Appendix 6 
MARICOPA COUNTY 

APPENDIX C 

FUGITIVE DUST TEST METHODS 

INDEX 

SECTION 1 – [RESERVED]

SECTION 2 – TEST METHODS FOR STABILIZATION

SECTION 3 – VISUAL OPACITY DETERMINATION OF EMISSIONS FROM DUSTGENERATING OPERATIONS

SECTION 4 – VISUAL OPACITY DETERMINATION OF EMISSIONS FROM 

LIVESTOCK ACTIVITIES – CORRALS, PENS, AND ARENAS 

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BLANK PAGE 

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Adopted 06/16/99 

Revised 02/16/00 

Revised 04/07/04 

Revised 03/26/08 

MARICOPA COUNTY 

AIR POLLUTION CONTROL REGULATIONS 

APPENDIX C 

FUGITIVE DUST TEST METHODS 

1. [RESERVED] 

2. TEST METHODS FOR STABILIZATION 

2.1 For Unpaved Roads and Unpaved Parking Lots: 

2.1.1 Opacity Test Method: The purpose of this test method is to estimate the 

percent opacity of fugitive dust plumes caused by vehicle movement on 

unpaved roads and unpaved parking lots. This method can only be conducted 

by an individual who has received certification as a qualified observer. 

Qualification and testing requirements can be found in Section 3.4 of this 

appendix. 

a. Step 1: Stand at least 16.5 feet from the fugitive dust source in order to 

provide a clear view of the emissions with the sun oriented in the 140° sector 

to the back. Following the above requirements, make opacity observations so 

that the line of vision is approximately perpendicular to the dust plume and 

wind direction. If multiple plumes are involved, do not include more than 

one plume in the line of sight at one time. 

b. Step 2: Record the fugitive dust source location, source type, method of 

control used, if any, observer's name, certification data and affiliation, and a 

sketch of the observer's position relative to the fugitive dust source. Also 

record the time, estimated distance to the fugitive dust source location, 

approximate wind direction, estimated wind speed, description of the sky 

condition (presence and color of clouds), observer's position to the fugitive 

dust source, and color of the plume and type of background on the visible 

emission observation from both when opacity readings are initiated and 

completed. 

c. Step 3: Make opacity observations, to the extent possible, using a 

contrasting background that is perpendicular to the line of vision. Make 

opacity observations approximately 1 meter above the surface from which 

the plume is generated. Note that the observation is to be made at only one 

visual point upon generation of a plume, as opposed to visually tracking the 

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entire length of a dust plume as it is created along a surface. Make two 

observations per vehicle, beginning with the first reading at zero seconds and 

the second reading at five seconds. The zero-second observation should 

begin immediately after a plume has been created above the surface 

involved. Do not look continuously at the plume but, instead, observe the 

plume briefly at zero seconds and then again at five seconds. 

d. Step 4: Record the opacity observations to the nearest 5% on an observational record sheet. Each momentary observation recorded represents the 

average opacity of emissions for a 5-second period. While it is not required 

by the test method, EPA recommends that the observer estimate the size of 

vehicles which generate dust plumes for which readings are taken (e.g. midsize passenger car or heavy-duty truck) and the approximate speeds the 

vehicles are traveling when readings are taken. 

e. Step 5: Repeat Step 3 (Section 2.1.1(c) of this appendix) and Step 4 (Section 

2.1.1(d) of this appendix) until you have recorded a total of 12 consecutive 

opacity readings. This will occur once six vehicles have driven on the source 

in your line of observation for which you are able to take proper readings. 

The 12 consecutive readings must be taken within the same period of 

observation but must not exceed 1 hour. Observations immediately 

preceding and following interrupted observations can be considered 

consecutive. 

f. Step 6: Average the 12 opacity readings together. If the average opacity 

reading equals 20% or lower, the source is in compliance 

2.1.2 Silt Content Test Method: The purpose of this test method is to estimate the 

silt content of the trafficked parts of unpaved roads and unpaved parking lots. 

The higher the silt content, the more fine dust particles that are released when 

cars and trucks drive on unpaved roads and unpaved parking lots. 

a. Equipment: 

(1) A set of sieves with the following openings: 4 millimeters (mm), 2 mm, 

1 mm, 0.5 mm and 0.25 mm (or a set of standard/commonly available 

sieves), a lid, and collector pan. 

(2) A small whisk broom or paintbrush with stiff bristles and dustpan 1 ft. in 

width. (The broom/brush should preferably have one, thin row of bristles 

no longer than 1.5 inches in length). 

(3) A spatula without holes. 

(4) A small scale with half-ounce increments (e.g., postal/package scale). 

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(5) A shallow, lightweight container (e.g., plastic storage container). 

(6) A sturdy cardboard box or other rigid object with a level surface. 

(7) A basic calculator. 

(8) Cloth gloves (optional for handling metal sieves on hot, sunny days). 

(9) Sealable plastic bags (if sending samples to a laboratory). 

(10) A pencil/pen and paper. 

b. Step 1: Look for a routinely traveled surface, as evidenced by tire tracks. 

