New Pennsylvania Air Quality General Permits for Boilers, CHP Projects & Coal Mine Methane Flares

Pennsylvania Department of Environmental Protection requires air quality permits for a variety of industrial and commercial operations including large combustion sources (e.g., boilers or emergency generators), paint spray booths, solvent degreasers, and large dust collectors.  These operations typically must obtain “Plan Approval” prior to construction/installation.  The Plan Approval process is lengthy (6-8 months), costly ($2,500 – $7,500 fee depending on type of source), involves public notice and comment opportunity, and requires that applicants utilize “Best Available Technology” (BAT) on a case-by-case basis to minimize air emissions.

Because of the complexity of the Plan Approval process, PA DEP has issued a number of “General Permits” for common air emissions source categories to expedite the permitting process and provide certainty for the permit requirements.  General Permits have lower application fees ($375 – $1,600) and the permits are issued within about 30 days after submittal of an application.  BAT is pre-established in the permit and public comments will not delay the permit issuance.

General Permits are available for multiple source categories including gas and oil boilers, diesel generators, burn-off ovens, portable stone crushing plants, asphalt plants, crematories, and certain printing operations.  The available General Permits are listed on PA DEP’s website here:

In January 2023, PA DEP revised one of the most commonly used General Permits, “GP-1” for gas/oil-fired boilers.  This Alert summarizes the changes made to GP-1 and the impact on Pennsylvania facilities that install new boilers and/or operate boilers under the current GP-1 permit.  This Alert also provides a general summary of two other General Permits: (1) GP-20 for Combined heat and Power (CHP) projects; and, (2) Proposed GP-21 for coal mine methane flare projects.

GP-1 – Gas/Oil Boilers

The GP-1 permit was first issued in 1995 and covered natural gas or distillate fuel oil boilers with rated heat inputs between 10-50 million Btu/hr (MMBtu/hr).  A 10 MM Btu/hr boiler is rated at about 250 hp.  Gas or oil boilers with heat inputs less than 10 MMBtu/hr are exempt from air permitting in Pennsylvania.  A lower threshold of 2.5 MMBtu/hr applies to solid fuel (coal or biomass) or to waste oil boilers.  PA DEP revised the GP-1 in January 2023 by imposing more stringent emissions limits for nitrogen oxides (NOx) and for carbon monoxide (CO) and by extending applicability to larger boilers up to 100 MMBtu/hr heat input.

The new GP-1 permit lowers the NOx limit for gas-fired boilers from 30 ppm to 9 ppm.  This dictates that new boilers be equipped with “low-NOx” combustion technology which typically requires “flue gas recirculation” but does not require use of much more expensive catalytic technologies.  The CO limit for gas-fired boilers has been lowered from 300 ppm to 130 ppm.  The fuel oil boiler NOx limit remains 90 ppm but the CO limit has been lowered from 300 ppm to 130 ppm.  Visible emissions (i.e., “opacity” or smoke) is limited to 10% opacity with up to 30% allowed for up to 3 minutes in any hour.

The GP-1 application fee is now $1,600 (significantly higher than the previous fee of $375) and the annual maintenance fee is $500.  Multiple boilers can be included on a single GP-1 permit.  The permits are issued for 5-years after which a renewal application must be submitted with a $750 fee.  Note that current GP-1 permit holders will be subject to the higher fees when their permits are up for renewal 5 years after issuance.

A new annual reporting requirement has been included in GP-1.  An annual report certifying compliance with all the GP-1 permit conditions must be signed by a company “responsible official” (officer of the company or Plant Manager) and must include air emissions calculations to show that annual emissions from all boilers do not exceed major source levels (e.g., 100 tons/year for NOx or CO).  This reporting requirement will require permittees to track monthly fuel usage in each boiler and to use a spreadsheet to track emissions using vendor-supplied emissions data and/or US EPA boiler emissions factors.

Source testing (i.e., initial “stack testing”) is required for large oil-fired boilers with heat inputs greater than 50 MMBtu/hr.  Gas-fired boilers and dual fuel (gas/oil) boilers that only fire oil during gas curtailments are excluded from source testing requirements.  All boilers are subject to annual tune-up requirements and must conduct tune-ups measuring NOx/CO once every 3 years.

Other Pennsylvania General Permit Developments

In 2021, PA DEP issued a General Permit, GP-20, for gas-fired combined heat and power (CHP) facilities.  CHP projects generate electricity from gas-fired engines or turbines and recover the waste heat for heating/cooling.  GP-20 covers CHP facilities rated at less than 25 MW of power output.  Gas-fired engines and turbines are subject to several federal air regulations (NSPS and NESHAP standards) which require the use of U.S. EPA certified engines and low emissions turbines that meet emissions standards on a “gram/kW” basis based on the gross electric output of the system.  The GP-20 imposes additional emissions standards on a “lb/MW” basis based on the total CHP energy output including both the electrical output and the “useful thermal output” of the heat recovery systems.

The GP-20 imposes emissions limits for carbon dioxide (CO2) for the first time in any of the PA General Permits.  The CO2 limits effectively impose an overall CHP heat recovery efficiency requirement. The GP-20 permit requires both initial source testing for all pollutants and then periodic testing for NOx/CO every 2500 hours of CHP operation.  The source testing is more complicated than is typical due to the need to measure the useful thermal output during the test program.

In July 2023, PA DEP proposed a new General Permit, GP-21, for coal mine methane flare projects.  The proposed permit imposes NOx and CO limits and the use of enclosed flares.  An increasing number of coal mine methane flare projects is expected in Pennsylvania based on  numerous similar projects having been permitted in coal mines in West Virginia over the past two years.  These projects result in greenhouse gas (GHG) reductions by combusting methane, a potent GHG gas, to CO2 which is a less potent GHG.  CO2 reduction credits are generated by these projects which are typically sold to states like California which have GHG reduction banking programs.

Liberty Environmental’ s Air Quality Practice has extensive experience with air permitting in Pennsylvania and in many other states.  We have secured numerous General Permits, Plan Approvals, and Operating Permits for a wide variety of clients.  Liberty submitted the first GP-20 application for a CHP project in Pennsylvania – a medical cannabis farm facility with electricity and chilled water supplied by a CHP system.  Liberty has also assisted clients with air permitting for coal mine methane abatement projects and we expect to be preparing GP-21 applications as soon as the permit is issued in final form.