### MONTANA SULPHUR & 

### CHEMICAL COMPANY

627 ExxonMobil Road • P.O. Box 31118 BILLINGS, MONTANA 59107-1118 OFFICE: 406-252-9324 • FAX: 406-252-8250

June4,2009



## u.s. EnvironmentalProtectionAgencyRegion 8 1595 Wynkoop Street Denver, Colorado 80202-1129

Attention: LaurelDygowski, 8P-AR

DearLaurel:



### RE: ResponsetoInformationRequestLetterof1/29/09Pursuantto Section 114(a) CleanAirAct

OnFebruary5, 2009,Montana Sulphur& ChemicalCo (MSCC)received a letterfromyouroffice requestinginformationregardingourfacility as it relatesto EPA'splansto address 'reasonableprogress andlong-termstrategies' for meetingrequirements undertheRegionalHazeRule (40 CFR51.308). The request was made, according to the letter, under authorityofSection 114(a)ofthe CleanAirAct [42 USC 7414(a)].

Accordingtotheletter, MSCChas 30businessdays torespondto therequest. OnMarch6, 2009, we sent

a letterto you requestingan extension ofthis deadline date for certainparts oftherequested lllformation. Sincewehadnotreceivedareplyfromyouregardingthatrequest, weprovidedas muchinformationas
wewereableto gatherandverifyas ofMarch20, 2009.

Subsequently, wereceivedaresponseto ourrequest for additionaldefinitions forthetermsthatwelisted inourMarch6request for anextension. Withthat additionalinsight intothedesireddata andadditional timeto examine ourrecords, weareherewithprovidingadditionalresponsetoyourrequest for information.

OursupplementinformationisprovidedinAttachmentA Addendum. Ifyouhave anyquestions regardingAttachmentA Addendum, pleasecontactus andwewillprovideclarificationasbestwecan.

IcertifyunderpenaltyoflawthatIhavepersonallyexaminedandamfamiliarwiththeinformation submittedinthis document and all artachnlents andthat, basedonmyinquiryofthose individuals immediatelyresponsible forobtaininginformation, Ibelievethatthe iriformationis true, accurate, and complete [insofaras is possibleatthis date]. I amawarethatthereare significantpenalties for submitting false information, includingthepossibilityoffine orinlprisonment.

Date: June4, 2009

## Addendunlto AttachmentA Montana Sulphur& 

## Chemical Company Request for InformationPursuantto Section 114 ofthe CAA January29, 2009

1. ContactInformation

a. Narne: MargaretHofackerandLarryZink b. Title: RegulatoryManagerandPresident, respectively

c. TelephoneNumber: 406.252.9324 d. FaxNumber: 406.252.8250

e. e-Mail: margaret@n10ntanasulphur.comandlarry@montanasulphur.com

2. ClausProcess d. Whatis thedesign efficiency ofthe Clausprocess? ANSWER: Thank you for the clarification of your definition of "design efficiency." MSCC takes this opportunity to provide additional response to this question.

You have stated:

We're looking for a value to compare to the NSPS efficiency level, which is 99.7%. (That is: at the NSPS level, less than 0.3% of the sulfur entering the unit would be emitted.) The efficiency is not explicitly defined in the NSPS rule, since the rule is expressed as ppm in the exhaust gas (250 ppmv is [sic] the gas is [sic] incinerated)

.
MSCC does not have readily available any measures directly comparable to the NSPS rule, which itself is not applicable to MSCC. The NSPS (40 CFR 60 Subpart J) does not address or represent efficiency of a Claus process per se, but rather addresses the emissions from downstream treatment unit(s) operating on Claus tail gas.

As to Claus processes generally, AP-42 provides estimates for typical process production efficiencies, as previously indicated in our response(s).

