Imperial County Air Pollution Control District Rule 800

800-1

RULE 800 GENERAL REQUIREMENTS FOR CONTROL OF FINE PARTICULATE 

MATTER (PM-10)

(Adopted 10/10/94; Revised 11/25/96; Revised 11/08/2005; Revised

10/16/2012)

A. General Description

The purpose of this regulation is to reduce the amount of fine Particulate Matter 

(PM-10) entrained in the ambient air as a result of emissions generated from 

anthropogenic (man-made) Fugitive Dust (PM-10) sources generated from within 

Imperial County by requiring actions to prevent, reduce, or mitigate PM-10 

emissions. The Rules contained within this Regulation have been developed 

pursuant to United States Environmental Protection Agency guidance for Serious 

PM10 Non Attainment Areas.

B. Applicability

The requirements of this rule shall apply to any Active Operation, and/or 

man-made or man-caused condition or practice capable of generating Fugitive 

Dust (PM-10) as specified in this Regulation except those determined exempt as 

defined in Part E of this Rule. The definitions, exemptions, requirements, 

administrative requirements recordkeeping requirements, and test methods set 

forth in this rule are applicable to all the rules under Regulation VIII (Fugitive Dust 

Requirements) of the Rules and Regulations of the Imperial County Air Pollution 

Control District. 

C. Definitions

For the purpose of this Regulation, the following terms are defined:

C.1 ACTIVE OPERATION: Activities capable of generating Fugitive Dust (PM10), including but not limited to, Earthmoving Activities, Construction 

activities, Unpaved Roads, Track-Out/Carry-Out, Bulk Material storage 

and transport, Unpaved Haul/Access Roads.

C.2 AGGREGATE MATERIALS: Consists of sand, Gravel, quarried stone 

and/or rock fragments that are typically used in Construction. Aggregates 

may be natural, artificial or recycled.

C.3 ANEMOMETRS: Are devices used to measure wind speed and direction 

in accordance with manufacturer’s performance standards, maintenance 

and calibration criteria.

C.4 ANNUAL AVERAGE DAILY VEHICLE TRIPS: annual average 24-hour 

total of all vehicles counted on a road.
Imperial County Air Pollution Control District Rule 800

800-2

C.5 APCD: The Imperial County Air Pollution Control District.

C.6 APCO: The Imperial County Air Pollution Control Officer.

C.7 AVERAGE VEHICLE TRIPS PER DAY: Means the average number of 

vehicles that cross a given point surface during a specific 24-hour period 

as determined by the most recent Institute of Transportation Engineers trip 

generation manual, tube counts, or observations.

C.8 BLM: The Bureau of Land Management.

C.9 BP: The United States Border Patrol.

C.10 BULK MATERIAL: Earth, rock, Silt, sediment, sand, Gravel, soil, fill, 

Aggregate, dirt, mud, debris, and other organic and/or inorganic material 

consisting of or containing Particulate Matter with five percent or greater 

Silt content. For the purpose of this Regulation, the Silt content level is 

assumed to be 5 percent or greater, unless the Person responsible for the 

Active Operation conducts the applicable laboratory tests and 

demonstrate that the Silt content is less than 5 percent. Active Operations 

seeking to determine if the Silt content is less than five percent are 

required to conduct the laboratory analysis in accordance with ASTM 

method C-136-a (Standard Test Method for Sieve analysis of Fine and 

Coarse Aggregates), or other equivalent test methods approved by EPA, 

ARB, and the APCD.

C.11 CANAL BANK: A rise of land on either side of an irrigation canal.

C.12 CHEMICAL STABILIZATION/SUPPRESSION: A means of Fugitive Dust 

(PM-10) control implemented to mitigate PM-10 emissions by applying 

petroleum resins, asphaltic emulsions, acrylics, adhesives, or any other 

materials approved for use by the California Air Resources Board (CARB), 

U.S. Environmental Protection Agency (U.S. EPA) and/or the APCO.

C.13 CONSTRUCTION: Any on-site mechanical activities preparatory to or 

related to the building, alteration, rehabilitation, or demolition of an 

improvement on real property, including, but not limited to, land clearing, 

excavation related to construction, land leveling, grading, cut and fill 

grading, and the erection or demolition of any structure. As used in 

Regulation VIII, a construction site may encompass several contiguous 

parcels, or may encompass only a portion of one parcel, depending on the 

relationship of the property boundaries to the actual construction activities.

C.14 DESIGNATED REPRESENTATIVE: The agent for a Person. The 

Designated Representative shall be responsible for and have the full 

authority to implement BACM on behalf of the Person.
Imperial County Air Pollution Control District Rule 800

800-3

C.15 DISTURBED SURFACE AREA: An area in which naturally occurring soils, 

or soils or other materials placed thereon, have been physically moved, 

uncovered, destabilized, or otherwise modified by grading, land leveling, 

scraping, cut and fill activities, excavation, bush and timber clearing, or 

grubbing, and soils on which vehicle traffic and/or equipment operation 

has occurred. An area is considered to be disturbed until the activity that 

caused the disturbance has been completed, and the disturbed area 

meets the stabilized surface conditions specified in this rule, or the area 

has been paved or otherwise covered by a permanent structure.

C.16 DPR: The California Department of Parks and Recreation.

