ADOPTS WITHOUT AMENDMENTS:

International Private Sewage Disposal Code 2012 (IPSDC 2012)

Heads up: There are no amended sections in this chapter.
The provisions of this chapter shall govern the design and installation of mound systems.
A minimum of three soil borings per site shall be conducted in accordance with Chapter 4 to determine the depth to seasonal or permanent soil saturation or bedrock. Identification of a replacement system area is not required.
A mound system shall be prohibited on sites not having the minimum depths of soil specified in Table 902.2. The installation of a mound in a filled area shall be prohibited. A mound shall not be installed in a compacted area or over a failing conventional system.

TABLE 902.2
MINIMUM SOIL DEPTHS FOR MOUND SYSTEM INSTALLATION
RESTRICTING FACTOR MINIMUM SOIL DEPTH TO
RESTRICTION (inches)
High ground water 24
Impermeable rock strata 60
Pervious rock 24
Rock fragments (50-percent volume) 24

For SI: 1 inch = 25.4 mm.
Percolation tests shall be conducted at a depth of 20 inches to 24 inches (508 mm to 610 mm) from existing grade. Where a more slowly permeable horizon exists at less than 20 inches to 24 inches (508 mm to 610 mm), percolation tests shall be conducted within that horizon. A mound system shall be suitable for such site condition where the percolation rate is greater than 60 minutes per inch and less than or equal to 120 minutes per inch (2.4 min/mm to 4.7 min/mm).
Percolation tests shall be conducted at a depth of 12 inches to 18 inches (305 mm to 457 mm) from existing grade. Where a more slowly permeable horizon exists within 12 inches to 18 inches (305 mm to 457 mm), percolation tests shall be conducted within that horizon. A mound system shall be suitable for such site condition where the percolation rate is between 3 minutes per inch and 60 minutes per inch (0.12 min/mm and 2.4 min/mm).
Percolation tests shall be conducted at a depth of 20 inches to 24 inches (508 mm to 610 mm) from existing grade. Where a more slowly permeable horizon exists at less than 20 inches to 24 inches (508 mm to 610 mm), percolation tests shall be conducted within that horizon. A mound system shall be suitable for such site condition where the percolation rate is between 0 minutes per inch and 60 minutes per inch (0 min/mm and 2.4 min/mm).
A minimum of 24 inches (610 mm) of unsaturated natural soil shall be over creviced or porous bedrock.
A minimum of 24 inches (610 mm) of unsaturated natural soil shall be present over high ground water as indicated by soil mottling or direct observation of water in accordance with Chapter 4.
A mound shall not be installed on a slope greater than 6 percent where the percolation rate is between 30 and 120 minutes per inch (1.2 and 4.7 min/mm). The maximum allowable slope shall be 12 percent where there is a complex slope (two directions).
The mound shall be located so the longest dimension of the mound and the distribution lines are perpendicular to the slope. The mound shall be placed upslope and not at the base of a slope. The mound shall be situated so the effluent is not concentrated in one direction where there is a complex slope (two directions). Surface water runoff shall be diverted around the mound.
A minimum of 60 inches (1524 mm) of soil shall be present over uncreviced, impermeable bedrock. Where the soil contains 50 percent coarse fragments by volume in the upper 24 inches (610 mm), a mound shall not be installed unless there is at least 24 inches (610 mm) of permeable, unsaturated soil with less than 50-percent coarse fragments located beneath this layer.
For one- and two-family dwellings and other buildings with estimated waste water flows less than 600 gallons (2271 L) per day, the mound dimensions shall be determined in accordance with this section or Tables 903.1(1) through 903.1(12). Dimensions and corresponding letter designations listed in the tables and referenced in this section are shown in Appendix A, Figures A-6 through A-10. For buildings with estimated waste water flows exceeding 600 gallons (2271 L) per day, the mound shall be designed in accordance with this section. Daily waste water flow shall be estimated as 150 gallons (568 L) per day per bedroom for one- and two-family dwellings. For other buildings the total daily waste water flow shall be determined in accordance with Table 802.7.2.

