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OAR Box 1875 

Prepped by Ollie Stewart 

Document Number: 

75) ll-F-22 

Docket Number: 

A-90-19 

Printed 12/1/2008 11:12:48 AM Sheet 75 of 86 
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A-90-19 

ll-F-22 

TO: Frank Hodsoll 

FROM: Michael Shapiro 

DATE: October 16, 1992 

Attached please find our write up of the rationale for the 

control level decision on process vents. We believe this 

reflects the results of our discussions earlier this week. In 

order the understand the first paragraph option 1 represents the 

floor level of control, option 2 represents the CTG level, option 

3 represents the NSPS level and option 4 represents EPA's orginal 

proposal. The one change we have made is to request comment on 

the full range of options between the floor and EPA's original 

proposal of process vents but we are focusing our request for 

comments on options 1 through 3. Please call either myself 260-

7304 or (703) 351-9389, or Lydia Wegman at (919) 541-5504. This 

write up has not yet been reviewed by EPA's attorneys. 

8 i B ll w IF r*A 

L 

1U DEC f | I96e 

EPA AIR PQCKETj 
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Draft Rationale for Decision on Existing Source Process Vents 

In selection of the proposed standard for existing sources, 

EPA determined that a level of emission reduction from process 

vents more stringent than the level associated with the floor is 

achievable. The EPA is proposing to require control level in 

Option 2, which has an incremental cost-effectiveness of 

$1,800/Mg and control vents that have TRE cost-effectiveness 

values of less than $2,000/Mg. Although EPA is proposing this 

specific control level, EPA is requesting comment on the range of 

options from l to 4 which would require control of vents with TRE 

cost-effectiveness values of less than $1,500/Mg to less than 

$5,000/Mg. The EPA anticipates -that in consideration of the 

final decision EPA will give more weight to options 1 to 3. As 

discussed more fully below, this decision is based on 

considerations specific to the SOCMI category and would not 

necessarily be appropriate for other source categories. 

Therefore, it should not be viewed as a benchmark for decisions 

on other standards. The EPA recognizes that there are differing 

views regarding the appropriate criteria for determining the 

control level. Consequently, EPA is requesting comments on the 

appropriateness of particular control choices within the range of 

options described above and asks that commenters provide 

supporting rationale for their preferences. 

The EPA selected the proposed control criteria considering 

the criteria enumerated in Section 112(d) of the Act: the cost 

of achieving such reductions; any non-air quality health and 

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environmental impacts; and energy requirements. As a matter of 

general policy in decisions to select control levels above the 

floor, EPA believes that a comparison of benefits, both 

quantifiable and nonquantifiable, and costs is an important 

consideration. Such an approach provides a means for determining 

the point at which the costs and other impacts become 

unreasonable relative to the health protection benefits. In this 

case, however, our ability to do such a comparison was severely 

limited due to the limited data on the characteristics of the 

emission sources and the complexity of the source category. 

Specifically, there was insufficient data to do a scientifically 

credible analysis of the cancer health benefits. Furthermore, 

there are no models to evaluate the non-cancer health effects of 

the complex mixtures of HAP's emitted by HON facilities. 

Consequently, EPA used benchmarks from previous air toxics 

regulatory decisions and past air toxics benefits studies as a 

surrogate measure for benefits considerations in the decision 

over the proposed control level. The information considered 

consisted of the Benzene NESHAP decisions and the Vinyl Chloride 

NESHAP. For example, a decision that reflected consideration of 

balancing emission reductions against costs was the benzene 

storage standard. In that decision, the cost-effectiveness of 

the selected option was estimated to range from $128/Mg to 

$909/Mg (need to be adjusted to 1989 dollars). However, in that 

rulemaking it was recognized that there were great uncertainties 

in the emission estimates and the cost estimates. 
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Although the cost-effectiveness measures from past decisions 

were examined in selection of the proposed option, other factors 

were also considered due to limited applicability of the benzene 

decisions to this rulemaking. In particular, at the time of the 

benzene decisions it was recognized that the risk assessments 

were incomplete in that not all health risks could be quantified 

and that some cost analyses were old and possibly understated 

control costs. The net effect of these two factors could not be 

quantified but was considered in the general consideration of the 

uncertainty. The cost estimates in the benzene storage decision 

reflect these uncertainties and in fact are believed to be 

understated. 

Additional considerations in the decision being made in this 

proposal include: (1) the magnitude of tha emission reduction 

available at a cost that would not result in unreasonable 

economic impacts; (2) consistency with past decisions in order to 

support efficient regulation; and (3) other non-quantifiable 

health and environmental benefits, eg. non-cancer and ecosystem 

effects. Further, technology capable of meeting these standards 

is widely applied in similar sources. 

Existing source process vents are the single largest 

contributor of HAP emissions from the SOCMI source category. The 

additional emission reduction beyond that achieved at the floor 

that would result from the proposed standard is about 4000 Mg/yr, 

which EPA considers to be a substantial reduction. The average 

cost effectiveness of the selected alternative is $230/Mg and the 
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additional increment of control has a cost effectiveness of 

Sl,eoo/Mg of HAP. The cost of the selected control requirements 

was judged to be reasonable and no unreasonable economic effects 

are expected. 

The EPA is requesting comment on a range of control options 

because of the uncertainties in the measure of the benefits of 

control and the uncertainties in the cost that would actually be 

experienced. Because of the conservative assumptions used to 

develop the control costs and the structure of the standard, it 

is unlikely that any source would actually incur cost at the TRE 

level (the criterion for defining vents that must apply control) 

that is equivalent to $2,000/Mg . The cost analysis used in 

developing the supporting information for this standard was based 

on use of a dedicated control device for each vent. Actual costs 

would be lower where one device could be used to control 

emissions from several vents. The cost of control would also be 

lower in those cases where it is feasible to use a boiler or 

process heater. Finally, the standard is structured using a TRE 

index approach. Since the standard is in a TRE format, many 

facilities may be able to use product recovery to change vent 

stream characteristics so that they are below the relevant 

applicability criteria. This flexibility is expected to allow 

some sources through changes in eguipment or operations to lower 

their cost of compliance. As a result, the impacts analysis may 

overstate the costs of complying with the proposed control 

requirement.