1. Transitioning from the Percolation Test to Soils Evaluation
Colorado Professionals in Onsite Wastewater
Annual Education Conference
2014
Roy Laws, P.E.
Jefferson County Public Health
Warren S. Brown, P.E.
Tri-County Health Department

2. Some Thoughts on Soil and Wastewater Treatment
Soil can provide an amazing amount of wastewater treatment!

3. What’s In Wastewater?
99.9% WATER (Municipal and Rural Sanitation, 1950)
Paper
Pee
Personal care products
Petrochemicals
Pharmaceuticals
Poop and puke (source of pathogens)
Pulverized produce from a garbage disposal

5. Soil Treatment Typical Concentration of Domestic Wastewater Contaminants
Parameter
Units
Septic Tank Influent
Septic Tank Effluent Applied to Soil Treatment Area (STA)
% removal after percolating through 3 to 5 feet of soil
Total suspended solids
Milligrams / liter
250 60
> 90 %
Biochemical oxygen demand
120
Fecal Coliform Bacteria
Coliform forming units / 100 milliliters
10 million
1 million
> %
Nitrogen
10 to 20 %
Phosphorus 10
8.1
0 to 100 %

6. Typical Soil Profile

7. What Is Soil?

8. OWS Transportation and Fate
Wastewater source
Pretreatment
Effluent delivery
Vadose zone
Ground water zone
Percolation
Ground water recharge
Infiltration
Capillary fringe
Network of trenches
Plant uptake
Straining and filtration
Adsorption
Ion X-C, precipitation
Biotransformation
Die-off and predation
Illustration of a common onsite wastewater system that relies on subsurface infiltration for treatment and disposal 8

9. How many soil scientists, engineers, and students does it take to figure out if it is soil?

10. Colorado Onsite Wastewater Regulations Suitable Soil Means…
a soil which will effectively treat and filter effluent
by removal of organisms and suspended solids
before the effluent reaches any highly permeable earth such as joints in bedrock, gravels, or very coarse soils
and which meets percolation test or soil test pit excavation requirements for determining LTAR
and has a vertical thickness of at least four feet below the bottom of the soil treatment area
unless treatment goal met by other performance criteria.

11. How Do I Know If The Soil Is Suitable?
Do an onsite soil test!
a physical examination of the soil that includes:
Percolation test
Visual-Tactile from a soil profile pit
Water table assessment

12. Onsite Soil Tests
Percolation Test
Visual-Tactile (Texturing)

13. Onsite Soil Tests
18 inches
36 inches
Soil Profile Hole

14. Percolation Test Dig hole Soak hole with water
Wait until hole is soaked
Fill hole with more water
Measure how water moves into the soil in minutes per inch

15. Lab Gradation Analysis
Grab a representative soil sample
Sieve sample to measure percent of
Clay
Sand
Silt
Go to USDA soil texture triangle!

16. Soil Textures USDA Textural Triangle

17. Soil Textures USDA Textural Triangle
Lab Result
50 % sand
40 % silt
10 % clay
Eureka!
It’s a Loam.

18. Visual – Tactile Evaluation
Soil Texture
Soil Structure
Redoximorphic Features
(evidence of groundwater)

19. How To Do Soil Texturing (Handout)
Demonstration by Presenters
Hand out field texture method and Table 10.1

20. Soil Texturing

21. Soil Texturing

22. Soil Texturing

23. Soil Texturing

24. Soil Structures Single grained Granular Blocky Prismatic & columnar
Platy
Massive

25. Granular Structure
USDA-NRCS, 1993

26. Blocky Structure
2 inches
USDA-NRCS,1993

27. Prismatic Structure
1 foot
USDA-NRCS, 1993

28. Platy Structure
1 foot
USDA-NRCS, 1993

29. Square Feet of Soil Treatment Area!
Now What?
Soil Texture +
Soil Structure +
Wastewater Quality
To determine LTAR
Wastewater Quantity / LTAR =
Square Feet of Soil Treatment Area!
Elude to table 10.1 and LTAR to determine field size

30. Long Term Acceptance Rate
LTAR means
Long Term Acceptance Rate
Rate that effluent enters the infiltration surface soil treatment unit in gallons per day per square foot
(g / ft2 / day)

31. Table 10.1 Long Term Acceptance Rates by Soil Texture, Structure, Grade and Treatment Level
WASTEWATER SITUATION
3 bedroom single-family septic tank effluent
= Treatment Level 1
= design flow 450 gallons per day

32. 900 square feet, gravity flow to rock or tire chip trench
Table Long Term Acceptance Rates by Soil Texture, Structure, Grade and Treatment Level
Soil Description
Soil texture = loam
Soil structure = granular
Structure grade = weak
LTAR = 0.50 gallons per day per square foot
Soil treatment area = 450 gpd / 0.50 gpd/ft2 =
900 square feet, gravity flow to rock or tire chip trench

33. THANK YOU! Questions? Roy Laws, P.E. Jefferson County Public Health
Warren S. Brown, P.E.
Tri-County Health Department