Mr. Guy Donaldson, Chief, Air Planning Section (6PD-L), 

Environmental Protection Agency, Region 6 

1445 Ross Avenue, Suite 1200 

Dallas, Texas 75202-2733 

Via Regulations.gov 

September 20, 2013 

Re: Proposed Approval of Oklahoma Regional Haze SIP Revision 

 Docket ID No. EPA-R06-OAR-2013-0227 

Dear Mr. Donaldson, 

 I write on behalf of Sierra Club and its 2.1 million members and supporters, 

including more than 3,000 members in Oklahoma, in strong support of the proposed 

approval of the Regional Haze SIP Revision.1 The SIP Revision meets federal requirements 

to reduce regional haze and interstate pollution from the Northeastern coal-fired power 

plant in Oologah, Oklahoma. In addition to protecting scenic views in the region’s most 

treasured parks, Public Service Company of Oklahoma’s (PSO’s) commitment to retire one 

Northeastern unit by 2016, along with retrofits and a steady ramp-down of capacity at the 

other toward retirement in 2026, will have enormous public health benefits. The SIP 

Revision is also a more cost-effective solution than requiring the installation of expensive 

scrubbers on both units. For these reasons, Sierra Club urges EPA to promptly approve and 

finalize the SIP Revision and withdrawal of the FIP as it relates to Northeastern. 

I. The SIP Revision Protects Our Parks. 

 In order to protect the “intrinsic beauty and historical and archeological treasures” 

at national parks, wilderness areas, and other designated “Class I” areas,” Congress set a 

national goal to reduce human-caused haze pollution and achieve natural visibility 

conditions by 2064.2 The Clean Air Act requires states to design an implementation plan to 

                                                            

1 More than 250 individual Sierra Club members have also submitted comments in support 

of EPA’s proposed action. 

2 See H.R. Rep. No.95-294, at 203-04 (1977); See 42 U.S.C. § 7491(a)(1); 40 C.F.R. § 

51.308(d)(1)(i)(B). 
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reduce haze from air pollution sources within its borders that cause or contribute to 

visibility impairment – i.e., hazy views – at any protected area located within or beyond 

that state’s boundaries. 

Haze-forming pollution from the Northeastern plant currently impacts visibility in 

four popular scenic areas in the region: Wichita Mountains National Wildlife Refuge in 

Oklahoma, Caney Creek Wilderness and Upper Buffalo Wilderness in Arkansas, and 

Hercules Glade Wilderness in Missouri. The Wichita Mountains is the oldest managed 

National Widlife Refuge in the U.S. Fish and Wildlife system. It was designated as a forest 

preserve in 1901 and became a NWR in 1903. Scenic mountains and prairies make up the 

refuge’s 59,020-acre landscape.3 In 2011, over 118,000 people visited the refuge for 

enjoyment and recreation.4 Hercules Glades, Caney Creek and Upper Buffalo are also 

valuable units of the national forest system. Hercules Glade includes some of “the most 

scenic and unique country in the Midwest,” while Caney Creek and Upper Buffalo possess 

breathtaking views of the region from ridge tops and steep slopes.5 Unfortunately, the 

views at these recreational areas are suffering from pollution from the region’s coal-fired 

power plants. Visitors at Caney Creek can experience views up to 81 miles on a clear air 

day, but on hazy days this view is reduced to just 17 miles.6 If visibility were at natural 

conditions, people would be able to see up to 170 miles into the distance.7 In Upper Buffalo, 

visitors can see only 18-78 miles into the distance, but under natural visibility conditions 

they would be able to see between 79 and 171 miles.8 

 Current emissions of haze-forming pollution from the Northeastern Units 3 and 4 

amount to approximately 32,000 tons per year sulfur dioxide (SO2) and more than 14,000 

tons per year nitrogen oxides (NOx).9 To reduce SO2 emissions, the SIP Revision makes 

enforceable PSO’s commitment to retire one unit by April 16, 2016 and requires that PSO 

retrofit the other with Dry Sorbent Injection by the same date.10 PSO will reduce the 

remaining unit’s capacity significantly starting in 2021, and retire the unit no later than 

December 31, 2026. The planned replacement power is a combination of cleaner resources: 

                                                            

3 U.S. Fish and Wildlife, Wichita Mountains Wildlife Refuge, 

http://www.fws.gov/refuge/Wichita_Mountains/about.html. 4 Phone interview between National Parks Conservation Association staff and Wichita 

Mountains Visitor Center representative (July 24, 2012). 

5 United States Forest Service, Hercules Glades Wilderness, 

http://www.fs.usda.gov/recarea/mtnf/recreation/hiking/recarea/?recid=21754&actid=51; See 

Univ. of Montana, College of Forestry, www.wilderness.net. 6 U.S. Dep’t of Agriculture, Caney Creek Wilderness – Natural Background Visiblity, 

http://www.fs.fed.us/air/technical/class_1/wilds.php?recordID=10. 7 Id. 

8 Id. 

9 Oklahoma Regional Haze SIP Revision (Mar. 20, 2013), at 6 (Table II-1). 

10 As EPA has already approved the portion of the Oklahoma SIP that addresses NOx, the 

SIP Revision properly focuses on SO2.  
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purchased power from an existing combined cycle natural gas plant, energy efficiency, and 

demand response programs.11

Implementation of the SIP Revision will drastically reduce both SO2 and NOx 

emissions by 2016 and fully eliminate them by 2026. By April 16, 2016, assuming an 85% 

capacity factor at the unit that continues operating past that date, emissions will be 

slashed to 7,111 tons per year SO2 and 2,667 tons per year NOx.12 Particulate matter 

emissions, which also contribute to haze and public health problems, will also see a drastic 

reduction. 

Clearing the haze at these parks will both protect the health of those who recreate 

there and promote local tourism by decreasing the number of days when pollution impairs 

scenic views. The Oklahoma Department of Environmental Quality’s (ODEQ) BART 

Determination predicts that the SIP Revision will reduce visibility impairment caused by 

the plant’s SO2 and NOx pollution by 80% or more in each of these regions compared with 

current conditions.13 For example, instead of contributing to an average of 1.5 “deciviews”14

of visibility impairment at Wichita Mountains, as it does now, after the retirement of one 

unit and installation of SO2 and NOx controls on the remaining unit, it will cause only .295 

deciviews of impairment. Likewise, the reduction of nitrogen oxides (NOx ) will result in 76 

fewer days each year in which the Northeastern plant is contributing to visibility 

impairment in the Wichita Mountains, compared with the baseline, and 95 fewer days of 

impairment in Caney Creek Wilderness.15 While EPA’s additional modeling analysis 

tempers these estimates somewhat by adjusting the baseline average impairment to reflect 

a lower SO2 emission rate, the benefits to visibility are still significant. 

