EPA Review of 

Hawaii Department of Health’s 

“Documentation for Natural Events Excluded Data

Hilo Air Monitoring Station, AQS ID 15-001-1006

Mountain View Air Monitoring Station, AQS ID 15-001-2023

Ocean View Air Monitoring Station, AQS ID 15-001-2020

Pahala Air Monitoring Station, AQS ID 15-001-2016

2012-2014 Sulfur Dioxide (SO2) Exceedances

Final Report, January 2016”

Regarding Exceedances of the 2010 1-hour SO2 NAAQS 

in 2012-2014

US Environmental Protection Agency, Region 9

January 2016
Page 2 of 13

Contents

1. Introduction.......................................................................................................................... 3

2. Summary of the Events........................................................................................................ 5

3. Requirements of the Exceptional Events Rule (EER) ......................................................... 5

4. Clear Causal Relationship (CCR)........................................................................................ 6

5. Concentrations in Excess of Normal Historical Fluctuations (HF) ..................................... 9

6. No Exceedance But For the Event (NEBF)....................................................................... 10

7. Criteria Set Forth in 40 CFR §50.1(j)................................................................................ 10

7.1. Affects Air Quality (AAQ)................................................................................................ 10

7.2. Natural Event ..................................................................................................................... 11

7.3. Not Reasonably Controllable or Preventable (nRCP) ....................................................... 11

8. Procedural Requirements................................................................................................... 13

9. Conclusion ......................................................................................................................... 13
Page 3 of 13

1. Introduction

On March 22, 2007, EPA adopted a final rule, Treatment of Data Influenced by Exceptional 

Events (EER), to govern the review and handling of certain air quality monitoring data for which 

the normal planning and regulatory processes are not appropriate.1 Under the rule, EPA may 

exclude data from use in determinations of National Ambient Air Quality Standard (NAAQS) 

exceedances and violations if a state demonstrates that an “exceptional event” caused the 

exceedances. Before EPA can exclude data from these regulatory determinations, the state must 

flag the data in EPA’s Air Quality System (AQS) database and, after notice and opportunity for 

public comment, submit a demonstration to justify the exclusion. After considering the weight of 

evidence provided in the demonstration, EPA decides whether or not to concur with each flag. 

On December 17, 2015, Hawaii Department of Health (HDOH) submitted documentation to EPA 

to demonstrate that exceedances of the 2010 1-hour SO2 NAAQS2 that occurred in 2012-2014 at 

the Hilo (AQS ID: 15-001-1006), Mountain View (AQS ID: 15-001-2023), Ocean View (AQS 

ID: 15-001-2020), and Pahala (AQS ID: 15-001-2016) Air Monitoring Stations located on the 

Island of Hawaii (Figure 1) resulted from volcanic-related exceptional events (“2015 

Demonstration”).3 This document sets forth the basis for EPA’s concurrence with HDOH’s 

claim that the exceedances summarized in Table 1 and listed in the 2015 Demonstration, 

Appendix D4 were the result of volcano-related exceptional events:

Number of Days for EPA Concurrence

Station 2012 2013 2014

Hilo 20 14 10

Mountain View 20 17 27

Ocean View 177 116 93

Pahala 293 214 174

Table 1. Number of days with hours requested for EPA Concurrence (from 2015 

Demonstration, Figure I-1, Procedure 2).5

 1 72 FR 13560, March 22, 2007. EPA has proposed revisions to the 2007 EER (80 FR 224, November 20, 2015). 

