U.S. Environmental Protection Agency	08-P-0020
Office of Inspector General	October 31 2007

At a Glance
Why We Did This Review
The 1990 Clean Air Act
Amendments required the
U.S. Environmental Protection
Agency (EPA) to develop
maximum achievable control
technology (MACT) standards
to reduce air toxics emissions
from stationary sources. In
2004, EPA completed the last
of its MACT standards. We
conducted this evaluation to
assess the effectiveness of
those standards in reducing air
toxics emissions.
EPA has issued 96 MACT
standards covering
174 different categories of
industrial sources of air toxics.
Now that the MACT standards
have been issued, EPA must
assess the public health risk
remaining after each MACT
standard is implemented. If
the risk from a MACT
category is "unacceptable,"
EPA must promulgate
additional regulations to
reduce air toxics emissions
from that category. Excess
exposure to air toxics can
increase one's risk of
developing cancer and other
serious ailments.
For further information,
contact our Office of
Congressional and Public
Liaison at (202) 566-2391.
To view the full report,
click on the following link:
Catalyst for Improving the Environment
Improvements in Air Toxics Emissions Data
Needed to Conduct Residuai Risk Assessments
What We Found
EPA's National Emissions Inventory (NEI) data indicate an overall decline in air
toxic emissions concurrent with implementation of the MACT standards.
Although NEI data reliability is uncertain, it is reasonable to conclude that air
toxics emissions have decreased. Our work suggests that the MACT program has
played a role in these reductions.
EPA plans to use NEI data to assess the public health risk remaining from MACT
sources" air toxics emissions, but the reliability of NEI data for site-specific
emissions varies considerably. EPA has not established objectives to define an
acceptable level of quality for NEI data used in the residual risk process. EPA
guidance recommends that program offices develop data quality objectives for
using data in such decision-making processes. Given the uncertainties associated
with NEI data, EPA could over- or under-estimate public health risk from MACT
sources" emissions. Overstating risk could result in EPA placing on industries
regulations that are not cost beneficial. Conversely, understating risk could result
in EPA not requiring regulations where needed to protect public health.
In our March 2004 report on EPA's air toxics performance measures, we
recommended that EPA require State reporting of air toxics emissions data. EPA
has not implemented this recommendation, citing unclear statutory authority and
the belief that voluntary reporting can achieve this goal. However, such a
requirement could help EPA obtain more reliable and complete NEI data.
In December 2006, EPA presented its plan for conducting residual risk
assessments to EPA's Science Advisory Board. The Board's June 2007 report
recommended several actions to improve this process. These recommendations
included developing a framework for improving the NEI data and conducting an
analysis to determine the impact of data uncertainty on the risk assessments. In
March 2007, EPA solicited public comment on the NEI and other data it plans to
use for conducting residual risk assessments.
What We Recommend
We recommend that EPA develop data quality objectives for using NEI data in
conducting residual risk assessments, and establish requirements for State
reporting of air toxics emissions data and compliance monitoring information.
EPA disagreed with our recommendations, but stated that it had activities
underway to improve the NEI data. However, EPA's planned actions do not
sufficiently address the problems identified, and we consider the issues unresolved.