TABLE 903.1(1)
DESIGN CRITERIA FOR A MOUND FOR A ONE-BEDROOM HOME ON A 0- TO 6-PERCENT SLOPE WITH LOADING RATES OF 150 GALLONS PER DAY FOR SLOWLY PERMEABLE SOIL
DESIGN PARAMETER SLOPE (percent)
0 2 4 6
A Trench width, feet 3 3 3 3
B Trench length, feet
Number of trenches
42
1
42
1
42
1
42
1
D Mound height, inches 12 12 12 12
F Mound height, inches 9 9 9 9
G Mound height, inches 12 12 12 12
H Mound height, inches 18 18 18 18
I Mound width, feeta 15 15 15 15
J Mound width, feeta 11 8 8 8
K Mound length, feet 10 10 10 10
L Mound length, feet 62 62 62 62
P Distribution pipe length, feet 20 20 20 20
Distribution pipe diameter, inches 1 1 1 1
Number of holes per distribution pipeb 9 9 9 9
Hole spacing, inchesb 30 30 30 30
Hole diameter, inchesb 0.25 0.25 0.25 0.25
W Mound width, feet 25 26 26 26

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon = 3.785 L.
  1. Additional width to obtain required basal area.
  2. Last hole is located at the end of the distribution pipe, which is 15 inches from the other hole.
TABLE 903.1 (2)
DESIGN CRITERIA FOR A TWO-BEDROOM HOME FOR A MOUND ON A 0- TO 6-PERCENT SLOPE WITH LOADING RATES OF 300 GALLONS PER DAY FOR SLOWLY PERMEABLE SOIL
DESIGN PARAMETER SLOPE (percent)
0 2 4 6
A Trench width, feet 3 3 3 3
B Trench length, feet
Number of trenches
42
2
42
2
42
2
42
2
C Trench spacing, feet 15 15 15 15
D Mound height, inches 12 12 12 12
E Mound height, inches 12 17 25 25
F Mound height, inches 9 9 9 9
G Mound height, inches 12 12 12 12
H Mound height, inches 18 18 18 18
I Mound width, feeta 12 20 20 20
J Mound width, feet 12 8 8 8
K Mound length, feet 10 10 10 10
L Mound length, feet 62 62 62 62
P Distribution pipe length, feet 20 20 20 20
Distribution pipe diameter, inches 1 1 1 1
Number of holes per distribution pipesb 9 9 9 9
Hole spacing, inchesb 30 30 30 30
Hole diameter, inches 0.25 0.25 0.25 0.25
R Manifold length, feet
Manifold diameter, inchesc
15
2
15
2
15
2
15
2
W Mound width, feet 42 46 46 46

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon = 3.785 L.
  1. Additional width to obtain required basal area.
  2. Last hole is located at the end of the distribution pipe, which is 15 inches from the other hole.
  3. Diameter dependent on the size of pipe from pump and inlet position.
TABLE 903.1(3)
DESIGN CRITERIA FOR A THREE-BEDROOM HOME FOR A MOUND ON A 0- TO 6-PERCENT SLOPE WITH LOADING RATES OF 450 GALLONS PER DAY FOR SLOWLY PERMEABLE SOIL
DESIGN PARAMETER SLOPE (percent)
0 2 4 6
A Trench width, feet 3 3 3 3
B Trench length, feet
Number of trenches
63
2
63
2
63
2
63
2
C Trench spacing, feet 15 15 15 15
D Mound height, inches 12 12 12 12
E Mound height, inches 12 17 20 25
F Mound height, inches 9 9 9 9
G Mound height, inches 12 12 12 12
H Mound height, inches 18 18 18 18
I Mound width, feeta 12 20 20 20
J Mound width, feeta 12 8 8 8
K Mound length, feet 10 10 10 10
L Mound length, feet 62 62 62 62
P Distribution pipe length, feet
Distribution pipe diameter, inches
Number of holes per distribution pipeb
Hole spacingb, inches
Hole diameter, inches
31
11/4
13
30
0.25
31
11/4
13
30
0.25
31
11/4
13
30
0.25
31
11/4
13
30
0.25
R Manifold length, feet
Manifold diameter, inchesc
15
2
15
2
15
2
15
2
W Mound width, feet 42 46 46 46

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon = 3.785 L.
  1. Additional width to obtain required basal area.
  2. First hole is located 12 inches from the manifold.
  3. Diameter dependent on the size of pipe from pump and inlet position.
TABLE 903.1(4)
DESIGN CRITERIA FOR A FOUR-BEDROOM HOME FOR A MOUND ON A 0- TO 6-PERCENT SLOPE WITH LOADING RATES OF 600 GALLONS PER DAY FOR SLOWLY PERMEABLE SOIL
DESIGN PARAMETER SLOPE (percent)
0 2 4 6
A Trench width, feet 3 3 3 3
B Trench length, feet
Number of trenches
56
3
56
3
56
3
56
3
C Trench spacing, feet 15 15 15 15
D Mound height, inches 12 12 12 12
E Mound height, inches 12 20 28 36
F Mound height, inches 9 9 9 9
G Mound height, inches 12 12 12 12
H Mound height, inches 24 24 24 24
I Mound width, feeta 12 20 20 20
J Mound width, feeta 12 8 8 8
K Mound length, feet 12 12 12 14
L Mound length, feet 80 80 80 84
P Distribution pipe length, feet
Distribution pipe diameter, inches
Number of holes per distribution pipeb
Hole spacing, inchesb
Hole diameter, inches
27.5
11/4
12
30
0.25
27.5
11/4
12
30
0.25
27.5
11/4
12
30
0.25
27.5
11/4
12
30
0.25
R Manifold length, feet
Manifold diameter, inchesc
30
2
30
2
30
2
30
2
W Mound width, feet 57 61 61 61

