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 New Hampshire Regional Haze SIP Revision 

Responses to EPA’s Comments 

On December 20, 2010, the New Hampshire Department of Environmental Services (NHDES) 

received comments from the U.S. Environmental Protection Agency (EPA) on New 

Hampshire’s draft final Regional Haze SIP, November 19, 2010 . The following are NHDES’s 

responses to EPA’s comments. Comments are written in italics and responses are written in 

regular font.

Low-Sulfur Fuel Strategy

1) New Hampshire's proposed SIP includes a demonstration that the MANE-VU low sulfur fuel 

oil strategy is reasonable...New Hampshire, however, has not yet adopted a regulation 

imposing these requirements. The proposed SIP indicates that New Hampshire plans to 

introduce legislation on this issue in January 2012. EPA urges New Hampshire to move 

forward with this strategy more quickly than stated in this proposal and include in its final SIP 

submittal a commitment to adopt and submit a final rule to EPA by a date certain in 2011. 

 NHDES Response: NHDES cannot make commitments as to the timing of

legislation but will recommend new legislation to implement the low-sulfur fuel oil 

strategy, as envisioned in the MANE-VU low-sulfur fuel strategy, as soon as fuel 

supply and cost data are deemed sufficient and favorable for legislative success. It 

remains New Hampshire’s goal to implement the MANE-VU strategy by 2018, in 

accordance with the original timetable. If, in EPA’s view, this statement of intention 

is insufficient, NHDES will remove the low-sulfur fuel strategy from the regional 

haze SIP.

BART Visibility Modeling

2) Tables 9-4 and 9-5 show the results of CALPUFF modeling for the visibility improvement 

from BART controls on the 20% worst visibility modeled days, based on baseline visibility 

conditions, at each nearby Class I area. However, 40 CFR Part 51, Appendix Y, Section 

(IV)(D)(5), "Step 5: How should I determine visibility impacts in the BART determination?" 

clearly states: 

"Use the 24-hour average actual emission rate from the highest emitting day of the 

meteorological period modeled (for the pre-control scenario). Calculate the model results 

for each receptor as the change in deciviews compared against natural visibility 

conditions." 

A BART analysis should determine the visibility impact of the source, not the impact of the 

source in conjunction with all other impacting sources. New Hampshire must recalculate the 

visibility improvement using the calculated worst 20% natural conditions: 12.4 deciviews (dv) 

for Acadia National Park; 11.7 dv for Lye Brook Wilderness; and 12.0 dv for Moosehorn 

Wilderness and Great Gulf Wilderness. 

 NHDES Response: NHDES has adjusted the visibility modeling for BART and 

made corresponding revisions to the descriptive text and tables of the regional haze 

SIP and BART analyses. Please see the attached CALPUFF Modeling Assessment.
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Newington Station NT1 BART – SO2

3) Based on the "Final Proposal" of Env-A 2300 "Mitigation of Regional Haze," posted on your 

web site and dated December 1, 2010,...it appears that NH DES has made a final decision that 

BART for NT1 is an SO2 emission limit of 0.5 1b/MMBtu on a 30-day rolling average basis. 

EPA has previously expressed concerns with such a limit since it is not consistent with the 

MANE-VU recommended level for BART SO2 control for non-CAIR EGUs, which is the use of 

natural gas or 0.3% sulfur content by weight fuel oil. The final SIP must include additional 

documentation to support an SO2 BART limit of 0.50 lbs per million BTU for NT1. 

Specifically, the BART Analysis for PSNH Newington Station Unit NT1 (Attachment X), Table 

2-5, Cost of Fuel Switching based on Historical Fuel Oil Prices indicates the cost of switching 

from 2% to 0.3% sulfur in fuel oil as ranging from $627 to $2,664 per ton, which is not 

unreasonable. As noted in comment #2, New Hampshire must re-calculate the visibility 

improvements associated with each control strategy. Although the costs of switching to 0.3% 

sulfur in fuel oil may be reasonable, it is appropriate to consider these costs along with the 

anticipated visibility improvement. A minimal additional visibility improvement for 0.3% 

sulfur in fuel oil would provide support for New Hampshire's proposed 0.5 lb/MMBtu limit. 

 NHDES Response: NHDES believes that 0.50 lb/MMBtu is appropriate as the 

BART control level for SO2 for this unit. This determination is based on a number of 

factors, the following in particular:

• The availability and cost of 0.3% sulfur residual fuel oil remain uncertain, i.e., 

Newington Station cannot be assured of a steady supply of this fuel at reasonable 

cost over the next 5-10 years. 

• The plant has a sizeable quantity of higher-sulfur residual fuel oil in storage tanks 

on site. There is no practical way to offload and replace this inventory with a 

lower-sulfur residual fuel oil, so the existing stock of higher-sulfur fuel oil will have 

to be used up before Unit NT1 can be fired exclusively with low-sulfur fuel oil. 

• Even if supplies could be guaranteed at reasonable cost, the visibility improvement 

in going from an emission limit of 0.50 lb/MMBtu to a fuel limitation of 0.3% S 

residual fuel oil is almost negligible. Please refer to the revised modeling results for 

Unit NT1 in Table 5-1 of the BART analysis (Attachment X). 

In addition, there are inconsistencies between the final BART limits in Env-A 2300 and the 

proposed November 19, 2010 New Hampshire Regional SIP that need to be addressed. Those 

inconsistencies are: 

a) The SO2 BART emission limit in Table 9.3 is stated as a calendar month average. 

b) The SO2 BART emission limit in Table 9.7 is stated as a calendar month average. 

 NHDES Response: The inconsistencies between Env-A 2300 and the SIP have been 

corrected in the final documents. 

4) For Table 9.3, New Hampshire's initial proposal (dated May 26, 2009) included a 1,742 ton 

per year (tpy) SO2 reduction from NT1. In the January 2010 SIP submittal and the November 

19, 2010 proposal, Table 9.3 indicates a 3,484 tpy SO2 reduction from this unit. However, 

Table 11.2 of the January 2010 SIP submittal and the November 19, 2010 proposal were not 

updated to reflect this change. 
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 NHDES Response: The projected emissions in Table 11.2 represent MANE-VU’s 

2018 “Best and Final” modeling emissions inventory that was used in the final 

visibility modeling and reflect the assumptions used at the time the modeling was 

performed. This inventory incorporates the additional reasonable control measures, 

including the targeted EGU strategy, the low-sulfur fuel strategy, and the timely 

implementation of BART. For the targeted EGU strategy for Unit NT1 specifically, a 

50% reduction in SO2 emissions was assumed, representing a switch from 2% to 1% 

sulfur fuel. This emissions inventory and modeling analysis, and therefore the values 

in Table 11.2, were not adjusted to reflect revisions made by NHDES to the BART 

analysis between the time of the initial proposal and the January 2010 submittal. 

