2014 MARTIN MARIETTA MATERIALS
FINAL TECHNICAL REPORT REVIEW OF DRAFT
AIR QUALITY PERMIT 13LR2446
Prepared for:
LARIMER COUNTY
ENVIRONMENTAL & SCIENCE ADVISORY BOARD
AND
CITY OF FORT COLLINS
AIR QUALITY ADVISORY BOARD
Prepared by:
D. HOWARD GEBHART
Air Resource Specialists, Inc.
1901 Sharp Point Drive, Suite E
Fort Collins, Colorado 80525
Telephone: 970-484-7941
Fax: 970-484-3423
August 2014
TABLE OF CONTENTS
Section
Page
1.0
1-1
1-1
1-1
1-3
2-1
2-1
2-2
3-1
3-1
3-4
4-1
4-1
4-2
5-1
6-1
2.0
3.0
4.0
5.0
6.0
Introduction
1.1
Background
1.2
Overview of Martin Marietta Asphalt Plant Site
1.3
Site Characteristics
Review of Emission Estimates
2.1
Criteria Air Pollutants
2.2
Hazardous Air Pollutants
Review of Dispersion Modeling
3.1
APCD Modeling Studies
3.2
Additional HAP Modeling Analysis
Reasonably Available Control Technology
4.1
RACT for VOC Emissions
4.2
RACT for CO Emissions
Technical Comments on Draft Permit
Summary & Conclusion
LIST OF FIGURES
Figure
1-1
1-2
4-1
Page
Martin Marietta Materials Google Earth Image
MMM Asphalt Batch Plant
Image of Recycle Air Collection Point at MMM Asphalt Plant
1-2
1-3
4-2
LIST OF TABLES
Table
2-1
2-2
3-1
3-2
3-3
3-4
3-5
3-6
4-1
Page
MMM Emissions (ton/year)
MMM Emissions (lbs/year)
1-Hour Averages CO Impact
8-Hour Average CO Impacts
Location of Public Receptors near MMM
MMM HAP Modeling Results – Acute Impacts
MMM HAP Modeling Results – Chronic Impacts
Background HAP Levels – Fort Collins, Colorado
RBLC Query Results: Asphalt Concrete Manufacturing
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
2-1
2-2
3-2
3-2
3-5
3-6
3-7
3-8
4-3
i
1.0
1.1
INTRODUCTION
Background
Martin Marietta Materials (MMM) operates a hot mix asphalt plant at 1800 North Taft
Hill Road, located within Larimer County, Colorado (County) and just outside the limits for the
City of Fort Collins (City). The County and City have requested the services of a qualified
environmental consultant to review the draft MMM air quality permit issued for public notice by
the Colorado Air Pollution Control Division (APCD) and provide input to the County’s
Environmental and Science Advisory Board (ESAB) and the City’s Air Quality Advisory Board
(AQAB). The ESAB and AQAB will be responsible for considering the draft permit and
providing any recommendations for submitting official comments on the draft permit by either
the County or City.
Air Resource Specialists, Inc. (ARS) has been selected by the County and City to assist in
the MMM draft permit review. ARS has been assigned the following work, which is documented
in this technical report.






Review Draft Air Permit and Permit Conditions
Review Air Emissions Inventory that supports the MMM Draft Permit
Review Air Dispersion Modeling that supports the MMM Draft Permit
Assess Potential Public Health Impacts of Hazardous Air Pollutant(HAP)
Emissions
Summarize Findings in a Technical Report
Present Findings to a Meeting(s) of the EASB and AQAB
In essence, this study is a “review of the review” conducted by APCD. The study
objectives are to confirm that APCD’s technical analysis supporting the permit decision is based
on sound science and standard regulatory practice. Also, ARS’ review is designed to ensure that
the issued permit is protective of public health and the environment.
The technical review work by Air Resource Specialists, Inc. (ARS) is described in this
report and has been jointly funded by the County and City. A single report has been prepared that
documents the results of the ARS studies.
1.2
Overview of MMM Asphalt Plant Site
According to MMM, mining and processing for aggregate materials has been conducted
at the North Taft Hill Road site since the 1950s. MMM acquired the asphalt plant site in 2011.
The current asphalt plant was relocated to the site under the authority of a “portable source”
permit. Under Colorado Air Pollution Control Commission Regulation #3, an emissions unit can
remain at a single site for only 18 months under a “portable source” permit. MMM wishes to
permanently locate the asphalt plant at the present site and as such, has requested a “stationary
source” permit pursuant to Regulation #3 from the APCD.
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
1-1
The MMM asphalt plant site is located at 1800 North Taft Hill Road, Fort Collins, CO.
On the west side of Taft Hill Road, MMM operates additional aggregate mining and processing
operations. An image of the asphalt plant site from Google Earth is shown as Figure 1-1.
Figure 1-1. Martin Marietta Materials Google Earth Image.
*Indicates the MMM Asphalt Location
According to materials provided by MMM, the plant produces “warm mix” asphalt,
which is a combination of liquid asphalt cement, aggregate, sand, asphalt binder, and recycled
asphalt pavement (RAP). Based on claims by MMM, a “warm mix” plant operates at
temperatures of less than 300 degrees F, which is 30-70 degrees F cooler than a more
conventional “hot mix” plant. The “warm mix” plant consumes about 20% less fuel.
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
1-2
Figure 1-2 shows a typical asphalt batch plant.
Figure 1-2. Asphalt Batch Plant (provided by MMM).