(Only collect samples from surfaces that are not damp due to precipitation or 

dew. This statement is not meant to be a standard in itself for dampness 

where watering is being used as a control measure. It is only intended to 

ensure that surface testing is done in a representative manner.) Use caution 

when taking samples to ensure personal safety with respect to passing 

vehicles. Gently press the edge of a dustpan (1 foot in width) into the surface 

four times to mark an area that is 1 square foot. Collect a sample of loose 

surface material using a whiskbroom or brush and slowly sweep the material 

into the dustpan, minimizing escape of dust particles. Use a spatula to lift 

heavier elements such as gravel. Only collect dirt/gravel to an approximate 

depth of 3/8 inch or 1 cm in the 1 square foot area. If you reach a hard, 

underlying subsurface that is < 3/8 inch in depth, do not continue collecting 

the sample by digging into the hard surface. In other words, you are only 

collecting a surface sample of loose material down to 1 cm. In order to 

confirm that samples are collected to 1 cm in depth, a wooden dowel or 

other similar narrow object at least one foot in length can be laid 

horizontally across the survey area while a metric ruler is held perpendicular 

to the dowel. 

At this point, you can choose to place the sample collected into a plastic bag 

or container and take it to an independent laboratory for silt content analysis. 

A reference to the procedure the laboratory is required to follow is at the end 

of this section. 

c. Step 2: Place a scale on a level surface. Place a lightweight container on the 

scale. Zero the scale with the weight of the empty container on it. Transfer 

the entire sample collected in the dustpan to the container, minimizing 

escape of dust particles. Weigh the sample and record its weight. 

d. Step 3: Stack a set of sieves in order according to the size openings specified 

above, beginning with the largest size opening (4 mm) at the top. Place a 

collector pan underneath the bottom (0.25 mm) sieve. 

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e. Step 4: Carefully pour the sample into the sieve stack, minimizing escape of 

dust particles by slowly brushing material into the stack with a whiskbroom 

or brush. (On windy days, use the trunk or door of a car as a wind barricade.) 

Cover the stack with a lid. Lift up the sieve stack and shake it vigorously up, 

down and sideways for at least 1 minute. 

f. Step 5: Remove the lid from the stack and disassemble each sieve 

separately, beginning with the top sieve. As you remove each sieve, examine 

it to make sure that all of the material has been sifted to the finest sieve 

through which it can pass (e.g., material in each sieve [besides the top sieve 

that captures a range of larger elements] should look the same size). If this is 

not the case, re-stack the sieves and collector pan, cover the stack with the 

lid, and shake it again for at least 1 minute. (You only need to reassemble 

the sieve(s) that contain material, which requires further sifting.) 

g. Step 6: After disassembling the sieves and collector pan, slowly sweep the 

material from the collector pan into the empty container originally used to 

collect and weigh the entire sample. Take care to minimize escape of dust 

particles. You do not need to do anything with material captured in the 

sieves; only the collector pan. Weigh the container with the material from 

the collector pan and record its weight. 

h. Step 7: If the source is an unpaved road, multiply the resulting weight by 

0.38. If the source is an unpaved parking lot, multiply the resulting weight 

by 0.55. The resulting number is the estimated silt loading. Then, divide by 

the total weight of the sample you recorded earlier in Step 2 (Section 

2.1.2(c) of this appendix) and multiply by 100 to estimate the percent silt 

content. 

i. Step 8: Select another two routinely traveled portions of the unpaved road or 

unpaved parking lot and repeat this test method. Once you have calculated 

the silt loading and percent silt content of the 3 samples collected, average 

your results together. 

j. Step 9: Examine results. If the average silt loading is less than 0.33 oz/ft2, 

the surface is STABLE. If the average silt loading is greater than or equal to 

0.33 oz/ft2, then proceed to examine the average percent silt content. If the 

source is an unpaved road and the average percent silt content is 6% or less, 

the surface is STABLE. If the source is an unpaved parking lot and the 

average percent silt content is 8% or less, the surface is STABLE. If your 

field test results are within 2% of the standard (for example, 4%–8% silt 

content on an unpaved road), it is recommended that you collect 3 additional 

samples from the source according to Step 1 (Section 2.1.2(b) of this appendix) and take them to an independent laboratory for silt content analysis. 

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k. Independent Laboratory Analysis: You may choose to collect 3 samples 

from the source, according to Step 1 (Section 2.1.2(b) of this appendix), and 

send them to an independent laboratory for silt content analysis rather than 

conduct the sieve field procedure. If so, the test method the laboratory is 

required to use is: U.S. Environmental Protection Agency (1995), “Procedures for Laboratory Analysis of Surface/Bulk Dust Loading Samples”, 

(AP-42 Fifth Edition, Volume I, Appendix C.2.3 “Silt Analysis”), Office of 

Air Quality Planning and Standards, Research Triangle Park, North 

Carolina. 

2.2 Stabilization Limitations for Open Areas and Vacant Lots: The test methods 

described in Section 2.3 through Section 2.7 of this appendix shall be used to determine whether an open area or a vacant lot has a stabilized surface. Should a disturbed 

open area or vacant lot contain more than one type of disturbance, soil, vegetation, or 

other characteristics, which are visibly distinguishable, test each representative surface 

separately for stability, in an area that represents a random portion of the overall 

disturbed conditions of the site, according to the appropriate test methods in Section 

2.3 through Section 2.7 of this appendix. 

2.3 Soil Crust Determination (the Drop Ball Test): 

2.3.1 Drop a steel ball with a diameter of 15.9 millimeters (0.625 inches) and a mass 

ranging from 16-17 grams (0.56-0.60 ounce) from a distance of one foot 

directly above (at a 90° angle perpendicular to) the soil surface. If blowsand is 

present, clear the blowsand from the surfaces on which the drop ball test is 

conducted. Blowsand is defined as thin deposits of loose uncombined grains 

covering less than 50% of a vacant lot or project site that have not originated 

from the representative surface being tested. If material covers a visible crust, 

which is not blowsand, apply the test method in Section 2.4: Determination of 

Threshold Friction Velocity (TFV) of this appendix to the loose material to 

determine whether the surface is stabilized. 

