Design Examples - Infiltrator Presby Advanced Enviro-Septic Design And Installation Manual

2.0 SYSTEM DESIGN
system sand extension on the down slope side of the AES system. [Please see sections titled "System
Sand Extensions (SSE)" on page 9 and "Elevated Bed Systems" on page 10].
Step #7: Calculate System Sand Extension (SSE):
a) Beds sloping 5% or less: SSE is divided in half and placed evenly on each side of AES pipes. Formula for
SSE on level sites [SSBW – (PLW + 1)] ÷ 2. There will be no SSEs if the SSBW ≤ PLW +1 ft.
b) Beds sloping > 5%: SSE placed entirely on the down slope side of the bed. Formula for SSE = SSBW –
(PLW + 1) and must be at least 2.5 ft (3 ft from the edge of the AES Pipe).

2.3 Design Examples

Design Example #1:
Single family residence, 4 bedrooms (480 gpd), SLR = 1.00 gpd/ft², level site, vertical separation greater than 2
feet.
Step #1: Determine System Sand Bed Area (SSBA) Required
SSBA: 480 gpd ÷ 1.00 gpd/ft² = 480 ft². 480 ft² * 0.90 = 432 ft².
Step #2: Calculate the Minimum Amount of AES Pipe Needed
AES pipe required: 70 ft/br * 4 br = 280 ft minimum.
Step #3: Determine Row Length and Quantity Needed
Using a row length of 70 ft requires 4 rows (280 ft ÷ 70 ft = 4 rows).
Step #4: Determine Pipe Layout Width (PLW)
PLW = [(4 – 1) * (1.5)] + 1 = 5.5 ft.
Step #5: Determine Minimum System Sand Bed Width (SSBW)
Minimum SSBW = 432 ft² ÷ (70 ft + 1 ft) = 6.08 ft (round up to 6.5 ft for ease of construction).
Step #6: Verify Final Bed Width Requirements
a) Beds sloping 5% or less: Minimum SSBW of 6.5 ft is equal to PLW +1 (5.5 ft + 1 ft.). Use Minimum
SSBW for design.
b) Not Applicable.
Step #7: Calculate System Sand Extension (SSE):
a) Beds sloping 5% or less: SSE is divided in half and placed evenly on each side of AES pipes. SSE = [6.5 ft
– (5.5 + 1)] ÷ 2 = 0.0 ft. No system sand extensions are needed for this design.
b) Not Applicable
Illustration of Example #1:
© Presby Environmental, Inc., Design & Installation Manual, September 2020 Edition 7