At the Taft Hill Road asphalt plant, the air emissions are routed through a fabric filter
emissions control system, also known as a baghouse, before existing through a stack located at
the edge of the baghouse. The fabric filter dust collector is primarily a control device for removal
of particulate matter (PM) emissions and is required to meet the emissions limitations in the
applicable New Source Performance Standards (NSPS) at 40 CFR 60 Subpart I. During a visit to
the facility, ARS confirmed that the baghouse is present to control emissions and appears to be
working effectively based on the lack of visible emissions in the stack exhaust. ARS staff also
observed additional pollution abatement measures not listed in the draft MMM permit. First,
there is a collection point along the product conveyor leading to the asphalt storage silos that
routes volatile organic compound (VOC) emissions lost through the conveyor back to the asphalt
plant burner for destruction. Also, MMM has installed condensers to collect VOC emissions lost
at the liquid asphalt storage tanks. Some of the collected VOC may also be regulated as
hazardous air pollutants (HAPs).
1.3
Site Characteristics
The immediate MMM plant site is rural in character, with some residential housing to the
south. The City of Fort Collins Poudre River Trail also abuts the MMM property on the south
side, with a parking lot for trail access along Taft Hill Road to the immediate south of the MMM
property. The Lincoln Middle School (operated by the Poudre School District) lies about
1 kilometer (km) southeast of the MMM plant site.
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
1-3
2.0
2.1
REVIEW OF EMISSION ESTIMATES
Criteria Air Pollutants
Table 2-1 summarizes the emissions data for the main stack at the MMM asphalt plant, as
determined by the APCD and summarized in the draft permit.
Stack
Fugitive
Total
PM
5.4
3.7
9.1
PM10
1.8
0.9
2.7
Table 2-1
MMM Emissions (ton/year)
PM2.5
NOX
1.3
6.5
0.1
1.4
SO2
0.8
VOC
7.6
CO
72.2
ARS confirmed that MMM emissions listed above were determined using the maximum
production rate in the permit of 475,000 tons/yr.
For NOX, VOCs, and SO2, the emissions were calculated using the AP-42 emission
factors for drum mix hot mix asphalt plants fired on natural gas. These emission factors and the
AP-42 citation are listed below:
NOX: 0.026 lb/ton, AP-42, Table 11.1-7
SO2: 0.0034 lb/ton, AP-42, Table 11.1-7
VOC: 0.032 lb/ton, AP-42, Table 11.1-8
For CO emissions, the AP-42 factor is 0.13 lb/ton, but MMM has requested
CO emissions equal to 0.291 lb/ton when combusting natural gas and 0.40 lb/ton when
combusting liquefied petroleum gas (LPG or propane). The reason for the higher CO emissions
at the MMM asphalt plant were not documented in the materials released to the public which
accompanied the draft permit. In response to ARS questions, APCD’s explanation for this
discrepancy is a claim that historical experience shows that the AP-42 CO factor is too low based
on emissions testing at other asphalt plants. For additional discussion of the CO emissions,
please refer to Section 4, Reasonably Available Control Technology.
The PM emissions were calculated by APCD and differ somewhat from the AP-42
values. AP-42 lists uncontrolled emission factors for PM and PM10 of 28 lb/ton and 6.5 lb/ton
respectively (See AP-42, Table 11.1-3). The Division’s PM factor is close to AP-42
(27.916 vs. 28 lb/ton) and the Division’s PM10 factor exceeds the AP-42 value by a small amount
(8.3748 lb/ton vs. 6.5 lb/ton).
PM2.5 is not directly tabulated in AP-42, but AP-42 Table 11.1-4 lists the particle size
distributions from asphalt plant drum mix dryers, and gives a PM2.5 fraction of 5.5% for the
uncontrolled emissions. When these data are applied to the AP-42 uncontrolled PM factor
(28 lb/ton), the derived PM2.5 factor is 1.54 lb/ton. APCD calculated 2.3476 lb/ton for the draft
permit.
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
2-1
The technical basis for the Division’s emission calculations for PM, PM10, and PM2.5
were not provided in the materials released to the public which accompanied the draft permit.
However, subsequent correspondence with APCD staff indicates that the Division’s PM
estimates were based on the grain loading from the applicable New Source Performance
Standard (NSPS) which is 0.04 gr/dscf. This is a reasonable approach as the PM emissions are
then consistent with the proposed permit limit.
2.2
Hazardous Air Pollutants (HAPs)
Table 2-2 summarizes the HAP emissions calculated by APCD for the MMM facility.
Please note that HAP emissions are reported in pounds whereas the other pollutant emissions are
listed in tons. All HAPs documented in the APCD materials are released at the asphalt plant
baghouse stack.
Acetaldehyde
618
Formaldehyde
1,473
Table 2-2
MMM Emissions (lbs/year)
Toluene
Benzene
Ethylbenzene
1,378
185
114
Quinone
76
HCl
95
ARS confirmed that the MMM HAP emissions listed above were determined using the
maximum production rate in the permit of 475,000 tons/yr.
HAP emissions listed for benzene, ethylbenzene, and formaldehyde match the AP-42
data for emissions from a natural gas-fired drum mix asphalt plant (AP-42, Table 11.1-10).
These factors are as follows: benzene (0.0039 lb/ton), ethylbenzene (0.00024 lb/ton), and
formaldehyde (0.0031 lb/ton). The APCD toluene factor (derived from the APCD’s emissions
estimate) is 0.0029 lb/ton, compared to the AP-42 factor of 0.00015 lb/ton. The toluene factor
used by APCD is the AP-42 factor for an asphalt plant fired on #2 fuel oil, so it appears that
APCD may have used this factor by mistake instead of the natural gas factor. After correcting for
this error, the toluene emissions would be reduced from 1,378 lb/yr to 71 lb/yr.
In the draft permit, APCD also listed HAP emissions for acetaldehyde, quinone, and
hydrochloric acid (HCl); however, these emissions are not included within the published AP-42
emissions data. In later correspondence with ARS, APCD acknowledged that the data were listed
in error and the expectation is that the estimates for these particular HAP pollutants will be
dropped when the final permit is released.
