# A Summary of

Historical Ambient SO 2 

# Monitoring in the Billings Area

For



# Billings-Laurel Air Quality Technical Committee

(BLAQTC)

700 ExxonMobil Road

P.O. Box 1163 Billings, Montana 59103

Prepared by: 

## Bison Engineering, Inc.

1400 11 th 

## Avenue
Helena, MT 59601 (406) 442-5768
www.bison-eng.com

February 9, 2013A Summary of Historical Ambient Page 2

SO 2 Monitoring in the Billings Area 2/9/2013



# EXECUTIVE SUMMARY

A review of the historical ambient air quality moni toring for sulfur dioxide (SO 2 

### ) in the Billings-Laurel area indicates a wealth of monitori ng sites and data. Continuous monitoring for sulfur dioxide was established in th e early 1970s and continues on today. The area has been heavily monitored over the past 4 + 

### decades and has extended over a large geographical area (see Figure 2). Approxima tely 31 locations have been monitored over the years in this airshed.

The monitoring over time has served two purposes:

1) Measure concentrations within population areas; and

2) Establish and measure areas of high concentratio n

Sulfur dioxide monitoring has been conducted at man y sites throughout Billings, Laurel, and Lockwood targeting populous or population sensi tive areas. At one time or another,

SO 2 

### monitoring has been conducted at or near public sc hools, local businesses, major street intersections, city parks, county fairground s, etc.

The preponderance of SO 2 

### monitoring throughout the Billings/Laurel valley ha s targeted areas of high SO 2 

### concentrations. Consistently and historically, the Coburn Road site has yielded the highest SO 2 

### concentrations in the monitoring networks.

Although the record is not well documented, the Cob urn Road site was chosen based on a sulfation plate study (an objective screening method) and a general belief that areas above the valley floor, and near major indust rial facilities, would be a prospective location for high concentrations. Dispersion modeli ng was also used to evaluate areas for high SO 2 

### concentrations, but dispersion modeling has not pro ven to be a useful tool to predict high SO 2 

### concentration. For example, the model did not predi ct Coburn Road as the highest SO 2 

### concentration area. Sites that were established pri marily based on dispersion modeling such as Sacrifice Cliff, Lower Coburn Board and Johnson Lane yielded lower concentrations than Coburn Road. Thus , Coburn Road appears to be the appropriate site to represent the highest concentra tions in the airshed.

The results of the entire monitoring effort, with o ne exception in the 1970s, indicate no violations of the National Ambient Air Quality Stan dards (NAAQS) as they have existed for the past 39 years (i.e., prior to the new 2010 1-hr SO 2 

### ambient standard). However, values were recorded in excess of the more stringen t Montana Ambient Air Quality Standards (MAAQS). These values were resolved durin g the mid-1980s. No

exceedances of these standards have been recorded s ince.A Summary of Historical Ambient Page 3

SO 2 Monitoring in the Billings Area 2/9/2013 

# 1.0 INTRODUCTION

The Billings-Laurel Air Quality Technical Committee (BLAQTC) has asked Bison Engineering, Inc. (Bison) to conduct a historical r eview of the SO 2 

### ambient air quality stations in the Billings/Laurel area. The purpose o f the study will be to create a history that describes the ambient monitoring that has been conducted in Billings over the past

30 + 

### years. In particular, the study will further attem pt to decipher the reasoning and

rationale for the selection of some of the monitori ng sites, especially sites targeting

concentration areas. The Coburn Road site is select ed for review to evaluate why this site is the appropriate ‘high concentration’ site f or this area.

This compendium will provide evidence to the public , to the Montana Department of Environmental Quality (MDEQ) and to the Environment al Protection Agency (EPA) as to why the Coburn Road site, and others, is most appro priately sited at a high SO 2 

### concentration area. The information is germane to t he ongoing designation process before EPA for Yellowstone County and Montana as a whole.A Summary of Historical Ambient Page 4

SO 2 Monitoring in the Billings Area 2/9/2013 

# 2.0 REFERENCE DOCUMENTS

The following is a list of documents and informatio n sources reviewed for this report. Copies of all of the referenced documents can be fo und in the Bison Engineering files. Other documents may exist in the files of MDEQ; how ever, they are stored off-site from MDEQ and are thought to be incomplete and difficult to access.