Thus, the table remains consistent with the completed MANE-VU modeling. Note, 

however, that the BART emission limit and expected emission reductions for Unit 

NT1 in the January 2010 SIP submittal are more stringent than those that were 

assumed in the final MANE-VU visibility modeling. NHDES has added a statement 

in the SIP to explain these differences. 

Newington Station NT1 BART – PM

5) New Hampshire has proposed that the existing PM permitted rate of 0.22 lb/MMBtu is BART 

for NT1. As noted in EPA's previous comments, this limit is well above the MANE-VU 

recommended limit of 0.02-0.04 lb/MMBtu. In the discussion of current PM emissions and 

controls, it is mentioned that NT1 has an electrostatic precipitator to capture PM emissions 

and a previous stack test at this facility indicated an emission rate 0.058 lb/MMBtu. At this 

point, DES has not presented sufficient evidence that the existing PM limit represents BART for 

unit NT1. The final SIP submittal must include further technical justification to demonstrate 

why it is not feasible for this unit to meet a more stringent limit. 

 NHDES Response: The single available stack test report for this unit is a decade old 

and is not a sufficient basis for resetting the PM emission limit. As indicated in the 

BART analysis of Attachment X, the facility’s Title V operating permit requires that 

a compliance stack test for PM emissions be performed on Unit NT1 before the 

permit expires on March 31, 2012. In recent years this unit has operated as a peaking 

plant. It is impractical to fire up the boiler for the sole purpose of stack testing. 

Therefore, some flexibility is needed with respect to the testing schedule. PSNH and 

NHDES will coordinate the effort to perform the testing at the earliest practical date 

but cannot commit to a specific test schedule under current circumstances. NHDES 

will review the new stack test results to ascertain the unit’s performance and 

incorporate any new limit into a permit amendment by the permit expiration date, as 

appropriate. Such limit will be made consistent with BART requirements. The 

permit expiration date precedes the effective date of proposed BART control 

measures by fifteen months, so the air quality benefits of a reduced PM emission limit 

will be realized earlier than would otherwise be the case under New Hampshire’s 

BART implementation schedule. 

Merrimack Station MK2 BART – NOx

6) Based on the "Final Proposal" of Env-A 2300 "Mitigation of Regional Haze," posted on your 

web site and dated December 1, 2010, it appears that NH DES has made a final decision that 

BART for MK2 is a NOx emission limit of 0.30 lb/MMBtu on a 30-day rolling average basis. 
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This is more stringent than the NOx emission rate that was originally proposed in Env-A 2300. 

However, as stated in our comments dated November 22, 2010, it appears MK2 is capable of 

meeting NOx emission rates lower than this on a 30-day rolling average. Specifically, data 

available from EPA's Clean Air Markets Division data base indicates that, in 2009, at no point 

did the unit exceed a 30-day rolling average of 0.25 lbs per million BTU. A level of 0.25 lbs 

NOx per million BTU on a 30-day rolling average seems to be an appropriate BART emission 

limitation for MKl based on our evaluation of the performance of the SCR over the last 5 years 

through September 30, 2010. In fact, prior to MK2 coming back on line in November 2009, the 

30-day rolling average NOx emission rate met by the SCR was generally below 0.20 lbs per 

million BTU. 

Moreover, it is unclear the basis of the statement in Attachment X saying that "the estimated 

costs of reducing the NOx limit to 0.34 lb/MMBtu (a reduction of 0.03 lb/MMBtu) would fall 

between $3,000 and $10,000 per ton of NOx removed," given that it does not appear that this 

rate has ever been exceeded in recent times. Therefore, in order to support a 0.30 lb per 

million BTU limit, further technical justification is necessary to demonstrate why it is not cost 

effective for this unit to meet a more stringent limit. 

 NHDES Response: In new data provided to support the BART analyses for Unit 

MK2 (see Attachment X), PSNH estimates that a reduction in the NOx emission 

limit to 0.30 lb/MMBtu (an effective reduction of 0.07 lb/MMBtu) would have an 

incremental cost of approximately $800 per ton of NOx removed, which falls within 

the generally accepted cost-effective range. At the same time, PSNH estimates that 

further reduction of the NOx emission limit to 0.25-0.30 lb/MMBtu would have 

diminishing returns, with an incremental cost per ton approximately one order of 

magnitude greater. In the context of BART requirements, NHDES finds that the 

higher costs associated with a NOx emission limit below 0.30 lb/MMBtu are not 

justifiable given the fact of negligible visibility benefit.

NHDES concurs with EPA that Unit MK2 is likely to surpass this performance level 

routinely by a significant margin. However, the ability of this unit to perform at a 

lower NOx emission rate most of the time does not, by itself, constitute BART. The 

facility needs some flexibility to operate at higher emission levels during occasional 

reduced-load incidents, which drive up the average emission rate. It is reasonable to 

expect that Unit MK2, in order to comply with a BART emission limitation of 0.30 

lb/MMBtu on a 30-day rolling average basis, will continue to operate well below 

this limit whenever it can so as to counterbalance the possible higher emissions that 

occur from largely unplanned periods of low-load operation. PSNH has stated, and 

the historical record suggests, that the company regularly operates at a target NOx 

emission rate that is 0.15 lb/MMBtu below the permitted limit. 

NHDES will be re-evaluating this unit for future compliance with NOx RACT 

requirements, which could be more stringent than BART. The BART analyses, 

whose intent is visibility improvement, will remain separate from the NOx RACT 

review process. The latter will be undertaken to assure compliance with pending 

revisions to the ozone standards. Being health-based, the ozone standards serve a 

different, albeit related, purpose.
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In addition, there are inconsistencies between the final BART limits in Env-A 2300 and the 

proposed November 19, 2010 New Hampshire Regional SIP and attachments that need to be 

addressed. Those inconsistencies are: 

a) The NOx BART emission limit in Table 9.2 is stated as 0.37 lb/MMBtu calendar 

b) The NOx BART emission limit in Table 9.6 is stated as 0.37 lb/MMBtu calendar 

monthly average. 

c) The discussion in section 6.1 of Attachment X saying that NHDES finds that the current 

NOx RACT limit, expressed as 0.37 lb/MMBtu, is also appropriate as a BART control 

level. 

 NHDES Response: These entries in the SIP have been updated to agree with the 

lower BART emission limit of 0.30 lb/MMBtu, 30-day rolling average basis.