C.17 EARTHMOVING ACTIVITIES: The use of any equipment for an activity 

that may generate Fugitive Dust emissions, including, but not limited to, 

cutting and filling, grading, leveling, excavation, trenching, loading or 

unloading of Bulk Materials, demolishing, drilling, adding to or removing 

bulk materials from open storage piles, weed abatement through disking, 

and back filling.

C.18 FUGITIVE DUST: The Particulate Matter entrained in the ambient air 

which is caused from man-made and natural activities such as, but not 

limited to, movement of soil, vehicles, equipment, blasting, and wind. This 

excludes Particulate Matter emitted directly in the exhaust of motor 

vehicles or other fuel combustion devices, from portable brazing, 

soldering, or welding equipment, pile drivers, and stack emissions from 

stationary sources.

C.19 GRAVEL: Gravel travelways shall have a three (3) inch minimum depth 

Stabilized Surface. The travelway shall have a relative compaction of not 

less than 95% as determined by Test Method No. California 216 of State 

of California, Business and Transportation Agency Department of 

Transportation, and conforming to the following grading:

3⁄4” Maximum

Sieve Designation Percent Passing

1” 100

3⁄4” 90-100

#4 35-60

#30 10-30

#200 2-9

Reference: California Department of Transportation Standard 

Specification Section 26/class II Aggregate Base
Imperial County Air Pollution Control District Rule 800

800-4

C.20 HAUL/ACCESS ROAD: Any on-site road used for commercial, industrial, 

institutional, and/or governmental traffic.

C.21 HAUL TRUCK: Any fully or partially open-bodied licensed motor vehicle 

used for transporting Bulk Material for industrial or commercial purposes.

C.22 IMPLEMENT OF HUSBANDRY: An unlicensed vehicle which is used 

exclusively in the conduct of Agricultural Operations. An Implement of 

Husbandry does not include a vehicle if its existing design is primarily for 

the transportation of persons or property on a highway, unless specifically 

designated as such by some other provision of the Vehicle Code of 

California.

C.23 NON-RESIDENTIAL AREA: Any unpaved vehicle and equipment traffic 

area operated at any commercial, manufacturing or government sites.

C.24 MODIFIED PAVED ROAD: Any Paved Road that is widened or improved 

so as to increase traffic capacity. This term does not include road 

maintenance, repair, chip seal, pavement or roadbed rehabilitation that 

does not affect roadway geometrics, or surface overlay work.

C.25 OFF-FIELD AGRICULTURAL SOURCE: Any Agricultural Source or 

activity at an Agricultural Source that falls into one or more of the following 

categories:

C.25.a Outdoor handling, storage and transport of Bulk Material;

C.25.b Paved Road;

C.25.c Unpaved Road; or

C.25.d Unpaved Traffic Area.

C.26 OFF-ROAD EVENT AND/OR COMPETITIONS: Means any of the 

following: any organized, sanctioned, or structured use, event or activity 

on public land in which two hundred and fifty (250) or more contestants 

compete and either or both of the following elements apply: (i) Participants 

register, enter, or complete an application for the event; (ii) A 

predetermined course or area is designated.

C.27 OFF- HIGHWAY VEHICLE(OHV): An off-highway vehicle is a motorized 

vehicle when operating off a highway, including a two-wheel, three-wheel 

or four-wheel vehicle, motorcycle, four-wheel drive vehicle, dune buggy, 

amphibious vehicle, ground effects or air cushion vehicle and any other 

means of land transportation deriving motive power from a source other 

than muscle or wind. "Highway" means the entire width between the 
Imperial County Air Pollution Control District Rule 800

800-5

boundary lines of every way publicly maintained by the federal 

government, a city, a town or a county if any part of the way is generally 

open to the use of the public for purposes of vehicular travel, excluding 

unpaved trails and paths specifically intended for recreational use.

C.28 ON-FIELD AGRICULTURAL SOURCE: Any Agricultural Source or activity 

at an Agricultural Source that is not an Off-Field Agricultural Source, 

including (but not limited to) the following:

C.28.a Activities conducted solely for the purpose of preparing land for 

the growing of crops or the raising of fowl or animals, such as 

brush or timber clearing, grubbing, scraping, ground excavation, 

land leveling, grading, turning under stalks, disking, or tilling;

C.28.b Drying or pre-cleaning of agricultural crop material on the field 

where it was harvested;

C.28.c Handling or storage of agricultural crop material that is baled, 

cubed, pelletized, or long-stemmed, on the field where it was 

harvested, and the handling of fowl or animal feed materials at 

sites where animals or fowl are raised;

C.28.d Disturbances of cultivated land as a result of fallowing, planting, 

fertilizing or harvesting.

C.29 OPEN AREA: Any of the following described in Subsection C.29.a through 

C.29.c of this rule. For the purpose of this rule, vacant portions of 

residential or commercial lots and contiguous parcels that are immediately 

adjacent to and owned and/or operated by the same individual or entity 

are considered one open area. An open area does not include any 

Unpaved Traffic Area as defined in this rule.

C.29.a An un-subdivided or undeveloped land whether or not it is 

adjoining a developed (or partially developed) residential, 

industrial, institutional, governmental, or commercial area.

C.29.b A subdivided residential, industrial, institutional, governmental, 

or commercial lot, which contains no approved or permitted 

building or structures of a temporary or permanent nature.

C.29.c A partially developed residential, industrial, institutional, 

governmental, or commercial lot and contiguous lots under 

common ownership. 

