wastewater report
Babygirl90
septicdesign13370-5.pptEHST 3370
Wastewater Management
On-site System Design
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Unit Objectives
- List several commonly used onsite wastewater treatment system technologies and their components
- List the positives and negatives of each technology
- Describe the soil and site conditions required for issuance of a permit to construct, install and operate the system
- Design the common onsite wastewater treatment systems (including determining design flow, long-term acceptance rate, tank size, dispersal field area, etc.,)
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Septic System Treatment and
Disposal Mechanisms
- Septic Tank- settling tank where wastewater is stratified, liquid effluent exits tank, solids remain
- Distribution Device- distribute effluent to dispersal field
- Drainfield trench- an aerobic environment where wastewater is stored until it infiltrates the soil
4) Soil beneath trench is aerobic, and most pollutant
transformation and removal occur
5) Setback distances- to allow further treatment processes such as dilution to occur
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3
2
4
5
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On-Site Wastewater Treatment and Disposal System Components
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Septic Tank
Drainfield Trenches
Distribution Box
Plan-View of On-Site Wastewater
Treatment and Disposal System
Soil
Soil
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sludge
liquid
scum
Sanitary Tee
With Filter
Baffle Wall
Outlet
Inlet
Manholes
Air vent
Plan View of Septic Tank
Cross-Section View of Septic Tank
Outlet
Inlet
Manholes
Air vent
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Septic Tank Effluent Filters
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Inlet
Available Outlets
Inlet
Outlet (in use)
Drainfield Trench
Cross-Section View of Distribution Box
Plan View of Distribution Box
Available Outlets
Outlet (in-use)
Soil Surface
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Off Center Hole
Flow Leveler/Speed Dial
Outlet Pipe insert
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Flow Divider
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Tipping D-Box
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Drop Boxes (Serial Distribution)
Step Downs (Serial Distribution)
Soil
Water Table
Physical Chemical Biological
Filtration Cation exchange Oxidation
Sedimentation Adsorption N-Transformations
Dilution Precipitation Predation
Dispersion
Soil Treatment
Soil Treatment Types
Soil Surface
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Ground Penetrating Radar Surveys
Electrical Resistivity Surveys (Plan-view)
Electrical Resistivity Surveys (Profile-view)
Cross-Section View of Drainfield Trench
Soil Surface
12” Washed Stone
4” Corrugated
Pipe
Washed Stone
Pipe
6” Soil Cover
18” Sandy Soil
12” loam, clay loam
or clay soil
Supply line
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Long Term Acceptance Rates (LTAR)
Soil Group LTAR (g/day/ft2)
- S, LS 1.2 - 0.8
- SL, L 0.8 - 0.6
- SCL, SiL, CL, 0.6 - 0.3
SiCL, Si
IV. SC, SiC, C 0.4 – 0.1
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System Types
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Septic Tank
Drainfield Trenches
Distribution Box
Plan-View of conventional septic system
Soil
Soil
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Seasonal High Water Table
Conventional Septic System Drainfield
9’
3’
24” Soil cover
12” Washed stone
with pipe
12” Suitable soil between
drainfield trench bottom
seasonal high water table
4’
6’
Notes
Trench bottom depth and width = 36”
Seasonal high Water table = 48” below soil surface
Trenches spaced 3 x trench width on center or 9’
Natural Soil Surface
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Septic Tank
Drainfield Trenches
Distribution Box
Plan-View of shallow placed conventional system
Soil
Soil
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Fill Material
Seasonal High Water Table
Notes
* Trench bottom depth 12” and trench bottom width 36”
* At least 6” of soil cover (fill material) was brought on site to achieve
soil cover requirement of 6” and landscaped to shed surface water
*The top of the washed stone in the drainfield trenches is level with
the natural soil surface.
9’
Precipitation
12” washed stone
12” suitable soil
3’
Natural soil surface
At-Grade or Ultra Shallow Conventional On-Site System
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Drainage Modifications
French or curtain drains are installed up-slope from the drainfield
and are used to intercept laterally moving water and prevent
trenches from becoming hydraulically overloaded with ground/soil
water.