2.3.2 A sufficient crust is defined under the following conditions: once a ball has 

been dropped according to Section 2.3.1 of this appendix, the ball does not sink 

into the surface, so that it is partially or fully surrounded by loose grains and, 

upon removing the ball, the surface upon which it fell has not been pulverized, 

so that loose grains are visible. 

2.3.3 Randomly select each representative disturbed surface for the drop ball test by 

using a blind “over the shoulder” toss of a throwable object (e.g., a metal 

weight with survey tape attached). Using the point of fall as the lower left-hand 

corner, measure a one-foot square area. Drop the ball three times within the 

one-foot by one-foot square survey area, using a consistent pattern across the 

survey area. The survey area shall be considered to have passed the drop ball 

test if at least two out of the three times that the ball was dropped, the results 

met the criteria in Section 2.3.2 of this appendix. Select at least two other 

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survey areas that represent a random portion of the overall disturbed conditions 

of the site, and repeat this procedure. If the results meet the criteria of Section 

2.3.2 of this appendix for all of the survey areas tested, then the site shall be 

considered to have passed the drop ball test and shall be considered sufficiently 

crusted. 

2.3.4 At any given site, the existence of a sufficient crust covering one portion of the 

site may not represent the existence or protectiveness of a crust on another 

portion of the site. Repeat the drop ball test as often as necessary on each 

portion of the overall conditions of the site using the random selection method 

set forth in Section 2.3.3 of this appendix for an accurate assessment. 

2.4 Determination of Threshold Friction Velocity (TFV): For disturbed surface areas 

that are not crusted or vegetated, determine threshold friction velocity (TFV) according 

to the following sieving field procedure (based on a 1952 laboratory procedure 

published by W. S. Chepil). 

2.4.1 Obtain and stack a set of sieves with the following openings: 4 millimeters 

(mm), 2 mm, 1 mm, 0.5 mm, and 0.25 mm or obtain and stack a set of 

standard/commonly available sieves. Place the sieves in order according to size 

openings, beginning with the largest size opening at the top. Place a collector 

pan underneath the bottom (0.25 mm) sieve. Collect a sample of loose surface 

material from an area at least 30 cm by 30 cm in size to a depth of 

approximately 1 cm using a brush and dustpan or other similar device. Only 

collect soil samples from dry surfaces (i.e., when the surface is not damp to the 

touch). Remove any rocks larger than 1 cm in diameter from the sample. Pour 

the sample into the top sieve (4-mm opening) and cover the sieve/collector pan 

unit with a lid. Minimize escape of particles into the air when transferring 

surface soil into the sieve/collector pan unit. Move the covered sieve/collector 

pan unit by hand using a broad, circular arm motion in the horizontal plane. 

Complete twenty circular arm movements, ten clockwise and ten counterclockwise, at a speed just necessary to achieve some relative horizontal motion 

between the sieves and the particles. Remove the lid from the sieve/collector 

pan unit and disassemble each sieve separately beginning with the largest sieve. 

As each sieve is removed, examine it for loose particles. If loose particles have 

not been sifted to the finest sieve through which they can pass, reassemble and 

cover the sieve/collector pan unit and gently rotate it an additional ten times. 

After disassembling the sieve/collector pan unit, slightly tilt and gently tap each 

sieve and the collector pan so that material aligns along one side. In doing so, 

minimize escape of particles into the air. Line up the sieves and collector pan in 

a row and visibly inspect the relative quantities of catch in order to determine 

which sieve (or whether the collector pan) contains the greatest volume of 

material. If a visual determination of relative volumes of catch among sieves is 

difficult, use a graduated cylinder to measure the volume. Estimate TFV for the 

sieve catch with the greatest volume using Table 1 of this appendix, which 

provides a correlation between sieve opening size and TFV. 

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Table 1. Determination of Threshold Friction Velocity 

Tyler Sieve No. ASTM 11 Sieve No. Opening (mm) TFV(cm/s)

5 5 4 135 

9 10 2 100 

16 18 1 76 

32 35 0.5 58 

60 60 0.25 43 

Collector Pan ⎯ ⎯ 30 

2.4.2 Collect at least three soil samples which represent random portions of the overall conditions of the site, repeat the above TFV test method for each sample and 

average the resulting TFVs together to determine the TFV uncorrected for nonerodible elements. Non-erodible elements are distinct elements, in the random 

portion of the overall conditions of the site, that are larger than 1 cm in 

diameter, remain firmly in place during a wind episode, and inhibit soil loss by 

consuming part of the shear stress of the wind. Non-erodible elements include 

stones and bulk surface material but do not include flat or standing vegetation. 

For surfaces with non-erodible elements, determine corrections to the TFV by 

identifying the fraction of the survey area, as viewed from directly overhead, 

that is occupied by non-erodible elements using the following procedure. For a 

more detailed description of this procedure, see Section 2.7 (Test Methods for 

Stabilization-Rock Test Method) of this appendix. Select a survey area of 1 

meter by 1 meter that represents a random portion of the overall conditions of 

the site. Where many non-erodible elements lie within the survey area, separate 

the non-erodible elements into groups according to size. For each group, 

calculate the overhead area for the non-erodible elements according to the 

following equations: 

 Average Length × Average Width = Average Dimensions Eq. 1 

 Average Dimensions × Number of Elements = Overhead Area Eq. 2 

 Overhead Area of Group 1 + Overhead Area of Group 2 (etc.) = Total Overhead Area Eq. 3 

 Total Overhead Area ÷ 2 = Total Frontal Area Eq. 4 

 (Total Frontal Area ÷ Survey Area) × 100 = Percent Cover of Non-Erodible Elements Eq. 5 

 Note: Ensure consistent units of measurement (e.g., square meters or square 

inches) when calculating percent cover. 

