BECC Paving Alternatives Analysis (TPD1503067)

TABLE OF CONTENTS

1. BACKGROUND……………………………………………………………………………………………………………………………………………… 1

1.1      Scope of Study…………………………………………………………………………………………………. 1

1.1.1          Existing Conditions Analysis……………………………………………………………………… 2

1.1.2          Research & Assessment of Dust Abatement Treatment Methods…………………………. 3

1.1.3          Results and Recommendations……………………………………………………………………. 3

1. CHARACTERISTICS OF EXISTING STUDY SITES……………………………………………………………………………………. 4

2.1      Camino Embarcadero, Santa Cruz County, Arizona……………………………………………… 4

2.1.1          Site Description………………………………………………………………………………………. 4

2.1.2          Current Maintenance and Operations………………………………………………………….. 5

2.1.3          Inventory of Available Resources………………………………………………………………… 6

2.2      Hidalgo County Road Co01, Hidalgo County, New Mexico……………………………………… 7

2.2.1          Site Description………………………………………………………………………………………. 7

2.2.2          Current Maintenance and Operations………………………………………………………….. 7

2.2.3          Inventory of Available Resources………………………………………………………………… 8

2.3      New Frontier Drive, Luna County, New Mexico……………………………………………………. 9

2.3.1          Site Description………………………………………………………………………………………. 9

2.3.2          Current Maintenance and Operations………………………………………………………….. 9

2.3.3          Inventory of Available Resources………………………………………………………………. 11

2.4      Fort Huachuca, Cochise County, Arizona…………………………………………………………… 11

2.4.1          Site Description…………………………………………………………………………………….. 11

2.4.2          Current Maintenance and Operations………………………………………………………… 12

2.4.3          Inventory of Available Resources………………………………………………………………. 13

2.5      University of Arizona Science and Technology Park, Pima County, Arizona……………. 13

2.5.1          Site Description…………………………………………………………………………………….. 13

2.5.2          Current Maintenance and Operations………………………………………………………… 14

2.5.3          Inventory of Available Resources………………………………………………………………. 15

2.6      Summary of Site Conditions for Study Sites……………………………………………………….. 16

2.6.1          Summary of Climatic and Soil Conditions…………………………………………………… 16

2.6.2          Land Use…………………………………………………………………………………………….. 18

1. ASSESSMENT OF DUST ABATEMENT TREATMENT METHODS………………………………………………………… 19

3.1      Material Treatments……………………………………………………………………………………….. 19

3.1.1          Improving the Road Design……………………………………………………………………… 19

3.1.2          Recycled Asphalt Millings……………………………………………………………………….. 20

3.1.3          Chip Seal…………………………………………………………………………………………….. 20

3.1.4          Paving………………………………………………………………………………………………… 20

3.2      Chemical Treatments………………………………………………………………………………………. 21

3.2.1          Water/Surfactants………………………………………………………………………………….. 21

3.2.2          Moisture Absorbing Products (Calcium Chloride)………………………………………… 22

3.2.3          Organic Petroleum Products (Asphalt Emulsions)………………………………………… 22

3.2.4          Organic Non-Petroleum Products (Lignosulfonates)……………………………………… 23

3.2.5          Synthetic Polymer Products (Soil Sement)…………………………………………………… 23

3.2.6          Electrochemical Stabilizers and Clay Additives (Bentonite)…………………………….. 23

3.3      Administrative Methods………………………………………………………………………………….. 24

3.3.1          Reduced Speed Limits…………………………………………………………………………….. 24

3.3.2          Reduced Usage……………………………………………………………………………………… 24

3.4      Environmental Requirements…………………………………………………………………………… 24

3.5      Summary of Dust Abatement Treatment Methods……………………………………………….. 26

1. 4.        ANALYSIS AND RECOMMENDATIONS FOR FUGITIVE DUST ABATEMENT APPLICATION………….. 35

4.1      Initial Cost of Dust Abatement Treatment Methods…………………………………………….. 35

4.2      Reduction of PM₁₀ Emissions……………………………………………………………………………. 36

4.3      Cost Effectiveness of Applications……………………………………………………………………… 37

4.4      Recommendations for Study Sites……………………………………………………………………… 38

4.5      Menu of Alternatives for Other Entities……………………………………………………………… 39

LIST OF RESOURCES………………………………………………………………………………………………………………………………………… 41

LIST OF FIGURES

Figure 1, Project Location Map………………………………………………………………………………………….. 2

Figure 2, Total Precipitation Map – 2013……………………………………………………………………………. 17

Figure 3, Initial Cost of Dust Abatement Method (Per 2-Mile Study Site)………………………………….. 35

Figure 4, Annualized Cost of Dust Abatement Method (Per 2-Mile Study Site)…………………………… 36

Figure 5, Annual PM₁₀ Reduction of Dust Abatement Method (Per 2-Mile Study Site)………………….. 37

Figure 6, Cost Effectiveness of Dust Abatement Method (Per 2-Mile Study Site)………………………… 37

Figure 7, Flow Chart for Dust Abatement Alternative Selection……………………………………………….. 40

LIST OF TABLES

Table 1, Data Collection…………………………………………………………………………………………………… 3

Table 2, Summary of Site Characteristics……………………………………………………………………………. 16

Table 3, Summary of Annual Precipitation………………………………………………………………………….. 17

Table 4, Summary of Land-Use………………………………………………………………………………………… 18

Table 5, State and Local Air Quality Requirements/Permits……………………………………………………. 25

Table 6, Recommended Alternative by Study Site………………………………………………………………… 38

LIST OF APPENDICES

1. Site Location Maps
2. Questionnaire Responses
3. Land Use and Drainage Maps
4. Soil Type Maps
5. Rainfall and Climate Data
6. Estimated Traffic Counts
7. Noxious Weed Management Pamphlets
8. Dust Issues Along I-10 in New Mexico
9. US Army Environmental Technology Branch Communication
10. Preliminary Species Lists
    1. City of Glendale Dust Control Requirements
    2. Dust Abatement Application Cost Analysis (Per 2-Mile Study Site)
    3. PM₁₀ Reduction Calculations (Per 2-Mile Study Site)
    4. NMED Groundwater Quality Bureau Guidance: Above Ground Use of Reclaimed Domestic Wastewater

1. BACKGROUND

The Border Environment Cooperation Commission (BECC) is committed to helping preserve, protect and enhance the environment and human health of the U.S.-Mexico border region through project certification, technical assistance, and capacity building. One of the facets of environmental quality monitored by the BECC is air quality in this region. The region has many unpaved dirt roads that serve  a diverse group of users including residents, farmers, ranchers, Border Patrol, military operations, commercial developments, travelers, outdoorsmen, renewable energy and solar facilities. The BECC  has been made aware of fugitive dust emitted along these dirt roadways by the agencies that own and maintain them. In response, the BECC commissioned a study of unpaved roadways in Arizona and  New Mexico within the 60-mile border region to provide a reference for dust abatement alternatives to the owner/operators of roadways. Five (5) sites were selected for study in the region to provide a  diverse subset of roadways based on land-use, ownership, and available resources. It is the intent of this document to help its users identify a representative study site that corresponds closely to their own respective roadway characteristics and use this information to understand the dust abatement applications that are commonly available, cost-effective, and work well with their maintenance/operations capabilities.

