1. Using Soil Classification & Description Data
(What you Need to Know, Especially for Risk Assessment and Modeling)
VAP Spring 2015
Certified Professional Coffee

2. Soil Classification & Description
Purpose of training
Briefly review the most commonly used soil classification systems (USDA & USCS)
Identify some limitations and (associated misuses) of each system
Address some concerns about the use of soil classification and description data (especially for risk assessment and modeling)

3. Soil Classification & Description
Purpose of soil classification and description?
Provides soil property data in an organized, systematic manner to support an activity (environmental remediation, agriculture, construction, etc.)
Foundation of the conceptual site model for environmental remediation projects

4. Soil Classification & Description
Johnson and Ettinger model for estimating subsurface vapor intrusion into buildings
Uses USDA Soil Conservation Survey soil classification data to provide site-specific data for the following model parameters:
Soil bulk density
Total porosity
Water-filled porosity

5. Soil Classification & Description
Poor quality data often result from
A laissez-faire approach to soil (geologic) logging, which leads to
Failure to learn and consistently follow standard soil classification & description methods
Indiscriminately using different classification systems (“mix and match”), or making it up as you log along

6. Soil Classification & Description
Even good quality data can be misused when the user doesn’t understand
The classification system and what the data actually indicate about soil properties
Data limitations, e.g.,
Field vs. laboratory classification
Properties used as basis for a particular classification (USDA silt vs. USCS silt)

7. Soil Classification Systems
Unified Soil Classification System
Engineering and environmental applications
ASTM D (lab), ASTM D a (field)
USDA Soil Classification System
Agricultural, land development and environmental applications
USDA Soil Survey Manual

8. USDA Soil Classification System
Origin and purpose
Early soil science work, 1930s through 1940s by American and Russian scientists
U.S. National Cooperative Soil Survey officially adopted the USDA system in 1965 and published it in (Soil Taxonomy: A Basic System of Soil Classification for Making and Interpreting Soil Surveys)
Evaluates soils for agriculture, ranching, forestry (land development, non-farm uses important after 1950)

9. USDA Soil Classification System
USDA “Texture Triangle Diagram”
Twelve soil classes defined by %’s sand, silt, clay
Silty Clay = 40-60% clay, % silt, 0-20% sand
Lab analyses or field “texture by feel” analysis
Gravel not included (used as modifier); %’s sand, silt clay normalized to 100% without gravel

10. USDA Soil Classification System Particle Size Limits
SAND
SILT
CLAY
GRAVEL
2.00 mm
0.050 mm
0.002 mm
(Hydrometer)
(Sieves)
75 mm

11. USDA Soil Classification System
Soil class identification (e.g., “sandy loam”)
May be based on field examination or lab analysis of soil samples
Field examination, estimate % sand/silt/clay by
Plasticity (ability to form a soil “ribbon”
Feel of soil (gritty vs. smooth vs. greasy)
Accuracy of field identification? At best, +/- 10% to 15% (sand/silt/clay)

12. USDA Soil Classification System (Field Testing)

13. USDA Soil Classification System (Field Testing)
ribbon
length
estimates
% clay
“Gritty”
“Smooth”
Grittiness estimates % sand versus % silt

14. Unified Soil Classification System (USCS)
Origin and purpose
Developed in 1942 by Professor Arthur Casagrande for airfield construction during WWII
Most commonly used soil classification system
Applicable ASTM standards
ASTM D , Standard Classification for Engineering Purposes (laboratory testing)
ASTM D a, Standard Practice for Description and Identification of Soils (field evaluation)

15. Unified Soil Classification System (USCS)
Separates soils into two broad categories and then uses a flow-chart approach to classify based on soil properties (%’s by weight)
Coarse-grained soils, > 50% sand and gravel
“G” stands for gravel or gravelly soils
“S” stands for sand or sandy soils
Fine-grained soils, >= 50% silt and clay
“M” stands for silt or silty soils
“C” stands for clay or clayey soils

16. Unified Soil Classification System (USCS) Coarse-Grained Soil Classification
Less than 5% “fines” (silt and clay)
If the % sand is >= % gravel, SAND (S)
If the % gravel is > % sand, GRAVEL (G)
Greater than 15% fines
SILTY SAND (SM) or CLAYEY SAND (SC)
SILTY GRAVEL (GM) or CLAYEY GRAVEL (GC)