C.30 PARTICULATE MATTER: Any material, except uncombined water, which 

exists in a finely divided form as a liquid or solid at 60 degrees F and one 
Imperial County Air Pollution Control District Rule 800

800-6

atmosphere pressure.

C.31 PAVED ROADS: An improved street, highway, alley, public way, that is 

covered by concrete, asphaltic concrete, or asphalt.

C.32 PERSON: Any individual, public or private corporation, partnership, 

association, firm, trust, estate, municipality, or any other legal entity 

whatsoever which is recognized by law as the subject of rights and duties, 

who is responsible for an Active Operation.

C.33 PM-10: Particulate Matter with an aerodynamic diameter smaller than or 

equal to a nominal 10 microns as measured by the applicable State and 

Federal reference test methods.

C.34 RECREATIONAL OFF-HIGHWAY VEHICLE (OHV) USE AREA: The 

entire area of a parcel of land, except for camping and approved buffer 

areas, that is managed for off-highway vehicle use through the 

development or designation of off-highway vehicle trails or areas.

C.35 RURAL: Areas not classified as urban constitute “rural.”

C.36 SILT: Any Aggregate Material with a particle size less than 75 

micrometers in diameter as measured by a No. 200 sieve as defined in 

ASTM D-2487 and as tested by ASTM-C-136 or other equivalent test 

methods approved by EPA, ARB, and the APCD.

C.37 STABILIZED SURFACE: Any disturbed surface area or open bulk storage 

pile that is resistant to wind blown Fugitive Dust emissions. A surface is 

considered to be stabilized if it meets at least one of the following 

conditions specified in this Section and as determined by the test methods 

specified in Appendix B, Section A, B and D-G tests of this rule:

C.37.a A visible crust; or

C.37.b A threshold friction velocity (TFV) for disturbed surface areas 

corrected for non-erodible elements of 100 centimeters per 

second or greater; or

C.37.c A flat vegetative cover of at least 50 percent that is attached or 

rooted vegetation; or unattached vegetative debris lying on the 

surface with a predominant horizontal orientation that is not 

subject to movement by wind; or

C.37.d A standing vegetative cover of at least 30 percent that is 

attached or rooted vegetation with a predominant vertical 

orientation; or
Imperial County Air Pollution Control District Rule 800

800-7

C.37.e A standing vegetative cover that is attached or rooted vegetative 

with a predominant vertical orientation that is at least 10 percent 

and where the TFV is at least 43 centimeters per second when 

corrected for non-erodible elements; or

C.37.f A surface that is greater than or equal to 10 percent of nonerodible elements such as rocks, stones, or hard-packed 

clumps of soil. 

C.38 STABILIZED UNPAVED ROAD: Any Unpaved Road or unpaved 

vehicle/equipment traffic area surface which meets the definition of 

Stabilized Surface as determined by the test method in Appendix B, 

Section C of this rule, and where VDE is limited to 20% opacity.

C.39 TACTICAL TRAINING: Training conducted by the U.S. Department of 

Defense, the U.S. military services, or its allies for combat, combat 

support, combat service support, tactical or relief operations. Examples 

include but are not limited to munitions training.

C.40 TEMPORARY UNPAVED ROAD: Any Unpaved Road surface which is 

created to support a temporary or periodic activity and the use of such 

road surface is limited to vehicle access for a period of not more than six 

months during any consecutive three-year period.

C.41 THRESHOLD FRICTION VELOCITY (TFV): The corrected velocity 

necessary to initiate soil erosion as determined by the test method 

specified in Appendix B, Section D, of this rule. The lower TFV, the greater 

the propensity for fine particles to be lifted at relatively low wind speeds.

C.42 TRACK-OUT/CARRY-OUT: Any and all Bulk Materials that adhere to and 

agglomerate on the exterior surfaces of motor vehicles and/or equipment 

(including tires) that may then fall onto the pavement.

C.43 TRACK-OUT PREVENTION DEVICE: A Gravel pad, grizzly, wheel wash 

system, or a paved area, located at the point of intersection of an unpaved 

area and a Paved Road that prevents or controls Track-Out.

C.44 UNPAVED ROADS: Streets, alley ways, or roadways that are not covered 

by one of the following: concrete, asphaltic concrete, asphalt, or other 

similar materials specified by the U.S.EPA, CARB and/or the APCO.

C.45 UNPAVED TRAFFIC AREA: Any nonresidential area that is:

C.45.a Not covered by asphalt, recycled asphalt, asphaltic concrete, 

concrete, or concrete pavement, and
Imperial County Air Pollution Control District Rule 800

800-8

C.45.b Used for fueling and servicing; shipping, receiving and transfer; 

or parking or storing equipment, haul trucks, vehicles, and any 

conveyances.

C.46 URBAN AREA: An area within an incorporated city boundary or within 

unincorporated areas completely surrounded by an incorporated city.

C.47 VDE: Visible dust emissions. Dust emissions that are visible to an 

observer.

C.48 VMT: Vehicle miles traveled.

C.49 WIND GUST: Is the maximum instantaneous wind speed as measured by 

an anemometer.

D. Compliance Schedule

D.1 Existing sources subject to this Regulation shall comply with its 

requirements no later than 90 days after its adoption date.

D.2 New sources subject to this Regulation shall comply with its requirements 

prior to initiation of activity.