Implementing BART and Reasonable Further Progress Limits

7) The proposed SIP includes the following attachments for Merrimack Station and Newington 

Station: 

Attachment EE - Temporary Permit for PSNH Merrimack Station 

Attachment HH - Draft Title V Operating Permit for PSNH Merrimack Station 

Attachment II - Title V Operating Permit for PSNH Newington Station 

As noted in our November 22, 2010 comments, the temporary permit for Merrimack Station has 

expired and the Title V operating permit is in draft form. As such, these documents should not 

be incorporated into the SIP. Therefore, it is not clear how some of the BART and reasonable 

further progress emission limits for MK2 and MK1, respectively, will be made enforceable. 

 NHDES Response: Temporary Permit TP-0008 is a valid permit, reissued on 

August 2, 2010, with an expiration date of September 30, 2011. Future reissuance(s) 

will be made as necessary in accordance with Env-A 607.09 until such time as the 

relevant provisions of the temporary permit have been incorporated into the final Title 

V Operating Permit for Merrimack Station. The previously issued permits for this 

facility remain in effect because of a timely application filing for renewal. The 

proposed Title V Operating Permit for Merrimack Station has passed the public 

comment phase but is under appeal before the New Hampshire Air Resources 

Council. The appeal hearing is tentatively scheduled for February or March 2011. 

The Title V Operating Permit for Newington Station is valid until its expiration on 

March 31, 2012. 

Because the Title V Permit for Merrimack Station is the only permit in this group that 

is not final, it would appear to be the one most relevant to the question of 

enforceability. For that permit, current state and federal rules adequately address 

enforceability. Please see response below. 

Specifically, for MK2, although the BART NOx emission limits and monitoring requirements 

are stated in Env-A 2300, this rule points to permit conditions for the associated testing 

requirements. Also, although the rule includes BART TSP emission limits and stack testing 

requirements for MK2, there are no associated monitoring requirements included in the rule. 
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In addition, the rule relies on permit conditions for the SO2 BART emission limits and testing 

requirements for MK2, and does not include any SO2 monitoring requirements for MK2. 

For MK1, Env-A 2300 relies on permit conditions for the NOx and SO2 emission limits and 

testing requirements, and is silent as to the associated monitoring requirements. In addition, 

although the rule includes TSP emission limits and testing requirements for MK1, the rule is 

silent as to the associated monitoring requirements. 

Therefore, since the Merrimack Station permits are not valid, and Env-A 3200 [sic] does not 

include all of the necessary emission limits, monitoring, and testing requirements, the DES will 

need to ensure that the deficient aspects noted above are addressed in the final SIP submittal, 

in order to ensure that all of the BART and reasonable further progress limits for Merrimack 

Station are enforceable. 

 NHDES Response: The monitoring, recordkeeping, and reporting requirements for 

Units MK1 and MK2 that are listed in both the Temporary Permit and the proposed 

Title V Operating Permit are based on existing federal and state requirements 

specified in one or more of the following regulations: 40 CFR Part 75 (federal CEM 

requirements), Env-A 800 (state testing and monitoring procedures), and Env-A 900 

(state recordkeeping and reporting requirements). Both Env-A 800 and Env-A 900 

are elements of New Hampshire’s SIP. Merrimack Station is subject to these 

provisions regardless of the status of the Title V Operating Permit or Env-A 2300 

(state regional haze rule). Moreover, NHDES anticipates that the proposed Title V 

Operating Permit will be issued in final form well before the BART implementation 

date of July 1, 2013. In summary, NHDES believes that Env-A 2300 already 

provides for the requisite monitoring and testing of emissions for enforcement of 

BART. Note that the inclusion of Unit MK1 in New Hampshire’s regional haze rule 

was done for practical reasons related to BART compliance (the two units will share a 

common stack) and was not meant to address reasonable further progress, although 

that may be an additional benefit.

Furthermore, for Newington Station, the final SIP submittal should indicate which provisions 

of the Attachment II permit are to be incorporated into the SIP. For example, the permit 

includes a 2% sulfur content by weight fuel oil requirement for NT1 that has since been 

superseded by the 0.5 lb/MMBtu limit in Env-A 3200 [sic]. In such a case, the provision in the 

permit should not be incorporated into the SIP. 

 NHDES Response: The New Hampshire Code of Administrative Rules, Env-A 100 

et seq., Rules Governing the Control of Air Pollution, and the permits issued by 

NHDES in accordance with those rules, contain many examples of overlapping 

requirements. The most stringent conditions always apply. In the present example, 

Unit NT1 must meet both the 2% maximum sulfur requirement and the 0.50 lb/MMBtu 

SO2 limitation. Because the latter standard is the more stringent, it will be the 

governing condition. Env-A 609.19 includes provisions for reopening permits for 

cause, but the example cited would not meet any of the criteria for reopening the 

existing Title V operating permit. NHDES believes that overlapping requirements, 

redundancies, etc. are most easily addressed by amending the permit upon renewal (in 

this case, no later than March 31, 2012).
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CALPUFF Modeling Assessment 

In its first regional haze State Implementation Plan (SIP) draft submitted to the Environmental 

Protection Agency (EPA) and the federal land managers (FLMs) for comment, the New 

Hampshire Department of Environmental Services (NHDES) used an alternative model 

(CALGRID) to provide visibility improvement estimates for potential best available retrofit 

technology (BART) emission controls. Both EPA and the FLMs requested that DES redo the 

analysis with the “preferred” model, CALPUFF, as it was anticipated that the model would 

provide higher visibility benefit estimates for each potential BART control scenario. NHDES 

provided the requested CALPUFF modeling results in its official final filing to EPA in January, 

2010. During a March 2010 meeting between EPA and NHDES, EPA requested additional 

documentation to support the modeling results and requested that a full year be modeled to 

better represent the visibility benefits due to NOx emission controls during periods of cold 

weather. NHDES revisited this modeling as requested and found that the modeling results did 

not change substantively. 

On April 21, 2010, NHDES provided a general description of the proposed CALPUFF 

modeling procedures to EPA for comment. In that communication, NHDES let EPA know that 

it planned to exercise some flexibility as allowed under guidance to better represent more 

realistic estimates of anticipated visibility benefits for potential BART controls. NHDES used 

CALPUFF as specified in the BART guidance; however, rather than allowing the model to 

calculate deciviews from default data, NHDES applied relative modeling changes to monitored 

extinction to deciview relationship data to determine more realistic deciview predictions for the 

New England airshed. On August 6, 2010, EPA provided brief comments expressing concern 

and confusion regarding the proposed NHDES process (see attached). NHDES had subsequent 

telephone discussions with EPA regarding how New Hampshire intended to use the modeling 

in a relative way. EPA also asked whether it was appropriate to introduce current monitoring 

data since the blend of atmospheric species in 2064 is likely to be very different than it is now. 

