2.0 SYSTEM DESIGN
© Presby Environmental, Inc., Design & Installation Manual, July 2020 Edition
6
2.1 Sizing
Table B: Minimum Design Flow, EnviroFin Units and System Sand Bed Area Required
Percolation Rate
(mpi)
EF Soil
Loading
Rate (SLR)
(gpd/ft²)
Number of Bedrooms & Design Flow (150 gpd per Bedroom)
Commercial Units
1
2
3
4
5
6
7
(75 gpd per EF Unit)
Minimum Number of EnviroFin Units (75 gpd per EF Unit)
(1, 2)
Commercial
Sizing per
100 gpd
(3)
2
4
6
8
10
12
14
Up to 10
6.74
34
45
67
90
112
134
156
14.84
11 - 15
4.49
51
67
101
134
168
201
234
22.28
16 - 20
3.37
67
90
134
179
223
268
312
29.68
21 - 25
2.69
84
112
168
224
279
335
391
37.18
26 - 30
2.25
100
134
200
267
334
400
467
44.45
31 - 35
1.92
118
157
235
313
391
469
547
52.09
36 - 40
1.68
134
179
268
358
447
536
625
59.53
41 - 45
1.50
150
200
300
400
500
600
700
66.67
46 - 50
1.35
167
223
334
445
556
667
778
74.08
51 - 55
1.22
185
246
369
492
615
738
861
81.97
56 - 60
1.12
201
268
402
536
670
804
938
89.29
Minimum System Sand Bed Area (ft
2
)
1. For additional bedrooms, multiply number of bedrooms by 150 gpd to determine total design flow; divide total design flow
by 75 gpd & round up to determine number of EF units; and then divide total design flow by the appropriate EF SLR to
determine minimum system sand bed area (SSBA).
2. For residential use, the number of EF units may be calculated at 150 gal/unit when using an Aquaworx Remediator (see page 22).
Consult technical support for commercial use. Minimum SSBA requirements are not impacted by this change in specifications.
3. For one-bedroom applications, area calculations are based on a design flow of 225 gpd per Env-Wq 1000 rules.
4. Consult PEI for high strength effluent requirements.
2.2 Design Layout
The EF units can be arranged in many different configurations and shapes to accommodate an array of site
challenges, provided the minimum full depth system sand bed treatment area and minimum system sand dispersal
area for the site soils (percolation rate) are utilized. For simplicity, this manual divides the EF design layout into
two basic shapes, rectangular and circular. Multi-Level™ beds are a variation of rectangular layouts. Beds may
incorporate system sand extensions (SSE), which may have irregular shapes and are allowed to slope with the
existing terrain up to 33%. The bottom of the treatment fins must always remain level.
Rectangular Design Layout
Utilizes minimum spacing to create efficient designs and minimize the amount of system sand required. Allows for
systems to be divided into multiple, single unit, EF beds using a D-box to split flows. Individual beds may be sized
for different soils (percolation rates) within the same system and site. Reference Env-Wq 1008.05(f) to determine
setback distances between separate beds.
Design Procedure
Task 1: Determine Number of EnviroFin Units Needed
Using the daily design flow (DDF) (number of bedrooms x 150 gal for residential or gpd for commercial), find the
minimum number of EF units required from Table B or calculate the number of units required manually.