Private Sewage Disposal System

Sanitary Science as Applied to Building

Private Sewage Disposal Systems

Absorption Rates

• General:
  • Percolation test is used.
  • Water pressure should be equal to or greater than the working pressure (50 psi according to UPC).
  • Air can also be used for testing, with 3m water column (5psi).
  • The test duration is 15 minutes.
• Location Considerations:
  • Permitted by Department of Environment & Natural Resources (DENR) regulations.
  • Building sewer may connect to a private sewage disposal system.
  • Determination based on soil porosity and groundwater level.
• System Components:
  • A septic tank discharges effluent into a subsurface disposal field, seepage pits, or a combination of both.
• Groundwater Level Considerations:
  • If groundwater is within 12 feet (3,658mm) of the surface, or if soil is porous with underlying rock or impervious soil, a septic tank and disposal field system is required.
  • System should be located outside flood hazard areas.
• Absorption Capacity:
  • Maximum absorption: Not more than 5.12 gal/ft² (208.6 L/m²) of leaching area per 24 hours.
  • Minimum absorption: Not less than 0.83 gal/ft² (33.8 L/m²) of leaching area per 24 hours.

Capacity of Septic Tanks

• Soil Type and Required Leaching Area:

  • Coarse sand or gravel: 20 sq. ft. per 100 gallons (0.005 m²/L), Maximum absorption capacity is $30 \frac{gals.}{sq. ft.}$ (203.7 L/m²)
  • Sandy loam or sandy clay: 25 sq. ft. per 100 gallons (0.006 m²/L), Maximum absorption capacity is $24 \frac{gals.}{sq. ft.}$ (162.9 L/m²)
  • Clay with considerable sand or gravel: 90 sq. ft. per 100 gallons (0.022 m²/L), Maximum absorption capacity is $15 \frac{gals.}{sq. ft.}$ (101.8 L/m²)
  • Clay: 120 sq. ft. per 100 gallons (0.030 m²/L), Maximum absorption capacity is $1.1 \frac{gals.}{sq. ft.}$ (44.8 L/m²)
    Note: Higher percolation has lower sq. ft. of leaching area, and lower percolation means higher sq. ft. of leaching area.

• Occupancy Type and Wastewater Generation (Gallons per Day):

  • Nursing home: 75 (283.9) per person
  • Rest home: 125 (473.1) per person
  • Laundries, self-service: 125 (473.1) per person
  • Commercial kitchen: 50 (189.3) per wash cycle
  • Parks, mobile homes: 20 (75.7) per parking space
  • Recreational vehicles:
    • Without water hook-up: 75 (283.9) per space
    • With water and sewer hook-up: 100 (378.5) per space
  • Restaurants-cafeterias: 20 (75.7) per employee, additional considerations for:
    • Kitchen waste: 7 (26.5) per customer
    • Garbage disposal: 6 (22.7) per meal
    • Check/Lounge: 2 (7.6) per customer
    • Disposable service: 2 (7.6) per meal
  • Schools:
    • Staff and office: 20 (75.7) per person
    • With gym and showers, add: 15 (56.8) per person
    • With cafeteria, add: 20 (75.7) per student
    • Boarding, total waste: 100 (378.5) per person
  • Service station, toilets: 1000 (3785) for 1st bay, 500 (1892.5) for each additional bay
  • Stores: 20 (75.7) per employee
  • Swimming pools: 1 per 10 sq. ft. (4.1 /m²) of pool surface area
  • Theaters, auditoriums: 10 (37.9) per person

• Residential: Determined by the number of bedrooms or apartment units in dwelling occupancies and the estimated waste/sewage design flow rate or the number of plumbing fixture units

• (a) Recommended Design Criteria:

  • Sewage disposal systems sized using estimated waste/sewage flows.
  • Waste/sewage flow, up to 1500 gallons/day (5677.5 L/day): Tank sized according to Flow x 1.5 = septic tank size.
  • Waste/sewage flow, over 1500 gallons/day (5677.5 L/day): Tank sized according to Flow x 0.75 + 1125 = septic tank size.
  • Secondary system is sized for the total flow per 24 hours.