We do measure, record and report to the Montana Department of Environmental Quality (MDEQ) the hourly average concentration of sulfur dioxide at the CEMS in
our main SRU stack. These data, which are not directly comparable to NSPS concentrations, are available to EPA and to the public. That being said, we note that the CEMS measurements on the main SRU stack are made on wet stack gas; no diluent gas measurements are made by the CEMS. The main stack is also a merged stack, thus there is generally a flow contribution to the measured stream from the Claus process, the SuperClaus 1M processes and the tail gas incinerator process, as well as from other gas-fired boilers at times. There are also uncertainties in the CEMS measurements, which are determined at the time of our annual RATA (Relative Accuracy Test Audit). A review of our RATA results show that our CEMS concentration measurements have ranged between +2.55 and +12.3 percent of the reference method (EPA Method 6/6C). Thus, the reported data are conservative and may overestimate the actual S02 emissions.

In addition, for the same stack, MSCC documented an Alternative Monitoring Plan (AMP) for MDEQ as part of the 1998 Stipulation requirements. This plan provides



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## Addendumto AttachmentA Montana Sulphtlf&Chemical Company RequestfOfInformationPtlfSuantto Section 114 ofthe CAA January29, 2009

methods for estimating emissions based on the calculation of a daily process efficiency value using CEMS S02 mass emission data and separate daily measurements of plant raw material feed gas inputs. This AMP methodology does not address the Claus process separately from the other SRU processes (Le., SuperClausTM/lncinerator) except to the extent that such other processes happen to be offline for a particular calculation.

There are also uncertainties in developing the AMP production process efficiency estimations. The amount of incoming sulfur is calculated using orifice plate metering and routine daily laboratory testing of several input streams for H2 S content. This information is determined on a daily basis and is adequate for commercial custody transfer purposes. This AMP calculation does not require information on stack gas water or oxygen content and is essentially insensitive to whether other boilers are contributing to the stack emission stream. The AMP method is directly affected by the above-mentioned uncertainties in CEMS measurement of S02 concentration in the stack gas and by plant input measurement (metering and laboratory) uncertainties. Accuracy is sensitive to process upsets related to the composition of the feed gases that may change throughout the day but are characterized by one daily grab sampling and analysis for H2 S content.
Subject to the comments above regarding uncertainties and a reiteration that the AMP calculated production process efficiency is not a measure of "design efficiency,"
a review of calendar year 2008 AMP calculated efficiencies was conducted. Our records indicate that production process efficiency levels (daily) averaged approximately 98.3 percent and varied in the range of 95.8 to 99.4 percent during days of SuperClausTM operation. (The standard deviation over the particular year was less than 0.2 percent.) This may represent a level of 'actual' efficiency during SuperClausTM operation for that year; please note, however, that uncertainties of measurement of both input and output sulfur can affect calculated efficiency substantially atthese high levels of recovery. Actual efficiencies will also be affected by process upsets as well as the catalyst ages and types, feed material quality, and conditions of related equipment. The year 2008 involved operation with both the 1998 unit and the 2008 unitfor parts ofthe year.

Also subject to the comments above, a review of older AMP calculated efficiencies
was conducted to identify (daily) periods during which neither of the SuperClausTM units was in operation for comparison. Over the past five years, several such periods
were identified. The longest ofthese identified periods was seventeen days between July 30 and August 17, 2002. However, after the initial SuperClausTM was first put into service, the only identified periods when the SuperClausTM was not in operation
were non-typical periods ofturnaround or malfunction. For that reason, data prior to the startup of the first SuperGlausTM on December 8, 1998, were examined. GEMS recordkeeping was initiated on January 1, 1998, and our records for calendar year 1998 indicate that prior to the SuperClausTM startup, the calculated process efficiencies averaged 95.5 percent and varied in the range between 91.0 and 96.6 percent. (Standard deviation ofthese values was 0.27 percent.) By comparison, with
new SuperGlausTM catalyst and equipment after the initial startup, the calculated



### 2

## Addendumto AttachmentA Montana Sulphur& 

## Chemical Company Request for InformationPursuantto Section 114 ofthe CAA January29, 2009

(average) process efficiency for December 9 through December 31, 1998, was seen to increase to 98.1 percent. These values may represent a level of 'actual' Claus process production efficiency, but, again, they are not suitable to be compared with the non-applicable NSPS requirements. Please also note again that uncertainties of measurement of both input sulfurto the Claus and final output sulfur at the stack can affect calculated production efficiency very substantially at these high levels of recovery.

