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Rural, Onsite & Small Community Wastewater & Waste Engineering

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.

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Rural, Onsite & Small Community Wastewater & Waste Engineering

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  1. Rural, Onsite & Small Community Wastewater & Waste Engineering Designing Soil Based Systems

  2. 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

  3. Septic System

  4. Leach Field

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

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

  7. Linear Loading Rate

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

  9. 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

  10. Soil Absorption System Design • Wastewater volume • Linear loading rate • Basal loading rate

  11. 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

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

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

  14. Soil Absorption System 36 feet long . 9 trenches each 2 feet wide

  15. 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

  16. Mound System

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

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

  19. Linear Loading Rate

  20. Basal Loading Rate • Based on characteristic of surface horizon • Silt loam, moderate structure • (I) 0.6 gpd/ft2

  21. 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

  22. Mound System Design • Wastewater volume • Linear loading rate • Basal loading rate

  23. 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

  24. Mound Size

  25. 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

  26. 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

  27. 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

  28. Overall Mound Size • Wastewater distribution system • 9 inches on top of sand • Aggregate or chambers

  29. 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

  30. 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

  31. 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

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

  33. 3:1 slope 1 ft 3 ft

  34. 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

  35. Slope Correction

  36. 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

  37. 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

  38. Overall Mound Size • 84 feet long along the contour • 29 feet wide • covers basal width of 10 feet

  39. 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

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