United States National Risk Management

Environmental Protection Research Laboratory

Agency Research Triangle Park, NC 27711

Research and Development EPA/600/SR-95/171 January 1996

E AP

Characterization of Mud/Dirt

Carryout onto Paved

Roads from Construction and

Demolition Activities

Project Summary

Michael M. Raile

Several urban areas of the country in

violation of the National Ambient Air

Quality Standard (NAAQS) for particulate matter have identified fugitive dust

generated by vehicular traffic on paved

streets and highways resulting from

mud/dirt carryout from unpaved areas

as a primary source of PM-10 (particles

≤ 10 μm in aerodynamic diameter).

Since little data are currently available

on the amount of mud/dirt carryout deposited on paved roads, this work characterizes the process and evaluates

selected control methods. These control technologies were evaluated for effectiveness in controlling mud/dirt

carryout from an unpaved construction

access area onto an adjacent paved

road. The first control used a street

sweeper to mechanically sweep the dirt

and debris from the paved road surface. The second applied a 6- to 12-in.

(15- to 30-cm) layer of woodchip/mulch

material onto the access area of the

construction site to a distance 100 ft

(30 m) from the paved road. The third

applied a 6-in. layer of gravel over the

access area. Street sweeping was found

to be only marginally effective (approximately 20%) in reducing average silt

loading on the paved road lanes. Treatment of the access area with a buffer

of woodchip/mulch was moderately effective, reducing average silt loading

by 38 to 46%. The gravel buffer showed

the greatest effectiveness, reducing the

average silt loading by 57 to 68%. These

silt loading reductions result in the following calculated PM-10 reductions:

street sweeping, 14%; woodchips, 27

to 33%; and gravel, 42 to 52%.

This Project Summary was developed

by EPA's National Risk Management

Research Laboratory's Air Pollution

Prevention and Control Division, Research Triangle Park, NC, to announce

key findings of the research project

that is fully documented in a separate

report of the same title (see Project

Report ordering information at back).

Introduction

Several areas of the country that are in

violation of the National Ambient Air Quality Standard (NAAQS) for PM-10 (particles

≤ 10 μm in aerodynamic diameter) have

conducted studies to identify the sources

of these emissions. A primary source of

PM-10 in many urban areas is the fugitive

dust generated by vehicular traffic on

paved streets and highways.

Road dust emissions occur whenever a

vehicle travels over a paved surface, such

as public and industrial roads and parking

lots. Particulate emissions originate primarily from the road surface material loading (measured as mass of material per

unit area). The surface loading is in turn

replenished by other sources (e.g., pavement wear, deposition of material from

vehicles, deposition from other nearby

sources, carryout from surrounding unpaved areas, and litter). Because of the

effects of the surface loading, available

control techniques attempt to either (a) prevent material from being deposited on the

surface or (b) remove (from the travel

lanes) any material that has been deposited.
2

According to the Environmental Protection Agency (EPA) publication, Compilation of Air Pollutant Emission Factors

(AP-42), the quantity of dust emissions

from vehicle traffic on a paved public road

(per vehicle kilometer traveled or VKT)

may be estimated using the empirical expression:

E = 4.6 (sL/2)0.65 (W/3)1.5

where: E = PM-10 emission factor

(g/VKT),

s = surface silt content (fraction

of particle < 75 μm in

physical diameter),

L = total road surface dust

loading (g/m2

), and

W = average weight (tons) of the

vehicle traveling on the

road.

Activities such as construction and

demolition projects can create a temporary, but substantial, increase in the

amount of fine particles on the surfaces of

adjacent paved roads. This increase in

fine particle loading is the result of mud/

dirt carryout from vehicles leaving the construction/demolition site.

Furthermore, carrying out material onto

a paved road is characterized by substantial spatial variation in loading about the

point of access to the site. This variation

complicates the estimation of emissions

caused by carryout as well as the emission reductions achievable by control of

carryout. The spatial variations and the

associated difficulties in estimating emissions become less important as the number of access points in an area increases.