1.1      Scope of Study

To assist roadway owners in selecting an appropriate dust abatement measure, this report presents a summary of the existing characteristics of each of the five (5) study sites in Section 2 and assesses commonly available dust abatement treatment methods in Section 3. Recommendations for effective fugitive dust abatement applications for each of the study sites are provided in Section 4, along with a menu for determining appropriate dust abatement methods for other agencies and unpaved road owners. Recommendations are based on effectiveness, initial start-up cost, and the annualized cost of reducing fugitive dust over the lifespan of the application. The unique study sites selected to represent the  diverse nature of the border region in Arizona and New Mexico and to identify effective dust abatement treatments/applications in this region are listed below and shown in Figure 1:

• Camino Embarcadero, Santa Cruz County, Arizona
• Hidalgo County Road Co01, Hidalgo County, New Mexico
• New Frontier Drive, Luna County, New Mexico
• Fort Huachuca, Cochise County, Arizona
• University of Arizona Science and Technology Park, Pima County, Arizona

For each of the five (5) study sites, the following study process was followed:

1.1.1           Existing Conditions Analysis

For each study site identified, a meeting was held with owner representatives to hear their concerns, learn details and history of the area, as well as to gather information about their current maintenance resources, abilities and procedures. Each study site was documented with field photos and observations. Field measurements, including length, width and condition notes were taken to help quantify costs especially for methods priced by the unit “surface area.” An agency representative from each of the five

(5) study sites received a questionnaire about their practices, methods, and internal resources. The completed questionnaires are attached in Appendix B and responses are summarized in Section 2.

This analysis of existing conditions includes inventories include local rainfall and seasonal climatology through existing studies and maps of the sites as well as on-site photos of vegetation and drainage conveyance and/or concerns.

Concerning traffic volumes, Kimley-Horn estimated the number of daily trips using the Institute of Transportation Engineers Trip Generation Handbook (9^th Edition). The trip generation was based on the number of existing housing units identified in Google Earth in the vicinity of the study roads. Also  taken into account with this data was additional traffic information such as the observed traffic volumes, types of traffic uses, vehicle types, and speeds. This information was gathered through the interview process with owner representatives from each agency (See questionnaire responses Appendix B).

Sections of roadway on open range land were noted in the field review, along with notable cattle crossings or impacts to the roadway. Soil conditions were also noted in the field and soil type maps  were compiled in Appendix D for reference. The length and width of roadways were inventoried, so that an accurate assessment of the quantity and cost of dust abatement can be estimated. Kimley-Horn’s review includes Federal, State, County, and local environmental requirements for the study sites and to identify documents that would be required if certain treatments/applications are used. Also included would be guidelines for construction to avoid environmental impacts.

Table 1 summarizes the type of data, collection method and significance of the data collected as part of the existing conditions analysis. This data was supplemented by field reconnaissance and the questionnaire responses from each agency in order to establish the existing characteristics, operations, and resources available for the five (5) study sites analyzed in this report.

Table 1, Data Collection

1.1.2           Research & Assessment of Dust Abatement Treatment Methods

Commonly available treatment methods for reducing fugitive dust on unpaved roads are described and compared in Section 3 of this report. These include a variety of material, chemical, and administrative treatment methods for reducing fugitive dust on unpaved roads. The results of the assessment are intended to assist regional road owners/operators to make informed decisions on products and methods being considered for dust abatement in their area.

1.1.3           Results and Recommendations

Based on the characteristics of the existing study sites (Section 2) and assessment of dust abatement treatment methods (Section 3), a recommendation for fugitive dust abatement application will be provided in Section 4 for each of the existing study sites.  The recommendations in Section 4 along  with the other findings in this report may be used as a guide to assist regional road owners/operators to make informed decisions on products/methods being considered for dust abatement in their area.

1. CHARACTERISTICS OF EXISTING STUDY SITES

Each of the five (5) study sites has its own unique characteristics, some of which are typical for many Counties along the U.S. and Mexico border. The sections below describe the characteristics of each of the study sites in this report, which are then summarized in Section 2.6, Tables 2, 3 and 4. Also in Section 2.6, estimated average daily traffic (ADT) counts were estimated based on the number of houses shown in aerial images, along with information gathered and observed in the field. For the installation type sites, ADTs were estimated solely on discussions with maintenance supervisors and field observations. A summary of climatic and soil conditions is provided in Section 2.6.1, and rainfall and climate data for the site is provided in Appendix E. Land-use, drainage, and soil type mapping of this location are available in Appendices C and D of this report.

2.1      Camino Embarcadero, Santa Cruz County, Arizona

2.1.1           Site Description

Camino Embarcadero is a dirt road that services a residential area near the Town of Rio Rico, in Santa Cruz County, Arizona. The terrain in this area is very hilly with an average elevation ranging from approximately 3,320 feet to 3,800 feet in the project area. For the purposes of this study, a two mile dirt stretch of Camino Embarcadero was analyzed, starting from the intersection of Pendleton Drive (chip sealed) and extending two miles northeast to the intersection of Camino Mar (dirt road). Camino Embarcadero is within a public right-of-way and maintained by Santa Cruz County. The estimated ADT on Camino Embarcadero is 258 vehicles per day

(VPD) and traffic is characterized as residential. The project site is in open range territory (not fenced off), but cattle are limited in the area. The climate is dry with seasonal rain and it snows once or twice a year.

Camino Embarcadero with Residence                                        Camino Embarcadero with Residence

2.1.2           Current Maintenance and Operations

Santa Cruz County currently maintains its dirt roads, including Camino Embarcadero, on a schedule based on class (A=4-6 times per year, B=2-4 times per year, C=1-2 times per year, P=Primitive as needed). Camino Embarcadero is considered a Class B road. Santa Cruz County  has staff on payroll for the maintenance of roads, and has the in-house resources to chip seal.

Operational tactics currently used to abate dust in Santa Cruz County include spraying water and improving upon the existing materials which include AB, asphalt millings, and chip seal. In some cases residents or businesses have paid for road improvements in their area. No proprietary products have been used in Santa Cruz County.

Primitive Road Adjacent to Camino Embarcadero

Dust is a year round challenge on Camino Embarcadero due to the dry climate, but especially in the drier seasons. This can be a challenge for the many homeowners in the area that live adjacent to the road. The steep and hilly terrain creates drainage challenges for the roadway. Camino Embarcadero has almost no cross-drainage pipes, requiring the drainage to cross at-grade. The integrity of the graded surface is diminished after rain storms due to the steep and highly erosive flow velocities that both create rills/gullies on the downstream side and deposit cobbles and sediment on the roadway. Drainage turnouts/lead-outs are evident but not effective as many times the road has been graded below the elevation of adjacent grade. Maintenance may be a challenge on this roadway because there are significant utilities that occupy the roadway right-of-way in this residential land-use area. There are some cattle in the area, but they have little impact on the roadway. Some signing is visible to alert road users to use caution in specific areas, but for liability reasons Arizona public agencies do not practice the posting of speed limits on dirt roads because of the variable surface conditions that may exist.

