1. OWTS Design Considerations Under Reg. 43
Presented by: Chuck Cousino, Onsite Wastewater Treatment System Coordinator, CDPHE
To: 2014 CPOW Annual Conference
Date: January 17, 2014

2. Questions that need to be addressed:
What are the major changes to the Regulations relative to OWTS design?
How do these changes effect what I do? Walk-through various design scenario’s

3. What Are some Major Changes in the new Regulations?
A major step toward “Performance Based Standards”.
(Let’s call them “Advanced Prescriptive”)
Allow for expanded design options to overcome site specific restrictions (may vary; local code decisions)
Allow for reduction in system size by incorporating proven technologies that reduce organic loading (local code decisions)
Requires enhanced OWTS system operation & maintenance oversight

4. Reg. 43 Highlights
Bed systems : Maximum width allowed will be 12’ (unless TL2+ or in repair situations; Local decision)
Trench length may now be 150’ if pressure distribution is utilized (Upon local approval)
Maximum depth to the soil treatment interface is 48” from ground surface
Percolation tests can still be conducted; However, now specific requirements on “how” they should be conducted.
Refer to section 43.5(D)
Focus on Long Term Acceptance Rate (LTAR) vs. only the percolation rate (Table 10.1)
How many Gallons/Sq.Ft./Day will this soil accept ?

5. Under ISDS, we used a… Soil Profile Hole Reg. 43 Highlights, cont.
A “Visual and Tactile” evaluation of the soils shall be conducted
Shall be conducted by a “competent technician “.
Optional until July 1, 2016; then required; (allows for a training period)
Focus on soil structure; Redoxymorphic features; restrictive layers; other visual items
Under ISDS, we used a…
Soil Profile Hole
Where on the site; hole dimensions; at what depth; hole prep; pre-soaking req’s., etc..

6. New Term: Soil Profile Test Pit Excavations
“Visual & tactile” evaluation of the soil

7. STRUCTURE

8. With all of this said… We need to realize that the majority of septic systems that will be installed in the upcoming years will most likely be “conventional gravity on-site wastewater treatment systems”. Properly sited, properly installed, properly maintained, a conventional gravity OWTS can be the best option for many sites
Chuck here…
Education of use & O/M

9. AWAY !! However, lets be mindful that…
Many feel that their septic system is “working” if they flush, and it goes where….
AWAY !!
Is the system really functioning (treating), or are just making sure that it goes away ?
We can do a better job of designing, installing and operating our Onsite Wastewater Treatment Systems.

10. How Reg. 43, Basic Design 101 Class; ISDS vs. OWTS
do these changes effect what I do?
Reg. 43, Basic Design 101 Class;
ISDS vs. OWTS
Let’s see how the designs compare…
What has changed???

11. 98 97 High Mountain Rd. 100 4-Bedroom Home 99 1,250 Gal. Septic Tank
Well
4-Bedroom Home
1,250 Gal. Septic Tank
Replacement Area
100 99 98 97
Old ISDS Design
Rock and Pipe Trench Installation
System Sizing; Daily Flow
4 Bedrooms x 150 = 600 gpd
600 gpd x 1.5 = 900 gpd = Q
Percolation Rate = “t” = 25 mpi
Q x square root “t”
A = 5
A = = 900 Sq.Ft.
Trench size: 3’ x 60’ = 180 Sq.Ft.
5 trenches x 180 = 900 Sq.Ft.
Note: Some Counties have additional requirements for proposed S.T.A. ie: Garbage disposal, Washing machine, etc… {900 x 1.6 = 1440 sq.ft. req.}
60’

12. 98 97 High Mountain Rd. 100 4-Bedroom Home 99 1,250 Gal. Septic Tank
Well
4-Bedroom Home
1,250 Gal. Septic Tank
Replacement Area
100 99 98 97
Old ISDS Design
“ Smallest footprint”
Chamber Trench 900 Sq.Ft.
ISDS Guidelines allows 50% Reduction in a chamber trench; (900 x 0.5) = 450 Sq.Ft.
Using a Quick 4+ Standard Chamber, Providing Sq.Ft./Chamber
Chamber Calculation:
450 / = 39 Chamber Units Req’d.
3 Trenches at 52’; 13 Chambers/Trench
However…
52’

13. 98 97 High Mountain Rd. 100 4-Bedroom Home 99 1,250 Gal. Septic Tank
Well
4-Bedroom Home
1,250 Gal. Septic Tank
Replacement Area
100 99 98 97
Old ISDS Design
“Largest footprint”
“Possible requirements”
If local H.D. requires additional Sq.Ft. for garbage grinders, washing machines, etc.. (900 x 1.6) = 1440 Sq.Ft.
&
If local H.D. only allows a 40% Reduction for a chamber trench; (1440 x 0.6) = 864 Sq.Ft.
Used a Quick 4 Plus Low Profile Chamber,
Provides for Sq.Ft./Chamber
Chamber Calculation:
864 / = 87 Chamber Units Req’d.
5 Trenches at 72’; 18 Chambers/Trench
We just went from 39 to 87 Chambers
72’