A prior field study specifically addressed

mud/dirt carryout onto urban paved roads.

It was conducted in 1982 as part of a

national demonstration study of construction-related dust emissions.

This report describes a field study undertaken to better understand the mechanisms of mud/dirt carryout as well as the

effectiveness of measures used to control

carryout. The study collected and analyzed surface material samples taken from

a paved road adjacent to a construction

site in the Brush Creek Flood Control

Project in the metropolitan area of Kansas

City, MO. The effects of mud/dirt carryout

control were evaluated by monitoring the

changes in paved road surface dust loading. Both preventive and mitigative measures for controlling carryout were considered. Preventive measures attempted to

keep material from being deposited on

roadways, while mitigative measures attempted to remove the material after being deposited. The mitigative control measure of interest in this study was combined water flushing and broom sweeping. The two preventive measures that

were studied involved covering the access area with a coarse material (gravel

and woodchips/mulch).

Site Description

The paved roadway segment that was

selected for this study was the north-south

section of Elmwood Avenue between Blue

Parkway and Brush Creek Boulevard in

east central Kansas City, MO. The roadway segment is approximately 1200 ft (365

m) long and 40 ft (12 m) wide. It carries

an annual average daily traffic volume of

~ 10,000 vehicles and is classified as a

minor arterial roadway. At the time of this

study, a pocket of construction activity associated with the Brush Creek Flood Control Project was located on the east side

of Elmwood Avenue. This activity noticeably impacted Elmwood Avenue in the

mud/dirt carryover.

With the construction of a dam and other

earthmoving activities, the Elmwood site

was expected to provide enough truck traffic to support a field sampling program

throughout the summer of 1994. Ten-wheel

dump trucks carried earth from the site,

south on Elmwood, and then on to their

final destination. On days that it rained,

the trucks could not enter the site due to

an incline near the site entrance that became too muddy to support vehicles safely.

On those days, the trucks were directed

to other sites where they could work.

Road Surface Sampling

This field sampling program was designed to efficiently collect paved road

surface material samples at various distances between 50 and 550 ft (15 and 170

m) from the construction site entrance on

Elmwood Avenue over an extended time

period. From previous studies of silt loading on paved roads, it was known that the

loadings could vary from one lane to the

next. For this reason, a sampling scheme

allowed for segregation of the two southbound lanes. If necessary, at the end of

the data reduction process, the data from

the two southbound lanes could be integrated with each other to represent just

the southbound portion of the roadway.

One area of southbound Elmwood Avenue, just north of the access point, was

designated for the collection of background

silt loading samples that ideally would not

be impacted by carryout from the construction site. Samples of the material on

the road surface were collected by dry

vacuuming and then analyzed for silt content according to the procedures outlined

in AP-42.

Source Activity Monitoring

Source extent and activity data were

also collected in the sampling program.

Vehicle-related parameters were acquired

using a combination of manual and automatic recording techniques. Pneumatic

tube axle counters were used to obtain

traffic volume data. However, because

these counters recorded only the number

of passing axles, it was necessary to obtain traffic mix information (e.g., number

of axles per vehicle) to convert axle counts

to the number of vehicle passes. Vehicle

mixes were observed visually.

Daily weather data were obtained from

a local newspaper, and rainfall measurements were made on site with a rain

gauge. A daily log was also maintained,

noting any activities that were observed at

the site or any communications that were

pertinent to the outcome of the project.

Study Conditions

In addition to the uncontrolled study condition, three different mud/dirt carryout controls were evaluated in the program: street

sweeping, installation of a woodchip/mulch

apron (buffer) at the site access point,

and installation of a gravel buffer at the

same point. These controls were evaluated sequentially as described below.

First, the paved road adjacent to the

site (Elmwood Avenue) was cleaned to

the extent practical using a combination

of broom sweeping and flushing. This

cleaning represented a “baseline” silt loading value for future reference. (In this context, “baseline” refers to as clean a road

surface as possible.)