D.3 BP and any person (including BLM and DPR) who owns or operates a 

Recreational OHV Use Area on public lands shall each comply with the 

following compliance schedule:

D.3.a Submit a draft dust control plan addressing all applicable 

portions of this Regulation including section F.5 and F.7 within 

three (3) months of the adoption date of this rule, to which the 

APCO shall respond within 60 days;

D.3.b Submit a final dust control plan addressing all APCO comments 

within two (2) months after receiving APCO’s comments, which 

the APCO shall transmit to CARB and U.S. EPA for 45-day 

review and comment;

D.3.c If comments received from CARB or EPA, submit to them and 

APCO a revised final dust control plan addressing all comments 

within two (2) months after receiving comments.

D.3.d Implement all final dust control plan elements within six (6) 

months of submittal; and

D.3.e Submit an updated dust control plan every two calendar years 
Imperial County Air Pollution Control District Rule 800

800-9

by the procedures described in D.3.a to D.3.d. The updated 

plans shall be transmitted to the District no later than 90 days 

after the end of the calendar year and, in addition to information 

required of the initial plan, shall include a summary of actions 

taken to prevent or mitigate PM10 emissions during the 

previous two years.

E. Exemptions 

The following activities are exempt from provisions of this Regulation:

E.1 Actions required by the Federal or State Endangered Species Act or any 

order issued by a court or governmental agency.

E.2 Off-Field Agricultural Sources necessary to minimize or respond to 

adverse effects on agricultural crops caused during freezing 

temperatures as declared by the National Weather Service.

E.3 Emergency maintenance of flood control channels and water spreading 

basins.

E.4 Any emergency operation activities performed to ensure public health 

and safety. Emergency activities lasting more than 30 days shall be 

subject to this Regulation, except where compliance would limit the 

effectiveness of the emergency activity performed to ensure public 

health and safety.

E.5 Blasting operations permitted by the California Division of Industrial 

Safety. Other activities performed in conjunction with blasting are not 

exempt from complying with the provisions of this rule.

E.6 The following military training activities conducted by the Department of 

Defense: (1) military Tactical Training, (2) maintenance, repair, and 

removal of targets and munitions associated with military Tactical 

Training, (3) open areas on active military ranges, including but not 

limited to designated impact areas, landing zones, and bivouac areas. 

However, unpaved roads, staging areas, parking lots, and other activities 

performed in conjunction with military Tactical Training are not exempt 

from complying with the provisions of this Regulation, as applicable.

F. General Requirements

F.1 Materials used for Chemical Stabilization of soils, including petroleum 

resins, asphaltic emulsions, acrylics, and adhesives shall not violate State 

Water Quality Control Board standards for use as a soil stabilizer. 

Materials accepted by the California Air Resources Board (ARB) and the 
Imperial County Air Pollution Control District Rule 800

800-10

United States Environmental Protection Agency (EPA), and which meet 

State water quality standards, shall be considered acceptable to the 

ICAPCD.

F.2 Any material prohibited for use as dust Suppressant by EPA, the ARB, or 

other applicable law, rule, or regulation is also prohibited under Regulation 

VIII.

F.3 Use of hygroscopic materials may be prohibited by the APCD in areas 

lacking sufficient atmospheric moisture of soil for such materials to 

effectively reduce Fugitive Dust emissions. The atmospheric moisture of 

soil is considered to be sufficient if it meets the application specifications 

of the hygroscopic product manufacturer. Use of such materials may be 

approved in conjunction with sufficient wetting of the controlled area.

F.4 Any use of dust Suppressants or gravel pads, and paving materials such 

as asphalt or concrete for paving, shall comply with other applicable 

District Rules.

F.5 Recreational OHV Use Area on Public lands Dust Control Plan 

Requirements

The BLM, DPR, or any other owner or operator of a Recreational OHV 

Use Area on public lands shall prepare a dust control plan to minimize 

PM-10 emissions. The dust control plan shall include at a minimum the 

following:

F.5.a A stipulation that all new authorizations for point and area 

stationary emission sources obtain all necessary permits and 

satisfy all applicable SIP provisions, including Regulation VIII 

specific control measures;

F.5.b A summary of:

F.5.b.1 The total miles of roads in the Recreational OHV Use 

Area on public lands that are paved, paved with 

unpaved shoulders, and unpaved roads with 50 or 

more average vehicle trips per day, including length 

and level of usage of each such road; the priority for 

control of road segments based on annual and 

episodic (e.g. event) usage; the plans for control of 

PM-10 emissions from these roads;

F.5.b.2 The location and extent (acreage and where feasible, 

estimate of number of vehicles) of open areas 

disturbed by legal and illegal Recreational Use, 
Imperial County Air Pollution Control District Rule 800

800-11

including maps such as those required by California

Public Resources Code (PRC) section 5090.34; the 

priority for control of these open areas based on 

annual and episodic (e.g. event) usage; the plans for 

control of PM-10 emissions from these areas;

F.5.c Unpaved Roads and Unpaved Vehicle/Equipment Traffic Area. 

The dust control plan shall be implemented on all days that 

traffic exceeds, or is expected to exceed, the number of average 

daily vehicle trips per day as specified in sections F.5.c.1 and 

F.5.c.2 of this rule, except where measures are demonstrated 

by owner/operator to be prohibited by federal or state laws, 

regulations, or approved plans concerning wilderness 

preservation and species management and recovery.