The improvements in visibility attributable to the SIP Revision have a tangible 

economic benefit. Sierra Club members and other Americans visit national parks, national 

forests, and wilderness areas to recreate and see amazing views. In doing so, they 

contribute substantially to the American economy. In 2010, activities associated with 

                                                            

11 Direct Testimony of Steven L. Fate on Behalf of Public Service Company of Oklahoma & 

Direct Testimony of Scott C. Weaver on Behalf of Public Service Company, Oklahoma 

Corporation Commission, Cause No. PUD 2012000054 (Sept. 26, 2012), attached as Exs. 1 

& 2. 

12 Oklahoma Regional Haze SIP Revision (June 14, 2013) at 8 (Table II-3). 

13 Id. at 8, Table II-4. 

14 “The deciview metric provides a scale for perceived visual changes over the entire range 

of conditions, from clear to hazy. Under many scenic conditions, the average person can 

generally perceive a change of one deciview. The higher the deciview value, the worse the 

visibility. Thus, an 

improvement in visibility is a decrease in deciview value.” U.S. EPA, Regulatory Impact 

Analysis for the Final Clean Air Visibility Rule or the Guidelines for Best Available Retrofit 

Technology (BART) Determinations, EPA-452/R-05-004 (June 2005). 

15 Oklahoma Regional Haze SIP Revision (June 14, 2013), Appendix II, Supplemental 

BART Determination Information (Nov. 9, 2012) (hereinafter “Supplemental BART 

Determination”), at 3-1 (Table 3-1). 
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national parks and other Department of Interior lands provided more than 2.2 million jobs, 

which generated $377 billion in economic activity.16 National Wildlife Refuges and other US 

Fish and Wildlife Service land management contributed over $4 billion to the economy and 

supported over 32,000 jobs in 2010.17 According to the Department of Agriculture, national 

forest land recreation visitors spend nearly $13 billion each year in rural communities 

surrounding national forests and wilderness areas.18 This spending results in over $14 

billion to the GDP and supports over 224,000 full and part time jobs.19 As scenic views are 

an important part of the visitor experience at these parks, clearing away human-caused 

haze — allowing for visibility exceeding 170 miles in some areas — will serve to make them 

even more attractive destinations, with the corresponding economic benefit. Visitors to 

National Wildlife Refuges, Wilderness Areas, and National Parks consistently rate 

visibility and clear scenic vistas as one of the most important aspects of their experience.20

Compared to EPA’s federal implementation plan (“FIP”), which EPA is proposing to 

replace with the SIP Revision, the SIP Revision provides more flexibility for PSO to comply 

with its obligations under the Clean Air Act’s haze provisions, but does not compromise 

public health or visibility. The FIP requires PSO to meet an SO2 emission limit of .06 

lbs/mmbtu, consistent with emissions reductions achievable with Dry Flue Gas 

Desulfurization units with Spray Dry Absorbers, by January 27, 2017 (five years after the 

rule’s effective date). While benefits to visibility as of January 27, 2017 would be slightly 

greater under the FIP, the advantage is temporary. The FIP scenario may have somewhat 

greater benefits for several years, but the SIP Revision better achieves the overall goals of 

the Regional Haze program because emissions from both units will be completely 

eliminated by 2026.21 Under the FIP scenario, both units are permitted to continue 

operating and polluting beyond 2026 and would likely do so until the plants are no longer 

economical to operate, regardless of the health or visibility impacts. By 2026, 

Northeastern’s contribution to haze in the region’s parks will be zero under the SIP 

Revision whereas under the FIP scenario the plants would continue to contribute to more 

than 1.5 deciviews of impairment (at much greater cost). 

In fact, the benefits of the SIP Revision for visibility as compared to the FIP are 

likely understated in ODEQ’s and EPA’s analysis, even for the first five years. ODEQ 

                                                            

16 Southwick Associates, The Economics Associated with Outdoor Recreation, Natural 

Resources Conservation and Historic Preservation in the United States, Oct. 10, 2011 at 4, 

available at 

http://www.trcp.org/assets/pdf/The_Economic_Value_of_Outdoor_Recreation.pdf. 17 Id. 

18 U.S. Forest Service, National Visitor Use Monitoring Results USDA Forest Service 

National Summary Report, 2005-2009, at 2, available at 

http://www.fs.fed.us/recreation/programs/nvum/nvum_national_summary_fy2009.pdf. 19 Id. 

20The Clean Air Task Force, Out of Sight: Haze in Our National Parks, Sept. 200, at 2, 

available at http://www.catf.us/resources/publications/files/Out_of_Sight.pdf . 21 Supplemental BART Determination, at 4-7; Oklahoma Regional Haze SIP Revision, 

Appendix III (making enforceable PSO’s commitment to retire Northeastern). 
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compares emission rates with DSI and NOx limits of .15 lb/mmbtu on one unit and the 

other unit’s retirement as of April 16, 2016 with the dry scrubber/SDA and the same NOx 

limit as of December 31, 2017 pursuant to the FIP. See Oklahoma Regional Haze SIP 

Revision (June 14, 2013), Appendix II, Revised BART Determination (hereinafter “Revised 

BART Determination”), pp. 7-10. EPA appears to have accepted this approach, which has 

several implications for the analysis. First, ODEQ did not evaluate the likely reductions in 

visibility impairment as the second unit ramps down capacity between 2016 and 2026, 

thereby reducing emissions. As a result, it is unclear how long the FIP scenario would hold 

even its small advantage in terms of visibility improvements. Additional modeling taking 

into account the emissions reductions after 2016 would provide further support for the SIP 

Revision. Another advantage of the SIP Revision is that it requires an earlier 

implementation of lower NOx emission limits than in the original SIP or EPA’s FIP. See 

Revised BART Determination at 12. As noted by ODEQ, “This early implementation 

schedule reducing emissions by 43% will provide previously unanticipated improvements in 

visibility as well as reductions in local formation and interstate transport of ozone.” ODEQ 

did not compare the reductions in visibility impairment during the three years from 

December 31, 2013, when the SIP Revision begins to require reductions, to January 2017, 

when the FIP would have done so. Similarly, the SIP Revision deadline for SO2 reductions 

of April 16, 2016 is 8.5 months earlier than the January 2017 FIP deadline, leading to an 

additional reduction of 26,700 tons of SO2. ODEQ did not model these reductions when 

comparing the visibility benefits of the SIP Revision with those of the FIP. Nor did EPA 

model these reductions in any of the scenarios it considered. Although not modeled, EPA 

does correctly “anticipate that this early implementation schedule [for NOx] will provide 

additional improvements in visibility.” TSD Document at 25. 

