( d) An operating requirement deviation is not a violation of the compliance option if the results of a performance test using the procedures in this paragraph demonstrate compliance with the compliance option requirements in Table 2. ( i) Conduct a performance test as specified in .... using the conditions of the operating requirement deviation. No maintenance or changes shall be made to the control system 2 164 after the beginning of the operating requirement deviation that would influence the results of the test. ( ii) If the results of the performance test specified in . . . ( i) of this section demonstrate compliance with the compliance option requirements in Table 2, then there is no violation of the limit. ( iii) If the results of the performance test specified in . . . ( i) of this section do not demonstrate compliance with the compliance option requirements in Table 2, then there was a violation of the limit. Commenter IV D 27 also recommended that sources be given up to 120 days after the deviation to demonstrate compliance; however, the commenter noted that the time frame should not alleviate the source from compliance issues if compliance could not be demonstrated at the extended parameter level.

Response: We did not include the requested language in the final PCWP rule because we believe that ( 1) the rationale for including this provision in the Pulp and Paper MACT I rule ( 40 CFR part 63, subpart S) is not applicable to the PCWP rule, and ( 2) this provision is unnecessary given the changes that we are making to the monitoring provisions in the final rule.

We note that the referenced language in the Pulp and Paper MACT I rule regarding "

postdeviation performance testing" only applies to open biological treatment units ( i. e., units used to biodegrade pulp mill condensates) and not to other types of control systems such as thermal oxidizers, gas scrubbers, and steam strippers. Subpart S requires pulp and paper mills that operate biological treatment units to conduct quarterly performance tests and to either monitor five different operating parameters or establish site specific operating parameters for the biological treatment unit. In the preamble to the final Pulp and Paper MACT I rule ( 63 FR 18524, April 15, 1998), we acknowledged that the type of biological treatment systems used at pulp and paper mills " can vary widely in their operation and performance, depending on their design, maintenance, and even their geographical location." Given this variability, the number of parameters that must be monitored, and the possibility that an excursion of one operating parameter might not, under certain circumstances, equate to an exceedance of the emission standard, subpart S also allows sources to conduct post deviation performance tests of the biological treatment unit to determine if the emission standards were actually exceeded during an operating parameter excursion. The performance test must be performed " as soon as practical"

after the beginning of the monitoring excursion. As discussed in subsequent sections of this document, we have reduced the number of operating parameters PCWP sources must monitor for 2 165 RTO, RCO, and biofilters to temperature only, and we believe that temperature is both a controllable parameter and a reliable indicator of control device performance. Therefore, we do not believe that a provision for post deviation performance testing is needed in the final PCWP rule. We also note that the PCWP rule allows sources to conduct multiple performance tests to establish the operating temperature limit; therefore, sources should be able to establish a minimum ( or maximum) temperature level that reflects the range of operating conditions expected.

2.7.8 Location for inlet sampling <IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 pointed out that the rule is not clear enough about the location for inlet sampling, especially for coupled control devices. The commenters recommended that the rule be reworded to clearly state that inlet sampling should take place at the functional inlet of a control device sequence or at the primary HAP control device inlet. For example, the commenters noted that the final rule needs to clarify that sampling should take place at the inlet of a WESP that precedes an RTO instead of between the two devices. The commenters noted that many WESP RTO control systems are too closely coupled to allow for a sampling location in between that meets the requirements of Method 1 or 1A, 40 CFR 60, appendix A.

Response: We agree with the commenters, and have revised the final PCWP rule to indicate that for HAP altering controls in sequence, such as a wet control device followed by a thermal oxidizer, sampling sites must be located at the functional inlet of the control sequence ( e. g., prior to the wet control device) and at the outlet of the control sequence ( e. g., thermal oxidizer outlet) and prior to any releases to the atmosphere. As discussed in response to comment No. <IP_ADDRESS>, we also clarified that facilities demonstrating compliance with the PBCO for a process unit with a wet control device must locate sampling sites prior to the wet control device.

2.7.9 Data collection and handling <IP_ADDRESS> Comment: Commenter IV D 03 stated that the proposed valid data requirements for CEMS ( i. e., monitoring 100 percent of the hours the process is operating except for monitor malfunctions, associated repairs, and QA/ QC activities) are much more " subjective" than other rules. The commenter noted that, instead of simply requiring valid data for greater than 95 percent of the hours each quarter ( as required in other rules), the proposed approach focuses more on recordkeeping and explaining the data that are not valid. According to the commenter, 2 166 the proposed approach would require inspectors to make judgement calls regarding whether a monitoring malfunction was unavoidable or caused by poor maintenance. To simplify the final rule, the commenter recommended that EPA require a certain percentage of data to be valid ( e. g.,

95 percent of the hours each quarter).

Response: We believe that the proposed requirement to conduct monitoring at all times when the process is operating is appropriate. This requirement is consistent with other rules that we have promulgated recently. We also believe it is appropriate that inspectors would have the flexibility to determine when monitoring malfunctions are unavoidable or caused by poor maintenance. Therefore, we did not modify the final rule to include the 95 percent data availability requirement suggested by the commenter.

<IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 recommended that section 63.2268( a)( 1) be revised to require the CPMS to simply be " capable" of completing a minimum of one cycle of operation for each successive 15 minute period. The commenters also stated that the proposed requirement in section 63.2268( a)( 1) for 15 minute data collection cycles is confusing and possibly inconsistent with the requirement for equally spaced cycles. Section 63.2268( a)( 1)

requires that the CPMS complete at least one cycle in each successive 15 minute interval and that a valid hourly calculation must include at least three equally spaced data points. The commenters pointed out that there are a number of situations for which these guidelines would not specifically determine the calculation requirements. For example, the guidelines listed above could be interpreted to mean that the hourly average must include three or more data points spaced evenly among themselves but not spaced equally over the hour, so an average of 6 data points taken at 5 minute intervals would satisfy the rule. After those six points were recorded, data collection might stop because of an SSM event, loss of control of the monitoring equipment, or calibration of a monitoring device. The commenters noted that the guidelines can also be taken together to mean that at least three successive 15 minute intervals are necessary. In that case, if the process starts up at 30 minutes past the hour, the final 30 minutes of that hour cannot be considered valid.

However, section 63.8( g)( 2) of the General Provisions indicates that two data points, each representing a 15 minute period, should be averaged in that case. The commenters pointed out that these examples prove that the proposed language " at least three equally spaced data values for that hour" is ambiguous and should be revised. The commenters recommended that EPA require facilities to average at least three data points taken at constant intervals, provided that the 2 167 interval is less than or equal to 15 minutes. The commenters contended that the best approach would be to ignore the concept of an hourly average and simply calculate the block average as the average of all evenly spaced measurements in the block period with a maximum measurement interval of 15 minutes. The commenters further noted that the rule does not specify how to calculate the 3 hour block average when one or more of the individual hours does not contain at least three valid data values. The commenters recommended that the final rule address this issue by stating that " a block average must contain at least two valid hourly averages."

Response: As requested by the commenters, we have revised the wording of § 63.2269( a)( 1) ( formerly § 63.2268( a)( 1) in the proposed rule) to state that " The CPMS must be capable of completing a minimum of one cycle of operation ( sampling, analyzing, and recording)..." We added the parenthetical " sampling, analyzing, and recording" for additional clarity of the meaning of a CPMS cycle of operation.

We agree that the proposed rule language regarding acceptable data and data averaging is somewhat ambiguous and we have revised the language accordingly. Following the commenters'

recommendation, we have removed the concept of an hourly average from the rule to allow block averages to be calculated as the average of all evenly spaced measurements in the 3 hour or 24

hour block period with a maximum measurement interval of 15 minutes. However, removal of the valid hourly average consisting of " at least three equally spaced data values for that hour" also eliminated any minimum data availability requirement. Therefore, we added a minimum data availability requirement specifying that to calculate data averages for each 3 hour or 24 hour averaging period, you must have at least 75 percent of the required recorded readings for that period using only recorded readings that are based on valid data. As discussed in response to comment No. <IP_ADDRESS>, we have clarified what constitutes valid data and we moved the rule language specifying how to calculate data averages to final § 63.2270( d) and ( e). The minimum data availability requirement appears in final § 63.2270( f).

<IP_ADDRESS> Comment: Commenter IV D 27 noted that section 63.2270( c) refers to a minimum data availability requirement, but that requirement is not included in subpart DDDD or the General Provisions. The commenter recommended that the reference to a minimum data availability requirement be removed.

Response: A minimum data availability requirement was included for the dry rotary dryer and veneer redryer work practices in proposed § 63.2268( a)( 4). ( Note that proposed § 63.2268 2 168 was renumbered § 63.2269 for the final rule.) In addition, we have extended this same minimum data availability requirement for all CPMS data averages. This requirement appears in § 63.2270( f) of the final rule. The requirement states that " To calculate data averages for each 3

hour or 24 hour averaging period, you must have at least 75 percent of the required recorded readings for that period using only recorded readings that are based on valid data..." Because the final PCWP rule contains a minimum data availability requirement, we disagree that the reference to a minimum data availability requirement in § 63.2270( c) should be removed.

<IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 made several suggestions to clarify sections 63.2268 ( What are my monitoring installation, operating, and maintenance requirements?) and 63.2270 ( How do I monitor and collect data to demonstrate continuous compliance?). The commenters found it difficult to understand exactly how to follow the requirements because the two sections use different words to discuss the same subjects. The commenters suggested that the two sections be rearranged slightly so that section 63.2268 includes only information about the monitoring devices and section 63.2270 discusses only the frequency and methods of data collection, handling, and reporting. To accomplish this, the commenters recommended that sections 63.2268( a)( 3) and 63.2268( a)( 4) be moved to section 63.2270. Also, the commenter pointed out that section 63.2270( c) needs to be consistent with section 63.2268 regarding data that should be excluded from data averages and calculations.

The two commenters also stated that proposed sections 63.2268( a)( 1), 63.2268( a)( 3), and 63.2268( a)( 4) need to be reworded to more clearly define which data should be included or excluded from the block averages. The commenters noted that proposed section 63.2270( b)

states that all data taken when the process unit is operating must be used in the hourly and block averages, which presumably excludes periods when the process unit is not operating. The commenters suggested that the final rule would be clearer and less confusing if EPA explicitly stated that any monitoring data taken during periods when emission control equipment are not accepting emissions from the production processes should be excluded from hourly or block averages. The commenters also noted that section 63.2268( a)( 3) states that any periods in which SSM occured or routine maintenance was performed should not be included in the block average calculation, but section 63.2270 does not include the same exception. The commenters stated that, because SSM events occur when the process is not in operation, there is no need to collect data from these periods, and thus, section 63.2270 should be changed to be consistent with 2 169 63.2268( a)( 3). The commenters also noted that sections 63.2268( a)( 1) and 63.2268( a)( 3) seem to imply that data collected during production downtime and SSM events would be included in the hourly averages but not in the block averages. The commenters also stated that the rule was unclear regarding whether or not data from any one hour averaging period containing a 15 minute period of SSM or a routine maintenance outage should be included in the block average. In addition, the commenters stated that the rule also was unclear regarding whether or not a block average would be calculated if the period contained a 15 minute period of SSM or maintenance downtime. To clear up the confusion, the commenters suggested that EPA should modify sections 63.2268( 1) and ( 3) to exclude periods that include SSM events from the hourly averages that are used to compute the block averages. The commenters requested that the wording in section 63.2268( a)( 4) also be revised to include this clarification.

Response: We agree with the commenters that there was some ambiguity in the structure of proposed § 63.2268 and § 63.2270 that could cause confusion. To remedy this, we rearranged the two sections as the commenters suggested. We moved proposed § § 63.2268( a)( 3) and ( 4) to final § 63.2270 ( now § 63.2270( d) and ( e)). Rather than repeating which data should be excluded from data averages in § 63.2270( d) and ( e), these new sections now refer to § 63.2270( b) and ( c)

when discussing data that should not be included in data averages. We also added data recorded during periods of SSM to the list of data that should be excluded from data averages in § 63.2270.

