of thirty-five thousand (35,000) psi and shall conform to the requirements of ASTM A139. It shall be fully coated on the exterior and interior with a coal tar coating. The casing pipe diameter shall be six (6) to eight (8) inches greater than the "bell" diameter of the carrier pipe.

Wherever steel casing is required, the carrier pipe shall be ductile iron pipe with push-on joints or PVC. Approved spacers made of stainless steel straps with nylon skids shall be used to center the carrier pipe; two (2) spacers per section of pipe will be used.

(11)

Wastewater lift stations. The following minimum requirements apply to wastewater lift stations:

(a)

General.

1.

Minimum pump size for pump stations shall be a minimum rated capacity of one hundred fifty (150) gpm and minimum ten (10) hp rated motors. Lift stations shall utilize two (2) submersible centrifugal pumps each having a capacity equal to the design flow. Provide a spare pump of identical capacity.

2.

Lift stations having a capacity of five hundred (500) gpm or more shall be reviewed on an individual basis and may have requirements differing from those outlined herein.

3.

Force mains shall be sized to provide a velocity of at least two (2) feet per second.

4.

The design shall allow for easy removal of any pump or equipment item without the need of shut-down of the entire lift station.

5.

The design engineer should consult the city water department after preliminary design data has been developed for information on approved pump manufacturers. The city reserves the right to review each application on an individual basis and to reject the use of non-approved manufacturers or designs.

(b)

Submittals.

1.

Submittal of construction plans shall include the following lift station information:

a.

Capacity calculations. Use one (1) gpm capacity per house on residential developments of less than two hundred (200) units, except that the minimum pump capacity shall be one hundred fifty (150) gpm.

b.

System head calculations; tabulated and plotted on the pump curve. Include a plot of force main velocity.

c.

Standard drawings, details and specifications sufficient to ascertain compliance with these regulations.

d.

Cycle time. Calculations showing determination of wet well volume and cycle time at design conditions. Wet well volume should be sufficient to provide a cycle time of no less than five (5) minutes from a pump "on" to the next pump "on" time.

e.

Storage volume. Calculations showing volume of storage available in the event of a power outage. The storage zone shall be delineated on plan and profile drawings of the sewer system. (See subsection (d), Standby power, below.)

f.

Construction drawings and specifications in sufficient detail to ascertain compliance with these regulations.

g.

Buoyancy computations showing that structures are protected against flotation.

2.

Shop drawings. After construction plan approval but before purchasing any lift station equipment, shop drawings shall be submitted including the following information:

a.

Manufacturer's catalog sheets, performance curves, installation drawings, specifications and list of options for the specific pump that is offered for approval.

b.

Similar catalog data for controls, valves, hatches, yard hydrants, precast wet well and other manufactured items.

3.

Certification. After installation and before placing the system into full operation, the work must be inspected by the developer's engineer who must then issue a certification to the city verifying that all work has been done in accordance with approved plans. After acceptance of the work by the city, a factory representative shall inspect and start up the system certifying rotation, capacity, amperage draw, lack of vibration and other standard check points. This certification shall state the beginning date of the warranty and include a copy of the warranty. The factory representative shall provide a minimum of four (4) hours training.

4.

O&M Manuals. On or before the date of start-up, five (5) sets of factory O&M manuals shall be delivered to the city. These shall include the name of the purchaser, the serial numbers of pumps, detailed wiring schematics, telephone number and address for purchase of parts.

5.

As-built drawings. After construction is complete as-built drawings shall be furnished including one (1) set of mylar sepias plus two (2) sets of prints.

(c)

Spare parts.

1.

Lift stations shall be supplied with one (1) complete spare pump, one (1) complete spare set of float switches plus a complete set of manufacturer's recommended spare parts.

2.

Reserved.

(d)

Standby power.

1.

The minimum requirement for standby power for lift stations shall be that each station have a permanent in-place generator and shall have an automatic transfer switch.

2.

Emergency standby power will be supplied by an on-site emergency generator. The generator shall be diesel powered with an automatic transfer switch and provisions for an automatic exercise cycle.

(e)

Site requirements.

1.