Overall, the SIP Revision is the less polluting option compared to the FIP. DEQ 

calculates that due to the decreased capacity utilization and early shutdown schedule, 

cumulative SO2 and NOx emissions from Northeastern Units 3 and 4 will ultimately 

amount to only 36% of the emission that could be emitted under the FIP. See Revised BART 

Determination at 12. This approach is consistent with Congress’s goal of eliminating 

human-caused haze by 2064, moving Oklahoma toward that goal more quickly than would 

the FIP. 

 Sierra Club recognizes that EPA has not taken the approach of comparing the SIP 

Revision to the FIP. Appropriately, EPA has simply reviewed ODEQ’s BART analysis for 

consistency with the Clean Air Act and the BART Guidelines. However, because in practical 

terms the Revised SIP will replace the FIP, Sierra Club agrees with ODEQ that the 

SIP/FIP comparison is worthwhile. The many environmental advantages of the proposed 

SIP Revision compared to the FIP – which would perpetuate the burning of coal at both 

units, and all its associated pollution, for years to come –weigh heavily in favor of the SIP 

Revision. 

II. The SIP Revision Protects Our Health. 

Pollutants that cause visibility impairment also harm public health. NOx is a 

precursor to ground level ozone, which is associated with respiratory diseases, asthma 
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attacks, and decreased lung function. In addition, NOx reacts with ammonia, moisture, 

and other compounds to form particulates that can cause and worsen respiratory diseases, 

aggravate heart disease, and lead to premature death.22 Similarly, SO2 increases asthma 

symptoms, leads to increased hospital visits, and can form particulates that aggravate 

respiratory and heart diseases and cause premature death.23 Both these pollutants 

contribute to formation of fine particulate matter (PM). PM can penetrate deep into the 

lungs and cause a host of health problems, such as aggravated asthma, chronic bronchitis, 

and heart attacks.24 By drastically reducing these pollutants and requiring the eventual 

retirement of the Northeastern plant, the SIP Revision will have significant public health 

benefits. 

 The Clean Air Task Force, a not-for-profit advocacy and research organization, 

commissioned a study by Abt Associates to quantify death and other health effects from 

coal-fired power plants’ PM pollution. The study’s conclusions for the Northeastern plant 

are reproduced below. Each number represents the impact on an annual basis. 

Northeastern 

Rogers County, Oklahoma 

Deaths: 62 

Heart Attacks: 94 

Asthma Attacks: 1,100 

Hospital Admissions: 44 

Chronic Bronchitis: 38 

Asthma ER Visits: 67 

Source: http://www.catf.us/fossil/problems/power_plants/existing/map.php?state=Oklahoma. 

By dramatically reducing the PM precursors SO2 and NOx, and directly emitted PM, the 

SIP revision will save lives and reduce hospital visits and asthma attacks. 

                                                            

22 EPA, Health – Nitrogen Dioxide, http://www.epa.gov/air/nitrogenoxides/health.html (last 

visited Apr. 1, 2011). 

23 EPA, Health – Sulfur Dioxide, http://www.epa.gov/air/sulfurdioxide/health.html (last 

visited Apr. 1, 2011). 

24 EPA, Health & Environment – Particulate Matter, 

http://www.epa.gov/air/particlepollution/health.html (last visited Apr. 1, 2011); National 

Ambient Air Quality Standards for Particulate Matter; Final Rule, 78 Fed. Reg. 3086, 3088 

(Jan. 15, 2013), available at http://www.gpo.gov/fdsys/pkg/FR-2013-01-15/pdf/2012-

30946.pdf. (“EPA is revising the annual PM2.5 standard by lowering the level from 15.0 to 

12.0 mg/m3 so as to provide increased protection against health effects associated with 

long-and short-term exposures.... This action provides increased protection for children, 

older adults, persons with pre-existing heart and lung disease, and other at-risk 

populations against an array of PM2.5- related adverse health effects that include 

premature mortality, increased hospital admissions and emergency department visits, and 

development of chronic respiratory disease.”) 

 
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The Northeastern plant’s NOx emissions, and their contribution to ozone, are 

particularly problematic for the region’s efforts to maintain healthy air quality levels. Tulsa 

has recently struggled with numerous “ozone-alert” days during the summer season. EPA is 

considering revising the 8-hour ozone National Ambient Air Quality Standard (NAAQS) 

from 75 ppb down to 60-70 ppb. EPA has stated that it will propose the revision in 2013 and 

issue a final rule in 2014. EPA predicts that if the NAAQS for ozone is revised to 65 ppb, 

the Tulsa metropolitan area will fall out of attainment.25 A “nonattainment” designation 

could have significant economic impacts as Tulsa is forced to find ways to cut existing 

emissions and limit new emissions-causing development. As DEQ has noted, the NOx 

reductions from the SIP Revision will help address local formation and interstate transport 

of ozone whereas “the FIP scenario provides no further improvement in ozone.” Revised 

BART Determination at 11. 

Northeastern’s SO2 emissions also threaten to cause exceedances of federal air 

quality standards. Sierra Club and EPA Region 6 have both conducted air dispersion 

modeling showing that the plant’s emissions contribute to ambient SO2 levels that exceed 

the 1-hour federal standard.26 The SIP Revision will address this problem by dramatically 

reducing SO2 emissions.27 

 In addition to SO2, NOx, and PM, Northeastern releases approximately 210 pounds 

of mercury to the environment each year.28 Atmospheric deposition of one gram of mercury 

is enough to contaminate fish in a 20-acre lake.29 The 210 pounds produced by Northeastern 

each year amounts to around 95,000 grams. The SIP Revision will drastically reduce these 

harmful releases by 2016 and fully eliminate them by 2026. 