 Drainage Turnout                              Drainage Crossing

Drainage Turnout                           Ditch Along Steep Hill with Check Dams

2.1.3           Inventory of Available Resources

Santa Cruz County does not operate its own quarry, but it can contract out locally for rock, AB, asphalt, and other paving materials. The County does operate a landfill and has stockpiles of asphalt millings  and rock materials there.

Materials Available Internally

• Asphalt Millings
• Large Rock
• Dirt
• Backfill Material

Equipment Available Internally

• Water Trucks (3)
• 9 Wheel Roller (1)
• Steel Wheel Roller (1)
• Dump Trucks (7)10 cubic yard, (1)16 cubic yard)
• Asphalt Laydown Machine (1 small and 1 large through IGA with City of Nogales)
• Chip Spreader

Experience

• Grading
• Chip Sealing

2.2      Hidalgo County Road Co01, Hidalgo County, New Mexico

2.2.1           Site Description

Hidalgo County Road Co01 is a dirt road that services a residential area near the Town of Animas, in Hidalgo County, New Mexico. The terrain in this area has gently rolling hills with elevations ranging from approximately 4,860 feet to 4,900 feet in the project area. A two mile stretch of County Road  Co01 was reviewed for the purposes of this study; starting from the end of the existing chip seal at Richards Road and extending south. This road is operated within dedicated public right-of-way and Hidalgo County has sole jurisdiction over this roadway.  The estimated ADT on County Road Co01 is

40 VPD and traffic is characterized as a mix of residential, agriculture, Border Patrol, and  governmental. The project site is mostly in open range territory and there are cattle in the area. The climate is dry with seasonal rain and it snows only a few times a year.

Hidalgo County Road Co01 Primitive Road        Hidalgo County Road Co01

2.2.2           Current Maintenance and Operations

Hidalgo County currently has dedicated staff on payroll for the maintenance of roads, including Hidalgo County Road Co01. The roadways are graded on a schedule of approximately 3 times per year, and additionally as needed.

Hidalgo County has employed chip seal to abate dust on its roads. These projects are contracted out and generally funded by the State, though the County has supplemented parts of these projects in the past to better serve the community. Proprietary products have not been used in this area.

There are a few unique challenges for road maintenance and dust control on Hidalgo County Road Co01. In general, the area is very dry with ambient dust in the area generated from the surrounding landscape and agricultural activities. These issues are especially noticeable in the spring and early summer dry seasons. See Appendix H for additional information on the ambient dust issues in the area. The site is in open range land and there have been issues with cattle breaking up road edges as they cross. Drainage is a minor issue on the sides of the road as it is so flat that water ponds in the bar ditches. Border Patrol operates in the area and sometimes drags the side ditches to create a smooth surface so that footprints will show up. There may be high speed vehicles on Hidalgo County Road Co01, along with heavy agricultural equipment. The segment of roadway analyzed has experienced rutting, potholes, and slick roads after rain or snow.

2.2.3           Inventory of Available Resources

Hidalgo County does not operate its own quarry, but it can utilize a Bureau of Land Management (BLM) local pit for dirt and rock material. The County does not operate a landfill. The nearest asphalt plant is located in the City of Deming or Silver City.

Materials Available Internally

• Dirt (BLM pit)
• Rock (BLM pit)

Equipment Available Internally

• Water Truck (2000 gallon)
• Dump Trucks (2-10 cubic yard)

Experience

• Grading

Hidalgo County Grading Equipment on Co01                           BLM Pit – Near Hidalgo County Road Co01

2.3      New Frontier Drive, Luna County, New Mexico

2.3.1           Site Description

New Frontier Drive is a dirt road that services an agricultural and residential area near the City of Deming, in Luna County, New Mexico. The terrain in this area is flat with an approximate elevation of 4,220 feet in the project area. A two mile stretch of New Frontier Drive was reviewed for the purposes of this study; starting from the intersection of Cottonwood Road (dirt) and Hermanas Grade Road (SR 331) (chip sealed), and extending two miles east to the intersection of County Road Co27 (dirt ends and chip seal begins here). New Frontier Drive is operated within a granted easement and is maintained by Luna County. The estimated ADT on New Frontier Road is 78 VPD and traffic is characterized as heavy agriculture, commercial, residential, and Border Patrol. The project site is in open range territory (not fenced off), and cattle are very common in the area. The climate is dry with seasonal rain and it snows occasionally, causing muddy road conditions and rutting.

2.3.2           Current Maintenance and Operations

Luna County currently maintains its dirt roads, including New Frontier Drive, on a 4-6 week schedule, or as requested. Luna County has dedicated staff on payroll for the maintenance of roads, and has the ability to chip seal in-house.

Luna County has employed all standard operational tactics used to abate dust on its roads. Proprietary products are not typically used because the dirt here is fine sand and there is little humidity, so the materials dry out quickly and become ineffective.

There are a few unique challenges for road maintenance and dust control on New Frontier Drive. In general, the area is very dry with not only fugitive dust issues on the road, but large amounts of ambient dust in the area from the surrounding landscape.  See Appendix H for additional information on the ambient dust issues in the area. Drainage is a minor issue on the sides of the road as it is so flat that water ponds in the bar ditches. Since  the roadway is on open range land, this ponding inadvertently attracts cattle by providing a source of water and vegetation for them to graze on along the roadway. The cattle tend to degrade the edges of the roadway and the bar ditches as they seek these water and food sources. The Border Patrol operates in the area and sometimes drags the bar ditches to create a smooth surface so that footprints will show up. There may be high speed vehicles on New Frontier Drive, along with heavy agricultural equipment. Luna County and other counties in southwestern New Mexico have experienced issues with noxious weeds, such as the African Rue, being spread by cattle and ground disturbance from grading activities. See Appendix G for further information on noxious weed issues in these areas.

Cattle Hooves Breaking up Bar Ditch from Cattle Eating Vegetation

African Rue on New Frontier Drive                                                        New Frontier Drive

2.3.3           Inventory of Available Resources

Luna County operates its own quarry and locally stockpiles most of its paving materials. The County has the ability to mix its own cold mix asphalt. The County does not operate a landfill.

Materials Available Internally

• Pit Run Material
• Dirt
• Asphalt Millings
• Crushed Fines
• Base Coarse
• ½” and ¾” Chips
• Cold Mix Asphalt (Mixed Internally)

Equipment Available Internally

• Water Truck
• 9 Wheel Roller (3)
• Sheep’s Foot Roller
• Dump Trucks (10-24 cubic yard)
• Chip spreader
• Emulsion Spray Truck

Experience

• Grading
• Chip Sealing

2.4      Fort Huachuca, Cochise County, Arizona

2.4.1           Site Description

Fort Huachuca is a United States Army installation under the command of the United States Army Installation Management Command. It is located just northwest of the City of Sierra Vista, in Cochise County, Arizona. Fort Huachuca is about 15 miles north of the border with Mexico. As of 2010, Fort Huachuca had a population of roughly 6,500 active duty soldiers, 7,400 family members and 5,000 civilians. This study site is unique in that is a contained system; only authorized personnel are allowed on the installation and the general public do not use the roads. The terrain in this area is hilly with an average elevation ranging from approximately 4,560 feet to 4,900 feet in the project area. There are a number of dirt utility access roads throughout the site, of which 2 miles of dirt road were reviewed, at 3 unique locations. These roads are identified, along with land-use, drainage, and soil type mapping of  this location in Appendices C and D of this report. The roads on this site are operated under the sole jurisdiction of Fort Huachuca. Estimated daily traffic counts on these utility access roads are 20 VPD and traffic is characterized as military, commercial, and residential. The project site locations are not in open range territory, and are fenced off. The climate is dry with seasonal rain and snows a couple of times per year.