We believe these changes to the structure and wording of the rule should fully address the commenters' concerns.

<IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 noted that the proposed PCWP rule does not provide any alternatives to the definition of a one hour period found in the General Provisions ( 40 CFR 63.2). The commenters requested that facilities be given the option of beginning a one hour period at a time that is convenient depending on shift changes, employee duties at the end of a shift, and settings on the systems that record data.

Response: A one hour period is defined in the General Provisions as follows:

One hour period, unless otherwise defined in an applicable subpart, means any 60 minute period commencing on the hour.

The final PCWP NESHAP exercises the flexibility of this definition and provides a different definition of one hour period for PCWP facilities as follows:

One hour period means a 60 minute period. 2 170 We removed the phrase " commencing on the hour" from the definition because when the hour commences is not as important as whether or not the timeframe for the block average is clearly defined and consistently applied.

<IP_ADDRESS> Comment: Commenter IV D 27 stated that section 63.2268( a)( 3) should include language that follows section 63.8( g)( 4) of the General Provisions on rounding of data. The commenter stated that hourly and block average data should be rounded to the number of significant digits of the relevant standard. According to the commenter, for parameters such as temperature, the number of significant digits would be the same as the measurement device tolerance or minor division on the appropriate chart recorder specified in section 63.2268.

Response: Table 10 to subpart DDDD ( Applicability of General Provisions to subpart DDDD) indicates that § 63.8( g), including § 63.8( g)( 4), applies to the PCWP NESHAP.

( Note that proposed § 63.2268 was renumbered § 63.2269 for the final rule.)

2.7.10 Selection of operating parameter limits   general <IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 objected to EPA's approach to selecting operating parameter limits because the approach does not distinguish between " naturally variable" parameters and controllable parameters, and because many of the selected parameters do not directly correlate to control device performance. The commenters argued that there is a difference between controllable parameters ( e. g., RTO temperature, scrubber liquid flow rate, and other parameters that are directly manipulated by the operator or facility) and " naturally variable"

parameters ( e. g., biofilter inlet temperature, moisture content of dryer exhaust, and uncontrolled THC emissions concentration), and the rule does not provide sufficient guidance for the variable parameters. The commenters stated that the normal operating range for controllable parameters can easily be set when the tests for initial compliance are run; however, " naturally variable"

parameters are influenced by the process performance, weather, raw materials, and similar factors,

and thus, they are difficult for an operator to manipulate. The commenters noted that the operating range for " naturally variable" parameters cannot be set as easily because the conditions during the initial compliance demonstration may or may not be average or normal. The commenters contended that, instead of using the initial compliance tests to establish limits for naturally variable parameters, the limits should be based on emission control design principles.

The commenters stated that examples of control equipment design based operating parameters would be RTO residence time, outlet THC concentration, and biofilter bed temperature. 2 171 The commenters also stated that EPA has made overly broad assumptions about relationships between operating parameters and emission control equipment performance and requested that those relationships be re examined. The commenters stated that the parameters for monitoring compliance should be specific to the process or control unit and based on design and scientific principles. The commenters noted, however, that the proposed rule contains requirements for operating parameters that may not exactly relate to the performance of that unit,

such as measuring the static pressure of a thermal oxidizer. The commenters' specific objections and recommendations regarding the selection of parameters to be monitored for specific processes and control devices are discussed in sections 2.7.11 through 2.7.15.

Response: We agree with commenters that there are naturally variable parameters and controllable parameters. We have reduced the parameters to be continuously monitored and controlled for all control devices to temperature only. Responses to comments regarding specific parameters are discussed in the sections below.

2.7.11 Selection of RTO and RCO monitoring parameters <IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 recommended changes to the proposed requirements to monitor the operating temperature of thermal and catalytic oxidizers in § § 63.2262 ( k)( 1) and ( l)( 1). The commenters stated that the method of determining a minimum combustion temperature is inappropriate. Because of the variation in combustion temperatures during normal conditions and the statistics involved in averaging, a facility will have to perform the initial test at lower than normal temperature conditions to ensure that the minimum combustion temperature will be maintained a majority of the time. The commenter argued that based on a Monte Carlo simulation, if the minimum temperature is set as the proposed rule requires, there is about a 30 percent chance that a facility will violate the limit once in a six month period and about a 10 percent chance that a facility will violate the limit more than ten times in six months, regardless of standard deviation. In addition, the commenter stated that a study by NCASI showed that increases and decreases in RTO operating temperature within the normal operating ranges had no effect on the destruction of HAP. Therefore, the commenters recommended that the final rule allow facilities to conduct the initial compliance test for RTOs at the design specifications of the control device, and then allow facilities to operate the thermal oxidizers up to 50 ° F lower than the average obtained by the test. 2 172 The commenters also noted that, for RCOs, when the THC concentration in the inlet is high, the RCO will not need any additional heat and can operate at temperatures higher than the set point. Therefore, if the initial compliance tests are conducted under these conditions, the operating temperature limit will be too high for production rates at less than full capacity. The commenters recommended that, rather than base the minimum catalyst temperature on " artificial conditions" designed to keep the THC concentration low enough during the compliance test to drop the RCO temperature to a minimum set point, operators should be allowed to set the operating limit at a level that is 100 ° F above the minimum operating temperature of the catalyst.

The commenters stated that these changes to the final rule for thermal and catalytic oxidizers would eliminate the practice of operating control devices below expected normal operating temperatures during the compliance test in order to provide a compliance margin. The commenters also noted that another option would be to perform tests at the boundaries rather than " representative" operating conditions, as discussed previously ( see Section 2.7.5).

Response: We disagree with the commenters' request to include a 50  F margin around the minimum operating temperature established during the compliance test. In general, selection of the representative operating conditions for both the process and the control device for conducting the performance test is an important, and sometimes complex, task. Establishing the add on control device operating limit at the level demonstrated during the performance test is appropriate. The PCWP rule allows a facility to select operating limits based on site specific operating conditions and the facility is able to consider the need for temperature fluctuations in this selection. The PCWP rule requires that the operating limit be based on the average of the three minimum temperatures measured during a 3 hour performance test ( rather than on the average temperature over the 3 hour period, for example) to accommodate normal variation during operation and ensure that the minimum temperature established represents the lowest of the temperatures measured during the compliant test. The facility does have the option of operating the oxidizer at a lower setpoint during the performance test in order to provide a margin of safety during normal operation. These provisions allow sufficient flexibility, and an additional tolerance for a 50 ° F ( 28 ° C) temperature variation is not necessary. Therefore, the final rule does not allow facilities to operate thermal oxidizers 50 ° F lower than the average temperature during testing. 2 173 Regarding the study conducted by NCASI, we note that the temperature range of RTOs tested as part of that study ranged from a low of 1430  F to a high of 1675  F ( no RCOs were tested). We agree that the study results show that, within that temperature range, there was no noticeable correlation between HAP destruction efficiency and temperature; however, the study did show that acceptable HAP destructions were achieved within that range for the five RTOs that were tested. The temperature range used during the study correlates with actual RTO operating temperatures reported by PCWP facilities ( i. e., 1425  F to 1625  F), and therefore,

acceptable destruction efficiencies would be expected to occur within the stated temperature range. 10 No testing was conducted at temperatures lower than the " minimum normal operating level," for the individual units and therefore, we cannot be assured that RTOs operating at 50  F below 1430  F ( i. e., 1380  F) will achieve the desired destruction efficiency. In addition, the final rule allows PCWP facilities to conduct multiple performance tests to set the minimum operating temperature for RCOs and RTOs, and therefore, PCWP sources would have the option to conduct their own studies ( under a variety of representative operating conditions) in order to establish the minimum operating temperature at a level that they could maintain and that would provide them with an acceptable " compliance margin."

With regard to RCOs, we agree with the commenters that when the THC concentration in the inlet is high, the RCO will not need any additional heat and it can operate at temperatures higher than the set point. Therefore, if the initial compliance tests are conducted under these conditions, the operating temperature limit will be too high for production rates at less than full capacity. However, the final rule requires emissions testing under representative operating conditions and not maximum operating conditions. In addition, we do not agree with the commenter's solution to set the operating limit at 100 ° F above the minimum operating [ design]

temperature of the catalyst. As with RTOs, we believe it is incumbent upon the facility to demonstrate performance and establish the operating limits during the compliance demonstration test. Therefore, the rule has not been changed, and it requires the facility to establish the minimum catalytic oxidizer operating temperature during the compliance test. As noted below,

we have provided more flexibility to the facility regarding temperature monitoring for an RCO.

We recognize that in a typical RTO and RCO, the combustion chamber contains multiple burners, and that each of these burners may have multiple thermocouples for measuring the temperature associated with that burner. The final rule requires establishing and monitoring a 2 174 minimum firebox temperature for RTOs. In an RTO, the minimum firebox temperature is actually represented by multiple temperature measurements for multiple burners within the combustion chamber. Thus, the final rule clarifies that facilities operating RTOs may monitor the temperature in multiple locations within the combustion chamber and calculate the average of the temperature measurements to use in establishing the minimum firebox temperature operating limit.

Finally, the final rule includes an option ( in lieu of monitoring oxidizer temperature) for monitoring and maintaining the oxidizer outlet THC concentration at or below the operating limit established during the performance test. Use of the THC monitoring option eliminates the concerns regarding establishing and monitoring oxidizer operating temperatures ( i. e., it provides facilities complete flexibility in operation of the control device, as long as the THC outlet concentration remains below the operating limit).

<IP_ADDRESS> Comment: Commenters IV D 21, IV D 23, and IV D 27 stated that, for RCOs,

instead of placing the thermocouple in a location to measure the gas stream before it reaches the catalyst bed, the thermocouple should be placed in a location to measure the temperature of the gas in the combustion chamber between the catalyst beds. Commenters IV D 21 and IV D 27 noted that, because the gas flow reverses direction in RCOs, the temperature monitor will not consistently measure the gas at the same point in the process, such that sometimes the gas temperature will be recorded after the catalyst beds instead of before. Also, the proposed PCWP rule does not provide a location for the temperature monitor if there are more than two catalyst beds. Commenter IV D 23 also noted that plugging near the temperature probe in the bed can cause inaccurate readings. Commenters IV D 21 and IV D 27 stated that placing the monitor inside the combustion chamber eliminates the need for multiple monitors and avoids problems such as overheating and burnout of the catalyst media caused by the temperature delay between the burner and the RCO inlet.

Response: Most RCOs have two or more catalyst sections with a " combustion chamber"

located in between and supplemental gas heating. The purpose of the supplemental gas heating is to provide the necessary heat input during startup, as well as to ensure that the minimum temperature necessary to initiate the combustion reaction on the catalyst is maintained during operation ( i. e., that a minimum catalyst inlet temperature is maintained). The operation of these units and the associated temperature measurement and monitoring is complex. The commenters properly indicated that because the gas flow reverses direction in RCOs, the temperature monitor 2 175 will not consistently measure the gas at the same point in the process, such that sometimes the gas temperature will be recorded after the catalyst beds instead of before ( i. e., at the inlet). We did not intend to require the separate measurement of each " inlet" temperature by switching the data recording back and forth to coincide with the flow direction into the bed. The intention is to monitor the " minimum" temperature of the gas entering the catalyst to ensure that the minimum temperature is maintained at the operating level during which compliance was demonstrated. This can be accomplished by measuring the temperature in the regenerative canisters at one or more locations. Measuring the inlet temperatures of each catalyst bed and then determining the average temperature for all catalyst beds is one approach; even though some of the beds are cooling and others are heating, the average across all of the catalyst beds should not vary significantly.

Another acceptable alternative is monitoring the " combustion chamber" temperature as suggested by the commenters. The monitoring location( s) selected by the facility may depend on the operating conditions ( i. e., THC loading to the unit) during the performance test and on how the unit is expected to be operated in the future. The objective is to establish monitoring and operating limits that are representative of the conditions during the compliance demonstration test( s) and representative of the temperature to which the catalyst is exposed. We recognize the need for flexibility in selecting the temperature( s) to be monitored as operating limits for RCOs.