Those changes have not yet been finalized. Accordingly, in making this concurrence determination, EPA is relying 

on the existing regulations, with additional support as provided in our 2013 Interim Guidance on implementing those 

regulations. See Stephen Page, Director, Office of Air Quality Planning and Standards to Regional Air Directors, 

“Interim Guidance to Implement Requirements for the Treatment of Air Quality Monitoring Data Influenced by 

Exceptional Events” and “Interim Exceptional Events Rule, Frequently Asked Questions,” U.S. EPA, May 2013. 2 The 2010 1-hour SO2 NAAQS is 75 parts per billion (ppb). 40 CFR 50.17(a); 75 FR 35520 (June 22, 2010). 3 “Documentation for Natural Events Excluded Data Hilo Air Monitoring Station, AQS ID 15-001-1006, Mountain 

View Air Monitoring Station, AQS ID 15-001-2023, Ocean View Air Monitoring Station, AQS ID 15-001-2020, 

Pahala Air Monitoring Station, AQS ID 15-001-2016, 2012-2014 Sulfur Dioxide (SO2) Exceedances, Final Report, 

January 2016” (“2015 Demonstration”).

4 On January 13, 2016, HDOH transmitted additional pages from Appendix D that had been inadvertently omitted 

from its December 17, 2015 submittal. Here forward, the terms “2015 Demonstration” and “Appendix D” refer to 

December 2015 and January 2016 submittals. 

5 40 CFR 50, Appendix T, 5(a)(i)(2).
Page 4 of 13

On June 3, 2010, the EPA revised the primary (health based) SO2 NAAQS by establishing a new 

one-hour standard at a level of 75 parts per billion (ppb) which is attained when the 3-year 

average of the 99th percentile of one-hour daily maximum concentrations does not exceed 75 

ppb.6 EPA is concurring on specific hours within each of the days identified in Table 1, totaling 

4,546 hours from the four monitors across the 3-year period of 2012-2014. A full list of dates 

and hours concurred upon are listed in the 2015 Demonstration, Appendix D. With EPA’s 

concurrence on these hours, the 2014 design values, which are calculated from 2012-2014 data, 

for the Hilo, Mountain View, Ocean View, and Pahala monitors do not violate the 2010 SO2

NAAQS.

Figure 1. Topographical map of Hawaii with locations of the Halema’uma’u and Pu’u O’o 

vents, air monitoring stations (regulatory: Hilo, Mountain View, Pahala, Ocean View, Kona; 

non-regulatory: Puna E, NPS Visitor’s Center, NPS Observatory), and power plants (from 2015 

Demonstration, Figure 2-12).

 6 75 FR 35520, June 22, 2010.
Page 5 of 13

2. Summary of the Events

Volcanic emissions primarily consist of water vapor, carbon dioxide and SO2. Kilauea Volcano, 

located on the southeastern shore of the Island of Hawaii, has been erupting almost continuously 

since 1983 resulting in releases of gas from vents located at the Halema’uma’u summit and Pu’u’ 

O’o rift zone craters (Figure 1). In 2008, a new gas vent opened at Halema’uma’u, increasing 

emissions at this location by a factor of 10.7 Elevated emissions have persisted since then with 

total Kilauea emissions estimated at 2,140,183 tons SO2 in 2014 (~93% from Halema’uma’u).8

HDOH explains that Kilauea emissions are blown by prevailing northeasterly trade winds 

towards the Pahala and Ocean View monitoring stations and less frequently by southerly (also 

referred to as Kona winds) towards the Hilo and Mountain View air monitoring stations, causing 

exceedances at these locations (Figure 2).9

HDOH submitted the 2015 Demonstration to show that emissions emanating from Kilauea 

Volcano are natural volcanic exceptional events and that the exceedances summarized in Table 1 

and listed in the 2015 Demonstration, Appendix D were caused by these natural volcanic 

exceptional events. 

Figure 2. Hawaii wind patterns (from 2015 Demonstration, Figure 2-9).

3. Requirements of the Exceptional Events Rule (EER)

Pursuant to 40 Code of Federal Regulations (CFR) §50.14(c)(3)(iv), a request for EPA’s 

concurrence on an exceptional event flag must be accompanied by a demonstration that: 

 7 See 2015 Demonstration, p.18. 8 See 2015 Demonstration, pp.33 and 88. 9 See 2015 Demonstration, p.3. 
Page 6 of 13

A. The event satisfies all of the criteria set forth in 40 CFR §50.1(j). It affects air quality; is 

not reasonably controllable or preventable; and is caused by human activity that is 

unlikely to recur at a particular location, or is a natural event; and is determined by the 

