Technical Support Document (TSD) 

For the Modeling Portions of the Document Entitled "Lower Beaver Valley Area Nonattainment Area for 

the 2008 Lead National Ambient Air Quality Standard", dated January 2015 

TSD Prepared June 2015 

Timothy A. Leon Guerrero 

Office of Air Monitoring and Analysis, 3AP40 

U.S. Environmental Protection Agency, Region 3 

1650 Arch Street 

Philadelphia, Pennsylvania 19103 

Reviewed by Alice Chow, Associate Director, 

Office of Air Monitoring and Analysis (3AP40) 

Date Signed 
Technical Support Document for the Modeling Portion Of the Commonwealth of Pennsylvania’s 

Lead State Implementation Plan (SIP) entitled Lower Beaver Valley Area Nonattainment Area for 

the 2008 Lead National Ambient Air Quality Standard dated January 2015

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Purpose of the Technical Support Document

This Technical Support Document (TSD) describes the Environmental Protection Agency’s 

(EPA’s) evaluation of the air dispersion modeling for the Lower Beaver Valley lead 

nonattainment area. The purpose of this TSD is to provide more detailed information than can 

be contained in the official notice published in the Federal Register. Readers who need more 

information than we provide in this TSD or want to review the modeling in more detail are 

encouraged to review the final State Implementation Plan (SIP) submitted by the Commonwealth 

of Pennsylvania1.

Introduction and Regulatory Framework

On October 15, 2008, the U.S. Environmental Protection Agency (EPA) promulgated a revised 

health-based primary and secondary National Ambient Air Quality Standards (NAAQS) for lead. 

The 2008 primary lead NAAQS, which is set at a level to protect public health from adverse 

effects, is 0.15 micrograms per cubic meter (μg/m3). The secondary standard, which is set at a 

level requisite to protect the public welfare from adverse effects, is identical to the primary 

standard.

In November of 2010, the US EPA designated three (3) areas in Pennsylvania as lead 

nonattainment areas based on 2007-09 air quality monitoring data. Vanport and Potter townships 

in Beaver County, PA were designated as the Lower Beaver Valley Nonattainment Area. In 

January of 2010, the Pennsylvania Department of Environmental Protection (PA DEP) 

commenced operation of a new source-oriented lead monitor referred to as the Beaver Valley 

monitor (AQS 42-007-0007) in Center Township, Beaver County, PA. This new monitor was

associated with the Horsehead Monaca Smelter facility in accordance with the network design 

requirements for the 2008 lead NAAQS. In 2011 the US EPA revised the lead NAAQS 

nonattainment area based on the 2008-2010 monitoring data by adding Center Township to the 

nonattainment area. Therefore, effective December 31, 2011, the Lower Beaver Valley 

nonattainment area was comprised of Vanport, Potter and Center townships all located in Beaver 

County, PA. Figure 1 displays the Lower Beaver Valley, PA nonattainment area along with the 

lead monitor sites.

 

1 http://www.elibrary.dep.state.pa.us/dsweb/View/Collection-12349
Technical Support Document for the Modeling Portion Of the Commonwealth of Pennsylvania’s 

Lead State Implementation Plan (SIP) entitled Lower Beaver Valley Area Nonattainment Area for 

the 2008 Lead National Ambient Air Quality Standard dated January 2015

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Figure 1. The municipal units and lead monitoring sites that are part of the Lower Beaver 

Valley, PA lead nonattainment area

Lead SIP regulations found at 40 CFR 51.117 require states to employ atmospheric dispersion 

modeling for the demonstration of attainment for areas in the vicinity of point sources listed in 

40 CFR 51.117(a)(1). Meteorological and other data are needed to complete the required air 

dispersion modeling. EPA notes that 40 CFR 51.117(a) provides that states must include, as a 

part of their attainment modeling demonstration, an analysis showing that the SIP will attain and 

maintain the standard in areas in the vicinity of certain point sources that are emitting significant 

emissions of lead and also in ‘‘any other area that has lead air concentrations in excess of the 

national ambient air quality standard concentration.” In doing the analysis, required under 40 