Therefore, the final rule provides flexibility by allowing facilities with RCOs to choose between basing their minimum RCO temperature limit on the average of the inlet temperatures for all catalyst beds or the average temperature within the combustion chamber. If there are multiple thermocouples at the inlet to each catalyst bed, then we would expect facilities to average the measurements from each thermocouple to provide a representative catalyst bed inlet temperature for each individual catalyst bed. The same would apply for facilities establishing a minimum catalytic oxidizer temperature based on multiple burner temperatures within the combustion chamber.

<IP_ADDRESS> Comment: Commenters IV D 03, IV D 21, and IV D 27 stated that PCWP facilities should not be required to measure and comply with limits on the static pressure at the inlet to a thermal oxidizer. According to the preamble ( 68 FR 1292), monitoring the static pressure at the inlet to a thermal oxidizer is supposed to indicate the exhaust flow rate entering the thermal oxidizer and the capture efficiency. However, the PCWP rule also states that facilities must maintain either the static pressure or the maximum process unit exhaust flow rate, making 2 176 EPA's real wishes unclear. The inlet static pressure to a thermal oxidizer is not a reliable indicator of the flow through the oxidizer, the destruction efficiency, or the capture efficiency.

The commenters also noted that the preamble to the PCWP rule says that monitoring the static pressure can indicate to the operator when there is a problem such as plugging. However, static pressure is usually the last indicator of these types of control device problems. The commenters agreed that measuring those parameters helps to assess the overall condition of the oxidizer, but EPA should not set limits on them. Instead, all of the measured parameters should be examined together to determine if there is a problem with the control device, and operators should follow the work practices to help ensure compliance. The operators should also keep track of a combination of parameters to tell them when maintenance should be performed to avoid those problems. Monitoring the static pressure actually helps to control the speed of the fan or the oxidizer dampers so that all the air flows are balanced. Static pressure is adjusted to avoid vacuum conditions in the ductwork of multiple dryer systems treated by one control device when one dryer is shut down, to improve emission collection efficiency and prevent fugitive emissions,

and to adjust the pressure drop across a bag filter as it fills with particulates, among others.

However, if operators are required to keep the static pressure within an operating range, it will limit their ability to maintain capture efficiency. Also, the normal static pressure at the oxidizer inlet may change over time as particulate matter accumulates in the heat exchanger. If EPA requires facilities to maintain the static pressure at a set level, the oxidizer would need to be cleaned more often, meaning that facilities would need more downtime. The commenter requested that the EPA recognize static pressure as one of a number of parameters that can ensure that the flow rate is sufficient instead of requiring facilities to measure it. The EPA should keep in mind that maintaining a certain static pressure does not necessarily ensure that a dryer is in compliance, and likewise, a deviation from the static pressure endpoint does not necessarily indicate that the dryer is out of compliance because there was likely no change in the capture or destruction rate. If static pressure monitoring becomes mandatory, then large operational,

maintenance, and reporting burdens will be placed on facility personnel. Facilities should be able to demonstrate that an appropriate air flow is being maintained by a combination of parameters that include monitoring static pressure, flow, and fan performance and documenting that the system was designed well. Also, if retained as an operating parameter, the minimum limit on the 2 177 static pressure should be removed, and the averaging period should be increased to 24 hours to avoid deviations caused by statistics.

Response: For the reasons stated by the commenters, we agree that the requirement to monitor and establish operating limits for static pressure ( as an alternative to air flow) should be dropped from the monitoring requirements for thermal and catalytic oxidizers. We deleted this requirement from the final rule.

<IP_ADDRESS> Comment: Commenters IV D 03, IV D 21, and IV D 27 stated that the monitoring and control requirements on air flow through control devices are unnecessary. The commenters noted that the preamble to the PCWP rule states that monitoring air flow would provide an indicator of capture efficiency; however the commenters contended that air flow, like static pressure, is an unreliable method of monitoring capture efficiency. Theoretically, the best performance is achieved when the temperature is above a minimum and flow is below a maximum.

However, applying a compliance limit to the maximum of the flow rate through a thermal oxidizer limits the possible capture efficiency. Establishing a minimum flow rate for the oxidizer could make sense, since any air not flowing through the oxidizer would go untreated. However, if such a limit is set, EPA should keep in mind that numerous factors affect the air flow through the control device, including the rate of water removal in dryers, leakage of tramp air into the process, the number of processes operating for control units that receive emissions from multiple production units, the controls placed on veneer dryers to avoid pulling too much cold air into the dryer, the retention time for rotary dryers, and the overall production speed due to process adjustments. If the air flow to the control device is not constant, then monitoring the air flow through the control device will not be an accurate measure of capture efficiency. Also, if EPA wants to require facilities to monitor air flow to demonstrate that press enclosures meet Method 204 standards, that condition should be part of the enclosure requirements, not those of the control device. Any limit to the air flow that would cause a minimum production rate should not be considered. Most systems are fixed flow, so the design of the system will define the flow. For oxidizers, EPA should not place a minimum on the air flow, and monitoring the air flow should be just one option for demonstrating capture efficiency.

Response: For the reasons stated by the commenters, we agree that the requirement to monitor and establish operating limits for air flow ( as an alternative to static pressure) should be 2 178 dropped from the monitoring requirements for thermal and catalytic oxidizers. We deleted this requirement from the final rule.

<IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 stated that one operating limit should be sufficient for each control device, but acknowledged EPA's historical preference for two operating limits per control device. The commenters noted that if EPA decided to delete the operating limits for static pressure and air flow, thus leaving only one operating limit ( temperature) for thermal and catalytic oxidizers, EPA could add a requirement to demonstrate appropriate oxidizer residence time during the initial performance test. According to the commenters, the demonstration test could involve demonstrating the required destruction efficiency while operating the oxidizer within 10 percent of maximum fan capacity. As long as the oxidizer cannot exceed the maximum design flow rate, then no further flow rate monitoring should be required. However, if there is a possibility that the actual residence time of oxidizer could be shorter than designed ( e. g., for those oxidizers with fan capacities that exceed the design oxidizer residence time), the facility should monitor either the flow rate or another parameter during operation to demonstrate that the residence time remains within the designed time.

Commenter IV D 27 gave an example whereby a facility installs a larger RTO or RCO than necessary to allow for future expansion, such that the fan would not be running at full capacity.

In such cases, the commenter stated that the facility could petition EPA to conduct the compliance tests at the anticipated operating conditions and limit either the fan speed or the air flow rate. In that case, air flow monitoring would be appropriate, but it should not be mandatory for everyone.

Response: As stated in the previous response, we have deleted air flow ( and static pressure) monitoring from the operating requirements for thermal and catalytic oxidizers in the final PCWP rule. The final rule requires continuous monitoring of temperature for thermal oxidizers. We believe that temperature is both a controllable parameter and a reliable indicator of control efficiency for thermal oxidizers, and that it is appropriate to require monitoring of a single parameter ( temperature) for this device. For catalytic oxidizers, the final rule requires continuous monitoring of temperature and an annual test of catalyst activity level ( see response to comment No. <IP_ADDRESS> below). We believe that these two requirements together will provide sufficient monitoring of the catalytic oxidizers. Therefore, the final rule does not include the initial residence time test suggested by the commenters. 2 179 <IP_ADDRESS> Comment: Commenter IV D 07 suggested that a catalyst sampling and testing method be incorporated into the rule. The current requirement to monitor inlet pressure may not be sufficient to detect catalyst problems such as poisoning, blinding, or degradation.

Response: We agree with the commenter that a catalyst activity level check is needed because catalyst beds can become poisoned and rendered ineffective. An activity level check can consist of passing an organic compound of known concentration through a sample of the catalyst,

measuring the percentage reduction of the compound across the catalyst sample, and comparing that percentage reduction to the percentage reduction for a fresh sample of the same type of catalyst. One company that performs this service charges less than $ 800; and in this case, the catalyst sample is removed from the bed by the facility and then shipped to the testing company where its ability to oxidize organic compounds is determined with a flame ionization detector. 26 In response to this comment, we added to the final rule a requirement for facilities with catalytic oxidizers to perform an annual catalyst activity check on a representative sample of the catalyst and to take any necessary corrective action to ensure that the catalyst is performing within its design range. Corrective actions may include washing or baking out the catalytic media,

conducting an emissions test to ensure the catalytic media is resulting in the desired emissions reductions, or replacing all or part of the media. Catalysts are designed to have an activity range over which they will reduce emissions to the desired levels, and therefore, the final rule specifies that corrective action is needed only when the catalyst activity is outside of this range. It is not our intention for facilities to replace catalyst if the catalytic media is not performing at the maximum level it achieved when the catalyst was new. The final rule specifies that the catalyst activity check must be done on " a representative sample of the catalyst" to ensure that facilities that may have recently conducted a partial media replacement do not sample only the fresh catalytic media from the catalytic oxidizer for the catalyst activity check.

2.7.12 Process incineration monitoring requirements <IP_ADDRESS> Comment: Commenter IV D 27 noted that combustion units with heat input capacity greater than or equal to 44 megawatts ( MW) that accept process exhausts into the flame zone would be exempt from the initial performance testing and operating requirements for thermal oxidizers as stated in the proposed rule. The commenter requested that EPA modify the language in the final PCWP rule to conform with similar language in the HON and the Pulp and Paper Cluster rule as follows ( modified text in italics): " Combustion units with heat input capacity 2 180 greater than or equal to 44 megawatts that accept process exhausts into the flame zone or with the combustion air are exempt from the initial performance testing and operating requirements for thermal oxidizers." The commenter gave an example whereby the process exhaust from a veneer dryer might be added as combustion air for a process boiler ( e. g., as under fire air, over fire air,

or both) instead of being added directly to the flame zone of the boiler. The commenter noted that in the HON and Cluster rules, EPA recognized that boilers greater than 44 MW typically had greater than 3/ 4 second residence time, ran hotter than 1500  F, and usually had destruction efficiencies greater than 98 percent. ( See 65 FR 3909, January 25, 2000 and 65 FR 80762,

December 22, 2000 at § 63.443( d)( 4)( ii)). The commenter stated that the design and construction of PCWP boilers follow the same principles that would allow for these operating conditions.

Response: As noted by the commenter, the HON ( subpart G) and the final Pulp and Paper MACT I rule ( subpart S) included the requested provision for boilers ( and for recovery furnaces at pulp and paper mills) with heat input capacity greater than 44 MW, because performance data showed that these large boilers achieve at least 98 percent combustion of HAP when the emission streams are introduced with the primary fuel, into the flame zone, or with the combustion air.

Lime kilns at pulp and paper mills were excluded from this provision because we did not have any data to show that lime kilns can achieve the required destruction efficiency when the HAP emission stream is introduced with the combustion air. Therefore, lime kilns at pulp and paper mills that accept HAP emission streams must introduce the stream into the flame zone or with the primary fuel. We do not have the data to show that the design and construction of large (> 44 MW) combustion units at PCWP plants would be similar to boilers found at pulp and paper mills.

Furthermore, combustion units at PCWP plants with heat input capacity of greater than 44 MW are less prevalent than smaller ( i. e., less than 44 MW) PCWP combustion units, and many of these smaller combustion units are not boilers. As discussed in the response to comment No. <IP_ADDRESS>,

we are eliminating the testing and monitoring requirements for these smaller combustion units,

provided that the HAP emission stream is introduced into the flame zone. For these reasons, the final PCWP rule does not extend the exemption from testing and monitoring to those boilers greater than 44 MW that introduce the HAP emission stream with the combustion air, as requested by the commenter. 2 181 <IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 noted that combustion units with a heat capacity input of greater than or equal to 44 MW ( 150 million BTU/ hr) are exempt from initial performance testing and operating requirements, and the commenter requested that combustion units with a heat capacity input of less than 44 MW that use process exhausts in the flame zone be exempt as well. The exemption would be based on the demonstration that the combustion unit's temperature and residence time are sufficient to destroy the necessary HAP.