Administrator in accordance with 40 CFR 50.14 to be an exceptional event; and

B. There is a clear causal relationship between the measurement under consideration and the 

event that is claimed to have affected the air quality in the area; 

C. The event is associated with a measured concentration in excess of normal historical 

fluctuations, including background; and 

D. There would have been no exceedance or violation but for the event. 

The EER also has procedural requirements. 40 CFR §50.14(c)(2)(iii) requires that data claimed 

to be due to an exceptional event be flagged in the AQS database, and that an initial description 

of the event be provided to EPA; both must occur by July 1 of the year following the event. In 

addition, 40 CFR §50.14(c)(3)(i) requires that the State: 

• submit a demonstration to EPA within three years of the calendar quarter of the event or 

12 months prior to an EPA regulatory decision; 

• provide notice and opportunity for public comment; and 

• submit any public comments along with the demonstration. 

The following sections provide EPA’s review of HDOH’s demonstration for the hours in question 

with respect to these requirements.

4. Clear Causal Relationship (CCR)

EPA considers a variety of evidence when evaluating whether there is a clear causal relationship

between the measurements under consideration and the event that an air agency claims affected 

the air quality in the area. Demonstrations typically include documentation showing that the 

events in fact occurred and that emissions related to the event were transported in the direction of 

the monitor(s) where elevated concentrations measurements were recorded; the size of the area 

affected by the transported emissions; the relationship in time between the event, transport of 

emissions, and recorded concentrations; and, as appropriate, pollutant species-specific 

information supporting a causal relationship between the event and the measured concentration.

Section 2 of the 2015 Demonstration includes a comprehensive conceptual model of the events, 

including details of the air monitoring stations, description of the topography and climate of 

Hawaii, a discussion of trade winds and Kona winds, and a summary of additional analyses

presented. Section 3 presents HDOH’s analysis to demonstrate that the CCR criterion is met. 

Section 6 of the 2015 Demonstration also summarizes the CCR element. We review HDOH’s 

analysis of CCR below. 
Page 7 of 13

Kilauea emissions were estimated at 2,140,183 tons SO2 in 2014 (~93% from Halema’uma’u), 

accounting for 99.9% of SO2 emissions from the Island of Hawaii.10 Illustrating the dominance 

of volcanic SO2 emissions on the Island of Hawaii, the 2015 Demonstration includes satellitebased measurements that show elevated SO2 columns originating near Kilauea Volcano and 

being blown by trade winds to the southwest and around the southern portion of the island, while 

nitrogen dioxide columns (NO2), an indicator of anthropogenic pollution, are elevated around the 

Island of Oahu, but low over the entire Island of Hawaii.

11

HDOH’s 2015 Demonstration describes two predominant regimes: (1) during prevailing trade 

wind conditions, emissions from Kilauea Volcano are blown to the southwest toward the Pahala 

and Ocean View monitors; and (2) during episodic Kona wind conditions, volcanic emissions are 

blown to the north toward the Mountain View and Hilo monitors. Focusing on the two monitors 

to the south of the volcano during prevailing trade wind conditions, the Pahala monitor, which is 

located closer to the volcano, measured both the higher 2014 design value (712 ppb, compared to 

533 ppb at Ocean View) and the higher number of days with hours requested for exceptional 

event concurrence (681 days from 2012-2014, compared to 386 days during 2012-2014 for 

Ocean View). Regarding the two monitors to the north of the volcano during (less frequent)

Kona winds, the Mountain View monitor, which is located closer to the volcano, had a 2014 

design value of 279 ppb and 64 days with hours requested for exceptional events concurrence, 

while the Hilo monitor had a 2014 design value of 180 ppb and 44 requested days. 