There are also other HAPs listed in the AP-42 data (AP-42, Table 11.1-10) that have
emissions comparable to the HAPs where emissions were calculated by APCD. These HAPs are
hexane (0.00092 lb/ton), xylene (0.00020 lb/ton), and polycyclic aromatic hydrocarbons or
PAHs (0.00019 lb/ton). The most prevalent PAHs based on AP-42 data are naphthalene and
2-methylnaphthalene. It is unknown why these HAPs were not considered given that the
emissions are comparable to other HAPs where emissions were tabulated by APCD. At the
maximum permitted production rate of 475,000 tons per year, the resulting emissions would be:
hexane 437 lb/yr, xylene 95 lb/yr, and PAHs 90 lb/yr.
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
2-2
3.0
3.1
REVIEW OF DISPERSION MODELING
APCD Modeling Studies
APCD conducted air quality dispersion modeling for CO emissions using the
US Environmental Protection Agency (US EPA) AERSCREEN model (Version 11126).
AERSCREEN is a simple “screening” model tool that predicts the worst-case concentration
expected from a single emission source over a wide range of possible meteorological dispersion
conditions.
Based on ARS’ review of the modeling documents provided by APCD, it has been
determined that the modeling was done correctly and followed the applicable regulatory
guidelines governing air quality dispersion modeling (40 CFR 51 Appendix W). If anything, for
reasons explained below, the modeling results are likely to be a significant overestimate of the
actual CO impacts which might be realistically expected for the MMM asphalt plant. These
conservatisms are especially pronounced for the 8-hour CO concentration modeling.
For the APCD modeling, the CO emission rate was set to 160 lb/hr, which equals the
expected CO emission rate at the maximum capacity of the asphalt plant (400 ton per hour) when
operating on LPG (emissions of 0.4 lb/ton). AERSCREEN returns the worst-case expected
concentration for an averaging time of 1-hour by calculating the expected concentrations from
the emission source under a wide array of different meteorological dispersion conditions. The
1-hour concentration predicted by AERSCREEN is then adjusted to other averaging times using
an EPA-recommended scaling factor. The 1-hour average AERSCREEN result was converted to
an 8-hour average by APCD for comparison with the 8-hour National Ambient Air Quality
Standard (NAAQS) using a scaling factor of 0.9.
The AERSCREEN modeling result is also added to a “background” concentration, which
accounts for ambient concentrations attributable any regional pollutant sources not explicitly
included in the modeling. APCD reports that it used ambient monitoring data collected over the
period 2004-2006 at the Fort Collins monitor located near the Colorado State University (CSU)
campus to determine the “background”. This is the only ambient CO monitor in the Fort Collins
region. APCD’s analysis states that using background data from the Fort Collins monitor likely
overstates the real background values at the MMM site and ARS concurs with that assessment.
The assumed background level accounts for about 1/3rd of the total ambient CO impact in
APCD’s modeling analysis.
AERSCREEN also parameterizes “building downwash”, which describes how the airflow
around nearby buildings and structures within the plant affect atmospheric dispersion and the
resulting pollutant concentrations. There are three (3) structures at MMM that were considered
by APCD for these effects: 1) the lime silo adjacent to the baghouse stack, 2) the product silos
south of the baghouse stack, and 3) the baghouse structure itself. Since AERSCREEN is limited
to addressing only a single building in any given model run, APCD executed the model
separately for each of the three building configurations and then selected the worst-case result
from these model runs. The AERSCREEN output showed that the building configuration with
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
3-1
the lime silo caused the highest ambient concentrations and was therefore used by APCD for the
CO modeling results.
AERSCREEN was set such that the minimum source-to-receptor distance modeled was
87 meters, which is the distance from the asphalt plant baghouse stack to the closest property
boundary along Taft Hill Road which borders the facility of the west side. ARS confirmed that
the 87 meter distance matches the distance from the MMM baghouse stack to the closest
property boundary.
AERSCREEN was modeled by APCD using a unit emission rate (1.0 grams per second).
The modeling results were then adjusted to the actual emission rate (160 lb/hr or 20.18 g/sec) by
multiplying the AERSCREEN model output by the emission rate in grams per second. This
methodology accounts for the known relationship in the model that concentrations are linearly
proportional to the emissions rate. The model results are compared to the National Ambient Air
Quality Standards (NAAQS). The CO NAAQS are:
1 – Hour: 35 ppm (40,000 ug/m3)
8 – Hour: 9 ppm (10,000 ug/m3)
AERSCREEN modeling results for the three building configurations are listed below in
Tables 3-1 and 3-2 for the 1-hour average and 8-hour average CO concentrations.
Table 3-1
1-Hour Average CO Impacts – Martin Marietta Materials
Micrograms per cubic meter
Building
Configuration
AERSCREEN
Concentration
Background
Concentration
Total
Concentration
NAAQS
Lime Silo
7,203
5,750
12,953
40,000
Product Silo
4,639
5,750
10,389
40,000
Baghouse Building
3,078
5,750
8.828
40,000
Table 3-2
8-Hour Average CO Impacts – Martin Marietta Materials
Micrograms per cubic meter
Building
Configuration
AERSCREEN
Concentration
Background
Concentration
Total
Concentration
NAAQS
Lime Silo
6,483
3,450
9,933
10,000
Product Silo
4,175
3,450
7,625
10,000
Baghouse Building
2,770
3,450
6,220
10,000
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
3-2
One can see from the APCD modeling results that the predicted concentration using
AERSCREEN complies with the NAAQS for all building scenarios, although the margin of
compliance is small for the worst-case 8-hour average impacts. However, there is ample
conservatism in the modeling analysis such that there is high confidence that the NAAQS would
not be exceeded. The model conservatisms are detailed below.
First, one can see that the modeling results are strongly dependent on which building
affects the airflow. Predicted AERSCREEN concentrations for the building configurations other
than the lime silo produce much lower concentrations compared to the worst-case result.
