CLARK COUNTY 

 AIR QUALITY REGULATIONS 

SECTION 90 - FUGITIVE DUST FROM OPEN AREAS AND VACANT 

LOTS

90.1 FUGITIVE DUST From OPEN AREAS AND VACANT LOTS

90.1.1 Purpose: To limit the EMISSION of PARTICULATE MATTER into the AMBIENT 

AIR from OPEN AREAS AND VACANT LOTS. 

90.1.2 Applicability: The provisions of this Regulation shall apply to OPEN AREAS 

AND VACANT LOTS which are located in the PM10 NONATTAINMENT AREA

(HYDROGRAPHIC BASIN 212) and the Apex Valley (HYDROGRAPHIC BASINS 216 

and 217). Nothing in Section 90 of these Regulations shall be construed to 

prevent enforcement of Section 40 (Prohibition of NUISANCE Conditions) of 

these Regulations. The provisions of this Regulation shall not apply to 

Normal Farm Cultural Practices or the raising of fowl or animals. The 

provisions of this Regulation shall not apply to STATIONARY SOURCES as 

defined in Section 0, except that these control measures shall be considered 

as part of a BACT determination. 

90.1.3 Effective Date Of This Regulation: 

90.1.3.1 Section 90, adopted by the Clark County Board of County Commissioners 

on June 22, 2000, shall be effective in HYDROGRAPHIC BASIN 212 on

January 1, 2001, except as otherwise provided herein. 

90.1.3.2 Section 90 shall be effective in HYDROGRAPHIC BASINS 216 and 217 on April

1, 2002, except as otherwise provided herein. 

90.2 Requirements: 

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90.2.1 OPEN AREAS AND VACANT LOTS: If OPEN AREAS AND VACANT LOTS are 

5,000 square feet or larger and are disturbed by any means, including use 

by MOTOR VEHICLES and/or OFF-ROAD MOTOR VEHICLES or material 

dumping, then the OWNER AND/OR OPERATOR of such OPEN AREAS AND 

VACANT LOTS shall implement one or more of the CONTROL MEASURES

described in Subsection 90.2.1.1 of this Regulation within 30 calendar 

days following the initial discovery of disturbance or vehicle use on OPEN 

AREAS AND VACANT LOTS. The OWNER AND/OR OPERATOR shall implement 

all control measures necessary to limit the disturbance of open areas and 
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vacant lots in accordance with the requirements of this regulation. 

Advisory Notice: In order to conserve water to the greatest extent 

practicable, the use of RECLAIMED WATER is highly encouraged. 

90.2.1.1 CONTROL MEASURES: 

(a) Where there is evidence of soil disturbance by MOTOR VEHICLES

and/or OFF-ROAD VEHICLE use, prevent MOTOR VEHICLE and/or OFFROAD VEHICLE trespassing, parking, and/or access, by installing 

barriers, curbs, fences, gates, posts, signs, shrubs, trees, or other 

effective traffic Control Measures. A stable surface area shall be 

established and maintained by using one of the CONTROL 

MEASURES set forth in Subsections 90.2.1.1(b) or (c) or by the 

effective application of water in compliance with the stabilization 

standards set forth in Subsection 90.2.1.2. Where measures to 

prevent vehicular trespassing and movement are not effective, the 

application of water will not be utilized for surface stabilization. For 

the purposes of this Subsection, use of or parking on OPEN AREAS 

AND VACANT LOTS for noncommercial and non-institutional purposes 

by the OWNER AND/OR OPERATOR of such OPEN AREAS AND VACANT

LOTS shall not be considered vehicle use under this Subsection. In 

addition, vehicle use related to landscaping maintenance shall not 

be considered vehicle use under this Subsection. For the purpose 

of this Regulation, landscape maintenance does not include 

grading, trenching, or any other mechanized surface disturbing 

activities performed to establish initial landscapes or to redesign 

existing landscapes; or 

(b) Where a DISTURBED SURFACE AREA exists (including disturbed 

surfaces caused by MOTOR VEHICLES), uniformly apply and maintain 

surface gravel or DUST PALLIATIVES to all areas disturbed by MOTOR 

VEHICLES in compliance with one of the stabilization standards 

described in Subsection 90.2.1.2 of this Regulation; or 

(c) Where a DISTURBED SURFACE AREA exists (including disturbed 

surfaces caused by MOTOR VEHICLES and/or OFF-ROAD MOTOR 

VEHICLES), apply and maintain an alternative CONTROL MEASURE

approved in writing by the CONTROL OFFICER and the Region IX 

ADMINISTRATOR of the Environmental Protection Agency (EPA). 