HDOH also examined 2012-2014 normalized daily mean SO2 values at the HDOH monitors and 

at two monitors operated by the National Park Service (NPS) near Halema’uma’u: the HAVOOB monitoring site (AQS ID: 15-001-0007), located 2 kilometers (km) to the north of the vent at 

the observatory, and the HAVO-VC (AQS ID: 15-001-0005) site located 4 km to the northeast of 

the vent at the visitor’s center (See Figure 1).12 The HAVO-VC and HAVO-OB sites are well 

correlated (r = 0.62). The HAVO-VC site is similarly correlated with Mountain View (r = 0.64)

and Hilo (r = 0.53). These correlations are consistent with transport of SO2 from the vents to the 

NPS stations, continuing north toward Mountain View, and further north to the Hilo monitor. 

In contrast, when SO2 concentrations are high at the Pahala and Ocean View monitors,

concentrations at the Mountain View and Hilo monitors are often low. There is also a slight 

negative correlation during these circumstances between the Pahala and Mountain View

monitors (r = -0.21), and the Pahala and Hilo monitors (r = -0.17).

13 These results are consistent 

with volcanic emissions being transported by trade winds to Pahala and Ocean View and 

conversely during Kona winds to Hilo and Mountain View. 

Monitors north of Kilauea: Hilo and Mountain View Specific Analysis

The majority of anthropogenic SO2 emissions on the island are from the Kanoelehua Hill and 

Puna electric power plants with combined 2014 SO2 emissions of 2,376 tpy (2015 

 10 See 2015 Demonstration, pp.33 and 88. 11 See 2015 Demonstration, Figures 2-20 and 2-21. 12See 2015 Demonstration, Figures 3-2 – 3-13. A summary of correlations between all the sites is presented in the 

2015 Demonstration, Table 3-5 at p.77 13 See 2015 Demonstration, p.40.
Page 8 of 13

Demonstration, Figure 1). Kanoelehua Hill (1,852 tpy SO2 in 2014) is located 4.1 miles to the 

east of the Hilo monitor and Puna (524 tpy SO2 in 2014) is located 4.1 miles to the northeast of 

the Mountain View monitor. Due to the proximity and magnitude of these sources, HDOH 

performed additional analysis to assess the effects of the power plants on monitored 

concentrations and to add to the weight of evidence supporting the conclusion that emissions 

from the volcano caused the flagged exceedances. 

Figure 3-15 in the 2015 Demonstration shows a distinct seasonal cycle in monthly mean and 

maximum SO2 concentrations at the Hilo and Mountain View monitors.

14 Concentrations peak 

October – March and are at a minimum during trade wind months of April – September. The 

correlation between monthly mean and monthly maximum concentrations at the two sites are r =

0.94 and 0.68, respectively. Figures 3-23 through 3-25 show 2012-2014 daily average power 

generation at the Kanoelehua Hill and Puna facilities. No significant seasonal cycle is seen in this 

data that would explain the observed seasonal cycle in monthly mean and maximum SO2

concentrations. Additionally, the atmospheric lifetime of SO2 peaks in summer when cloud cover 

is smallest, so the observed SO2 seasonality cannot be attributed to atmospheric chemistry.15 The 

seasonal cycle is consistent with persistent trade winds blowing Kilauea emissions to the south in 

the summertime and Kona wind conditions blowing volcanic emissions toward the Mountain 

View and Hilo monitors in the wintertime.

Figure 3-16 in the 2015 Demonstration shows wind roses at the Hilo and Mountain View 

monitors. The area is governed by a land sea-breeze with winds approaching from the west 

(from the land) in the evening/night and from the northeast (from the sea) in the 

morning/afternoon. SO2 pollution roses show that generally the highest SO2 concentrations at 

both locations are associated with winds approaching from a southerly direction, consistent with 

the location of Kilauea Volcano. 

To quantify the impact of the power plants, HDOH analyzed hourly SO2 monitored values from 

the Hilo and Mountain View monitors in a two-step approach to select data that were less likely 

to be influenced by the volcano. First, to remove days influenced by Kona winds, which 

transport volcanic emissions to Mountain View and Hilo, HDOH removed monitored values

when winds were from the south for the measurement day or the preceding day.