F.5.c.1 On each day of an Off-Road Event and/or 

Competition that 50 average vehicle daily trips per 

day will occur on an unpaved road segment, the 

owner/operator shall limit VDE to 20% opacity and 

comply with the requirements of a stabilized unpaved 

road by application and/or re-application/maintenance 

of at least one of the following control measures:

F.5.c.1.1 Watering;

F.5.c.1.2 Uniform layer of washed gravel;

F.5.c.1.3 Paving;

F.5.c.1.4 Restrict access;

F.5.c.1.5 Restrict speed limit at or below 15 mph;

F.5.c.1.6 Chemical/organic dust suppressants;

F.5.c.1.7 Roadmix;

F.5.c.1.8 Any other method(s) that can be

demonstrated that effectively limits VDE to 

20% opacity and meets the conditions of a 

stabilized unpaved road.

F.5.c.2 On each day of an Off-Road Event and/or 

Competition that 50 average vehicle daily trips per 

day will occur on an unpaved surface area dedicated 

to any vehicle parking and Unpaved Traffic Area, the 

owner/operator shall limit VDE to 20% opacity and 

comply with the requirements of a stabilized unpaved 

road by application and/or re-application/maintenance 

of at least one of the following control measures:

F.5.c.2.1 Watering;

F.5.c.2.2 Uniform layer of washed gravel;
Imperial County Air Pollution Control District Rule 800

800-12

F.5.c.2.3 Paving;

F.5.c.2.4 Restricted access below the limit;

F.5.c.2.5 Restrict speed limit at or below 15 mph;

F.5.c.2.6 Chemical/organic dust suppressants;

F.5.c.2.7 Roadmix;

F.5.c.2.8 Any other method(s) that can be

demonstrated that effectively limits VDE to 

20% opacity and meets the conditions of a 

stabilized unpaved road.

F.5.d The dust control plan must describe all PM-10 control measures 

that will be implemented, such as restricted use areas, 

stabilization of Unpaved Traffic Areas and current Recreation 

Area Management Plan (RAMP) measures, all applicable soil 

and habitat conservation requirements, and all monitoring and 

corrective actions taken to reduce PM10 emissions during OffRoad Events and/or Competitions on public land and include all 

those measures that are feasible and not prohibited by the laws, 

regulations and plans described in F.5.c;

F.5.e Use BLM-standard road design and drainage specifications 

when maintaining existing roads or authorizing road 

maintenance and new road construction;

F.5.f Include public educational information on reducing PM-10 

emissions with agency (e.g., BLM and DPR) open area 

literature (e.g. identification of restricted areas and/or applicable 

speed limits) and on related information signs in heavily used 

areas; and

F.5.g The owner or operator of a recreational OHV use area on public 

lands shall not permit Off-Road Events and/or Competitions 

from June 15th to August 15th, unless a specific dust control plan 

is submitted to and approved by the ICAPCD. The dust control 

plan shall include specific fugitive dust control measures and 

demonstrate that all control measures, including the 

requirements of this rule, can be implemented and enforced. 

F.6 Border Patrol (BP) Requirements

The BP shall prepare a dust control plan designed to minimize PM10 

emissions from sources under the control of the BP. The dust control plan 

shall include the following fugitive dust control measures:

F.6.a A stipulation that all new authorizations for point and area 

stationary emission sources obtain all necessary permits and 
Imperial County Air Pollution Control District Rule 800

800-13

satisfy all applicable SIP provisions, including Regulation VIII 

specific control measures;

F.6.b Implement alternatives to tire-dragging that result in fewer PM10 

emissions, unless BP demonstrates such alternatives to be 

inconsistent with the monitoring of immigration across the U.S.-

Mexico border;

F.7 New Recreational OHV Use Area(s) on Public Land Requirements

Before a public agency (including BLM and DPR) designates a property as 

“New Recreational OHV Use Area” (hereafter referred to as “New 

Recreational OHV Use Area”) for OHV recreation, the agency shall meet 

and confer with ICAPCD. A “New Recreational OHV Use Area” shall 

include areas physically undisturbed by OHV usage as of January 1, 

2013. After development and approval of an agency’s first Dust Control 

Plan under Section D.3 of this rule, “New Recreational OHV Use Area also 

includes areas not described in the previous public agency’s dust control 

plan.”

F.7.a ICAPCD shall review the public agency’s draft General Plan, 

Specific Plan, or RAMP and/or related documents for 

consistency and compliance with the rules and requirements 

applicable to and/or implementing Imperial County’s plan for 

attainment and/or maintenance of the 24-hour federal PM-10 

standard. During the applicable public comment period, 

ICAPCD may provide comments on the applicable plan to the 

public agency related to consistency and compliance with such 

rules and requirements, and where applicable, describe 

additional measures necessary for consistency and compliance 

with such rules and requirements.

F.7.b For any New Recreational OHV Use Area(s) with PM-10 

emissions of 70 tons per year or above, the public agency must 

demonstrate in a federal- and/or state-required environmental 

assessment that these emissions would not:

F.7.b.1 Cause or contribute to any new violations of any PM10 NAAQS in the area.

F.7.b.2 Interfere with provisions in the applicable PM-10 SIP 

for maintenance of the PM-10 NAAQS.

F.7.b.3 Increase the frequency or severity of any existing 

violation of PM-10 NAAQS; or
Imperial County Air Pollution Control District Rule 800

800-14

F.7.b.4 Delay timely attainment of the PM-10 NAAQS or any 

required interim emission reductions or other 

milestones in any area including, where applicable, 

emission levels specified in the applicable SIP for 

purposes of: (i) a demonstration of reasonable further 

progress; (ii) a demonstration of attainment; or (iii) a 

maintenance plan.

