Time Dose vs. “Pump & Dump” Michael A. Schwartz, P .E.
May 29, 2015
Time Dose vs. “Pump & Dump”
Michael A. Schwartz, P.E.
This is what we want to avoid, right!?
So here’s what we’ll learn about:
Basic System LayoutOperationsMajor Components of Each System•Identify differences for each system•Design criteria (engineering standpoint)•ExamplesField Example - Conversion
• Major Components of a Traditional Gravity System• Septic Tank• Distribution Box
• Drain field (Disposal Area)
Background
•Major Components of a Pump System• Septic Tank• Dose Chamber
Background
• Pump• Drainfield (Disposal Area)
Types of Pump Systems
• Septic Tank• Dosing Chamber• Pump• Conventional Disposal Area
• Raised or at Grade• Traditional Trench or Bed • Containing 4” PVC Diameter
Laterals (Non-pressurized)
“Pump & Dump”
Types
• Septic Tank• Dosing Tank • Pump• Conventional Disposal Area• Raised or at Grade
Time Dose
• Traditional Trench or Bed • Containing Small Diameter
Laterals (1”-2”)• Lateral with Orifices (small holes)• Pressurized System
Types
Typical Trench Cross-Section
Types
“Pump & Dump”• Float 1 – High Water
Alarm• Float 2 – Lag Pump On • Float 3 – Lead Pump On• Float 4 – Pumps Off• Float 5 – Redundant
Off / Low level Alarm
Time Dose• Float 1 – Lag Pump –
Timer Over-Ride (HWA) • Float 2 – Lead Pump -
Timer Over-Ride (HWA)• Float 3 – Pumps Off /
Timer Enable• Float 4 – Redundant
Off / Low level Alarm
Float Operation Comparison
Major Components
Septic Tank• Remains the same size for the 3 systems• Traditional Gravity• Pump & Dump• Time Dose
• Sizing is currently based on hold time• 24-hours or 72-hours (food service)• Exception (minimal size –typically 1,000
gals)• Purpose – Pretreatment (separate - solids,
FOG, liquid)
Septic Tank
Dosing Tank
Pump
Disposal Area
Major Components
Major Components
Septic Tank• Example #1• 2,400 gallons per day • Non-Food Service Establishment• Loamy Sand• Typically perform topographic and
boundary survey, soils evaluation and flow determination to determine constraints
• Septic Tank Size = 24-hour flow• Therefore minimum tank size = 2,400
gallons
Septic Tank
Dosing Tank
Pump
Disposal Area
Major Components
Major Components “Pump & Dump”:Dose Tank & Pump
“Pump & Dump”• Sizing• Dosing Chamber
• The liquid capacity of the dosing tank must be sufficient to dose the soil absorption field or bed no more than three (3) to four (4) times a day at design flow.
• Pump• Pumps should be sized to empty the dosing
tank in no more than 20 minutes. • Automatic alternating pumps shall be
provided in all systems where design flow exceeds 2,000 gallons/day and in locations where continuous reliability is essential.
Septic Tank
Dosing Tank
Pump
Disposal Area
Major Components
“Pump & Dump”• Example #2• 2,400 gallons per day • Non-Food Service Establishment• Loamy Sand• Since Flow > 2,000 gallons per day, design
system with 2 pumps
Septic Tank
Dosing Tank
Pump
Disposal Area
Major Components
“Pump & Dump”• Example #3• 2 Pumps to 1 Disposal Area• Dose Chamber = 2,400 / 3 = 800 gal• Dose Chamber = 2,400 / 4 = 600 gal• Dosing Tank Size = 1,000 gallon – 1,200
gallon
Septic Tank
Dosing Tank
Pump
Disposal Area
Major Components
“Pump & Dump”• Example #4• 2 Pumps to ½ of the disposal area each• Dose Chamber = 2,400 / 6 = 400 gal• Dose Chamber = 2,400 / 8 = 300 gal• Dosing Tank Size about 500-750 gallon
Septic Tank
Dosing Tank
Pump
Disposal Area
Major Components
“Pump & Dump”• Example #5• Pumps should be sized to empty the
dosing tank in no more than 20 minutes.• 300 gallons / 20 minutes = 15 gpm
(minimum)• Pumps need 2 items to specify
• GPM• TDH (Total Dynamic Head)
• TDH = Static Lift + Friction Lost• Friction Loss also known as “head lost” is
divided into two main categories, "major losses" associated with energy loss per length of pipe, and "minor losses" associated with bends, fittings, valves, etc.
Septic Tank
Dosing Tank
Pump
Disposal Area
Major Components
Major Components “Pump & Dump”:
Disposal Area
“Pump & Dump”• Disposal Area Sizing• Absorption systems shall be sized on the
basis of the maximum daily sewage flows, according to the following table:
Septic Tank
Dosing Tank
Pump
Disposal Area
Major Components
“Pump & Dump”• Example #6• 2,400 gallons/day • Non-Food Service Establishment• Loamy Sand• Assuming a trench layout:• Loamy Sand = 0.75 gal per day / square
foot• 2,400 g.p.d. / 0.75 g.p.d./sq.ft. = 3,200 sq.
ft.