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon = 3.785 L.
  1. Additional width to obtain required basal area.
  2. Last hole is located at the end of the distribution pipe, which is 15 inches from the previous hole.
  3. Diameter dependent on the size of pipe from pump and inlet position.
TABLE 903.1(5)
DESIGN CRITERIA FOR A ONE-BEDROOM HOME FOR A MOUND ON A 0- TO 12-PERCENT SLOPE WITH LOADING RATES OF 150 GALLONS PER DAY FOR SHALLOW PERMEABLE SOIL OVER CREVICED BEDROCK
DESIGN PARAMETER PERCOLATION RATE (minutes per inch)
SLOPE (percent)
3 to 60 3 to less than 30
0 2 4 6 8 10a 12a
A Bed width, feetb 10 10 10 10 10 10 10
B Bed length, feet 13 13 13 13 13 13 13
D Mound height, inches 24 24 24 24 24 24 24
E Mound height, inches 24 26 29 31 34 36 38
F Mound height, inches 9 9 9 9 9 9 9
G Mound height, inches 12 12 12 12 12 12 12
H Mound height, inches 18 18 18 18 18 18 18
I Mound width, feet 12 13 14 17 18 21 26
J Mound width, feet 12 11 10 10 9 9 9
K Mound length, feet 12 12 12 13 13 13 15
L Mound length, feet 37 37 37 39 39 39 43
P Distribution pipe length, feetc
Distribution pipe diameter, inches
Number of distribution pipes
12.5
1
6
12.5
1
6
12.5
1
6
12.5
1
6
12.5
1
6
12.5
1
6
12.5
1
6
R Manifold length, feet
Manifold diameter, inchesc
6
2
6
2
6
2
6
2
6
2
6
2
6
2
S Distribution pipe spacing, feet 3 3 3 3 3 3 3
  Number of holes per distribution piped 6 6 6 6 6 6 6
  Hole spacing, inchesd 30 30 30 30 30 30 30
  Hole diameter, inches 0.25 0.25 0.25 0.25 0.25 0.25 0.25
W Mound width, feet 34 34 34 37 37 41 45

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon = 3.785 L, 1 minute per inch = 2.4 s/mm.
  1. On sites with a 10- to 12-percent slope, the fill depth (D) shall be reduced to a minimum of 1.5 feet or the bed width shall be reduced to decrease E [downslope fill depth, feet (mm)].
  2. Bed widths shall not be limited.
  3. Use a manifold with distribution pipes on only one side.
  4. Last hole is located at the end of the distribution pipe, which is 15 inches from the previous hole.
TABLE 903.1(6)
DESIGN CRITERIA FOR A TWO-BEDROOM HOME FOR A MOUND ON A 0- TO 12-PERCENT SLOPE WITH LOADING RATES OF 300 GALLONS PER DAY FOR SHALLOW PERMEABLE SOIL OVER CREVICED BEDROCK
DESIGN PARAMETER PERCOLATION RATE (minutes per inch)
SLOPE (percent)
3 to 60 3 to less than 30
0 2 4 6 8 10a 12a
A Bed width, feetb 10 10 10 10 10 10 10
B Bed length, feet 25 25 25 25 25 25 25
D Mound height, inches 24 24 24 24 24 24 24
E Mound height, inches 24 26 29 31 34 36 38
F Mound height, inches 9 9 9 9 9 9 9
G Mound height, inches 12 12 12 12 12 12 12
H Mound height, inches 18 18 18 18 18 18 18
I Mound width, feet 12 13 14 17 18 21 26
J Mound width, feet 12 11 10 10 9 9 9
K Mound length, feet 12 12 12 13 13 13 15
L Mound length, feet 49 49 49 51 51 51 55
P Distribution pipe length, feetc
Distribution pipe diameter, inches
Number of distribution pipes
12
1
6
12
1
6
12
1
6
12
1
6
12
1
6
12
1
6
12
1
6
R Manifold length, feet
Manifold diameter, inches
6
2
6
2
6
2
6
2
6
2
6
2
6
2
S Distribution pipe spacing, feet
Number of holes per distribution piped
Hole spacing, inchesd
Hole diameter, inches
3
5
30
0.25
3
5
30
0.25
3
5
30
0.25
3
5
30
0.25
3
5
30
0.25
3
5
30
0.25
3
5
30
0.25
W Mound width, feet 34 34 34 37 37 41 45