STATE OF MONTANA - 2010 AIR MONITORING NETWORK ASSE SSMENT

MONTANA AIR MONITORING NETWORK REVIEW 2001

MONTANA AIR MONITORING NETWORK REVIEW FOR 1996

MONTANA 1986 NETWORK REVIEW

STATE OF MONTANA – AIR QUALITY CONTROL IMPLEMENTATI ON PLAN,

1979

BILLINGS SO 2 

### STUDY – DATA ANALYSIS, MODEL VALIDATION AND SOURCE DETERMINATION, 1984

MONTANA AIR QUALITY DATA & INFORMATION SUMMARY FOR:

o 1979-1980

o 1982

o 1983

o 1984

o 1985

o 1986

o 1987

o 1988 & 1999

MONTANA AIR POLLUTION STUDY FINAL REPORT JUNE 1981

Phone Interview: Mike Machler: Formerly of the Air Quality Bureau of MDEQ 1



### , GeoResearch Inc., and Bison Engineering, Inc.
Phone Interview: Steve Duganz, formerly of Yellowst one County Health Department
Phone Interview, Bob Jeffrey, formerly of MDEQ, Air Quality Section
Phone Interview, Hoby Rash, MDEQ Air Quality Monito ring Section
Personal Interview, Hal Robbins, formerly Air Quali ty Bureau Chief of MDEQ 2



### , currently at Bison Engineering, Inc.

1 The agency was known as the Department of Health a nd Environmental Sciences at this time. It was later to become the Department of Environmental Qua lity.

2 Ibid.A Summary of Historical Ambient Page 5

SO 2 Monitoring in the Billings Area 2/9/2013 

# 3.0 EARLY SO 2 

# MONITORING HISTORY (UP TO ~ 1980)

There appears to be little surviving written inform ation surrounding early SO 2 

### monitoring efforts (pre-1975). Brief oral histories were taken from people involved in these activities and were used in this report to fill in some gaps.

The surviving written history of SO 2 

### monitoring in Yellowstone County starts about 1974-75. The earlier written accounts have very lit tle detail or resulting data collected. As time progresses, the available written reports b ecome more detail oriented.

The 1979 State of Montana Air Quality Control Imple mentation Plan reports SO 2 

### monitoring stations 3 

### were installed and operating in Billings on January 1, 1972. The

Plan also shows three SO 2 

### bubblers operating in the Billings/Laurel area in 1975 (City Hall, Laurel and “Refinery Area”). The results from the monitoring showed compliance with the National Ambient Air Quality Standards (NA AQS), although problems were identified in Laurel, about 15 miles west-southwest of downtown Billings. The Plan also shows one continuous analyzer in operation in 1975, at “Sewage Treatment Plant E. on road to Fairgrounds, Billings.” 4



### In addition, the Montana Department of Health and E nvironmental Sciences (the predecessor to MDEQ), Yellowstone County and the Cr ow Tribe operated an extensive network of sulfation plates throughout the Billings -Laurel area. 5 

### Although MDEQ knew that the sulfation plates were not “exact”, air qua lity officials knew the plates provided an objective measurement of relative levels and trends of ambient SO 2 

### at many locations throughout the valley. In fact, there was a Montana Ambient Air Quality Standard for this pollutant during this time period. The standard was known as “Reactive Sulfur.” 6 

### These sulfation plates could be easily deployed and thus create a geographical picture of local

trends. Little information was found on the time fr ames of operation, or results of the

3 The sampling methodology at that time used what wa s referred to as a “bubbler” sampler. This method

was the official SO 2 reference method (per 40 CFR 50, Appendix A) until only a few years ago. The method bubbles ambient air through a liquid solutio n of potassium tetrachloromercurate (0.4 M) for typically 24 hours. The solution is then analyzed t o determine ambient SO 2 concentrations. This method

is sometimes referred to as the “Pararosaniline Met hod.”

4 Although the document provides no details, it is a ssumed (from a past MDEQ employee) that this continuous analyzer operated on the principal of co ulimetric titration and was manufactured by Beckman (Model 906A).

5 These “sulfation plates” are usually referred to a s the “Huey Sulfation Plates.” These plates, as fa r as can be determined, were invented by Norm Huey who w as an air quality engineer who worked for EPA in the Region 8 office in Denver. These are static sam plers in which a plastic petri dish was coated with a layer of PbO. The device was mounted outdoors and a llowed to react with ambient SO 2 to form PbSO 4

. The samplers were usually exposed to the atmosphere for about a month and then analyzed for SO 2

. More information may be obtained from the following publications: N. A. Huey “The lead dioxide estimation of sulfur dioxide pollution,” J. Air Poll. Control Assoc . 18:610 (1968) and Paul E. Rider et al. “Studies of Huey Sulfation Plates at High Ambient S O 2 Concentrations,” J. Air Poll. Control Assoc , 27:10, 1011-1013 (1977).

6 The standard was codified in 16-2.14(1)-S14040 (as was the rule structure at that time).A Summary of Historical Ambient Page 6

SO 2 Monitoring in the Billings Area 2/9/2013 

### sulfation plate network. Figure 1 shows the network of sulfation plates in 1986. From vague references, it appears that the sulfation pla tes operated from approximately 1970 through 1990.