CFR 51.117(a)(2), EPA expects the state will take into consideration all sources of lead 

emissions within the nonattainment area that may be required to be controlled.
Technical Support Document for the Modeling Portion Of the Commonwealth of Pennsylvania’s 

Lead State Implementation Plan (SIP) entitled Lower Beaver Valley Area Nonattainment Area for 

the 2008 Lead National Ambient Air Quality Standard dated January 2015

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Overview of Commonwealth of Pennsylvania’s General Modeling Approach

PA DEP examined data from a meteorological monitoring tower located near the Bruce 

Mansfield Power Station to determine rough transport winds in the Lower Beaver Valley 

nonattainment area. This meteorological tower is operated by the Beaver Valley Nuclear Power 

Station near Shippingport, PA. The analysis showed predominantly west-southwesterly winds, 

which are mainly in response to the Ohio River Valley’s terrain orientation. This wind pattern 

was generally maintained when looking at winds on the days when the Vanport monitor 

exceeded the lead NAAQS though wind speeds were generally lower during these times. PA 

DEP attributed the lower wind speeds to more stable atmospheric conditions during periods of 

high monitored lead concentrations. Stronger vertical temperature inversions and light wind 

speeds probably contributed to high ambient lead levels in the Lower Beaver Valley 

nonattainment area.

To conduct the modeling attainment demonstration, PA DEP had to compile a lead emission 

inventory for significant sources near the noncompliant air monitoring sites. During 

promulgation of the 2008 standard, US EPA revised the requirements in 40 CFR 51.117(e) for 

lead nonattainment area SIP inventories from a 5 tons per year (tpy) threshold associated with 

the previous standard to a 0.5 tpy threshold. This was the threshold used to identify major lead 

sources in the vicinity of the Lower Beaver Valley nonattainment area.

PA DEP identified two (2) facilities whose lead emissions exceeded 0.5 tpy. These were the 

Horsehead Monaca Smelter (Horsehead) and the Bruce Mansfield Power Station (Bruce 

Mansfield). Air-dispersion modeling done in 2009 for Bruce Mansfield showed the facility had 

no impact on the Lower Beaver Valley nonattainment area thus it was excluded from further 

analysis. AES Beaver Valley, a coal-fired power plant in the lead nonattainment area, was 

included as another point source in the lead emission inventory though its lead emissions were 

less than 0.5 tpy. Lead emissions from nonpoint sources and mobile sources were also examined

but found to be insignificant and while included in PA DEP’s lead inventory they were not 

included in the lead modeling demonstration. Section 211(n) of the Clean Air Act prohibited the 

use of any gasoline containing lead or lead additives for use as fuel in motor vehicles after 

December 31, 1995 (42 U.S.C.A. §7545) making mobile source lead emissions much smaller 

than the point source contribution. Leaded fuels are still used for some aviation purposes. No 

airports were located in or near the Lower Beaver Valley nonattainment area so no lead 

emissions from the aviation sector were included in the modeling analysis. Horsehead and AES 

Beaver Valley were therefore the only lead sources included in the final model emission 

inventory.
Technical Support Document for the Modeling Portion Of the Commonwealth of Pennsylvania’s 

Lead State Implementation Plan (SIP) entitled Lower Beaver Valley Area Nonattainment Area for 

the 2008 Lead National Ambient Air Quality Standard dated January 2015

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Lead model emission inventories for the two point sources in the Lower Beaver Valley were 

constructed for 2010 and 2015. The 2015 lead emissions were used in the model attainment 

demonstration to determine if projected (future) emission rates would comply with the lead 