• Office Example:

  • 100 employees x 20 gallons per day = 2,000 gallons per day total.
  • Septic Tank Size = (2,000 x 0.75) + 1125

Table k-2 Capacity of Septic Tanks

• Single Family Dwellings:
  • 1 or 2 Bedrooms: 750 Gallons (2838 liters)
  • 3 Bedrooms: 1000 Gallons (3785 liters)
  • 4 Bedrooms: 1200 Gallons (4542 liters)
  • 5 or 6 Bedrooms: 1500 Gallons (5678 liters)
• Capacity of Septic Tanks: Multiple Dwelling Units or Apartments - One Bedroom Each
  • 2 Units: 1000 Gallons (3785 liters)
  • 3 Units: 1200 Gallons (4542 liters)
  • 4 Units: 1500 Gallons (5678 liters)
  • 5 Units: 2000 Gallons (7570 liters)
  • 6 Units: 2250 Gallons (8516 liters)
  • 7 Units: 2500 Gallons (9463 liters)
  • 8 Units: 2750 Gallons (10,409 liters)
  • 9 Units: 3000 Gallons (11,355 liters)
    Note: Septic tank sizes in this table include sludge storage capacity and the connection of domestic food waste disposal units without further volume increase.

Area of Disposal Fields & Seepage Pits

• No excavation for a leach line or leach bed shall extend within 1.5m of the water table.
• When disposal fields are installed, it shall have:
  • Minimum of $14m^2$ of trench bottom shall be provided for each system
  • Side wall area of the required 304.8mm & not to be exceed 914.4mm below leach line
• When leaching beds are permitted in lieu of trenches:
  • The area of each such bed shall be at least 50% greater than the tubular requirements for trenches.
• No excavation for a seepage pit shall extend within 3m of the water table.

Septic Tank Construction

• Inlets and Outlets:
  • Should have open-end sanitary tees or baffles to distribute flow and retain scum.
  • A baffle type fitting shall not be less than the size of the connecting sewer nor less than 102mm horizontal dimension from inlet & outlet pipe inverts.
  • The inlet & outlet pipe or baffle shall extend 102 mm above & at least 305mm below the water surface.
  • The invert of the inlet pipe shall be at level not less than 51mm above the invert of the outlet pipe.
• Compartments:
  • Septic tanks shall have a minimum of 2 compartments.
  • Inlet compartment of any septic tank shall not be less than 2/3 of the total capacity of the tank nor less than 500 gallons ($1.9 m^3$)
  • Minimum dimension 0.9mx1.5m (3ft width x 5ft length) for inlet compartment
  • Secondary compartment of any septic tank shall have a minimum capacity of 250 gallons ($1m^3$) & max capacity of 1/3 the total capacity of the tank.
  • 0.762m(2.5 ft) min &1.829m(6ft) max. liquid depth
  • Septic tank having over $5.7m^3$ capacity, secondary compartment of such septic tank shall have a min. 5feet (1.5m) length.
• Manholes:
  • Septic tanks shall have a min. of 2 manholes with 508 mm min. dimension.
  • One (1) access manhole shall be located over the inlet and one (1) access manhole shall be located over the outlet.
  • Whenever a first compartments exceeds 12 feet (3.7m) in length, additional manhole shall be provided.
• Piping and Baffles:
  • Size of the vertical leg of around inlet & outlet fittings shall not be less than the size of the connecting sewer nor less than102mm.
  • A baffle type fitting shall not be less than the size of the connecting sewer nor less than 102mm horizontal dimension from inlet& outlet pipe inverts.
  • The inlet & outlet pipe or baffle shall extend 102mm above & at least 305mm below the water surface.
  • The invert of the inlet pipe shall be at a level not less than 51mm above the invert of the outlet pipe.
• General Construction:
  • Side walls shall extend at least 229mm above the liquid depth. The cover of the septic tank shall be at least 51mm above the back vent openings.
  • Partitions or baffles between compartments shall be of solid durable material & shall extend at least 102 mm above the liquid level.
  • An inverted fitting equivalent in size to the tank inlet, but in no case less than four (4) inches (102 mm) in size, shall be installed in the inlet compartment side of the baffle with the bottom of the fitting placed midway in the depth of the liquid.
  • Wooden baffles are prohibited.