 Repeat this procedure on an additional two distinct survey areas that represent a 

random portion of the overall conditions of the site and average the results. Use 

Table 2 of this appendix to identify the correction factor for the percent cover of 

non-erodible elements. Multiply the TFV by the corresponding correction 

factor to calculate the TFV corrected for non-erodible elements. 

 

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Table 2. Correction Factors for Threshold Friction Velocity 

Percent Cover of Non-Erodible Elements Factor

Correction 

Factor

Greater than or equal to 10% 5

Greater than or equal to 5% and less than 10% 3

Less than 5% and greater than or equal to 1% 2

Less than 1% None

2.5 Determination of Flat Vegetative Cover: Flat vegetation includes attached (rooted) 

vegetation or unattached vegetative debris lying on the surface with a predominant 

horizontal orientation that is not subject to movement by wind. Flat vegetation, which 

is dead but firmly attached, shall be considered equally protective as live vegetation. 

Stones or other aggregate larger than 1 centimeter in diameter shall be considered 

protective cover in the course of conducting the line transect test method. Where flat 

vegetation exists, conduct the following line transect test method. 

2.5.1 Line Transect Test Method: Stretch a 100-foot measuring tape across a survey 

area that represents a random portion of the overall conditions of the site. 

Firmly anchor both ends of the measuring tape into the surface using a tool 

such as a screwdriver, with the tape stretched taut and close to the soil surface. 

If vegetation exists in regular rows, place the tape diagonally (at approximately 

a 45° angle) away from a parallel or perpendicular position to the vegetated 

rows. Pinpoint an area the size of a 3/32 inch diameter brazing rod or wooden 

dowel centered above each 1-foot interval mark along one edge of the tape. 

Count the number of times that flat vegetation lies directly underneath the 

pinpointed area at 1-foot intervals. Consistently observe the underlying surface 

from a 90° angle directly above each pinpoint on one side of the tape. Do not 

count the underlying surface as vegetated if any portion of the pinpoint extends 

beyond the edge of the vegetation underneath in any direction. If clumps of 

vegetation or vegetative debris lie underneath the pinpointed area, count the 

surface as vegetated, unless bare soil is visible directly below the pinpointed 

area. When 100 observations have been made, add together the number of times 

a surface was counted as vegetated. This total represents the percent of flat 

vegetation cover (e.g., if 35 positive counts were made, then vegetation cover is 

35%). If the survey area that represents a random portion of the overall conditions of the site is too small for 100 observations, make as many observations as 

possible. Then multiply the count of vegetated surface areas by the appropriate 

conversion factor to obtain percent cover. For example, if vegetation was 

counted 20 times within a total of 50 observations, divide 20 by 50 and multiply 

by 100 to obtain a flat vegetation cover of 40%. 

2.5.2 Conduct the line transect test method, as described in Section 2.5.1 of this 

appendix, an additional two times on areas that represent a random portion of 

the overall conditions of the site and average results. 

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2.6 Determination of Standing Vegetative Cover: Standing vegetation includes 

vegetation that is attached (rooted) with a predominant vertical orientation. Standing 

vegetation, which is dead but firmly rooted, shall be considered equally protective as 

live vegetation. Conduct the following standing vegetation test method to determine if 

30% cover or more exists. If the resulting percent cover is less than 30% but equal to or 

greater than 10%, then conduct the test in Section 2.4 (Determination of Threshold 

Friction Velocity [TFV]) of this appendix in order to determine if the site is stabilized, 

such that the standing vegetation cover is equal to or greater than 10%, where threshold 

friction velocity, corrected for non-erodible elements, is equal to or greater than 43 

cm/second. 

2.6.1 For standing vegetation that consists of large, separate vegetative structures 

(e.g., shrubs and sagebrush), select a survey area that represents a random 

portion of the overall conditions of the site that is the shape of a square with 

sides equal to at least 10 times the average height of the vegetative structures. 

For smaller standing vegetation, select a survey area of three feet by three feet. 

2.6.2 Count the number of standing vegetative structures within the survey area. 

Count vegetation, which grows in clumps as a single unit. Where different 

types of vegetation exist and/or vegetation of different height and width exists, 

separate the vegetative structures with similar dimensions into groups. Count 

the number of vegetative structures in each group within the survey area. Select 

an individual structure within each group that represents the average height and 

width of the vegetation in the group. If the structure is dense (e.g., when 

looking at it vertically from base to top there is little or zero open air space 

within its perimeter), calculate and record its frontal silhouette area, according 

to Equation 6 of this appendix. Also, use Equation 6 of this appendix to 

estimate the average height and width of the vegetation if the survey area is 

larger than nine square feet. Otherwise, use the procedure in Section 2.6.3 of 

this appendix to calculate the frontal silhouette area. Then calculate the percent 

cover of standing vegetation according to Equations 7, 8, and 9 of this 

appendix. 

 Average Height × Average Width = Frontal Silhouette Area Eq. 6 

 Frontal Silhouette Area of Individual Vegetative Structure × 

 Number of Vegetation Structures Per Group = Frontal Silhouette Area of Group Eq. 7 

 Frontal Silhouette Area of Group 1 + Frontal Silhouette Area of Group 2 (etc.) 