Based on ARS’ review of the actual AERSCREEN modeling output files provided by
APCD, the lime silo only affects ambient concentrations when winds are generally in a
north-south direction and there is no building effect on concentrations when winds are in an
east-west orientation. However, the minimum distance to the property line of 87 meters occurs
directly to the west of the baghouse stack, which is a direction where the building effects from
the lime silo would be non-existent. So, the worst-case modeling result reported by APCD
actually occurs for an unrealistic scenario. The AERSCREEN output file indicates that the worstcase flow vector is 300 degrees, and the distance to the property boundary was calculated to be
about 97 meters for that direction. The AERSCREEN modeling results also show that
concentrations decrease rapidly as the downwind distance increases. For the AERSCREEN
results for 300 degrees at 100 meters, the predicted concentration decreases by about 10 percent,
which drops the 8-hour CO level to less than 9,300 micrograms per cubic meter and provides
additional compliance margin, assuming that all other model inputs are unchanged.
Another important conservatism is that APCD’s modeling is based on the higher
short-term emission rate (160 lb/hr) which occurs only when the asphalt plant is fired on LPG.
Under normal operations when the unit is fired on natural gas, the maximum allowable emissions
would be 0.291 lb/ton or 116.4 lb/hr. LPG is a back-up fuel and limited to no more than40,000
tons per year production under the draft permit (which would equal 100 hours per year of
operation at the maximum 400 tph asphalt production rate). If the natural gas CO emissions rate
were applied instead, the modeling result would be more than 25% lower, and the resulting
8-hour CO concentration would be somewhere near 8,160 micrograms per cubic meter, assuming
that all other model inputs are unchanged.
Additional conservatism is introduced by the 0.9 factor used to estimate the 8-hour
concentration. First, the meteorological conditions must be relatively persistent at the worst-case
dispersion condition for the entire 8-hour period for this factor to provide a realistic modeling
result. Second, the asphalt plant must also operate at or near its maximum operating capacity
(400 tons per hour) and use LPG fuel for the entire 8-hour period. Neither condition is likely to
persist for any consecutive 8-hour period, making the APCD modeling results conservative from
that perspective too.
Lastly, as indicated previously, the assumed background concentration (which accounts
for about 1/3rd of the total CO impact for the worst-case condition) is also a conservative
overestimate of the true CO background for the MMM plant site given that the background data
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
3-3
comes from monitoring data at an urban site (downtown Fort Collins) with considerably more
vehicular traffic emissions.
In summary, the CO modeling results presented by APCD demonstrate compliance with
the NAAQS, although compliance is by a small margin for the 8-hour average NAAQS.
However, the APCD modeling analysis contains a number of conservative assumptions, all
which must occur simultaneously with the worst-case dispersion condition for the predicted
impacts to be a realistic depiction of the actual CO impacts. Given that it is unlikely that all of
the conservative model assumptions would occur simultaneously, there is high confidence based
on the APCD modeling that the NAAQS standards will be achieved in the area surrounding the
MMM asphalt batch plant.
3.2
Additional HAP Modeling Analysis
At the request of Larimer County and the City of Fort Collins, ARS conducted an
assessment of the public health impacts associated with the reported hazardous air pollutant
(HAP) emissions from the MMM asphalt plant. This analysis goes beyond the regulatory
analysis conducted by APCD given that HAP concentrations in the ambient air are not
specifically regulated by the State of Colorado.
The HAP modeling analysis was conducted using the modeling results reported for the
APCD modeling analysis of CO emissions. The results for each HAP of interest were determined
using the APCD unit emissions rate modeling by simply multiplying the APCD AERSCREEN
modeling results by the appropriate emissions data for the HAP pollutant of interest. APCD’s
analysis reports emissions for the following HAPs: acetaldehyde, formaldehyde, toluene,
benzene, ethyl benzene, quinone, and hydrochloric acid. Please note that ARS included
acetaldehyde, quinone, and hydrochloric acid in our analysis despite the understanding that
APCD has since determined these emissions were listed in error. Also, the ARS HAP modeling
is based on the corrected toluene emissions data.
The additional HAP modeling was conducted for specific receptors near MMM where
people were known to live and/or congregate. The locations are as follows:
1) Residence located near the Poudre River Trail parking lot, 2) Residence on Stonecrest Drive
(3rd house west from Taft Hill Road, which was determined to be the closest residence along that
street to the MMM asphalt plant emissions stack), and 3) Lincoln Middle School. The UTM
coordinates for each of these locations were determined along with the baghouse stack using
Google Earth and the distance and azimuth of each receptor point relative to the baghouse stack
was calculated using simple geometric relationships. These data are listed below along with the
worst-case AERSCREEN result for that receptor based on the unit emission rate APCD
modeling (1.0 gram per second).
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
3-4
Table 3-3
Location of Public receptors near MMM
Distance
(meters)
Azimuth
(degrees from North)
Worst-Case
AERSCREEN
Model Result
(ug/cubic meter)
Residence near Trailhead
239
160.2
232.9
Stonecrest Drive (3rd House)
632
194.3
146.7
Lincoln Middle School (NW Corner of
school building)
1,130
155.6
13.57
As documented previously, the modeling results considered ambient air quality impacts
under three (3) separate scenarios where the influence of nearby buildings and structures were
considered. However, not every building scenario influences pollutant transport in all directions.
For the purpose of this HAP impact analysis, the model results for a given building scenario
were considered only when transport in the direction of the receptor was impacted by that
particular building. Then, the worst-case AERSCREEN model result at the distance of the
receptor of interest was tabulated and using the remaining AERSCREEN data that result was
scaled by the appropriate emissions rate for the HAP pollutant of interest.
The HAP modeling analysis prepared by ARS considered both acute (short-term) and
chronic (long-term) health effects of the pollutant of interest. For the acute effects analysis, ARS
estimated the maximum 1-hour concentration of each HAP and for the chronic effects analysis,
ARS estimated the maximum annual average concentrations for each HAP. The annual
concentration was scaled from the 1-hour AERSCREEN model prediction using the
EPA-recommended factor of 0.1.