16 Next, to focus 

on power plant-influenced hours, HDOH selected data to focus on local winds arriving from the 

power plants’ general direction: north of Mountain View (0-90o, 270-360o) and east of Hilo (0 -

180o). Based on this filtered 2012-2014 dataset, HDOH concluded that the maximum SO2

concentrations at the Hilo and Mountain View monitors that could be attributed to power plants 

would be 15.8 ppb and 12.3 ppb, respectively.17 While the filtered dataset could have some 

remaining volcanic influence (e.g., from the rift zone or due to recirculation), HDOH asserts 

 14 See 2015 Demonstration, Figure 3-15 at p. 53. 15 The atmospheric lifetime is the average time an SO2 molecule will spend in the atmosphere before being 

chemically converted to sulfate aerosol or removed by dry/wet deposition.

16 HDOH used wind data from the NPS HAVO-VC monitoring site to reflect when southerly winds were 

transporting Kilauea emissions to the north toward Hilo and Mountain View. 17 At Hilo, 12.3 ppb was the maximum value of the filtered dataset. At Mountain View, two data points were 

removed, 72.4 and 20.2 as being consistent with volcanic emissions. No data points at either site exceeded the 

NAAQS.
Page 9 of 13

these results are a conservative estimate for the maximum concentrations attributable to the 

power plants at Mountain View and Hilo.18 Both results are well below the 2010 1-hour SO2 

NAAQS of 75 ppb. 

Monitors South of the Volcano: Pahala and Ocean View Specific Analysis

Mean and maximum SO2 concentrations at Pahala correlate reasonably well with those at Ocean 

View (r = 0.34 and r = 0.26, respectively). While the magnitude of these values is not as large as 

those associated with correlations between Hilo and Mountain View, this observation is 

consistent with the complexity of the transport path from Pahala to Ocean View. Specifically, 

SO2 is transported clockwise around the southern edge of the island and up the leeward coast to 

Kona. Throughout this process, diurnal winds move the SO2-containing air mass out over the 

water and back inland. Concurrently, SO2 is removed from the air mass through dilution 

processes (e.g., conversion to sulfate particulates). In addition, when the very large magnitude of 

the SO2 concentration levels at Pahala (frequently more than 500 ppb to more than 1000 ppb) 

and Ocean View (frequently about 300 ppb to more than 1000 ppb) are considered, along with 

the lack of nearby significant sources, Kilauea Volcano is the only reasonable source of 

exceedances at these monitors. 

Flagged Data

HDOH reviewed the hourly SO2 concentrations associated with the Hilo, Mountain View, 

Pahala, and Ocean View monitors with respect to the winds measured at the HAVO-OB monitor. 

For Hilo and Mountain View, if any measured winds from HAVO-OB were from the south, 

HDOH concluded that volcanic emissions caused all flagged measurements in AQS greater than 

or equal to 75.5 ppb for that day. For Pahala and Ocean View, if any measured winds from the 

HAVO-OB were from the north, HDOH concluded that volcanic emissions caused all flagged 

measurements in AQS for that day.19

EPA has reviewed HDOH’s analysis, as summarized above, and EPA concurs that there was a 

clear causal relationship between uncontrollable emissions generated from Kilauea Volcano and 

the exceedances measured at the Hilo, Mountain View, Ocean View, and Pahala air monitoring

stations.

5. Concentrations in Excess of Normal Historical Fluctuations (HF)

Pursuant to 40 CFR § 50.14(c)(3)(iv)(C), the demonstration must show that “the event is 

associated with a measured concentration in excess of normal historical fluctuations.” There is 

no “bright line” or specific threshold test for this requirement, but concentrations in the high 

percentiles can provide supporting evidence.