 = Total Frontal Silhouette Area. Eq. 8 

 (Total Frontal Silhouette Area ÷ Survey Area) × 100 

 = Percent Cover of Standing Vegetation Eq. 9 

 [(Number of Circled Gridlines within the Outlined Area Counted that are not Covered 

 by Vegetation ÷ Total Number of Gridline Intersections within the Outlined Area) × 100] 

 = Percent Open Space Eq. 10 

 100 – Percent Open Space = Percent Vegetative Density Eq. 11 

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 Percent Vegetative Density ÷ 100 = Vegetative Density Eq. 12 

 

 Max. Height × Max. Width × (Vegetative Density ÷ 0.4)0.5 = Frontal Silhouette Area Eq. 13 

 Note: Ensure consistent units of measurement (e.g., square meters or square 

inches) when calculating percent cover.

2.6.3 Vegetative Density Factor: Cut a single, representative piece of vegetation (or 

consolidated vegetative structure) to within 1 cm of surface soil. Using a white 

paper grid or transparent grid over white paper, lay the vegetation flat on top of 

the grid (but do not apply pressure to flatten the structure). Grid boxes of 1-inch 

or 1⁄2-inch squares are sufficient for most vegetation when conducting this 

procedure. Using a marker or pencil, outline the shape of the vegetation along 

its outer perimeter, according to Figure B, C, or D of this appendix, as appropriate. (Note: Figure C differs from Figure D primarily in that the width of 

vegetation in Figure C is narrow at its base and gradually broadens to its tallest 

height. In Figure D, the width of the vegetation generally becomes narrower 

from its midpoint to its tallest height.) Remove the vegetation, count and record 

the total number of gridline intersections within the outlined area, but do not 

count gridline intersections that connect with the outlined shape. There must be 

at least 10 gridline intersections within the outlined area and preferably more 

than 20, otherwise, use smaller grid boxes. Draw small circles (no greater than 

a 3/32-inch diameter) at each gridline intersection counted within the outlined 

area. Replace the vegetation on the grid within its outlined shape. From a 

distance of approximately 2 feet directly above the grid, observe each circled 

gridline intersection. Count and record the number of circled gridline 

intersections that are not covered by any piece of the vegetation. To calculate 

percent vegetative density, use Equations 10 and 11 of this appendix. If percent 

vegetative density is equal to or greater than 30, use an equation (one of the 

Equations 14, 15, or 16 of this appendix) that matches the outline used to trace 

the vegetation (Figure B, C, or D) to calculate its frontal silhouette area. If 

percent vegetative density is less than 30, use Equations 12 and 13 of this 

appendix to calculate the frontal silhouette area. 

Figure B. Cylinder

 Frontal Silhouette Area = Maximum Height × Maximum Width Eq. 14 

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Figure C. Inverted Cone 

 Frontal Silhouette Area = Maximum Height × 1⁄2 Maximum Width Eq. 15 

Figure D. Upper Sphere 

 Frontal Silhouette Area = (3.14 × Maximum Height × 1⁄2 Maximum Width) ÷ 2 Eq. 16 

2.7 Rock Test Method: The Rock Test Method, which is similar to Section 2.4 (Test 

Methods for Stabilization-Determination of Threshold Friction Velocity [TFV]) of this 

appendix, examines the wind-resistance effects of rocks and other non-erodible elements on disturbed surfaces. Non-erodible elements are objects larger than 1 centimeter 

(cm) in diameter that remain firmly in place even on windy days. Typically, nonerodible elements include rocks, stones, glass fragments, and hard-packed clumps of 

soil lying on or embedded in the surface. Vegetation does not count as a non-erodible 

element in this method. The purpose of this test method is to estimate the percent cover 

of non-erodible elements on a given surface to see whether such elements take up 

enough space to offer protection against windblown dust. For simplification, the 

following test method refers to all non-erodible elements as “rocks”. 

2.7.1 Select a 1-meter × 1-meter survey area that represents the general rock 

distribution on the surface. (A 1-meter × 1-meter area is slightly greater than a 

3-foot × 3-foot area). Mark off the survey area by tracing a straight, visible line 

in the dirt along the edge of a measuring tape or by placing short ropes, yard 

sticks, or other straight objects in a square around the survey area.

2.7.2 Without moving any of the rocks or other elements, examine the survey area. 

Since rocks > 3/8 inch (1 cm) in diameter are of interest, measure the diameter 

of some of the smaller rocks to a get a sense for which rocks need to be 

considered. 

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2.7.3 Mentally group the rocks > 3/8 inch (1 cm) diameter lying in the survey area 

into small, medium, and large size categories. Or, if the rocks are all approximately the same size, simply select a rock of average size and typical shape. 

Without removing any of the rocks from the ground, count the number of rocks 

in the survey area in each group and write down the resulting number. 

2.7.4 Without removing rocks, select one or two average-size rocks in each group 

and measure the length and width. Use either metric units or standard units. 

Using a calculator, multiply the length times the width of the rocks to get the 

average dimensions of the rocks in each group. Write down the results for each 

rock group. 

2.7.5 For each rock group, multiply the average dimensions (length times width) by 

the number of rocks counted in the group. Add the results from each rock group 

to get the total rock area within the survey area. 