The modeling results were compared to “safe” concentration levels determined for each
HAP pollutant and averaging time. The “safe” concentration level was determined from data
reported by USEPA in the document A Preliminary Risk-Based Screening Approach for Air
Toxics Monitoring Data Sets (October 2010), including any subsequent updates to the data tables
from that report. Where multiple concentration thresholds were listed by USEPA’s Risk-Based
Screening Approach, the most conservative threshold, i.e., lowest concentration, was selected
provided that the concentration threshold was for the appropriate averaging time.
For the acute exposures, the lowest concentration threshold in the USEPA Risk-Based
Screening Approach was generally the California “Reference Exposure Level” (REL), which is
defined as the expected concentration level for the pollutant of interest below which no adverse
health effects are anticipated. Most California RELs are derived for an exposure of one hour and
are available online at http://ww.oehha.ca.gov/air/acute_rels/index.html. For ethylbenzene, the
most stringent threshold listed is from the Acute Exposure Guideline Levels (AEGL) developed
by USEPA’s Office of Prevention, Pesticides, and Toxic Substances. The AEGL-1 is the
published threshold for mild health effects. For quinone, the only listed threshold is based on the
Immediately Dangerous to Life & Health (IDLH) concentrations divided by a safety factor of 10.
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
3-5
The IDLH concentrations were developed by the National Institute for Occupational Safety &
Health (NIOSH).
The acute HAP modeling results are shown below in Table 3-4 for each receptor of
interest.
Table 3-4
MMM HAP Modeling Results – Acute Impacts
Calculated
1-Hour Average HAP Exposure
(micrograms/cubic meter)
Pollutant
Max
Hourly
Emissions
(g/sec)
Acetaldehyde
“Safe”
Concentration
Threshold
(micrograms/cubic
meter)
Receptor:
Residence near
Trailhead:
AERSCREEN
= 232.9 ug/
cubic meter
Receptor:
Stonecrest
Drive (3rd
House):
AERSCREEN
= 146.7 ug/
cubic meter
Receptor:
Lincoln Middle
School:
AERSCREEN
= 13.57 ug/
cubic meter
0.0656
15.3
9.6
0.9
470
Formaldehyde
0.1564
36.4
22.9
2.1
55
Toluene
0.0076
1.8
1.1
0.1
37,000
Benzene
0.0197
4.6
2.9
0.3
1,300
Ethylbenzene
0.0121
2.8
1.8
0.2
140,000
Quinone
0.0081
1.9
1.2
0.1
10,000
Hydrogen
Chloride
0.0101
2.3
1.5
0.1
2,100
For the chronic exposure threshold, a “safe” concentration for HAPs rated as a
carcinogen was determined based on the unit risk factors published by USEPA in the May 21,
2012 update to Table 1 in the Risk-Based Screening Threshold document and assuming an
acceptable excess cancer risk of 1-in-1 million. The potential carcinogens are acetaldehyde,
formaldehyde, benzene, and ethylbenzene. For non-carcinogens, the chronic inhalation threshold
concentration from the USEPA Risk-Based Screening Threshold document was selected. In the
USEPA report, no data are reported for chronic exposures to quinone.
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
3-6
The chronic HAP modeling results are reported in Table 3-5 below.
Table 3-5
MMM HAP Modeling Results – Chronic Impacts
Calculated
Annual Average HAP Exposure
(micrograms/cubic meter)
Pollutant
Max
Hourly
Emissions
(g/sec)
Acetaldehyde*
“Safe”
Concentration
Threshold
(micrograms/cubic
meter)
Receptor:
Residence
near
Trailhead:
AERSCREEN
= 232.9 ug/
cubic meter
Receptor:
Stonecrest
Drive (3rd
House):
AERSCREEN
= 146.7 ug/
cubic meter
Receptor:
Lincoln
Middle
School:
AERSCREEN
= 13.57 ug/
cubic meter
0.0089
0.207
0.130
0.012
2.2
Formaldehyde*
0.0212
0.494
0.311
0.029
13
Toluene
0.0010
0.024
0.015
0.001
5,000
Benzene*
0.0027
0.062
0.039
0.004
7.80
Ethylbenzene*
0.0016
0.038
0.024
0.002
2.50
Quinone
0.0011
0.025
0.016
0.001
n/a
Hydrogen
0.0014
0.032
0.020
0.002
20
Chloride
*Denotes HAP pollutants that are carcinogens. For these pollutants, the “safe” concentration represents
the threshold for a 1-in-1 million excess cancer risk.
Background concentrations for HAPs were not considered in the above modeling
analysis. Generally, background concentrations for HAPs are low compared to the “safe”
concentration levels; as such, the inclusion of a background level does not significantly alter the
modeling results. Background HAP measurements in Fort Collins were derived from a limited
set of samples collected by APCD in July 2006 at a site near the Colorado State University
Foothills Campus (3414 West Laporte Avenue). Table 3-6 summarizes the limited HAP
measurement data from Fort Collins.
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
3-7
Table 3-6
Background HAP Levels – Fort Collins, Colorado
Monitoring Data from Three Samples Collected in July 2006
Samples Collected Near Foothills Campus (3414 West Laporte Ave)
Pollutant
Acetaldehyde
Formaldehyde
Toluene
Benzene
Hexane
As n-hexane
Xylene
As m-xylene/
p-xylene
Ethylbenzene
Sample Concentrations (ppb)
Average
(ppb)
(ug/m3)
2.73
3.55
0.788
0.433
2.41
2.94
0.685
0.395
3.02
4.09
1.01
0.696
2.72
3.53
0.83
0.51
0.276
0.324
0.958
0.52
0.7
0.634
0.725
0.69
2.97
0.226
0.149
0.245
0.21
0.90
MW
4.89
4.32
3.11
1.62
44
30
92
78
1.83
86
106
106
Based on the analysis presented above, the HAP emissions from the MMM Fort Collins
asphalt plant have been determined to present no significant risk to public health at nearby
receptors frequented by members of the general public.