17. Unified Soil Classification System (USCS) Coarse-Grained Soil Classification: Grading
Well Graded (Poorly Sorted) Poorly Graded (Well Sorted)

18. Well Graded vs Poorly Graded

19. Unified Soil Classification System (USCS) Coarse-Grained Soil Classification
Between 5 and 15% fines (approx. 10%)?
Dual Symbol: two symbols separated by a hyphen, e.g., SP-SC, Poorly Graded Sand with Clay
1st symbol (SP) identifies sand or gravel and grading
2nd symbol (SC) identifies the type of fines (silt or clay)
Hydraulic conductivity significance (fines lower K by reducing effective porosity) + other soil properties

20. Unified Soil Classification System (USCS) Dual Symbols, Coarse-Grained Soils
Poorly Graded Gravel with Silt (GP-GM)
Poorly Graded Gravel with Clay (GP-GC)
Well-Graded Gravel with Silt (GW-GM)
Well-Graded Gravel with Clay (GW-GC)
Poorly Graded Sand with Silt (SP-SM)
Poorly Graded Sand with Clay (SP-SC)
Well-Graded Sand with Silt (SW-SM)
Well-Graded Sand with Clay (SW-SC)

21. Unified Soil Classification System (USCS) Fine-Grained Soil Classification
Fine-grained soil > or = 50% silt and/or clay
The USCS grain size limit for the silt (M) and clay (C) fractions is the same mm (passes #200 sieve)
(USDA system: silt fraction is between 0.05 and mm, clay fraction < or = mm)
USCS silt and clay classification is based on plastic properties (Atterberg Limits) and not particle size distribution

22. Unified Soil Classification System (USCS)
Atterberg Limits (based on laboratory testing, ASTM D2487)
Plastic Limit (PL), water content at which soil starts to exhibit plastic behavior
Liquid Limit (LL), water content at which soil starts to exhibit liquid behavior
Plasticity Index, PI, numeric difference between LL and PL, measure of plasticity; clays have a high PI, silts have a low PI

23. Unified Soil Classification System (USCS) Fine-Grained Soil Classification, Plasticity Chart

24. Unified Soil Classification System (USCS) Fine-Grained Soil Classification, Field Plasticity Tests (based on Table 12, ASTM D a)

25. Unified Soil Classification System (USCS) Fine-Grained Soil Classification
Percentages of sand or gravel?
If < 15% sand or gravel, no qualifier needed, e.g., “lean clay”
If 15-25% sand or gravel, add “with sand” (%S > or = %G) or “with gravel” (%G > %S), e.g., “lean clay with sand”
If > 30 % sand or gravel, add “sandy” (%S > or = %G) or “gravelly” (%G > %S), e.g., “sandy lean clay”

26. USCS vs. USDA Particle Size Comparison
Unified Soil Classification System
GRAVEL
SAND
SILT and CLAY
75 mm
4.75 mm
0.074 mm (#200 sieve)
CLAY
SILT
USDA Soil Classification System
2.00 mm
0.05 mm
0.002 mm
ATTERBERG LIMITS

27. Misuse of Soil Classification Systems Scenario #1
A model utilizes USDA soil classification data (the results will be used to evaluate risk). Is substituting USCS soil type data for “equivalent” USDA soil type data appropriate? For example, can we assume that that USCS lean clay and sandy clay are equivalent to USDA clay and sandy clay?

28. USDA Soil Types
Direct Comparison of USCS & USDA Lab
Classification of 62 Soil Samples From
Cuyahoga, Franklin, Hamilton, Lucas and
Montgomery Counties (DERR County Background Sampling)

29. Misuse of Soil Classification Systems Scenario #1
Ohio EPA geotechnical laboratory data indicates
USCS lean clay may classify as USDA silty clay, clay loam, silty clay loam, loam or silt loam (but not clay)
USCS clayey sand classifies as USDA sandy loam (not clayey sand)

