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Site and Soil Investigations

Site and Soil Investigations. Terry L. Bovee Steve Lawler Professional Soil Scientists Henderson, MN 56044 Rochester, MN 55906 507-248-9626 507-282-4090 Tbovee@frontiernet.net slawler@charterinternet.com 2006 Minnesota Onsite Wastewater Convention March 13-15, 2006.

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Site and Soil Investigations

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  1. Site and Soil Investigations Terry L. Bovee Steve Lawler Professional Soil Scientists Henderson, MN 56044 Rochester, MN 55906 507-248-9626 507-282-4090 Tbovee@frontiernet.net slawler@charterinternet.com 2006 Minnesota Onsite Wastewater Convention March 13-15, 2006

  2. Site & Soil EvaluationforMedium and Large Sized Sewage Treatment Systems(MSTS and LSTS)

  3. From this…

  4. To this…

  5. You Need A Lot of Information!

  6. What is the Purposeof a Site Evaluation??

  7. Site Evaluation PURPOSE • To provide a large MSTS/LSTS system designer with specific information about the landscape and soils of a site to determine suitability for the proposed use.

  8. Site Evaluation REASONS • Required by Minnesota Rules - small & medium sized systems • LSTS Guidance considerations

  9. Site EvaluationGetting the BIG Picture… • The Designer is RESPONSIBLE for accurate & complete site/soil observations, evaluation, interpretations and conclusions. • BOTTOM LINE: WILL THE TREATED WATER STAY BELOW THE SOIL SURFACE??

  10. Site Evaluation Two Stages of Evaluating a Site: 1st – Preliminary Data Collection 2nd – Field Data Collection

  11. Preliminary Data • Cultural features; ownership, parcel boundaries, buildings, easements, setbacks, field roads, wells, property lines, current & historic land use & vegetation • Sources: P & Z, SWCD, aerial photos

  12. Preliminary Data • Natural features; floodplains, wetlands, surface waters, direction of surface water runoff, groundwater flow direction, topography • Sources: P & Z, SWCD = surface water data; USGS/MGS/MDH = ground water flow direction

  13. Preliminary Data

  14. Preliminary DataSOILS: Online Soil Surveyhttp://websoilsurvey.nrcs.gov

  15. Preliminary Data • Design parameters; daily flows, size of proposed treatment area, size of area being considered • Regulatory input; meet w/permitting authority, LGUs, technical consultants, developer Is everyone… on the same page?

  16. Preliminary Data Before going into the field: Cultural and Natural Features should be recorded on a sketch map. OK…time to get into the field!

  17. Field DataWhat Is It? • Geomorphic Features - large scale units • Soil Features - small scale units

  18. Field DataWhy is it Important? DESIGN, DESIGN, DESIGN! • Accurate Soils Descriptions : Critical! • Interpretation of Soils Data : Critical!

  19. Field Data • Geomorphic Features - Parent Material: till, residuum, loess? - Landform: till plain, bedrock, outwash? - Landscape Position: side slope or toe slope? - Slope Characteristics: shape, position, length, gradient, aspect

  20. Field DataSlope Shapes

  21. Soil…what is it? • Natural body that occurs on the land surface, occupies space and is characterized by one or both of the following: - Horizons or layers, and/or - Ability to support rooted plants in a natural environment

  22. Field Data • Soil Features…what are they? - Horizons, Textures, Structure - Colors, Redoximorphic Features, Mottles - Consistance, Roots, Pores - Depth to Bedrock, Coarse Fragments, Lithologic Discontinuities - Water Status

  23. The Soils are REALLY Important!

  24. Recording Soil Descriptions

  25. Horizons • Influenced by: Time, Landscape, Parent Material, Vegetation, Climate

  26. Texture • Numerical proportion of sand, silt, clay (% by weight) • Usually done in field by hand (qualitative) • Important factor in influencing soil water movement

  27. Structure • Naturally occurring arrangement of soil particles…Peds • Grade, size, type, consistance • Important factor in soil water movement • Best described by excavations

  28. Color • Matrix: predominant color • Redoximorphic Features: chemistry, secondary color • Mottles: usually geologic, secondary color • Best described by natural light – avoid dawn/dusk

  29. Interpreting Soil Color • Color is an INDICATOR of … soil wetness • Critical Part of Evaluation…. and must be done correctly!

  30. Redoximorphic Features…What Are They?

  31. Redoximorphic Features(RMF) • Anaerobic conditions: - soil is saturated • Prolonged absence of O2 alters chemical process • Reduction of Fe and Mn oxides – results in distinct characteristics

  32. RMF and Minnesota MSTS & LSTS Guidance • RMF are used to determine: - Depth to Seasonally Saturated Soil (a restricting layer) - Operating Separation Distance (needed distance to meet treatment and hydraulic performance requirements)

  33. RMF Interpretation Problems • Not all wet soils develop RMF - Low amounts of soluble organic carbon (sands) - High pH - Cold temperatures - Low amounts of Fe (sands or parent material) - Aerated ground water (floodplains?) - Masking of RMF (overthickened topsoils)

  34. Soil Drainage Classes

  35. Soil Drainage as Related to Landscape

  36. Soil Water Movement…What Is It? • It Is: - Rate of flow OVER the soil (runoff) - Rate of flow INTO the soil (infiltration) - Rate of flow WITHIN the soil (hydraulic conductivity)

  37. Soil Permeability • NRCS Description - Qualitative analysis - Measured in units of length/time - Estimations derived from percolation tests, soil texture and structure - Concept has changed over time: Emphasis is now on quantitative data vs. qualitative data

  38. Soil Permeability

  39. Hydraulic Conductivity…A Better Way? • Quantifies soil’s ability to transmit water under standard conditions and units (pressure, length, cross-sectional area) • Saturated conditions are easiest to assess • Highly variable (pores, etc), therefore multiple reps recommended per area of interest • Field methods (natural conditions) generally more reliable than lab methods

  40. Hydraulic Conductivity…A Better Way? • Provides “measured” data in soil horizons: The horizon with the lowest Ksat value should be used for design purposes. • Field tools available: permeameters, infiltrometers, etc

  41. Hydraulic Conductivity…A Better Way?

  42. Soil Interpretation • Are the soil properties described favorable to downward movement of water? • Will the soils on the proposed site support the density of the intended use? • Do you have sufficient soils information to justify moving forward on this site?

  43. REVIEW

  44. Review • Preliminary Map - topography - conceptual MSTS/LSTS layout - Any existing soils data - Wells, roads, etc.

  45. Review • Mark-up Preliminary map - Soils data - Surface water - Soil water monitoring - Problem areas - Field notes

  46. Review • Discussion w/ Designer - Soil Descriptions - Soil Water - Soil Sizing Factors - Additional data needed - Revise layout? - Other issues?

  47. Review • Additional Soils Data?? - More soil borings per regulatory request? - Additional soil pits? - Piezometer data? - Hydraulic Conductivity data?

  48. CONCLUSION Large-scale MSTS/LSTS projects can benefit from professionals in the area of soil science and geology that can: 1) accurately describe soil properties, 2) model ground water characteristics, and 3) provide the designer with interpretation of water movement through the soils and substratums of the landscape.

  49. Resources • Soil Surveys: http://websoilsurvey.nrcs.gov • Soil Scientists: Minnesota Assoc. of Professional Soil Scientists http://mnsoilscientist.org • Geologists & Groundwater: http://usgs.gov www.geo.umn.edu.mgs www.mgwa.org www.health.state.mn.us/divs/eh/cwi

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