
2018 Indiana Design and Installation Manual
17
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3.1 Subsurface Bed Design Example
Example 2: Subsurface Bed System – A42 Modules – 0.0 – 0.5% Slope
House size:
4 Bedrooms
Design Flow:
600 gpd
Soil Loading Rate:
0.3 gpd/ft
2
Absorption Field Type:
Bed
Site Slope:
Less than 0.5%
Calculate Minimum Basal Area and Units Required
Refer to Table 4 for the minimum number of units and minimum basal area required for installation.
Units required per bedroom x bedrooms = Total units required
A42: 12 units/bedroom x 4 bedrooms = 48 A42s
B43: 10 units/bedroom x 4 bedrooms = 40 B43s
Calculate Minimum Bed Basal Area Length
For This Example, Assume the Number of Bed Rows Equals Two (this encourages the longest and
narrowest subsurface bed design):
Modules per row: Modules Needed ÷ Rows
A42: 48 units ÷ 2 rows =
24 modules per row
A42: 24 units x 4 ft/unit +1 ft = 97 linear ft
B43: 40 units ÷ 2 rows =
20 modules per row
B43: 20 units x 4 ft/unit +1 =
81 linear ft
Calculate Bed Basal Area Width
a) Minimum A42 Basal Area Width
a) A42: Rows x 3 ft = 2 x 3 ft =
6 ft
or
b) Proposed Basal Area Width
b) Minimum Basal Area ÷ Length of System
b) A42: 1340 ft
2
÷ 97 ft = 13.8 ft,
b) round to
14 ft
A42: Use greater width of a or b:
14 ft
a) Minimum B43 Basal Area Width
a) B43: Rows x 4 ft = 2 x 4 ft =
8 ft
or
b) Proposed Basal Area Width
b) Minimum Basal Area ÷ Length of System
b) B43: 1340 ft
2
÷ 81 ft = 16.5 ft,
b) round to
17 ft
B43: Use greater width of a or b:
17 ft
Determine Lateral Spacing
Lateral to Lateral Spacing = Bed Width ÷ Rows
A42: 14 ft ÷ 2 rows =
7 ft
B43: 17 ft ÷ 2 rows =
8.5 ft
Upper Edge to Lateral Spacing = Lateral to Lateral Spacing ÷ 2
A42: 7 ft ÷ 2 =
3.5 ft
B43: 8.5 ft ÷ 2 =
4.25 ft
3
4
5
0.3
1005
1340
1675
12
10
Soil
Loading
Rate
(gpd/sf)
Minimum Basal Area Required
(Square Feet)
Bedrooms per House
A42
Modules per
Room
B43
Modules per
Room
A42
B43
A42
B43
Slope
Lateral to Lateral Spacing
Upper Edge to Lateral Spacing
Less than or
Equal to 0.5%
Lateral to Lateral Spacing ÷ 2
Basal Area width divided by
number of rows
Содержание GSF A42
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