Fort Huachuca

2.4.2           Current Maintenance and Operations

Fort Huachuca

Fort Huachuca currently operates a continuous water spraying schedule on its dirt roads, while performing other road maintenance on an as needed basis. They do not have dedicated staff on payroll for the maintenance of roads, so this work is always contractor owned contractor operated (COCO).

Operational tactics specifically used to abate dust on the site include a continuous water spraying schedule and laying asphalt millings on the roads. Asphalt millings are not allowed in some areas of the site. No propriety dust abatement products are known to be used on the site at this time.

Dust is an issue year round with the roads on this site and can have an adverse effect on the equipment, residents, and workers on the site. Dust from the roads can impact visibility on State Route 90 (SR-90). The roads on the site are general depressed below the adjacent ground, creating the need for drainage turnouts. The US Army has a history of applications of different methods for controlling dust around  the nation. Many of the effective applications in humid parts of the country are not as effective in the arid climate of the BECC region. See Appendix I for communication with the US  Army  Environmental Technology Branch, Fort Sam Houston, TX.

2.4.3           Inventory of Available Resources

Fort Huachuca does not operate its own quarry, but does operate a landfill for dirt and concrete materials only. Hot mix and cold mix asphalt are available from nearby plants in Sierra Vista and Tucson. Below is a summary of the materials, equipment, and experience available to Fort Huachuca internally:

Materials Available Internally

• AB
• Gravel
• Cold Mix Asphalt
• Snow Sand
• Asphalt Millings

Equipment    Available   Internally (COCO)

• Water Truck
• Steel Wheel Roller
• Pneumatic Roller
• Dump Trucks (3-10 ton)
• Homemade Hydro Seeder

Experience

• None (Contract only)

2.5      University of Arizona Science and Technology Park, Pima County, Arizona

2.5.1           Site Description

The University of Arizona Science and Technology Park is an affiliate of the University of Arizona which integrates technology commercialization, industry collaboration, and campus activities at the University of Arizona on a single site. This project site is located just southeast of Tucson, in Pima County, Arizona. There are a number of different technological activities going on at this site, including a large field of solar panels that are being used for research. The terrain in this area is flat with an approximate elevation of 2,900 feet in the project area. There are a number of private utility access roads throughout the site, of which 2 miles of dirt road were reviewed. These roads are identified, along with land-use, drainage, and soil type mapping of this location in Appendices C and D of this report. The roads on this site are operated under the sole jurisdiction of the University of Arizona Science and Technology Park. Estimated daily traffic counts on these private utility access roads are 20 VPD and traffic is characterized as commercial/governmental/utility. The project site is not in open range territory, and is completely fenced in. The climate is dry with seasonal rain and it very rarely snows. A summary of climatic and soil conditions is provided in Section 2.6.1, and rainfall and climate data for the site is provided in Appendix E.

2.5.2           Current Maintenance and Operations

The University of Arizona Science and Technology Park currently maintains its dirt roads annually, or more often on an as needed basis. They do not have dedicated staff on payroll for the maintenance of roads, so this work is always contracted out.

Operational tactics used to abate dust on the site include spraying with water, lime treated AB, AB, and Gorilla-Snot®  (Proprietary).   The lime treated AB has been considered a successful way to harden      the roadway surface, provide good drainage, and reduces dust emissions. Gorilla-Snot is a liquid polymer  type  dust  abatement  treatment  that  is  applied  to  the  ground   surface.   In   the   experience of the maintenance managers at this site, these types  of  materials  work  well  in  low  traffic areas, but degrade quickly in higher traffic areas. They have also found that the Gorilla-Snot liquid polymer application needs to be reapplied at least once a year due to the effects of weather   and/or being broken apart by heavy use.

General challenges with the roads on this site include rutting and weed control. Dust is an issue year round and can have an adverse effect on the many solar panels on the site. Drainage is a minor issue on the site.

Dust Buildup on Solar Panels

2.5.3           Inventory of Available Resources

The University of Arizona Science and Technology Park does not operate its own quarry or landfill.  The Technology Park does not have any of its own equipment available and contracts out its maintenance work. Materials and equipment are readily available in the local area.

Materials Available Internally

• Dirt

Equipment Available Internally

• Water Truck (Rented as needed)

Experience

• None (Contract only)

2.6      Summary of Site Conditions for Study Sites

As described in Sections 2.1 to 2.5 above, each of the study sites have their own unique characteristics, while some characteristics are typical for many Counties along the U.S. and Mexico border.  A summary of the general characteristics of each project site are located in Table 2 below. Functional roadway classifications for each study site were gathered based on available resources for each jurisdiction. If no resources were available, a classification was determined based upon the functional categories provided in the AASHTO Policy on Geometric Design of Highways and Streets. ADT  counts were estimated based on the number of houses shown in aerial images, along with information gathered and observed in the field. For the installation type sites, ADTs were estimated solely on discussions with maintenance supervisors and field observations.

Table 2, Summary of Site Characteristics

2.6.1           Summary of Climatic and Soil Conditions

All of the study sites are located in the desert southwest and often experience dry and/or windy conditions. Average annual precipitation may impact fugitive dust creation on roads in these locations

so this data was collected from the Western Regional Climate Center database (See Appendix E for annual precipitation data). A summary of the precipitation characteristics of each project site are  located in Table 3 below:

Table 3, Summary of Annual Precipitation

As a frame of reference, Figure 2 below provides a map of the total precipitation in the project areas during 2013.

Figure 2, Total Precipitation Map – 2013

2.6.2           Land Use

Land-use maps and drainage maps for each of the study sites are available in Appendix C. A summary of this data is provided in Table 4 below:

Table 4, Summary of Land-Use

1. ASSESSMENT OF DUST ABATEMENT TREATMENT METHODS

Established treatment methods available to reduce fugitive dust on unpaved roads may be classified to include material, chemical, and administrative treatment methods:

• Material treatments are generally materials applied to the structure of the roadway to physically stabilize the surface. These methods may include organic/asphalt emulsions, asphalt millings, improved aggregate base material, chip seal, and paving.
• Chemical treatments are generally applied to the roadway surface and are designed to either bind fine particles together or absorb moisture from the ambient air to help keep the road surface bound together and compacted.
• Administrative methods of dust abatement include reducing posted speeds, developing road use restriction programs, and community dust awareness programs.