Not surprisingly, the AMP information can be seen to confirm that operations with the SuperClausTM processing online result in substantially lower emissions and higher efficiencies in sulfur recovery based on the CEMS measurements.

After reviewing our data in light of the additional information that you provided, we respectfully decline to provide a design efficiency or a surrogate for "design" efficiency for the Claus Process. We find that term is not defined in applicable law or regulations. As we stated in our earlier response to this question, "design efficiency" is not a concept used in designing or running the subject processes at MSCC or at comparable sources. We note that NSPS itself does not use the term, but instead
uses a specific "adjusted" ppmv measurement, corrected for watervapor and oxygen content, and which we presume is based on thermal incineration rather than catalytic incineration. The non-comparable regulatory measure for MSCC would be S02 mass emissions, which is measured and used for regulatory purposes other than for comparison with NSPS. These values should not be directly compared with the nonapplicable NSPS measurements.

e. Whatis the expectedremainingequipmentlife oftheClausprocess? ANSWER: Thank you also for the clarification of your definition of "expected remaining equipment life." MSCC takes this opportunity to provide additional comment on this question.

In your clarification you have stated:

Does the company expect to take the emission source out of service within the 15-20 [year] time period over which the cost of pollution controls would be amortized. If so, for how many more years will the source be generating emissions[?]

We have again reviewed our available information and find that MSCC has insufficient information to know or estimate when the emission source(s) will be taken out of service. That said, MSCC has no current plans or expectation to take the emission source(s) permanently out of service. See prior response. Thus "expected" remaining useful life remains indeterminate.



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### Addendumto AttachmentA Montana Sulphur& Chemical Company Request for InformationPursuantto Section 114 ofthe CAA January29, 2009

3. SuperClausprocess d. Whatis thedesign efficiency? ANSWER: In our initial response dated March 20, 2009, MSCC reserved the right to supplement these responses at a later date if additional information were obtained. Review ofthe process engineering design package forthe SuperClausTM indicates that the licensor offered an initial performance guarantee of 98.5 percent recovery of sulfur with a three-stage Claus process followed by a SuperClausTM process with all new catalyst and condenser equipment and very specific process and feed conditions. Please note that this number is not a design efficiency value, but is an initial process production "performance" value taken in conjunction with the Claus process. No other additional design efficiency information has been identified. Please see the response to item 2.d above, which provides some insight into 'actual' process production efficiencies ofthe combined SuperClausTM and Claus processes, subject to the uncertainties of measurement and variations of day-to-day operation discussed there.

h. Expectedrenlaininglife ofthe mostrecentSuperClausprocess? ANSWER: MSCC reserved the right to supplement this response at a later date if additional information or definition were obtained. Please see the response to item 2.e above. The expected life ofthise equipment remains indeterminate.

i. Expectedremaininglife ofthe older SuperClausprocess? ANSWER: In our March 20, 2009, submittal, MSCC reserved the right to supplement this response at a later date if additional information or definition were obtained. Please
see the response to item 2.e above. The expected life of the equipment remains indeterminate.

j. Is there sufficient physical space in the facility to add an additional tail gas treatment unit afterthe SuperClauseffluentunits? ANSWER: In the March 20, 2009, submittal, MSCC reserved the right to supplement this response at a later date if additional information or definition were obtained. No additional clarification was provided.
Making room for additional significant tail gas treatment units afterthe SuperClausTM units is not viewed as practical; and no discernible or significant improvement in regional haze could result. Please note that MSCC's processing equipment, including the two SuperClausTM units, and incineration equipment, now occupy a space originally designed, in 1954, to accommodate one Claus train. Please note also that MSCC is sited on a narrow parcel of land with roadways and railroad on either side making expansion onto adjacent land (owned by others) infeasible.