 As discussed further below, the Clean Air Act and the regulations governing DEQ’s 

BART determination instruct DEQ to consider the “non air-quality environmental impacts,” 

of emissions of the pollutant in question. 70 Fed. Reg. 39,104, 39,169 (July 6, 2005). “Such 

                                                            

25EPA, Counties Projected to Violate Primary 8-hour Ground-Level Ozone Standard in 

2020, at http://www.epa.gov/glo/pdfs/CountyOzoneLevels2020primary.pdf. 

26 Preliminary 1-Hour SO2 Modeling of Some Coal-Fired EGUs in Oklahoma: Preliminary 

Results, EPA Region 6 Air Modeling Team (2011); Letter from A. Issod, Sierra Club to E. 

Terrill, Air Quality Division Director, attaching modeling report of C. Sears (June 3, 2011). 

27 Sierra Club’s air dispersion modeling for the Northeastern plant demonstrated that the 

Northeastern plant’s emissions causes ambient air concentrations of SO2 that are 

significantly higher than the 2010 1-hour SO2 NAAQS (259.3 ug/m3, compared with the 

NAAQS of 196 ug/m3). On the assumption that ambient air concentrations correlate to 

emissions on a roughly linear basis, eliminating half of the plant’s hourly SO2 emissions by 

2016 should resolve this problem. 

28 See EPA, Toxic Release Inventory, TRI Explorer, at

http://iaspub.epa.gov/triexplorer/tri_release.facility (input Oklahoma/Rogers 

County/mercury compounds/all industries). 

29 Minnesota Pollution Control Agency, Michigan Dep’t of Natural Resources, Wisconsin 

Dep’t of Natural Resources, “Mercury in the Environment: The Waste Connection,” 1995 

(discussed at http://www.newmoa.org/prevention/mercury/mercurylake.pdf). 
8 of 18 

environmental impacts include solid or hazardous waste generation and discharges of 

polluted water from a control device.” Id. Accordingly, ODEQ and EPA can properly 

consider that the SIP Revision will ensure that all of the human health and environmental 

impacts of coal combustion will be addressed by 2026, not just selected air emissions. 

 While EPA’s proposed approval of the SIP Revision recognizes certain 

environmental benefits of the plan described in the revision, such as reductions in mercury 

deposition and water and energy usage, there are others that EPA does not mention. EPA 

should note in its final rule the full suite of environmental benefits (“non air-quality 

environmental impacts”) resulting from the phased retirement of the Northeastern plant, 

which is made enforceable by the SIP Revision. This includes impacts on water quality, 

discussed below, as well as water usage. See 70 Fed. Reg. at 39,169. 

 Coal-fired power plants produce huge amounts of coal combustion waste, or coal ash. 

Laden with heavy metals and other harmful toxics known to contaminate water supplies, 

these wastes cause injury and death to livestock and wildlife, and threaten human health 

with birth defects, cancer, and organ and neurological damage. The Northeastern plant 

currently disposes of its waste coal ash (more than 200,000 tons of it in 2011) by putting it 

into an unlined (or “clay-lined”) landfill. This natural barrier does not adequately protect 

against groundwater contamination.30 A 2011 review of water samples from groundwater 

wells contaminated by coal ash from the Northeastern plant revealed that levels of 

chromium, a cancer-causing metal, were more than four times higher than the federal 

drinking water standard.31 The enforceable commitment to retire Northeastern will help 

stem further contamination. 

Wastewater discharge from coal-fired power plants, particularly those with SO2 

scrubbers, also poses major environmental and public health problems. Scrubbers at coalfired power plants have the unfortunate consequences of transferring air pollution to water 

pollution if not properly treated.32 EPA has stated: “More than 23,000 miles of rivers and 

streams are damaged by steam electric plant discharges, which include arsenic, mercury, 

lead, boron, cadmium, selenium, 

                                                            

30 EPA, Frequent Questions: Coal Combustion Residues (CCR) - Proposed Rule. (Available 

at http://www.epa.gov/wastes/nonhaz/industrial/special/fossil/ ccr-rule/ccrfaq.htm#8.)

(“EPA’s risk assessment suggests, and damage cases confirm, that the management of 

CCRs in unlined and clay-lined landfills and surface impoundments may present risks to 

human health and the environment through leaching. For landfills and surface 

impoundments the primary concern is cancer risk from arsenic in drinking water. Surface 

impoundments also showed high non-cancer risks from cobalt and nitrate/nitrite in 

drinking water.”) 

31 Lisa Evans, Earthjustice, et al., EPA’s Blind Spot: Hexavalent Chromium in Coal Ash

(Feb. 2011), p. 7, available at http://www.psr.org/resources/epas-blind-spot-hexavalentchromium-coal-ash.html. 32 See Cleansing the Air at the Expense of Waterways, The New York Times (Oct. 12, 2009), 

at http://www.nytimes.com/2009/10/13/us/13water.html?_r=4&ref=us& (describing how 

scrubber retrofits on coal-fired power plants have lead to increased water pollution)
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 chromium, nickel, thallium, vanadium, zinc, nitrogen, chlorides, bromides, iron, 

copper and aluminum. For example, each year nearly 65,000 pounds of lead and 3,000 

pounds of mercury are discharged, leading to lowered IQs among children exposed to these 

pollutants via drinking water or by eating fish. Many of these toxic pollutants, once in the 

environment, remain there for years. Additionally, each year nearly 80,000 pounds of 

arsenic is released into surface waters, increasing the risk of cancers and other health 

effects in humans exposed to these pollutants through drinking water and by eating fish.”33 

By requiring the retirement of one coal-burning unit in 2016 and the other by 2026, 

the SIP Revision will reduce both the production of dangerous coal ash that leaks into 

groundwater supplies and the discharge of pollutants in scrubber wastewater. 

III. The SIP Revision Will Conserve Water Resources. 

 In citing the non-air quality benefits of the SIP Revision, EPA correctly recognizes 

that the SIP Revision will reduce water usage. The SIP Revision’s impact on the state’s 

dwindling water resources is important in light of the extreme drought conditions facing 

Oklahoma. In response to Sierra Club data requests in proceedings before the Oklahoma 

Corporation Commission, PSO has estimated that the increase in water consumption at the 

Northeastern plant if it were to add dry scrubbers to both units would be at least 65 times 

greater than with a retrofit of ACI and DSI at one unit pursuant to the SIP Revision.34

Under continued drought, PSO’s daily need for water resulting from scrubber retrofits could 

increase the potential for conflict with other needs in the Tulsa area. The Northeastern 

units currently intake water from the City of Tulsa, and the surrounding area includes a 

variety of farms and ranches. 