30. Misuse of Soil Classification Systems Scenario #1
USCS and USDA are not “mix and match” systems (soil types aren’t equivalents)
Some soil classification types may not occur in a given geographic area or site locations
USCS elastic silt (MH) is not common in Ohio
Based on DERR’s county soil data to date, USDA clay, sandy clay, and sandy clay loam are not common in Ohio

31. U.S. Army Corps of Engineers,
Electromagnetic Power Attenuation in Soils,
ERDC/EL TR-05-5, August 2005

32. USCS vs. USDA Particle Size Comparison
Unified Soil Classification System
GRAVEL
SAND
SILT and CLAY
75 mm
4.75 mm
0.074 mm (#200 sieve)
CLAY
SILT
USDA Soil Classification System
2.00 mm
0.05 mm
0.002 mm
ATTERBERG LIMITS

33. Misuse of Soil Classification Systems Scenario #1 (Continued)
If you perform hydrometer analysis (ASTM D422) to determine the clay (> mm) fraction for a soil sample classified according to the USCS, can you use the clay data with the USCS sand and silt %’s to determine the USDA soil type?

34. USCS vs. USDA Particle Size Comparison
Unified Soil Classification System
GRAVEL
SAND
SILT and CLAY
75 mm
4.75 mm
0.074 mm (#200 sieve)
CLAY
SILT
USDA Soil Classification System
2.00 mm
0.05 mm
0.002 mm
ATTERBERG LIMITS

35. USCS vs. USDA Lab Testing
USCS “Must Haves”
USDA “Must Haves”
Sieve Sizes
#4 (gravel/sand)
#200 (sand/[silt+clay])
Atterberg Limits
Sieve Sizes
#10 (gravel/sand)
Hydrometer
0.05 mm fraction (sand/silt)
0.002 mm fraction
(silt /clay)

36. USCS vs. USDA Lab Testing
USCS Options
USDA Options
Sieve Sizes
¾” (c. gravel/f. gravel)
#10 (c. sand/m. sand)
#40 (m. sand/f. sand)
Hydrometer
0.005 mm or mm fractions (clay)
Sieve Sizes
#18 (v.c. sand/c. sand)
#35 (c. sand/m. sand)
#60 (m. sand/f. sand)
#140 (f. sand/v.f. sand)

37. Misuse of Soil Classification Systems Scenario #2
You are reviewing existing soil boring logs for a new site. The previous consultant’s assessment report states that they logged soils using the USCS per ASTM D a. You note that the terms “loam” and “loamy” are used with USCS terminology, and that “silty clay” appears frequently as a field soil description. Do you have any concerns?

38. Misuse of Soil Classification Systems Scenario #2
Problems with consultant’s soil classification:
Never appropriate to combine USCS and USDA soil classification terminology
USCS silty clay or USDA silty clay? (significant difference)
USCS silty clay? Should have used the term “lean clay” instead per ASTM D a and ASTM D (“silty clay” can’t be classified in the field)

39. Unified Soil Classification System (USCS) Fine-Grained Soil Classification, Plasticity Chart

40. Misuse of Soil Classification Systems Scenario #3
You need to determine USDA soil types for a Phase II property assessment in Hamilton County. You have soil type data from several sites in Franklin County. Both counties are covered with till, which consistently classifies as clay loam or silty clay loam at the Franklin County sites. Would assuming that the Hamilton County soils are clay loam or silty clay loam based on the Franklin County data be appropriate?

41. (DERR County Background Sampling, Soil Laboratory Results)
Comparison of USDA Soil Classification for Franklin and Hamilton Counties
(DERR County Background Sampling, Soil Laboratory Results)

42. (DERR County Background Sampling, Soil Laboratory Results)
Comparison of USDA Soil Classification for Franklin, Lucas, and Hamilton Counties
(DERR County Background Sampling, Soil Laboratory Results)

43. Recommendations for Using Soil Classification Data
Become familiar with both the USCS and USDA soil classification system basics
Never substitute USCS data for USDA soil classification data (directly or by manipulation)
Request soil laboratory testing/classification for modeling and risk assessment purposes

44. Recommendations for Using Soil Classification Data
Question soil classification (field or lab) that doesn’t appear to follow a standard system
Never assume the soil type(s) at one site is/are comparable to another site based on the origin of geologic material (or proximity)

45. Thanks for your time and attention!
Questions?
Thanks for your time and attention!