F.7.c The public agency shall not approve the applicable General 

Plan, Specific Plan, or RAMP unless and until it has 

incorporated ICAPCD’s comments and recommended mitigation 

measures or explained why a comment or recommended 

mitigation measure does not apply or is infeasible. If the public 

agency does not accept a mitigation measure or comment, the 

public agency shall consult with ICAPCD to identify an 

alternative measure or way to address ICAPCD’s concern. In 

any event, all New Recreational OHV Use Areas shall comply 

with Section F.5 above.

G. Administrative Requirements

G.1 Test Methods

G.1.a Determination of VDE Opacity

Opacity observations to determine compliance with VDE 

standards shall be conducted in accordance with the test 

procedures for “Visual Determination of Opacity” as described in 

Appendix A of this rule. Opacity observations for sources other 

than unpaved traffic areas (e.g., roads, parking areas) shall be 

conducted per Section B of Appendix A and shall require 12 

readings at 15-second intervals.

G.1.b Determination of Stabilized Surface

Observations to determine compliance with the conditions 

specified for a stabilized surface, in any inactive disturbed 

surface area, whether at a work site that is under construction, 

at a work site that is temporarily or permanently inactive, or on 

an open area and vacant lot, shall be conducted in accordance 

with the test methods described in Appendix B of this rule. If a 

disturbed surface area passes any of the applicable Appendix 

B-Section A, B and D-G tests, then the surface shall be 

considered stabilized.

G.1.c Determination of Soil Moisture Content
Imperial County Air Pollution Control District Rule 800

800-15

Soil moisture content shall be determined by using ASTM 

Method D2216-98 (Standard Test Method for Laboratory 

Determination of Water [Moisture] Content of Soil and Rock by 

Mass), or other equivalent test methods approved by the EPA, 

ARB, and the APCO.

G.1.d Determination of Silt Content for Bulk Materials

Silt content of a Bulk Material shall be determined by ASTM 

Method C136a (Standard Test Method for Sieve Analysis of 

Fine and Coarse Aggregates), or other equivalent test methods 

approved by EPA, ARB, and the APCD.

G.1.e Determination of Silt Content for Unpaved Roads and Unpaved 

Vehicle/Equipment Traffic Areas

Silt Content for Unpaved Roads and Unpaved Traffic Areas 

shall be determined by using Section C of Appendix B of this 

Rule or other equivalent test methods approved by EPA, ARB, 

and the APCO.

G.1.f Determination of Threshold Friction Velocity (TFV)

TFV shall be determined by using Section D of Appendix B of 

this Rule or other equivalent test methods approved by EPA, 

ARB, and the APCO.

H. Record of Control Implementation

Any Person subject to the requirements of this rule shall compile and retain 

records that provide evidence of control measure application and compliance 

with this rule (i.e., receipts and/or purchase records). Such Person shall 

describe, in the records, the type of treatment or control measure, extent of 

coverage, and date applied. For control measures which require multiple daily 

applications, recording the frequency of application will fulfill the recordkeeping 

requirements of this rule (i.e., water being applied three times a day and the 

date) Records shall be maintained and be readily accessible for two years after 

the date of each entry and shall be provided to the APCD upon request.

I. Violations

Failure to comply with any provisions of this rule shall constitute a violation of 

Regulation VIII. Failure to comply with the provisions of an APCO approved dust 

control plan shall also constitute a violation of this Regulation. Regardless of 

whether an APCO approved dust control plan is being implemented or not, or 
Imperial County Air Pollution Control District Rule 800

800-16

whether a Person responsible for an Active Operation(s) is complying with an 

approved dust control plan, the Person is still subject to the requirements of 

Regulation VIII at all times.
Imperial County Air Pollution Control District Rule 800

800-17

APPENDIX A

Visual Determination of Opacity

SECTION A Test Method For Unpaved Roads and Unpaved Traffic Areas

SECTION B Test Method For Time-Averaged Regulations

SECTION A TEST METHOD FOR UNPAVED ROADS AND UNPAVED TRAFFIC 

AREAS

A 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 Traffic Areas. This method can only be conducted by an individual 

who has current certification as a qualified observer.

A.1 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.

A.2 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 form both when opacity readings are 

initiated and completed.

A.3 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 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.

A.4 Step 4: Record the opacity observations to the nearest 5% on an 

observational record sheet. Each momentary observation recorded 
Imperial County Air Pollution Control District Rule 800

800-18

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 the vehicles which generate dust plumes for which 

readings are taken (e.g. mid-size passenger car or heavy-duty truck.) and 

take the approximate speeds the vehicles are traveling when the readings 

are being taken.

A.5 Step 5: Repeat Step 3 (Section A.3. of this appendix) and Step 4 (Section 

A.4. 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.

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

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

standard described in the applicable rule.

SECTION B TEST METHOD FOR VISUAL DETERMINATION OF OPACITY OF 

EMISSIONS FROM SOURCES FOR TIME-AVERAGED REGULATIONS

B Applicability. This method is applicable for the determination of the opacity of 

emissions from sources of visible emissions for time-averaged regulations. A 

time-averaged regulation is any regulation that requires averaging visible 

emission data to determine the opacity of visible emissions over a specific time 

period.

B.1 Principle. The opacity of emissions from sources of visible emissions is 

determined visually by a qualified observer who has received certification.