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### Addendtlffito AttachmentA Montana Sulphur& Chemical Company Request for InformationPursuantto Section 114 ofthe CAA January29,2009

k. Conditionsofthe SuperClausexhaustgas (combined streamfrombothunits)? ANSWER: 

### MSCC has developed a spreadsheet to respond more fully to this question. The spreadsheet is based on information and estimates provided by the designer of the first SuperClausTM unit, which in turn were based on various assumptions. (The second unit, added in 2008, is substantially identical; each unit is designed to be capable of handing Claus tail gases for up to 170 LT per day of upstream Claus feed rate, at specific identified conditions. The two SuperClausTM 

### units together are believed to be at least adequate for the entire output stream from the upstream Claus process and are licensed to process up to 250 L TSE/d). This spreadsheet estimates the following values: i. Maximum volumetric flow rate (acfm): 

### The expected flow rate at the design rate (170 LT/day) is 17,650 acfm for either one of the two units. For both of the units together, operating at maximum licensed Claus unit sulfur input (250 L

T/day), this spreadsheet indicates a maximum combined expected flow of 25,958 acfm at the effluent of the SuperClausTM 

### process equipment. Actual maximum expected rates would be different underdifferent assumptions. ii. Average volumetric flow rate (acfm): 

### The estimated flow rate at the average 

### 2008 process rate of 106 L TSE/d plant input rates was approximately 62 percent ofthe design rate for one SuperClausTM unit at approximately 11,006 acfm. Of course, actual rates will vary substantially with feed gas hydrocarbon composition. iii. Temperature (OF): 

### The temperature of the process gas from the SuperClausTM 

### condenser was modeled by the designer to be approximately 260°F and typical actual is more like 290°F. The higher temperature was subsequently suggested by the designers to help address corrosion issues found with the original design and the feed that is specific to this plant. For 12 'randomly' selected days (one day each month) in calendar year 2008, the SuperClausTM condenser gas outlet temperature measurement averaged 283°F. iv. Moisture (percent): 

### The process gas 'from the SuperClausTM 

### condenser was modeled to contain approximately 23 weight percent water. This also can vary substantially, depending on feed composition and otherfactors.

v. Hours of operation: 

### The sulfur recovery process at MSCC is a continuous operation. While operation of the SuperClausTM process is voluntary, one or both of the two SuperClausTM 

### units typically operates 24 hours a day, seven days a week. This provides a substantial margin of safety for MSCC in meeting main stack emission limitations. The primary exceptions to this schedule are short (typical durations areef minutes to hours) emergency bypass events to protect the expensive and delicate SuperClausTM 

### catalyst from excessively high temperatures and reducing conditions such as may be caused by utility interruptions, training events, and startup/shutdown events. A primary purpose of the second SuperClausTM 

### is to ensure that one unit is available for the sulfur recovery process at MSCC, while the other is shut down for maintenance. Ofcourse, unusual conditions, such as force majeure events, could result in both units being down at the same time.

5

## Addendumto AttachmentA Montana Sulphur& 

## Chemical Company Request for InformationPursuantto Section 114 ofthe CAA January29, 2009

vi. S02 concentration (ppm): The S02 concentration in the process gas from the SuperClausTM condenser was estimated to be approximately 4600 ppm by weight. 

### vii. H2S concentration (ppm): The H2 S concentration in the process gas from the SuperClausTM condenser was estimated to be approximately 385 ppm by weight. Other reduced sulfur species, including elemental sulfur, are estimated to total about 1250 ppm by weight; these species and H2 S typically oxidize to S02 in the downstream incineratorwhich is used for control ofodor and opacity.



### Please note that all detailed process information, other than direct emission rates and temperatures at the main stack, relating to the SuperClausTM 

### process as modeled oroperated is Confidential Business Information.

4. Tailgasincinerator

a. Whatis theexpectedremainingequipmentlife ofthetailgas incinerator? ANSWER: In our submittal of March 20, 2009, MSCC reserved the right to supplement this response at a later date if additional information or definition were obtained. Please
see the response to item 2.e above. The expected life of the equipment remains indeterminate.

b. Is thereenough physical spaceto adda scrubber afterthe tail gasincinerator? ANSWER: More information is needed about the operation, requirements, size, footprint and height of the "scrubber" technology being contemplated by EPA. The area is occupied by existing equipment, such as the existing Claus and SuperClausTM equipment. See response above. A photograph of the area in question is shown on the final page ofthis attachment.

