## *Exhibit 618-16 Wind Erodibility Groups (WEG) and Index. (Revised by MO6 March 2008)* 

+-----------------------------------------------------------------------+
| **Dry soil Wind**                                                     |
|                                                                       |
| **aggregates erodibility**                                            |
|                                                                       |
| **Properties of soil more than index (I)**                            |
|                                                                       |
| **WEG ^1^ ^3\ 4\ 5^ surface layer 0.84 mm (wt.%) (tons/ac/yr)**       |
+=======================================================================+
| 1 Very fine sand, fine sand, sand or coarse sand^2^ 1 310             |
|                                                                       |
| 2 250                                                                 |
|                                                                       |
| 3 220                                                                 |
|                                                                       |
| 5 180                                                                 |
|                                                                       |
| 7 160                                                                 |
+-----------------------------------------------------------------------+
| 2 Loamy very fine sand, loamy fine sand, loamy sand, loamy coarse     |
| sand; 10 134                                                          |
|                                                                       |
| very fine sandy loam and silt loam with 5 or less percent clay        |
|                                                                       |
| and 25 or less percent very fine sand; and sapric soil materials (as  |
| defined                                                               |
|                                                                       |
| in [Soil                                                              |
| Taxonomy](http://soils.usda.gov/classification/taxonomy/tax.pdf));    |
| except Folists                                                        |
+-----------------------------------------------------------------------+
| 3 Very fine sandy loam, fine sandy loam, sandy loam, coarse sandy     |
| loam; 25 86                                                           |
|                                                                       |
| and noncalcareous silt loam that has 20 to 50 percent very fine       |
|                                                                       |
| sand and 5 to 12 percent clay                                         |
+-----------------------------------------------------------------------+
| 4 Clay, silty clay, noncalcareous clay loam that has more than 35     |
| percent clay, and\                                                    |
| noncalcareous silty clay loam that has more than 35 percent clay. 25  |
| 86                                                                    |
|                                                                       |
| All of these do not have sesquic, parasesquic, ferritic, ferruginous, |
| or                                                                    |
|                                                                       |
| kaolinitic mineralogy (high iron oxide content).                      |
+-----------------------------------------------------------------------+
| 4L Calcareous ^6^ loam, calcareous silt loam, calcareous silt,        |
| calcareous sandy clay, 25 86                                          |
|                                                                       |
| calcareous sandy clay loam, calcareous clay loam and calcareous silty |
| clay loam                                                             |
+-----------------------------------------------------------------------+
| 5 Noncalcareous loam that has less than 20 percent clay;              |
| noncalcareous silt loam with 40 56\                                   |
| 12 to 20 percent clay; noncalcareous sandy clay loam; noncalcareous   |
| sandy clay;\                                                          |
| and hemic materials (as defined in [Soil                              |
| Taxonomy](http://soils.usda.gov/classification/taxonomy/tax.pdf)).    |
+-----------------------------------------------------------------------+
| 6 Noncalcareous loam and silt loam that have more than 20 percent     |
| clay; noncalcareous 45 48                                             |
|                                                                       |
| clay loam and noncalcareous silty clay loam that has less than 35     |
| percent clay;                                                         |
|                                                                       |
| silt loam that has parasesquic, ferritic, or kaolinitic mineralogy    |
| (high iron oxide                                                      |
|                                                                       |
| content)                                                              |
+-----------------------------------------------------------------------+
| 7.  Noncalcareous silt; noncalcareous silty clay, noncalcareous silty |
|     clay loam, and 50 38                                              |
|                                                                       |
| noncalcareous clay that have sesquic, parasesquic, ferritic,          |
| ferruginous, or                                                       |
|                                                                       |
| kaolinitic mineralogy (high content of iron oxide) and are Oxisols or |
| Ultisols;                                                             |
|                                                                       |
| and fibric material (as defined in [Soil                              |
| Taxonomy](http://soils.usda.gov/classification/taxonomy/tax.pdf))     |
+-----------------------------------------------------------------------+
| 8 Soils not susceptible to wind erosion due to rock and pararock      |
| fragments at the surface \-\-- 0                                      |
|                                                                       |
| and/or wetness; and Folists                                           |
+-----------------------------------------------------------------------+

^1^ For all WEGs except sands and loamy sand textures, if percent rock
and pararock fragments (\>2mm) by volume is 15-35, reduce \"I\" value by
one group with more favorable rating. If percent rock and pararock
fragments by volume is 35-60, reduce \"I\" value by two favorable groups
except for sands and loamy sand textures which are reduced by one group
with more favorable rating. If percent rock and pararock fragments is
greater than 60, use \"I\" value of 0 for all textures except sands and
loamy sand textures which are reduced by three groups with more
favorable ratings. An example of more favorable \"I\" rating is next
lower number - \"I\" factor of 160 to \"I\" factor of 134 or \"I\"
factor of 86 to \"I \"factor of 56. **[Note -- WEG is to be reduced an
amount equal to the what the "I" factor is reduced. For example, if "I"
is reduced from 160 to 134 then the WEG should be correspondingly
reduced from WEG 1 to WEG 2.]{.underline}**

^2^ The \"I\" values for WEG 1 vary from 160 for coarse sands to 310 for
very fine sands. Use an \"I\" of 220 as an average figure.

^3^ All material that meets criterion 2 in the requirements for andic
soil properties in Soil Taxonomy, regardless of the fine earth texture,
are placed in WEG 2.

^4^ All material that meets criterion 1 in the requirements for andic
soil properties in Soil Taxonomy, regardless of the fine earth texture,
are placed in WEG 6 except for medial classes of Cryic Spodosols having
MAAT \< 40 degrees F. which are placed in WEG 2.

^5^ Surface layers or horizons that do not meet andic soil properties
criteria but do meet Vitrandic, Vitritorrandic, and Vitrixerandic
subgroup criteria (thickness requirement excluded) move one group with
less favorable rating.

^6^ Calcareous is a strongly or violently effervescent reaction of the
fine-earth fraction to cold dilute (1N) HCL; a paper \"Computing the
Wind Erodible Fraction of Soils\" by D. W. Fryear et.al (1994) in the J.
Soil and Water Conservation 49 (2) 183-188 raises a yet unresolved
question regarding the effect of carbonates on wind erosion.