 In addition to using less water while the units are still operating, in light of PSO’s 

enforceable commitment to retire Northeastern, water currently used by one unit will be 

released for other uses by 2016, and after 2026, the units will no longer demand water 

resources pursuant to the SIP Revision. Sierra Club supports a plan that will ease pressure 

on the state’s water supplies. 

IV. The SIP Revision is Less Costly Than Requiring Scrubbers. 

Due to its agreement to phase out the Northeastern units instead of investing in 

expensive new flue gas desulfurization equipment (scrubbers) at both units, PSO estimates 

that the cost-effectiveness in terms of dollars per ton of SO2 removed is $942/ton for the SIP 

                                                            

33 EPA Fact Sheet: Proposed Effluent Limitation Guidelines & Standards for the Steam 

Electric Power Generating Industry, EPA - 821-F-13-002 (April 2013). 

34 Oklahoma Corporation Commission, Cause No. 201200054, PSO Response to Sierra Club 

Data Request 5-9 (Dec. 20, 2012) (attached hereto as Exhibit 3) (Controls pursuant to EPA 

settlement will consume approximately 11,250 gallons of water per day, compared with the 

DFGD option, which would consume approximately 737,000 - 805,000 gallons of water per 

day for two units).   
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Revision compared with $1,544/ton under the FIP.35 DEQ similarly estimates that the cost 

per ton reduction for DSI is $1,005/ton compared with $1,544/ton for scrubbers. EPA 

considered a revised cost-effectiveness analysis to account for a more realistic SO2 baseline 

and an operating life of the equipment of 10 years (2016-26). This revised analysis showed 

the cost-per-ton reduction to be $3,211/ton for scrubbers compared to $1,758/ton for DSI. 

Sierra Club has not evaluated these analyses in detail but agrees that the SIP Revision is 

more cost-effective – and, indeed, less costly overall. (Section VI below discusses costeffectiveness in more detail.) 

 Because ODEQ is charged only with revising the SIP as it pertains to BART for SO2, 

it was appropriate for EPA and ODEQ to consider the cost of control per removal of a ton of 

SO2. The scope of this cost analysis, focusing on the direct control costs for each type of 

emissions control (DSI or scrubbers) properly follows the mandatory federal guidelines for 

BART Determinations. These guidelines instruct ODEQ to “(1) Identify the emissions units 

being controlled, (2) Identify design parameters for emission controls, and (3) Develop cost 

estimates based upon those design parameters.” 70 Fed. Reg. at 39,166. The Guidelines 

further instruct ODEQ to consider estimates of capital and annual costs for the “control 

equipment” or the “control technology.” Id. 

 As ODEQ complied with the above guidelines (discussed further below), the BART 

analysis is complete and legally sufficient. ODEQ correctly responded to comments raising 

other cost issues during the state process that it would not be legally sound for ODEQ to 

consider the costs of replacement power or any other costs beyond those of emission controls 

in its BART analysis. However, because some interested parties may comment on overall 

cost of the SIP Revision and its impact on electric rates, Sierra Club briefly addresses this 

issue as well to provide EPA, and the public, with a complete picture. 

 The SIP Revision not only permits PSO to avoid the high cost of installing and 

operating scrubbers; by providing for the retirement of a unit in 2016, it also assures that 

PSO will avoid the costs of other upcoming regulations that would require that unit to 

internalize the costs of its air, water, and coal ash pollution and other harm to the 

environment. Pursuant to the SIP Revision, PSO will avoid costs associated with an array 

of future regulations at one or both units, including:36 

 Coal Combustion Residuals. The EPA proposed two alternative rules on June 21, 2010, 

but has not yet finalized either rule. The Northeastern facility’s coal ash landfill has 

only an “in-situ clay liner,” meaning that the landfill currently does not have a synthetic 

liner to protect against toxics that may be leaching into groundwater or surface water 

and causing risks to human health.37 Regardless of how the rule is finalized, it is 

reasonable to expect that to continue operating beyond 2016, Northeastern would have 

                                                            

35 Id. at 4-4. 

36 Although PSO may have to implement changes at the unit that continues to operate until 

2026, its costs will be lower than if both units continued to operate. 

37 See supra note 30. 
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to address this issue. To convert its landfill to appropriately handle ash waste could cost 

$30 million or more.38 

 Effluent Limitations Guidelines. EPA issued proposed effluent limitations for coal-fired 

power plants in April 2013. The proposed rule would establish new requirements for 

wastewater streams from FGD (scrubbers), fly ash, bottom ash, and flue gas mercury 

control, all of which would be present at the Northeastern units if they continued to 

operate. EPA has proposed four options, with varying degrees of control for each waste 

stream, including specific limits for certain pollutants in the FGD waste stream, dryhandling (zero discharge) of fly ash or bottom ash, or both. This rule could pose 

significant costs for the Northeastern units were they to continue to operate, especially 

because scrubbers create enormous amounts of polluted wastewater. 

 Revised NAAQS for Ozone. As noted above, EPA predicts that Tulsa will be out of 

attainment in 2020 if the ozone standard is revised to 65 ppb or lower. Oklahoma would 

need to further reduce regional NOx emissions, which could ultimately require 

installation of expensive Selective Catalytic Reduction units at the Northeastern units. 

DEQ estimated in its original BART determination for Northeastern that the capital 

cost of installing SCR at the Northeastern units would be $290 million, with an annual 

cost of control (including both capital and operational costs) amounting to 

approximately $48 million 39

 One-Hour SO2 Primary NAAQS. As noted above, the one-hour SO2 standard poses 

significant challenges for coal-fired power plants. A study by Burns & McDonnell 

concluded that “both scrubbed and unscrubbed boilers will have difficulty complying 

with the new one-hour SO2 NAAQS during short-term high emissions.”40 Further 

reducing SO2 emissions, even after installing scrubbers, would require additional 

investments not necessary under the SIP Revision. 

 Cross State Air Pollution Rule (CSAPR). The EPA has a statutory duty to require states 

to address emissions that “contribute significantly to nonattainment in, or interfere 

with maintenance by, any other State with respect to [the NAAQS].”41 As the NAAQS 

get tighter, there is greater likelihood that an upwind state will contribute to 

nonattainment in a downwind state. As a result, although the 2010 version of CSAPR is 

                                                            

38 North American Reliability Council, 2010 Special Reliability Assessment Scenario: 

Resource Adequacy Impacts of Potential U.S. Environmental Regulations, October 2010, p. 