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon = 3.785 L, 1 minute per inch = 2.4 s/mm.
  1. On sites with a 10- to 12-percent slope, the fill depth (D) shall be reduced to a minimum of 1.5 feet or the bed width shall be reduced to decrease E [downslope fill depth, feet (mm)].
  2. Bed widths shall not be limited.
  3. This design is based on a manifold with distribution pipes on both sides. An alternative design basis is 24-foot distribution pipes, with manifold at the end.
  4. Last hole is located 9 inches from the end of the distribution pipe.
TABLE 903.1(7)
DESIGN CRITERIA FOR A THREE-BEDROOM HOME FOR A MOUND ON A 0- TO 12-PERCENT SLOPE WITH LOADING RATES OF 450 GALLONS PER DAY FOR SHALLOW PERMEABLE SOIL OVER CREVICED BEDROCK
DESIGN PARAMETER PERCOLATION RATE (minutes per inch)
SLOPE (percent)
3 to 60 3 to less than 30
0 2 4 6 8 10a 12a
A Bed width, feetb 10 10 10 10 10 10 10
B Bed length, feet 38 38 38 38 38 38 38
D Mound height, inches 24 24 24 24 24 24 24
E Mound height, inches 24 26 29 31 34 36 38
F Mound height, inches 9 9 9 9 9 9 9
G Mound height, inches 12 12 12 12 12 12 12
H Mound height, inches 18 18 18 18 18 18 18
I Mound width, feet 12 13 14 17 18 21 26
J Mound width, feet 12 11 10 10 9 9 9
K Mound length, feet 12 12 12 13 13 13 15
L Mound length, feet 62 62 62 64 64 64 68
P Distribution pipe length, feetc
Distribution pipe diameter, inches
Number of distribution pipes
18.5
1
6
18.5
1
6
18.5
1
6
18.5
1
6
18.5
1
6
18.5
1
6
18.5
1
6
R Manifold length, feet
Manifold diameter, inches
6
2
6
2
6
2
6
2
6
2
6
2
6
2
S Distribution pipe spacing, feet
Number of holes per distribution piped
Hole spacing, inchesd
Hole diameter, inches
3
8
30
0.25
3
8
30
0.25
3
8
30
0.25
3
8
30
0.25
3
8
30
0.25
3
8
30
0.25
3
8
30
0.25
W Mound width, feet 34 34 34 37 37 41 45

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon = 3.785 L, 1 minute per inch = 2.4 s/mm.
  1. On sites with a 10- to 12-percent slope, the fill depth (D) shall be reduced to a minimum of 1.5 feet or the bed width shall be reduced to decrease E [downslope fill depth, feet (mm)].
  2. Bed widths shall not be limited.
  3. Use a manifold with distribution pipes on only one side.
  4. Last hole is located at the end of the distribution pipe, which is 27 inches from the previous hole.
TABLE 903.1(8)
DESIGN CRITERIA FOR A FOUR-BEDROOM HOME FOR A MOUND ON A 0- TO 12-PERCENT SLOPE WITH LOADING RATES OF 600 GALLONS PER DAY FOR SHALLOW PERMEABLE SOIL OVER CREVICED BEDROCK
DESIGN PARAMETER PERCOLATION RATE (minutes per inch)
SLOPE (percent)
3 to 60 3 to less than 30
0 2 4 6 8 10a 12a
A Bed width, feetb 10 10 10 10 10 10 10
B Bed length, feet 50 50 50 50 50 50 50
D Mound height, inches 24 24 24 24 24 24 24
E Mound height, inches 24 26 29 31 34 36 38
F Mound height, inches 9 9 9 9 9 9 9
G Mound height, inches 12 12 12 12 12 12 12
H Mound height, inches 18 18 18 18 18 18 18
I Mound width, feet 12 13 14 17 18 21 26
J Mound width, feet 12 11 10 10 9 9 9
K Mound length, feet 12 12 12 13 13 13 15
L Mound length, feet 74 74 74 76 76 76 78
P Distribution pipe length, feetc
Distribution pipe diameter, inches
Number of distribution pipes
24.5
1
6
24.5
1
6
24.5
1
6
24.5
1
6
24.5
1
6
24.5
1
6
24.5
1
6
R Manifold length, feet
Manifold diameter, inches
6
2
6
2
6
2
6
2
6
2
6
2
6
2
S Distribution pipe spacing, feet
Number of holes per distribution piped
Hole spacing, inchesd
Hole diameter, inches
3
10
30
0.25
3
10
30
0.25
3
10
30
0.25
3
10
30
0.25
3
10
30
0.25
3
10
30
0.25
3
10
30
0.25
W Mound width, feet 34 34 34 37 37 41 45