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
3-8
4.0
REASONABLY AVAILABLE CONTROL TECHNOLOGY
Because of the MMM location in Fort Collins, emissions control for selected pollutants
must meet the regulatory definition of “reasonably available control technology” or RACT. The
RACT controls are required for nitrogen oxides (NOX) and volatile organic compounds (VOCs),
which are precursors to ozone formation. Fort Collins lies within the Colorado Front Range
ozone “non-attainment area”, meaning that existing concentrations for ozone do not comply with
the National Ambient Air Quality Standards (NAAQS). RACT is also triggered for CO
emissions at MMM. Fort Collins is a CO “maintenance area”, meaning that Fort Collins was
formerly designated as non-attainment for CO, but is currently in attainment with the NAAQS.
The definition of Reasonably Available Control Technology (RACT) is found in the
Colorado Air Quality Control Commission Common Provisions Regulation:
Technology that will achieve the maximum degree of emission control that a
particular source is capable of meeting and that is reasonably available
considering technological and economic feasibility. It may require technology
that has been applied to similar, but not necessarily identical, source categories.
It is not intended that extensive research and development be conducted before a
given control technology can be applied to the source. This does not preclude
requiring a short-term evaluation program to permit the application of a given
technology to a particular type of source.
This report section contains additional information about the proposed MMM controls
and considers whether the proposed emission controls listed in the permit constitute RACT. The
ARS report covers only VOC and CO emissions. NOX emissions were not reviewed because
these emissions are already low (NOX emitted at the MMM asphalt plant only totals 6.5 tons per
year) and as such there would be little perceived environmental benefit associated with improved
NOX emission controls.
4.1
RACT for VOC Emissions
As mentioned previously, MMM has implemented certain voluntary measures aimed at
curbing VOC and HAP emissions which have not been explicitly required in the draft air quality
permit. These measures are:


Collecting exhaust air from the asphalt product conveyer and recycling this air to
the asphalt plant burner for destruction of any associated VOCs and/or HAPs.
Installation of vapor condensers on the liquid asphalt tanks.
Figure 4-1 shows a picture of the recycle air collection point on the MMM asphalt
product conveyor.
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
4-1
Figure 4-1. Image of Recycle Air Collection Point at MMM Asphalt Plant
Because the above controls have been voluntarily implemented by MMM, it is reasonable
to conclude that these measures are reasonably available considering technological and
economic feasibility, which is the legal definition of RACT under Colorado’s air quality
regulations. The MMM draft air quality permit should be revised to legally require the
installation and operation of MMM’s voluntary VOC/HAP pollution control measures as RACT.
4.2
RACT for CO Emissions
The draft MMM air permit has established CO emission limits equal to 0.291 lb/ton when
the asphalt plant is fired on natural gas and 0.40 lb/ton when the asphalt plant is fired on back-up
LPG fuel. As noted above, the AP-42 CO factor for natural gas-fired drum mix asphalt plants is
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
4-2
0.13 lb/ton. APCD staff stated to ARS that they believe that the CO AP-42 emissions are not
technically achievable and as such, the proposed CO emissions (0.291 lb/ton and 0.40 lb/ton) are
RACT because additional emission controls are not cost-effective. However, the MMM permit
and APCD’s supporting technical information provided to the public do not provide any
substantive support for this RACT claim. Based on the permit record, there is no evidence that
APCD in fact evaluated the technical feasibility and cost of any alternative emission controls for
the CO RACT analysis.
The fact that AP-42 data present significantly lower CO emissions (0.13 lb/ton) suggests
that better CO control is indeed technically achievable and likely has been achieved in practice at
other asphalt plants. Given this finding, a technical and economic review of improved CO
controls should have been performed for the MMM draft permit. Without such an analysis, the
CO RACT analysis is deficient.
At the request of the AQAB and ESAB, ARS conducted a review of other asphalt plant
permits to determine if lower CO emissions are in fact technically achievable. ARS conducted a
query using the USEPA RACT/BACT/LAER Clearinghouse (RBLC) that turned up emissions
data for two asphalt plants located in Clark County, Nevada (Las Vegas). These data are
summarized in Table 4-1. It should be noted that both asphalt plants listed in the RBLC were
subject to “best available control technology” (BACT) as the applicable emissions standard and
not RACT. However, the selection of lower CO emissions to meet BACT requirements
documents the technical feasibility of improved CO emissions control and as such, mandates that
such controls be considered as RACT.
Table 4-1
RBLC Query Results: Asphalt Concrete Manufacturing
Source ID
Nellis Air Force Base
Aggregate Industries – Sloan Quarry
RBLC ID
NV-0047
NV-0045
CO Permit Limit (BACT)
0.13 lb/ton, 16.25 lb/hr
0.10 lb/ton, 45.0 lb/hr
ARS also located four recent USEPA permits for asphalt plants located on tribal lands in
the western United States. These permits are:




Pioneer Asphalt, Inc. – Permit R10NT502400 (Draft)
Granite Construction Company – Permit R10NT502300 (9/19/2012)
Knife River, Inc. – Permit R10NT502200 (9/19/2012)
Mickelsen Construction, Inc. – Permit R10NT502501 (Draft)
For all of the USEPA permits listed above, the CO emissions control was not subject to
RACT, BACT, or any other emissions standard. Nevertheless, all permits were issued based on
CO emissions at 0.13 lb/ton, which equals the AP-42 emissions value for a natural gas-fired
drum mix asphalt plant. However, none of the USEPA permits appear to have required emissions
testing for CO, so it is unknown if the 0.13 lb/ton emissions level was actually achieved in
practice at any of these facilities.
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
4-3
In summary, for those cases where asphalt plant emissions control data are posted in the
RBLC and in other asphalt plant permits issued by USEPA Region X, the CO emissions are
significantly lower than the RACT limit established by APCD in the MMM draft permit. The
APCD RACT analysis is deficient without a detailed evaluation of CO emission control options
that might lead to better emissions control and lower allowable CO emissions under the permit.