Once baseline levels were reached, the

surface loading was allowed to increase

to its “steady state” condition, with sampling conducted before and after precipitation throughout the “conditioning” period.

Post-precipitation sampling was performed

once the road surface became dry enough

to collect surface samples. The data from

these samples established both the magnitude and extent of the uncontrolled mud/

dirt carryout from the site and provided a

time history of the overall carryout process starting from an essentially clean

surface.

When the uncontrolled tests were completed, the paved road was thoroughly

cleaned again (sweeping and flushing) to

baseline condition prior to evaluation of

street sweeping as the first control method.
3

Thereafter, the road was swept periodically, using the fleet of street sweepers

that were already being used to control

carryout in the immediate vicinity. Sweeping occurred every other workday, except

on days that it rained. Surface sampling

was conducted at approximately the same

time periods before and after precipitation, as was done for the uncontrolled

sampling, to determine the overall reduction in silt loading.

Prior to evaluating the second control

method, the paved road was again aggressively cleaned (sweeping and flushing) to reestablish the baseline condition.

Coordinated with the cleaning, the

woodchip/mulch material was applied in a

6- to 12-in. layer to the site access point

and adjacent areas to provide a 100-ft

buffer between the paved and unpaved

surfaces. The buffer allowed the mud/dirt

carried on the truck tires and underbodies

to deposit in the buffer area, rather than

on the paved road. Reductions in silt loading were then quantified by appropriate

surface sampling at comparable time periods before and after precipitation.

Finally, after the paved road was

cleaned again (sweeping and flushing) to

the baseline condition, the previously installed woodchip/mulch buffer area was

replaced with a gravel buffer (100 ft long

and 6 in. deep). Comparable surface sampling was performed before and after

precipitation in a manner similar to that

described above.

Note that the original test plans had

called for the evaluation of street sweeping, the gravel buffer, and an asphalt

buffer. However, the construction site supervisor responded to the city's request

for controlling on-site fugitive dust by using a woodchip/mulch buffer. Because the

woodchip/mulch buffer was an actual control measure chosen by the contractor, it

was decided to evaluate this buffer’s effectiveness.

By the time that the gravel buffer was to

be evaluated, traffic into and out of the

site had been reduced and was not expected to pick up until concrete pouring

began in earnest at the dam site. Because of schedule constraints, it was jointly

decided by the EPA work assignment manager and the contractor to generate “captive” traffic to complete the evaluation of

the gravel buffer. The “captive” traffic that

was used was a 10-wheeled truck that

was identical to the type of trucks that

were originally hauling material from the

site. The captive truck was half-loaded to

represent the average of a loaded and an

unloaded condition.

Time History of the Project

The field sampling portion of the program spanned from the end of May until

mid-September 1994. The long time span

was the result of many delays caused by

the weather. There were consecutive days

when no sampling activity occurred. During those days, there was either no hauling activity at the site or it had rained the

evening before. This prevented any trucks

from entering the site and also prevented

surface samples from being taken.

The sampling program was also affected

by the trucks' originally leaving the site

going south and later began exiting to the

north. This change in direction caused

problems in maintaining a constant flow of

traffic from the test site over the southbound lanes of Elmwood. Also, because

of interference from a power pole, trucks

exiting north from the construction site

were forced to swing into the southbound

lane, thereby impacting the silt loading

background area.

Traffic into and out of the site slowed

after the earthmoving activities were largely

completed and concrete pouring for the

dam had not yet begun. Therefore, supplemental “captive” traffic was generated by

hiring a truck and driver to drive into and

out of the test site for the remaining portion of the field sampling program; i.e., the

evaluation of the gravel buffer.

Data Analysis/Results

The silt loading data were plotted as a

function of distance from the site access

point. Because earlier studies found a rapid

decrease in silt loading with distance, the

data were plotted on a semi-logarithmic

graph. The data were grouped by control

technology (e.g., uncontrolled, woodchip/

mulch) to construct a single plot for each

control. The data were then regressed for

each lane and for each control method.

