Emission Regulations Summary for Colorado
Stationary Internal Combustion Engines
By: Dennis Roundtree, Onsite Power Inc.
With special thanks to Paula Menten, CDPHE
This is a general summary of emission regulations and permitting information for the
State of Colorado as they apply to generator sets under 2 MWe and stationary
reciprocating internal combustion engines. It is intended as a summary informational
guide only, and is up to date as of the date of publication. However, Onsite Power Inc.
takes no responsibility for errors, omissions and out-of-date information, and
recommends that all information be verified with the authority having jurisdiction prior to
any action in regard to equipping or permitting your engine.
Who has authority over air pollution regulations and permitting in the state of?
The Colorado Department of Health and Environment, Air Pollution Control Division,
Stationary Sources Program. There is a link to their website on our “Emission
Authorities” page. There is also a downloadable link to their application forms and
documents.
What is the requirement and process for complying with emission regulation and
permitting regulations? Unless specifically exempted by Regulation 3 (see below for
examples), all air emission sources in Colorado are required to apply for a permit.
Generally speaking, the first step in the process is the filing of the Construction Permit
Application together with the Air Pollution Emission Notice (APEN). One APEN is
required for each emission source, with the exception of certain types of installations that
are APEN-exempt (see below). If a facility has more than one piece of similar equipment
(e.g. 3 engines of the same make and model), they may submit them on a single APEN.
See Reg 3 II B.4. source grouping guidelines for more information. APEN requirements
also differ depending on whether the source is in a non-attainment area In general, an
APEN is required for all sources in excess of 2 tons per year of any criteria pollutant in
an attainment area and 1 ton per year of any criteria pollutant in any non-attainment area.
It is helpful to include both manufacturer data and site derated data to expedite the permit
evaluation process. Permit approval is required prior to initial operation, AND
construction. The Initial approval permit will generally be drafted within 65days after all
requested information is received. The permit charges (~$60/hr actual time spent on the
permit) will be invoiced and must be paid before the permit is issued. with selfcertification required within 180 days after the permit issue date for final approval. There
is no sunset on the permit unless the equipment is modified or the source requests a
change such as an increase in emissions or the source requests the permit be cancelled,
but relocation of equipment requires filing of a relocation notice.
If the APEN evaluation results in a determination that the source will exceed certain
levels of criteria pollutants, a regular construction permit approval process will
commence from the same application. Those limitations are set forth in Reg. 3, Part B,
II.D.2 for nonattainment areas and II.D.3 for attainment areas. Those thresholds are five
(5) tons per year each of VOC or PM 10, ten (10) tons per year of CO, SO2, NOx or total
suspended particulate, or 200 lbs. of lead. Exemptions to this requirement specific to
stationary internal combustion engines are noted in II.D.1.c and in general apply to
engines less than 50 hp or 5 tons per year in nonattainment areas and 100 hp or 10 tons
per year in attainment areas.
Sources of Hazardous Air Pollutants (HAPS) do not require permits unless there has been
a federal NSPS or MACT standard rule set for the pollutant and type of installation, or
unless the emissions of criteria pollutants at the site is > the permit thresholds listed in
Reg 3 Part B II D 3. This is the case for reciprocating internal combustion engines
located at major sources for HAPS, defined as any source exceeding 10 tons per year of
individual HAPS or 25 tpy of total HAPS. In this case, the engine comes under the RICE
MACT (40 CFR Part 63 Subpart ZZZZ) regulation. More detail on this regulation can be
obtained by going to the EPA links listed on our Emission Information web page.
What permits are required for the following types of equipment:
Standby Generators: APEN-exempt under the following limitations: (Reg. 3,
Part A II.D.1.TTT). Construction permit is still required if minimum thresholds
are exceeded:
 Rated horsepower of less than 260
 Operate no more than 250 hrs. per year and have a rated horsepower of
less than 737
 Operate no more than 100 hrs. per year and have a rated horsepower of
less than 1840
Load control generators (standby generators operated for peak loads
interruptible rate or other non-standby uses): Requires general construction
permit and APEN if limits set in Regulation 3, Part A II.D.ttt are exceeded
Prime Power Generators including Cogeneration: Standard construction
permit and APEN
Utility generators (recip under 10 MW only): Standard construction permit
and APEN
Mobile Generators: APEN exempt if it meets the general exemption
requirements related to horsepower and hours of operation noted in Regulation 3.
Otherwise, general permit and APEN, note as mobile source. Must file relocation
notice if moved. Cannot be moved to a major source location.
Gas Compressors: General permit and APEN
Portable Drilling Rigs: APEN exempt
Engines at major source locations for Criteria Pollutants: General permit and
APEN is required. Each individual source is considered separately unless the
applicant specifically requests a site-wide assessment.
Engines at major source locations for Hazardous Air Pollutants: Subject to
RICE MACT regulation
Special Circumstances:
Location specific: Special regulations exist for what is known as the 8
hour Ozone Control Area, which includes all of the counties of Adams,
Arapahoe, Boulder, Douglas, Elbert, Jefferson, Larimer, Morgan and
Weld. These controls are for emission of volatile organic compounds.
Rich burn gas engines are required to have non-selective catalyst (3-way
catalyst) and air fuel ratio controller. Lean burn gas engines are required
to have oxidation catalysts. See Reg. 7, sections 12 (oil and gas only) and
16.
Industry specific: There are regulations regarding VOC’s specific to the
oil and gas industry on locations within the 8 hour Ozone Control Area.
Refer to Reg. 7 Section 12.
Other Special Applications: Stationary internal combustion engines are
APEN-exempt under the following circumstances (Reg. 3, Part A
II.D.1.sss)
 Less than or equal to 175 HP operating less than 1,450 hours per
year
 Greater than 175 HP but less than or equal to 300 horsepower
operating less than 850 hours per year
 Greater than 300 HP but less than or equal to 750 HP per year that
operate less than 340 hours per year
RICE MACT enforcement (refer to RICE MACT regulation section on our website
for more information): The RICE MACT regulation is incorporated to state regulations
by reference and without modification.
What are the operating limits for Criteria Pollutants? Refer to Regulation 3
There are no specific operating limits for criteria pollutants in stationary internal
combustion engines. However, there are regulations that establish minimum thresholds
for construction permits, APEN’s and Title V operating permits that encourage operators
to minimize emissions and utilize clean-burning technologies.