NAAQS. Emissions for 2010 were broken down into actual lead emissions and maximum 

allowable emission rates. Maximum allowable emission rates were used in the model attainment 

demonstration. Table 1 summarizes lead emissions compiled by PA DEP. Horsehead’s 2010 

emissions include point and fugitive sources while only point source emissions were calculated 

for AES Beaver Valley. Roughly 95% of Horsehead’s 2010 lead emissions came from point 

sources with the balance made up of fugitives, mainly from material handling activities. AES 

Beaver Valley used maximum throughput numbers and AP-42 emission factors to calculate its 

maximum allowable lead emission rate. This emission rate was used for AES Beaver Valley for 

both 2010 and 2015 model inventories.

Table 1. Lower Beaver Valley Lead Point Source Emissions Summary 

Lead Source 2010 Lead Emissions 2015 Projected Lead 

Emissions

Actual (tpy) Max Allowable (tpy) Max Allowable (tpy)

Horsehead 5.5531 12.128 0.1

AES Beaver Valley 1.367 1.367

Horsehead’s 2015 projected (future) lead emissions were substantially reduced through a consent 

order and agreement (COA) executed between PA DEP and Horsehead on November 21, 2012.

This COA stated that Horsehead would permanently discontinue production of zinc metal from 

its Potter Township Furnace Plant, Sinter Plant, and Secondary Materials Operations on or 

before October 1, 2014. Horsehead would then be subject to an aggregate potential lead 

emission rate of 0.1 tpy over each consecutive 12-month rolling period from all of its remaining 

stationary sources.

Dispersion Modeling for the Model Attainment Demonstration

PA DEP performed an air-dispersion modeling analysis for the Lower Beaver Valley 

nonattainment area. The air-dispersion modeling analysis was completed for base year and future 

year emission inventories representing two (2) facilities, Horsehead and AES Beaver Valley, 

with reported lead emissions in 2010 and projected (future) emissions for 2015. The modeling 

was conducted in accordance with 40 CFR Part 51, Appendix W – Guideline on Air Quality 

Models.
Technical Support Document for the Modeling Portion Of the Commonwealth of Pennsylvania’s 

Lead State Implementation Plan (SIP) entitled Lower Beaver Valley Area Nonattainment Area for 

the 2008 Lead National Ambient Air Quality Standard dated January 2015

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The American Meteorological Society/Environmental Protection Agency Regulatory Model 

(AERMOD) was utilized for the model attainment demonstration. There are two (2) input data 

preprocessors that need to be run to utilize the AERMOD modeling system; AERMET, which 

preprocesses representative meteorological data and AERMAP, which preprocesses terrain data 

from the United States Geological Survey (USGS) Digital Elevation Data. In order to diagnose 

building downwash effects, the Building Profile Input Program for Plume Rise Model 

Enhancements (BPIPPRM) was executed. Since the current regulatory version of AERMOD is 

incapable of calculating the rolling three-month average concentrations necessary for 

demonstrating lead NAAQS compliance, the EPA post-processor LEADPOST was used. In its 

three-month average calculation, LEADPOST utilizes monthly average files created by 

AERMOD.

A summary of the model versions used in PA DEP’s model attainment demonstration is 

presented in Table 2. Generally, the most recent versions of the AERMOD and its related 

preprocessors were used in the air-dispersion modeling analysis.

Table 2. Summary of AERMOD Used in PA DEP’s Modeling Analysis

Model Version Description

AERMOD 14134 Regulatory Air Dispersion Model

BPIPPRM 04274 Building Downwash Calculations for AERMOD

AERMET 14134 AERMOD Meteorological Data Preprocessor

AERSURFACE 13016 Preprocessor for AERMETusing1992 Land Use/Land Cover

AERMAP 11103 Terrain Processor, Preprocessor for AERMOD

Lead Post 13262 Post Processor for AERMOD, Lead NAAQS Calculator

Air-Dispersion Model Meteorological Data Development

The Lower Beaver Valley modeling analysis utilized a 5-year (2006-2010) surface 

meteorological dataset from the Beaver Valley Nuclear Power Station (BVNPS) along with a 

concurrent 5-year (2006-2010) surface meteorological dataset from the Automated Surface 