Pump to conventional septic system
Septic tank
Pump tank
D-box
Drainfield Trench
Supply line
Electrical Box
Land Surface
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Pump Off
Pump On
High Water Alarm
Pump
Electrical Box
Alarm
Supply line
Pump Tank
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Pressure Manifold Distribution
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Manifold Box
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Water Table
Natural Soil
Fill
Cross-Section View of Mound System
12+” to Seasonal High Water Table
18+” of suitable soil
Sand or loamy sand fill material
Mound must shed water, grass cover
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5’ Fill Extension (level)
Mound System (Fill)
8’ Fill Extension (sloping)
Septic tank
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Pump to a Fill System (Mound)
Septic Tank
Pump Tank
Electrical Box
Supply Line
Manifold
Laterals with
Turn-ups at end
Plan-view of Low Pressure Pipe System
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12” Suitable soil
8” Washed stone
4” Soil cover
5’ Spacing
1.5’
Seasonal High Water Table
Low Pressure Pipe (LPP) System
Equal distribution
Wetting/drying cycles
Typically uses 25-30% less area
Requires 24” suitable soil (20” at-grade)
Maintenance agreement required
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12” Suitable soil
8” Washed stone
4” Soil cover
5’ Spacing
1.5’
Low Pressure Pipe (LPP) System
LTAR is reduced by ½ when using LPP systems, however, the area between drainfield trenches is also considered disposal area when designing LPP.
LTAR for LPP Systems
Soil Group LTAR (g/day/ft2)
- S, LS 0.6 - 0.4
- SL, L 0.4 - 0.3
- SCL, SiL, CL, 0.3 - 0.15
SiCL, Si
IV. SC, SiC, C 0.2 – 0.05
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*
Gravel-less Systems
36”
12”
12”
12”
36” x 0.6 = 21.6”
Total depth = 36” + 21.6”
= 58”
21.6”
36”
Large Diameter Pipe System
8” and 10” Pipes
Septic Tank
Drainfield Trenches
Distribution Box
Plan-View of Polystyrene Aggregate System
Soil
Soil
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Soil
Polystyrene Aggregate System
12”
12”
More porous than washed stone More easily compacted
Cleaner than washed stone May float in trench
Less labor intensive to install Not much longevity testing
compared to gravel
25% reduction in drainfield area
Water Table
Soil surface
Cover Paper
Polystyrene Bundle
4” pipe
3’
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*
Storage Space
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Septic Tank
Drainfield Trenches
Distribution Box
Plan-View of Chamber System
Soil
Soil
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12-18” suitable soil
Chamber System
More storage area than
gravel system
Less labor intensive than
gravel systems
25% reduction in drainfield
area vs. gravel
Does not have long term
testing like gravel
Trench bottom must be relatively
straight vs. gravel or polystyrene
aggregate
3’
Water Table
Soil surface
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12-18” suitable soil
Low Profile Chamber System
Less labor intensive than
gravel systems
Trench height (8”) so soil depth
requirement is 20-26” minimum
Trench bottom must be relatively
straight vs. gravel or polystyrene
aggregate
3’
Water Table
Soil surface
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Chamber Systems
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Bed System
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System Designs
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Design Considerations
Soil and Site Evaluation
- Soil texture* 7) Landscape position
- Soil structure 8) Slope
