time dose vs. pump & dump - mike schwartz

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

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Existing Septic Tank / Pump Chamber

System Conversion

Existing Septic Tank / Pump Chamber

Proposed Drain Field

System Conversion

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Construction

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Final Site Photos

System Conversion

System Conversion

Final Site Photos

Do You Have Questions?

Thank you.

E-mail Mike: Michael A. Schwartz, P.E.mschwartz@preinnewhof.com