Observing System (ASOS) at the Pittsburgh International Airport (KPIT). BVNPS is located 

approximately 9 kilometers southwest of the Horsehead facility and KPIT is located 

approximately 23 kilometers south of the Horsehead facility. The analysis also utilizes morning 

upper-air soundings from KPIT. Both meteorological data sets were reviewed for completeness 

and representativeness of the Lower Beaver Valley nonattainment area. The meteorological data 
Technical Support Document for the Modeling Portion Of the Commonwealth of Pennsylvania’s 

Lead State Implementation Plan (SIP) entitled Lower Beaver Valley Area Nonattainment Area for 

the 2008 Lead National Ambient Air Quality Standard dated January 2015

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sets were found to meet the completeness requirements outlined in section 5.3.2 of EPA’s 

Meteorological Monitoring Guidance for Regulatory Modeling Applications (EPA-454/R-99-

005, February 2000) and are representative of atmospheric conditions in the vicinity of 

Horsehead and the Lower Beaver Valley nonattainment area.

Surface meteorological data from the BVNPS included wind and temperature measurements 

from multiple heights (10.7 meters, 45.7 meters and 152.4 meters). Additionally, measurements 

of standard deviation of the horizontal wind direction and vertical temperature differences were 

used. ASOS winds, temperatures, surface pressure and sky cover were processed using 

AERMET as well as morning soundings from KPIT. The meteorological data was process in 

AERMET such that the ASOS wind data was not substituted for any missing BVNPS wind data.

In addition to the meteorological data, AERMET needs surface characteristic information 

including surface roughness, albedo and Bowen Ratio. This information was constructed using 

AERSURFACE (version 13016) which extracts this information from the USGS National Land 

Cover Database (NLCD, 1992). AERSURFACE was run at a seasonal resolution using a default 

1-kilometer radius with twelve 30-degree sectors for surface roughness length. Surface moisture 

conditions were used in the Bowen Ratio calculation and were based on averaged precipitation 

data for Pennsylvania Climate Division 9. Specific seasonal surface moisture conditions were

derived from precipitation data and comparing it to a 30-year climatological average to 

determine if a particular season was considered dry, average or wet. Snow cover information 

was also examined to ensure there was no continuous snow cover occurring on a seasonal basis.

Air-Dispersion Model Receptor Grid Development:

PA DEP developed ground-level model receptors for areas defined as “ambient air” in 

accordance with 40 CFR §50.1(e). These model receptor points, once defined, are used by 

AERMOD to calculate air concentrations from lead emission sources. Facilities that have 

sufficient limitations on public access to their sites, a fence or other suitable physical barrier, do 

not have to establish model receptor points within their property boundary. Horsehead has 

sufficient restrictions to public access and therefore model receptors were not placed within these 

restricted areas except for a portion of I-376 that crosses over the eastern section of Horsehead’s 

property (where public access would occur). AES Beaver Valley did not have sufficient public 

access limitations so model receptors were placed within this facility’s property line in 

accordance with EPA’s June 22, 2007 memorandum entitled “Interpretation of ‘Ambient Air’ In 

Situations Involving Leased Land Under the Regulations for Prevention of Significant 

Deterioration (PSD)”.
Technical Support Document for the Modeling Portion Of the Commonwealth of Pennsylvania’s 

Lead State Implementation Plan (SIP) entitled Lower Beaver Valley Area Nonattainment Area for 

the 2008 Lead National Ambient Air Quality Standard dated January 2015

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PA DEP limited its model receptor grid to the three (3) townships that make up the Lower 

Beaver Valley nonattainment area. This configuration appears to be sufficient to allow the 

dispersion model (AERMOD) to calculate the maximum projected (future) modeled 

concentration, which occur within 50 meters of Horsehead’s southern ambient-air boundary.