Flooding. Lift stations shall remain fully operational and accessible during the twenty-five-year flood. All electrical controls shall be above the one-hundred-year flood level. All motors and mechanical equipment shall be protected against physical damage from the one-hundred-year flood.

2.

Access road. Access roads shall be paved with a twelve-foot wide surface of either concrete (four (4) inches thick with wire mesh) or asphalt (six (6) inches graded aggregate base plus two (2) inches Type E asphalt). Maximum grade shall be twenty (20) percent.

3.

Ownership. Both the lift station site and the access road right-of-way shall have ownership dedicated to the city, and this shall be indicated on the subdivision plat. The dedicated space for the lift station shall include sufficient space for parking of two (2) trucks, plus turn-around, plus slope maintenance. The dedicated width on road right-of-way shall be thirty (30) feet minimum.

4.

Fencing. Lift station sites shall be fenced with a minimum of six-foot high chain link fencing topped with three (3) strands of barbed wire. Access gates shall be a minimum of fifteen (15) feet in width. The space inside the fencing shall be large enough to facilitate service vehicle access to the pumping station wet well and other facilities. A paved turn around area shall be provided whenever the access road length exceeds two hundred (200) feet or when the road grade exceeds ten (10) percent.

5.

Water supply. A metered water supply line (three-fourths-inch minimum size) shall be installed to the site, and a freeze-proof yard hydrant located near the wet well. The hydrant shall be equipped with a suitable backflow preventer.

6.

Lighting. One (1) pole-mounted, photo cell controlled, one-hundred-watt high pressure sodium security light shall be installed. It shall be equipped with a manual on/off switch (located in the main control panel) to override the photo cell control.

7.

Screening. Where natural screening is not present to screen the site from view of residences, special plantings shall be installed to screen the site.

8.

Ground covers. All unpaved ground areas inside the fence and extending four (4) feet beyond the fence shall be treated with a herbicide and covered with a geotextile fabric, followed with a four-inch thick layer of #57 stone. The geotextile fabric shall be a non-woven polypropylene weighing eight (8) oz./S.Y. with a minimum burst strength of two hundred fifty (250) psi, such as Amoco type 4553 or equal.

(f)

Design features.

1.

Wet well volume. The wet well volume shall be sized to limit pump cycles to no more than four (4) cycles per hour under worst conditions.

2.

Ventilation. For wet wells, the minimum requirement shall be a single six-inch vent with stainless steel mesh screen designed for natural ventilation. Where conditions are conducive to formation of hazardous conditions (in the design engineer's opinion) then mechanical ventilation shall be provided. For dry wells, mechanical ventilation shall be required.

3.

Structures. Submersible lift stations shall have a wet well structure and a separate valve pit. Both structures shall be precast concrete with a monolithic base. The valve pit shall be a minimum of four (4) feet × four (4) feet × five (5) feet deep with manhole steps, and provided with a floor drain pipe, and a three-foot × three-foot lockable aluminum access hatch. Wet wells may be either round or rectangular and shall have a diameter or width of at least four (4) feet. Wet wells shall be sized to meet cycle time requirements with a drawdown (i.e. the distance between high water level and low water level) of not more than three (3.0) feet. The wet well shall have a lockable aluminum hatch large enough for easy removal of pumps. Riser sections in precast units shall be sealed watertight using two (2) strands of mastic and a coating of mortar on the inside and outside of the structure. Structures shall be adequately reinforced for all loading conditions normally encountered during shipping, construction and service. All openings (for pipes, hatch, conduits) shall be either cast in place or neatly cut. Sewer pipe connections shall utilize rubber boot connectors, and be watertight. The wet well shall be equipped with an aluminum ladder.

4.

Accessories. All materials inside the wet well and valve pit shall be corrosion resistant. Mechanical equipment requiring ferrous metals shall have a coal tar epoxy coating. Guide rails for pumps shall be stainless steel. Miscellaneous metals including fasteners shall be aluminum or stainless steel; anchor bolts shall be stainless steel.

5.

Pressure gauge. A pressure gauge shall be installed on the force main downstream of the gate valves, inside the valve pit and visible from ground level. A corporation stop shall be installed on the tap to allow removal of the gauge.

6.