The uncontrolled silt loadings did not exhibit any discernible trend to increase with

time. This is probably due to the fact that,

because of the steep slope of the access

road, no truck haulage occurred for 1 or 2

days after rainfall. Thus, at the study site,

precipitation did not enhance carryout onto

Elmwood, but rather rainfall at least partially cleaned the road surface. The trucks

were diverted to haul from other sites in

the area during these periods.

The area under the silt loading distribution curve was determined using the

trapezoidal rule for each sampling event.

When the resulting area was divided by

500 ft, the average silt loading (sL) was

found. The average silt loadings measured

for the uncontrolled condition ranged from

2.6 to 8.9 g/m2

 for the “A” lane and from

1.0 to 5.8 g/m2 for the “B” lane. These

ranges correspond approximately to the

upper 20th-percentile of the silt loading

data base presented in AP-42. Thus,

carryout clearly resulted in heavy silt loadings on Elmwood Avenue. In addition, the

curb or “A” lane was roughly twice as

heavily loaded as the other southbound

lane (“B”). This was expected because

the loaded trucks tended to travel almost

exclusively in the “A” lane in preparing to

turn west onto Blue Parkway.

Because of problems encountered in

defining an appropriate “background value”

of silt loading (as a result of the impacts

of construction vehicles occasionally exiting to the north on Elmwood), the control

efficiency of reduction in sL (presented in

Table 1) is in terms of a range between a

lower bound and an upper bound. The

lower bound was obtained by assuming a

background value of zero for silt loading.

The upper bound was obtained by subtracting the relatively high background

value of 0.5 g/m2

. This high background

value was determined from an average

daily traffic value of 10,000 using the relationship between silt loading and traffic

volume.

The overall control efficiency for street

sweeping was found to be 19 and 27% for

the “A” and “B” lanes, respectively, based

on the reduction in sL. Street sweeping

was found to be much more effective in

reducing total surface loadings. Part of

the poor performance for removal of silt

loading can be attributed to the abrasion

of coarse material left on the roadway

after sweeping; i.e., the sweeper generated additional material in the silt fraction

by breaking large particles into smaller

ones. In addition, the same sweeper already was being used to control carryout

from construction sites in the immediate

vicinity.

The woodchip/mulch buffer proved to

be more effective than the street sweeper

in reducing average silt loading. Over the

two sampling events, an average control

efficiency of 33 to 37% for the “A” lane

and 49 to 64% for the “B” lane was found

for the woodchip/mulch buffer. This control measure is of considerable interest

because it represents a “real world” solution to the problems of carryout in that the

contractor constructed a buffer from waste

material collected on-site. This resulted in

a far more cost-effective (i.e., reduction in

silt loading per unit cost) control than street

sweeping.

An important potential drawback was

observed during the use of woodchip/
4

mulch. Because woodchip/mulch is soft

and easily compressed by vehicles, the

weight of a passing vehicle will displace

the air contained in the buffer. This effect

caused substantial fugitive dust clouds that

could be seen when a vehicle traveled

over the buffer. Although the buffer was

effective in controlling the carryout of materials from the site, on-site reentrained

fugitive dust vehicular emissions may have

increased due to the woodchip/mulch

buffer.

The gravel buffer was found to be the

most effective control studied in this report, reducing average silt loadings by 56

to 64% in the “A” lane and 58 to 76% in

the “B” lane. In addition, unlike the

woodchip/mulch material, the gravel buffer

probably reduced on-site reentrained fugitive dust vehicle emissions by covering

the travel surfaces with a coarser material.

Quality Assurance (QA) Results

Eight sets of co-located surface samples

were collected (using the “embedded” sampling approach) and analyzed. The regular and the QA samples yielded comparable results for total loading, silt loading,

and overall silt content (as determined by

dividing the total loading by the silt loading). The silt loading range percent values

fell well within the ±50% guideline set

forth in the test plan, with an overall mean

of 17% in absolute value of range percent.