B.2 Procedures. A qualified observer who has been certified shall use the 

following procedures for visually determining the opacity of emissions.

B.2.a Position. Stand at a position at least 5 meters from the Fugitive 

Dust source n 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. The 

observer may follow the Fugitive Dust plume generated by mobile 

earthmoving equipment, as long as the sun remains oriented in the 

140° sector to the back. As much as possible, if multiple plumes 

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

at one time.
Imperial County Air Pollution Control District Rule 800

800-19

B.2.b Field Records. Record the name of the site, Fugitive Dust source 

type (i.e., pile, material handling (i.e., transfer, loading, sorting)), 

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 relative to the fugitive dust 

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

visible emission observation form when opacity readings are 

initiated and completed.

B.2.c Observations. Make opacity observations, to the extent possible, 

using a contrasting background that is perpendicular to the line of 

sight. For storage piles, make opacity observations approximately 

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

extraction operations and the loading of haul trucks in open-pit 

mines, make opacity observations approximately one meter above 

the rim of the pit. 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. For Fugitive Dust from 

Earthmoving equipment, make opacity observations approximately 

1 meter above the mechanical equipment generating the plume.

B.2.d Recording Observations. Record the opacity observations to the 

nearest 5% every 15 seconds on an observational record sheet. 

Each momentary observation recorded represents the average 

opacity of emissions for a 15-second period. 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 equipment generating 

the plume travels outside of the field of observation, resulting in the 

inability to maintain the orientation of the sun within the 140° sector 

or if the equipment ceases operating, mark an “x” for the 15 –

second interval reading. Readings identified as “x” shall be 

considered interrupted readings.

B.2.e Data Reduction For Time-Averaged Regulations. For each set of 

12 or 24 consecutive readings, calculate the appropriate average 

opacity. Sets must consist of consecutive observations, however, 

readings immediately preceding and following interrupted readings 

shall be deemed consecutive and in no case shall two sets overlap, 

resulting in multiple violations.
Imperial County Air Pollution Control District Rule 800

800-20

APPENDIX B

Determination of Stabilization

SECTION A Test Methods for Determining Stabilization

SECTION B Visible Crust Determination

SECTION C Determination of Silt Content for Unpaved Roads and Unpaved 

Vehicle/Equipment Traffic Areas

SECTION D Determination of Threshold Friction Velocity

SECTION E Determination of Flat Vegetative Cover

SECTION F Determination of Standing Vegetative Cover

SECTION G Rock Test Method

SECTION A TEST METHODS FOR DETERMINING STABILIZATION

The test methods described in Section B through Section G of this appendix shall be 

used to determine whether an area has a Stabilized Surface. Should a disturbed area 

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 B through Section G of 

this appendix, and include or eliminate it from the total size assessment of disturbed 

surface area(s) depending upon test method results.

SECTION B VISIBLE CRUST DETERMINATION

B.1 Where a visible crust exists, 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 (at a 90° angle perpendicular to ) the soil 

surface. If blowsand is present, clear the blowsand from the surfaces on which 

the visible crust test method is conducted. Blowsand is defined as thin deposits 

of loose uncombined grains covering less than 50% of a site which have not 

originated from the representative site surface being tested. If material covers a 

visible crust, which is not blowsand, apply the test method in Section D of this 

appendix to the loose material to determine whether the surface is stabilized.

B.2 A sufficient crust is defined under the following conditions: once a ball has been 

dropped according to section B.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.

B.3 Drop the ball three times within a survey area that measures 1 foot by 1 foot and 

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

The survey area shall be considered to have passed the Visible Crust 

Determination Test if the results of at least two out of the three times that the ball 
Imperial County Air Pollution Control District Rule 800

800-21

was dropped, met the criteria in section B.2 of this appendix. 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 

section B.2 of this appendix for all of the survey areas tested, then the site shall 

be considered to have passed the Visible Crust Determination Test and shall be 

considered sufficiently crusted.

B.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 visible crust test as often as necessary on each 

random portion of the overall conditions of the site for an accurate assessment.

SECTION C DETERMINATION OF SILT CONTENT FOR UNPAVED ROADS AND 

UNPAVED VEHICLE/EQUIPMENT TRAFFIC AREAS

The purpose of this test method is to estimate the silt content of the trafficked parts of 

Unpaved Roads and Unpaved vehicle/equipment Traffic Areas. The higher the Silt 

content, the more fine dust particles that are released when vehicles travel on Unpaved 

Roads and Unpaved vehicle/equipment Traffic Areas.

C.1 Equipment:

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

1mm, 0.5mm and 0.25 mm, a lid, and collector pan.

C.1.b 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.)

C.1.c A spatula without holes.

C.1.d A small scale with half-ounce increments (e.g., postal/package scale.)

C.1.e A shallow, lightweight container (e.g., plastic storage container.)

C.1.f A sturdy cardboard box or other rigid object with a level surface.

C.1.g A basic calculator.

C.1.h Cloth gloves (optional for handling metal sieves on hot, sunny days.)

C.1.i Sealable plastic bags (if sending samples to a laboratory.)

C.1.j A pencil/pen and paper.

C.2 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 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 
Imperial County Air Pollution Control District Rule 800

800-22

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 a 1cm 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. (Optional: 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.3 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.

C.4 Step 3: Stack a set of sieves in order according to the size openings specified 

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

collector pan underneath the bottom (0.25mm) sieve.