MSCC may supplement this response as additional information and clarification are obtained.

c. Incineratoroperatingcharacteristics: ANSWER: i. Maximumheatinput? MSCC reserved the right tQfAaY supplement this response as additional information and clarification weare obtained. MSCC has no information to expand on the design information provided earlier of35 MMBtu/hr. This value is documented in MSCC's Air Quality Permit AQP2611-03 and also is applicable for the new redundant incinerator operating in non-catalytic mode ofoperation. A review ofthe 2008 data suggests that the actual maximum heat (daily) input during the calendar year was approximately 8 million Btu/hr for the existing incinerator, which runs essentially all of the time. Heat input varies with production rates, weather conditions, and operating temperatures. Fuel use, operating temperature, flow, inerts and CO2errtissions are expected to be substantially higherwhen the less energy efficient non-catalytic option is used.

6

### Addendumto Attachmel1tA Montana Sulphur & Chemical Company Request for InformationPursuantto Section 114 ofthe CAA January29, 2009

ii. Averageheatinput? The review of calendar 2008 data suggests that the average heat input to the existing incinerator was 4 to 5 million Btu/hr. Average heat input will vary with average plant throughput and mode of operation. The unit operated in the more energy efficient catalytic mode during the year 2008.

e. Conditions oftheincineratorexhaustgas: ANSWER: MSCC does not directly measure conditions at the outlet of the tail gas incinerator other than temperature at this time. The conditions in the main SRU stack are the most characteristic data available forthe variety of information requested, as much of the gas at that stack arises from the incinerator outlet flows. As stated above, the main SRU stack is a merged stack, with contributions to the measured stream from the Claus process and the SuperClausTM process feeding the incinerator, along with intermittent contributions from other gas-fired boilers, etc. CEMS and operating data for 2008 were reviewed to identify periods when the Claus and one or more SuperClausTM processes were operating, but other gas-fired boilers were not operating and thus not expected to be contributing significant flow to the merged stack stream. The responses below generally provide main-stack CEMS values characteristic of such periods. Main stack moisture percentage is measured only during the annual RATA. These values are the most representative actual measurement data for the tail gas incinerator output stream for the calendar year 2008. i. Maximum volumetric flow rate (acfm): The CEMS measures the flow rate

continuously and records the information in units of wet standard cubic feet per hour. The CEMS also measures stack temperature and stack pressure continuously and records these data on an hourly basis. Using that information, the maximum hourly average volumetric flow rate when no gas-fired boilers were operating, but the Claus and SuperClausTM processes were operating in calendar year 2008 was determined to be 29,057 ac'fm. No specific design information was identified as to potential "maximum volumetric 'flow." ii. Average volumetric flow rate (acfm): Using the same methodology as discussed

in i. above, the hourly average volumetric flow rate for calendar year 2008 when
no gas-fired boilers were operating, but the Claus and SuperClausTM processes were operating was determined to be 24,704 ac'fm.

Ill. Temperature (OF): The CEMS measures the stack temperature continuously and records these data on an hourly basis. The average stack temperature for calendar year 2008 when no gas-fired boilers were operating, but the Claus and SuperClausTM processes were operating was determined to be 548°F. Over these selected periods in calendar year 2008, the stack temperature ranged from 497°F to 612°F at the CEMS. The temperature at the incinerator outlet is somewhat higher than the temperature observed at the stack. A random sampling of incinerator outlet temperature process data for calendar year 2008 showed an average of608°F and a range of 550°F to 648°F (standard deviation of 2.9°F). The maximum expected temperature at the main stack is -1200°F, which might be seen in the event ofnon-catalytic operation ofthe incinerator.