NHDES took this question to the Cooperative Institute for Research in the Atmosphere (CIRA) 

for its thoughts on the matter. Based on CIRA's input, NHDES slightly revised the 

methodology to take a more speciated approach and calculated extinction before introducing 

the monitoring data into the calculations. This approach was incorporated into the NHDES 

analysis and is described in greater detail below. 

EPA also expressed concern regarding NHDES’s interpretation of the EPA BART modeling 

guidance. The concern focused on the wording for using the 20% worst modeled days, which 

NHDES interpreted to mean 20% worst visibility days since the two correlate so highly in the 

northeast region of the country. This interpretation also made logical sense to NHDES since 

the regional haze rule targets visibility improvement on those 20% worst visibility days while 

maintaining current visibility on the 20% best days. As was recently pointed-out, EPA’s intent 

was to use the worst (or maximum) modeled BART source impacts as applied to the best 

visibility days. The wording of the guidance has been made clearer since its draft version, but 

having been told that the guidance had not been changed substantively, NHDES did not notice 

its misinterpretation until recently. NHDES’s continued misinterpretation of the modeling 

guidance is demonstrated in the April 2010 correspondence between NHDES and EPA, where 

EPA recommends the use of the 98th percentile data (for BART source modeling) and NHDES 

responds by asking if this was for the 98th percentile worst days of monitoring (see attached 

NHDS-EPA correspondence). Now with a correct interpretation of the guidance, NHDES 

provides the requested CALPUFF modeled data for the 20% best visibility days in addition to 

the 20% worst visibility days. Even though these new results have been added, it is NHDES’s 

opinion that any benefits predicted based on the 20% best visibility days are not likely to be 
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realized in 2018 because of the wind patterns in the area and the alignment of sources with 

Class I areas. Given the alignment of the New Hampshire BART source to Class 1 areas and 

how there is a strong correlation of this alignment with that wind direction for worst visibility 

days, NHDES believes that the data provided for the 20% worst visibility days is a much more 

realistic prediction for anticipated benefits of controls, than the estimate for the 20% best days. 

Additional process description and data are provided in sections below. 

Description of the NHDES Modeling Process

The EPA modeling guidelines suggest that using models in a “relative” way could be useful to 

estimate the expected visibility benefits of BART controls. As explained above, while 

CALPUFF is EPA’s preferred model for visibility assessments of individual sources, it still has 

some weaknesses. NHDES prefers the relative approach to improve the non-linear (deciview) 

visibility assessment with actual response data measured at nearby Class 1 areas rather than 

using national default data. 

As specified by guidance, the NHDES modeling uses CALPUFF to estimate the benefits of 

BART controls on a single source under the conditions of 20% best (and worst visibility days). 

The model calculates the concentration benefits from the chosen source controls, but the 

conversion of the data into deciview units involves a non-linear estimation heavily dependent 

on background air pollution levels which can vary greatly in species concentrations. The 

resulting concentrations were normalized to match the scale of the previously submitted 

MANE-VU CALPUFF modeling to ensure consistency and comparability with the original 

MANE-VU modeling platform. Next, the normalized modeled species concentrations were 

used to calculate predicted visibility extinctions using the EPA-recommended reconstructed 

extinction equation. Finally, these results were used to calculate design values based on a bestfit equation for observed design value to extinction data for nearby New England Class I areas 

(Acadia NP, Great Gulf NWR, and Lye Brook NWR) (see Figure 1). Because of the 

logarithmic relationship of deciviews and concentration, background visibility must be added to 

the modeled concentrations prior to the extinction calculation so that the correct portion of the 

curve is applied. Extinctions corresponding to 20% best visibility days at Acadia NP (12.4 dv), 

Great Gulf / Presidential Range (12.0 dv) and Lye Brook (11.7 dv) were used. 22.8 dv was 

used for 20% worst visibility days. 

Figure 1. Monitored PM2.5 Extinction to Deciview Relationship in the Northeast 

SO4, NO3, EC Extinction vs DV

0

5

10

15

20

25

30

35

0 50 100 150 200 250 300

Extinction (1/Mm)

DV
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In short, the CALPUFF post-processor (CALPOST) uses a generic blend of background 

visibility conditions and then performs deciview benefit calculations in a crude way based on 

specification of background conditions. NHDES’s approach rigorously assesses relative 

changes predicted in CALPUFF modeling with (monitor-based) monitoring data derived 

visibility benefits. The NHDES approach allows visibility calculations to be made at any level 

of background visibility within the range of observed data at the nearby Class 1 areas. 

EPA guidelines recommend the use of five years of meteorology for BART modeling. 

Further, in order to prevent a single outlier from dominating the process, the 98th percentile 

single source impact should be used for BART determination. Because NHDES has only one 

year of meteorology suitable for regional CALPUFF modeling, it was decided to use the single 

maximum impact for that one year. This reduced the likelihood that a higher 98th percentile 

was missed and ensured that conservative results were used. 

Emission Scenarios:

Each leading BART control option was modeled for visibility benefit at nearby Class I areas. 

However, scenarios were not modeled where affected units are currently operating at lower 

emission rates, or at rates equal to potential BART emission limits. If there are no actual 

emission reductions to be gained from lower emission limits, then there are no benefits that 

would result through modeling. 

CALPUFF Modeling Inputs and Assumptions

The inputs and assumptions that were used in the CALPUFF BART visibility impact modeling 

are listed below. 

Models Used

CALPUFF Version 6.262 

CALPOST Version 6.221 

CALPro Standard 6.4.0.05_27_2008 Graphical User Interface 

Meteorology

CALMET 1990 (full year) meteorological field produced by NHDES on 8/26/2005 

Reason for NHDES Process

While recognizing that CALPUFF is the recommended model for long distance visibility 

assessments for Class I areas, NHDES disagrees with EPA that CALPUFF provides the best 

and most useful predictions of the visibility benefit of BART controls. CALPUFF excels at 

predicting worst-case impacts in the mid- to long-field, thus looking for that maximum point, 

and it does reasonably well at predicting that related concentration. It does not do as well in 

predicting the related deciview impact because the model is not wired to match a facility’s 

impact with the actual background visibility for any specific day. Instead, the worst-case 

concentration is simply added to a generalized model background concentration for a deciview 

target specified in a model post-processor (CALPOST). This is perhaps the purpose of the 

exercise, to be conservative and theoretical rather than to produce a truly realistic anticipated 

benefit. As a result, it does not track realistic modeled impacts as they might relate to 

background visibility, best visibility, and worst visibility days. Extra effort by the modeler is 

needed to present a realistic modeling result that aligns wind directions with appropriate, 

manually entered background conditions. 
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Because the model handles wind fields without regard to visibility conditions, CALPUFF’s 

predictions can be very conservative and possibly oversensitive to changes in visibility 

conditions when assessing the most likely benefits of emission controls. In the case of the New 

