rural, onsite & small community wastewater & waste engineering designing soil based systems

Rural, Onsite & Small Community Wastewater & Waste Engineering

Designing Soil Based Systems

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

Septic System

Leach Field

Wastewater Volume 120 gallons/bedroom 3 bedroom home 3 * 120 = 360 gpd

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

Linear Loading Rate

Basal Loading Rate Based on characteristics at trench

depth (18 inches) Loam, moderate structure (I) 0.6 gpd/ft2

Basal Loading Rate

gpd/ft2A. Is the horizon gravelly coarse sand or coarser? 0.0B. Is consistence stronger than firm or hard, or any cemented class? 0.0C. Is texture sandy clay, clay or silty clay of high clay content and structure massive or weak, or silt loam and structure massive? 0.0D. Is texture sandy clay loam, clay loam or silty clay loam and structure massive? 0.0E. Is texture sandy clay, clay or silty clay of low clay content and structure moderate or strong? 0.2F. Is texture sandy clay loam, clay loam or silty clay loam and structure weak? 0.2G. Is texture sandy clay loam, clay loam or silty clay loam and structure moderate or strong? 0.4H. Is texture sandy loam, loam, or silt loam and structure weak? 0.4I. Is texture sandy loam, loam, or silt loam and structure moderate or strong? 0.6J. Is texture fine sand, very fine sand, loamy fine sand, or loamy very fine sand? 0.6K. Is texture coarse sand with single grain structure? 0.8

Soil Absorption System Design Wastewater volume Linear loading rate Basal loading rate

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

System Length As long as possible System length = Wastewater volume / Linear loading rate

System Length = 360 gpd / 10 gpd/ft System Length = 36 feet

Number of Trenches Backhoe bucket width - 2 ft No. of trenches = System width / Bucket width No. of trenches = 17 ft / 2 ft = 9 trenches

Soil Absorption System

9 trenches each 2 feet wide

36 feet long

.

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

Mound System

Wastewater Volume 120 gallons/bedroom 3 bedroom home 3 * 120 = 360 gpd

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

Linear Loading Rate

Basal Loading Rate Based on characteristic of surface

horizon Silt loam, moderate structure (I) 0.6 gpd/ft2

Basal Loading Rate

gpd/ft2A. Is the horizon gravelly coarse sand or coarser? 0.0B. Is consistence stronger than firm or hard, or any cemented class? 0.0C. Is texture sandy clay, clay or silty clay of high clay content and structure massive or weak, or silt loam and structure massive? 0.0D. Is texture sandy clay loam, clay loam or silty clay loam and structure massive? 0.0E. Is texture sandy clay, clay or silty clay of low clay content and structure moderate or strong? 0.2F. Is texture sandy clay loam, clay loam or silty clay loam and structure weak? 0.2G. Is texture sandy clay loam, clay loam or silty clay loam and structure moderate or strong? 0.4H. Is texture sandy loam, loam, or silt loam and structure weak? 0.4I. Is texture sandy loam, loam, or silt loam and structure moderate or strong? 0.6J. Is texture fine sand, very fine sand, loamy fine sand, or loamy very fine sand? 0.6K. Is texture coarse sand with single grain structure? 0.8

Mound System Design Wastewater volume Linear loading rate Basal loading rate

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

Mound Size

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

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

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

Overall Mound Size Wastewater distribution system

9 inches on top of sand Aggregate or chambers

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

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

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

Safety for mowing 3:1 slope Slope drops 1 foot in 3 feet

3:1 slope

1 ft

3 ft

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

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

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

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

Overall Mound Size 84 feet long along the contour 29 feet wide

covers basal width of 10 feet

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