For SI: 1 inch 25.4 mm, 1 foot = 304.8 mm, 1 gallon = 3.785 L, 1 minute per inch = 2.4 s/mm.
  1. On sites with a 10- to 12-percent slope, the fill depth (D) shall be reduced to a minimum of 1.5 feet or the bed width shall be reduced to decrease E [downslope fill depth, feet (mm)].
  2. Bed widths shall not be limited.
  3. Use a manifold with distribution pipes on only one side.
  4. Last hole is located 9 inches from the end of the distribution pipe.
TABLE 903.1(9)
DESIGN CRITERIA FOR A ONE-BEDROOM HOME FOR A MOUND ON A 0- TO 12-PERCENT SLOPE WITH LOADING RATES OF 150 GALLONS PER DAY FOR PERMEABLE SOIL WITH A HIGH WATER TABLE
DESIGN PARAMETER PERCOLATION RATE (minutes per inch)
SLOPE (percent)
0 to 60 0 to less than 30
0 2 4 6 8 10 12
A Bed width, feet 4 4 4 4 4 4 4
B Bed length, feet 32 32 32 32 32 32 32
D Mound height, inches 12 12 12 12 12 12 12
E Mound height, inches 12 13 14 14 16 17 18
F Mound height, inches 9 9 9 9 9 9 9
G Mound height, inches 12 12 12 12 12 12 12
H Mound height, inches 18 18 18 18 18 18 18
I Mound width, feet 9 10 11 12 13 14 15
J Mound width, feet 9 9 8 8 7 7 6
K Mound length, feet 10 10 10 10 10 11 11
L Mound length, feet 52 52 52 52 52 53 53
P Distribution pipe length 15.5 15.5 15.5 15.5 15.5 15.5 15.5
Distribution pipe diameter, inches 1 1 1 1 1 1 1
Number of distribution pipes 2 2 2 2 2 2 2
Number of holes per distribution pipea 7 7 7 7 7 7 7
Hole spacing, inchesa 30 30 30 30 30 30 30
Hole diameter, inches 0.25 0.25 0.25 0.25 0.25 0.25 0.25
W Mound width, feet 22 23 23 24 24 25 25

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon = 3.785 L, 1 minute per inch = 2.4 s/mm.
  1. Last hole is located at the end of the distribution pipe, which is 21 inches from the previous hole.
TABLE 903.1(10)
DESIGN CRITERIA FOR A TWO-BEDROOM HOME FOR A MOUND ON A 0- TO 12-PERCENT SLOPE WITH LOADING RATES OF 300 GALLONS PER DAY FOR PERMEABLE SOIL WITH A HIGH WATER TABLE
DESIGN PARAMETER PERCOLATION RATE (minutes per inch)
SLOPE (percent)
0 to 60 0 to less than 30
0 2 4 6 8 10 12
A Bed width, feet 6 6 6 6 6 6 6
B Bed length, feet 42 42 42 42 42 42 42
D Mound height, inches 12 12 12 12 12 12 12
E Mound height, inches 12 13 14 17 18 19 22
F Mound height, inches 9 9 9 9 9 9 9
G Mound height, inches 12 12 12 12 12 12 12
H Mound height, inches 18 18 18 18 18 18 18
I Mound width, feet 9 10 11 12 13 15 16
J Mound width, feet 9 9 8 8 7 7 6
K Mound length, feet 10 10 10 10 10 11 11
L Mound length, feet 62 62 62 62 62 64 64
P Distribution pipe length, feeta
Distribution pipe diameter, inches
Number of distribution pipes
20
1
4
20
1
4
20
1
4
20
1
4
20
1
4
20
1
4
20
1
4
R Manifold length, feet
Manifold diameter, inches
3
2
3
2
3
2
3
2
3
2
3
2
3
2
S Distribution pipe spacing, feet
Number of holes per distribution pipeb
Hole spacing, inchesb
Hole diameter, inches
3
9
30
0.25
3
9
30
0.25
3
9
30
0.25
3
9
30
0.25
3
9
30
0.25
3
9
30
0.25
3
9
30
0.25
W Mound width, feet 24 25 25 26 26 28 29