Septic Tank
Dosing Tank
Pump
Disposal Area
Major Components
“Pump & Dump”• Example #7 – Network Layout• 3,200 sq. ft. bottom area required• Assume trench is 3’ wide: 3,200 / 3’ =
1,070 LF of trench required• Probably use 12 trenches that are 90 feet
long x 3’ wide with 4’ undisturbed earth between trenches.
• With 2 pumps, each pump would discharge to 6 of the 12 trenches.
Septic Tank
Dosing Tank
Pump
Disposal Area
Major Components
Time Dose
• Septic Tank• Dosing Tank • Pump• Conventional Disposal Area• Raised or at Grade
Time Dose
• Traditional Trench or Bed • Containing Small Diameter
Laterals (1”-2”)• Lateral with Orifices (small holes)• Pressurized System
Major Components
• Why Time Dose?• Pressure distribution is a recent modification to the
conventional dosed sewage system. Uniform distribution over the bottom area of the drain field is achieved and provides certain advantages over conventional systems as follows:1. Formation of the clogging mat is substantially delayed.2. System provides for unsaturated flow into underlying soil.3. System design is not limited to rectangular configuration.
Time Dose
Major Components
• Why Time Dose?
Time Dose
Same Different
Septic Tank x
Conventional Disposal Area x
Raised or at Grade x
Traditional Trench or Bed x
Containing Small Diameter Laterals (1”-2”) x
Lateral with Orifices (small holes) x
Pump x
Dosing Tank x
Major Components
• Order of Design• Septic Tank – Same (based on retention time)
• Disposal Area Network• Orifices (small holes) – Spacing & Size• Laterals Diameter
• Pump• Dosing Tank
Time Dose
Major Components
Major Components Time Dose:
Disposal Area
Time Dose
1. Configure Disposal Area Network2. Determine Length of Lateral• Example: 2,400 gallons per day, Non-Food
Service Establishment, Loamy Sand• Assuming a trench layout:
• Loamy Sand = 0.75 gal per day / sq. foot• 2,400 g.p.d. / 0.75 g.p.d./sq.ft. = 3,200 sq.
ft.• Assume trench is 3’ wide:
• 3,200 / 3’ = 1070 LF of trench required• Use 12 trenches that are 90 feet long x 3’
wide with 4’ undisturbed earth between trenches
Septic Tank
Disposal Area
Pump
Dosing Tank
Major Components
Time Dose
3. Determine “orifice” spacing and size• Michigan Criteria for Subsurface Sewage Disposal
reference “Pressure Distribution Network Design Manual,” Technical Guide for Pressure Mound Systems (June 2003 MDEQ)• Pressure distribution system design should generally comply with
currently accepted design practice including the following features:• Design shall provide uniform doses with no more than 0.5 gallons
per orifice per dose.• Distribution cell area per orifice shall not exceed 12 sq.ft.• To reduce orifice plugging, high head pumps are recommended.• Orifice shields should be provided.• Provisions for flushing must be incorporated at the ends of all
laterals.• Geotextile fabric which prevents the downward migration of fine
materials but allows for free passage of air and water should be placed over the stone in the distribution cell prior to placement of final cover.
Septic Tank
Disposal Area
Pump
Dosing Tank
Major Components
Time Dose
3. Determine “orifice” spacing and size• Distribution cell area per orifice shall not
exceed 12 sq.ft.• Spacing is typically 3-5 feet apart (some
health department code books dictate spacing.