20

 18 For a full description of the approach see 2015 Demonstration, Section 3.2.5.5, pp. 72-74.

19 HDOH repeated this analysis using the HAVO-VC data and found no inconsistencies in SO2 measurements

flagged. See 2015 Demonstration p.78. 20 72 FR 13569, March 22, 2007.
Page 10 of 13

The 2015 Demonstration, Figure 5-1 shows the 99th percentile SO2 concentrations measured at 

the Hilo air monitoring station for 2000-2014. A spike is seen in the 2008 value, coinciding with 

the opening of the new Halema‘uma‘u vent. From 2000-2007, values range from 121 ppb to 267 

ppb (before Halema‘uma‘u event). The value spikes again in 2010 to 745 ppb despite the 

significant decrease in SO2 emissions from Hilo power plants beginning in 2010 (2015 

Demonstration, Figure 4-2). No large spikes are recorded at the monitor in 2005, 2006, 2007, and 

2009 when emissions from power plants on the Hilo side of the island were high relative to those 

from 2010 to 2014 (2015 Demonstration, Figure 4-2). The large spikes appear to be associated 

with increased SO2 emissions at the volcano’s summit after the Halema’uma’u vent opened in 

2008. As shown in the 2015 Demonstration, Figure 2-16, higher amounts of SO2 were 

discharged from the summit between 2008 and 2014 relative to that between 1992 and 2007. 

EPA concurs that HDOH’s analysis sufficiently establishes that the SO2 concentrations measured 

at Kilauea were in excess of normal historical fluctuations.

6. No Exceedance But For the Event (NEBF)

The NEBF demonstration is similar to and informed by the demonstration of the nRCP and CCR

requirements and is expected to show that the measured concentration would have been below 

the applicable NAAQS without the effect of the event.

HDOH provided a summary of the analyses and information regarding both the nRCP (discussed 

below) and CCR requirements and stated that, “on the basis of the weight of evidence described 

above, the federal 1-hour SO2 standard in 2012-2014, in the Hilo, Mountain View, Ocean View, 

and Pahala areas would not have occurred but for the continuous volcanic emissions from 

Kilauea volcano.”21

Based on the 2012-2014 data, the maximum SO2 concentrations at the Hilo and Mountain View 

stations that could be attributed to power plants in the vicinity of these monitors would be 15.8 

ppb and 12.3 ppb, respectively, well below the 2010 1-hour SO2 NAAQS of 75 ppb. 

EPA considered the previously-discussed analysis of volcanic emissions versus anthropogenic 

emissions, satellite information regarding SO2 and NO2 concentrations, SO2 monitoring

concentrations and wind data, analysis of emission source locations and transport pathways, and 

estimates of the effects of local anthropogenic sources. Based on our review of this information, 

EPA concurs that HDOH’s analyses satisfy the NEBF criterion.

7. Criteria Set Forth in 40 CFR §50.1(j) 

7.1. Affects Air Quality (AAQ)

As stated in the preamble to the EER, the event in question is considered to have affected air 

quality if it can be shown that there is a clear causal relationship between the monitored 

exceedance and the event, and that the event is associated with a measured concentration in 

excess of normal historical fluctuations.22 The criteria and the evidence supporting this criterion 

 21 See 2015 Demonstration, p. 117. 22 72 FR 13569, March 22, 2007.
Page 11 of 13

are discussed in detail in Sections 5.0 and 6.0 above and allow EPA to reasonably concur that the 

volcanic events in question affected air quality.

7.2. Natural Event

The EER states a “[n]atural event means an event in which human activity plays little or no 

direct causal role.”23 Therefore, ambient SO2 concentrations due to volcanic emissions will be 

considered for treatment as an exceptional event. The analysis submitted by HDOH and 

reviewed by EPA above, shows that Kilauea volcanic emissions caused each of the identified 

exceedances (Section 4.0 of this TSD) and that the exceedances would not have occurred but-for 

the volcano (Section 6.0 of this TSD). We concur that the events identified should be considered 

natural, volcanic events.