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon = 3.785 L, 1 minute per inch = 2.4 s/mm.
  1. Use a manifold with distribution pipes only on one side.
  2. Last hole is located at the end of the distribution pipe, which is 15 inches from the previous hole.
TABLE 903.1(11)
DESIGN CRITERIA FOR A THREE-BEDROOM HOME FOR A MOUND ON A 0- TO 12-PERCENT SLOPE WITH LOADING RATES OF 450 GALLONS PER DAY FOR PERMEABLE SOIL WITH A HIGH WATER TABLE
DESIGN PARAMETER PERCOLATION RATE (minutes per inch)
SLOPE (percent)
0 to 60 0 to less than 30
0 2 4 6 8 10 12
A Bed width, feet 8 8 8 8 8 8 8
B Bed length, feet 47 47 47 47 47 47 47
D Mound height, inches 12 12 12 12 12 12 12
E Mound height, inches 12 12 16 18 19 22 24
F Mound height, inches 9 9 9 9 9 9 9
G Mound height, inches 12 12 12 12 12 12 12
H Mound height, inches 18 18 18 18 18 18 18
I Mound width, feet 9 11 12 13 15 17 18
J Mound width, feet 9 9 8 8 7 7 6
K Mound length, feet 10 10 10 10 10 11 12
L Mound length, feet 67 67 67 67 69 69 71
P Distribution pipe length, feet
Distribution pipe diameter, inches
Number of distribution pipes
23
1
6
23
1
6
23
1
6
23
1
6
23
1
6
23
1
6
23
1
6
R Manifold length, feet
Manifold diameter, inches
64
2
64
2
64
2
64
2
64
2
64
2
64
2
S Distribution pipe spacing, feet
Number of holes per distribution pipea
Hole spacing, inchesa
Hole diameter, inches
32
10
30
0.25
32
10
30
0.25
32
10
30
0.25
32
10
30
0.25
32
10
30
0.25
32
10
30
0.25
32
10
30
0.25
W Mound width, feet 26 28 28 29 30 32 32

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon = 3.785 L, 1 minute per inch = 2.4 s/mm.
  1. Last hole is located at the end of the distribution pipe, which is 21 inches from the previous hole.
TABLE 903.1(12)
DESIGN CRITERIA FOR A FOUR-BEDROOM HOME FOR A MOUND ON A 0- TO 12-PERCENT SLOPE WITH LOADING RATES OF 600 GALLONS PER DAY FOR PERMEABLE SOIL WITH A HIGH WATER TABLE
DESIGN PARAMETER PERCOLATION RATE (minutes per inch)
SLOPE (percent)
0 to 60 0 to less than 30
0 2 4 6 8 10 12
A Bed width, feet 10 10 10 10 10 10 10
B Bed length, feet 50 50 50 50 50 50 50
D Mound height, inches 12 12 12 12 12 12 12
E Mound height, inches 12 14 17 19 22 24 26
F Mound height, inches 9 9 9 9 9 9 9
G Mound height, inches 12 12 12 12 12 12 12
H Mound height, inches 18 18 18 18 18 18 18
I Mound width, feet 9 11 13 14 17 18 19
J Mound width, feet 9 9 8 8 7 7 6
K Mound length, feet 10 10 10 10 11 11 12
L Mound length, feet 70 70 70 70 72 72 74
P Distribution pipe length, feet
Distribution pipe diameter, inches
Number of distribution pipes
24.5
1
6
24.5
1
6
24.5
1
6
24.5
1
6
24.5
1
6
24.5
1
6
24.5
1
6
R Manifold length, feet
Manifold diameter, inches
6
2
6
2
6
2
6
2
6
2
6
2
6
2
S Distribution pipe spacing, feet
Number of holes per distribution pipea
Hole spacing, inchesa
Hole diameter, inches
3
10
30
0.25
3
10
30
0.25
3
10
30
0.25
3
10
30
0.25
3
10
30
0.25
3
10
30
0.25
3
10
30
0.25
W Mound width, feet 28 29 31 32 34 35 36