- Soil depth 9) Available space
- Soil color 10) Organic soils
- Soil mineralogy 11) Restrictive horizons
- Soil wetness
*There are 4 soil textural groups, each with a given range of loading rates
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Long Term Acceptance Rates (LTAR)
Soil Group LTAR (g/day/ft2)
- S, LS 1.2 - 0.8
- SL, L 0.8 - 0.6
- SCL, SiL, CL, 0.6 - 0.3
SiCL, Si
IV. SC, SiC, C 0.4 – 0.1
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*
*
(Hodges et al., 2000)
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Landscape Position: side slope
Soil Texture: Clay – Group IV
Slope 6-10%
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Drainfield trenches must be Installed on contour when slope > 2%
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Long Term Acceptance Rates (LTAR)
Soil Group LTAR (g/day/ft2)
- S, LS 1.2 - 0.8
- SL, L 0.8 - 0.6
- SCL, SiL, CL, 0.6 - 0.3
SiCL, Si
IV. SC, SiC, C 0.4 – 0.1
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Design Considerations
*Wastewater characteristics
- Domestic
- Commercial
*Daily Water Use
- Residential
- 120 gal/BR or 60 gal/person
*Garbage disposal/grinder
*System Type (LTAR for LPP is ½ other systems, Mound
must use lowest LTAR in soil group)
*Setbacks
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House
10’
Repair Area
50’ x 30’
Site Plan for 3 Bedroom On-Site System with Group II
Sandy loam soil (0.6 g/d/ft2 LTAR)
3BR * 120g/d/BR = 360 g/d
Initial
360 g/d = 600 ft2
0.6 g/d/ft2
600 ft2 = 200 ft
3 ft trench
Total
600 ft2 * 2 = 1200 ft2
200 ft * 2 = 400 ft
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House
10’
Repair Area
80’ x 39’
Site plan for 3 bedroom on-site system with group IV
clay soil (0.3 g/d/ft2 LTAR)
3BR = 360 g/d
Initial
360 g/d = 1200 ft2
0.3 g/d/ft2
1200ft2 = 400 ft
3 ft trench
Total
1200 ft2 * 2 = 2400 ft2
400 ft * 2 = 800 ft
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House
10’
Repair Area
75’ x 30’
Site plan for 3 bedroom on-site system with group IV
Clay soil (0.3 g/d/ft2 LTAR) using a polystyrene aggregate system
3 BR = 360 g/d
360 g/d = 1200 ft2
0.3 g/d/ft2
1200 ft2 * 0.75 = 900 ft2
900 ft2 = 300 ft
3 ft trench
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House
10’
Repair
15’ x 60’
Site Plan for 3 Bedroom On-Site System with Group II
Sandy loam soil (0.6 g/d/ft2 LTAR) with Bed system
3BR * 120g/d/BR = 360 g/d
Initial
360 g/d = 600 ft2
0.6 g/d/ft2
600 ft2 *1.5 = 900 ft2
900 ft2 = 60 ft
15 ft width
Total
900 ft2 * 2 = 1800 ft2
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House
10’
Repair
Area
80’ x 30’
Site plan for 4 bedroom on-site system with group III
sandy clay loam soil (0.5 g/d/ft2 LTAR)
4 BR * 120 g/b/d = 480 g/d
Initial
480 g/d = 960 ft2
0.5 g/d/ft2
960 ft2 = 320 ft
3 ft
Total
960 ft2 * 2 = 1920 ft2
320 ft * 2 = 640 ft
1000 g tank
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House
10’
Repair
Area
55’ x 21’
Site plan for 2 bedroom on-site system with group III
sandy loam soil (0.5 g/d/ft2 LTAR)
2 BR * 120 g/d/BR =
240 g/d
Initial
240 g/d = 480 ft2
0.5 g/d/ft2
480 ft2 = 160 ft
3ft trench
Total
480 ft2 * 2 = 960 ft2
160 ft * 2 = 320 ft
900 g tank
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House
Site plan for 4 bedroom on-site system with group III
sandy clay loam soil (0.5 g/d/ft2 LTAR)
20’
16’
66’
4 BR * 120 g/b/d = 480 g/d
Initial
480 g/d = 960 ft2
0.5 g/d/ft2
960 ft2 = 320 ft
3 ft
Total
960 ft2 * 2 = 1920 ft2
320 ft * 2 = 640 ft
1000 g tank
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20’
16’
First lot
Permitted
Second lot
Permitted
Third Lot
Permitted
Drainfield
Drainfield
150’
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