7.3. Not Reasonably Controllable or Preventable (nRCP)

A determination of whether a particular event was reasonably controllable or preventable 

depends on the specific facts and circumstances surrounding the event. Therefore, EPA addresses 

this and other criteria of the EER on a case-by-case basis.24 We conclude that HDOH has 

demonstrated that the flagged exceedances were caused by natural, volcanic events. Volcanic 

emissions cannot be prevented and are uncontrollable, therefore EPA concurs that HDOH has 

satisfied the nRCP criterion.25

HDOH provided additional information on the current set of required controls for all stationary 

permitted sources, temporary permitted sources, and airports (together, “anthropogenic sources” 

or “anthropogenic emissions”). While we are not reviewing this material for the purposes of 

evaluating the nRCP element, we summarize the provided information below. HDOH included

the following: facility name, distance from the monitoring stations, equipment type, emission 

totals, applicable regulatory measures, and compliance information during exceedance days.26

Air pollution control measures for minimizing SO2 from permitted sources include Hawaii 

Administrative Rules (HAR), Hawaii’s Renewable Energy Portfolio Standard (RPS), Hawaii’s 

Energy Efficiency Portfolio Standard (EEPS), Prevention of Significant Deterioration/Best 

Available Control Technology (PSD/BACT), New Source Performance Standards (NSPS), and 

National Emission Standards for Hazardous Air Pollutants (NESHAP).

The majority of anthropogenic SO2 emissions on the island are from the Kanoelehua Hill and 

Puna electric power plants, which emitted 1,852 and 524 tons SO2 in 2014, respectively. By 

comparison, total SO2 emissions from anthropogenic sources on the Island of Hawaii were 2,711 

tons in 2014. Kanoelehua Hill is located 6.5 km to the east of the Hilo monitoring station. Puna 

is located 6.6 km to the northeast of the Mountain View station, and is 9 km south of Kanoelehua 

 23 72 FR 13580, March 22, 2007. 24 72 FR 13562, March 22, 2007. 25 For uncontrollable natural events, such as wildfires, EPA has stated that air agencies can document reasonable 

controls with a brief statement. See, “Interim Exceptional Events Rule, Frequently Asked Questions,” U.S. EPA, 

May 2013, at pp. 23-24; see also, Stephen Page, Director, Office of Air Quality Planning and Standards to Regional 

Air Directors, “Interim Guidance to Implement Requirements for the Treatment of Air Quality Monitoring Data 

Influenced by Exceptional Events,” May 10, 2013, at pp. 4-5, footnote 10. 26 See 2015 Demonstration, Chapter 4.
Page 12 of 13

Hill (Figure 1). These power plants are subject to Hawaii Administrative Rules, PSD, NSPS, 

and NESHAP requirements as described in 2015 Demonstration Tables 4-2, pages 85-86 and 4-

23, pages 108-109. There are no significant sources of anthropogenic SO2 located near the 

Pahala and Ocean View monitors.

According to the 2015 Demonstration, SO2 emissions from the power plants on the Hilo side of 

the Island of Hawaii have decreased significantly starting in 2010 as a result of Hawaii’s 

Renewable Portfolio Standard and Energy Efficiency Portfolio Standard, which establish 

reductions in greenhouse gases and increase use of renewable energy. Emissions and are 

projected to decline further as the facilities are planned for closure and decommissioning.27 

HDOH inspects permitted sources regularly, with Title V sources inspected each year and minor 

sources inspected at least every 3 to 5 years to ensure equipment is operated within the terms of 

the permits. HDOH also investigates public complaints that may involve Title V or minor 

sources. Additionally, as part of preparing its exceptional events demonstration, HDOH reviewed 

inspection reports and correspondence from 2012 to 2014 and found no indication of source 

noncompliance with standards involving SO2 emissions.28

The United States Geological Survey (USGS) provides daily reports of volcanic emissions from 

Kilauea.29 It should be noted that, starting in 2014, USGS began using a more accurate technique 

to report emissions from the Halema’uma’u vent, resulting in a two to four-fold increase in 

reported values when compared to previous years. This increase reflects the change in technique 

rather than a change in the volcanic emission rates. Pu’u O’o emissions are approximately an 

order of magnitude lower than emissions from Halema’uma’u. Reported 2014 SO2 emissions 

from both locations at the Kilauea Volcano were 2,140,183 tons. A comparison of volcanic 

emissions to those from anthropogenic sources on the Island of Hawaii (2,711 tons SO2 in 2014) 

shows that SO2 from anthropogenic sources comprise 0.1% of the combined yearly emissions 

from anthropogenic and volcanic SO2 sources.30

The State of Hawaii, including Hawaii County (i.e., the Island of Hawaii), is currently designated 

“better than national standards” for the 1971 primary and secondary SO2 NAAQS.31 To date, 

EPA has not promulgated area designations for either the State of Hawaii or Hawaii County for 

the 2010 1-hour primary SO2 NAAQS.32

Based on the above, EPA concurs that HDOH’s exceptional events analyses satisfy the nRCP 

element. 

