Rural, Onsite

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Rural, Onsite Small Community Wastewater
Waste Engineering

• Designing Soil Based Systems

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Site Soil Assessment Results

• Mapping Unit
• Wea
• Soil type at site
• Wea
• Gravelly sand at 66 inches
• 0 - 3 slope
• At 18 inch depth - loam, moderate structure

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Septic System
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Leach Field
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Wastewater Volume

• 120 gallons/bedroom
• 3 bedroom home
• 3 120 360 gpd

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Linear Loading Rate

• Based on nature of limiting condition
• Gravelly loam
• (c) 8 - 10 gpd/lf

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Linear Loading Rate
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Basal Loading Rate

• Based on characteristics at trench depth (18
  inches)
• Loam, moderate structure
• (I) 0.6 gpd/ft2

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Basal Loading Rate

• gpd/ft2
• A. Is the horizon gravelly coarse sand or
  coarser? 0.0
• B. Is consistence stronger than firm or hard, or
  any cemented class? 0.0
• C. Is texture sandy clay, clay or silty clay of
  high clay content and structure massive
• or weak, or silt loam and structure massive?
  0.0
• D. Is texture sandy clay loam, clay loam or silty
  clay loam and structure massive? 0.0
• E. Is texture sandy clay, clay or silty clay of
  low clay content and structure
• moderate or strong? 0.2
• F. Is texture sandy clay loam, clay loam or silty
  clay loam and structure weak? 0.2
• G. Is texture sandy clay loam, clay loam or silty
  clay loam and structure moderate
• or strong? 0.4
• H. Is texture sandy loam, loam, or silt loam and
  structure weak? 0.4
• I. Is texture sandy loam, loam, or silt loam and
  structure moderate or strong? 0.6
• J. Is texture fine sand, very fine sand, loamy
  fine sand, or loamy very fine sand? 0.6
• K. Is texture coarse sand with single grain
  structure? 0.8

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Soil Absorption System Design

• Wastewater volume
• Linear loading rate
• Basal loading rate

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System Width

• Long thin along the contour of lot
• System width linear loading rate / basal
  loading rate
• System Width 10 gpd/ft / 0.6 gpd/ft2
• System Width 17 feet

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System Length

• As long as possible
• System length Wastewater volume / Linear
  loading rate
• System Length 360 gpd / 10 gpd/ft
• System Length 36 feet

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Number of Trenches

• Backhoe bucket width - 2 ft
• No. of trenches System width / Bucket width
• No. of trenches 17 ft / 2 ft 9 trenches

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Soil Absorption System
36 feet long
.
9 trenches each 2 feet wide
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Site Soil Assessment Results

• Mapping unit
• Kendallville
• Soil type at site
• Miamian
• Dense till at 28 inches
• 2-4 slope
• Surface horizon - silt loam, moderate structure

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Mound System
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Wastewater Volume

• 120 gallons/bedroom
• 3 bedroom home
• 3 120 360 gpd

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Linear Loading Rate

• Based on nature of limiting condition
• Moderately dense till
• (b) 5 - 6 gpd/lf

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Linear Loading Rate
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Basal Loading Rate

• Based on characteristic of surface horizon
• Silt loam, moderate structure
• (I) 0.6 gpd/ft2

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Basal Loading Rate

• gpd/ft2
• A. Is the horizon gravelly coarse sand or
  coarser? 0.0
• B. Is consistence stronger than firm or hard, or
  any cemented class? 0.0
• C. Is texture sandy clay, clay or silty clay of
  high clay content and structure massive
• or weak, or silt loam and structure massive?
  0.0
• D. Is texture sandy clay loam, clay loam or silty
  clay loam and structure massive? 0.0
• E. Is texture sandy clay, clay or silty clay of
  low clay content and structure
• moderate or strong? 0.2
• F. Is texture sandy clay loam, clay loam or silty
  clay loam and structure weak? 0.2
• G. Is texture sandy clay loam, clay loam or silty
  clay loam and structure moderate
• or strong? 0.4
• H. Is texture sandy loam, loam, or silt loam and
  structure weak? 0.4
• I. Is texture sandy loam, loam, or silt loam and
  structure moderate or strong? 0.6
• J. Is texture fine sand, very fine sand, loamy
  fine sand, or loamy very fine sand? 0.6
• K. Is texture coarse sand with single grain
  structure? 0.8

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Mound System Design

• Wastewater volume
• Linear loading rate
• Basal loading rate

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Sand Width

• Long thin along the contour of lot
• Abs. Area Width linear loading rate / sand fill
  loading rate
• Abs. Area fill loading rate 1 gpd/ft2
• Abs. Area Width 6 gpd/ft / 1 gpd/ft2
• Abs. Area Width 6 feet

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Mound Size
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Sand Length

• As long as possible
• Abs. Area Length Wastewater volume / Linear
  loading rate
• Abs. Area Length 360 gpd / 6 gpd/ft
• Abs. Area Length 60 feet

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Sand Height

• Sand soil 4 feet
• Sand height 4 ft - soil depth
• Sand height 4 ft - 28 inches
• Sand height 48 inches - 28 inches
• Sand height 20 inches

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Sand Height down slope

• Sand height down slope height upslope slope
  width
• Sand height down slope 20 inches 0.04 6 ft
• Sand height down slope 20 in 0.04 72 in
• Sand height down slope 23 inches

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Overall Mound Size

• Wastewater distribution system
• 9 inches on top of sand
• Aggregate or chambers

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Cover with soil fill

• Insulate - protect from freezing
• 12 inches
• Shed water - crown top
• Additional 6 inches
• Cover soil to prevent breakout at mound toe
• Based on basal loading rate
• Slope sides for safety when mowing

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Overall Mound Height

• Mound height
• sand aggregate insulating soil fill crown
• Mound height 20 in 9 in 12 in 6 in
• Mound height 47 inches at top
• Mound height at downslope sand edge
• 23 in 9 in 12 in
• Mound height at downslope sand edge
• 44 inches

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Width to avoid breakout at toe

• Basal width
• Linear loading rate / basal loading rate
• Basal width 6 gpd/ft / 0.6 gpd/ft2
• Basal width 10 feet

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Safety for mowing

• 31 slope
• Slope drops 1 foot in 3 feet

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31 slope
1 ft
3 ft
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Overall Mound Width

• Mound width
• Abs. Area width upslope width downslope width
• Upslope width side slope mound height slope
  corr.
• Upslope width 3 47 inches 0.89 126 inches
• Downslope width
• side slope downslope height slope corr.
• Downslope width 3 44 inches 1.14 151 in

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Slope Correction
Slope Downslope Corr. factor Upslope Corr. factor
0 1.00 1.00
1 1.03 0.97
2 1.06 0.94
3 1.10 0.92
4 1.14 0.89
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Overall Mound Width

• Mound width
• Abs. Area width upslope width downslope width
• Mound width 6 ft 129 in 151 in
• Mound width 72 in 129 in 151 in
• Mound width 352 inches 29 feet

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Overall Mound Length

• Mound length
• Abs. Area length 2 endslope length
• Endslope length 3 mound height
• Endslope length 3 47 in
• Endslope length 141 inches 12 feet
• Mound length 60 feet 2 12 feet
• Mound length 84 feet

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Overall Mound Size

• 84 feet long along the contour
• 29 feet wide
• covers basal width of 10 feet

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Reading

• Crites Tchobanoglous 905 - 918
• Burkes Minnis 142 - 161
• Bull 813 Mound Systems for Onsite Wastewater
  Treatment
• AEX 743 Septic tank - Soil Absorption Systems
• AEX 744 Septic tank - Mound Systems