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon = 3.785 L, 1 minute per inch = 2.4 s/mm.
  1. Last hole is 9 inches from the end of the distribution pipe.
The following symbols and notations shall apply to the provisions of this section.
A=Bed or trench width, feet (mm).
AA=Required absorption area, square feet (m2).
B=Bed or trench length, feet (mm).
BA=Basal area, square feet (m2).
C=Trench spacing, feet (mm).
CI=Infiltration capacity of natural soil, gallons per foot
per day (L/mm/day).
D=Fill depth, feet (mm).
E=Downslope fill depth, feet (mm).
F=Bed or trench depth, feet (mm).
G=Minimum cap and topsoil depth, feet (mm).
H=Cap and topsoil depth at center of mound, foot
(mm).
I=Downslope width, feet (mm).
J=Upslope width, feet (mm).
K=End slope length, feet (mm).
L=Total mound length, feet (mm).
N=Number of trenches.
P=Distribution pipe length, feet (mm).
R=Manifold length, feet (mm).
S=Distribution pipe spacing, feet (mm).
SD=Downslope correction factor.
SU=Upslope correction factor.
TW=Total daily waste-water flow, gallons per day
(L/day).
W=Total mound width, feet (mm).
X=Slope, percent.
The absorption area shall be sized based on the daily waste-water flow and the infiltrative capacity of the medium sand texture fill material, equaling 1.2 gallons per square foot (0.03 L/m2) per day. The required absorption area shall be determined by the following equation:
(Equation 9-1)
For SI: 1 square foot = 0.0929 m2, 1 gallon = 3.785 L.
Effluent shall be distributed in the mound through a trench system for slowly permeable soils with or without high ground water. Trench length shall be selected by determining the longest dimension perpendicular to any slope on the site. Trench width and spacing is dependent on specific site conditions. Trenches shall be 2 feet to 4 feet (610 mm to 1219 mm) wide. Trench length (B) shall be not more than 100 feet (2540 mm). Trenches shall be of equal length where more than one trench is required. A mound shall not have more than three trenches. Trench spacing (C) shall be determined by the following equation:
(Equation 9-2)
For SI: 1 gallon = 3.785 L, 1 square foot = 0.0929 m2.

The calculated trench spacing (C) shall be measured from center to center of the trenches. Facilities with more than 1,500 gallons (56 775 L) per day shall be specifically engineered and approved for use with a trench system.

A long, narrow bed design shall be used for permeable soils with high water tables. The bed shall be square or rectangular for shallow permeable soils over bedrock. The bed length (B) shall be set after determining the longest dimension available and perpendicular to any slope on the site.
The mound height consists of the fill depth, bed or trench depth, the cap and topsoil depth.
The fill depth (D) shall be not less than 1 foot (305 mm) for slowly permeable soils and permeable soils with high water tables and not less than 2 feet (610 mm) of fill shall be required for shallow permeable soils over bedrock. Additional fill shall be placed at the downslope end of the bed or trench where the site is not level so the bottom of the bed or trenches is level. The downslope fill depth for bed systems shall be determined by the following equation:
E = D + XA(Equation 9-3)

For SI: 1 foot = 304.8 mm.

The downslope fill depth for trench systems shall be determined by the following equation:

E = D + X (C + A)(Equation 9-4)

For SI: 1 foot = 304.8 mm.

The bed or trench depth (F) shall be not less than 9 inches (229 mm) and not less than 6 inches (152 mm) of aggregate shall be placed under the distribution pipes and not less than 2 inches (51 mm) of aggregate shall be placed over the top of the distribution pipes.
The cap and topsoil depth (H) at the center of the mound shall be not less than 18 inches (457 mm), which includes 1 foot (305 mm) of subsoil and 6 inches (152 mm) of topsoil. Outer edges of the mound, G (the minimum cap and topsoil depth), shall be not less than 1 foot (305 mm), which includes 6 inches (152 mm) of subsoil and 6 inches (152 mm) of topsoil. The soil used for the cap shall be topsoil or finer textured subsoil.
The total mound length (L) shall be determined by the following equation:
L = B + 2K(Equation 9-5)

For SI: 1 foot = 304.8 mm.

where:

The mound width for a bed system shall be determined by the following equation:

W = J + A + I (Equation 9-6)

For SI: 1 foot = 304.8 mm.

The mound width for a trench system shall be determined by the following equation:

(Equation 9-7)

For SI: 1 foot = 304.8 mm.

where:
J = 3(D + F + G)SU

I = 3(E + F + G)SD

The upslope correction factor (SU) and the downslope correction factor (SD) shall be determined based on the slope in accordance with Table 903.5.5.