90.2.1.2 Stabilization Standards: 

(a) A visible crust shall be established, as determined by 

Subsection 90.4.1.1 (The Drop Ball/Steel Ball Test) of these 

Regulations; or, 
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(b) A percent cover that is equal to or greater than 20% for nonerodible elements shall be established, as determined by 

Subsection 90.4.1.2 (Rock Test Method) of these Regulations; or, 

(c) A threshold friction velocity, corrected for non-erodible elements of 

100 cm/second or higher, shall be established, as determined by 

Subsection 90.4.1.3 (Determination Of Threshold Friction Velocity) 

of this Regulation; or, 

(d) An alternative test method approved in writing by the CONTROL 

OFFICER and the Region IX ADMINISTRATOR of the EPA. 

90.2.2 Dust Mitigation Plans Required: Any OWNER AND/OR OPERATOR of OPEN 

AREAS AND VACANT LOTS having a cumulative area of 10,000 acres or 

greater must submit a dust mitigation plan to the Department of Air Quality 

and Environmental Management for approval by March 31, 2003, in a 

format prescribed by the CONTROL OFFICER. 

90.2.3 Mechanized Weed Abatement and/or Trash Removal: If machinery is 

used to clear weeds and/or trash from OPEN AREAS AND VACANT LOTS of 

5,000 square feet or larger, then the following Control Measures set forth 

in Subsection 90.2.3.1 shall be applied. Advisory Notice: In order to 

conserve water to the greatest extent practicable, the use of RECLAIMED 

WATER is highly encouraged. 

90.2.3.1 CONTROL MEASURES

(a) Pre-wet surface soils before mechanized weed abatement and/or 

trash removal occurs; and, 

(b) Maintain dust control measures while mechanized weed abatement 

and/or trash removal is occurring; and, 

(c) PAVE, apply gravel, apply water, or apply a suitable DUST 

PALLIATIVE, in compliance with the stabilization standards set forth 

in Subsection 90.2.1.2 of this Regulation, after mechanized weed 

abatement and/or trash removal occurs. 

90.3 Record Keeping Requirements 

90.3.1 Record Keeping: Any PERSON subject to the requirements of this 

Regulation shall compile and retain records that provide evidence of 

CONTROL MEASURE application, by indicating type of treatment or CONTROL 

MEASURE, extent of coverage, and date applied. The records and 

supporting documentation shall be made available to the CONTROL 

OFFICER within 24 hours of a written request. 
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90.3.2 Record Retention: Copies of the records required by Subsection 90.3.1 

(Record Keeping Requirements) of this Regulation shall be retained for at 

least one year. 

90.4 Test Methods 

90.4.1 Stabilization Standards For OPEN AREAS AND VACANT LOTS: The test 

methods described in Subsections 90.4.1.1 through Subsections 90.4.1.3 of

this Regulation 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, or other 

characteristics which are visibly distinguishable, each representative 

surface must be tested separately for stability in an area that represents a 

random portion of the overall disturbed conditions of the site, utilizing the 

appropriate test methods in Subsections 90.4.1.1 through Subsections 

90.4.1.3 of this Regulation. Depending upon test method results, include or 

eliminate each representative surface from the total size assessment of 

the DISTURBED SURFACE AREA(S). 

90.4.1.1 Soil Crust Determination (The Drop Ball Test): Drop a steel ball with a 

diameter of 15.9 millimeters (0.625 inches) and a mass ranging from 16-

17 grams from a distance of 30 centimeters (one foot) directly above the 

soil surface. If blowsand is present, clear the blowsand from the surfaces 

on which the soil crust test method is conducted. Blowsand is defined as 

thin deposits of loose uncombined grains covering less than 50% of an 

OPEN AREA or VACANT LOT which have not originated from the 

representative OPEN AREA or VACANT LOT surface being tested. If material 

covers a visible crust, which is not blowsand, apply the test method in 

Subsection 90.4.1.3 (Determination Of Threshold Friction Velocity) of this 

Regulation to the loose material to determine whether 

the surface is stabilized. 

(a) A sufficient crust is defined under the following conditions: once a 

ball has been dropped according to Subsection 90.4.1.1 of this 

Regulation, the ball does not sink into the surface, so that it is 

partially or fully surrounded by loose grains and, upon removal of 

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

that loose grains are visible. 