Construction of Disposal Fields

• Number of Drain lines per field: 1
• Length of each line:$100 ft (30,480 mm)$
• Bottom width of trench: 12 inches (305mm) to 36 inches (914mm)
• Spacing of pipes: level
• Spacing of lines, center to center: 6 feet (1,829mm)
• Depth of earth cover lines: 18 inches (457 mm) Preferred (457mm)
• Grade of lines: 25mm/m
• Filter material under drain lines: 12 inches (305mm)
• Filter material over drain lines: 2 inches (51mm)
• Spacing between leaching beds or trenches (1): 4 feet (1,219mm)
• Additional 2ft (610mm) spacing of leaching beds or trenches for each additional foot (305mm) below the bottom of the drain line.
  • No part of the perimeter of leaching beds shall be more than 3 feet (914mm) from a distribution drain line.
  • Disposal fields, trenches, and leaching beds shall not be paved over or covered by concrete or any material that can reduce or inhibit any possible evaporation of sewer effluent.

Table K-1. Location of Sewage Disposal System Minimum Horizontal Distance In Clear Required From:

• When disposal fields and/or seepage pits are installed in sloping ground, the minimum horizontal distance between any part of the leaching system and ground surface shall be fifteen (15) feet (4572 mm).
• Including porches and steps, whether covered or uncovered, breezeways, roofed porte-cocheres, roofed patios, carports, covered walks, covered driveways and similar structures or appurtenances.
  *See also Section 313.3 of the Uniform Plumbing Code.
• All drainage piping shall clear domestic water supply wells by at least fifty (50) feet (15240 mm). This distance may be reduced to not less than twenty-five (25) feet (7620 mm) when the drainage piping is constructed of materials approved for use within a building.
• Plus two (2) feet (610 mm) for each additional (1) foot (305 mm) of depth in excess of one (1) foot (305 mm) below the bottom of the drain line. (See also Section K 6.)
• See Section 720.0 of the Uniform Plumbing Code.
• For parallel construction - For crossings, approval by the Health Department shall be required.
• These minimum clear horizontal distances shall also apply between disposal field, seepage pits, and the ocean mean higher high tide line.

Storm Drainage System

Elements of Rainwater Collection

• Gutter: Located along the entire perimeter of the roof.
• Strainers or Roof Drain: Designed to receive water collecting on the surface of a roof and discharge it into a downspout; prevents clogging.
• Downspout: Located every 8 to 10 meters and at every corner of the roof (ideally every 4 to 6 meters to avoid clogging).
• Conductor: A pipe inside the building that conveys storm water from the roof to a storm drain, combined building sewer, or other approved disposal point.
• Leader: An exterior vertical drainage pipe for conveying storm water from roof or gutter drains.
• Shoe: At the bottom of the roof leader, directs rainwater towards the nearest catch basin.
• Catch Basin:
  • Downspouts should terminate in a catch basin (can serve more than one downspout).
  • Delivers water to the sewers in the street via gravity.
  • Area drain Catch Basin also collects surface water

Storm Sewers

• Carries only rainwater collected from the storm drain or from the streets
• Terminates at natural drainage areas (i.e., lakes, rivers, and water reservoirs).
• Require manholes to serve as clean-outs and to make sewers accessible for inspection and repair built at depths of about 2 or 3 meters; diameter ranging from 0.6m to 1.2meters.

Systems in Collecting Storm Water

• Independent System:
  • A.k.a. 'Separate System'
  • Brings collected water directly to the water reservoir
• Combined System:
  • Combines storm water with sanitary wastes

Storm Drainage System Code Requirements

Where Required

• Roofs, paved areas, yards, courts, and courtyards shall be drained into a separate storm sewer system or combined sewer system.
• In the case of one and two family dwellings, storm water shall be permitted to be discharged on flat areas such as streets or lawns.

Storm Water Drainage to Sanitary Sewer Prohibited

• Storm water shall not be drained into sewers intended for sanitary drainage only.