For example, some plants install a combustion unit between the press and the dryer so that the emissions from the press can provide heat for the dryer. These units can also burn the emissions from small process units, such as blenders, without requiring supplemental fuel. For most of these setups, it would be difficult to conduct a compliance test because many of the combustion units do not have a real vent to serve as a sampling location, and the dryer emissions do not have the same composition as the gas traveling from the combustion output to the dryer input. Since most wood products dryers have a heat capacity of 20 to 50 million Btu/ hr, they would not meet the exemption discussed above. If P2 measures are being applied to the dryer, it may not have a control device, meaning that the entire setup may not be in compliance with the proposed PCWP rule. However, there are three possible scenarios for the actual emissions from this setup and similar configurations, and all three point to the conclusion that the combustion unit does not need to undergo initial compliance tests or control requirements. In the first scenario, a process dryer is fed by emissions from any source and the exhaust is fed to a control device. The control device would ensure at least 90 percent destruction efficiency, and testing the burner would be unnecessary. In the second scenario, the burner of a process dryer is fed by emissions from a noncredit generating source such as a press, and the dryer meets the requirements of the PBCO. The dryer emissions would include the HAP created by the dryer and the undestroyed HAP from the burner. Presumably, to meet the PBCO, destruction of press vent emissions would need to meet or exceed the 90 percent destruction efficiency requirement. EPA should allow the facility to meet the PBCO limit plus 10 percent of the press emissions, since that would be equivalent to 90 percent control. The third scenario is similar to the second, except the dryer is fed by a creditgenerating source such as a blender. Since the burner exhaust cannot be measured directly, EPA should provide a method for counting the credits generated by destroying the HAP from that source. The facility could measure the dryer outlet and subtract 10 percent of credit generation rate to determine compliance with the PBCO. This approach would give 100 percent credit for 2 182 destruction of the credit generation emission, whereas the proposed rule does not allow for credits based on more than 90 percent destruction. Alternatively, the rule could just require that the PBCO be met with no credit given for emissions from the credit generating source that were not destroyed in the process burner. This approach would assume 100 percent destruction of the credit generating emission and then only 90 percent would be applied to the PBCO. In any case,

regardless of the heat capacity input, none of the combustion units would need to be tested, and the commenters requested that the following phrases be added to the PCWP rule:

40 C. F. R. § 63.2260( a) [ add] . . . Process heaters used to oxidize emissions from presses or other sources that exhaust into dryers are exempt from the initial performance testing requirements for thermal oxidizers. 63.2262( d) Location of sampling sites. ( 1) For testing control devices located prior to final discharge to the atmosphere, sampling sites must be located at the inlet of the control sequence and at the outlet of the control device prior to any releases to the atmosphere. ( 2) For testing control devices located between process units, such as process burners, sampling sites must be located at the inlet of the control sequence. ( 3) Sampling sites for process based emission limits in Table 1A are to be located prior to any releases to the atmosphere.

Finally, the commenter provided an alternative to the exemption requested above for combustion units with a heat capacity of less than 44 MW. If these units must be tested, the test method should be able to distinguish between the HAP generated by the combustion unit and the HAP generated by other parts of the process. During the 90 percent reduction performance test,

the combustion emissions should be tested first separate from the process unit emissions and then with those emissions. If the difference between the two emission measurements is not statistically significant, then the combustion unit is in compliance. The description of a similar test is located at 40 CFR 60, appendix C.

Response: As noted by the commenter, the HON ( subpart G) and the final Pulp and Paper MACT I rule ( subpart S) exempt from testing and monitoring requirements combustion devices with heat input capacity greater than or equal to 44 MW. The HON also exempts from testing and monitoring combustion devices with capacity less than 44 MW if the exhaust gas to be controlled enters with the primary fuel. If the exhaust gas to be controlled does not enter with the primary fuel, then testing and continuous monitoring of firebox temperature is required by the HON. Similarly, the final Pulp and Paper MACT I rule ( subpart S) exempts from testing and monitoring requirements combustion devices ( including recovery furnaces, lime kilns, boilers or 2 183 process heaters) with capacity less than 44 MW if the exhaust stream to be controlled enters into the flame zone or with the primary fuel. Based on the precedent established in the HON and Pulp and Paper MACT I rules, the final PCWP rule extends the exemption from testing and monitoring requirements to combustion units with heat input capacity less than 44 MW, provided that the exhaust gas to be treated enters into the combustion unit flame zone. If the exhaust gas enters into the combustion unit flame zone, the required 90 percent control efficiency may be assumed.

If the exhaust gas does not enter into the flame zone, then the testing and monitoring requirements for thermal oxidizers will apply. Given that few combustion units would require testing, the final rule does not specify how to differentiate between the HAP generated by the combustion unit and the HAP generated by other parts of the process. Facilities may petition the Administrator to determine if such differentiation will be allowed, and how to measure to emissions.

Regarding the first scenario presented by the commenters ( where a process dryer is fed by emissions from any source and the exhaust is fed to a control device), we agree that the control device would ensure at least 90 percent destruction efficiency, and testing the burner would be unnecessary.

The second operating scenario presented by the commenters involves a dryer burner used to control press emissions, while the dryer meets the PBCO. We believe that the commenter's suggestion of allowing the facility to meet the dryer PBCO plus 10 percent of the press emissions is overly complicated. The final PCWP rule already contains three sets of compliance options ( six add on control system compliance options, PBCO limits for each process unit, and emissions averaging). We believe that adding additional provisions for combining compliance options for the numerous potential process unit and control system exhaust configurations would complicate the rule to the point that enforcability of the rule would be hampered. Therefore, a source with a dryer used to control press emissions that chooses to comply with the PBCO must meet the dryer PBCO as stated in the final rule and would not be allowed to account for any uncombusted press emissions. The press emissions routed to the dryer burner would be assumed to be reduced by 90 percent, provided that the press emissions are introduced into the dryer burner's flame zone.

The third operating scenario presented by the commenters involves routing exhaust from an emissions averaging credit generating unit ( e. g., blender) to a dryer burner while the dryer complies with the PBCO. In this scenario, the uncontrolled blender emissions would be measured 2 184 prior to entering the dryer burner. For purposes of calculating emissions averaging credits, the blender emissions directed to the dryer burner would be assumed to be reduced by 90 percent,

provided that the blender emissions are introduced into the dryer burner's flame zone. We disagree that the dryer PBCO should be changed to accommodate the blender emissions for two reasons. First, as noted for scenario 2 above, altering the PBCO to account for process emissions added to the dryer burner would introduce unnecessary complexity to the rule. Second, the final rule does not allow combining of emissions averaging and the PBCO as discussed previously in sections 2.6.3 and 2.6.4 of this document.

The wording we incorporated into the final rule is less specific than the wording suggested by the commenter; however, it still accomplishes the goal of exempting from the testing and monitoring requirements combustion units that accept process exhausts into the flame zone. We have also included definitions of " flame zone" and " combustion unit" in the final rule.

2.7.13 Selection of biofilter monitoring parameters <IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 agreed that temperature is a parameter that should be monitored for biofilters, but argued that the location of the temperature monitor should be changed from the biofilter inlet to the biofilter bed. The bed temperature has the greatest impact on biological activity. The biofilter inlet temperature is not a good indicator of the bed temperature and can change very rapidly depending on the operating rate of the press,

the humidity, and the ambient temperature. Although biofilters can operate in a wide range of temperatures, it is important to make sure that the biofilter remains in that range to support biological activity and maintain performance level. For that reason, the temperature should be monitored at an alternate location, such as the biofilter bed, the biofilter outlet, or the support media for the biological material. To compensate for low inlet temperatures due to low humidity,

some biofilters have supplemental heat added to the humidifier. However, EPA can not require that facilities measure humidifier inlet temperature, because some systems do not have a humidifier. The commenter requested that EPA change the temperature monitoring location to the biofilter exhaust or the biological media/ bed.

Response: We agree with the commenter that the biofilter bed temperature has the greatest impact on biological activity and that the location for monitoring the biofilter temperature should be changed. We did not propose monitoring of biofilter bed temperature because we thought that monitoring of biofilter inlet temperature would be simpler because only one 2 185 thermocouple would be required. The temperature inside the biofilter bed can change in different areas of the bed, and therefore, depending on the biofilter, multiple thermocouples may be necessary to get an accurate picture of the temperature conditions inside the biofilter bed. Prior to proposal we rejected the idea of monitoring the biofilter exhaust temperature because temperature measured at this location can be affected by ambient temperature ( especially for biofilters with short stacks) more than the temperature inside the biofilter bed. Thus, we now conclude that there is no better, more representative way to monitor the temperature to which the biofilter microbial population is exposed than to directly monitor the temperature of the biofilter bed. According to our MACT survey data, most facilities with biofilters are already monitoring biofilter bed temperature. Therefore, the final rule requires continuous monitoring of the temperature inside the biofilter bed.

We acknowledge that biofilter bed temperature can vary with seasonal conditions, and that the biofilter can reduce HAP within a relatively wide temperature range ( e. g., 70 to 100 ° F).

Biofilters are currently located in different areas of the United States, including the upper Midwest and the South. Biofilter bed temperature is a controllable parameter; the exhaust stream entering the biofilter can be cooled through humidification or heated using steam as necessary to maintain the biofilter bed within its optimal temperature range. However, we believe that the optimal temperature range for individual biofilters is based on site specific conditions ( e. g., type of media and microbes, climate at the facility, whether the biofilter is located above or below ground). Therefore, we believe it is appropriate that the temperature range for each individual biofilter be verified through emissions testing. Facilities experiencing large seasonal variations in their biofilter bed temperatures may choose to expand their temperature operating range by conducting performance tests during winter and summer months.

The proposed rule would have allowed facilities to specify their own monitoring methods,

monitoring frequencies, and averaging times for the proposed biofilter operating parameters ( i. e.,

inlet temperature, effluent pH, and pressure drop). However, as discussed elsewhere in section 2.7.13, for the final rule we have reduced the biofilter parameters to be monitored to temperature only. Monitoring of temperature is not as subjective as monitoring biofilter effluent pH and pressure drop, and therefore, as an outgrowth of our decision not to require monitoring of biofilter effluent pH and pressure drop, the final rule specifies the monitoring method, frequency,

and averaging time for biofilter bed temperature monitoring. The final rule requires that each 2 186 thermocouple be placed in a representative location, and clarifies that multiple thermocouples may be used in different locations within the biofilter bed. The temperature data ( e. g., average temperature across all the thermocouples located in the biofilter bed if multiple thermocouples are used) must be monitored continuously and reduced to a 24 hour block average. A 24 hour block average was selected for biofilter temperature monitoring because we recognize that there may be some diurnal variation in temperature. Facilities wishing to reflect a diurnal temperature variation when establishing their biofilter temperature may wish to perform some test runs during peak daily temperatures and other test runs early in the morning when temperatures are at their lowest.

<IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 stated that the operating requirements for pressure drop across the biofilter bed should be removed from the PCWP rule.