Applying these dust treatment methods can come with varying application, labor and equipment, and maintenance costs. However, dust control can lower roadway operating costs significantly in the long run by:

• Reducing the need for grading and roadway repair.
• Reducing the cost of cleaning vehicles, equipment, property, vegetation, and homes.
• Reducing the expense of damage to vehicles caused by roadways with poor grading or that are in need of repair (i.e. replacing vehicle windshields cracked by kicked-up gravel or repairs resulting from potholes and rutting).

The following sections describe available treatment methods for reducing fugitive dust on unpaved roads. Some of the treatment methods in this report may be proprietary products. The BECC and the authors do not endorse any specific product or manufacturer, though specific trade or manufacturer names may appear in this report for clarity or to describe existing practices at the study sites.

3.1      Material Treatments

Material treatments are generally materials applied to the structure of the roadway to physically stabilize the surface. These may range from simply improving the roadway design or stabilizing the soil, to fully paving the road. Material methods may have greater up front cost and typically require more labor and equipment than other types of treatments. However, material treatments such as paving or chip sealing can be more permanent and may provide a better roadway surface and overall value over longer time periods.

3.1.1           Improving the Road Design

Improving geometric design can be an effective way to reduce fugitive dust. Beneficial roadway features include a well-defined crown to facilitate drainage, a proper gradation/mix of fine particles and larger gravel material, and a positive flow of drainage off of and alongside the road. If puddles form in or around the roadway then fine particles near the roadway surface will float to the top, allowing them  to be blown away by vehicles as fugitive dust more easily. Once this dust blows or is washed away, the larger particles are not bound together as well and can be kicked off the road by vehicle tires.  Eventually this can lead to potholes forming and the degradation of the roadway, along with fugitive dust. In addition, improved roadway geometry may also help enhance the effectiveness of other chemical dust treatments by preventing them from washing away.

A good structural design for the roadway can also be an effective way to reduce fugitive dust. This can be achieved when the road is constructed or by applying and maintaining gravel to improve the structural section of an unpaved road. A good mix of gravel and fine particles helps bind the materials together and create a hard sturdy surface. This will help limit the disturbance of dust blown off by passing vehicles.

As a supplement to positive drainage and a good structural roadway design, geotextile fabrics or road fabrics may be integrated into the structural design of the roadway. These are made of high strength polymer mesh. Road fabrics protect the gradation mix of large/fine particles in the roadway by anchoring larger particles to the road surface, thus stabilizing the roadway surface and reducing fugitive dust emissions.

Improving the road design is considered a supplemental activity to enhance the dust abatement alternatives analyzed in Section 4.

3.1.2           Recycled Asphalt Millings

Surface materials such as asphalt millings may provide a layer of cover to keep fine particles down, while stabilizing the unpaved roadway. Asphalt millings are created from recycled asphalt that is crushed and mixed with an aggregate and binder, and then re-applied as a road base. Roads surfaced with recycled asphalt millings are not as strong as traditional asphalt roadways but with slightly more structural strength than chip-sealed roads. However, these roads would provide an improved surface compared to unpaved roads, while being a more cost effective way to reduce dust than full paving. An asphalt milling surface would also eliminate the need for regular grading on unpaved roads. These materials would hold up best on low volume roads without much heavy commercial traffic.

Milled asphalt materials can often be recycled from regional roadway resurfacing projects. These materials are often stockpiled in regional County and Department of Transportation (DOT) maintenance yards or landfills and may provide an accessible and low cost method to reduce fugitive dust emissions. As a result, asphalt millings may be available at a discounted price in more developed areas. It should  be noted when using recycled asphalt millings that they may dry out and lose their oil content, becoming less effective if stockpiled for long periods of time.

3.1.3           Chip Seal

Thin bituminous treatments, like chip seals, can be applied as a semi-permanent solution for reducing fugitive dust and armoring the unpaved roadway surfaces. Chip sealing can be applied as a double-chip application right on top of native or a prepared sub-grade. Service life will be extended if a base  material is placed under the bituminous layers. Chip sealing requires a higher initial investment than dust suppression applications, but has a longer service life. Chip seal treatments can deteriorate more easily than a fully paved roadway surface.

Chip seals are generally considered safe for the environment and are commonly used throughout the United States. Like other forms of paving or dust control measures, a petroleum based asphalt emulsion is used in the construction of a chip seal surface. This rubber/asphalt material may have some impact on the natural environment, similar to paving or sprayed dust control treatments.

3.1.4           Paving

Paving is the most effective method to control dust from unpaved roads, yet it comes with the highest initial cost. Asphalt and Portland concrete provide durable and effective surfaces that prevent the breakdown of soil surfaces. High initial investment in pavement yields a longer serviceable roadway, as

much as 20-years if maintained properly. A paved roadway may also provide a better driving surface and other benefits, aside from dust control. Paved roads may still accumulate some dust as it is tracked onto the roadway from unpaved side roads or settles onto the roadway surface. Some agencies may require a field design to install a new paved road, adding to the cost of this treatment.

3.2      Chemical Treatments

Chemical treatments may either increase moisture content or chemically bind fine roadway surface particles together and onto larger gravel. Within each of these categories there are multiple products available, of which suitable examples for the conditions common in the U.S. and Mexico border regions are described in this report.

Increasing moisture content in the surface of dirt roads causes fine roadway surface particles to stick together and onto larger gravel. The moisture content of dirt roads can be increased by spreading water or surfactant mixtures. Moisture content can also be increased by applying moisture absorbing salts, such as calcium chloride (CaCl₂) or magnesium chloride (MgCl₂). These chemicals attract water from the ambient air and retain it in the surface soil, helping the roadway surface to maintain higher water content. Surface treatments that increase moisture content in roads are described in Sections 3.2.1 through 3.2.2.

Roadway surface treatments which chemically bind fine roadway surface particles together and onto larger gravel include organic petroleum-based products (asphalt emulsions), organic nonpetroleum products (lignosulfonates), synthetic polymer products (Soil Cement), and electrochemical stabilizers and clay additives (bentonite). Specific surface treatments which bind particles together in roads are described in Sections 3.2.3 through 3.2.6.

3.2.1           Water/Surfactants

Watering is an effective temporary way to control fugitive dust on roadways. Moisture in the surface of dirt roads causes fine particles to stick together and adhere to larger gravel. However, in the U.S. and Mexico border regions it is common to have dry conditions with little annual precipitation (See Appendix E for climate data on the five sites reviewed). These dry conditions lead to rapid evaporation of watering treatments, usually within a single day, providing only temporary relief. As a result, watering operations would need to be nearly  constant and require high labor and equipment costs.  Other types of treatments may be more expensive up front but last longer, while constant watering operations can become expensive over time.

Reclaimed water is commonly used in the southwest as a way to conserve limited water resources and is generally available in developed areas in the regions of the project sites. For safety reasons, most municipalities do not recommend bathing in or drinking reclaimed water, however it is commonly used for dust control, golf courses, and parks. The New Mexico Environment Department has issued guidance for the above ground use of reclaimed domestic wastewater (See Appendix N).  Depending  on the location and treatment facilities available, reclaimed water can be 15%-50% cheaper than potable water for dust control purposes if the source of the water is equidistant to the project site. In general, reclaimed water has fewer sources, making it less available or further from most job sites. A project specific cost analysis should be performed to determine if the transport costs do not offset potential savings by using reclaimed water.