• If the trench is 3’ wide and each orifice is to “distribute” effluent to 12 sq.ft. than spacing is 4’ apart
Septic Tank
Disposal Area
Pump
Dosing Tank
Major Components
Time Dose
3. Determine “orifice” spacing and size• Orifice sizes can range from 1/8” diameter
to 5/8” diameter.• Typically 1/8”, 3/16” or 1/4” diameter• 3/16” diameter is most common sized
used• Larger holes will be problematic on finding
a pump to produce adequate design flow• Some health departments provides
recommended size• Ultimately up to the design engineer
Septic Tank
Disposal Area
Pump
Dosing Tank
Major Components
Time Dose
4. Determine lateral pipe diameter
Septic Tank
Disposal Area
Pump
Dosing Tank
Want the 1st orifice to distribute approximately equal to the last orifice (this table is for 3/16” orifices)
Major Components
Time Dose
5. Determine Number of Orifices/Lateral• # of orifices = Length of Lateral / Spacing
of orifice• Example: 90 ft lateral / 4 ft spacing = 23
orificesSeptic Tank
Disposal Area
Pump
Dosing Tank
Major Components
Major Components Time Dose:
Pump
Time Dose
6. Determine Lateral Discharge Rate
Septic Tank
Disposal Area
Pump
Dosing Tank
If 3/16” orifice with 4 ft pressure = 0.83 gal/orifice23 orifice / lateral x 0.83 gal/orifice = 19.09 gal/lateral
Major Components
Time Dose
7. Determine Network Discharge Rate (zone)
• Determine how many laterals are in the network (per pump or zone) and multiple by GPM per lateral
• 12 trenches (laterals) with each pump utilizing 6 laterals each (network has 2 zones)
• 6 laterals x 19.09 gal / lateral = 114.5 gpm• This is the minimum pump flow required
Septic Tank
Disposal Area
Pump
Dosing Tank
Major Components
Time Dose• Pump Comparison Sizing• Pump & Dump”
• 20 minutes to empty septic tank• Time Dose
• # of orifices (more orifices = more gpm)• Size of Orifices (larger orifices = more gpm)• Spacing of orifices (closer space = more
gpm)• Example: 15 gpm vs. 114.5 (6 – 90’
trenches per pump)• Each on is dosing 1,600 sq ft of area• “Pump & Dump” = 20 minutes• Time Dose = very short timeframe
Septic Tank
Disposal Area
Pump
Dosing Tank
Major Components
Time Dose
8. Calculate Manifold Size 9. Determine the Total Dynamic Head• TDH = Static Lift + Friction Lost +
Perforation Head• Perforation head = 1.3(Q/(11.79*d^2))^2• Perforation head = 1.3(squirt height)
10. Select Pump• Pumps need 2 items to specify (GPM &
TDH) • Repeat if necessary
Septic Tank
Disposal Area
Pump
Dosing Tank
Major Components
Pump Curve
Major Components: Time Dose
Major Components Time Dose:
Dose Chamber
Time Dose
11. Determine Dose Volume• Technical Guide for Pressure Mound
Systems (June 2003 MDEQ)• Design shall provide uniform doses with no
more than 0.5 gallons per orifice per dose.• Example: 6 laterals with 23 orifices per
lateral = 138 orifices• 138 orifices x 0.5 gal per orifice dose rate =
69 gals per dose
Septic Tank
Disposal Area
Pump
Dosing Tank
Major Components
Time Dose
12. Calculate Run Time of Pump• Run Time = (Dose Volume + “Empty” Pipe
Volume) / Pump Rate• Example:
• Dose Volume = 69 gallons• Volume to “fill” pipe = 17 gallons• Pump Rate = 114.5 gpm• Run Time = (69 gal +17 gal) / 114.5 gpm =
0.75 minutes = 45 seconds
Septic Tank
Disposal Area
Pump
Dosing Tank
Major Components
Time Dose
13. Calculate Number of Doses/Day• Gallons per day = 2,400 • Gallons per dose = 69 • Doses per day = 2400 / 69 = 34 doses• Therefore each pump will operate 17
times per day
Septic Tank
Disposal Area
Pump
Dosing Tank
Major Components
Time Dose
• Calculation Check• Dose = 0.5 gallons / dose / orifice• # of doses per day = 17• Gallons per day / orifice = 8.5 gallons• Soil Load Rate 0.75 gal/sq. ft.• Each orifice is dosing 12 sq. ft.• Dose < 0.75 gal/sq. ft. x 12 sq. ft. = 9
gallons• Numbers check
Septic Tank
Disposal Area
Pump
Dosing Tank
Major Components
Time Dose
14. Calculate Programmable Timer Settings• Previous step determined number times a
pump turns on (34 times)• If want to equal dose over 22 hours
(account for peak days)• Duration is up to the design engineer• 22 hours x 60 min/hour = 1320 minutes• 1320 minutes / 34 times = 38.8 minutes• Therefore a pump will run 45 seconds and
no pump will run for 38 minutes• (76 minutes off time per pump)
Septic Tank
Disposal Area
Pump
Dosing Tank
Major Components
Time Dose
15. Size the Dose Chamber• Up to the judgment of the engineer• Based on off time and timing of incoming
flow Septic Tank
Disposal Area
Pump
Dosing Tank
Major Components
System Conversion
• Conversion of a “Pump & Dump” to a Time Dose System• Flushing Elementary, Flushing, MI
System Conversion
Existing Drain Field
System Conversion
Drawing
System Conversion
Existing Septic Tank / Pump Chamber
System Conversion
System Conversion
Existing Septic Tank / Pump Chamber
System Conversion
Existing Septic Tank / Pump Chamber
System Conversion
Existing Septic Tank / Pump Chamber
Proposed Drain Field
System Conversion
System Conversion
System Conversion
System Conversion
Construction
System Conversion
Construction
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System Conversion
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Construction
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Construction
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Construction
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Final Site Photos
System Conversion
System Conversion
Final Site Photos