ADPH – PUBLIC HEALTH AREA VIII TRAINING FOR PROFESSIONAL ENGINEERS And Associated Onsite System Professionals

3. One of the 6 factors (Rule 420-3-1-.71)
Certain limits for OSS on steeper slopes
There are 4 soil related factors
And 2 site related factors
All are to be evaluated on each site

4. What is the slope?
% Slope = (Rise ÷ Run) x 100
Rise 40 ft
Run
100 ft
% Slope =
(40/100) x 100 =
40%

5. • Requires Engineer Design
• Start with Table 4 in Rules
• Rules require
Deeper trenches
More space between trenches
More cover over trenches

6. Minimum
Minimum
Trench
Cover
Depth**
Percent
Slope
26-30
31-40
Trench Spacing (Side
Wall to Side Wall)*
6 feet
7 feet
28”
33”
16”
21”

7. Table 4
Slope
Spacing of Trenches
Based on Width of Trench
and Slope
* The distances between trenches are
measured between adjacent sidewalls.
** If the minimum trench depth is
measured on the downhill side of the
trench, the minimum cover as listed
in the table should be assured.

8. Some general guidelines are:
• Make a detailed evaluation of the site to
determine options
Generally, the larger the lot, the more options
The steeper the slope, the more difficult to overcome
• Select the best location and landform
• Keep it as simple as possible
• Use a pump (effluent) if needed
• Renew your liability insurance
Then:
• If it doesn’t pass the “feel good” test; walk away

9. • Gravity
• Erosion
• Soil Stability
• Variable Soil Depth
• Shallow Rock
• Surface Water
• Spring Activity

10. Certain Landforms
• Headslopes
• Toeslopes
• Depressions
• (These are all concave
shapes)
• Also:
• Drains
• Rock Outcrops
• Complex Slopes

12. Focus On The Better
Landforms Where
Waters Diverge
• Convex Ridges,
Sideslopes

14. Requires deep soils
Must meet setbacks
• Uphill
• Downhill
• Over Rock

16. .67(2)c
Requires geologist’s report & PSC map
(subject to LHD)

18. .67(2)f
Does not allow downhill pushover fill for EDF for
>25% slope

20. The amount of wastewater that can be
applied each day over an indefinite
period of time to a square foot of soil
such that the effluent is absorbed and
properly treated.

21. 1
Horizontal Flow
2
3

22. If Benching is proposed
• Setbacks may be difficult to meet
• 25’ setback from uphill cut unless pretreatment
• 25’ setback from downhill slope over 40%
Consider Drip technology

23. Try to read and interpret
• Landforms
• Soils
• Water movement & concentration
Use these to best advantage – avoid bad
locations
Design for the long term
Call in other professionals if needed

25. Permeability
Depth To ASHES (ave
seasonal high
extended saturation)
Depth To Rock and
Other Restrictions
Slope and Landform
Limitations
Flooding Frequency
Hydric Soils

26. ABILITY OF SOIL TO ALLOW
WATER TO PASS THRU IT
Permeability is
affected by anything
that affects PORES
(pathways for
water to travel)
Texture
Structure
Consistence
Bulk Density
Clay Mineralogy
Dissimilar Layers

28. From Surface To Gray
Colors
Chroma 2 or less
2% or more of the volume
6” or more thick

29. >2%
6”
Thick

30. OBVIOUS COLOR
CONTRAST
LESS OBVIOUS

32. HARD VS. SOFT ROCK

33. THEY SAID DIDN’T FLOOD
WATER FRONT LOTS FOR
SALE

34. SOUTH AL HYDRIC SOIL
NORTH AL HYDRIC SOIL

35. If perc test are used check results against
what the soil says
Some signs are obvious
Some are more subtle

36. A 10 min/Inch perc
rate during the dry
season in a sticky,
plastic clay in an area
dominated by cedars
and red buds is a...
Non-Representative
Perc Result.

37. A 10 Min/Inch Perc
Rate In A Soil With A
Sandy Loam Texture
But Has A High Bulk
Density Layer at ~ 24”
(Fragipan)
Is Also NonRepresentative

38. A 10 min/inch perc
rate at 12” in this
sandy topsoil is likely
System may actually
be underdesigned
for the long term
Because of the clay
texture just below.

39. Consider all 6 factors or limitations
Interpret the soil and site characteristics
Compare test results w/ what’s present
If questions arise – ask for assistance
If we can a avoid a problem down the
road - we all win

41. Filling a drainage channel for an EDF is
not recommended
Most undisturbed natural soils are stable
• They can be trusted to stay in place and retain
their integrity
Fill requires time to develop stability
• Or use stabilizing practices
Establish vegetation
Retaining walls
Extended shoulders (aprons)

43. Table 15
SYSTEM
LIMITATION
ENGINEERED
CONVENTIONAL
SLIGHT
MODERATE
SEVERE
EXTREME
AT Required
1. Percolation
(Min/In) (1)
5-30
31-90
91-120
1-<5
121-240
>240
1a MVS (2) from
Redox(3)
24
18
18
36
18
12
1b MVS from
Hard Rock
18
18
18
18
12
1c MVS from
Other R/L (4)
12
12
12
12
6
Min trench depth
for above
12” below NGS Natural Ground Surface (3)
1-<5<1
24
w/AT
May vary but either 6” above or below(not
exactly at) the fill/soil interface
2% Slope (%)
0-15
16-25
26-40
>40 (7)
3. Flooding Frequency
Chance/Year
None
Rare
<5%
Occasional
5-50%
Frequent (7)
>50%
4. Landform
(Slope Position)
Summit
Shoulder
Back &
Other
Linear or
Convex
Lower Back
Foot & Other
Slightly
Concave
Toe
Head
Depression
& Other Concave
Swamp, Wetlands, Floodplain
Drain, Gully, Mine Spoil, Hydric
Soil Area (7)

44. Conv
Conv
Perc
Rate
5-60
MVS
/2
Hard
Rock
Soft
Rock
Other
Eng
Eng
61-90 91120
120240
24”
18”
18”
18”
18”
18”
18”
18”
>240 1-<5
w/AT 1-<5
12”
36”
24”
12”
24”
12”
12”
12”
12”
6”
24”
12”
12”
12”
12”
6”
24”
7-15
16-25 26-40
Slope 0-6
Conv
Eng*
> 40