There are some products, called surfactants, which can be added to water to reduce evaporation rates and keep dust down. These additives can slightly increase the efficiency of water as dust control, requiring less water and allowing for longer intervals between watering. Though mildly beneficial, surfactant water treatments still evaporate relatively quickly, add cost to the watering operation, and can leave residues behind.

3.2.2           Moisture Absorbing Products (Calcium Chloride)

Moisture absorbing products attract and retain moisture in the surface of unpaved roads, helping fine particles to stick together and adhere to larger gravel. This reduces dust on the surface of the road and promotes a hard stable surface. Common products used for this purpose include calcium chloride (CaCl₂), magnesium chloride (MgCl₂), and sodium chloride (NaCl) salts. These products are hygroscopic, meaning that they have the ability to attract and hold water from the surrounding environment. Specific salts which are so hygroscopic that they dissolve into the water they absorb are referred to as deliquescent. These dissolved solutions help reduce the rate of evaporation, thereby increasing the product’s effectiveness in dust control. Calcium chloride and magnesium chloride are deliquescent salts and create solutions which resist evaporation when they mix with water. All of these salts function in similar ways for dust control, providing similar benefits and limitations. However, calcium chloride remains in liquid form under slightly warmer and drier conditions than magnesium chloride. For this reason, calcium chloride may be better for suppressing dust in the warm dry conditions which are common in the U.S. and Mexico border regions and will be discussed in this report. Sodium chloride is a solid under most summer climate conditions and offers no dust suppression capability.

Calcium chloride may be applied in the form of flakes, pellets, or liquids.  It can be applied in solid  form with a standard spreader, or in liquid form with standard bitumen distributor with spray bar. This equipment is commonly owned by DOTs and other public agencies. It is affordable, readily available, and already used to treat icy roads in many parts of the country. Deliquescent salts require moisture in the ambient air to be effective, so they work better in humid than dry climates. However, even in drier climates they may be able to absorb water in humid cycles or at night and then retain it into the drier times. Unlike some other types of surface treatments for dust, deliquescent salts can be mixed into the roadway surface and be re-graded; either pulling moisture deeper into the roadway surface, or the salt leaching closer to the top over time. Calcium chloride is generally considered to have minimal impact on the environment, though salts may leach out of the roads into other areas. This should be monitored as needed by the agency using the treatment.

There are some drawbacks to the use of calcium chloride and other deliquescent salts. With the dry conditions common in the U.S. and Mexico border regions, the effectiveness of calcium chloride in pulling water out of the ambient air may be reduced. However, even if it is hot and dry during the day, nighttime conditions could be favorable enough to allow some absorption of water into the soil. This could keep the soil moist below the surface and on top of the surface until the moisture evaporates. Deliquescent salts are highly soluble in water so rainfall may attract the salts out of the roadway surface and wash them away over time. Proper grading for drainage can help avoid this. These treatments may attract extra water to the roadway surface in wet conditions making roadway slippery. Finally, salts in high concentrations can corrode metals on vehicles and equipment.

3.2.3           Organic Petroleum Products (Asphalt Emulsions)

Emulsified asphalt is a mix of asphalt and water which penetrates road surface gravel. This coating weighs down fine particles and binds them together with gravel to reduce fugitive dust. Emulsified asphalt can be mixed into the top inch or two of road surface with a grader, and remain effective after being graded multiple times. Though commonly used for dust suppression, these products may contaminate waterways due to runoff and are generally not considered anymore. Asphalt is generally considered to have minimal impact on the environment, though salts may leach out of the roads into other areas. This should be monitored as needed by the agency using the treatment.

Other common organic petroleum-based binders include cutback asphalt, Bunker C, and dust oils.

3.2.4           Organic Non-Petroleum Products (Lignosulfonates)

Lignosulfonates are a common type of organic non-petroleum dust treatment product. This treatment is made from a naturally occurring polymer in trees called lignin, which naturally holds tree fibers and pulp together. Lignosulfonate treatment products naturally bind fine road surface particles and gravel together, like glue. In addition, lignosulfonates contain sugars that are hygroscopic, meaning that they have the ability to attract and hold water from the surrounding environment (similar to the effect of moisture absorbing products such as calcium chloride). This increased moisture contributes to binding particles together. As the moisture evaporates from the surface soils lignosulfonates become sticky, holding roadway surface particles together even during dry times. Lignosulfonates work well in dry environments, on unpaved roads with clay or sandy surfaces. Lignosulfonates used for dust control are natural, and generally considered to have minimal impact on the environment. However, the effects of this application should be monitored as needed by the agency using the treatment.

Lignosulfonates are water soluble and may mix into the roadway surface or wash away with rain. However, over time the effects of the sun reduce the solubility of the lignosulfonate and leave a hard stable surface. Due to the effect of weathering, lignosulfonates may need to be reapplied 1-2 times per year. Lignosulfonates are generally not corrosive, but may corrode aluminum under certain conditions.

Other common organic nonpetroleum-based binders include resins, animal fats, molasses/sugar beet, tall oil emulsions, and vegetable oils.

3.2.5           Synthetic Polymer Products (Soil Sement)

Synthetic polymer products include polyvinyl acrylics and acetates. They bind soil particles and form a semi-rigid crust on the roadway surface. This crust prevents fugitive dust on roads  from passing vehicles and wind, while stabilizing the surface. However, these products do not hold up against heavy traffic volumes compared to some other treatments.

Synthetic polymer products are either liquids or powders and are mixed with water and applied in liquid form with a standard bitumen distributor with spray bar, water truck, agricultural sprayers, or hydro seeding equipment. These products require up to a day of drying time before traffic can be introduced.

There are a number of common synthetic polymer products available, Soil Sement being one readily available product in the region of this study.

3.2.6           Electrochemical Stabilizers and Clay Additives (Bentonite)

Electrochemical stabilizers and clay additives such as bentonite rely on “electrochemical” bonding to attract water and allow bonds to form between fine particles and gravel roadway materials. In the dry climates common in the U.S. and Mexico border regions, bentonite may work better than the than the moisture absorbing solutions that require humidity. Bentonite is applied by working it deep into the roadway surface with a grader. Because it is fully mixed into the structure of the roadway, frequent grading and/or rain will not strip the treatment away from the surface as much as with other surface treatments. As a result bentonite does not need to be reapplied as often as the surface treatments,  leading to long term cost savings. It should be stressed that because bentonite and other clays disperse when exposed to water, they must be thoroughly mixed in and only used on roads with good drainage. Caution must be exercised before selecting this treatment: Bentonite has been applied successfully on limestone roads by binding to the limestone aggregate, but has been proven to be ineffective on sandy or gravelly roads. Testing of the road soil or evaluation of the road material chemistry should be undertaken prior to applying this treatment. If not applied properly and under the right conditions, rutting and dips may form. Bentonite is a naturally occurring material, is considered safe for the

environment, and won’t cause corrosion. Bentonite is not considered to be quite as effective as moisture absorbing treatments overall, but it does remain effective longer and can be cheaper to acquire and  apply than other surface treatments. Other common electrochemical stabilizers and clay additives include enzymes, ionic stabilizers, sulfonated petroleum oils, and montmorillonite.