A review of asphalt plant permits issued elsewhere would suggest that improved CO controls are
technically achievable, so control options to achieve improved CO controls should have been
evaluated by APCD for application as RACT. There is no evidence in the MMM permit record
that such an analysis was conducted.
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
4-4
5.0
TECHNICAL COMMENTS ON DRAFT PERMIT
This section summarizes possible comments that might be offered by Larimer County
and/or the City of Fort Collins with respect to the proposed Martin Marietta Materials asphalt
plant permit.
HAP Emissions: It appears that the draft permit used the AP-42 toluene factor for drum mix
asphalt plants fired on #2 fuel oil. The AP-42 factors for natural gas drum mix asphalt plants
were used to calculate HAP emissions for other pollutants. This appears to be an oversight and
should be corrected. There are also other HAPs listed in the AP-42 data (AP-42, Table 11.1-10)
that have emissions comparable to the HAPs where emissions were calculated. These HAPs are
hexane (0.00092 lb/ton), xylene (0.00020 lb/ton), and PAHs (0.00019 lb/ton). It is unknown why
these HAPs were not considered by APCD given that the emissions are comparable to other
HAPs where emissions were tabulated.
General Comment: In assessing the asphalt plant, the APCD appears to have considered only the
emissions directly related to the asphalt plant in its analysis. However, MMM owns and operates
other air emission sources in the immediate vicinity of the asphalt plant, including an aggregate
materials mining and processing operation on the west side of Taft Hill Road immediately to the
west of the asphalt plant. Under the Clean Air Act, a “source” is defined as “Any building,
structure, facility, equipment, or installation, or any combination thereof belonging to the same
industrial grouping that emit or may emit any air pollutant subject to regulation under the
Federal Act that is located on one or more contiguous or adjacent properties and that is owned
or operated by the same person or by persons under common control.” MMM’s other aggregate
processing activities located across Taft Hill Road are located on “contiguous or adjacent
properties” and should therefore be considered in the assessment of the overall facility emissions.
ARS’ understanding is that all of the aggregate used in the asphalt plant comes directly from
MMM operations on the west side of Taft Hill Road, so the adjoining operations are “support
facilities” and as such, it cannot be claimed that the asphalt plant is part of a separate source
based on the differences in Standard Industrial Classification (SIC) code. It is probably unlikely
that the added emissions from adjoining MMM operations will alter the minor/major source
classification of the asphalt plant, but a complete and accurate analysis requires that these
emissions also be considered when determining the total emissions of the “source”.
Condition 3, Operating & Maintenance Plan: This permit condition requires that MMM submit
an Operating & Maintenance (O&M) Plan for APCD approval. The plan describes the ongoing
monitoring and recordkeeping activities that MMM will undertake to document compliance with
the terms and conditions of its permit. In essence, any commitments for compliance monitoring
and recordkeeping made by MMM in the O&M Plan will become enforceable requirements of
the permit. While the O&M Plan is not normally subject to review and comment by the public,
due to the sensitivity of emissions to the nearby public in this case, an opportunity for public
input on the O&M Plan could be requested to ensure that the approved O&M Plan provides the
necessary compliance monitoring and recordkeeping to assure permit compliance.
Condition 7, Emissions Control Equipment: This condition lists the pollution control equipment
that MMM must employ to abate pollutant emissions to the atmosphere. However, MMM has
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
5-1
voluntarily installed additional equipment to mitigate volatile organic compound (VOC) and
associated hazardous air pollutant (HAP) emissions, including recycling exhaust air from the
asphalt plant outlet conveyor back to the asphalt plant burner along with installing condensers on
the liquid asphalt storage tanks. These voluntary measures adopted by MMM to abate emissions
should be made enforceable legal requirements through the APCD’s air permit. This will assure
that such emissions abatement practices continue going forward. Please also refer to comments
on Condition #10 (Odors) and Condition #13 (RACT).
Condition 10, Odor Control: This is a general requirement referencing Regulation #2 concerning
control and abatement of odors. Given that the MMM asphalt plant has in the past been the
subject of odor complaints, additional requirements for abatement of odors should be considered
for the air quality permit. The voluntary controls that MMM has applied at the asphalt plant
(See Condition 7 above) could be made enforceable requirement on the basis that such controls
are needed to assure compliance with Condition 10 and the associated odor requirements under
Regulation #2.
Condition 13, Reasonably Available Control Technology (RACT) – VOC Emissions: The
Fort Collins region lies within the designated non-attainment area for ozone, and new/modified
emissions of ozone precursors (including VOCs) within the non-attainment area are required
under Regulation #3, Part B, III.E to install reasonably available control technology (RACT) for
emissions control. The APCD has determined that “no additional control” meets RACT.
However, MMM has voluntarily installed additional control for VOC emissions, including
recirculating exhaust air from the asphalt plant product conveyor to the asphalt plant burner and
installing condenser equipment on the liquid asphalt tanks. The mere presence of such equipment
at the MMM Taft Hill Road facility demonstrates the technical feasibility and economic viability
of such emissions controls and therefore mandate that such controls be deemed RACT. As
described under Condition #7, the voluntary VOC emission controls implemented by MMM
should be classified as RACT and required under Permit Condition 13.
Condition 13, Reasonably Available Control Technology (RACT) – CO Emissions: The
Fort Collins region lies within the designated attainment-maintenance area for carbon monoxide
(CO), and new/modified CO emission sources within this area are required under Regulation #3,
Part B, III.E to install reasonably available control technology (RACT) to control emissions. The
APCD has determined that “no additional control” meets RACT. However, it is noted that AP-42
listed emissions for CO at natural gas-fired of 0.13 lb/ton, which is less than 50% of the
0.291 lb/ton limit established at Condition 16 of the draft permit. Permits issued in other
jurisdictions have also set CO permit limits at the AP-42 emissions value (0.13 lb/ton) or lower.