2.7.6 Divide the total rock area, calculated in Section 2.7.5 of this appendix, by two 

(to get frontal area). Divide the resulting number by the size of the survey area 

(making sure the units of measurement match), and multiply by 100 for percent 

rock cover. For example, the total rock area is 1,400 square centimeters, divide 

1,400 by 2 to get 700. Divide 700 by 10,000 (the survey area is 1 meter by 1 

meter, which is 100 centimeters by 100 centimeters or 10,000 square 

centimeters), and multiply by 100. The result is 7% rock cover. If rock 

measurements are made in inches, convert the survey area from meters to 

inches (1 inch = 2.54 centimeters). 

2.7.7 Select and mark off two additional survey areas and repeat the procedures 

described in Sections 2.7.1 through 2.7.6 of this appendix. Make sure the 

additional survey areas also represent the general rock distribution on the site. 

Average the percent cover results from all three survey areas to estimate the 

average percent of rock cover. 

2.7.8 If the average rock cover is greater than or equal to 10%, the surface is stable. If 

the average rock cover is less than 10%, follow the procedures in Section 2.7.9 

of this appendix. 

2.7.9 If the average rock cover is less than 10%, the surface may or may not be 

stable. Follow the procedures in Section 2.4 (Determination of Threshold 

Friction Velocity [TFV]) of this rule and use the results from the rock test 

method as a correction (i.e., multiplication) factor. If the rock cover is at least 

1%, such rock cover helps to limit windblown dust. However, depending on the 

soil’s ability to release fine dust particles into the air, the percent rock cover 

may or may not be sufficient enough to stabilize the surface. It is also possible 

that the soil itself has a high enough TFV to be stable without even accounting 

for rock cover. 

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2.7.10 After completing the procedures described in Section 2.7.9 of this appendix, 

use Table 2 of this appendix to identify the appropriate correction factor to the 

TFV, depending on the percent rock cover. Multiply the correction factor by the 

TFV value for a final TFV estimate that is corrected for non-erodible elements. 

3. VISUAL OPACITY DETERMINATION OF EMISSIONS FROM DUSTGENERATING OPERATIONS 

3.1 Applicability: This method is applicable for the determination of opacity of fugitive 

dust plumes from dust-generating operations. 

3.2 Principle: the opacity of emissions from sources of visible emissions is determined 

visually by an observer qualified according to the procedures of Section 3.4 of this 

appendix. 

3.3 Procedures: An observer qualified in accordance with Section 3.4 of this appendix, 

shall use the following procedures for visually determining the opacity of emissions. 

3.3.1 To determine the opacity of non-continuous dust plumes caused by activities 

including, but not limited to, bulk material loading/unloading, nonconveyorized screening, or trenching with backhoes: 

a. Position: Stand at least 25 feet from the dust-generating operation in order 

to provide a clear view of the emissions with the sun oriented in the 140o 

sector to the back. Choose a discrete portion of the operation for observation, 

such as the unloading point, not the whole operation. Following the above 

requirements, make opacity observations so that the line of vision is approximately perpendicular to the dust plume and wind direction. If multiple 

plumes are involved, do not include more than one plume in the line of sight 

at one time. 

b. Initial Fallout Zone: The initial fallout zone within the plume must be 

identified. Record the distance from the equipment or path that is your 

identified initial fallout zone. The initial fallout zone is that area where the 

heaviest particles drop out of the entrained fugitive dust plume. Opacity 

readings should be taken at the maximum point of the entrained fugitive dust 

plume that is located outside the initial fallout zone. 

c. Field Records: Note the following on an observational record sheet: 

(1) Location of dust-generating operation, type of operation, type of 

equipment in use and activity, and method of control used, if any; 

(2) Observer's name, certification data and affiliation, a sketch of the 

observer's position relative to the dust-generating operation, and 

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observer’s estimated distance and direction to the location of the dustgenerating operation; 

(3) Time that readings begin, approximate wind direction, estimated wind 

speed, description of the sky condition (presence and color of clouds); 

and 

(4) Color of the plume and type of background. 

d. Observations: Make opacity observations, to the extent possible, using a 

contrasting background that is perpendicular to the line of vision. Make two 

observations per discrete activity, beginning with the first reading at zero 

seconds and the second reading at five seconds. The zero-second observation 

should begin immediately after a plume has been created above the surface 

involved. Do not look continuously at the plume but, instead, observe the 

plume briefly at zero seconds and then again at five seconds. 

e. Recording Observations: Record the opacity observations to the nearest 

5% on an observational record sheet. Each momentary observation recorded 

represents the average opacity of emissions for a five-second period. Repeat 

observations until you have recorded at least a total of 12 consecutive 

opacity readings. The 12 consecutive readings must be taken within the same 

period of observation but must not exceed one hour. Observations 

immediately preceding and following interrupted observations can be 

considered consecutive (e.g., vehicle traveled in front of path, plume 

doubled over). 

f. Data Reduction: Average 12 consecutive opacity readings together. If the 

average opacity reading equals 20% or lower, the dust-generating operation 

is in compliance. 

3.3.2 To determine the opacity of continuous dust plumes caused by equipment and 

activities including but not limited to graders, trenchers, paddlewheels, blades, 

clearing, leveling, and raking: 

a. Position: Stand at least 25 feet from the dust-generating operation to provide 

a clear view of the emissions with the sun oriented in the 140o sector to your 

back. Following the above requirements, make opacity observations so that 

the line of vision is approximately perpendicular to the dust plume and wind 

direction. 

b. Dust Plume: Evaluate the dust plume generation and determine if the 

observations will be made from a single plume or from multiple related 

plumes. 

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(1) If a single piece of equipment is observed working, then all measurements should be taken off the resultant plume as long as the equipment 

remains within the 140o sector to the back. 