56. 

39 DEQ, Air Quality Division, Northeastern BART Application Analysis (Jan. 19, 2010), 

Table 5. 

40 Robynn Andracsek, et al, Burns & McDonnell, “Flue Gas Desulfurization-Equipped CoalFired Power Plants: Will They Comply with the 1-Hour National Ambient Air Quality 

Standard for Sulfur Dioxide?”, TECHBriefs 2011 No. 2, p. 2, available at 

http://www.burnsmcd.com/Resources/Article/Flue-Gas-Desulfurization-Equipped-CoalFired-Power-Plants. 41 See Clean Air Act Section 110(a)(2)(d)(i). 
12 of 18 

still under legal review, future regulations on interstate air pollution implemented to 

could be even stricter. The regulations will have to address lower annual standards for 

fine particulate matter (PM2.5), which were finalized in January 2013, as well as 

updated ozone standards, which are expected to be finalized in 2014.42 By agreeing to 

phase out its coal units, PSO likely avoids significant costs of this future rule. 

 Greenhouse Gas New Source Performance Standards for Existing Units. The EPA has 

indicated that it plans to issue rules to address greenhouse gases from existing coalfired power plants. Although EPA has not determined a specific timeline, its statutory 

duty to do so will be triggered when it finalizes its proposed regulations for new units, 

now expected in September 2013. (See Clean Air Act, Section 111(d), which requires 

EPA to prescribe regulations addressing any air pollutant “to which a standard of 

performance under this section would apply if such existing source were a new source”). 

The costs of compliance for old coal plants could be significant. A 2012 study by Synapse 

Energy Economics reports that, in 55 publicly available forecasts of allowance prices by 

electric utilities, the forecasted price for 2030 ranges from $10/ton (2012$) to $80/ton 

(2012$).43

By transitioning to cleaner alternatives than coal, PSO will avoid these and other future 

regulatory costs, all of which could have been passed on to ratepayers. These cost savings 

are in addition to the millions of dollars saved by installing DSI instead of scrubbers. 

V. The SIP Revision is Consistent with the State Energy Plan. 

Although not directly relevant to ODEQ’s statutory obligations or EPA’s review, 

Sierra Club also supports the SIP Revision because it is consistent with the State of 

Oklahoma’s energy plan. The state energy plan prioritizes the increased use of Oklahoma’s 

energy resources such as wind and natural gas, and protection of public health and the 

environment.44 Oklahoma is an exporter of both natural gas and wind, but a major importer 

of coal, including the coal burned by the Northeastern units. In 2012, Northeastern 

imported more than 3.6 million tons of coal from mines in Wyoming and other out-of-state 

mines at a cost of more than $75 million.45 Adding scrubbers would have continued those 

imports, requiring rail transport of large amounts of coal. The SIP Revision will instead 

                                                            

42 National Ambient Air Quality Standards for Particulate Matter; Final Rule, 78 Fed. Reg. 

3086 (Jan. 15, 2013), available at http://www.gpo.gov/fdsys/pkg/FR-2013-01-15/pdf/2012-

30946.pdf. 43 Synapse Energy Economics, Inc., 2012 Carbon Dioxide Price Forecast, October 4, 2012, p. 

22, available at http://www.synapse-energy.com/Downloads/SynapseReport.2012-10.0.2012-

CO2-Forecast.A0035.pdf. 

44 Governor Mary Fallin & Secretary of Energy Michael Ming, Oklahoma First Energy Plan 

(2011), at 3, 5, available at 

http://www.ok.gov/governor/documents/Governor%20Fallin's%20Energy%20Plan%20-

%20Jan%202012.pdf 

45 SNL Financial (based on Energy Information Administration Form EIA-923 filings). 
13 of 18 

encourage use of Oklahoma resources and the elimination of Northeastern’s coal imports by 

2026. 

 Transitioning from coal to gas, wind, energy efficiency, and demand response also 

has significant benefits for the overall reliability of the grid. As the amount of wind in 

Oklahoma and the Southwest Power Pool (SPP) rises, fossil generation will need to ramp 

production up and down more frequently, and to shut down for various periods of time 

during high wind production. Switching to natural gas, wind, energy efficiency and demand 

response, result in resources better suited to integrate with variable wind generation, both 

technically (since coal plants generally ramp more slowly than gas plants and often require 

longer periods between starts and stops) and economically (since the large investment in 

scrubbing and other environmental compliance will be partially stranded if coal units are 

often ramped down to accommodate wind energy, while gas plants would avoid their fuel 

costs). 

 American Electric Power (AEP), PSO’s parent company, has acknowledged that this 

transition to cleaner, local, more flexible fuel sources will impact its employees currently 

employed in the coal sector. Sierra Club shares the concern that the transition occur in a 

way that is sensitive to the employees and communities affected by plant retirements, not 

least because Sierra Club members also live in these communities. As the largest power 

company in the country, AEP has extraordinary resources to help redeploy its coal sector 

employees, and has committed to doing so.46 Oklahoma will be in need of workers in the 

power sector throughout the state’s transition away from coal. New jobs will be created in 

transmission line construction, wind energy, solar power, and energy efficiency. The 

gradual nature of the PSO plan allows for PSO and the overall state economy to make the 

transition to a power fleet without coal in a way that allows for gradual placements of 

workers into new positions within the power industry. AEP notes that attrition across its 

company may create opportunities; the number of employees may increase at units where 

environmental controls are retrofit; and potential acquisition (purchase or construction) of 

replacement power may create openings. AEP plans to provide a variety of assistance 

programs, from advising its hiring managers when applicants are from impacted facilities 

to providing education assistance programs.47 While these issues are not factors that EPA 

may consider in its review of ODEQ’s BART analysis, Sierra Club believes they are 

important issues for the public to be aware of. 

