U S I N G T H E N E W R E G U L AT I O N S

DESIGNING OWTS…

Prepared for the Colorado Professionals in Onsite Wastewater (CPOW) 2014 Conference

by Roger J. Shafer, P.E.

A CLASSIC EXAMPLE“THE EASY LOT”

High Mountain Rd.

Well

SOIL TREATMENT AREA SIZING

• 3 Bedroom Home = (3) x (150 GPD) = 450• No 1.5 factor

• Sandy Loam Soil (16-25 MPI)• LTAR = 0.6 GPD/ft² (Taken from Table 10.1)

• STA = 450 ÷ 0.6 = 750 ft² required

USE 3 TRENCHES – 3’ WIDE BY 84’ LONG

High Mountain Rd.

Well

100’

99’

98’

TRENCHES VERSUS BEDS

• Trench Cons• Trenches take up more area

• 6 foot separation between trenches

• Harder to install• Especially with 3+ trenches• Slower to install dispersal gravel

• Inspection coordination can be difficult

TRENCHES VERSUS BEDS, CONT.

• Trench Pros• Sidewall Area

• Three 3’ X 60’ trenches have 189 s.f. of sidewall versus a 9’ X 60’ bed has 69 s.f. of sidewall area

• Trench resting or alternating• Maintain shallow depths on steep hillsides• Greater dispersion• Greater oxygen transfer• Less soil compaction…

SERIAL VERSUS PARALLEL DISTRIBUTION

• Serial Distribution• Sequential trench failure• Biomat for treatment (creates unsaturated flow)

• Parallel Distribution• Lower loading (hydraulic and organic) to the soils• Allows trench resting• Requires dosing (siphon or pump)• Requires d-box or distributing valve

High Mountain Rd.

Well

100’

99’

98’

IT ALL FLOWS DOWNHILLOR DOES IT?

High Mountain Rd.

Well

100’

99’

98’

PUMP SYSTEM REQUIREMENTS

• Section 43.8 I – Wastewater Pumping and Dosing Systems (items to note)• Floats to be mounted on a stem separate from the pump

discharge assembly• Discharge assembly must have a disconnect union• Must have access riser to grade, and have a watertight

connection to the pump tank• Splice box outside the access riser• Pump breaker separate from alarm breaker• A switch to manually operate the pump• Panels to be UL listed

EXAMPLES

Not good Not good

EXAMPLES

Not good Good

EXAMPLES

Not good Good

EXAMPLES

Not good

SPECIFYING A PUMP SYSTEMWHAT TO PUT IN AND WHAT TO LEAVE OUT

SPECIFYING A PUMP SYSTEM, CONT.

• THE TANK; COMPARTMENT; BASIN• Size• State Approved• Materials (concrete; fiberglass; plastic)• Bury depth• Risers to grade• Type of risers• Inlet and Outlet locations• Anti-floatation• Make and Model

SPECIFYING A PUMP SYSTEM, CONT.

• THE PUMP SYSTEM• Horsepower• Total Dynamic Head and Flow Rate• Voltage• Conventional low-head or well-style• Floats (mechanical; low-voltage; transducer)• Splice Box• Control Panel (indoor; outdoor; etc.)• Audible and Visual Alarm• Make and Model

WHAT ABOUT THE NEIGHBOR’S WELL?

High Mountain Rd.

Well

100’

99’

98’

100’ radius Well

High Mountain Rd.

Well

100’

99’

98’

100’ radius

Well

TABLE 10.2 SIZE ADJUSTMENT FACTORS

Gravity Bed = (450 GPD) ÷ (0.6 GPD/ft²) x (1.2 factor) = 900 ft²

Pressure Dosed Bed = (450 GPD) ÷ (0.6 GPD/ft²) x (1.0 factor) = 750 ft²

TABLE 10.3 SIZE ADJUSTMENT FACTOR

Reduction for Chambers:

Gravity Bed = (900 ft²) x (0.7 factor) = 630 ft² required

Pressure Dosed Bed = (750 ft²) x (0.7 factor) = 525 ft² required

High Mountain Rd.

Well

100’

99’

98’

100’ radius

Well

High Mountain Rd.

Well

100’

99’

98’

100’ radius Well

Well100’

radius

ADVANCED TREATMENT LOADING RATES

SOIL TREATMENT AREA SIZING

• 3 Bedroom Home = (3) x (150 GPD) = 450 GPD• No 1.5 factor

• Sandy Loam Soil (16-25 MPI)• LTAR = 1.0 GPD/ft² (Taken from Table 10.1 for TL3N)

• STA = (450 GPD) ÷ (1.0 GPD/ft²) = 450 ft² required

• Pressure Dosed Bed = (450 ft²) x (1.0 factor) = 450 ft²

• No additional reduction for chambers

• Compared to 525 ft² for a bed with chambers• Not that much difference!

MINIMUM DISTANCES

PRESSURE DOSING REQUIRED

ITEM OWTS DESIGN CONSIDERATION

Treatment Levels 1 and 2

Treatment Level 2N

Treatment Level 3

Treatment Level 3N

Horizontal Separation Distances

1 Distance from soil treatment area to on-site well

Greater than or equal to 100 feet

Greater than or equal to 100 feet

Greater than or equal to 100 feet

Greater than or equal to 75 feet

2 Distance from soil treatment area to pond, creek, lake, or other surface water feature

Greater than or equal to 50 feet

Greater than or equal to 25 feet

Greater than or equal to 25 feet

Greater than or equal to 25 feet

3 Distance from soil treatment area to dry gulch or cut bank

Greater than or equal to 25 feet

Greater than or equal to 10 feet

Greater than or equal to 10 feet

Greater than or equal to 10 feet

Vertical Separation Distances

4 Depth in feet from soil treatment area infiltrative surface to restrictive layer or ground water

4 feet (3 feet with pressure dosing)

Greater than or equal to 2 feet

Greater than or equal to 2 feet

Greater than or equal to 2 feet

TABLE 7-2SEPARATION DISTANCES FROM SOIL TREATMENT AREA

High Mountain Rd.

Well

100’

99’

98’

100’ radius Well

Well100’

radius

75’ radius

Alt. area

REAL-WORLD EXAMPLES

> 25 feet with TL3N

Soil Treatment Area

Residence

Treatment Unit

Stream

Retaining Wall Retaining Wall

STREAM

PROPERTY LINE

HOUSE

WELL

SOIL TREATMENT AREA

TREATMENT UNIT

> 25’ with TL3

<75’ with TL3

WHY USE ADVANCED TREATMENT?

• Separation Distance Reduction• Horizontal and vertical

• Required by County• Special Watershed Requirement• Lot Size Requirement• Distance Reduction to Wells (for counties with greater

distance requirements)

• Higher loading rates = smaller STA• If you don’t use chambers or chamber reduction not

allowed in your county

WHY USE ADVANCED TREATMENT, CONT.

• In Very Clayey Soils• Biomat plugging a bigger issue in clayey soils

• An accumulation of risk factors• Development Density• Shallow bedrock or ground water• Proximity to surface water• Lack of repair field location• Steep slopes

QUESTIONS?R O G E R J . S H A F E R , P. E

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