Hampshire BART sources, the alignment of the sources to the most affected Class I area 

(Acadia N.P.) is also the direct alignment of the most common wind trajectory on worst 

visibility days; thus maximum source contributions occur at times when transported air 

pollution from further away is also at a maximum. This phenomenon can lead to some of the 

worst visibility days. This alignment also makes it very difficult for NH BART sources to 

contribute maximum impacts at times when impacts from additional transport are not 

occurring, which would be the case on best visibility days. Therefore, when the best visibility 

day results are artificially overlaid on maximum source impact days and then the modeling 

results are used to calculate the benefits of emission controls, those benefits can be 

unrealistically overstated. As a result, predicted deciview improvements and the calculated 

cost-per-deciview ($/dv) BART control metric are not truly anticipated or expected. If a 

control is deemed reasonable because full attention is given to a scenario that is unlikely ever to 

occur based on monitored observations, NHDES questions the validity of calling the modeled 

results as an “anticipated benefit.” The exception to this case, however, is Lye Brook: because 

of its location in southern Vermont and its alignment with NH BART sources, the impacts from 

those sources are likely to be highest at Lye Brook on best visibility days when winds are from 

the east. Therefore, for Lye Brook, the predictions for best visibility days may be reasonable.

EPA recommends and encourages states to use the CALPUFF model for BART modeling, 

largely because regional models have not yet been proven to be effective for modeling impacts 

from individual sources. However, unlike CALPUFF and other dispersion models, regional 

grid models such as CALGRID excel at accounting for the impacts of widespread sources 

contributing to the species that cause visibility impairment. To that end, for the impact 

assessment of New Hampshire’s BART-eligible sources, NHDES originally chose to use 

CALGRID, the sister model to CALPUFF. CALGRID includes much of the same chemistry as 

CALPUFF but uses gridded dispersion as opposed to the puff dispersion used in CALPUFF. In 

fact, CALGRID2.45 includes about 20 percent more enhanced aerosol chemistry than 

CALPUFF and is therefore considered to be the more advanced model. Moreover, CALGRID 

easily matches and isolates the 20% best and worst visibility days to allow a direct, realistic 

result without the need for manual modeling adjustments to account for those specifics. 

CALGRID can easily isolate the best visibility days where a BART source actually contributes 

to visibility impairment, giving a more realistic sense of what benefits are reasonably 

anticipated. CALPUFF always assumes maximum emissions impact at Class I areas on both 

best and worst days – conditions that may or may not happen in reality. While the CALPUFF 

model’s CALPOST post-processor has an option for application on 20% best visibility days, it 

does not isolate those 20% best days for analysis. It simply changes the background values 

used by the model to what is estimated to be appropriate background conditions. The postprocessed results do not account for wind directions that may be preferentially included or 

excluded on such days. Even though NHDES sees value in the application of CALGRID for 

identifying anticipated visibility impacts with consideration to daily contributions of a single 

source relative to all sources, NHDES has agreed to also apply the CALPUFF model. NHDES 

still applies significant credibility to the CALGRID modeling results because they provide 

substantial insight into what scenarios are most realistic and just how much benefit is likely to 

occur in a given year. 
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CALPUFF Modeling Results

Merrimack Station Unit MK2: BART Eligibility Modeling 

The BART eligibility modeling conducted by MANE-VU used natural visibility conditions 

(about 7 dv) to produce the most conservative modeling results to minimize sources from 

modeling out of BART. Under natural background conditions, uncontrolled emissions from Unit 

MK2 produce CALPUFF worst-case impacts of 2.24 dv at Acadia National Park. This value 

was replicated in the NHDES CALPUFF modeling effort. EPA considers it acceptable to 

exempt sources when this form of conservative modeling indicates that a source produces less 

than 0.5 dv of impact. MANE-VU considers an exemption level of 0.2 to 0.3 dv to be more 

appropriate but prefers, and has applied, a more conservative exemption level of 0.1 dv. 

CALPUFF modeling results for baseline emissions from Unit MK2 exceed all of these 

exemption levels. 

According to EPA regional haze documentation, a difference of 1 deciview is visibly noticeable 

by observers and a difference of 0.1dv is the minimum perceptible by the human eye. 

Merrimack Station Unit MK2: BART Benefit Assessment Modeling 

The BART assessment modeling provides a comparison of visibility impacts from 

current allowable emissions with those from the post-control emission level (or levels) 

being evaluated. In accordance with EPA guidance, NHDES used CALPUFF to estimate 

the magnitude of the source’s impacts on visibility after implementation of BART 

controls. Results are tabulated for the average of the 20% best and worst visibility (in 

this case, about 11.7 to 12.4 dv for best and 22.8 dv for worst) modeled days at each 

nearby Class I area. For any pair of control levels evaluated, the difference in the level 

of impairment predicted is the degree of improvement in visibility expected. 

For Merrimack Station Unit MK2, the CALPUFF-predicted visibility benefits from BART 

controls on 20% best and 20% worst visibility days are shown below. 

CALPUFF Modeling Results for Merrimack Station Unit MK2: 

Visibility Improvements from BART Controls 

On the 20% Best Visibility Days (deciviews) 

Pollutant Control Level Acadia Great Gulf Lye Brook

SO2 90% with FGD 1.07 0.83 0.17 

NOx Additional 25% with SCR upgrade 0.21 0.18 0.10 

PM 90% with upgraded controls 0.16 0.12 0.03 

On the 20% Worst Visibility Days (deciviews) 

Pollutant Control Level Acadia Great Gulf Lye Brook

SO2 90% with FGD 0.26 0.20 0.03 

NOx Additional 25% with SCR upgrade 0.07 0.06 0.03 

PM 90% with upgraded controls 0.07 0.05 <0.01* 

* below sensitivity limit of model 

Note: Values in boldface are considered as having greater validity in the modeling estimation of maximum 

visibility benefits from BART controls. 
Page 12 of 18 

While Unit MK2 was predicted by the MANE-VU modeling to have up to 2.24 dv impact at 

Acadia National Park under natural conditions, the basis of the BART assessment evaluation 

changes to 20% worst visibility days. On those days, a 90% reduction in sulfur emissions at 

Unit MK2 results in only a maximum of 0.26 dv visibility improvement. At first these results 

may appear to be too low; however, on further examination, it is found that CALPUFF predicts 

the same amount of sulfate from Unit MK2 reaching Acadia under both best and worst visibility 

conditions. The difference is that there is greater than an order of magnitude more background 

sulfate coming from other sources on the 20% worst visibility days, raising the background 

concentrations (and deciviews) to much higher levels. Because the deciview scale is 

logarithmic, the same mass reduction of 0.259 μg/m3

 of sulfate from this one source results in 

wide differences in deciview impacts for different background visibility conditions at opposite 

ends of the range. 