3.3      Administrative Methods

The administrative dust abatement methods described below are considered a supplemental activity to enhance the dust abatement alternatives analyzed in Section 4.

3.3.1           Reduced Speed Limits

Fast moving vehicles can stir up fugitive dust on unpaved roads. Though unpaved roads are not commonly posted with regulatory speed limits, agencies could introduce special signage promoting slower speeds for dust control. Other physical means to reduce speeds may include utilizing drainage channel dip crossings or speed bumps. Law enforcement and community awareness programs may also help promote slower speeds for dust control and safety.

3.3.2           Reduced Usage

High volumes of traffic, heavy vehicles, and fast moving vehicles can stir up fugitive dust on unpaved roads. To limit these impacts, traffic can be reduced voluntarily or by special programs. For example programs could encourage walking, carpooling, modifying routes to use paved roads, or reducing unnecessary trips on high dust days. Traffic can be reduced by restricting vehicle weight or type, or by limiting motor vehicle access to local traffic only on dirt roads.

Some counties, such as Maricopa County in Arizona, designate high pollution advisory days which limit certain activities to reduce fugitive dust generation and vehicle emissions on the worst days. Appendix K provides an example document outlining administrative dust control requirements implemented to reduce fugitive dust on unpaved roads in the City of Glendale, Arizona. This document outlines City and County ordinances for residence, along with suggesting additional optional measures they can do to improve air quality in their City.

3.4      Environmental Requirements

Environmental requirements are reviewed as a part of the evaluation of the five (5) unique project study sites and potential dust treatments/applications. This review includes a screening of National Ambient Air Quality Standards (NAAQS), State and Local Air Quality Requirements/Permits, Impaired Waters, Threatened and Endangered Species, and National Environmental Policy Act requirements for each of the five (5) unique project study sites. Also, the dust abatement alternatives analyzed in Section 3.5 are reviewed for environmental impact or concerns.

National Ambient Air Quality Standards (NAAQS)

The Clean Air Act (CAA), last amended in 1990, lead to the creation of NAAQS by the Environmental Protection Agency (EPA). The EPA has set NAAQS standards for six criteria pollutants; Carbon Monoxide, Lead, Nitrogen Dioxide, Ozone, Particle Pollution (PM_2.5 and PM₁₀), and Sulfur Dioxide. According to the EPAs Currently Designated Nonattainment Areas for All Criteria Pollutants, all five

(5) locations included in this study are in attainment for the six criteria pollutants.

State and Local Air Quality Requirements/Permits

Table 5, State and Local Air Quality Requirements/Permits

Impaired Waters

Under section 303(d) of the Clean Water Act, states, territories, and authorized tribes are required to develop lists of impaired waters. Of the five (5) locations included in this study, Camino Embarcadero is the only location that is within proximity to an impaired water. The Santa Cruz River is over 0.25 miles west of the study area.

Threatened and Endangered Species

The US Fish and Wildlife Services’ (USFWS) Information, Planning and Conservation (IPac) website was accessed for the study locations. Threatened and Endangered species and or their  associated habitats are known to occur in proximity to all locations included in this study. Preliminary species lists are included in Appendix J. Prior to implementation of a dust abatement project, a qualified biologist should review current official species list from both the USFWS and the Arizona Game and Fish Department and New Mexico Game and Fish Department to determine if any species surveys, mitigation or formal consultation are required prior to construction.

National Environmental Policy Act

The National Environmental Policy Act (NEPA) of 1969 requires that all projects that receive federal funding or require federal approvals comply with the NEPA. Since there is a possibility that federal funds will be utilized for implementation of dust control measures at any one of the five (5) study locations, the project proponent should initiate NEPA compliance studies with the lead federal agency prior to implementation of a dust-abatement project. These studies could include biology, hazardous materials, Clean Water Act and Clean Air Act compliance, cultural resource surveys and Section 106 consultation, etc. as well as NEPA compliance clearances which would likely be in the format of a Categorical Exclusion for each of the locations.

Dust Abatement Alternatives

Material, chemical and administrative methods are being analyzed as alternatives for dust abatement for the five (5) study locations.

Material methods including improving the roadway design, recycled asphalt millings, chip seal and paving are traditional methods of dust control and are generally considered environmentally acceptable methods.

Chemical methods including water/surfactants, moisture absorbing products (calcium chloride), organic petroleum products (asphalt emulsions), organic non-petroleum products (lignosulfonates), synthetic polymer products (Soil Sement), and electrochemical stabilizers/clay additives (bentonite) are mostly commonly used forms of dust suppression by many state and county DOTs and are generally considered environmentally acceptable methods.

Administrative methods including reduced speed limits and reduced usage are considered environmentally acceptable methods for dust abatement. In some instances lower speeds may cause increased vehicle idling which can contribute to overall air quality concerns, but when reduced speeds are utilized on dirt roads, the potential increase in vehicular pollutants offsets the reduction in particulate matter pollutants.

3.5      Summary of Dust Abatement Treatment Methods

As discussed in Sections 1 and 2, five (5) study sites were selected to represent the diverse nature of the border region and provide a diverse subset of roadways based on land-use, ownership, and available resources. Choosing the appropriate treatment method to reduce fugitive dust on unpaved roads will require consideration of initial investment, maintenance cost, equipment availability, cost of applications, environmental impact, effect to roadway performance, and effect on vehicles. The matrix below provides a summary of how the treatment methods discussed may work for the five (5) study  sites considered in this report, or other sites in the border region. Qualitative initial and annual maintenance costs are shown assuming two mile segments of two lane roadways (matching the study sites) and include the material, equipment, and labor required for treatment. Factors that may impact the cost at an individual site may include: site specific roadway characteristics (sharp curves and hills), site locations, distance to material sources, and for the ability to contract or internally provide resources (materials, labor, and equipment). Please refer to Sections 1 and 2 for details on the unique characteristics of each site. Treatments/applications for each of the study sites are recommended in Section 4.

1.   ANALYSIS   AND   RECOMMENDATIONS   FOR   FUGITIVE   DUST ABATEMENT APPLICATION

Nine (9) different dust abatement alternatives were identified within Section 3, along with a summary matrix of benefits and limitations of each. This section utilizes the findings of Sections 2 and 3 to analyze the initial cost, annualized cost, and annual reduction of PM₁₀ (air suspended particles with a diameter of 10 micrometers or less) for each of the 2-mile study sites. Further analysis of these findings determines the cost effectiveness of reducing PM₁₀ for each fugitive dust abatement application considering service life (See Figure 6). Detailed cost analysis for each fugitive dust abatement application is provided in Appendix L. For the purpose of calculating PM₁₀ reduction, the fugitive dust abatement applications were classified as using water trucks, topical/chemical treatments, and hard surface treatments. Dust abatement alternatives such as improving roadway design and administrative methods (discussed in Section 3), may be used to supplement the applications analyzed in this section but are not included independently for this analysis. Details of the PM₁₀ reduction analysis are provided in Appendix M.