(b) Randomly select each representative DISTURBED SURFACE for the 

drop ball test by using a blind “over the shoulder” toss of a 

throwable object (for example, a metal weight with survey tape 

attached). Using the point of fall as the lower left hand corner, 

measure a 1-foot square area. Drop the ball three times within the 

1-foot by 1-foot square survey area, using a consistent pattern 
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across the survey area. The survey area shall be considered to 

have passed the Soil Crust Determination Test if at least two of the 

three times the ball was dropped, the results met the criteria in 

Subsection 90.4.1.1(a) of this Regulation. Select at least two other 

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 Subsection 90.4.1.1(a) of this Regulation 

for all of the survey areas tested, then the site shall be considered 

to have passed the Soil Crust Determination Test and shall be 

considered sufficiently crusted. 

(c) 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 

soil crust test as often as necessary on each portion of the overall 

conditions of the site using the random selection method set forth in 

Subsection 90.4.1.1(b) of this Regulation for an accurate 

assessment. 

90.4.1.2 Rock Test Method: The Rock Test Method, which is similar to Subsection 

90.4.1.3 (Determination Of Threshold Friction Velocity) of this Regulation, 

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, non-erodible elements include rocks, stones, glass 

fragments, and hardpacked 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.” 

(a) Randomly select a 1 meter by 1 meter survey area within an area 

that represents the general rock distribution on the surface (a 1 

meter by 1 meter area is slightly greater than a 3 foot by 3 foot 

area). Use a blind “over the shoulder” toss of a throwable object 

(for example, a metal weight with survey tape attached) to select 

the survey surface and using the point of fall as the lower left hand 

corner, measure a 1 meter by 1 meter survey 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. 

(b) Without moving any of the rocks or other elements, examine the 

survey area. Since rocks greater than 3/8 inch (1 cm) in diameter 
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are of interest, measure the diameter of some of the smaller rocks 

to a get a sense of which rocks need to be considered. 

(c) Mentally group the rocks greater than 3/8 inch (1cm) diameter lying 

in the survey area into small, medium, and large size categories. 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. 

(d) 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. 

(e) 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. 

(f) Divide the total rock area, calculated in Subsection 90.4.1.2(e) of 

this Regulation, by two (to get frontal area). Divide the resulting 

number by the size of the survey area (make 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 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). 

(g) Select and mark-off two additional survey areas and repeat the 

procedures described in Subsection 90.4.1.2(a) through Subsection 

90.4.1.2(f) of this Regulation. 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. 

(h) If the average rock cover is greater than or equal to 20%, the 

surface is stable. If the average rock cover is less than 20%, follow 

the procedures in Subsection 90.4.1.2(i) of this Regulation. 

(i) If the average rock cover is less than 20%, the surface may or may 

not be stable. Follow the procedures in Subsection 90.4.1.3 

(Determination Of Threshold Friction Velocity) of this Regulation 
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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 

Threshold Friction Velocity (TFV) to be stable without accounting 

for rock cover. 

(j) After completing the procedures described in Subsection 90.4.1.2(i) 

of this Regulation, use Table 2 of this Regulation 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. 

90.4.1.3 Determination Of Threshold Friction Velocity (TFV): For DISTURBED 

SURFACE AREAS that are not crusted or vegetated, determine TFV 

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

laboratory procedure published by W. S. Chepil). 

(a) 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 
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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 Subsection, which provides a correlation between sieve 

opening size and TFV. 

Table 1. Determination Of Threshold Friction Velocity

 

Tyler Sieve No. ASTM 11 Opening TFV 

 Sieve No. (mm) (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 

(b) 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 non-erodible elements. Nonerodible 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. Nonerodible elements include stones and bulk surface material but do 

not include flat or standing vegetation. For surfaces with nonerodible 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 

Subsection 90.4.1.2 (Rock Test Method) of this Regulation. Select 

a survey area of 1 meter by 1 meter that represents a random 

portion of the overall conditions of the site. Where many nonerodible elements lie within the survey area, separate the nonerodible elements into groups according to size. For each group, 

calculate the overhead area for the non-erodible elements 

according to the following equations: 
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Eq. 1: (Average length) x (Average width) = Average Dimensions. 

Eq. 2: (Average Dimensions) x (Number of Elements) = Overhead Area. 

Eq. 3: Overhead Area Of Group 1 + Overhead Area Of Group 2 (etc.) = 

Total Overhead Area. 

Eq. 4: Total Overhead Area/2 = Total Frontal Area. 

Eq. 5: (Total Frontal Area/Survey Area) x 100 = Percent Cover Of NonErodible Elements. 

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 Subsection 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. 

Table 2. Correction Factors For Threshold Friction Velocity

Percent Cover Of Non-Erodible Elements 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 

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History: Initial adoption: June 22, 2000 

Amended: November 16, 2000; November 20, 2001; December 17, 2002; June 3, 2003; July 1, 

2004.