14. 98 97 High Mountain Rd. 100 4-Bedroom Home 99 1,250 Gal. Septic Tank
Well
4-Bedroom Home
1,250 Gal. Septic Tank
Replacement Area
100 99 98 97
Old ISDS Design
If a “Bed /Chamber” system is proposed
Best Case:
ISDS Guidelines allows 40% Reduction in a bed; (900 x 0.6) = 540 Sq.Ft.
Quick 4 Plus Standard Chamber
Provides for Sq.Ft.
540 / = 47 Chamber Units Req’d.
Worst Case:
If the 1.6 factor was applied; and only a 25% reduction given, then 1080 Sq.Ft. Req’d.
1080 / = 94 Chamber Units Req’d.
30’
15’
92’
12’

15. Notable Changes Old ISDS Design Design Flows:
4 Bedrooms x 150 = 600 gpd
600 gpd x 1.5 = 900 gpd
Percolation Rate = “t” = 25 mpi
Q x t
Formula for Area Req’s. A = 5
Possible Additional Sq.Ft. Requirements ( x 1.6 )
Reductions allowed for chambers
25%, 40%, 50% ….
Varied Sq.Ft. / Chamber Calc’s.
Regulation 43
Design Flows: (Suggested)
150 gpd for first 3 bedrooms
75 gpd for each additional bdrms
Perc Rate; related to a defined Soil Type; (Table 10.1; Soil Type 2)
Long Term Acceptance Rates; (Table 10.1)
Additional Safety Factors Eliminated
Reductions are more defined; dependant on “Methods of Application” (Table 10.2 & 10.3)
Chamber sizing given a standard 0.7 reduction (Table 10.3)

16. Table 10-1 Soil Treatment Area Table 10-1: Soil Treatment Area Long-Term Acceptance Rates by Soil Texture, Soil Structure, Percolation Rate, Treatment Level by Soil Texture, Soil Structure, Percolation Rate and Treatment Level
Soil Type, Texture, Structure and Percolation Rate Range
Long Term Acceptance Rate (LTAR); Gallons per day per square foot
Soil Type
USDA Soil Texture
USDA Soil Structure-Shape
USDA Soil Structure-Grade
Percolation Rate (MPI)
Treatment Level 11
Treatment Level 21
Treatment Level 2N1
Treatment Level 31
Treatment Level 3N1
Soil Type 1 with more than 35% Rock (>2mm); Soil Types 2-5 with more than 50% Rock (>2mm) --
Single Grain (0)
<5
Minimum 3 foot deep unlined sand filter required2
MINIMUM 2 FOOT DEEP UNLINED SAND FILTER REQUIRED2 1
Sand, Loamy Sand
5-15
0.80
1.25
1.40 2
Sandy Loam, Loam, Silt Loam
PR (Prismatic) BK (Blocky)
GR (Granular)
2 (Moderate)
3 (Strong)
16-25
0.60
0.90
1.00 2A
PR, BK, GR
0 (none)
1 (Weak)
Massive
26-40
0.50
0.70 3
Sandy Clay Loam, Clay Loam, Silty Clay Loam
2, 3
41-60
0.35 3A
61-75
0.30
0.40 4
Sandy Clay, Clay, Silty Clay
76-90
0.20 4A
91-120
0.15 5
Soil Types 2-4A
Platy
1, 2, 3
121+
0.10
Higher Level Treatment increases the LTAR, so a smaller Soil Treatment Area can be used.

17. STA Adjustments– Methods of Application Table 10-2 (All TLs)
Type of Soil Treatment Area
Method of Effluent Application from Treatment Unit Preceding Soil Treatment Area
Gravity
Dosed
(Siphon or Pump)
Pressure Dosed
Trench
1.0
0.9
0.8
Bed
1.2
1.1

18. STA Adjustments– Methods of Application Table 10-3 (TL1 only)
Type of Soil Treatment Area
Type of Storage/Distribution Media Used in Soil Treatment Area
Rock or Tire Chips
Manufactured Media Other Than Chambers
Chambers
Trench or Bed
1.0
0.9
0.7

19. ? New Reg. 43 Design 98 97 High Mountain Rd. 100 4-Bedroom Home 99
Well
4-Bedroom Home
1,250 Gal. Septic Tank
Replacement Area
100 99 98 97 ?
New Reg. 43 Design
System Sizing; Daily Flow
4 Bedroom Home
(3 x 150) + (1 x 75) = 525 gpd
Q = 525 gpd
16 – 25 min./inch perc = Soil Type 2
Treatment Level 1, Long Term Acceptance Rate (LTAR) for Soil Type = 0.6 Gal/Sq.Ft./Day
Gallons/Day
A =
LTAR (Gal./Sq.Ft./Day)
525
A = = 875 Sq.Ft.
0.6
875 Sq.Ft. of Soil Treatment Area (S.T.A.) required. But…
Need additional information…