A total of 24 QA samples were obtained

by riffle splitting of field samples of road

surface loading. Each subsample was

taken through sieve analysis. The QA statistic (relative value, RV) for 17 of the 24

pairs (71%) fell within the ±0.05 guideline

established in the test plan, with an absolute

maximum of 0.154 for Sample 2-B-R-593 (i.e.,

having a “regular” silt content of 10.5% contrasted with a QA value of 9.3%). In general, larger absolute values of the QA

statistic are associated with lower silt fractions.

Conclusions

The testing and evaluation program that

was conducted led to several conclusions.

• A broad range of paved road silt loadings were measured near the construction site access point under the

uncontrolled condition and each controlled condition, but no condition exhibited clearly discernible time trends.

In other words, silt loadings did not

tend to increase with time. This may

be the result of rainfall partially cleaning the surface between different sampling events and largely reducing access road traffic until the steep slope

had dried. Once access point traffic

was restored to its normal level,

reentrainment and displacement to

nontraveled parts of the road (i.e.,

curb) offset the additional loading from

carryout so that a new “equilibrium”

was established.

• Street sweeping was found to be only

marginally effective (approximately

20%) in lowering average paved road

silt loading values in carryout areas.

Table 1. Silt Loading Control Efficiencies

A Lane B Lane Both Lanes

Control (lower limit/upper limit)

Street sweeping 19/22% 21/27% 20/24%

Woodchip/mulch application 33/37% 49/64% 38/46%

Gravel application 56/64% 58/76% 57/68%

In general, total loadings were reduced far more effectively, but the

street sweeper appears to have

abraded the remaining material, thus

“creating” additional material in the

silt fraction.

• The 6- to 12-in. layer of woodchip/

mulch was moderately effective in

controlling carryout, with average

paved road silt loadings being reduced

38 to 46%. This control measure was

implemented by the construction contractor at the request of Kansas City

officials. Furthermore, the control

made use of material that was available on-site at no cost. Although the

woodchip/mulch buffer was moderately effective in controlling off-site

emissions, it was noted that this buffer

may have increased on-site PM-10

emissions. The buffer was fairly “soft”

and was readily compressed by vehicles traveling over it. This compression displaced the trapped air, and

puffs of fugitive dust were observed.

• The 6-in. layer of gravel was found to

reduce average paved road silt loadings by 57 to 68%. This was the highest efficiency found in the present

study. Unlike the other buffer material, gravel formed a far stronger surface that did not yield under vehicular

traffic, and no on-site increase in fugitive dust emissions was noted.

• Based on these measured reductions

in silt loading and using the PM-10

emission equation, the following calculated PM-10 reductions would result: street sweeping would reduce

PM-10 by approximately 14%; treatment of the access area with

woodchips/mulch would moderately

reduce PM-10 by 27 to 33%; the

gravel buffer would result in the largest reduction of PM-10, by 42 to 52%;

and the PM-10 control efficiencies are

somewhat lower than the silt loading

reductions, because of the 0.65 power

on silt loading in the PM-10 emission

equation.
5

Michael M. Raile is with Midwest Research Institute, Kansas City, MO 64111.

Charles C. Masser is the EPA Project Officer (see below).

The complete report, entitled "Characterization of Mud/Dirt Carryout onto Paved

Roads from Construction and Demolition Activities," (Order No. PB96-129028;

Cost: $28.00, subject to change) will be available only from:

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

Telephone: 703-487-4650

The EPA Project Officer can be contacted at:

Air Pollution Prevention and Control Division

National Risk Management Research Laboratory

U.S. Environmental Protection Agency

Research Triangle Park, NC 27711

United States

Environmental Protection Agency

National Risk Management Research Laboratory (G-72)

Cincinnati, OH 45268

Official Business

Penalty for Private Use $300

EPA/600/SR-95/171

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EPA

PERMIT NO. G-35