In 1978, the Montana Air Pollution Study (MAPS) imp lemented an SO 2 

### monitoring

network. The network consisted of four continuous a nalyzers which operated from 1978-1980. The locations were Central Park, Lockwoo d School, 27 th 

### and Montana, and Laurel Farm east of CHS (formerly Cenex). The Laure l site recorded exceedances of the NAAQS. This data, combined with previous analyz er data, resulted in a portion of the Laurel area (1 kilometer circle) being designat ed as non-attainment for SO 2 

### in

1978. 7



### During this time period, no violations of the NAAQS were found at any other site. It is worth noting that in accordance with a 1977 stipula tion 8 

### between valley industries and MDEQ (DHES at that time); Cenex implemented some co rrective measures aimed at bringing the area below the NAAQS. Once these effor ts were concluded, no further
violations of the NAAQS have been recorded.

Starting in 1980, better written accounts of SO 2 

### monitoring history have been made by the MDEQ. Section 4 provides more detail on this mo nitoring.

7 43 FR 8964 (3/3/78) and 43 FR 40427 (9/11/78)

8 This is reference to what is commonly referred to as the “1977 Stipulation” which was between the maj or industries (CHS, Phillips 66, Western Sugar, ExxonM obil, Montana Sulphur & Chemical Co., and PPL)
and MDEQ.A Summary of Historical Ambient Page 7

SO 2 Monitoring in the Billings Area 2/9/2013 

## Figure 1: Sulfation Plate Network - 1986A Summary of Historical Ambient Page 8

SO 2 Monitoring in the Billings Area 2/9/2013 

# 4.0 MDEQ BILLINGS MONITORING HISTORY (~ 1978)

The following history is a collection of excerpts f rom the STATE OF MONTANA - 2010 AIR MONITORING NETWORK ASSESSMENT, and the MONTANA AIR MONITORING NETWORK REVIEW FOR 1996. Bob Jeffrey recounted spec ifically compiling the monitoring network histories for the state, as he t hought they would be useful as a historical reference. The following paragraphs are taken from these reports, and specifically deal with SO 2 

### monitoring in Yellowstone County.

In preparing this “Summary of Historical Ambient SO 2 

### Monitoring in the Billings Area”

document various comments and annotations are made as appropriate.

“ Yellowstone County

The Billings/Laurel area in Yellowstone County has dealt with SO 2 issues for several decades dating back to the beginning of local and Montana a ir quality programs in the 1960s. There is a long history of SO 2 monitoring in the cities of Billings and Laurel whi ch are located in the Yellowstone River Valley, which runs southwest to n ortheast and has a major influence on the airflow in the area. To the west near Laurel, t he valley is approximately 12 miles wide but heading east the valley narrows and on the east edg e of Billings, the sandstone cliffs or rimrocks result in a constriction that is approxima tely one mile wide and which channels the air flows. The major industrial SO 2 sources are all located in the Billings/Laurel area along the river valley and, as a result, the nearby elevated terrain is often higher than the tallest

smokestacks.”

9

“Wind roses for the area reflect the orientation of the Yellowstone River Valley. The predominant wind direction is from the southwest an d the second most predominant direction is from the northeast; i.e., the wind flows up and down the river valley. As with many areas in Montana, the area experiences inversions in the fal l and winter months which causes pollutants to become trapped and concentrated. The breakup of the temperature inversions right after sunrise can force those concentrated la yers of SO

2 to the ground, resulting in high

SO 2 concentrations being measured at the ground level m onitoring stations.”



### While the observation offered by MDEQ has some vali dity, it seems that more recent data, at least, offers an equally valid alternative explanation. A review of the wind speeds and directions during periods of observed hi gh concentrations at Coburn indicates that the high concentrations are more lik ely the result of convective air movement with perhaps some accumulation (but not al ways) from inversions or stable

air masses aloft. 10 

### The reasoning is that if, indeed, inversion (therm al) breakups were the cause of some of these relatively higher concen trations (after sunrise) then such events would likely be accompanied by low wind spee ds. A typical inversion break-up (associated with sunrise) is typically caused by th e sun heating the ground. This causes some vertical movement in the atmosphere which brin gs concentrations of SO 2 

### in the

9 Note that this is especially true for the Coburn s ite, the primary subject of this report, and the Sa crifice

Cliff site which is discussed later in this documen t.

10 This is technically breaking up an inversion, but not in the more traditional sense when coupling it with an assumed sunrise (solar heating).A Summary of Historical Ambient Page 9

SO 2 Monitoring in the Billings Area 2/9/2013 

### upper atmosphere (a few hundred vertical feet) down to the ground and thus breaks up

the inversion. 11



### Observed high concentrations at Coburn are almost a lways associated with medium strength wind speeds; between 8 and 12 mph. Such an event will, of course, break up an inversion, but it does so by moving the air from one location to another and mixing the air in the interim (from turbulence). Other tim es during relatively higher SO 2 

### concentrations observed at Coburn Road, the wind wa s also blowing at a steady 8-12 mph from approximately 240 degrees. The Coburn Road SO 2 

### monitor routinely records higher SO 2 

### concentrations during this steady southwest wind p attern.

That issue aside, MDEQ continues with their discuss ion of ambient monitoring.