Pressure drop is a good parameter to monitor voluntarily because it indicates the permeability and age of the biofilter bed, which helps determine maintenance and replacement needs. However, it is not an indicator of destruction efficiency. Because of normal wear and tear, the pressure drop gradually increases over the two to five year life span of the biofilter, so it would not be possible to maintain a constant operating pressure. Monitoring pressure drop should only demonstrate that a biofilter is operating within the design specifications. The commenter noted that the OAQPS Background Information Document ( BID) for the Proposed Plywood and Composite Wood Products NESHAP only mentions pressure drop as an indication of age and life of the filter bed, but it does not provide proof that pressure drop indicates destruction efficiency. The three documents referenced by the BID, Summary of the Responses to the 1998 EPA Information Collection Request ( MACT Survey)  General Summary ( Docket II B 30), Proposed Monitoring Protocol for Biofiltration Systems From the Forest Products Industry ( II D 495), and Minutes of the August 5, 1998 Meeting with Envirogen, Inc. ( II E 15), do not support the idea that pressure drop indicates control efficiency, but they do support the idea that pressure drop indicates age and life of the biofilter bed. The third source listed does discuss a situation in which a biofilter became clogged and efficiency decreased, but the manufacturer found that inlet temperature change was to blame, not the pressure drop in the biofilter bed. The current PCWP rule does not allow for the normal increase in pressure drop, but simply monitoring the pressure drop would indicate when maintenance is needed. If biofilter pressure drop remains a mandatory control parameter,

facilities will be forced to change the biofilter media before the end of its useful life. During the times that the biofilter is being replaced, a large amount of HAP escapes to the atmosphere, so 2 187 changing the bed more often could result in a net increase in HAP. An absolute limit on pressure drop is impractical, since action is only necessary when the pressure drop increases rapidly from current conditions. Facilities could be allowed to retest existing biofilters when they reach the end of their useful lives to determine the new operating range. Since the results from compliance tests performed before a modification cannot be used to set operating limits on the modified unit, a new operating range could only be determined in this manner if changing a biofilter bed or media type is not considered a modification of the biofilter.

Response: We agree with the commenters that increases in pressure drop will occur over time and will not necessarily equate to a reduction in control efficiency, making an absolute limit on pressure drop ineffective in demonstrating continuous compliance. Therefore, we have removed the requirement to monitor pressure drop from the operating requirements for biofilters in the final PCWP rule.

<IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 stated that the operating requirements for pH of the biofilter bed effluent should be removed from the PCWP rule. The commenters noted that pH is a good parameter to monitor voluntarily because it indicates the environmental conditions inside the biofilter bed and can indicate the presence of organic acids and THC decomposition products, but it is not a reliable indicator of destruction efficiency. If other environmental factors are favorable, a pH between 6.0 and 7.5 is sufficient to allow the existing microorganisms to oxidize the organic material and sustain biological activity. The pH within a biofilter system tends to regulate itself well, and small fluctuations of pH are expected and have little effect on the biofilter performance. However, the narrow range of pH values that would be established as an operating range by the initial compliance tests should not be used alone to determine biofilter performance or the need for major adjustments. Those major adjustments are only needed if the pH falls below 6.0. Another issue with monitoring biofilter pH is the ability to continuously monitor that parameter. Some biofilter units operate with periodic irrigation of the bed, meaning that the effluent is not constant and continuous monitoring is not possible.

Attempting to irrigate these types of beds continuously would block mass transfer and severely reduce the performance of the biofilter. Because the effluent is not continuous, there is no good location for measuring the pH of a biofilter, and monitoring a stagnant sample of water certainly would not achieve the goal. The commenters pointed to an NCASI survey that confirmed that pH monitoring would be impractical for the facilities surveyed. Further, since none of the facilities 2 188 surveyed could find a link between pH alone and biofilter production, none of those facilities currently have pH monitors on their biofilters. If a facility chooses to measure this parameter,

readings should only be taken once a week, and calibration should not be performed more often then that. The pH changes fairly slowly, so recording the pH frequently is unnecessary.

Commenter IV D 03 suggested that checking the pH meter calibration quarterly rather than every eight hours would be a lot more realistic and would relieve a large burden of monitoring time,

labor, recordkeeping, and other factors.

Response: Although pH is an indicator of the health of the microbial population inside the biofilter, we agree with the commenters that including continuous pH monitoring as an operating requirement for biofilters may not be appropriate. We acknowledge that there is not a good location for continuously measuring pH in some biofilters and that pH is not necessarily a reliable indicator of destruction efficiency. Therefore, we have removed the requirement to monitor pH from the operating requirements for biofilters in the final PCWP rule. We have also deleted the pH meter calibration procedures that commenter IV D 03 refers to from the rule.

<IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 requested that EPA give facilities some flexibility in choosing the biofilter operating parameters that will be subject to operating ranges and controls. Many facilities that currently operate biofilters measure the temperature and pressure, along with other physical characteristics, but the readings are only observed, and not subject to limits. To demonstrate HAP removal, most of these facilities use periodic stack testing or CEMS for THC. Since biofilters have not been in use long enough for a thorough study of monitoring requirements, EPA should leave room in the PCWP rule to allow facilities to monitor and control the parameters that they feel best demonstrate compliance. The commenter agreed that outlet temperature could be an acceptable parameter for control.

Response: We have eliminated the proposed requirements for monitoring biofilter pressure drop and pH, and we have revised the biofilter temperature monitoring requirement. The only parameter required to be monitored and controlled for the final PCWP rule is biofilter bed temperature. Facilities may choose to observe other parameters, but will not be required to record or control them for the PCWP rule. We believe that many factors can affect biofilter performance, either alone ( e. g., a media change) or in concert with one another ( e. g., a loss of water flow resulting in a sharp change in temperature and pH), and the factors that have the greatest effect on biofilter performance are likely to be site specific. However, based on the 2 189 comments we have received, we conclude that extensive biofilter parameter monitoring is not the best method for ensuring continuous compliance. Therefore, to promote enforceability of the PCWP rule, we have added a requirement to perform repeat testing of biofilters. The final rule requires facilities to conduct a repeat test every two years and every time they replace at least 50 percent ( by volume) of the biofilter media. Each repeat test must be conducted within two years of the previous test ( e. g., two years after the initial compliance test, or two years after the test following a media change). Facilities using a THC CEMS that choose to comply with the THC compliance options ( i. e., 90 percent reduction in THC or outlet THC concentration less than or equal to 20 ppmvd) may use the data from their CEMS in lieu of conducting repeat performance testing.

<IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 stated that replacing the biofilter media should not be considered a modification of the biofilter. The frequency of replacement can be as often as two years, and it is unnecessary for facilities to establish new operating ranges every time the media is replaced. Instead, the operating range used for the previous bed should be appropriate for the replacement bed. The EPA may choose to require one test to confirm that the new bed is still operating within the same range after the bed is acclimated. The wording of section 63.2262( m)( 2) ( How do I conduct performance tests and establish operating requirements?  Establishing biofilter operating requirements) indicates that EPA does not consider the replacement of a biofilter bed to be in the same category as new biofilters. The commenters requested that the following sentence be added to section 63.2262( m)( 1):

" Replacement of biofilter media with the same type of material is not considered a modification for purposes of this paragraph."

Response: We agree that facilities replacing the biofilter media with any amount of the same type of media should not be required to reestablish their biofilter bed temperature. Section 63.2262( m)( 1) of the proposed rule stated that " If you use data from previous performance tests,

you must certify that the biofilter and associated process unit( s) have not been modified subsequent to the date of the performance tests" ( emphasis added). We agree that it is appropriate to use data from previous performance tests to establish the biofilter bed temperature range when the biofilter has not been " modified" in a way that will affect its long term performance. We believe that substantial replacement of the biofilter media ( i. e., replacement of 50% or more of the biofilter bed) with the same type of media may affect short term performance 2 190 of the biofilter while the replacement media becomes acclimated. Therefore, to ensure that the media is acclimated, the final PCWP rule requires a repeat performance test within 180 days following replacement of 50 percent or more ( by volume) of biofilter media with the same type of media. We have added the sentence suggested by the commenters to § 63.2262( m)( 1) to indicate that a new biofilter bed temperature range need not be established following replacement of the biofilter bed media with the same type of material. During repeat testing following replacement with the same type of media, facilities can verify that their biofilter remains within the temperature range established previously or establish a new compliant temperature range.

As discussed in response to comment No. <IP_ADDRESS> below, for purposes of § 63.2262( m)( 1)( 3) we do consider replacing the biofilter media with another type of media as a " modification" of the biofilter that necessitates establishment of a new biofilter bed temperature range. The final PCWP rule requires facilities to conduct a repeat performance test following every replacement of the biofilter media with any volume of a different media ( e. g., if the media is changed from bark to synthetic material). Facilities using a different type of media must reestablish their temperature range.

<IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 stated that EPA should allow new biofilters a longer period than 180 days to establish operating parameter levels. The commenters suggested a one year period, since that would be long enough to observe the full seasonal variation in parameters and find the true operating maxima and minima. For example, it is not very likely that 180 days would be long enough to observe the complete temperature range within which biofilters can effectively remove water soluble HAP. Section 63.2262 ( m)( 2) ( How do I conduct performance tests and establish operating requirements?  Establishing biofilter operating requirements) should be completely replaced by the following section:

( 2) If historical operating records are not readily available for new biofilters, biofilters that have been physically modified, or biofilters with media replaced with a new or different type of media, you will be allowed up to 1 year following the compliance date to gather and complete the requirements of paragraph ( m)( 1) of this section.

A long establishment period would also allow the biofilter to become completely acclimated and provide a better understanding of its regular operation. Since biofilters have a slow response time, compliance testing under different conditions does not give reliable results. Instead the best ways to determine operating ranges for a new biofilter are to accept data from previous biofilters 2 191 or observe the performance of the unit for a year. If a facility has to establish a pressure drop operating range, the period of time to establish that range would be much longer than a year. An appropriate operating range would need to be based on the pressure drop at the end of the life span of the biofilter. The commenter stated that waiting that long to establish compliance parameters is impractical, and the situation provides another argument for omitting pressure drop requirements from the PCWP rule.

Response: We disagree that more than 180 days is necessary to establish operating parameter limits for biofilters. As mentioned previously, we have eliminated the proposed requirement to establish operating limits for pH and pressure drop. The final PCWP rule contains two options for biofilter operating parameter limits: biofilter bed temperature range, and outlet THC concentration. While allowing one year to establish the biofilter bed temperature operating range is reasonable due to seasonal temperature variations, 1 year is not necessary for establishing an outlet THC concentration limit. Furthermore, the final PCWP rule already allows facilities to expand their operating ranges ( see § 63.2262( m)( 3)) through additional emissions testing.

The compliance date for existing facilities is 3 years after promulgation of the final PCWP rule, and existing facilities are allowed 180 days following the compliance date to conduct performance testing and establish the operating parameter limits. If there is concern that 180 days is not long enough for a new biofilter installation to operate under the full range of biofilter bed temperatures, then existing facilities begin operation of their biofilter well before the compliance date ( e. g., 180 days prior to the compliance date if 1 year is needed). Facilities also have the option of testing their biofilter prior to the compliance date to establish one extreme of their biofilter bed temperature range. The compliance date for new PCWP facilities is the effective date of the rule ( if startup is before the effective date) or upon initial startup ( if the initial startup is after the effective date of the rule), and biofilters installed at new PCWP facilities would have up to 180 days following the compliance date to establish the operating parameter limits. To address situations where a new biofilter is installed at an existing facility more than 180 days after the compliance date ( e. g., to replace an existing RTO), we have included section § 63.2262( m)( 2)

in the final PCWP rule, which allows existing sources that install new biofilters up to180 days following the initial startup date of the biofilter to establish the operating parameter limits. Thus,

new biofilter installations ( i. e., those with initial startup dates after the compliance date) are given 2 192 time for establishment of operating parameter limits regardless of where they are installed at new or existing sources.

2.7.14 Continuous THC monitoring <IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 supported the option to continuously monitor THC at control device outlets to demonstrate compliance, but stated that either the procedure for determining the operating limits or the length of the averaging periods needs to be altered. The THC concentration at a control device outlet is not a parameter that can be easily adjusted by operators. The concentration is mainly influenced by the THC content in the wood, which is dependent on the location and age of the timber, the season, and the length of time between cutting the timber and drying the wood. These are not factors that can be directly changed by operators over short periods of time just to maintain a certain THC concentration. A different method is needed to determine whether or not a facility is in compliance. The proposed PCWP rule requires that the operating limits be set as the average of the three highest 15 minute block reporting periods during the 3 hour compliance demonstration emission test. However, the commenter stated that based simply on the variability of the process, three hours is not a long enough block to avoid deviations from compliance. The commenter provided a table of analyzed THC data from a biofilter outlet. The table showed multiple deviations occurring over the twomonth period after compliance when a 3 hour block set the operating limits and few to zero deviations when a 24 hour or 7 day block set the operating limits. In order to avoid numerous deviations under the proposed PCWP rule, a mill would have to try to set the operating limits when emissions are at a maximum, but that situation occurs less than 5 percent of the time that the device is operating. The commenter recommended adopting the 7 day block average because it provides a better overall picture of the control device performance. Since HAP destruction efficiency of biofilters does not vary much with time, the longer block would not be environmentally dangerous. Alternatively, EPA could establish a 24 hour block operating limit as the highest 1 hour average THC reading in the week preceding and following the compliance demonstration test.