C.5 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 vehicle as a wind barrier. Cover the 

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

sideways for at least 1 minute.

C.6 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, restack 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 require further sifting.

C.7 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 not 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 materials from the collector pan and 

record its weight.

C.8 Step 7: If the source is an unpaved road, multiply the resulting weight by 0.38. If 

the source is an Unpaved vehicle/equipment Traffic Area, multiply the resulting 

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

the total weight of the sample you recorded earlier in Step 2 (Section C.4) and 
Imperial County Air Pollution Control District Rule 800

800-23

multiply by 100 to estimate the percent Silt content.

C.9 Step 8: Select another two routinely traveled portions of the Unpaved Road or 

Unpaved vehicle/equipment Traffic Area 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.

C.10 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 C.2) and take them to an independent laboratory for Silt content 

analysis.

C.11 Independent Laboratory Analysis: You may choose to collect samples from the 

source, according to Step 1 (section C.2) 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: “Procedures For 

Laboratory Analysis for Surface/Bulk Dust Loading Samples,” (Fifth Edition, 

Volume 1, Appendix C.2.3 “Silt Analysis,” 1995,) AP-42, Office of Air Quality 

Planning & Standards, U.S. Environmental Protection Agency, Research Triangle 

Park, North Carolina.

SECTION D 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).

D.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 
Imperial County Air Pollution Control District Rule 800

800-24

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.

Table 1. Determination of Threshold Friction Velocity (TFV)

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

D.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 non 

erodible 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 

Section 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. 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: 
Imperial County Air Pollution Control District Rule 800

800-25

Average Dimensions =

(Average Length) x ( Average Width) Eq. 1

Overhead Area =

(Average Dimensions) x (Number of Elements) Eq. 2

Total Overhead Area =

Overhead Area Of Group 1 + Overhead Area of Group 2 

(etc)

Eq. 3

Total Frontal Area =

Total Overhead Area/2 Eq. 4

Percent Cover of Non-Erodible Elements =

(Total Frontal Area/Survey Area) x 100 Eq. 5

Note: Ensure consistent units of measurements (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.

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

SECTION E 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 
Imperial County Air Pollution Control District Rule 800

800-26

conduction the line transect test method. Where flat vegetation exists conduct the 

following line transect test method.

E.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 vegetations 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%.

E.2 Conduct the line transect test method, as described in section E.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.

SECTION F 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 D; “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 nonerodible elements, is equal to or greater than 43cm/second.

F.1 For standing vegetation that consists of large, separate vegetative structures 

(e.g., shrubs and sagebrush,) select a survey area that represents a random 
Imperial County Air Pollution Control District Rule 800

800-27

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.

F.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 F.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.

Frontal Silhouette Area =

(Average Height) x (Average Width) Eq. 6

Frontal Silhouette Area Of Group=

(Frontal Silhouette Area Of Individual Vegetative Structure) 

x (Number Of Vegetation Structures Per Group)

Eq. 7

Total Frontal Silhouette Area =

Frontal Silhouette Area Of Group 1 + Frontal Silhouette 

Area Of Group 2 (etc.)

Eq. 8

Percent Cover Of Standing Vegetation =

(Total Frontal Silhouette Area/Survey Area) x 100 Eq. 9

Percent Open Space =

[(Number Of Circled Gridlines Within The Outlined Area 

Counted That Are Not Covered By Vegetation/Total Number 

Of Gridline Intersections Within The Outlined Area) x 100]

Eq.10

Percent Vegetative Density =

100 – Percent Open Space Eq. 11

Vegetative Density =

Percent Vegetative Density/100 Eq. 12

Frontal Silhouette Area =

[Max. Height x Max. Width] x [Vegetative Density/.04]o.5 Eq. 13
Imperial County Air Pollution Control District Rule 800

800-28

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

inches when calculating percent cover.)

F.3 Vegetative Density Factor. Cut a single, representative piece of vegetation (or 

consolidated vegetative structure) to within 1cm 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-Equations 

16, 17, or 18 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 x Maximum Width Eq.16
Imperial County Air Pollution Control District Rule 800

800-29

Figure C. Inverted Cone

Frontal Silhouette Area = Maximum Height x 1⁄2 Maximum Width Eq. 17

Figure D. Upper Sphere

Frontal Silhouette Area = (3.14 x Maximum Height x 1⁄2 Maximum Width)/2 Eq.18

SECTION G ROCK TEST METHOD

The Rock Test Method, which is similar to Section D, Test Methods For StabilizationDetermination Of Threshold Friction Velocity (TFV) of this appendix, examines the windresistance 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 nonerodible elements as ‘rocks.”

G.1 Select a 1 meter by 1 meter survey 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. 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, 
Imperial County Air Pollution Control District Rule 800

800-30

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

G.2 Without moving any of the rocks or other elements, examine the survey area. 

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

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

G.3 Mentally group the rocks >3/8 inch (1cm) 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.

G.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.

G.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.

G.6 Divide the total rock area, calculated in section G.5 of this appendix, 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.7 Select and mark-off two additional survey areas and repeat the procedures 

described in section G.1 through section G.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.

G.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 G.9 of 

this appendix.

G.9 If the average rock cover is less than 10%, the surface may or may not be stable. 

Follow the procedures in Section D.3 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 
Imperial County Air Pollution Control District Rule 800

800-31

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.

G.10 After completing the procedures described in Section G.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.