City of Milpitas
Engineering Design Guidelines
Sanitary Sewer

The information and guidelines contained herein are to be used whenever applicable. In the event a development is to be constructed in stages, master utility plans are required prior to submittal of the first stage improvement plans. The master utility plans shall show all improvements, including interim (phased) and ultimate improvements. For information regarding these guidelines contact the Land Development Section of the Engineering Division, at (408) 586-3329.

Sanitary Sewer

The City’s sewer collection system generally flows by gravity to the main pump station located to the northwestern part of the City. One small pump station is located within a residential area (the Pines) of the City.

All design submittal shall show all lines necessary for the development, including planned City Master Sewer Plan Lines.*  Show sizes, sewer pipes, appurtenant, manhole & lateral locations and all sewer profiles (slopes, invert elevations and proposed surface elevations).  Also show Cleanouts and sewer backflow devices.

*City of Milpitas Sewer Master Plan Revision, RMC Inc., August 2004.

Note:

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Design Criteria

1. Material

1. Vitrified Clay Pipe (VCP): Vitrified clay pipe shall conform to the specifications for extra strength pipe of ASTM Designation, C700, Class II as amended to date on file in the office of the City Engineer. VCP shall have a dense wall and shall not leak through the barrel more than the allowable when tested in accordance with “Hydrostatic Pressure Test” as described in “Clay Pipe Engineering Manual,” dated 1978.  The vitrified clay pipe shall not absorb moisture in excess of eight (8) percent of its dry weight.  Each length of pipe shall produce a clear, metallic ring when placed on end and struck with a light hammer.
   
   The City Engineer reserves the right to test sections of pipe at the site of manufacture and the supplier will furnish all materials and equipment, necessary to conduct such tests.
   
   
   1. Joints:   Except where otherwise specified or directed, the Contractor shall provide mechanical compression joints on all vitrified clay pipes sewer lines under this contract.  Joints for vitrified clay pipe shall meet requirements of ASTM C425.
   2. Fittings:  for VCP shall be of the same manufacturer as the pipe.
   3. Caps: Caps shall be furnished with branch pipes that are to be left unconnected.  Caps shall consist of the same materials as the pipe.  For vitrified clay pipes, a disk, 0.06-foot thick, fitting snugly in the bell of the branch pipe and secured in place with pipe joint material, shall serve as a cap.
      
      
2. Polyvinyl Chloride (PVC) Pipe: PVC sewer pipe and fittings shall conform to ASTM D3034 (SDR 35) for pipe diameters four (4”) inches through fifteen (15”) inches and ASTM F679 for pipe diameters from eighteen (18”) inches through twenty-four (24”) inches, as amended to date. PVC Sewer Pipe shall only be allowed for residential sewage flows.
   
   
   1. Joints: PVC pipe joints shall be bell gasketed joints. Gaskets meet the requirements of ASTM F477.  The joints shall meet the requirements of ASTM D3212.
   2. Fittings: For PVC shall be of the same manufacturer as the pipe.
   3. Caps: Caps shall be furnished with branch pipes that are to be left unconnected.  Caps shall consist of the same materials as the pipe.  For PVC pipes, caps of the type recommended by the pipe’s manufacturer shall be used.
      
      
3. Reinforced Concrete Pipe (RCP): RCP sewer pipe shall be Class III and conform to ASTM C76 for sewer pipe and lined with PVC T-lock sheets applied at the top 300degrees of the pipe. Portland Cement used in the manufacturer of reinforced concrete sewer pipe shall conform to the requirements of the specifications for Type V Portland Cement, ASTM C150 as amended to date, unless otherwise specified in the special provisions or shown on the plans.
   
   
   1. Joints: RCP sewer pipe shall have rubber gasket joints. Gaskets shall conform to AWWA C302 Paragraph 3.3 and 3.4.  Neoprene compound gaskets shall be used.
   1. Fittings: For RCP shall be of the same manufacturer as the pipe.
   2. Caps: Caps shall be furnished with branch pipes that are to be left unconnected.  Caps shall consist of the same materials as the pipe.  For RCP pipes, caps of the type recommended by the pipe’s manufacturer shall be used.
      