“There are seven major SO 2 sources in the Billings/Laurel area. In Billings, t hese include ExxonMobil (oil refinery), Phillips 66 (oil refiner y), PPL-MT Corette (coal-fired electric power generating facility), Western Sugar (coal-fired sug ar beet factory), Yellowstone Energy Limited Partnership (coke-fired cogeneration power plant), and Montana Sulphur & Chemical (sulfur recovery facility). In Laurel, the major so urce is the Cenex Harvest States (CHS - oil refinery). All of these sources combined contribute to the SO

2 in the Billings/Laurel airshed.

In March 1978, based on ambient air monitoring data , the Laurel area was designated

nonattainment for SO 2. 12 In anticipation of the pending nonattainment desig nation, the Billings/Laurel industries and the State signed a s tipulation requiring the industries to employ various control options in December 1977. This stip ulation was incorporated into the SIP, and it provided the framework to bring the area into co mpliance. The 1977 stipulation also commissioned the Department (with industrial fundin g) to conduct an ambient air quality study to more fully describe the magnitude and geog raphical extent of the SO 2 concentrations. Another major goal of the study was to identify the relative source

contributions from each industrial source.”



### Another related goal of the study was to investigat e the validity of computer modeling in predicting concentrations at relevant sites.

“In 1981-82, the Department (through a cooperative effort with the industries) designed and

installed a local SO 2 monitoring network. The network consisted of eight SO 2 monitoring sites with meteorological monitoring that included upper air measurements from acoustic radar and pilot balloons. Six of the SO 2 sites were in Billings and two were in Laurel. Usin g the monitoring data, the Department attempted to valida te a mathematical model 13 that could predict concentrations from the various SO 2 sources. The model failed for the following

reasons: 14

• a lack of good emissions data;

11 As the air mixes vertically, temperature no longer increases with increasing elevation and thus an inversion no longer exists.

12 The “area” referred to by MDEQ consisted only of a 1 kilometer circle around Tank 26 at the CHS refinery.

13 This was, in fact, a “Gaussian” model.

14 The reader is reminded that these are MDEQ conclus ions.A Summary of Historical Ambient Page 10

SO 2 Monitoring in the Billings Area 2/9/2013 • high concentrations caused by inversion breakup 15 and direct plume impact which the

model could not handle;

• over-prediction of plume rise by the model; and

• small changes in wind direction could cause large d ifferences in predicted versus actual

concentrations at receptors located close to the so urces.”



### The reader is reminded that the conclusions above a re those of MDEQ only and not the

authors of this document.

“A novel approach was developed using directional a nalysis and mass emissions to

characterize source contributions to the annual ave rage at the worst-case receptor (highest estimated ground-level SO 2 concentration). This was useful but could not be ap plied as a predictive tool for short-term averages or at other receptors in the valley.

Following the 1981-82 study, the S02 monitoring net work was scaled down in various stages until it reached a minimum early in 1987. As mentio ned previously, eight S02 monitoring stations were in operation in 1982 during the S02 s tudy. Following the conclusion of that study, the network was scaled down to four sites in 1983. These included Coburn Road (30- 111-0066), Lockwood Park (30-111-0065), North Johns on Lane (30-111-0064) and Taft School (30-111-0064). It should be noted that no si tes were kept in the Laurel area since the two sites in the 1981-82 study showed compliance wi th the NAAQS and MAAQS. The Department felt that greater emphasis was needed in the Billings/Lockwood area. In December 1983, the Taft School site was shut down t o reduce the operator's workload in Billings. The network of three continued until June 1986 when a leasing problem caused the Department to shut down the North Johnson Lane site . In January 1987, the Department shut

down its Lockwood Park site due to further cutbacks of personnel in the Billings office. At that time the network was reduced to a single site, Cobu rn Road, which has been the backbone of

the network.”



### The Coburn Road site was chosen as what MDEQ descri bes as the “backbone of the network” because, based on opinion and experience C oburn was “the” monitoring site that yielded the most information for regulatory pu rposes. MDEQ clearly had an interest in monitoring in the Billings area for many reasons including population exposure. However, it was believed that if one continues to m onitor at the “highest” reporting station and that station was reporting concentratio ns below the ambient standards, then

it was reasonable to assume that the rest of the Co unty was also below the ambient

standard.