(2) If there are multiple related sources or multiple related points of 

emissions of dust from a particular activity, or multiple pieces of 

equipment operating in a confined area, opacity readings should be taken 

at the densest point within the discrete length of equipment travel path 

within the 140o sector to the back. Readings can be taken for more than 

one piece of equipment within the discrete length of travel path within 

the 140o sector to the back. 

c. Initial Fallout Zone: The initial fallout zone within the plume must be 

identified. Record the distance from the equipment or path that is your 

identified initial fallout zone. The initial fallout zone is that area where the 

heaviest particles drop out of the entrained fugitive dust plume. Opacity 

readings should be taken at the maximum point of the entrained fugitive dust 

plume that is located outside the initial fallout zone. 

d. Field Records: Note the following on an observational record sheet: 

(1) Location of the dust-generating operation, type of operation, type of 

equipment in use and activity, and method of control used, if any; 

(2) Observer's name, certification data and affiliation, a sketch of the 

observer's position relative to the dust-generating operation, and 

observer’s estimated distance and direction to the location of the dustgenerating operation; and 

(3) Time that readings begin, approximate wind direction, estimated wind 

speed, description of the sky condition (presence and color of clouds). 

e. Observations: Make opacity observations, to the extent possible, using a 

contrasting background that is perpendicular to the line of vision. Make 

opacity observations at a point beyond the fallout zone. The observations 

should be made at the densest point. Observations will be made every 10 

seconds until at least 12 readings have been recorded. Do not look continuously at the plume, but observe the plume momentarily at 10-second 

intervals. If the equipment generating the plume travels outside the field of 

observation or if the equipment ceases to operate, mark an “X” for the 10-

second reading interval. Mark an “X” when plumes are stacked or doubled, 

either behind or in front, or become parallel to line of sight. Opacity readings 

identified as “X” shall be considered interrupted readings. 

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f. Recording Observations: Record the opacity observations to the nearest 

5% on an observational record sheet. Each momentary observation recorded 

represents the average opacity of emissions for a 10-second period. 

g. Data Reduction: Average 12 consecutive opacity readings together. If the 

average opacity reading equals 20% or lower, the dust-generating operation 

is in compliance. 

3.4 Qualification and Testing: 

3.4.1 Certification Requirements: To receive certification as a qualified observer, a 

candidate must be tested and demonstrate the ability to assign opacity readings 

in 5% increments to 25 different black plumes and 25 different white plumes, 

with an error not to exceed 15% opacity on any one reading and an average 

error not to exceed 7.5% opacity in each category. Candidates shall be tested 

according to the procedures described in Section 3.4.2 of this appendix. Any 

smoke generator used pursuant to Section 3.4.2 of this appendix shall be 

equipped with a smoke meter which meets the requirements of Section 3.4.3 of 

this appendix. Certification tests that do not meet the requirements of Sections 

3.4.2 and 3.4.3 of this appendix are not valid. The certification shall be valid for 

a period of 6 months, and after each 6-month period the qualification 

procedures must be repeated by an observer in order to retain certification. 

3.4.2 Certification Procedure: The certification test consists of showing the 

candidate a complete run of 50 plumes, 25 black plumes and 25 white plumes, 

generated by a smoke generator. Plumes shall be presented in random order 

within each set of 25 black and 25 white plumes. The candidate assigns an 

opacity value to each plume and records the observation on a suitable form. At 

the completion of each run of 50 readings, the score of the candidate is 

determined. If a candidate fails to qualify, the complete run of 50 readings must 

be repeated in any retest. The smoke test may be administered as part of a 

smoke school or training program, and may be preceded by training or 

familiarization runs of the smoke generator, during which candidates are shown 

black and white plumes of known opacity. 

3.4.3 Smoke Generator Specifications: Any smoke generator used for the purpose 

of Section 3.4.2 of this appendix shall be equipped with a smoke meter installed 

to measure opacity across the diameter of the smoke generator stack. The 

smoke meter output shall display in-stack opacity, based upon a path length 

equal to the stack exit diameter on a full 0% to 100% chart recorder scale. The 

smoke meter optical design and performance shall meet the specifications 

shown in Table 3 of this appendix. The smoke meter shall be calibrated as 

prescribed in Section 3.4.3(a) of this appendix prior to conducting each smoke 

reading test. At the completion of each test, the zero and span drift shall be 

checked, and if the drift exceeds plus or minus 1% opacity, the condition shall 

be corrected prior to conducting any subsequent test runs. The smoke meter 

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shall be demonstrated, at the time of installation, to meet the specifications 

listed in Table 3 of this appendix. This demonstration shall be repeated following any subsequent repair or replacement of the photocell or associated 

electronic circuitry, including the chart recorder or output meter, or every 6 

months, whichever occurs first. 

a. Calibration: The smoke meter is calibrated after allowing a minimum of 30 

minutes warm-up by alternately producing simulated opacity of 0% and 

100%. When stable response at 0% or 100% is noted, the smoke meter is 

adjusted to produce an output of 0% or 100%, as appropriate. This calibration shall be repeated until stable 0% and 100% readings are produced 

without adjustment. Simulated 0% and 100% opacity values may be produced by alternately switching the power to the light source on and off while 

the smoke generator is not producing smoke. 

b. Smoke Meter Evaluation: The smoke meter design and performance are to 

be evaluated as follows: 

(1) Light Source: Verify, from manufacturer's data and from voltage 

measurements made at the lamp, as installed, that the lamp is operated 

within plus or minus 5% of the nominal rated voltage. 

