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

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

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

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 > 99.99 % Nitrogen 10 to 20 % Phosphorus 10 8.1 0 to 100 %

Typical Soil Profile

What Is Soil?

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

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

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.

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

Onsite Soil Tests Percolation Test Visual-Tactile (Texturing)

Onsite Soil Tests 18 inches 36 inches Soil Profile Hole

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

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

Soil Textures USDA Textural Triangle

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

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

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

Soil Texturing

Soil Texturing

Soil Texturing

Soil Texturing

Soil Structures Single grained Granular Blocky Prismatic & columnar Platy Massive

Granular Structure USDA-NRCS, 1993

Blocky Structure 2 inches USDA-NRCS,1993

Prismatic Structure 1 foot USDA-NRCS, 1993

Platy Structure 1 foot USDA-NRCS, 1993

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

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)

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

900 square feet, gravity flow to rock or tire chip trench Table 10.1 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

THANK YOU! Questions? Roy Laws, P.E. Jefferson County Public Health rlaws@jeffco.us Warren S. Brown, P.E. Tri-County Health Department wbrown@tchd.org