“Following the 1987 Legislature session, a committe e of the Billings/Laurel industries, the local chamber of commerce, and air pollution profes sionals united to monitor and report on the area's air quality. The Billings/Laurel Air Qua lity Technical Committee (BLAQTC) was formed in the spring of 1987. The Department was a non-paying member of BLAQTC and worked with the group on site selection, quality as surance, and ambient monitoring. BLAQTC hired a contractor, purchased equipment and install ed three SO

2 monitoring stations. Two of the sites were in Billings: Lockwood Park (30-111-1 065) and Coulson Road (30-111-2004),

15 MDEQ believed that these high concentrations were caused by inversion break-up, but this was not necessarily a known fact.A Summary of Historical Ambient Page 11

SO 2 Monitoring in the Billings Area 2/9/2013 and one in Laurel: Laurel-BLAQTC (30-111-0016). By the end of 1987 the combined Department-BLAQTC network consisted of five sites.



### This organization known as “BLAQTC” continues today . Over time, the group has become a loose organization that primarily consists of six of the seven industrial facilities in the Billings/Laurel airshed.

“The layout of the monitoring network remained the same until October 1989. Upon agreement between the Department and BLAQTC, the Sc ottish Rites site was moved to Ponderosa School (30-111-0076) and the Coulson Road site was moved to Brickyard Lane (30-111-2005). The group felt that the old sites ha d served their purpose and that higher SO 2 concentrations might be found at the new sites. The EPA approved all of these sites in a letter dated May 14, 1990. On June 30, 1992, the Po nderosa School site was shut down due to low readings. EPA approved this action in a lett er dated June 22, 1992. The monitoring shelter from Ponderosa was moved and replaced the a ging shelter at Coburn Road.

Due to interest from EPA and environmental groups, in November 1988 the Department began collecting peak 5-minute SO 2 averages for each valid hour of data. 16 At a meeting with the Department and BLAQTC in February 1990, EPA off ered two SO

2 analyzers to conduct peak monitoring in the range from 1 to 5 ppm. In Se ptember 1990, the Department and
BLAQTC installed these monitors at the Coburn Road and Lockwood Park sites. These monitors collected peak 5-minute data for 6 months until March 1991. Peak data was also collected at the other three sites with analyzers i n the range of 0 to 1 ppm. After completion of the study, an EPA contractor reviewed and analyzed the data but the results were not conclusive. The Department continued to collect pea k 5-minute SO 2 data through 2003, but none was collected at the industry sites. It’s wort h noting that for calendar year 2002, the Department collected and reported not just the maxi mum 5-minute value in each hour, but all

of the 5-minute values in each hour.

In 1990, E. H. Pechan and Associates (Pechan) devel oped an SO 2 emission inventory for the Billings/Laurel area. The final report, submitted t o EPA in 1991, indicated a large difference between actual and potential SO 2 emissions for most sources. Also in 1990, the City of Billings contracted with GeoResearch Inc. to conduc t an SO 2 dispersion modeling study for the Billings area utilizing recently gathered meteo rological data and the Pechan SO 2 emission inventory. The dispersion modeling results predicte d violations of the SO 2 NAAQS at both the potential to emit and maximum actual emission rates .”



### The purpose of the study commissioned by the City o f Billings was to identify areas in the city and its environs where new or expanding in dustry might be sited successfully. Given the use of emission rates (from the Pechan st udy) far beyond those reported in actual use, the study, not surprisingly, predicted ambient concentrations well beyond those actually observed at the monitoring sites.

“The Department reviewed and refined the results of those latest modeling studies 17 and

concluded additional SO 2 monitoring sites were needed. At the location of th e modeled

maximum SO

2 "hot-spot" the Department installed an SO 2 monitor. That max site, Sacrifice Cliff (30-111-0080), was approved by EPA effective May 19, 1993, and sampling began.

16 MDEQ does not mention in this summary that the ind ustries themselves, via BLAQTC, also participated in the collection of short-term (5 minute) data.

17 MDEQ is primarily referring to dispersion modeling studies conducted by the “YELP-BGI” facility in support of its air quality permit application (1991 ).A Summary of Historical Ambient Page 12

SO 2 Monitoring in the Billings Area 2/9/2013 Also, as a result of the permitting process, YELP-B GI was required to operate SO 2 monitors at two other modeled "hot-spots" at Johnson Lane (3 0-111-2006) and Pine Hills (30-111- 2007). EPA approved both sites on March 7, 1994, wi th data collection starting on November 2, 1993. Through 1996, the Sacrifice Cliff site mea sured the highest SO 2 concentrations in the Billings/Laurel monitoring network but a change to low sulfur coal at the YELP-BGI facility 18
resulted in a dramatic drop in ambient SO 2 concentrations. After the fuel switch, the Sacrific e Cliff site consistently measured lower concentratio ns than the values at Coburn Road and the

Sacrifice Cliff site was shut down in June 2001.



