April 27, 2000


Carolina Espejel-Schutt, Supervisor
Metro District-Major Facilities Section
Air Quality Division
Minnesota Pollution Control Agency
520 Lafayette Road
St. Paul, Minnesota 55155

Dear Ms. Espejel-Schutt:

The United States Environmental Protection Agency (EPA) has reviewed Air Emission Permit No. 16300003-002 for Marathon Ashland Petroleum, LLC for its facility located at 459 3rd Avenue, St. Paul Park, Washington County, Minnesota. The permit action is for installation and operation of emission units subject to Prevention of Significant Deterioration (PSD) for nitrogen oxides under the New Source Review regulations. The permit would authorize Marathon Ashland Petroleum (MAP) to operate diesel engines rented from outside vendors and transported to the site. MAP expects to use the engines on a temporary basis for most of its refinery operations for a period of 5 years, based upon their Best Available Control Technology (BACT) analysis. Our office has the following comments:

1. The technical support document states that the Minnesota Pollution Control Agency (MPCA) determined that design modification for the rental units would be BACT. Design modification includes modifications to the engine operation. These modifications can include timing retard, aftercooling, and turbocharging. The permit does not include a BACT emission limit for nitrogen dioxides, which should be the applicable emission rate. The BACT emission rate is normally in terms of lb/MMbtu, in some other comparable form, or the percent reduction that is expected to be achieved. An emission rate should be applied to each unit subject to PSD, unless there is clear justification for otherwise.

The permit also includes an “equivalent” control technology requirement. According to the permit, “equivalent” means other types of design modifications reviewed and approved by the MPCA if the control technology can achieve and meet the same or greater reduction in nitrogen oxide emissions. This allows MAP to change its selected control technology over time. The permit must show an emission rate that comports with the BACT PSD regulations under the Clean Air Act. Any control methodology used must be able to achieve this emission rate. The permit should also contain reference methods for determining compliance, and adequate reporting and recordkeeping so that the compliance status of the source can be determined.

2. The permit contains a BACT limit of 20,000,000 hp-hr per year using a 12-month rolling sum calculated on a monthly basis. This appears to be the only limit for BACT. This alone is not an acceptable BACT limit.

3. BACT limits in terms of tons per year using a 12-month rolling sum alone are also not acceptable limits. The permit should specify emission limits in pounds per hour (lb/hr) to ensure protection of short term National Ambient Air Quality Standards (NAAQS). Limits in terms of tons per year alone are unacceptable to ensure maintenance of applicable air quality standards. The permit should also contain emission limits with appropriate averaging times that are consistent with the applicable reference method so that the limits are enforceable as a practical matter. This information and limits should be consistent with the modeling analysis for the new source.

4. The permit documents does not show exactly how many rental units MAP expects to install on an annual basis. We would like clarified in the permit the number of units within any given year MAP is allowed to install.

We hope that the information outlined in this letter is useful to you to assure that the permit meets the requirements of the Clean Air Act. If you have any questions on this letter, please contact Shaheerah Fateen at (312) 353-4779.

Sincerely yours,


Robert B. Miller, Chief
Permits and Grants Section