(2) Spectral Response of Photocell: Verify from manufacturer's data that 

the photocell has a photopic response (i.e., the spectral sensitivity of the 

cell shall closely approximate the standard spectral-luminosity curve for 

photopic vision which is referenced in (b) of Table 3 of this appendix). 

(3) Angle of View: Check construction geometry to ensure that the total 

angle of view of the smoke plume, as seen by the photocell, does not 

exceed 15°. Calculate the total angle of view (φv) as follows: 

 Total Angle of View = 2 tan-1 (d/2L) 

 where: 

 d = The photocell diameter + the diameter of the limiting aperture; and 

 L = The distance from the photocell to the limiting aperture. The 

limiting aperture is the point in the path between the photocell and the 

smoke plume where the angle of view is most restricted. In smoke 

generator smoke meters, this is normally an orifice plate. 

(4) Angle of Projection: Check construction geometry to ensure that the 

total angle of projection of the lamp on the smoke plume does not exceed 

15°. Calculate the total angle of projection (φp) as follows: 

 Total Angle of Projection = 2 tan-1 (d/2L) 

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 where: 

 d = The sum of the length of the lamp filament + the diameter of the 

limiting aperture; and 

 L = The distance from the lamp to the limiting aperture. 

(5) Calibration Error: Using neutral-density filters of known opacity, 

check the error between the actual response and the theoretical linear 

response of the smoke meter. This check is accomplished by first 

calibrating the smoke meter, according to Section 3.4.3(a) of this 

appendix, and then inserting a series of three neutral-density filters of 

nominal opacity of 20%, 50%, and 75% in the smoke meter path length. 

Use filters calibrated within plus or minus 2%. Care should be taken 

when inserting the filters to prevent stray light from affecting the meter. 

Make a total of five nonconsecutive readings for each filter. The 

maximum opacity error on any one reading shall be plus or minus 3%. 

(6) Zero and Span Drift: Determine the zero and span drift by calibrating 

and operating the smoke generator in a normal manner over a 1-hour 

period. The drift is measured by checking the zero and span at the end of 

this period. 

(7) Response Time: Determine the response time by producing the series of 

five simulated 0% and 100% opacity values and observing the time 

required to reach stable response. Opacity values of 0% and 100% may 

be simulated by alternately switching the power to the light source off 

and on while the smoke generator is not operating. 

Table 3. Smoke Meter Design and Performance Specifications 

Parameter Specification 

a. Light source Incandescent lamp operated at nominal rated voltage. 

b. Spectral response of photocell Photopic (daylight spectral response of the human eye)

c. Angle of view 15° maximum total angle

d. Angle of projection 15° maximum total angle

e. Calibration error Plus or minus 3% opacity, maximum

f. Zero and span drift Plus or minus 1% opacity, 30 minutes 

g. Response time Less than or equal to 5 seconds

4. VISUAL OPACITY DETERMINATION OF EMISSIONS FROM LIVESTOCK 

ACTIVITIES – CORRALS, PENS, AND ARENAS 

4.1 Applicability: This method is applicable for the determination of opacity of fugitive 

dust plumes from livestock activities (corrals, pens, and arenas). 

4.2 Principle: The opacity of emissions from livestock activities (corrals, pens, and 

arenas) is determined visually by an observer qualified according to Section 3.4 of this 

appendix. 

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4.3 Procedures: An observer qualified in accordance with Section 3.4 of this appendix, 

shall use the following procedures for visually determining the opacity of emissions: 

4.3.1 Position: Stand at a position at least 5 meters from the livestock activities 

(corrals, pens, and arenas) in order to provide a clear view of the emissions with 

the sun oriented in the 140° sector to the back. Consistent as much as possible 

with maintaining the above requirements, make opacity observations from a 

position such that the line of sight is approximately perpendicular to the plume 

and wind direction. As much as possible, if multiple plumes are involved, do 

not include more than one plume in the line of sight at one time. 

4.3.2 Field Records: Record the name of the site, method of control used, if any, 

observer's name, certification data and affiliation, and a sketch of the observer's 

position relative to the livestock activity (corrals, pens, and arenas). Also, 

record the time, estimated distance to the livestock activity (corrals, pens, and 

arenas) location, approximate wind direction, estimated wind speed, description 

of the sky condition (presence and color of clouds), observer's position relative 

to the livestock activity (corrals, pens, and arenas), and color of the plume and 

type of background on the visible emission observation from when opacity 

readings are initiated and completed. 

4.3.3 Observations: Make opacity observations, to the extent possible, using a 

contrasting background. For storage piles, make opacity observations 

approximately 1 meter above the surface from which the plume is generated. 

The initial observation should begin immediately after a plume has been created 

above the surface involved. Do not look continuously at the plume, but instead 

observe the plume momentarily at 15-second intervals. 

4.3.4 Recording Observations: Record the opacity observations to the nearest 5% 

every 15 seconds on an observational record sheet. If a multiple plume exists at 

the time of an observation, do not record an opacity reading. Mark an “X” for 

that reading. If the livestock activity (corrals, pens, and arenas) ceases 

operating, mark an “X” for the 15-second interval reading. Readings identified 

as “X” shall be considered interrupted readings. 

4.3.5 Data Reduction: Within any 60-minute period, count at least three minutes 

that are greater than 20% opacity. If at least 13 readings are greater than 20% 

opacity, the livestock activity (corrals, pens, and arenas) is not in compliance. 

Readings immediately preceding and following interrupted readings shall be 

deemed consecutive and in no case shall two sets overlap, resulting in multiple 

violations. 
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