### There are two items of note regarding DEQ’s comment s above. First, the agency states

that the SO 2 

### concentration dropped as a result of a fuel switch (to lower sulfur coal) at

PPL-Montana’s Corette station. 19 

### While indeed PPL emissions were reduced during thi s period, it is equally true that emissions from othe r industries also reduced their emissions as well. The emissions from the major nea rby facilities during the same period (3 year average prior to 1996 versus the 3-y ear average beginning in 1996) were

as follows:

Emissions and Ambient Comparison

1993 - 1995 vs. 1996 - 1998

Emissions a



### 1993 – 1995 1996 – 1998 Difference

PPL (Corette) 7,250 2,570 -65 % ExxonMobil 10,300 5,600 -46 %

Phillips 66 1,800 1,090 -40 % CHS 5,100 3,150 -39 %

Western Sugar 470 140 -70 % MSCC 3,500 3,700 +8 %

YELP n/a 2,000 n/a

Ambient Data b



### Coburn Road 87 40 -54 %
Sacrifice Cliff 61 33 -46 %

Notes:

a. Emission values are in tons/year and are rounded for convenience b. Ambient data units = ppb c. Ambient data averaging period = 2 nd high 24-hour value (3-year average); consistent wi th one of the averaging period of the NAAQS at that ti me. d. Emission values are rounded for convenience e. YELP began operation in late 1995.



### Second, a review of the data during this period sho ws that the Sacrifice Cliff data indeed yielded among the highest concentrations in the val ley. On the other hand, the pre-1996 values were nearly identical to that of Coburn Road . Some statistics indicated pre-1996

18 This is an apparent error on MDEQ’s part. YELP-BGI does not combust coal. It is assumed that MDEQ was, or should have been, referring to the Corette plant.

19 See footnote above. MDEQ mistakenly refers to YELP -BGI when it should have stated PPL.A Summary of Historical Ambient Page 13

SO 2 Monitoring in the Billings Area 2/9/2013 

### Sacrifice Cliff as the highest concentration while others show that Coburn ranks higher. Regardless, the SO 2 

### concentrations at Sacrifice Cliff, after a short t ime, were reduced and thus the site no longer served its purpose. The site was no longer the highestreporting site and it (and Coburn Road) failed to s how any values in excess of the ambient air quality standards.

In order to characterize population exposure, BLAQT C installed an SO 2 

### analyzer at the Mount Olive site in late 1995. This was an already established air monitoring site that was measuring continuous carbon monoxide values. Th e site was located near the

corner of 24 th 

### and Central Avenue, two major thoroughfares in Bil lings.

At about the same time, another station was started at Senior High School. This site was also established for population measurement cov erage. The Senior High site included carbon monoxide and meteorological paramet ers (wind speed, wind direction and temperature).

Due to measured concentrations well below the ambie nt air quality standards and values below Coburn Road, both sites were discontin ued in 1997.

Another monitoring site was installed near the Cobu rn Road site in 1999 in an attempt to find yet-higher reporting monitoring values than Coburn Road itself. The site was chosen, in part, from dispersion modeling data. Thi s new site was located about 1⁄2 miles from the Coburn site, at an elevation well below Co burn, but elevated from the valley

floor. This became known as the Lower Coburn site. Monitoring continued here for about three years. Again, monitoring was discontinu ed since no exceedances of any ambient air quality standards were observed and the monitored values were well below

those measured at Coburn Road.

MDEQ describes the next few years of monitoring bel ow. As before, none of these sites, despite their geographical and population intent, y ield ambient air quality values above

ambient standards. All results remain well below th ose found at Coburn Road.

(from DEQ)

“To better document population exposure and monitor trends in the growing west end of Billings, the Mount Olive site (30-111-0079) was re opened and monitoring begun for SO 2 and CO in October 2001. In July 2001, SO 2 monitoring was added to the Bridal Shop CO site (30

- 111-0082). The results from Mount Olive showed a su bstantial reduction in ambient SO 2 concentrations in the west end of Billings as compa red to the earlier monitoring results from the late 1990s, so the Mount Olive site was shut do wn in September 2004. At the same time,

a review of the SO 2 results from the Bridal Shop site indicated very lo w concentrations with the occasional elevated reading only when winds wer e blowing directly from the ConocoPhillips refinery, so the Bridal Shop site wa s shut down in June 2004.

Since the 1980s, there has been substantial residen tial and commercial development on the high bench located above and northeast of downtown Billings. As the population in Billings Heights increased so did the number of complaints a bout air pollution. The “Heights” is located just north of several SO 2 -emitting industrial sources in the Lockwood Park a rea, and given the frequency of south winds during the summe r months, the Department decided toA Summary of Historical Ambient Page 14

SO 2 Monitoring in the Billings Area 2/9/2013 install a new air monitoring site to investigate th e public’s air pollution complaints. As a result, the Beartooth Elementary site (30-111-0084) began c ollecting SO 2 data in August 2003. Over the next 3 years, the site did monitor a few period s of elevated SO 2 but they were of short duration and very infrequent, so the site was shut down in December 2006. 20