Response: While THC emissions at the outlet of a biofilter may vary, the THC emissions at the outlet of an thermal or catalytic oxidizer should not vary greatly. Although, as stated by the commenters, the HAP destruction efficiency of biofilters is not subject to large short term variations, the same is not true for thermal and catalytic oxidizers ( e. g., a sudden significant 2 193 decrease in temperature could result in a sudden decrease in HAP reduction). Therefore, we believe it is appropriate to maintain the 3 hour block averaging requirement for THC monitoring for thermal and catalytic oxidizers. However, we have expanded the THC averaging requirement for biofilters to a 24 hour block average to provide more flexibility. The THC operating limit for biofilters would be established as the maximum of three 15 minute recorded readings during emissions testing. We also note the continuous monitoring of THC is not required for all APCD,

but is an alternative to continuous monitoring of temperature. Furthermore, facilities can conduct multiple performance tests at different operating conditions to increase their maximum THC concentration operating limit.

2.7.15 Selection of monitoring parameters for uncontrolled process units <IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 recommended changing the title of section 63.2262 ( n) ( How do I conduct performance tests and establish operating requirements?  Establishing uncontrolled process unit operating requirements) to " Establishing operating requirements for production based compliance option process units." The current title implies that no controls of any kind are being applied to these process units, when in fact facilities may be voluntarily controlling these units or using P2 techniques to reduce emissions. Also, the wording within the section itself assumes that controlling the temperature is the only method of reducing emissions. The commenter's suggested changes to the section are shown below:

( n) Establishing operating requirements for production based compliance option process units: Establishing uncontrolled process unit operating requirements. If you operate a process unit that meets a compliance option in Table 1A of this subpart without the use of a control device, you must establish your process unit operating parameters according to paragraphs ( n)( 1) through ( 2) of this section. ( 1) During the initial performance test, you must identify and document continuously monitor the process unit controlling parameter( s) critical to maintaining compliance with the limits listed in Table 1A of this subpart. For example, if the controlling parameter is inlet temperature or operating temperature, ( whichever applies, as specified for different process units in Table 2 of this subpart) during the initial performance test, you must continuously monitor the process unit during each of the required 1 hour test runs. The maximum inlet temperature or maximum operating temperature must would then be established as the average of the three maximum 15 minute temperatures monitored during the three test runs. Limits for other controlling will be established using the same method. Multiple 3 run performance tests may be conducted to establish a range of parameter values under different operating conditions. ( 2) You may establish a different operating parameter range maximum temperature for your process unit by submitting the notification specified in § 63.2280( g) and conducting a 2 194 repeat performance test as specified in paragraph ( n)( 1) of this section that demonstrates compliance with the compliance options in Table 1A of this subpart.

If these changes are made, then the following adjustments would have to be made to Table 2 to Subpart DDDD:

( 5) Process unit that meets a compliance option in Table 1A of this subpart Maintain the controlling operating parameter 3 hour block average inlet temperature below the maximum inlet temperature established during the performance test if for the process unit is a green rotary dryer, tube dryer, or strand dryer; OR maintain the 3 hour block average process unit operating temperature below the maximum operating temperature established during the performance test if the process unit is a hardboard oven, press predryer, or reconstituted wood product press; OR maintain the 3 hour block average operating temperature in each of the hot zones below the maximum hot zone temperatures established during the performance test if the process unit is a fiberboard mat dryer or softwood veneer dryer. Maintain the 3 hour block average THC concentration a in the process unit exhaust below the maximum concentration established during the performance test Response: There are two situations in the PCWP rule where process units may not have an add on control device: ( 1) when process units meet the PBCO, or ( 2) when process units used to generate emissions averaging debits do not have an add on APCD that partially controls emissions. To clarify this for the final rule and to address the commenters concern regarding applicability of § 63.2262( n), we changed the title of the section to " Establishing operating requirements for process units meeting compliance options without a control device."

We agree with the commenters that temperature alone is not necessarily the sole controlling parameter for some process units. The final rule requires testing at representative operating conditions, defined in the rule as " operation of a process unit during performance testing under the conditions that the process unit will typically be operating in the future,

including use of a representative range of materials ( e. g., wood material of a typical species mix and moisture content or typical resin formulation) and representative operating temperature range." The rule requires facilities to describe their representative operating conditions in each performance test report for the process and control systems and explain why these conditions are 2 195 representative ( see § 63.2262( b)( 2)). The process unit specific conditions identified in each test report as being " representative" would be the most appropriate conditions to record for process units without controls. We recognize that it is not practical to continuously monitor every process unit specific factor that could affect uncontrolled emissions ( e. g., there is not way to monitor and determine a 3 hour block average of wood species mix for a particleboard plant).

However, some parameters are suitable for continuous monitoring ( e. g., process operating temperature, furnish moisture content) and are already monitored as part of normal operation, but not for compliance purposes. We believe that daily records of most parameters would be sufficient to ensure ongoing compliance ( e. g., daily average process operating temperature,

furnish moisture, resin type, wood species mix) if the parameters do not deviate from the ranges for these parameters during the initial compliance test. Therefore, in the final PCWP rule, we have replaced the proposed 3 hour block average temperature monitoring requirements for process units without control devices with a requirement to maintain on a daily basis the process unit controlling operating parameter( s) within the ranges established during the performance test.

This allows facilities the flexibility to decide which parameters they will monitor and control,

while providing enforcement records with which to assess and compare the day to day operation of the process unit to the controlling operating parameters. Facilities are also allowed to decide for each parameter the appropriate monitoring methods, monitoring frequencies, and averaging times ( not to exceed 24 hours) for continuously monitored parameters such as temperature and wood furnish moisture.

We also note that the commenters suggested removing the option of monitoring THC concentration instead of process unit operating parameters. While we believe it is unlikely that facilities with uncontrolled process units would elect to monitor THC, we have retained this as an option in the final rule because this alternative is offered for all of the other operating requirements.

2.7.16 Performance specifications for temperature monitors <IP_ADDRESS> Comment: Commenters IV D 03, IV D 21, and IV D 27 made a few suggestions for revising the sections discussing temperature measurement. First, the phrase " minimum tolerance of 0.75 percent" found in sections 63.2268( b)( 2), 63.2268( c)( 3), and 63.2268( e)( 2) should be revised to read " accurate within 0.75 percent of sensor range." These commenters stated that, because tolerances usually refer to physical dimensions, this revision 2 196 more accurately reflects the intent of the PCWP rule. Commenter IV D 03 recommended that the temperature sensor tolerance be adjusted to 1 percent of the temperature range. Second,

commenters IV D 21 and IV D 27 stated that the phrase " of at least 20 ° F" found in section 63.2268( b)( 3) should be replaced with " minor divisions of not more than 20 ° F." The current wording means that minor divisions could be 30 ° F or 50 ° F, but since EPA probably means that 20 ° F is the largest minor division that a facility can use, the suggested revision is more accurate.

Commenter IV D 27 also stated that the thermocouple calibration and inspection requirements are too strict. The PCWP rule should be revised to consider any reading within 50 ° F of the process temperature sensor's reading adequate. Commenter IV D 27 further stated that quarterly inspections on thermocouples should not be required. The commenter noted that the only way to completely perform these inspections is to withdraw the thermocouple from its location in the combustion chamber. This often causes damage to the sensor, requiring it to be replaced. If a thermocouple provides readings that correspond with other thermocouple readings,

then the thermocouple should be considered valid.

Response: We acknowledge that the term " tolerance" is often used to mean accuracy in the sense of physical dimensions. Therefore, we have changed the requirement in § 63.2269( b)( 2)

( formerly proposed § 63.2268( b)( 2)) to read " minimum accuracy of 0.75 percent of the temperature value." As discussed below, we eliminated proposed sections § § 63.2268( c) and 63.2268( e) from the final rule because we deleted the requirements for monitoring of pressure or flow. As requested by the commenters, we also revised proposed § 63.2268( b)( 3) to state that " If a chart recorder is used, it must have a sensitivity with minor divisions of not more than 20 ° F."

We disagree that the proposed thermocouple calibration and inspection requirements are too strict and we have not changed these requirements for the final rule. We further disagree that the requirement for the temperature sensor to agree with the reading of a redundant sensor within 30 ° F during a calibration check is too stringent. The sensor is required to be " accurate" within 0.75 percent of the measured temperature. Measurements from redundant temperature sensors with 0.75 percent accuracy should differ by not more than 1.5 percent ( and rarely by this much).

If, for example, the temperature being monitored is 1600 ° F, 1.5 percent is less than 25 ° F which is well within the 30 ° F allowance. 2 197 2.7.17 Performance specifications for pressure monitors <IP_ADDRESS> Comment: Commenters IV D 03, IV D 21, and IV D 27 suggested a few changes for revising the section on pressure monitoring ( 63.2268( c)). Commenters IV D 21 and IV D 27 stated that the instrument tolerance should be 1.0 inch of water for a gauge or a minimum of 2 percent of the pressure range for a transducer. These values are realistic for the commonly used instrumentation in the industry. Second, daily checks for plugging of pressure taps are unnecessary. If pressure monitoring is included in the PCWP rule, facilities should be required to include pressure tap plugging in a maintenance program and encouraged to develop effective methods of plugging detection, such as a computer based alarm system. Commenter IVD 03 stated it would be excessive and potentially unsafe to check pressure taps for plugging daily,

and suggested a check of the pressure reading to ensure that it is normal and not stagnant.

Commenter IV D 03 stated that pressure instrumentation should not be limited to manometers only; alternatives should include instruments such as an NIST traceable calibrator. This commenter recommended that both the pressure calibrator and the transducer output should be checked on a quarterly basis. Commenter IV D 27 stated that facilities should not be required to use a manometer to check the calibration of the pressure gauge, and instead, EPA should require a validation check between the two gauges with acceptance criteria of 0.75 inches of water.

Response: We have removed all pressure monitoring requirements from the PCWP rule.

( Note that proposed § 63.2268 was renumbered § 63.2269 for the final rule.)

2.7.18 Performances specifications for flow monitors <IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 disagreed with a few of the requirements for flow monitoring ( section 63.2268( e)  What are my monitoring installation,

operating, and maintenance requirements?  Flow monitoring). First, the 2 percent minimum tolerance for the flow rate measurements is too low, and it is not supported by the MACT floor.

According to manufacturers' specifications, the flow rate sensors used on dryer and press exhausts only have an accuracy of ± 5 percent to ± 7 percent. The repeatability is only ± 0.5 percent. Adjusting the accuracy and repeatability of a sensor is not possible since the systems are designed and set by the manufacturer. Field adjustments for specific flow conditions such as temperature can be made, so there is a need to conduct flow relative accuracy test audits ( RATA)

at a certain frequency to verify that the monitor is operating properly. The EPA should allow facilities to achieve ± 10 percent accuracy to ensure that compliance will be met. This value is 2 198 used in EPA Method 2 for manual measurements of pitot tubes. Commenter IV D 27 further stated that checking the flow sensor calibration twice a year for both pitot tubes and thermal convection mass flowmeters is not necessary. The commenter noted that industry experience indicates that comparing the flow to a reference method test on the same periodicity of the compliance tests required by the facility's permit is adequate to ensure compliance. Also, facilities can compare the measured flow and the calculated flow rates once a year to validate the sensor.