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### Addendllmto AttachmentA Montana Sulphur& 

### Chemical Company Request for InformationPursuantto Section 114ofthe CAA January29, 2009

iv. Moisture (percent): The moisture in the SRU stack is measured only during the a.nnual RATA. Over the past three years, only the RATA conducted in 2006 occurred on a day when there were no additional contributions from gas-fired boilers. The moisture ranged from 17.85 to 18.64 during the RATA on November 21,2006.

v. Hours of operation: The sulfur recovery process at MSCC is a continuous

operation. Thus, the incinerator normally operates 24 hours a day, seven days a week. The prima.ry exceptions to this schedule would be for repairs to the incinerator itself, training events, malfunctions, utility interruptions, or other force majeure events. vi. S02 concentration (ppm): During such hours of non-operation of other boiler contributors to the stack in calendar year 2008, the average 1-hour S02 concentration was determined to be 2,629 parts per million by volume (ppmv). The CEMS value ranged from 6,191 ppmv to 1,442 ppmv. The higher value occurred during an hour that a Claus recovery boiler was re-started after being off-line for approximately two weeks because of very low input gas feed flows. Concentrations of S02 at the main SRU stack are generally lower during periods of fuel gas boiler operation with this merged stack, since these fuel gas-fired boilers contribute onlytrivial amounts ofsulfur dioxide. vii. H2S concentration (ppm): The purpose of the tail gas oxidizer (TGO) is to oxidize substantially all of the H2 S and other reduced sulfur in the incoming stream to the TGO to S02. H2 S is not monitored in the stack gas, nor is it expected to be present in significant amounts or concentrations due to the operation ofthe incinerator itself.

5. Flares

a. Areanycontrolmeasurescurrentlyinuse orplannedfor flares atMS&CC? ANSWER:
See the March 20, 2009, response. MSCC may supplement this response as additional information and clarification are obtained. MSCC is considering the possibilities of re-routing certain low volumetric (currently defined as de minimis) flows of potentially waste gases that are currently potentially sent to the flare system to more beneficial destinations in the facility. Details are not available at this time. No significant impact on flare or plant S02 emissions is expected from this possible work.

c. Is there any impediment to installing a flare gas recovery system, which would hold flare gases untiltheycanbetreated to remove sulfurorreturnedto therefineryfuel gas system? ANSWER: Thank you for the clarification of your thinking concerning a flare gas recovery system. MSCC takes this opportunityto provide additional response to this question. Please also see our response in the March 20, 2009, submittal.

You have stated:

Flare gas recovery system



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### Addendumto AttachmentA Montana Sulphur& Chemical Company Request for InformationPursuantto Section 114 ofthe CAA January29, 2009

We were thinking of a system referred to in a STAPPA/ALAPCO

menu of controls, which states: "Refineries can also install flare gas recovery systems to collect and treat refinery gases, reducing the need for flaring while at the same time recovering the gas for

use in refinery furnaces and boilers. Several such installations already exist in New Jersey

... " This and other examples of potential flare controls are discussed by the California Bay Area APCD at http://www.baagmd.gov/enf/flares.htm.



### MSCC is considering how such a system might be constructed and operated and the implications associated with re-routing some low volumetric flows ofgases otherwise destined for combustion at the flare. Safety concerns preclude "holding" flare gases that might arise in large volumes from emergency, malfunction, or startup/shutdown activities at MSCC. Please note that MSCC is not a refinery.

Review of the documentation referred to in EPA's response did not fiRidentifya a system in use that claims to Ihold' gases of high H2

### S concentration per

### se for future treatment or use. Our review found refinery flare gas recovery systems that appear to treat gases (up to some flow, pressure, concentration ortemperature limit) as they arrive, by limited redirection to a refinery fuel gas recovery system. As previously indicated, operations at MSCC already assist in the successful operation of such a limited system at a nearby refinery. However, these methods by their nature presuppose and require the operation ofthe fuel gas treatment system (e.g., amine unit) and downstream sulfur recovery plant operations, and are therefore impractical or limited during periods of malfunction, startup or shutdown affecting either 

### of those critical systems. They also require an appropriate and large enough user to be operating at the facility to consume the fuel as it is recovered. Since most significant flaring that occurs at MSCC currently arises from startup/shutdown and malfunction events affecting precisely these two types of systems (sulfur recovery and fuel gas treatment), we must conclude that such a system would not be practical here for mitigating such events.

d. What volume of gas would have to be held by a flare gas recovery system in order to reduceflare emissionsofS02by900 /O? ANSWER: 

### In the March 20, 2009, submittal, MSCC reserved the right to supplement this response as additional information and clarification are obtained. No such additional information or clarification was identified. It may be noted that the volume of toxic and flammable gases hypothetically "held" identified in the March 20, 2009, response could be much larger if the concentration of H2

### S in flare gases were lower than the 90 percent H2

### S assumed in the example.

6. Otherpollutioncontrolequipment(ifapplicable)

c. Whatis the expectedremainingequipmentlife ofthe controlequipment? ANSWER: 

### In our subrrlittal of March 20, 2009, MSCC reserved the right to supplement this response at a later date if additional information or definition were obtained. Please
see the response to item 2.e above.