20. ? 98 97 High Mountain Rd. 100 4-Bedroom Home 99 1,250 Gal. Septic Tank
Well
4-Bedroom Home
1,250 Gal. Septic Tank
Replacement Area
100 99 98 97 ?
New Reg. 43 Design
875 Sq.Ft. of S.T.A. Required
Utilize Table 10.2: (Which can be used for “ALL” treatment levels)
Gravity (Sq.Ft. x 1.0)
Pump or Siphon (Sq.Ft. x 0.9)
Pressure Dosed (Sq.Ft. x 0.8)
Our system is “Gravity”
875 x 1.0 = 875 Sq.Ft.
But… Still need additional information…

21. ? 98 97 High Mountain Rd. 100 4-Bedroom Home 99 1,250 Gal. Septic Tank
Well
4-Bedroom Home
1,250 Gal. Septic Tank
Replacement Area
100 99 98 97 ?
New Reg. 43 Design
875 Sq.Ft. of S.T.A. Required
Utilize Tables 10.3: (For TL1 only)
Rock & Pipe (Sq.Ft. x 1.0)
- Mfgr. Media (Sq.Ft. x 0.9)
Chambers (Sq.Ft. x 0.7)
Chamber calc’s. simplified…
REG. 43: “If the width of the chamber is within 90% of the width of the excavation, it may be approved for the equivalent width of the excavation”.
Note: All chambers 4’ long x 33”-36” wide are calculated at 12.0 Sq.Ft./Chamber. ( ie: 33/36 = 0.92 )
Therefore, all of the sq.ft. calculations for each specific chamber models is now gone.

22. 98 97 High Mountain Rd. 100 4-Bedroom Home 99 1,250 Gal. Septic Tank
Well
4-Bedroom Home
1,250 Gal. Septic Tank
Replacement Area
100 99 98 97
New Reg. 43 Design
Chamber Trench Installation:
875 Sq.Ft. of S.T.A. Required
Design Assumption:
Utilize Tables 10.2:
Gravity (Sq.Ft. x 1.0)
= 875 Sq.Ft. x 1.0 = 875 Sq.Ft.
Utilize Tables 10.3:
Chambers (Sq.Ft. x 0.7)
= 875 Sq.Ft. x 0.7 = 613 Sq.Ft.
Chamber Calculation:
613 / 12.0 = 51 Chamber Units
(Use 52 to provide equal length; chambers / trench)
Again note: All of the 1.5 and 1.6 multipliers/safety factors are gone !
52’

23. 98 97 High Mountain Rd. 4-Bedroom Home 1,250 Gal. Septic Tank 100 99
Well
4-Bedroom Home
1,250 Gal. Septic Tank
Replacement Area
100 99 98 97
New Reg. 43 Design
Chamber Bed Installation:
875 Sq.Ft. of S.T.A. Required
Design Assumption:
Utilize Tables 10.2:
Gravity (Sq.Ft. x 1.2)
= 875 Sq.Ft. x 1.2 = 1050 Sq.Ft.
Utilize Tables 10.3:
Chambers (Sq.Ft. x 0.7)
= 1050 Sq.Ft. x 0.7 = 735 Sq.Ft.
Chamber Calculation:
735 / 12.0 = 62 Chamber Units
Again note: All of the 1.5 and 1.6 multipliers/safety factors are gone !
Bed
84’ 9’

24. OWTS Sizing Comparison
Old ISDS Regulations
Regulation 43 Requirements
4 Bedroom home = 600 gpd
Requires between sq.ft. S.T.A. (Trench)
Chamber Units Req’d.
Bed system:
S.T.A. Req’d. = sq.ft.
Chamber Units Req’d.
4 Bedroom home = 525 gpd
Chambers: Requires 613 sq.ft. S.T.A. (Gravity / Trench)
51 Chamber units (at 12.0 sq.ft. / chamber) Req’d.
Bed system:
S.T.A. Req’d. = 735 sq.ft.
62 Chamber units (at 12.0 sq.ft. / chamber); Max. 12’ wide.

25. Regarding OWTS Design, Regulation 43….
Provides for more Consistent and Uniform Design
Looks at Both Soil Texture and Structure
Focuses on Long Term Acceptance Rates,
And Ultimately….
Focuses on Wastewater Treatment

26. Thank You! Next…… Roger Shafer will take our design to the next level
How to design for a more difficult site; using the options provided for in Reg. 43
QUESTONS ??
Thank You!