Commenter IV D 27 also stated that inspection of flow sensors should be changed from four times a year to once a year. Industry experience has shown that annual inspection is enough to ensure proper operation.

Response: We have removed all gas flow monitoring requirements from the PCWP rule.

( Note that proposed § 63.2268 was renumbered § 63.2269 for the final rule.)

2.7.19 Performance specifications for moisture monitors <IP_ADDRESS> Comment: Commenter IV D 27 supported EPA's conclusion that dry rotary dryers, hardwood veneer dryers, and veneer redryers have inherently low HAP emissions and thus should be exempt from control requirements as long as certain work practices are met. The commenter specifically supported the work practices for hardwood veneer dryers, softwood veneer dryers, and veneer redryers listed in Table 3 to subpart DDDD, as well as the exemption from work practice requirements for facilities required by some other regulatory action to install a control device on a dry rotary dryer. In response to EPA's request for comment in the proposal preamble on issues related to the work practice requirements, the commenter recommended that EPA allow plants more flexibility in choosing moisture monitors.

Although most particleboard plants currently use near infrared ( NIR) technology,

technologies change over time, so EPA should specify an accuracy limit rather than a specific technology. Monitor choice should be limited to units with a ± 1 percent accuracy capability in the 25 to 35 percent moisture content range. This range is currently met by NIR technology and is consistent with section 63.2268( f)( 1) ( What are my monitoring installation, operation, and maintenance requirements?  Wood moisture monitoring). The commenter noted that the accuracy of equipment specification is typically based on equipment capabilities and measurements taken under well controlled conditions. Plants strive to maintain the best conditions possible, since product quality depends on moisture content, but conditions outside the operators' control are certain to be a factor at times. The commenter argued that the work 2 199 practices should not be written in a way that would unnecessarily restrict dryer operation or require facilities to maintain their monitors to the level of accuracy indicated by monitor specification sheets. For moisture monitors at the outlet of softwood veneer dryers and the inlet of veneer redryers, monitor choices should be limited to units with a ± 3 percent accuracy capability in the 15 to 25 percent moisture content range. Reliance on a vendor's certification should be considered adequate for demonstration of compliance with the precision requirement.

Commenters IV D 21 and IV D 27 objected to the sampling procedure used to check the calibration of continuous wood moisture content monitors, stating that the procedure in proposed § 63.2268( f)( 3) is impractical. The moisture content of the wood at any one point in the process varies so much that a truly representative sample of wood would have to be fairly large. For example, a representative sample of veneer would require multiple sheets. The sheets pulled for the sample would not pass by the moisture meter because, for safety reasons, they would have to be pulled from the process before they reached the redryer. The commenters pointed out that each moisture monitor manufacturer includes calibration procedures in the operation and maintenance recommendations for their meters. These calibration procedures ( commonly modified to meet site specific requirements) will correct any drift that occurs. The commenters recommended that facilities include the moisture meter manufacturer's calibration procedures in the plant's operation and maintenance plan and follow those procedures once during each semiannual compliance reporting period. Adjustments to the procedures may be made for any plant specific needs. Commenter IV D 27 attached examples of moisture monitor manufacturer's calibration procedures.

Commenter IV D 27 requested that the ASTM D1037 test method be added to the list of test procedures referenced in the rule. This test method should be the default method for moisture analysis and calibration of machines used to analyze grab samples, as well as continuous moisture monitors ( recognizing that moisture monitor manufactures may have alternative methods for calibrating their equipment). The reference should be added to section 63.2268( f) ( What are my monitoring installation, operation, and maintenance requirements?  Wood moisture monitoring). The PCWP rule should use the ASTM D1037 method for setting grab sample requirements, which recommends drying the wood sample " until approximately constant weight is attained." The drying time is not specified because wood, sample size, and lab variability factors make the constant weight timing difficult to predict. The regulation should go no further than 2 200 specifying that either this test method be used or a moisture analyzer calibrated by this test method be used. More specific guidance and examples can be included in implementation documents rather than in the national rule. The commenter attached a copy of ASTM D1037.

Response: Proposed § 63.2268 was renumbered § 63.2269 for the final rule. We proposed requirements for the continuous moisture sensor and grab sampling in § 63.2268( f). We noted in the preamble to the proposed rule that we planned to add to § 63.2268( f) performance specifications for the continuous moisture sensor to include such parameters as the amount of drift allowed. We requested comment on drift and any other performance specifications that should be added to ensure moisture content is being measured accurately, to ensure flexibility in the type of continuous moisture sensor that can be used by a facility, and to ensure compliance and enforceability. We also stated in the proposal preamble that we planned to add specifications to the grab sample requirements, such as including the period of time a sample must maintain a constant weight. We requested comment on what this period of time should be and any other specifications that should be added to ensure accurate and precise results.

We acknowledge the commenters' support of the work practice requirements for dry rotary dryers, hardwood veneer dryers, softwood veneer dryers, and veneer redryers. In response to the commenters' suggestions, we have modified the work practice requirements for moisture monitoring in the final rule; these changes are discussed in subsequent paragraphs. In addition to the changes regarding moisture monitoring, the final rule also exempts from the work practice requirements those PCWP facilities that elect to designate their dry rotary dryer as a green rotary dryer, and thus elect to meet the standards for green rotary dryers which are more stringent than the work practice standards for dry rotary dryers. The same exemption is provided for PCWP facilities that elect to designate their hardwood veneer dryer or veneer redryer as a softwood veneer dryer, and thus elect to meet a more stringent standard.

Based on the feedback provided by the commenter, we have revised proposed § 63.2268( f)( 1) to specify that moisture monitors used at the inlet of dry rotary dryers must have a minimum accuracy of 1 percent ( dry basis) in the 25 to 35 percent ( dry basis) moisture content range, and that moisture monitors used at the inlet of veneer redryers must have minimum accuracy of 3 percent ( dry basis) in the 15 to 25 percent ( dry basis) moisture content range.

Alternatively, facilities may use a moisture monitor with a minimum accuracy of 5 percent ( dry basis) moisture or better for dry rotary dryers used to dry furnish with less than 25 percent ( dry 2 201 basis) moisture or for veneer redryers used to redry veneer with less than 20 percent ( dry basis)

moisture.

We have also revised proposed § 63.2268( f)( 3) to eliminate the proposed grab sample procedure for calibration of continuous moisture monitors and to specify that continuous moisture monitors must be calibrated based on the procedures specified by the moisture monitor manufacturer at least once per semiannual compliance period ( or more frequently if recommended by the moisture monitor manufacturer). Because we dropped the grab sample requirements, we clarified that all moisture measurements must be on a dry basis to prevent facilities from using a wet basis ( e. g., 30 percent moisture on a dry basis is equivalent to 23 percent moisture on a wet basis). We added an equation to the rule to convert from wet basis moisture content to dry basis moisture content ( as needed). We did not incorporate the ASTM D1037 test method into the rule because no method for determining grab sample moisture content is needed.

2.7.20 Work practice requirements for dryers <IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 noted that Table 8 to subpart DDDD ( Continuous Compliance with the Work Practice Requirements) does not include averaging periods for work practice requirements, and stated that EPA needs to add those where applicable.

Response: We revised Table 8 to subpart DDDD to restate the averaging periods for the dry rotary dryer and veneer redryer work practices.

<IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 noted that although the equation to determine the percent reduction through a control device includes a term for capture efficiency,

the method for determining that efficiency for dryers is not specified in the PCWP rule. The capture efficiency for rotary dryers should be assumed to be 100 percent, and it should be assumed to be 100 percent for veneer dryers as long as the facility follows the work practices listed in Table 3 to subpart DDDD. The floor for capture efficiency for dryers was not determined, but the emission data provided to EPA assumed that the efficiency was 100 percent.

The EPA cannot establish that the floor must be 100 percent capture efficiency if it does not have the data to support that requirement. Commenter IV D 43 suggested that hardboard ovens be treated like softwood veneer dryers in terms of determining capture efficiency. If work practices are followed, then the capture efficiency should be assumed to be 100 percent. Hardboard ovens were not specifically covered in the rule, and clarification of the situation is necessary. 2 202 Response: We agree that the capture efficiency for dryers and hardboard ovens is typically 100 percent because those dryers operate under negative pressure and exhaust from these dryers is directed through a stack. For some types of dryers, the negative pressure air flow acts to pneumatically convey the wood material through the dryer as well as to prevent emissions leakage and minimize buildup of combustible gases. For hardboard ovens, a loss of negative pressure would lead to product quality problems. We also agree that the capture efficiency for veneer dryers can be assumed to be 100 percent as long as the facility follows the work practices listed in Table 3 to subpart DDDD. Process units that may have less than 100 percent capture are presses or board coolers with partial wood products enclosures. In equations where capture efficiency ( CE) is a variable, the rule defines CE as " capture efficiency, percent ( determined for reconstituted wood product presses and board coolers as required in Table 4 of this subpart)."

Thus, the capture efficiency term does not apply for dryers or other process equipment with assumed 100 percent capture.

<IP_ADDRESS> Comment: Commenters IV D 21 and IV D 27 recommended changing the averaging period for inlet moisture and temperature monitoring for dry rotary dryers. The current averaging period is listed as 24 hours in Table 3 to subpart DDDD and section 63.2268( a)( 4)

( What are my monitoring installation, operation, and maintenance requirements?  General continuous parameter monitoring requirements), but it should be extended to a period chosen by the individual facilities of up to 30 days. Also, plants should be given the option to operate green rotary dryers as dry rotary dryers. This option provides the flexibility to implement low cost options, but environmental managers need certainty that they can meet the necessary work practice requirements. Extending the averaging period would provide the operator with time to adjust the moisture of the raw material purchased or coming from upstream operations. There is precedence in other NESHAP to use extended averaging periods for compliance tests, such as the Leather Finishing NESHAP ( Subpart TTTT), particularly where seasonal factors are likely, as is the circumstance here. Several other factors support a long averaging period as well. Operators and producers have limited control over short term availability of the raw materials chosen for the plant, and the weather and seasons can have a dramatic effects on the moisture content of the raw material over a one day period. Many dryers that could potentially operate as dry rotary dryers are close to the work practice limit, and a longer compliance time would provide more certainty about the results. If a plant has a large amount of data, then the standard deviation will be small 2 203 and the plant will be secure with the resulting decisions. The hourly HAP emissions do not change if the moisture content of the material going into the dryer changes because the work practice rules for dry dryers limit the dryer inlet temperature to 600 ° F. Finally, the inlet moisture restriction is meant to be a method of distinguishing between types of processes, not as an operating restriction that assures compliance with a HAP emission limit. Since there is no shortterm emission limit for demonstrating compliance, the short term compliance monitoring parameter is inappropriate. Basically, a variability in raw materials does not translate to emission variability, and therefore does not require compliance monitoring appropriate to assure compliance with a short term emission limit.

The commenters noted that the preamble to the PCWP rule states that green rotary dryers and dry rotary dryers are essentially the same in terms of equipment design, but the rule does not allow plants to permit a unit that is nominally a green rotary dryer with controls as a dry rotary dryer without control requirements under an alternative operating scenario. This option should be specifically addressed in the final rule. Section 63.2263 ( Initial compliance demonstration for a dry rotary dryer) should be changed to read as follows:

If you operate a dry rotary dryer, you must demonstrate that your dryer processes furnish with an inlet moisture content of less than or equal to 30 percent ( by weight, dry basis) and operates with a dryer inlet temperature of less than or equal to 600 ° F. You must designate and clearly identify each unit to be operated as dry rotary dryer. You must choose an averaging period for the measurement of the moisture content and temperature parameters of no longer than 30 days. You must record the inlet furnish moisture content ( dry basis) and inlet dryer operating temperature according to § 63.2268( a), ( b), and ( f) for a minimum of 3 averaging periods 30 calendar days. You must submit the highest recorded 24 hour average inlet furnish moisture content and the highest recorded 24 hour average dryer inlet temperature with your Notification of Compliance Status. In addition, submit with the Notification of Compliance Status a signed statement by a responsible official that certifies with truth, accuracy, and completeness that the dry rotary dryer will dry furnish with a 30 day block average inlet moisture content less than or equal to 30 percent ( by weight, dry basis) and will operate with a 30 day block average inlet temperature of less than or equal to 600 ° F in the future.