A Cartesian grid, centered on Horsehead, was used in the development of the model receptor 

grid. Model receptor points were placed along Horsehead’s ambient-air boundary (and a section 

of I-376) at a 25 meter spacing. A fine Cartesian 50-meter spaced grid extended from 

Horsehead’s ambient-air boundary out to 2 kilometers. Grid spacing increased to every 100 

meters from 2 to 5 kilometers from Horsehead’s ambient air boundary and then every 500 meters 

for areas beyond 5 kilometers that were still within the Lower Beaver Valley nonattainment area. 

The model receptor grid (see Figure 2) contains nearly 7,000 grid points.

Once the model receptor grid was established, it was run through AERMAP to determine each 

receptor’s elevation and terrain height scale, a parameter needed by AERMOD. These values 

were calculated from terrain data generally provided and maintained by the U.S. Geological 

Survey or USGS. PA DEP utilized the USGS National Elevation Dataset (NED) with a 

resolution of one-third arc-second (approximately 10 meters). 
Technical Support Document for the Modeling Portion Of the Commonwealth of Pennsylvania’s 

Lead State Implementation Plan (SIP) entitled Lower Beaver Valley Area Nonattainment Area for 

the 2008 Lead National Ambient Air Quality Standard dated January 2015

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Figure 2. AERMOD Model Receptor Grid for the Lower Beaver Valley, PA Lead 

Nonattainment Area

Lead Emission Rates and Building Downwash Development

Projected lead emissions from the Horsehead facility were based on the November 21, 2012

COA, which contains a plant-wide lead emission limit of 0.1 tpy. As stated previously, 

Horsehead agreed to permanently discontinue production of zinc metal from its Furnace Plant, 

Sinter Plant, and Secondary Materials Operations on or before October 1, 2014. These 

operations appeared to have shut down in the second quarter of 2014. Lead emissions from AES 

Beaver Valley were based on AP-42 factors and maximum throughput information.

A total of eight (8) point sources were modeled for the projected (future) case; four (4) from 

Horsehead and four (4) from AES Beaver Valley. Since material handling operations at 
Technical Support Document for the Modeling Portion Of the Commonwealth of Pennsylvania’s 

Lead State Implementation Plan (SIP) entitled Lower Beaver Valley Area Nonattainment Area for 

the 2008 Lead National Ambient Air Quality Standard dated January 2015

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Horsehead have ceased, no fugitive lead emissions were carried forward into the projected 

(future) modeling case.

Projected building and stack configurations at Horsehead and AES Beaver Valley were run 

through EPA’s BPIP program to determine building downwash parameters to be used in 

AERMOD. BPIP requires building locations and heights as well as stack height information to 

determine building downwash parameters. Downwash output from BPIP is then used as input 

into AERMOD.

AERMOD Results Summary

Two pieces of information are needed to determine if a nonattainment area will meet the lead 

NAAQS. These include a modeled lead concentration from an air dispersion model like 

AERMOD and a representative background lead concentration. A dispersion model like 

AERMOD will estimate the ambient lead concentrations based on hourly lead emissions that are 

included as model inputs. The purpose of a representative background lead concentration is to 

account for minor ancillary sources that may not be explicitly modeled.

PA DEP reviewed monitoring data from the Shippingport monitor in Potter Township to 

determine the maximum 3-month lead concentration to be used as a background concentration in 

the model attainment demonstration. It found the maximum 3-month lead concentration at 

Shippingport between 2010 and 2013 was 0.08 μg/m3. After reviewing the data, PA DEP 

determined that there were times during this 3-month period where emissions from Horsehead 

significantly impacted the monitor’s lead concentration. The maximum concentration was then 

re-averaged to exclude these periods when Horsehead was impacting the monitor to remove the 

possibility of “double counting” since Horsehead emissions would be included in both the 

background concentration and the modeled concentration. The final adjusted background lead 

concentration was 0.05 μg/m3.