VI. The SIP Revision Satisfies EPA and ODEQ’s Obligations Under the Clean Air Act. 

The Clean Air Act charges each state with the initial responsibility for preparing a 

                                                            

46 See AEP, Human Resources for Employees, 

http://www.aep.com/community/PlantRetirements/HumanResourcesProgramsForEmployee

s.aspx (“AEP will do everything it can to assist employees whose jobs will be eliminated due 

to the premature retirements of generating units.”; listing wide variety of programs) 

47 See AEP, Human Resources for Employees, 

http://www.aep.com/community/PlantRetirements/HumanResourcesProgramsForEmployee

s.aspx. 
14 of 18 

Regional Haze SIP, but grants EPA with oversight authority. This oversight ensures that 

each State’s SIP considers each statutory factor in a way that is rational, supported by the 

evidence, and consistent with nationwide standards. EPA approved the majority of the 

Regional Haze SIP submitted by Oklahoma in 2010, but disapproved of Oklahoma’s 

approach to SO2 BART. Oklahoma’s BART determination did not require any coal-fired 

power plants to actively reduce SO2 emissions, requiring them only to continue using lowsulfur coal. Finding that Oklahoma had not properly evaluated the cost-effectiveness of 

scrubbers according to federal guidelines, EPA issued its own plan for SO2 emissions and 

required that six coal-fired units meet an emissions limit of .06 lbs/mmbtu, either by 

installing dry flue gas desulfurization units or switching to natural gas. 

The SIP Revision is a practical and legally sufficient response to EPA’s disapproval 

of Oklahoma’s BART determinations for SO2 for the Northeastern units.48 The SIP 

Revision will also contribute to the state’s “reasonable progress toward meeting the 

national goal” of eliminating human-caused visibility impairment by 2064. 42 U.S.C. § 

7491(b)(2). 

In making a BART determination, the Clean Air Act requires states to consider (1) 

the costs of compliance; (2) the energy and nonair quality environmental impacts of 

compliance; (3) any existing pollution control technology in use at the source; (4) the 

remaining useful life of the source; and (5) the degree of improvement in visibility which 

may reasonably be anticipated to result from the use of such technology. 42 U.S.C. § 

7491(g)(2); 40 C.F.R. 51.308(e)(1)(ii). 

Pursuant to the BART regulations issued by EPA, the first step before evaluating 

costs is identifying technically feasible control options. ODEQ evaluated two control 

options: installing Dry FGD with Spray Dry Absorber on both units (the FIP scenario) and 

installing DSI on one unit only, accompanied by the company’s commitment to retire that 

unit by 2026 and the other by 2016 (the settlement scenario). In this scenario, EPA 

analyzed the additional scenario of installing DFGD/SDA on the unit that the company 

plans to continue operating until 2026. EPA considered a 10-year operating life for the 

scrubber even though, as EPA noted, the company likely would choose to operate the 

                                                            

48 EPA has also concluded that, with respect to the Northeastern units, the SIP Revision 

addresses the state’s obligation to address the visibility impacts of pollution transported to 

other states. To ensure compliance with this obligation, the SIP Revision should require 

that the additional SO2 reductions that Oklahoma has committed to -- should the controls 

at Northeastern not suffice -- come from sources affecting the same Class I areas as 

Northeastern. It is not clear that emissions from the “northeast quadrant” or elsewhere 

would do so. Moreover, ODEQ should work to identify such reductions over the next three 

years in advance of the monitoring report required by the Settlement Agreement such that 

the reductions can be implemented immediately should the monitoring report reveal that 

they are needed. The timeframe set forth for obtaining the additional reductions (not later 

than “the end of the first full Oklahoma legislative session” occurring after the monitoring 

report) is untethered from the statutory requirements for interstate visibility protection. 
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scrubber longer than ten years if it made that investment. See Technical Support Document 

for the AEP/PSO BART Revision (July 2013) at 21. 

EPA and ODEQ properly took into account the company’s proposal to retire one unit 

by 2016 as part of the control scenario. The statute instructs states to contemplate “the 

remaining useful life of the source,” 42 U.S.C. § 7491(g)(2), and EPA’s BART Guidelines 

acknowledge that a unit may “agree to shut down” prior to the statutory deadline for BART 

controls. 70 Fed. Reg. 39,104, 39,127 (July 6, 2005). It is well within ODEQ’s discretion, and 

makes good practical sense, to take into account PSO’s enforceable commitment to retire 

one unit by 2016 in comparing costs. The BART Guidelines require that if the “date the 

facility permanently stops operations [. . .] affects the BART determination, this date 

should be assured by a federally- or State-enforceable restriction preventing further 

operation.” 70 Fed. Reg. at 39,169. ODEQ has satisfied this requirement by entering into an 

“enforceable administrative order” with AEP/PSO. See Revised Haze SIP at 6 & Appendix 

III. Although styled as an agreement between ODEQ and PSO, EPA should clarify in the 

final rule that the agreement is incorporated as part of the SIP and is therefore enforceable 

by citizens, the state, and EPA. 

The next step is calculating the annual costs for each scenario. Sierra Club did not 

conduct a detailed evaluation of EPA or ODEQ’s cost assumptions, but supports the 

approach of using a methodology consistent with EPA’s Air Pollution Control Cost Manual 

and EPA’s analysis supporting the FIP.49 EPA’s addition of a unit-by-unit analysis is also 

appropriate (although EPA acknowledges that the commitment to a 2026 retirement date 

would likely not be realistic were PSO to invest in a scrubber on the remaining unit). 

Next, the state must evaluate cost-effectiveness, or the cost per ton of SO2 reduced. 

Because the unit with controls will cease operating in 2026, DEQ annualized the DSI 

option’s costs over 10 years. Id. at 6. ODEQ compared this option to a scenario in which 

both units operate with DFGDs for 30 years. Pursuant to this approach, DEQ concluded 

that the DSI option, at $1005/ton reduced, is more cost-effective than DFGD, at $1,544/ton. 

Id. at 7. ODEQ considered emissions reductions with the DSI option as if the controlled unit 

would consistently operate at 85% capacity through 2026. Revised BART Determination at 

6-7. However, the Revised SIP includes an enforceable commitment by PSO to steadily 

ramp down capacity starting in 2021. Taking into account the capacity reductions, the gap 

in cost-effectiveness is larger. According to the company’s estimate, 26,558 tons of SO2 will 

be removed under the DSI/shutdown scenario through 2026, resulting in a costeffectiveness of $942/ton. Supplemental BART Determination, Appendix A, at 2. While 

EPA’s unit-by-unit approach showed an even wider disparity in cost-effectiveness between 

the DSI and scrubber options ($1,758/ton compared to $3,211/ton), the conclusion is the 

same that the DSI option is more cost-effective, taking into account the remaining useful 

life of the plant. Sierra Club agrees with this conclusion. 