The EPA should note that the capital expense of the control requirement is only one part of the expense equation, and the potential to eliminate the operating costs for control equipment would exist by allowing this option. Since the moisture in the raw materials does change based on the weather and the season, the option would give more regulatory flexibility to plants with regular swings in raw material moisture above and below 30 percent. Since the drier material would 2 204 probably be available in the summer, the option to switch dryer operation would allow facilities to shut off NO x generating oxidizers during ozone seasons to reduce collateral damage to the environment. On the other hand, the moisture content demanded by market could decrease, and this option would give plants the flexibility to permit units both ways based on anticipated changes.

Response: We believe that enforceability of the rule as it applies to rotary particle dryers would be severely hampered if we were to incorporate the commenters' suggestions into the rule.

We note that commenter IV D 27 specifically requested a 24 hour averaging time for dry rotary dryer moisture monitoring ( based on either laboratory analysis of grab samples or continuous inline moisture meters) in their white paper submitted to EPA in May 2001.27 We granted the commenter's request for a 24 hour averaging time prior to proposal of the PCWP rule. We maintain that a 24 hour averaging time is enforceable but allows flexibility by preventing shortterm slugs of high moisture wood from causing an exceedance of the 30 percent moisture requirement. We extended this 24 hour averaging period to the 600 ° F temperature work practice for dry rotary dryers.

We do not believe it is appropriate to allow dryers to operate green rotary dryers at some times and dry rotary dryers at other times, especially with a 30 day averaging period for the moisture and temperature work practices. A 30 day averaging period could allow facilities to operate their dry rotary dryer as a green rotary dryer for up to half of the days in the averaging period, making the rule virtually unenforceable with respect to rotary particle dryers and causing the rule not to achieve the emission reduction it is required to achieve from green rotary dryers.

The same would be true of any averaging period more than 24 hours. The final rule does not allow facilities to operate a dryer as green rotary dryer some of the time and as dry rotary dryers at other times. For the rule to be enforceable, there must be a clear distinction between dry rotary dryers and green rotary dryers ( given that dry and green rotary dryers are the same equipment operated differently). Facilities must carefully determine which dryers they will distinguish as dry rotary dryers considering seasonal variability in wood moisture, economics, and other site specific factors. Plants needing the flexibility to accommodate highly variable furnish moisture may find it more economical to designate all of their dryers as green rotary dryers. Although the final rule does not allow dual designation of a dryer as both a dry rotary dryer and a green rotary dryer,

facilities from may change the designation of a dryer as a dry rotary dryer or a green rotary dryer 2 205 in the future. Such a change in designation could be made through the appropriate permitting conduits.

<IP_ADDRESS> Comment: Commenter IV D 27 requested clarification on the compliance methods for a facility that decides to switch from drying softwood to drying hardwood. The current proposal of the PCWP rule establishes a MACT floor of " no control" for existing hardwood veneer dryers, provided they have been drying hardwood for a year. If the facility switches from softwood to hardwood at least a year before the promulgation date for the rule,

then it would logically follow the compliance guidelines for hardwood veneer dryers. However, if the facility makes the switch after the compliance date for the PCWP rule, the implication is that the facility would have to continue to operate the incineration controls for a year after they are no longer necessary. To clarify and remedy the situation, the commenter suggested that EPA allow the switch from softwood to hardwood with the title V permit restriction that the material dried in the dryer must be less than 30 percent softwood. A facility would then follow the work practice requirements associated with the amounts of hardwood and softwood dried for the year after the permit went into effect.

Response: The final rule does not contain language to allow for switching back and forth from softwood to hardwood veneer drying for two reasons. First, we do not believe there will be widespread switching from softwood to hardwood veneer drying because facilities must use the wood supply available to them, and because product characteristics can change if hardwoods are used instead of softwoods. Second, allowing dryers to operate as softwood veneer dryers some of the time and as hardwood veneer dryers at other times would make the rule unenforceable with respect to veneer dryers. The final rule requires facilities to clearly designate their veneer dryers as either softwood veneer dryers or hardwood veneer dryers prior to the compliance date.

However, the final rule does not prevent switching designation of a dryer from a softwood veneer dryer to a hardwood veneer dryer after the compliance date. Such a change in designation could be made through the appropriate permitting conduits. The language in the rule requires facilities to submit with their Notification of Compliance Status " the annual volume percentage of softwood species dried in the dryer based on your dryer production for the 12 months prior to the compliance date specified for your source in § 63.2233" ( emphasis added). This requirement applies before the compliance date. There is no explicit requirement for facilities switching designation of their veneer dryer to a hardwood veneer dryer after the compliance date to 2 206 document their wood species for 12 months before their dryer is considered a hardwood veneer dryer.

2.8 COMPLIANCE DURING PERIODS OF NON ROUTINE OPERATION 2.8.1 Control device downtime allowance <IP_ADDRESS> Comment: Commenters IV D 19, IV D 21, IV D 23, and IV D 27 supported inclusion of a routine control device maintenance exemption ( RCDME) in the PCWP rule.

Commenter IV D 19 stated that experience with RTO and RCO technology since 1995 proves routine maintenance is the only way to maximize the life of the devices, especially since ten years of research have not solved the media problems that this technology experiences.

Commenter IV D 27 stated that control devices used to reduce HAP emissions in the PCWP industry require significant periodic maintenance because the emissions contain PM,

alkaline salts, and acidic compounds that rapidly degrade components of the control equipment.

These conditions are not present in other industries that use similar equipment, and performing the necessary maintenance and repairs requires significant emission control downtime. To support this claim, the commenter provided an NCASI Technical Bulletin discussing actual data from RCO and RTO usage at various plants and the required maintenance and repairs. If the downtime allowance is not adequate, the industry will lose millions of dollars associated with the inability to continue production within compliance during APCD downtime.

Commenter IV D 23 also noted that the proposed control devices were designed for facilities with cleaner air streams, such as chemical plants, and the PCWP plants that use these control technologies will need time for more frequent cleaning and maintenance.

Response: We acknowledge the need for an RCDME for the PCWP industry and have included such an exemption in the final rule. As explained in the proposal preamble, the most widely used add on control systems at PCWP facilities are RTOs, RCOs, and biofilters. As with any control device in any industry, these control devices require routine maintenance. Routine maintenance includes activities such as cleaning or replacement of corroded parts, media replacement, bakeouts ( RTOs and RCOs), washouts ( RTOs and RCOs), and cleaning of ducts.

Some PCWP drying processes release particulates and salts that can plug and weaken RTO and RCO media beds. Frequent bakeouts and washouts are necessary to combat the particulate and 2 207 salt buildup. Partial or total media replacement is done when bakeouts and washouts are no longer effective. We have allowed an RCDME for the PCWP industry to ensure that facilities will perform the maintenance necessary to ensure that their APCDs are operated properly.

<IP_ADDRESS> Comment: Commenters IV D 19, IV D 21, IV D 23, and IV D 27 supported the RCDME but objected to the discretionary nature of the exemption. Commenters IV D 19 and IV D 21 objected to the treatment of downtime as an unusual occurrence rather than an inherent characteristic of the wood products MACT floor control technology. The frequency of the necessary maintenance indicates that the MACT floor includes downtime for this routine maintenance. Commenter IV D 19 stated that the proposed discretionary downtime allowance increases the burden on state Administrators because the permitting authorities are required to review and approve downtime requests.

Commenter IV D 27 argued that the downtime allowance should not be discretionary and that each affected facility should not be required to request a routine control device maintenance exemption from the Administrator. The commenter pointed out that in similar situations ( e. g., 63 FR 18529 ( April 15, 1998) for the Pulp and Paper MACT rule), EPA has included control device downtime allowances without requiring approval from the Administrator. The wording of section 63.2251( a) ( What are the requirements for the routine control device maintenance exemption?)

implies that downtime is an unusual occurrence rather than an inherent characteristic of the control technology. Some routine maintenance activities, such as duct cleaning, valve cleaning,

adjustment, repair, and replacement of external parts, can be scheduled to coincide with planned process shutdowns, but events such as offline bakeouts, washouts, valve cleaning, and media replacement must be performed when they are needed or the control devices will not operate properly. When emission control devices need repair, the repair cannot wait until an annual extended process outage, especially because equipment failures that result from these repairs not being completed right away are considered preventable. Also, repairs that require cooling and reheating of the oxidizers, such as media replacement, burner repairs, and replacement of internal corroded parts or insulation, will take longer than scheduled process outages. The EPA recognized that frequent maintenance is necessary, but it should have made the downtime exemption automatic rather than discretionary. Because of the nature of the proposed downtime exemption, the request for exemption will be a standard feature of any permit application for facilities using add on controls, creating additional work for the permitting agency evaluating the 2 208 requests. It is possible that the granting of permission for the exemptions will be uneven depending on the State and a company's ability to prepare and submit a request that fully explains the need for the exemption. Because there is a lack of back up control devices and routine maintenance must be performed frequently, EPA should include downtime for routine maintenance in the MACT floor. The commenter argued that if EPA retains its approach of making this exemption discretionary, then the 90 percent control requirement that EPA has identified as the MACT floor is simply incorrect, because no facility achieves a steady 90 percent removal rate over a several year period. The EPA instead would need to recalculate the MACT floor to reflect the actual downtime experienced by control devices in this industry, and prorate the percent removal requirement ( and concentration based requirements) to incorporate the 0 percent removal achieved during routine maintenance. The EPA also would need to modify its compliance methodologies to assess compliance on an annual basis   rather than the 3 hour average that currently is in the rule   to account for the sporadic nature of equipment downtime.

Obviously, a simpler approach is to include a control device downtime provision in the rule,

without making it discretionary.

The commenter claimed that in Sierra Club v. EPA, 167 F. 3d 658, 665 ( D. C. Cir. 1999),

the D. C. Circuit decided that the MACT floor should represent the performance of the best performing sources " under the most adverse circumstances which can reasonably be expected to recur." Downtime is an " adverse circumstance," so the MACT floor for wood products facilities should include a nondiscretionary provision for control equipment downtime. The commenter recommended that EPA state explicitly in the final rule that downtime is part of the MACT floor determination as supported by the record and that sources will not be required to provide justification to be allowed a routine control device maintenance exemption. Commenters IV D

21 and IV D 27 suggested the following language for § § 63.2251( a) and ( c):

63.2251( a). Periods of deviation from compliance options in § 63.2240( b) reported under § 63.2271 shall not be a violation of § 63.2240( b) provided that the time of deviation ( excluding periods of start up, shutdown, or malfunction) in an annual period does not exceed the values in § 63.2251( b).

63.2251( c). The routine control device maintenance exemption specified in § 63.2251( a) shall be incorporated in the affected source's title V permit. 2 209 Commenter IV D 07 suggested that instead of an RCDME, each facility should be required to write and submit an operation, maintenance, and monitoring ( OM& M) plan. Anything covered in the plan would not need to be included in the deviation report, but anything outside of the plan would need to be listed in the deviation report. The commenter argued that the proposed downtime allowance amounts to a lowering of the bar nationally in the performance expectation for the industry, whereas site by site plans with the close participation of the enforcement staff of the permitting authority would allow a better, site specific performance expectation to be developed based on the skills and abilities of each facility.

Response: We believe the need for an RCDME is site specific, and therefore, we maintain that the RCDME should be left to the discretion of the permitting/ enforcement regulatory agency.

As one commenter has pointed out, close participation of the permitting and enforcement regulatory agencies is needed to develop site specific performance expectations. Therefore, the final rule requires facilities to submit a request for an RCDME for approval by the applicable regulatory authority.