On the 20% best visibility days, if the full impact (or benefit of control for the FGD) could 

somehow be realized at nearby Class I areas without the influence of regional transport from 

other sources, then the benefit could be as high as 1.07 dv. NHDES does not believe this 1.07 

dv of benefit is a realistic expectation for this SIP, which focuses on 2018. 

Detailed CALPUFF Modeling Results for Merrimack Station Unit MK2 for 20% Best Days: 

20% Best Days Acadia Acadia Acadia Acdia Great Gulf Great Gulf Great Gulf Great Gulf Lye Brook Lye Brook Lye Brook Lye Brook

DV DV DV DV Source DV DV DV DV Source DV DV DV DV Source

Load Base Control Benefit Contribution Base Control Benefit Contribution Base Control Benefit Contribution

MK2 Base 14.65 14.65 - 2.25 13.81 13.81 - 1.81 12.31 12.31 - 0.61

MK2 FGD 13.57 14.65 1.07 1.17 13.81 12.98 0.83 0.98 12.31 12.14 0.17 0.44

MK2 SNCR

MK2 SCR Upgrade 14.44 14.65 0.21 2.04 13.81 13.62 0.18 1.62 12.31 12.21 0.097 0.51

MK2 Baghouse 14.98 14.65 (0.33) 2.58 13.81 14.07 (0.26) 2.06 12.31 12.37 (0.06) 0.67

MK2 ESP Upgrade 14.49 14.65 0.16 2.09 13.81 13.69 0.12 1.68 12.31 12.28 0.03 0.58

Detailed CALPUFF Modeling Results for Merrimack Station Unit MK2 for 20% Worst Days: 

20% Worst Days Acadia Acadia Acadia Acdia Great Gulf Great Gulf Great Gulf Great Gulf Lye Brook Lye Brook Lye Brook Lye Brook

DV DV DV DV Source DV DV DV DV Source DV DV DV DV Source

Load Base Control Benefit Contribution Base Control Benefit Contribution Base Control Benefit Contribution

MK2 Base 23.85 23.85 - 1.02 23.58 23.58 - 0.76 24.72 24.72 - 1.89

MK2 FGD 23.59 23.85 0.26 0.76 23.58 23.38 0.20 0.56 24.72 24.68 0.03 1.86

MK2 SNCR

MK2 SCR Upgrade 23.78 23.85 0.07 0.95 23.58 23.52 0.06 0.70 24.72 24.69 0.03 1.86

MK2 Baghouse 23.99 23.85 (0.14) 1.16 23.58 23.69 (0.11) 0.87 24.72 24.74 (0.02) 1.91

MK2 ESP Upgrade 23.78 23.85 0.07 0.96 23.58 23.53 0.05 0.71 24.72 24.71 0.009 1.88

The above analysis indicates that CALPUFF and CALGRID have aligned better in their 

predictions than might be expected on worst visibility days. As presented in earlier drafts of the 

New Hampshire regional haze SIP, CALGRID predicted a maximum visibility benefit of about 

0.1 dv (on the more realistic worst visibility days vs. 0.26 dv on the best visibility days) at Acadia

National Park for a 90% reduction in SO2 emissions. This result may be attributed to the similar 

chemistry used in both models and to the specific circumstances of this case in which the 

prevailing wind direction on the 20% worst visibility days carries Unit MK2 emissions directly 

toward Acadia National Park. The big discrepancy occurs under best visibility days, when 

CALGRID does not account for meteorology that brings significant New Hampshire BART 

source contributions to nearby Class I areas on best visibility days. 

Newington Station Unit NT1: BART Eligibility Modeling 

The BART eligibility modeling conducted by MANE-VU used natural visibility conditions 

(about 7 dv) to produce the most conservative modeling results to minimize sources from 

modeling out of BART. Under natural background conditions, uncontrolled emissions from Unit 
Page 13 of 18 

NT1 produce theoretical CALPUFF worst-case impacts of 1.22 dv at Acadia National Park. As 

in the case of Unit MK2, CALPUFF modeling results for baseline emissions from Unit NT1 

exceed all of the EPA and MANE-VU exemption levels.

Newington Station Unit NT1: BART Benefit Assessment Modeling 

For Newington Station Unit NT1, the CALPUFF-predicted visibility benefits from BART 

controls on 20% best and 20% worst visibility days are smaller than those for Merrimack 

Station Unit MK2: 

CALPUFF Modeling Results for Newington Station Unit NT1: 

Visibility Improvements from BART Controls 

On the 20% Best Visibility Days (deciviews) 

Pollutant Control Level Acadia Great Gulf Lye Brook 

FGD 

(90% sulfur reduction*) 0.57 0.45 0.09 

1.0%-S residual fuel oil 

(50% sulfur reduction*) 0.30 0.24 0.05 

0.5%-S residual fuel oil 

(75% sulfur reduction*) 0.46 0.36 0.07 

0.3%-S residual fuel oil 

(85% sulfur reduction*) 0.52 0.40 0.08 

0.50 lb SO2/MMbtu 

(77% sulfur reduction*) 0.47 0.37 0.08 

SO2 

Switch from 0.50 lb SO2/MMbtu emission 

limit to 0.3%S residual fuel oil <0.05 0.03 <0.01*** 

SNCR 

(25% NOx reduction**) NOx 0.11 0.10 0.04 

SCR 

(78% NOx reduction**) 0.34 0.30 0.12 

PM Baghouse 

(85% PM reduction**) 0.05 0.04 0.01 

On the 20% Worst Visibility Days (deciviews) 

Pollutant Control Level Acadia Great Gulf Lye Brook 

FGD 

(90% sulfur reduction*) 0.13 0.10 <0.01*** 

1.0%-S residual fuel oil 

(50% sulfur reduction*) 0.07 0.06 <0.01*** 

0.5%-S residual fuel oil 

(75% sulfur reduction*) 0.11 0.09 0.01 

0.3%-S residual fuel oil 

(85% sulfur reduction*) 0.13 0.10 0.01 

0.50 lb SO2/MMbtu 

(77% sulfur reduction*) 0.11 0.09 0.01 

SO2 

Switch from 0.50 lb SO2/MMbtu emission 

limit to 0.3%S residual fuel oil 0.01 0.01 <0.01*** 

SNCR 

(25% NOx reduction**) NOx 0.04 0.03 0.01

SCR 

(78% NOx reduction**) 0.11 0.10 0.03 

PM Baghouse 

(85% PM reduction**) 0.02 0.02 <0.01*** 

 * from maximum permitted level 

 ** from baseline level with existing controls 

 *** below sensitivity limit of model 

Note: Values in boldface are considered as having greater validity in the modeling estimation of maximum 

visibility benefits from BART controls. 
Page 14 of 18 

As presented in an earlier draft of the New Hampshire regional haze SIP, CALGRID predicted a 

maximum negligible visibility benefit (less than 0.1 dv) at Acadia National Park for a 75% 

reduction in SO2 emissions. 

