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U.S. Environmental Protection Agency
Office of Inspector General
At a Glance
19-P-0207
June 27, 2019
Why We Did This Project
We conducted this audit to
determine whether selected
continuous emissions monitoring
data meet applicable quality
assurance and quality control
criteria.
Continuous emissions monitoring
systems (CEMSs) are required
under some U.S. Environmental
Protection Agency (EPA)
regulations and programs to
continuously monitor actual
emissions from stationary
sources. Two programs that
require the use of CEMSs are the
Acid Rain Program (ARP) and
the Cross-State Air Pollution
Rule (CSAPR), which are
intended to reduce emissions of
sulfur dioxide and nitrogen
oxides. These emissions trading
programs are designed to
improve air quality by setting
emissions limits and monitoring
emissions from power plants. It is
important that the CEMS data
reported to the EPA be accurate
and meet regulatory
requirements because these data
are used to assess compliance
with trading program emission
limits and progress toward
environmental goals.
This report addresses the
following:
• Improving air quality.
EPA Effectively Screens Air Emissions Data
from Continuous Monitoring Systems but Could
Enhance Verification of System Performance
What We Found
The EPA's automated screening of facility-reported
CEMS data worked as intended and was effective in
verifying the quality of the reported data. However,
we found a small number of inaccuracies and
inconsistencies in the reported data. While these
instances had no impact on whether the data met
quality assurance requirements, the inaccurate data
could have a negative impact on data users by
providing inaccurate or misleading information. The
EPA can prevent these problems by adding specific
screening checks to its existing reporting software.
Although the EPA's automated screening process was effective, the validity of
the reported data can only be fully established when that process is
supplemented with on-site field audits to verify that CEMS monitoring
requirements were met. However, we found that the EPA and state agencies
conducted a limited number of these audits. Out of over 1,000 facilities subject
to ARP and/or CSAPR requirements, the EPA conducted field audits at only
16 facilities between 2016 and the end of June 2018. In addition, nine of the
10 state agencies we contacted were not conducting field audits. In response to
our work, the EPA initiated a process to develop a streamlined CEMS field audit
approach that state and local agencies can use when conducting other on-site
visits at facilities.
Recommendations and Planned Agency Corrective Actions
We recommend that the Assistant Administrator for Air and Radiation develop
and implement electronic checks to retroactively evaluate CEMS data where
monitoring plan changes have occurred, and develop and distribute to state and
local agencies a streamlined field audit process. The EPA agreed with our
recommendations and provided acceptable corrective actions and completion
dates. All recommendations are considered resolved with corrective actions
pending.
Data from CEMS are
used to determine
whether sources, such
as power plants,
comply with emissions
limits designed to
improve air quality and
achieve environmental
and public health goals
Address inquiries to our public
affairs office at (202) 566-2391 or
OIG WEBCOMMENTS@epa.gov.
List of OIG reports.

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