Subsoil Drains

• Shall be provided around the perimeter of buildings having basements, cellars, crawl spaces, or floors below grade.
• Inside or outside the footing
• Shall be perforated or open-jointed approved drain tile or pipe.
• 75mm (3") minimum diameter
• Prevent clogging
• Shall be laid in gravel, slag, crushed rock, approved 3/4 inch crushed, recycled glass aggregate, or other approved porous material with no less than 4" surrounding the pipe on all sides.
• Filter media shall be provided for exterior subsoil piping.
• Where it is not possible to convey the drainage by gravity, subsoil drain shall discharge to an accessible sump provided with automatic electric pump.
  Sump: 375mm minimum diameter, 450mm minimum depth with fitted cover.
  Sump pump-15gpm minimum flow rate sanitary- 20qpm
• Discharge piping - 40mm minimum diameter with union or approved quickly-disconnect assembly to make the pump accessible for servicing.
• Subsoil drain subject to backflow when discharging into a storm drain shall be provided with a backwater valve in the drain line so located as to be accessible for inspection and maintenance.
• Discharging to a properly graded open area, provided that:
  • (1) Do not serve continuously flowing springs or groundwater.
  • (2) Point of discharge is not less than 3m from any property line.
  • (3) It is impracticable to discharge such storm drains to an approved water course, to front street curb or gutter, or to an alley.

Areaway Drains

• 2" minimum diameter for 100 ft2 ($9.3m^2$)
• Greater than 100 ft2 shall be size according to Table 11-2

Window Areaway Drains

• 10 ft2 ($0.9m^2$) maximum shall be permitted to discharge to the subsoil drains through a 2" pipe.
• More 10 ft2 shall be handled same manner as areaway

Filling Stations and Motor Vehicle Washing Establishments

• Shall have paved area sloped toward sumps or gratings within the property lines, Curbs not less than 6" high shall be placed where required to direct water to gratings or sumps.

Roof Drainage

Primary Roof Drainage

• Roof areas of building shall be drained by roof drains or gutters.
• Roof drains, gutters, vertical conductors or leaders, and horizontal storm drainage shall be based on a storm duration of 60 minutes and 100 year return period.
• Refer to the latest edition of rainfall data published by the Philippine Atmospheric Geophysical and Astronomical Authority (PAGASA).

Secondary Drainage

• Or emergency roof drainage shall be provided by one of the following methods:
  • 1. Roof Scupper or Open side - scupper openings shall not be less than 4" and have a width equal to the circumference of the roof drain required.
  • 2. Secondary roof drain - shall be located not less than 2" above the roof surface.
• Separate piping system
• Secondary roof drainage shall be separate system of piping, independent of the primary roof drainage system.
• The discharge shall be above grade observable by building occupants and maintenance.
• Combined System
• Secondary roof drains shall connect to the vertical piping of the primary storm drainage conductor downstream of any horizontal offset below the roof.
• The combined secondary and primary roof drain system shall be sized based on double the rainfall rate for the local area.
• Shall comply with the requirements of Section 719.0

Cleanouts

• Rain leaders and conductors connected to a building storm sewer shall have a cleanout installed at the base of the outside leader or outside conductor before it connects to the horizontal drain.

Rainwater Sumps

• Serving public use" occupancy buildings shall be provided with dual pumps arranged to function alternately in case of overload or mechanical failure.

Traps on Storm Drains and Leaders

• When connected to combined sewer, floor and area drains shall be trapped.
• No traps required for leaders and conductors connected to a sewer carrying storm water exclusively.
• Trap size shall be same size as the horizontal drain to which they are connected.

Methods of Installation of combined sewer

• 1. Individual Storm-water traps serving each storm water inlet.
• 2. Single trap in the main storm drain just before its connection with the combined building sewer, shall be provided with cleanout on the outlet side of trap.