There is no discussion in the permit record as to why lower CO emissions cannot be achieved by
MMM, although APCD has claimed in separate communications with ARS staff that the AP-42
CO emission levels are not achievable. Absent any evidence to the contrary, it would be prudent
for APCD to find that CO emissions at the listed AP-42 value for natural gas-fired drum mix hot
asphalt plants (0.13 lb/ton) represents RACT. Such a limit should be considered for this permit
or APCD should provide the technical basis for its decision and these data should be made
available for review by the public and other interested parties. This comment also affects the
allowable emissions limit for CO contained in Permit Condition 16.
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
5-2
Condition 14 – O&M Plan: Condition 14 duplicates Condition 3. There is no need to repeat the
O&M Plan requirements in the permit.
Condition 15 – Opacity Testing: This permit condition requires opacity testing to show
compliance with the underlying permit requirements. Since the asphalt plant is approved to
operate on both natural gas and LPG as fuel, the opacity testing should be completed for the
plant on both approved fuels.
Condition 16 – Emissions Testing: This permit condition requires emissions testing to show
compliance with the specified limits for emissions of particulate matter (PM), carbon monoxide
(CO), and oxides of nitrogen (NOx). Since the asphalt plant is approved to operate on both
natural gas and LPG as fuel, the emissions testing should be completed for the plant on both
approved fuels. Also, for clarity, the permit should specify whether or not the particulate testing
is required to include condensable particulate matter (CPM). The hot exhaust from the baghouse
emissions stack suggest that CPM emissions may be present, so the CPM fraction of the PM
emissions needs to be regulated even if not otherwise included in the proposed permit limits.
Condition 16 – Emissions Testing – HAPs: The draft permit as written does not require any
testing for emissions of regulated hazardous air pollutants (HAPs). Generally, without any
authority for regulating HAPs at sources within Colorado, emissions are not tested as there is no
enforceable emissions limit and/or standard for comparison of the testing results. However, HAP
testing could be requested, especially for those HAPs which are known to be carcinogenic
(acetaldehyde, formaldehyde, benzene, etc.). This would provide more reliable data from which
to make a reliable assessment of the possible impact of these emissions on public health.
Condition 21 – Change in Location: It is presumed that the intent of this condition restricts
relocating the asphalt plant within the MMM property. If so, the condition should be clarified
given that a typical hot asphalt plant is known to change locations on a regular basis.
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
5-3
6.0
SUMMARY & CONCLUSIONS
The major findings of the ARS technical review are summarized below.

The emissions data used for the MMM permit are generally supported by AP-42 and other
appropriate data. However, the CO emissions used by APCD are higher than the
corresponding AP-42 data. APCD claims that historical emissions data do not support the
lower emissions reported by AP-42; however, this claim has not been substantiated by
APCD. Because Fort Collins is a designated maintenance area, CO emissions are required to
meet RACT. AP-42 data along with permits issued to asphalt plants in other jurisdictions
suggest that lower CO emissions are in fact achievable and would represent RACT. APCD
should require lower CO emissions or better document why the selected CO emissions level
is in fact RACT.

MMM has voluntarily adopted emission controls for reduction of VOC and HAP emissions;
specifically, recycling exhaust air from the product conveyor to the asphalt plant burner and
capturing emissions at the liquid asphalt tanks using condensers. The adoption of these
control measures by MMM in fact means that such controls are both technically achievable
and economically viable. Any voluntary controls adopted by MMM would meet the criteria
for RACT and should be legally required under the air quality permit.

The MMM draft permit used the AP-42 toluene emissions factor for drum mix asphalt plants
fired on #2 fuel oil. The AP-42 factors for natural gas drum mix asphalt plants were used to
calculate HAP emissions for other pollutants. This appears to be an oversight by APCD and
should be corrected. Also, other HAPs listed in the AP-42 data (AP-42, Table 11.1-10) where
emissions are comparable to the HAPs calculated by APCD. These HAPs are hexane, xylene,
and PAHs. It is unknown why these HAPs were not considered by APCD given that the
emissions are comparable to other HAPs where emissions were tabulated. APCD’s permit
analysis should be amended to address hexane, xylene, and PAH emissions in addition to the
other HAPs.

In assessing the asphalt plant, the APCD appears to have considered only those emissions
directly related to the asphalt plant. However, MMM owns and operates other air emission
sources in the immediate vicinity of the asphalt plant, including an aggregate materials
mining and processing operation on the west side of Taft Hill Road. MMM’s other aggregate
processing activities are located on “contiguous or adjacent properties” and should therefore
be considered in the assessment of the overall facility emissions. It is unlikely that the added
emissions from adjoining MMM operations will alter the minor/major source classification
of the asphalt plant, but a complete and accurate analysis by APCD requires that these
emissions also be considered when determining the total emissions of the “source”.
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
6-1

The AERSCREEN modeling for MMM’s CO emissions has been conducted following
standard regulatory practices and principles. This modeling also employed several significant
conservative assumptions. Although the modeling showed that MMM’s emissions comply
with the NAAQS by a small margin, the conservatisms inherent in the modeling study means
that MMM’s operations will comply with the NAAQS, very likely with a substantial safety
margin.

ARS used APCD’s AERMOD modeling results to make an assessment of potential HAP
impacts on public health and the environment. The HAP modeling results from MMM were
compared to “safe” concentration levels determined using USEPA’s Risk-Based Screening
Approach. ARS’ modeling assessment determined that HAP emissions from MMM’s asphalt
plant operations would not cause ambient concentrations above the “safe” concentration
levels determined from USEPA data.

Recommendations have been provided for consideration by the ESAB and AQAB on formal
comments on the draft MMM air quality permit. This includes making any voluntary
pollution control practices adopted by MMM enforceable requirements under the permit.
These recommendations are intended to make the final permit more protective of public
health and the environment.
Martin Marietta Materials Air Permit Review – Technical Report
Prepared by D. Howard Gebhart
Air Resource Specialists, Inc.
6-2