As of this writing 21 , there are six SO 2 monitoring sites in the Billings/Laurel area; two o perated due to permit requirements (Johnson Lane and Pine H ills), three by BLATQC (Brickyard Lane, Lockwood Park, Laurel), and one by the Depart ment (Coburn Road). Over the years,

SO 2 has been monitored at 31 locations in the Billings/Laurel area. In summary, those sites, their AIRS codes and years of operation are as foll ows:

• Lockwood School Billings (30-111-0006), 1975-81

• Laurel BN (30-111-0015), 1981-82

• Laurel BLAQTC (30-111-0016), 1987- present

• Hi-Ball Trucking (30-111-0035), 1974-75

• Division & Grand (30-111-0052), 1975

• 27 th & Montana (30-111-0053), 1975-78

• Central Park Billings (30-111-0059), 1978-81

• Metra Park Billings (30-111-0061), 1981-82

• Taft School Billings (30-111-0062), 1980-83

• Shawnee Park Billings (30-111-0063), 1982

• North Johnson Lane DHES (30-111-0064), 1982-86

• Lockwood County Park DHES (30-111-0065), 1981-87

• Coburn Road (30-111-0066), 1981- present

• Scottish Rites Billings (30-111-0073), 1987-89

• Ponderosa School (30-111-0076), 1989-92

• Mount Olive Billings (30-111-0079), 1995-97 & 2001- 04

• Sacrifice Cliff (30-111-0080), 1993-2001

• Bridal Shop (30-111-0081), 2001-04

• Lower Coburn Road (30-111-0083), 1999-2003

• Beartooth Elementary (30-111-0084), 2003-06

• Laurel Jr. High (30-111-1001), 1973

• Laurel Water Plant (30-111-1005), 1976

• East Laurel (30-111-1008), 1973-76

• Laurel East Farm Cenex (30-111-1009), 1976-80

• Laurel New Farm (30-111-1014), 1980-82

20 A cursory review of the data indicates that values at this site were about 1⁄3 of the values recorded at Coburn. Since Coburn was, itself, below the ambient air quality standards, the results did not justify continued monitoring.

21 2010.A Summary of Historical Ambient Page 15

SO 2 Monitoring in the Billings Area 2/9/2013 • Lockwood Park BLAQTC (30-111-1065), 1987- present

• Coulson Road BLAQTC (30-111-2004), 1987-89

• Brickyard Lane BLAQTC (30-111-2005), 1989 - present

• Johnson Lane YELP (30-111-2006), 1993 - present

• Pine Hills YELP (30-111-2007), 1993 – present

• Senior High (30-111-2008), 1995-97



### A map depicting the locations of all 31 monitoring stations is included here as Figure 2.

The reader will observe that continuous ambient sam pling for SO 2 

### has occurred throughout the Billings-Laurel-Lockwood area. The s ampling includes not only a wide geographical area; it also includes locations of hi gh population density, public interest (schools), industrial activity, road intersections, and various elevations.DRAFTA Summary of Historical Ambient Page 17

SO 2 Monitoring in the Billings Area 2/4/2013 

# 5.0 HISTORY OF COBURN ROAD MONITOR

The written records of Billings ambient monitoring, Coburn Road in particular, have

been reviewed. The records indicate an extensive ef fort by MDEQ, the county and the industrial sector to pick ambient monitoring statio ns that represented a plethora of purposes. Those purposes ranged from health study i nvestigations such as the 1981 Montana Air Pollution Study, population exposure, s pecial requests and peak impacts. A total of 31 sites, other than sulfation plate stu dies, have been monitoring since the early 1970s.

The Coburn Road continuous SO 2 

### analyzer was installed in 1981. In various forms, an ambient SO 2 

### analyzer has been operating at that site ever sinc e.

Based on the review of the data no specific written record was found that describes the specific logic behind the location of the Coburn Ro ad monitoring station. However, interviews from a number of persons who were involv ed, in one form or another, with either the original site selection or its operation yielded some common recollections.

Bob Jeffrey and Steve Duganz had similar recollecti ons in their interviews, as follows:

The sulfation plate network, previously described, was used to locate a station at Coburn Road. This was based, in part, on the fact t hat this location routinely recorded among the highest sulfation rates. In addi tion, the site also had three other attributes that are required to establish an ambient monitoring station: a cooperative landowner, (easy) access, and available power.

In addition to the sulfation plate information, the site also represented an area above the valley floor. This site seemed intuitive to MDEQ since it was suspected that the prevailing southwest wind would yield elev ated SO 2 

### concentrations from upwind industrial facilities.

Bob Jeffrey recalled that the Coburn Road site was moved several times, and received

new shelters several times. None of the moves was m ore than 100 yards from the

current site.

Some selected text from the MDEQ 1986 MONTANA NETWO RK REVIEW about the Coburn Road site is copied here for further informa tion.