 27 The Puna facility is scheduled to be deactivated in 2018 and decommissioned in 2020, Kanoelehua Hill 5 is 

scheduled to be deactivated in 2018 and decommissioned in 2022, and Kanoelehua Hill 6 is scheduled to be 

deactivated in 2022 and decommissioned in 2024. See 2015 Demonstration, p.87. Emissions from power plants near 

Hilo are projected to decrease to a total of 1,852 tons per year (tpy) by 2018, 1,148 tpy by 2020, and 0.2 tpy SO2 by 

2022. See 2015 Demonstration Figure 4-3 at p. 88 28 See 2015 Demonstration, p.111.

29 USGS, Hawaiian Volcano Observatory, "Recent Kilauea Status Reports, Updates, and Information Releases, 

HAWAIIAN VOLCANO OBSERVATORY DAILY UPDATE": http://hvo.wr.usgs.gov/activity/kilaueastatus.php. 30 See 2015 Demonstration, Figure 4-7 at p.103. 31 See 40 CFR §81.312. 32 78 FR 47191, August 5, 2013.
Page 13 of 13

8. Procedural Requirements

The EER at 40 CFR §50.14(c) requires that data claimed to be due to an exceptional event must 

be flagged in the AQS database and an initial description of the event be provided to EPA by 

July 1 of the year following the event. The EER at 40 CFR §50.14(c)(3)(i) requires that the State 

submit a demonstration to EPA within 3 years of the event that has been subject to public notice 

and opportunity for comment, and that any public comments be submitted along with the 

demonstrations. 

HDOH flagged the events in AQS in accordance with 40 CFR §50.14. On December 17, 2015

HDOH submitted a package to EPA for the 2012-2014 events. By publication in two local 

newspapers, HDOH notified the public of an opportunity to comment on the 2015 Demonstration

from November 16, 2015 to December 16, 2015. In addition, HDOH posted the 2015 

Demonstration on its website. No public comments were received.

Immediate public notification of NAAQS exceedances is provided on the HDOH website.

33 

Notification of the 2012-2014 exceedances of the 1-hour SO2 NAAQS were also posted once the 

data were validated. In addition, the State of Hawaii’s Clean Air Branch maintains a publically 

available SO2 advisory page, Hawaii Short Term SO2 Alert Index,

34 and advises residents to 

receive updates and advice from the website and Hawaii Civil Defense local radio broadcasts. 

Additionally, the Big Island (i.e., the island of Hawaii) Emergency Operations Center

coordinates efforts from various government agencies. Based on this information, EPA concurs 

that HDOH has met the EER procedural requirements for this demonstration. 

9. Conclusion

Documentation submitted by HDOH claims that emissions emanating from the Kilauea Volcano 

are natural, volcanic exceptional events, which caused the flagged exceedances listed in the 2015 

Demonstration, Appendix D at the Hilo, Mountain View, Ocean View, and Pahala air monitoring 

stations. As described above, EPA has reviewed this information and determines that the weight 

of evidence submitted by HDOH is sufficient for concurrence on the flagged data for the 

monitors identified in the 2015 Demonstration, Appendix D. These concurrences do not 

constitute final EPA action to exclude these data from consideration for purposes of determining 

the attainment status of the area. Final actions will come only after EPA completes notice and 

comment rulemaking on any such determinations. 

 33 http://health.hawaii.gov/cab/notification-of-exceedance-of-a-national-ambient-air-quality-standard 34 http://www.hiso2index.info