Detailed CALPUFF Modeling Results for Newington Station Unit NT1 for 20% Best Days: 

20% Best Days Acadia Acadia Acadia Acdia Great Gulf Great Gulf Great Gulf Great Gulf Lye Brook Lye Brook Lye Brook Lye Brook

DV DV DV DV Source DV DV DV DV Source DV DV DV DV Source

Load Base Control Benefit Contribution Base Control Benefit Contribution Base Control Benefit Contribution

NT1 Base 13.62 13.62 - 1.22 12.99 12.99 - 0.99 11.98 11.98 - 0.28

NT1 1% S 13.32 13.62 0.30 0.92 12.99 12.75 0.24 0.75 11.98 11.93 0.05 0.23

NT1 0.5% S 13.16 13.62 0.46 0.76 12.99 12.63 0.36 0.63 11.98 11.91 0.07 0.21

NT1 0.50 lb SO2/MMBtu 13.15 13.62 0.47 0.75 12.99 12.62 0.37 0.62 11.98 11.91 0.08 0.21

NT1 0.3% S 13.10 13.62 0.52 0.70 12.99 12.59 0.40 0.58 11.98 11.90 0.08 0.20

NT1 FGD 13.05 13.62 0.57 0.65 12.99 12.54 0.45 0.54 11.98 11.89 0.09 0.19

NT1 SNCR 13.51 13.62 0.11 1.11 12.99 12.89 0.10 0.89 11.98 11.94 0.04 0.24

NT1 SCR 13.28 13.62 0.34 0.88 12.99 12.69 0.30 0.69 11.98 11.86 0.12 0.16

NT1 ESP (real) 13.08 13.62 0.54 1.11 12.99 12.56 0.43 0.89 11.98 11.87 0.12 0.24

NT1 Baghouse 13.03 13.62 0.05 1.11 12.99 12.51 0.04 0.89 11.98 11.86 0.01 0.24

Detailed CALPUFF Modeling Results for Newington Station Unit NT1 for 20% Worst Days: 

20% Worst Days Acadia Acadia Acadia Acdia Great Gulf Great Gulf Great Gulf Great Gulf Lye Brook Lye Brook Lye Brook Lye Brook

DV DV DV DV Source DV DV DV DV Source DV DV DV DV Source

Load Base Control Benefit Contribution Base Control Benefit Contribution Base Control Benefit Contribution

NT1 Base 23.42 23.42 - 0.59 23.24 23.24 - 0.42 24.61 24.61 - 1.79

NT1 1% S 23.34 23.42 0.07 0.52 23.24 23.19 0.06 0.36 24.61 24.61 0.008 1.78

NT1 0.5% S 23.31 23.42 0.11 0.48 23.24 23.16 0.09 0.33 24.61 24.60 0.01 1.78

NT1 0.50 lb SO2/MMBtu 23.30 23.42 0.11 0.48 23.24 23.15 0.09 0.33 24.61 24.60 0.01 1.78

NT1 0.3% S 23.29 23.42 0.13 0.47 23.24 23.14 0.10 0.32 24.61 24.60 0.01 1.78

NT1 FGD 23.28 23.42 0.13 0.46 23.24 23.14 0.10 0.31 24.61 24.60 0.01 1.78

NT1 SNCR 23.38 23.42 0.04 0.56 23.24 23.21 0.03 0.38 24.61 24.60 0.01 1.78

NT1 SCR 23.31 23.42 0.11 0.48 23.24 23.14 0.10 0.32 24.61 24.58 0.03 1.76

NT1 ESP (real) 23.19 23.42 0.23 0.56 23.24 23.06 0.18 0.38 24.61 24.58 0.04 1.78

NT1 Baghouse 23.17 23.42 0.02 0.56 23.24 23.04 0.02 0.38 24.61 24.57 0.003 1.78

Emissions and Reduction Scenarios as Follows:

Maximum Source Contributions to Nearby Class I Areas after Potential BART 

Controls at MK2 on 20% Best Visibility Days 

BART Controls Control Level (%) 

CALPUFF Source 

Contribution (DV) 

Highest 24-Hour Period 

SO2 Lower S Coal (ex) 40 

NOx SCR (ex) 85 

PM Two ESPs (ex) 99+ 

2.25 

SO2 FGD 90 1.17 

NOx SCR Upgrade to 90 2.04 

PM ESP Upgrade 99.5 2.09 

Note: Currently permitted emissions produced a CALPUFF visibility impact of 2.25 dv on 20% 

Best visibility days. 
Page 15 of 18 

Maximum Source Contributions to Nearby Class I Areas after Potential BART 

Controls at NT1 on 20% Best Visibility Days 

Note: Currently permitted emissions produced a CALPUFF visibility impact of 1.22 dv on 20% 

Best visibility days. 

Federal Register Modeling recommendations (FR 69/87 May 5, 2004) 

Page 25193 

For modeling an individual BART-eligible source located more than 50 km from a Class I area, 

we propose that an air quality model, such as CALPUFF be used. 

Page 25194 

Converting a 5 percent change in light extinction to a change in deciviews yields a change of 

approximately 0.5 deciviews. This is a natural breakpoint at which to set the exemption level, 

since visibility degradation may begin to be recognized by human observer at this extinction 

level. Thus we are proposing a 0.5 deciview change as the threshold for determining that an 

individual source is causing visibility impairment at a Class I area. This level would be 

calculated by measuring the air quality screening modeling results for an individual source 

against natural visibility conditions. 

Page 25189 and Page 25203 

For assessing the 5th factor, the degree of improvement in visibility from various BART control 

levels, we are proposing that States require individual sources to run CALPUFF, or other EPAapproved model, using site-specific data. To estimate a source’s impact on visibility, the 

source would run the model using current allowable emissions, and then again at the postcontrol emissions level (or levels) being assessed. Results would then be tabulated for the 

average of the 20% worst modeled days at each receptor. The difference in the resulting level 

of impairment predicted is the degree of improvement in visibility expected. 