“8. The Coburn Road site is located on the top of a ridge which separates the city of Billings from the Lockwood area. The Conoco oil ref inery, the Montana Power Co. Corette Plant, and the Western Sugar refinery are s ulfur dioxide sources which are located on the Billings side of the ridge within tw o miles of the monitoring site. On the other side of the ridge in Lockwood are the Exxon o il refinery and the Montana Sulphur and Chemical Company. Both of these sulfur dioxide sources are approximately two

miles northeast of the Coburn Road site. The site i s at an elevation of 3380 feet MSL or approximately 280 feet above the surface of the Yel lowstone Valley. Wind patterns at

the Coburn Road site are somewhat different than at the other sites located within the valley. In general, the wind speed is 0.5 to 1.0 me ter per second faster with a muchA Summary of Historical Ambient Page 18

SO 2 Monitoring in the Billings Area 2/4/2013

greater predominance from the west-southwest. Appar ently, terrain features have

much less effect on wind at the Coburn Road site.”

“10. The department suspects that the Coburn Road s ite is located at an optimum elevation, so that during periods of multiple layer ed inversions, the plumes of the various sources are trapped in a layer at the same height. This might explain why sulfur dioxide concentrations at Coburn Road are generally higher and often do not follow the concentrations at the other valley locations.

11. Since Coburn Road consistently records high sul fur dioxide concentrations, the department intends to continue to monitor sulfur di oxide at this location. In addition, the site will be the key site in determining the amount of sulfur dioxide control necessary at each plant.”



### In addition to those comments directly from MDEQ, H al Robbins 22 

### offered some of his thoughts and recollections of this site. He recalls reviewing and discussing the selection of the site with various agency staff. In particula r he recalls that there were two primary factors that led to the selection of this site (bey ond site access, power availability, etc.). The first, and most important, was the results of t he sulfation network previously

described in this document. The sulfation network i ncluded a large geographical area which helped narrow where the ideal maximum concent ration site might be located. The

sulfation network indicated that the Coburn Road ar ea consistently showed either the highest or near the highest concentrations of measu red ambient SO 2



### .

The second factor was elevation. It was thought at the time that monitoring efforts in the valley may be useful, relative to population exposu res and the geographical extent of the network, but the valley monitoring may not char acterize the peak impacts. (MDEQ wanted, consistent with EPA policy, to be sure that the monitoring network included areas with the maximum concentration.) A site that was above the valley floor, and thus closer to stack height, coupled with high sulfation plate readings was thought to be a prudent location.

Hal also recalls working with David (Dave) Maughan during this time period. Dave was in charge of special projects and conducted a numbe r of investigations into the extent and nature of ambient readings. This included fluor ide studies in Butte-Anaconda, SO 2 

### mapping in Anaconda, lead (Pb) snow-deposition stud ies in East Helena, etc. Dave was involved in the sulfation plate analysis and select ion discussions. The Yellowstone County Health Department played an important role i n these discussions as well.

22 Hal was the Bureau Chief of the Montana Air Qualit y Bureau from 1980 through 1987, worked in the air monitoring and dispersion modeling section of the a gency from 1975 to 1980, and was directly involved in the selection of Coburn as a high concentration sit e.A Summary of Historical Ambient Page 19

SO 2 Monitoring in the Billings Area 2/4/2013 

# 6.0 SUMMARY AND CONCLUSIONS

This document has reviewed the historical ambient a ir quality monitoring for SO 2 

### in the Billings-Laurel area. The review has indicated a la rge number of monitoring sites have been in place over the past 40 years. The sites hav e included places on high terrain, low terrain, near schools, adjacent to major inters ections, high population areas, low population areas, and near major industrial facilit ies. With one exception in the late 1970s, none of these monitoring sites yielded ambie nt concentrations above the National Ambient Air Quality Standards (NAAQS) as t hey existed prior to 2010.

The siting of these stations was typically driven b y a desire to capture the location that produces the highest concentration. However, in som e cases, the monitoring was established to ascertain population exposure or for a specific study or request.

As it regards siting a station at an area of highes t concentration, a combination of passive monitoring (sulfation plate studies), profe ssional judgment and dispersion modeling were employed. In retrospect, the sulfatio n plate study along with some professional judgment appears to have been the most successful means of achieving that goal.

On a consistency basis, the Coburn site has recorde d, and continues to record, the highest concentrations of SO 2 

### in the Billings airshed since it was installed in 1981; 32 years ago. This observation remains despite the fac t that dispersion modeling has indicated other locations which should, according t o the model, record higher concentrations. Modeling was used to site additiona l samplers (Lower Coburn, Sacrifice Cliff and others), but those stations did not recor d values higher than Coburn Road.

The geographical distribution (see Figures 1 and 2) coupled with the length of the monitoring periods has well characterized the conce ntration of SO 2 

### in the Billings-Laurel

airshed.