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### Addendumto AttachmentA Montana Sulphur& 

### Chemical Company Request for InformationPursuantto Section 114 ofthe CAA Jal1uary 29,2009

7. Finalcontrolledemissions:

a. What were the total controlled S02 emissions from the process, after all control devices, in themostrecentyearforwhich data areavailable? ANSWER: 

### In the March 20, 2009, submittal, MSCC reserved the right to supplement this response as additional information and clarification are obtained. Final or total emissions from the main stack (and flares) have already been identified and are publicly available. No additional information was identified.

c. Werethe SuperClausunitsbypassed atanytime duringthecourseoftheyear? ANSWER: 

### In our submittal of March 20, 2009, MSCC reserved the right to supplement this response as additional information and clarification are obtained. No such additional information was identified; however, we would like to expand on our previous response.
Yes, on information and belief, bypass certainly occurred as needed. Bypass is an essential design function ofthe catalytic selective oxidation process and is necessary during startup/shutdown and malfunction to prevent damage to the system and to the selective oxidation catalyst in particular. MSCC does not maintain records specifically that allow ready identification of all periods of bypass for a particular SuperClausTM unit orfor the SuperClausTM process as a whole. However, the unit(s) and/or process were bypassed from time to time during calendar 2008, as appropriate, for periods involving utility interruptions and for startup and shutdown of particular units in the process or during startup/shutdown activities related to the upstream Claus system. The identified activities for the SuperClausTM units are shown in the table below. It shows that the second unit was brought online for the first time on May 5, 2008. The first SuperClausTM unit was normally running during calendar year 2008 though occasionally it was bypassed for short periods of time until it was shut down for repairs on November 11. During the second unit startup, testing and conditioning time, the second unit was bypassed numerous times as needed. The first unit was taken offline (and fully bypassed) on November 11, 2008, and remained shut down until March 12, 2009. During that remaining period in 2008, the second SuperClausTM process was normally running, although it may have been occasionally bypassed for short periods oftime.



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### Addendumto AttachmentA Montana Sulphur& Chemical Company Request for InformationPursuantto Section 114 ofthe CAA January29, 2009

Date

1/1/2008 5/5/2008 6/30/2008

7/3/2008

7/22/2008 8/17/2008

10/24/2008

10/3112008 SuperClausTM West (first unit) Operating normally

Shut down for maintenance at 16:40 Returned to service after maintenance

Hot temperature trip during flare event (minutes) SuperClausTM East (second unit)

Started upforfirst time Down 1.25 hours due to malfunction between 20:30 and 21 :45

Shut down for a few hours for repairs High concentration trip during flare event (minutes) Bypassed for 199 minutes for troubleshooting and maintenance Trip (12 minutes) due to electrical interruption

d. What would emissions have been in that year with no bypassing ofthe SuperClaus units, if different? ANSWER: MSCC reserved the right to supplement this response as additional information and clarification are obtained. No such additional specific information was identified. Since, on information and belief, one or both units were running during substantially the entire year, we do not believe emissions would have been substantially different if there had been uno periods of bypass" of the SuperClausTM process arising from malfunction, startup, shutdown, or maintenance/training activities for the year 2008. The SuperClausTM process does not process tail gas during periods when there is no normal Claus processing upstream; for example, during periods of startup/shutdown ofthe entire upstream Claus process. One such period occurred on a partial day in 2008 as has been previously reported in our March 20, 2009, submittal. It should be noted that Ubypass" during certain adverse input conditions and malfunctions is a design necessity for this process to prevent damage to the process itself; operation during such conditions could actually lead to increased emissions arising from equipment damage and downtime.

11