4.1      Initial Cost of Dust Abatement Treatment Methods

Initial start-up costs for dust treatment will play a significant role in the selection and recommendation of a particular dust abatement method. Available budget and funding can limit the types of treatment that are available for a road agency or owner. For this reason, Figure 3 attempts to quantitatively and graphically present the initial cost per treatment method at each of the five (5) study sites (2-mile segments). Asphalt paving and recycled millings applications exceed the limits of this chart because of the significant startup costs of these options. For example, a 2-mile segment of roadway paving may cost approximately $1.5 million.

Figure 3, Initial Cost of Dust Abatement Method (Per 2-Mile Study Site)

While some treatments may come with a higher upfront cost, they may have a longer service life. For example, asphalt paving is assumed to last twenty (20) years, recycled asphalt millings ten (10) years, chip seal eight (8) years, and bentonite treatment two-three (2-3) years. Chemical/polymer surface treatments may need to be applied 1-4 times a year to be effective based depending on traffic volumes

on the roadway. To account for this, Figure 4 provides an annualized cost of each dust abatement method for each 2-mile study site based on initial cost, service life, and number of applications required (depending on traffic volumes). The analysis and assumptions behind the annualized cost of dust abatement methods presented in Figure 4 are available in Appendix L. Note that the high traffic volumes on Camino Embarcadero in Santa Cruz County and New Frontier Drive in Luna County cause the annualized cost of chemical/polymer surface treatments to become more costly than other locations because they have to be applied multiple times per year.

Figure 4, Annualized Cost of Dust Abatement Method (Per 2-Mile Study Site)

4.2      Reduction of PM10 Emissions

Using Arizona Department of Transportation (ADOT) and Federal Highways Administration (FHWA) methodology for calculating PM₁₀ reductions, the different alternatives were compared for each 2-mile study site using estimated PM₁₀ reduction by dust abatement method. PM₁₀ reductions were calculated  at 2-mile study site for water trucks, chemical/polymer surface treatments, and hard surface treatments. See Figure 5 for comparisons. Each 2-mile study site generates different quantities of emissions due to the type of road and traffic counts. As a result, the Santa Cruz County study site shows a significant reduction of PM₁₀ primarily because it is generating much more PM₁₀ emissions due to the higher number of daily trips. Each site can also be looked at independently to compare the effectiveness of the different methods.

Figure 5, Annual PM10 Reduction of Dust Abatement Method (Per 2-Mile Study Site)

4.3      Cost Effectiveness of Applications

There is a significantly different picture painted when the cost of treatment and its effectiveness are combined into one chart, showing the annualized cost of the treatment divided by the PM₁₀ reduction. Time between applications range from daily to annually. When service life is considered, the hard surface methods (recycled millings, chip-seal, and paving) present a more cost-effective alternative to the more frequently applied chemical/polymer and watering surface treatments methods. Figure 6 reveals the annualized Cost ($/kg PM₁₀ reduced) for the dust treatment methods at each 2-mile study site.

Figure 6, Cost Effectiveness of Dust Abatement Method (Per 2-Mile Study Site)

Explanation: Each bar represents the dollars spent to reduce the PM₁₀ by one kg of dust. The lower the bars in the chart represent more cost effective treatment methods. The taller bars in the chart show a higher cost for the same reduction of PM₁₀.

4.4      Recommendations for Study Sites

There are a number of factors that may influence the selection of a dust abatement method. Each study site has considerations to take into account including cost, availability of materials, labor and equipment logistics, staff experience, available budget, and local resources. Without knowing the  available  funding that a particular road owner has access to, the cost-effectiveness presented in Figure 6 is the best indicator of what treatments provide the greatest PM₁₀ reduction for the lowest cost. Figures 4 and 6 clearly show that chip-sealing is one of the most cost-effective treatments to reduce fugitive dust on an annualized basis. However, Figure 3 shows that chip-sealing has a higher start-up cost than other methods. For Hidalgo County, Fort Huachuca, and the UA Tech Park the initial start-up cost (contracted) is on the order of 3 to 4 times more expensive than the initial application of another product. Santa Cruz County and Luna County have lower costs to chip seal because of their internal resources and experience gained through their annual chip seal maintenance programs.

There are additional considerations when you hard surface a road. These sometimes include roadway design fees, signing, striping, survey, drainage improvements, open range issues, etc. While providing an improved driving surface and safety benefits, hard surface roads are sometimes viewed as an invitation for vehicles to travel more quickly which creates additional issues including wildlife conflicts, added law enforcement, and pothole maintenance. With these considerations in mind and without understanding the individual sentiments of each road owner towards these considerations, the following recommendations were made based on strictly quantitative comparison and knowledge of road owner capabilities.

Table 6, Recommended Alternative by Study Site (2-miles each)

These recommendations are based on understanding the operations from an interview with each road owner and what resources are on hand. If an external funding source became readily available, such as Congestion Mitigation Air Quality (CMAQ) funds administered by the State Departments of

Transportation, then the recommendation would change to the most cost-effective treatment which would be chip-seal.

4.5      Menu of Alternatives for Other Entities

Based on the findings in this report, other agencies and owners with unpaved roads may want to identify what the best application for their roadway is. The sites studied here provide a diverse set of characteristics that should allow other road owners to find a study site that best reflects their circumstances (See Table 2, Section 2.6 for a summary of the individual study site characteristics). The agency/owner is encouraged to review the study sites presented and determine how closely their site matches the characteristics of one or more of the sites studied. Based on how their sites match up a dust abatement treatment alternative recommendation may be identified/reviewed in Table 6 to see if it meets the owner’s expectations. Below is a simple flow chart that may assist in selecting an alternative for an unstudied site in the arid U.S./Mexico border region.

Based on the analysis in Sections 4.1 to 4.4, the three most cost effective categories of dust abatement treatment are shown in Figure 7 below: Chip seal (hard surface material); Chemical/polymer; and  water truck. The chemical/polymer classification can apply to any topical polymer/glue/soil amendment that involves adding chemicals to stabilize or bind particles to the surface. Likewise, chip seal is the cheapest and most cost-effective application, but certainly an owner could choose a higher investment such as recycled millings or asphalt pavement instead.

Figure 7, Flow Chart for Dust Abatement Alternative Selection

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APPENDIX A: SITE LOCATION MAPS

APPENDIX B: QUESTIONNAIRE RESPONSES

APPENDIX C: LAND USE AND DRAINAGE MAPS

APPENDIX D: SOIL TYPE MAPS

APPENDIX E: RAINFALL AND CLIMATE DATA

APPENDIX G: NOXIOUS WEED MANAGEMENT PAMPHLETS

APPENDIX I:   US ARMY ENVIRONMENTAL TECHNOLOGY BRANCH COMMUNICATION

APPENDIX J: PRELIMINARY SPECIES LISTS

APPENDIX K: CITY OF GLENDALE DUST CONTROL REQUIREMENTS

APPENDIX L:    DUST ABATEMENT APPLICATION COST ANALYSIS (PER 2-MILE STUDY SITE)

APPENDIX  M:     PM10 REDUCTION CALCULATIONS (PER 2-MILE STUDY SITE)

APPENDIX N: