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Soil Interpretation

Soil Interpretation. Septic Systems – Can we do better?. Name change. Onsite wastewater treatment and dispersal system. Current Interpretations. Soil depth (separation distance) Based on 1948 Public Health Service 120 cm needed to “restriction” Slope “Perc” rate Too slow Too fast

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Soil Interpretation

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  1. Soil Interpretation Septic Systems – Can we do better?

  2. Name change Onsite wastewater treatment and dispersal system

  3. Current Interpretations • Soil depth (separation distance) • Based on 1948 Public Health Service • 120 cm needed to “restriction” • Slope • “Perc” rate • Too slow • Too fast • Hydraulic measurements

  4. State Code – Interpretations? • Soil depth (separation distance) • Focus on treatment • 45 – 60 cm needed for treatment • Slope • Slope correction • Installation up to 30% • NO perc test • System sized on soil properties

  5. Georgeville – fine, kaolinitic, thermic, Typic Kanhapludults Soil Survey Interp – Moderate – percs slow Local Health Dept. Interp – Suitable

  6. Revised Interpretation • Conventional system as a baseline • Modification to a conventional system results in more limitations • Fill over system • Slope issues (< 30%) • Mineralogy (clay only) • All of above lead to a issue with soil depth

  7. How much soil is needed? 30% slope 90 cm trench A” 117 cm 15 cm 15 cm 30 cm 30 cm 45 cm Td = 45 + 30 + 15 + 27 = 117 x A = S x W A = 27 A = 0.3 x 90

  8. Slight

  9. Conventional (≥105 cm of usable soil) Shallow Placed (90 cm of usable soil) 30 cm or more 15 cm 30 cm 30 cm 45-60 cm ≥ 45-60 cm Unsuitable Material Unsuitable Material Note all depths are slope corrected

  10. Moderate

  11. Ultra-shallow or At-grade (75cm of usable soil) 15 cm Suitable Cover 30 cm 45-60 cm Unsuitable Material Note all depths are slope corrected

  12. Severe

  13. Fill System Suitable Cover 15 cm 30 cm 15 cm Suitable Cover Suitable Fill 30 cm 60-75 cm 45 to 60 cm unsuitable Unsuitable Material Unsuitable Material Note all depths are slope corrected

  14. Unsuitable Material • Clay mineralogy • Very sticky • Very Plastic • Very Firm • Water table • Aquic • Oxyaquic • Impermeable • Rock • Horizons – root restrcitive

  15. Unsuitable

  16. Additional variables • Coarse fragments • Slope • Depth • Installation • Equipment • Stabilization • Silt content • Mica content • Slope • Position • Description

  17. What about a “perc” test? Saturated hydraulic conductivity (Ksat)

  18. Hydropedology of a Benchmark Carolina Slate Belt Catena NCSS – NCSU Research Project

  19. Georgeville-Tatum-Chewacla Catena

  20. LTAR – Soil Survey, Lab, Field, Morphology Soil Survey: 0.75 to 2.5 gpd/sq. ft.

  21. Recomendations • Review current literature on treatment and dispersal • Use a conventional system as a baseline • Suitable for conventional - SLIGHT • Ultra-shallow – Moderate • Fill or at-grade - Severe • Adapt to state code as needed • Consult with CIDWT for additional detatils

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