Valves. The discharge pipe of each pump shall have a check valve followed by a gate valve before the two (2) pipes join into a common force main.

7.

Surge control valves. The pumping system shall be checked to determine if a surge control valve is required. If a valve is required, it shall be located within the valve pit on the common force main and a drain line installed to drain to the wet well.

(g)

Pump features. Pumps shall have the following features:

1.

Non-clog impeller.

2.

Be capable of passing a three-inch sphere.

3.

Be capable of dry operation without overheating.

4.

Have dual mechanical seals with seal leak indicator light in the control panel.

5.

Pump and motor casings shall be cast iron, and all fasteners shall be stainless steel.

6.

Motor shall be selected to be non-overloading under all operating conditions.

7.

Motor winding shall have a heat sensor with auto reset to prevent overheating; three-phase motors shall have two (2) sensors.

8.

Operating speed of the pump shall not exceed one thousand eight hundred (1,800) rpm without special approval.

9.

Motor shall have upper and lower roller bearings.

10.

The pump shall be automatically connected to the discharge connection elbow when lowered into place, and shall be easily removed for inspection or service. There shall be no need for personnel to enter pump well. Sealing of the pumping unit to the discharge connection elbow shall be accomplished by a simple linear downward motion of the pump. Each pump shall be equipped with a chain (of aluminum or other non-corrosive material) for easy removal.

(h)

Force main.

1.

The force main shall be sized for a minimum velocity of two (2) feet per second with one (1) pump operating.

2.

Force mains shall be ductile iron pipe.

3.

The force main profile shall slope continuously upward where practical. If high points occur where air could be trapped in the pipe, then an air release valve (of the type made for sewage applications) will be installed (in a manhole) at the high points.

(i)

Electrical.

1.

Lift station controls and electrical components shall be factory-wired in completely weather proof stainless steel metal cabinets (NEMA 4X stainless steel). The cabinet shall be provided with condensate heaters. Spare fuses of each type that is used in the electrical/control system shall be furnished.

2.

A main circuit breaker shall be installed to disconnect power to the entire station.

3.

Three-phase power will be provided for all motors at the developers expense.

4.

Protection against voltage surge and loss of a phase shall be provided.

5.

The factory-wired panel shall be equipped with a ground bus and neutral bus. Terminal shall be suitable for either aluminum or copper wire. All internal panel wiring shall be copper.

6.

Motors shall be suitable for either two hundred thirty (230) volt or four hundred sixty (460) volt operation. Design engineer shall consult with the city electrical department to verify specifics pertaining to electrical power availability.

7.

Wet well level shall be controlled by four (4) sealed mercury tube float switches. All floats shall be provided with twenty-five (25) feet of Type SJO flexible cord and shall be attached to a bracket mounted at the top of the wet well. Float functions shall be as follows:

Float No. 1	Low Level (Pumps Off)
Float No. 2	High Level (Lead Pump On)
Float No. 3	Extra High Level (Lag Pump On)
Float No. 4	Surcharge Level (Alarm Activated)

 

8.

The pump control system shall include the following features:

a.

Lead pump/lag pump alternator.

b.

Alarm light and horn to indicate high water level.

c.

Seal failure indicating light.

d.

Pump failure indicating light.

e.

Condensate heater.

f.

Lead pump selector switch.

g.

H-O-A switch and run light for each pump.

h.

Control voltage shall be one hundred twenty (120) V.

i.

Wiring shall be neatly tied and number coded to facilitate maintenance. A schematic diagram shall be furnished with the panel.

j.

A one hundred twenty (120) V GFCI type electrical receptacle shall be located at the control panel.

k.

Pump stations will be equipped with a remote transmitting unit and telemetering circuitry connecting to the city's SCADA system. The design engineer should consult the city for specific requirements at the beginning of design.

(j)

Warranty. Regardless of the manufacturer's warranty terms, the developer will be responsible for all repairs necessary within one (1) year from the date the station is completed and approved by the city. The developer will be required to furnish such assurances to the city as deemed appropriate by the city to ensure prompt action.

(Ord. No. 32-98, § 1, 8-27-98; Ord. No. 50-98, § 4, 1-7-99)