System Design; System Sizing; Design Procedure - Infiltrator Presby Advanced Enviro-Septic Design And Installation Manual

2.0 SYSTEM DESIGN

2.1 System Sizing

All residential AES systems require the use of 70 linear feet (lf) of AES pipe per bedroom (br). In non-residential or
commercial applications, divide the DDF by 2.14 gal to calculate the minimum amount of AES pipe required.
In accordance with the Rules, daily design flow (DDF) is calculated as follows: the minimum flow rate shall be one
hundred twenty gallons (120 gals.) per day per bedroom. When the occupancy of a single family dwelling exceeds
two (2) persons per bedroom, the volume of sewage shall be determined by the maximum occupancy at a rate of
sixty gallons (60 gals.) per person per day.
The minimum absorption area (known as the system sand bed area or SSBA) for the AES system is determined
using the formulas provided in Table A below and is based on the soil loading rate (SLR) as established by a soil
morphology evaluation.
Table A: AES Minimum Pipe Requirements and System Sizing Formulas for Residential Systems
Actual Soil Loading
Rate at Site
2
(gpd/ft )
1.20 – 0.30
0.29 – 0.10

2.2 Design Procedure

Step #1: Determine System Sand Bed Area (SSBA) Required
Based upon the SLR on the site as established by a soil morphology evaluation, use the formulas from
Table A above to calculate the minimum SSBA required.
Step #2: Calculate the Minimum Amount of AES Pipe Needed
Residential systems: multiply the number of bedrooms in the design by 70 ft.
Non-residential or commercial applications: divide the DDF by 2.14.
This results in the minimum amount of AES pipe that must be used in the system.
Step #3: Determine Row Length and Quantity Needed
Select a row length suitable for the site and calculate the number of rows needed (round up to whole
number).
Step #4: Determine Pipe Layout Width (PLW)
Calculate the PLW using a 1.5 ft minimum center-to-center row spacing (larger spacing allowed).
Formula for PLW = [(# of rows – 1) * spacing (1.5)] + 1.
Step #5: Determine Minimum System Sand Bed Width (SSBW)
Calculate the minimum SSBW by dividing the SSBA from Step #1 by the selected row length from Step #3
+ 1 ft (1 ft allows for 6 inches of sand on each end of the AES rows).
Step #6: Verify Final Bed Width Requirements
a) Beds sloping 5% or less: If the minimum SSBW is less than the PLW + 1 ft, use (PLW + 1 ft) as the new
minimum SSBW.
b) Beds sloping > 5%: If the minimum SSBW is less than the PLW + 3.5 ft, use PLW + 3.5 ft as the new
minimum SSBW. Adding 3.5 ft to the pipe layout width accounts for the minimum required 2.5 ft
© Presby Environmental, Inc., Design & Installation Manual, September 2020 Edition
Minimum
AES Pipe System Sand Bed Area
per Bedroom (SSBA) Formula
(ft)
70
SSBA = DDF/SLR * 0.90
70 SSBA = DDF/SLR
Soil Loading Rate
Rule Reference
Table 13
Table 14
6