BART Controls Control Level (%) 

CALPUFF Source 

Contribution (DV) 

Highest 24-Hour Period 

2% S Oil (from existing 1.5%) 0 

NOx overfire (ex) 33 

PM ESPs (ex) 42 

1.22 

SO2 FGD 90 0.63 

SO2 1% S (from 1.5%) 50 0.92 

SO2 0.5% S 75 0.76 

SO2 0.3% S 85 0.70 

SO2 0.50 lb SO2/MMBtu 77 0.75 

NOx SNCR 50 1.11 

NOx SCR 85 0.88 

PM Fabric Filters 99 1.11 
Page 16 of 18 

Attachment: 

Email Communication with EPA Region 1 Regarding BART Modeling 

-----Original Message----- 

From: mcwilliams.anne@epamail.epa.gov 

[mailto:mcwilliams.anne@epamail.epa.gov] 

Sent: Friday, August 06, 2010 1:22 PM 

To: Healy, David 

Subject: Fw: PSNH BART Modeling with CALPUFF 

Hi Dave, 

I have concerns regarding the approach to BART visibility impact modeling 

proposed in Jeff's e-mail of 4/20/10 (below). In this e-mail, NHDES is 

proposing to determine visibility improvement from installation of controls 

in respect to current background conditions. 

 " The changes in predicted concentrations (with and without 

 control) were converted to changes in visibility (DV) using the 

 logarithmic relationship between DV and concentrations at the regional 

 Class 1 areas (based on actual monitoring data collected from 1996 to 

 2008)." 

 CFR Part 51, Appendix Y clearly states: 

 "For each source, run the model, at pre-control and post-control 

emission rates according to the accepted methodology in the protocol. 

 Use the 24-hour average actual emission rate from the highest emitting 

day of the meteorological period modeled (for the pre-control scenario). 

Calculate the model results for each receptor as the change in deciviews 

compared against natural visibility conditions." 

The goal of the Regional Haze Rule is to return the Class 1 areas to natural 

visibility conditions by 2064. By calculating the expected visibility 

improvements of BART controls based on current conditions, the analysis is 

not supporting this goal. Furthermore, if the BART determination is based 

on current conditions, the impact of that source on visibility in the Class 

1 areas will increase over time as the influence of other sources are lessen 

through the installation of controls, once again leading to a failure to 

adequately assess the impact of BART controls for that source on the Class 1 

area. 

Anne 

Anne McWilliams 

Air Quality Planning 

EPA - New England 

Tel: 617 918-1697 

Fax: 617 918-0697 

Mailing Address: 

EPA Region 1 

Five Post Office Square - Suite 100 

Mail Code - OEP05-02 

Boston, MA 02109-3912 
Page 17 of 18 

----- Forwarded by Anne McWilliams/R1/USEPA/US on 08/06/2010 12:56 PM 

----- 

 

 From: "Underhill, Jeff" <Jeffrey.Underhill@des.nh.gov> 

 To: Anne McWilliams/R1/USEPA/US@EPA 

 Cc: "Healy, David" <David.Healy@des.nh.gov> 

 Date: 04/20/2010 03:30 PM 

 Subject: RE: PSNH BART Modeling with CALPUFF 

 

Anne, 

I'm having a little trouble understanding the 98th percentile approach you 

describe below. Are you referring to the 98th percentile (8th highest DV 

day) based on monitoring for baseline year (2002), for annual CALPUFF 

modeling with all sources, or for maximum impact days for the BART facility 

in question? 

NHDES took a different approach to this CALPUFF modeling since I have 

concerns with how the model actually works. I have to believe that the NH 

alternative approach gives realistic results that are supported by 

traditional science, but the approach is different which may cause you 

concern for consistency. The guidance for modeling does provide latitude 

and I believe we are within that guidance. 

While we are working on a more formal write-up, I can briefly describe the 

process to you. CALPUFF was used to model the NH BART sources with and 

without controls. A full year of met data was used. Maximum predicted 24-

hour concentrations for the source were isolated for each Class 1 area. The 

changes in predicted concentrations (with and without 

control) were converted to changes in visibility (DV) using the logarithmic 

relationship between DV and concentrations at the regional Class 1 areas 

(based on actual monitoring data collected from 1996 to 2008). This last 

step provides for the application of using the model in a relative way as 

preferred by EPA guidance. For BART exemption purposes, a background 

visibility of 7DV (natural conditions) was used to define the set point and 

for 20% worst days, the baseline 22.8DV submitted with the SIP was used. 

These set points reflected the location on the DV to concentration 

logarithmic relationship curve to use a starting point for visibility impact 

benefit assessment. 

We chose this approach because CALPUFF uses a generic approach to 

calculating DVs based on national averages. I would suggest that our use of 

actual regional IMPROVE monitoring is more scientifically rigorous and 

defendable based on the nature of our prevailing mix of concentrations. 

So, if I have a question in here somewhere, it would be, would you prefer 

that we capture CALPUFF's 8th highest impact for the year (instead of the 

1st highest) to use for our assessment? Or would you prefer that we use the 

8th worst visibility day for the baseline year 

(2002) to use as background DV? I think we have the second option 

relatively well covered by using the baseline value which is the average of 

the 20% worst days. 

Thanks! 

Jeff 

-----Original Message----- 

From: Healy, David 

Sent: Friday, April 16, 2010 4:31 PM 

To: Underhill, Jeff 

Subject: FW: PSNH BART Modeling with CALPUFF 
Page 18 of 18 

Hi again, Jeff. FYI, here are some communications that I've been having 

with Anne McWilliams. 

Dave 

-----Original Message----- 

From: mcwilliams.anne@epamail.epa.gov 

[mailto:mcwilliams.anne@epamail.epa.gov] 

Sent: Friday, April 16, 2010 4:22 PM 

To: Healy, David 

Subject: RE: PSNH BART Modeling with CALPUFF 

Hi Dave, 

Many of the BART visibility protocols call for the visibility change 

expected on the 8th highest 24 hr visibility impact day (98th 

percentile) due to the installation of control. This value was used in 

conjunction with the use of 3 yrs of meteorology. In discussions with Maine 

and Massachusetts, we have discussed using the change in visibility due to 

installation of controls on highest impacted day when only using 1 yr of 

meteorology. However, several of the sources still included the change in 

visibility impact for the 8th highest visibility impacted day. 

Anne 

Anne McWilliams 

Air Quality Planning 

EPA - New England 

Tel: 617 918-1697 

Fax: 617 918-0697 

Mailing Address: 

EPA Region 1 

Five Post Office Square - Suite 100 

Mail Code - OEP05-02 

Boston, MA 02109-3912