Leaders, Conductors, and Connections

• Roof Drains
• Shall not be used as soil, waste, or vent pipes
• Protection of leaders installed along alleyways, driveways, or other locations where exposed to damage shall be protected by metal guards, recessed into the wall, or constructed from ferrous pipe.
• Combining storm with sanitary drainage - building storm drain shall be connected in the same horizontal plane through single wye fittings to combined building sewer not less than 3m downstream from any soil stack.
• Shall be of cast-iron, copper or copper alloy, or plastic.
• Dome Type Strainer or Strainer for general use
• Strainers should extend not less than 4" above the surface of the roof.
• Strainers shall have a minimum inlet area no less than one and one-half (1 ½) times the area of the conductor or leader to which the drain is connected.
• Strainers for Flat Decks / Roof Deck Strainers
• Inlet area not less than 2 times the area of conductor or leader to which the drain is connected.
• Roof Drain Flashings
• Connection between the roof and roof drains that pass through the roof and into the interior of the building shall be made water tight
• Lead flashing material shall not be less than 4 pounds per square foot ($19.5 kg/m^2$)
• Copper flashing material shall not be less than 12 ounces per square foot ($3.7 kg/m^2$)

Size of Leaders, Conductors, and Storm Drains

• the sizing of roof drains, leaders, conductors, storm drains, storm sewers, and roof gutters shall be based on the latest rainfall rates issues by PAGASA.
• Vertical Conductors and Leaders

• Horizontal Storm Drains and Sewers

Size of Roof Gutters

• Vertical piping may be round, square or rectangular provided that the area of a rectangular piping shall have at least the equivalent cross-sectional area of a circular piping.
• Sidewalls Draining onto a Roof
  • (1) For 1 wall-add 50% of area of the wall to the roof area
  • (2) For 2 adjacent walls - add 35% of the total wall areas to the roof area
  • (3) For 2 adjacent walls of unequal height - add 35% of the total common wall and 50% of the remaining height of the highest wall
  • (4) For 2 walls opposite each other & of the same heights - add NO additional area
  • (5) For 2 walls opposite each other & of different heights - add 50% of the wall area above the top of lower wall
  • (6) Walls on 3 sides - add 50% of the area of the inner wall below the top of the lowest wall, plus allowance for the area of the wall above the top of the lowest wall, per (3) and (5) above.
  • (7) Walls of 4 sides - no allowance for wall areas below the top of the lowest wall - add for areas above the top of the lowest wall per 1, 3, 5, and 6 above.

Values of Continuous Flow

• When continuous flow discharge into the building storm drain or building storm sewer, as from a pump, ejector, air conditioning plant, or similar device a minimum of 1 gpm is equivalent to $2.2 m^2$ of roof area, based upon a rate of 4" per hour.

Controlled-Flow Roof Drainage

• water from a 25 year frequency storm shall not be stored on the roof exceeding 24 hours.
• During storm, the water depth on the roof shall not exceed the depths specified in Table 11-4
• No less than 2 drains shall be installed in roof areas of 10,000 ft2 ($929 m^2$) and additional 1 drain for every 10,000 ft2 of roof area.
• each roof drain shall have a precalibrated, fixed (nonadjustable), and proportional weir notched in a standing water collar inside the strainer. No mechanical devices or valves shall be allowed.
• Pipe sizing shall be based on calibrated flow rate (gpm) of the pre-calibrated weir for maximum allowable depth, and Tables 11-1 and 11-2.
• Rood design live load is not less than 30 lbs/ft2
• Scuppers shall be provided on parapet walls and openings shall no less than 4" high and width equal to the circumference of the roof drain required.
• At any wall or parapet, 45 degree cants shall be installed
• Separate storm and sanitary drainage systems shall be provided

Testing

• Required on new or existing building storm drainage system that have been altered, extended, or repaired.
• Shall be tested upon completion of rough piping's installation by air or water and proved tight.
• Plastic pipe shall not be tested with air.
• Water test - entire system, all openings shall be tightly closed except the highest opening and filled with water to the point of over flow. If tested in section, each opening shall be plugged except for the highest opening and shall be filled with water but no section shall be tested less than 3m head of water.
  Air test - closing all opening and forcing air into system of 5 psi using air compressor. Duration - the water shall be kept in system not less than 15 minutes before inspection.