TABLE 903.5.5
DOWNSLOPE AND UPSLOPE WIDTH CORRECTIONS
FOR MOUNDS ON SLOPING SITES
SLOPE
(percent)
DOWNSLOPE
CORRECTION FACTOR
(SD)
UPSLOPE
CORRECTION FACTOR
(SU)
0 1 1
1 1.03 0.97
2 1.06 0.94
3 1.10 0.915
4 1.14 0.89
5 1.18 0.875
6 1.22 0.86
7 1.27 0.83
8 1.32 0.80
9 1.38 0.785
10 1.44 0.77
11 1.51 0.75
12 1.57 0.73
The minimum basal area required shall be determined by the following equation:

(Equation 9-8)

For SI: 1 square foot = 0.0929 m2.

The infiltrative capacity of natural soil shall be determined on the percolation rate in accordance with Table 903.6.

TABLE 903.6
INFILTRATIVE CAPACITY OF NATURAL SOIL
PERCOLATION RATE
(minutes per inch)
INFILTRATIVE CAPACITY
(gallons per foot per day)
Less than 30 1.2
30 to 60 0.74
More than 60 to 120 0.24

For SI: 1 gallon per foot per day = 0.012 L/mm/day,
  1 minute per inch = 2.4 s/mm.
The available basal area for a bed system shall be determined by one of the following equations:
BA = B( A + I) for sloping sites (Equation 9-9)
BA = BW for level sites(Equation 9-10)
For SI: 1 square foot = 0.0929 m2.
The available basal area for a trench system shall be determined by one of the following equations:
for sloping sites(Equation 9-11)
for level sites (Equation 9-12)
For SI: 1 square foot = 0.0929 m2.
The downslope width (I) on a sloping site shall be increased or the upslope width (J) and downslope (I) widths on a level site shall be increased until sufficient area is available if the basal area available is not equal to or greater than the basal area required.
The dose volume and pump shall conform to the requirements of Chapters 7 and 8.
Construction shall not commence where the soil is so wet a soil wire forms when the soil is rolled between the hands. Installation of mound systems where the soil on the site is frozen shall be prohibited for new construction.
Excess vegetation shall be cut and removed from the mound area. Small trees shall be cut to grade surface, leaving the stumps in place.
The force main from the pumping chamber shall be installed before the mound site is plowed. The force main shall be sloped uniformly toward the pumping chamber so the force main drains after each dose.
The site shall be plowed with a moldboard plow or chisel plow. The site shall be plowed to a depth of 7 inches to 8 inches (178 mm to 203 mm) with the plowing perpendicular to the slope. Rototillers shall not be used. The sand fill shall be placed immediately after plowing. All foot and vehicular traffic shall be kept off the plowed area.
The fill material shall be medium sand texture defined as 25 percent or more very coarse, coarse and medium sand and a maximum of 50 percent fine sand, very fine sand, silt and clay. The percentage of silt plus one and one-half times the percentage of clay shall not exceed 15 percent. Fill materials with higher content of silt and clay shall not be used.
The medium sand fill shall be moved into place from the upslope and side edges of the plowed area. Vehicular traffic shall be prohibited in the area extending to 25 feet (7620 mm) beyond the downslope edge of the mound. The sand fill shall be moved into place with a track-type tractor and not less than 6 inches (152 mm) of sand shall be kept beneath the tracks at all times.
The bed or trenches shall be formed within the sand fill. The bottom of the trenches or bed shall be level. The elevation of the bottom of the trenches or bed shall be checked at the upslope and downslope edges to ensure that the fill has been placed to the proper depth.
A minimum of 6 inches (152 mm) of coarse aggregate ranging in size from 1/2 inch to 21/2 inches (12.7 mm to 64 mm) shall be placed in the bed or trench excavation. The top of the aggregate shall be level.
Distribution systems shall be placed on the aggregate, with the holes located on the bottom of the distribution pipe. The ends of all distribution pipes shall be marked at the surface, and an observation pipe shall be placed to the bottom of the bed or each trench.
The top of the bed or trenches shall be covered with not less than 2 inches (51 mm) of aggregate ranging in size from 1/2 inch to 21/2 inches (12.7 mm to 64 mm) and not less than 4 inches to 5 inches (102 mm to 127 mm) of uncompacted straw or marsh hay or approved synthetic fabric shall be placed over the aggregate. Cap and topsoil covers shall be in place and the mound shall be seeded immediately and protected from erosion.
When the septic tank is pumped, the pump chamber shall be inspected and pumped to remove any solids present. Excess traffic in the mound area shall be avoided.
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