      
4. Ductile Iron Pipe: Ductile Iron pipe for sewer laterals shall conform to the requirements of ANSI A21.50 (AWWA C150). Ductile Iron pipe shall only be allowed for sewer laterals, unless otherwise specified in the special provisions or shown on the plans.
   
   
   1. Joints: Ductile Iron pipe shall have rubber gasket push-on joints with the rubber gasket forming the sole element relied upon for sealing. Joints shall conform to requirements of ANSI A21.11 (AWWA C11).
   2. Fittings: For Ductile Iron pipe shall be of the same manufacturer as the pipe.
   3. Caps: Caps shall be furnished with branch pipes that are to be left unconnected.  Caps shall consist of the same materials as the pipe.  For RCP pipes, caps of the type recommended by the pipe’s manufacturer shall be used.

1. Coefficient of friction "n" shall be 0.013
2. Minimum velocity shall be 2 feet per second
3. Maximum velocity shall be 8 feet per second

1. Collection System Capacity Required (Q):
   Q = Peak Factor (PF) x Average Daily Flow (QADF) + Rainfall Inflow and Infiltration (I/I) + Groundwater Infiltration (GWI)
   *See Exhibit A and Exhibit B for I/I and GWI flow information
   *See Sanitary Sewer Drainage Basin Map for each basin
   
2. Collection System Peak Flow (PF)
   PF = 0.96 x (QADF raised to the power of –0.21)
   (QADF = Average Daily Flow in Million Gallons per Day (MGD))
   PF shall not be less than 1.6 in any event.
   
3. Average Day Flow Generation Factors:
   

   Commercial:	Town Center	1,700 Gallons per Day (GPD)/Net Acre
   	Mixed Use	1,500 GPD/Net Acre
   	All Other	1,000 GPD/Net Acre
   Industrial:		1,000 GPD/Net Acre
   (Net area is defined as area excluding major private streets, freeways and railroad)
   Single Family:	Very Low	330 GPD/DU
   	Low	260 GPD/DU
   	Medium	245 GPD/DU
   	Hillside	330 GPD/DU
   Multiple Family:	Very High	245 GPD/DU
   	High	245 GPD/DU
   	Medium	310 GPD/DU
   Mobile Homes:		110 GPD/DU

   
   
   
4. New pipe design shall be based on maximum allowable d/D of 0.8 for peak hour.
   
   

   The above provides criteria for minimum required capacity. Note that engineering judgments shall be used for small and some individual developments since the capacity determined by calculations may be inadequate.

4. Easements

Minimum 10 feet wide. Trees and deep-rooted plants are not permitted within easements.

5. Pipeline Locations

1. Street centerline, when a landscaped median is located on centerline, no deep-rooted plants or trees shall be permitted within the median.
2. The minimum pipe crossing clearance with other utilities is one foot. Where the minimum clearance cannot be met, encasement or cap shall be designed by the developer's engineer and approved by the City Engineer.
3. Also, see Exhibit C of potable water section for October 16, 2003 California Department of Health Services guidance criteria for minimum separation distance between potable, storm, and recycled water lines.
4. Lines shall be constructed through the development to serve upstream properties, and include capacity for the upstream area.
5. Provide stubs for future extensions.

5. Manholes

1. 500 feet apart maximum and at all change of flow direction.
2. Change direction or size only at a manhole.
3. Allow 0.2 foot drop around a 90° bend in manhole. Allow 0.1 foot drop for all others.
4. Flushing inlets or manholes are required on all dead-end lines. Manholes are preferred.

7. Pipe Cover

5 feet (minimum)

8. Pipe Size (minimum)

1. Mains
   1. Residential = 6 inches
   2. Industrial/Commercial = 8 inches
      
2. Laterals
   1. Residential = 4 inches
   2. Industrial/Commercial = 6 inches

9. Laterals Grade ( minimum)

Lateral grade = 1/4" per foot.  Clean out to grade shall be constructed.  Sewer backflow device may be required per City Standard Drawing No.624.  Manholes maybe required in lieu of clean outs.

10. Pretreatment

Special pre-treatment may be required per City code for discharge of individual or commercial wastewater to the sewer at the Developer's expense. Inquire with San Jose/Santa Clara Water Pollution Control Plant at (408) 945-3000 to determine if a Industrial Wastewater Discharge Permit is required.

See Section titled Plans General Requirements for more information