AERMOD does not directly calculate 3-month lead concentrations in the form of the lead 

NAAQS. LEADPOST must be run using specific output files generated by AERMOD to 

calculate a modeled 3-month lead concentration. LEADPOST takes AERMOD output files and 

calculates a rolling 3-month average lead concentration. This modeled concentration is then 

added to the background concentration and compared with the lead NAAQS to determine 

compliance.
Technical Support Document for the Modeling Portion Of the Commonwealth of Pennsylvania’s 

Lead State Implementation Plan (SIP) entitled Lower Beaver Valley Area Nonattainment Area for 

the 2008 Lead National Ambient Air Quality Standard dated January 2015

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The highest projected 3-month modeled lead concentration from LEADPOST was 0.0274 μg/m3. 

Projected (future) modeled 3-month maximum lead concentrations are shown in Figure 3. 

Again, this was based on the remaining projected lead sources and emission rates at Horsehead 

after its COA took effect along with lead emission rates from AES Beaver Valley. The final 

modeled lead concentration is the maximum projected 3-month lead concentration from 

LEADPOST plus the background monitored concentration from the Shippingport monitor. This 

yields a projected lead concentration of 0.0274 μg/m3plus 0.05 μg/m3, or ~0.08 μg/m3, which is

significantly lower than the lead NAAQS of 0.15 μg/m3. This indicates that projected lead 

concentrations based on current operations at Horsehead and AES Beaver Valley (plus a 

representative background concentration) will meet the 2008 lead NAAQS.

Figure 3. Projected (future) maximum 3-month lead concentrations from PA DEP’s

AERMOD analysis. The peak receptor is highlighted and is located within 50 meters of 

Horsehead’s southern ambient air boundary.
Technical Support Document for the Modeling Portion Of the Commonwealth of Pennsylvania’s 

Lead State Implementation Plan (SIP) entitled Lower Beaver Valley Area Nonattainment Area for 

the 2008 Lead National Ambient Air Quality Standard dated January 2015

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Summary of EPA’s Technical Findings

EPA has reviewed PA DEP’s modeling analysis for the Lower Beaver Valley lead nonattainment 

area. PA DEP conducted air dispersion modeling using EPA’s AERMOD modeling system. In

general, PA DEP followed procedures outlined in 40 CFR Part 51, Appendix W – Guideline on 

Air Quality Models. Meteorological data met data completeness requirements, was 

representative of atmospheric conditions in the Lower Beaver Valley nonattainment area and was 

properly processed using AERMOD’s preprocessors AERMET and AERSURFACE. The model 

receptor grid was designed to capture the maximum projected (future) modeled concentrations 

and properly processed using appropriate terrain information via AERMAP. Projected (future) 

lead emission inventories were developed for use in AEMOD along with source building and 

stack configurations to calculate building downwash conditions. An appropriate representative 

background lead concentration was determined using monitoring data from the Shippingport 

monitor.

PA DEP’s projected maximum rolling 3-month modeled lead concentration was added to the 3-

month background concentration from the Shippingport monitor. The final projected model 

concentrations was 0.0274 μg/m3. This concentration was added to the background lead 

concentration of 0.05 μg/m3to yield a total projected (future) 3-month lead concentration of 0.08

μg/m3. This projected (future) lead concentration is well below the 2008 lead NAAQS (0.15 

μg/m3) and demonstrates that Lower Beaver Valley nonattainment area will reach attainment 

with the lead standards established by the US EPA.

Recommendation of Approval of PA DEP’s Model Attainment Demonstration

EPA has evaluated the information provided in PA DEP’s lead SIP and concludes that the 

Commonwealth’s model attainment demonstration shows current lead control and emission

limits will provide for attainment of the 2008 lead NAAQS.