                                                            

49DSI may have greater than zero landfill costs, contrary to ODEQ’s analysis. However, 

even if landfill costs were included, the DSI/shutdown scenario would be more cost-effective 

than DFGDs. 
16 of 18 

EPA also instructs states to evaluate “incremental cost-effectiveness,” or the cost of 

each additional ton removed by the more expensive option that achieves greater 

reductions.50 In ODEQ’s analysis, the incremental cost-effectiveness of the DFGD option is 

$4,718/ton in the first year. Taking into account additional reductions in SO2 as the unit 

decreases its capacity utilization, the incremental cost-effectiveness worsens to $7,794/ton. 

See Supplemental BART Determination, Appendix A, at 2-3. EPA likewise found that the 

incremental cost-effectiveness of installing DFGD rather than DSI would be $7,362/ton. As 

noted in the BART regulations, “[o]f course, there may be other differences between these 

options, such as, energy or water use, or non-air environmental effects, which should also 

be considered in selecting a BART technology.” 70 Fed. Reg. at 39,167. 

The state is next instructed evaluate these “other differences,” including whether 

each control option results in energy penalties or benefits. Neither ODEQ nor EPA 

evaluated the differences in energy use between the two options in detail, but ODEQ notes 

that energy consumption will be reduced by half as a result of the shutdown of one unit 

under the SIP Revision. ODEQ and EPA also could have considered the greater energy 

requirements of DFGD technology as compared to DSI as a factor supporting its BART 

selection. 

Next, the state must consider “non-air quality environmental impacts.” This is a 

broad category, including “relative quantities of water used and water pollutants produced 

and discharged as result of the use of each alternative emission control system,” and “where 

possible, . . . the effect on ground water and . . . local surface water quality parameters.” 70 

Fed. Reg. at 39,169. The state may also consider the “quality and quantity of solid waste . . . 

that must be stored and disposed of or recycled;” the “irretrievable commitment of resources 

(for example, use of scarce water resources,” and other adverse environmental impact such 

as hazardous waste discharges. Id. 

DFGD would use an enormous amount of water in comparison to DSI. As discussed 

above, PSO has estimated that the increase in water consumption at the Northeastern 

plant if it were to add dry scrubbers to both units would be at least 65 times greater than 

with a retrofit of ACI and DSI at one unit pursuant to the SIP Revision.51 Another crucial 

disadvantage of adding a DFGD at each unit is that it would create a new source of highly 

polluted wastewater at the plant. EPA has recently initiated a rulemaking to address, 

among other issues, the toxic-laden wastewater associated with SO2 scrubbers. In light of 

the clear disadvantages of scrubbers with respect to water usage and water quality impacts, 

and taking into account the limited remaining life of the plan, this factor weighs in favor of 

ODEQ’s BART selection. 

                                                            

50 (Total Annualized Cost for Option 1 – Total Annualized Cost for Option 2)÷ (Annual 

Emissions for Option 1 – Annual Emissions for Option 2). 70 Fed. Reg. at 39,167. 

51 Oklahoma Corporation Commission, Cause No. 201200054, PSO Response to Sierra Club 

Data Request 5-9 (Dec. 20, 2012) (attached hereto as Exhibit 3) (Controls pursuant to EPA 

settlement will consume approximately 11,250 gallons of water per day, compared with the 

DFGD option, which would consume approximately 737,000 - 805,000 gallons of water per 

day for two units). 
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Finally, the state must determine the visibility impacts of its BART determination. 

The deciview improvements are “weighed among the five factors, and [the state is] free to 

determine the weight and signficance to be assigned to each factor.” 70 Fed. Reg. at 39,170. 

Sierra Club has not reviewed the modeling assumptions and protocol in detail but supports 

ODEQ’s approach of following the modeling that EPA conducted in support of the FIP. 

EPA’s adjustments and unit-by-unit approach also appear reasonable in this context, as 

does EPA’s determination that “the relative results are similar and the differences are not 

such that it changes our overall conclusions.” 78 Fed. Reg. at 51,692. 

ODEQ notes that visibility improvements would slightly greater if the company 

installs DFGD in 2016, but that these improvements would “trivial.” Revised BART 

Determination at 11. Although we agree with DEQ’s overall conclusion that the proposed 

SIP Revision is preferable to the FIP, we agree with EPA that DEQ may not simply 

disregard a .1 deciview improvement without considering the full context. 52 See EPA 

Technical Support Document for the AEP/PSO BART Revision (July 2013) at 19. EPA 

correctly states: “In the preamble to the BART guidelines, ‘[e]ven though the visibility 

improvement from an individual source may not be perceptible, it should still be considered 

in setting BART because the contributions to haze may be significant relative to other 

source contributions in the Class I areas.’ Overall, the Regional Haze process envisions 

reductions that are both ‘perceptible’ and ‘not perceptible’ will be necessary as part of the 

overall path to obtain necessary reductions to meet Regional Haze goals.” In some cases, 

the improved visibility and environmental benefits of the more expensive scenario might 

outweigh cost considerations. Here, considering all the factors together, the Revised SIP is 

an appropriate BART selection despite greater visibility improvements achievable in the 

short-term with DFGD. 

While Sierra Club does not necessarily agree with each and every rationale ODEQ 

and EPA have relied upon in their analysis, Sierra Club supports the proposed SIP 

Revision because it ultimately will achieve natural visibility on a faster timeline than 

would the FIP (as discussed in Section I above), it complies with the BART guidelines, and 

it will provide a host of environmental and public health benefits that could not be achieved 

by a scrubber retrofit alone. 

 

The state has the discretion to choose the “best” option, so long as it has considered 

the above factors consistent with the BART guidelines, and “provide[d] a justification.” 70 

Fed. Reg. at 39,170-71. For all of the reasons above, and in light of PSO’s commitment to 

gradually phase-out the Northeastern coal units, Sierra Club believes ODEQ correctly and 

justifiably selected the DSI option as BART. We enthusiastically support EPA’s approval of 

the SIP Revision and urge EPA to promptly move forward with finalizing the rule. 

                                                            

52 We disagree, however, with EPA’s apparent suggestion that a .1 dv to .27 dv impact does 

not “contribute” to visibility impairments. Id. “Failing to consider less-than-perceptible 

contributions to visibility impairment would ignore the CAA’s intent to have BART 

requirements apply to sources that contribute to, as well as cause, such impairment.” 70 

Fed. Reg. at 39,129.