Site and Soil Investigations Terry L. BoveeSteve Lawler Professional Soil Scientists Henderson, MN 56044Rochester, MN Minnesota Onsite Wastewater Convention March 13-15, 2006

Site & Soil Evaluation for Medium and Large Sized Sewage Treatment Systems (MSTS and LSTS)

From this…

To this…

You Need A Lot of Information!

What is the Purpose of a Site Evaluation??

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.

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

Site Evaluation Getting 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??

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

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

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

Preliminary Data

Preliminary Data SOILS: Online Soil Survey

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?

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!

Field Data What Is It? Geomorphic Features - large scale units Soil Features - small scale units

Field Data Why is it Important? DESIGN, DESIGN, DESIGN! Accurate Soils Descriptions : Critical! Interpretation of Soils Data : Critical!

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

Field Data Slope Shapes

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

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

The Soils are REALLY Important!

Recording Soil Descriptions

Horizons Influenced by: Time, Landscape, Parent Material, Vegetation, Climate

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

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

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

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

Redoximorphic Features… What Are They?

Redoximorphic Features (RMF) Anaerobic conditions: - soil is saturated Prolonged absence of O 2 alters chemical process Reduction of Fe and Mn oxides – results in distinct characteristics

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)

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)

Soil Drainage Classes

Soil Drainage as Related to Landscape

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)

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

Soil Permeability

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

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

Hydraulic Conductivity… A Better Way?

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?

REVIEW

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

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

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

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

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.

Resources Soil Surveys: Soil Scientists: Minnesota Assoc. of Professional Soil Scientists Geologists & Groundwater: