# Presentation: 265863

## Hg Monitoring  Options and Requirements

## Hg Monitoring Options 

- CEMS
- Sorbent Trap – Appendix K
- Hg LME

## Hg CEMS

- Initial Certification
- 7-day calibration error test
- Linearity Check (elemental Hg)
- 3-level System Integrity Check (oxidized Hg)monitors with Hg converter only
- Cycle Time Test
- RATA
- Bias Test

## Hg CEMS

- On-going Quality Assurance
- Daily calibration error test (elemental or oxidized Hg)
- Weekly 1-level System Integrity Check
- Required when daily calibrations use elemental Hg for monitors with Hg converters
- Weekly = 168 operating hours
- Quarterly Linearity Check (elemental Hg) **or** 3-level System Integrity Check (oxidized Hg)
- Required for each QA operating quarter
- Annual RATA (no semi-annual threshold)
- Bias Test

## Calibration Tests

- The initial 7-day calibration error test and subsequent Daily calibrations may be conducted using either elemental Hg or a NIST-traceable source of oxidized Hg.
- Specification:  ≤ 5.0 % of span value with alt spec of ≤ 1.0 μg/scm absolute difference
- The form of Hg used for daily calibrations will need to be reported in the Monitoring Plan so that EPA can track whether Weekly System Integrity Checks are required.
- The monitoring plan may be updated as needed

## Weekly System Integrity Check

- On point version of the 3-level System Integrity Check required for initial certification of Hg monitors with an Hg converter.
- Required only if daily calibrations are performed using elemental Hg and the monitor uses an Hg converter to monitor total mercury.
- Required once every 168 unit/stack operating hours.
- Specification:  ≤ 5.0 % of span value with alt spec of ≤ 0.6 μg/scm absolute difference

## Linearity Check

- Linearity Checks are performed with an elemental Hg standard
- Required for initial certification of all Hg monitors
- Required for quarterly QA unless a 3-level System Integrity Check is substituted
- Specification:  ≤ 5.0 % of _span_ value with alt spec of ≤ 0.6 μg/scm absolute difference
- Note that the specification is in terms of % of SPAN and not % of Reference Value, which is used for NOx and SO2 linearity tests.

## 3-level System Integrity Check

- System Integrity Checks are performed with an oxidized Hg standard generated from a NIST-traceable source
- Required for initial certification of Hg monitors with Hg converters
- 3-level System Integrity Check may be used instead of a linearity for Quarterly QA.
- Specification:  ≤ 5.0 % of _span_ value with alt spec of ≤ 0.6 μg/scm absolute difference

## Relative Accuracy Test Audit (RATA)

- Required for initial certification of all Hg monitors
- Required annually (once every 4 QA operating quarters) thereafter
- For Reference Methods that require paired sampling, the RM value for each run should be the average of the values observed from each of the paired samples for the run.
- Specification:  ≤ 20.0 % RA with alt spec of ≤ 1.0 μg/scm if average RM value is ≤ 5.0 μg/scm
- No semi-annual threshold

## Bias Test

- Use standard bias test logic
- Low Emitter BAF cap is 1.250 for when the average RM concentration is < 5.0 μg/scm

## Appendix K – Sorbent Trap System Basics

- Appendix K – Sorbent Trap systems consist of a pair of sampling trains that collect an integrated sample over a specified collection period
- Sorbent traps collect the Hg and have 3 sections.
- Section 1; Main Sample Collection Section
- Section 2; Breakthrough Sample Collection Section
- Section 2; Spiked Section for QA
- Each sampling train uses a dry gas meter to record the volume of stack gas sampled over the course of each sample collection period.

## Appendix K – Sorbent Trap Systems

- Initial Certification
- RATA
- Bias Test
- Initial 3-level Dry Gas Meter Calibrations
- Initial DGM Temperature Sensor and Calibration Check
- Initial DGM Barometer Calibration Check

## Appendix K – Sorbent Trap Systems

- On-going Quality Assurance for Appendix K systems and components:
- Annual RATA (no semi-annual threshold)
- Annual Bias Test
- Quarterly Dry Gas Meter Calibrations
- Quarterly DGM Temperature Sensor and Calibration Check
- Quarterly DGM Barometer Calibration Check
- Quality Assurance for each Appendix K sample collection period:
- Pre- and Post- sample collection Leak Check
- Monitor Ratio of stack gas flow to sample collection flow
- Sorbent Trap Breakthrough check (section 2 of trap)
- Percent Trap Agreement
- Spike Recovery (section 3 of trap)

## Appendix K Dry Gas Meters

- Dry Gas Meter Calibrations
- Initially conducted at 3-levels to establish calibration factor (Y)
- Conduct a single-level calibration check at least once quarterly to verify Y
- Single-level calibration factor (Y) must be within 5% of the average calibration factor (Y) established in the most recent 3-level check
- If single-level check is failed, conduct a full 3-level calibration of the DGM to establish a new calibration factor (Y)

## Appendix K Dry Gas Meters

- Each of the following QA checks are required initially and at least once quarterly for each DGM component used in an Appendix K sorbent trap system
- Quarterly DGM Temperature Sensor and Calibration Check
- Absolute Temperature within ± 1.5% of reference
- Test at either one or two points per Method 2 section 10.3
- Quarterly DGM Barometer Calibration Check
- Absolute Pressure within ± 10 mmHg of reference barometer
- Number of points unspecified
- Each will be reported as a miscellaneous test similar to calibrations for fuel flowmeters

## Appendix K – Sample QA

- The following QA is applicable to each sample collection period for evaluating the acceptability of each sorbent trap sample collected
- If any of the following QA checks are failed, the sample for that trap is invalidated.
- If data for the other trap is validated, a single trap adjustment factor may be used to adjust the data from that trap for uncertainty in lieu of applying substitute data for the collection period.
- If the QA checks are failed for both samples then substitute data must be used for the entire collection period.

## Appendix K – Sample QA

- Each sampling train must pass a pre- and post-sample collection leak check.  The post collection check will be reported to validate each sample
- The Ratio of the hourly Stack Gas Flow Rate to the hourly Sample Flow Rate must be maintained to within ± 25% of the initial ratio from the first hour of each collection period.  Samples are invalidated if more than either 5 hours or 5% of the hourly ratios do not meet this criteria.
- Sorbent Trap Breakthrough check (section 2 of trap); The mass of Hg captured on section 2 of the trap must be ≤ 5% of the total Hg collected on section 1.
- Spike Recovery (section 3 of trap);  The analysis of Hg on section 3 must result in 75% - 125% of the spike referenced spike level for the trap.

## Appendix K – Calculating the Collection Period Concentration

- The Hg concentration for each trap sample is calculated by adding the Hg mass from section 1 and section 2 of the trap, normalizing by the amount of Hg spike recovery and then dividing by the total volume of dry sample gas metered during the collection period.

- Percent Trap Agreement; For each pair of traps, the Relative Deviation (RD) must be ≤ 10%.  (Alternate Specification: ≤ 20% if average Hg concentration is ≤1.0μg/scm)
- If the Percent Trap Agreement is within spec., the average Hg concentration is reported for each hour of the collection period
- If the Percent Trap Agreement is not within spec., the higher of the two Hg concentrations is reported for each hour of the collection period

## Substitute Data for CEMS and Appendix K

- In August 2006, EPA proposed to consolidate the Substitute Data requirements for CEMS and Appendix K.
- This decision allows for the use of an Appendix K system as a back-up to CEMS in a way that does not complicate the Substitute Data requirements for when neither system is available.
- For hours where there is valid data from the CEMS, that data will be used to populate the lookback.  This is also the value that must be used to calculate Hg mass for the hour.
- The Appendix K data will populate the lookback period for any hour where CEMS data are unavailable.
- For hours where neither system is available, substitute data is determined from the consolidated lookback of actual concentration data used for the previous hourly emissions calculations.

## Substitute Data for CEMS and Appendix K

- The substitute data for Hg has four tiers:
- Tier 1; If the PMA is 90 or more:
- If the duration of the outage is less than 24 hrs substitute the average of the hour before and after
- If the duration is greater than 24 hrs, substitute the higher of the hour before/hour after average or the 90th percentile value from a 720 hour lookback
- Tier 2; If the PMA is less than 90 and equal to 80 or more:
- If the duration of the outage is less than 8 hrs substitute the average of the hour before and after
- If the duration is greater than 8 hrs, substitute the higher of the hour before/hour after average or the 95th percentile value from a 720 hour lookback

## Substitute Data for CEMS and Appendix K

- Tier 3; If the PMA is less than 80 and equal to 70 or more, substitute the maximum value from the 720 hour lookback
- Tier 4; If the PMA is less than 70 substitute the maximum potential concentration.
- For units with add-on controls, if the controls are documented to be operated properly per §75.34, the unit may substitute the **greater of** the following instead of the maximum potential concentration:
- The maximum expected concentration as listed in the monitoring plan, or
- 1.25 times the maximum controlled value measured from the previous 720 hour lookback

## Hg-LME Monitoring Methodology  

- Rather than install Hg analyzers or sorbent traps, affected units with lower potential levels of Hg may qualify for an excepted monitoring methodology
- This method is referred to as the Hg-LME methodology
- The Hg-LME excepted methodology is found in §75.81

## Hg LME

- Low Hg emitting units (≤ 29 lbs/yr potential emissions) may qualify for the Hg-LME methodology
- This methodology requires an initial and on-going emission testing
- Initial test stack test results are used in Eq. 1, with the maximum potential stack flow rate to demonstrate that the unit’s potential to emit is not greater than the 29 lb threshold.
- The Hg concentration from the test is then used with actual stack flow data to determine hourly emissions
- Ongoing retesting is required annually if the calculated potential Hg emissions are ≤ 9 lb/yr, and semiannually if the potential emissions are between 9 and 29 lb/yr (NO GRACE PERIODS!)
- Actual reported Hg mass is used for ongoing qualification.

## Hg-LME Testing

- A minimum of 3 runs at normal load are required
- Minimum run time is 1 hour per run is required for the instrumental method
- Run time for other methods to be determined by the amount of sampling needed to acquire a measurable amount of Hg
- Use the highest Hg concentration from the 3 runs or 0.50 μg/scm (whichever is greater) when calculating the potential to emit
- The same default is used for hourly reporting until the completion of the next test.

## Hg LME

- Equation 1 in §75.81 provides the conservative estimate of the annual Hg mass emissions from the unit (i.e., potential to emit)
- Equation 1 is also used to determine whether ongoing test should be performed semi-annually or annually
- Equation 1 uses the  Hg concentration determined based on reference method testing consisting of three runs

## Hg LME

- Equation 1: E = 8760 K CHg Qmax
- E = Estimated annual Hg mass emissions from       	      	     	    the affected unit, (ounces/year)
- K = Units conversion constant, 9.978 x 10-10 		        	       	       oz-scm/μg-scf
- 8760 = Number of hours in a year
- CHg = The highest Hg concentration (μg/scm) from any 	        	       of the test runs or 0.50 μg/scm, whichever is 	    	        	       greater (paired sampling trains are required for each test run)
- Qmax = Maximum potential flow rate, determined according to 	      	         section 2.1.4.1 of appendix A to this part, (scfh)

## Hg LME

- On August 22, 2006, EPA proposed revisions to 40 CFR 75 and 72.2
- Proposed revisions include the following requirements
- Coal combusted during testing must be from the same source of supply as the coal combusted at the start of the Hg mass emissions reduction program
- Identical units in accordance with §75.19(c)(1)(iv)(B) sharing a common stack may test a subset of units in lieu of testing each unit individually
- The calculated value of E shall be divided by the number of units sharing the stack.  If the result, when rounded to the nearest ounce, does not exceed 464 ounces, the units qualify to use the low mass emission methodology

## Status of Mercury Monitoring-Where Do We Go From Here ?

- EPA Assessment of Hg Monitoring Systems
- Both Hg CEMS and sorbent traps have been demonstrated to be capable of accurately measuring Hg emissions
- As a result, EPA believes that consistent, reliable Hg measurements will be achievable by the rule implementation date (2009), using either monitoring approach.  However, to ensure this......A number of outstanding issues must be resolved in the coming months.  These include:
- Further refinement of the monitoring system components to enhance performance.
- Development of NIST-traceability for the elemental Hg and HgCl2 calibration standards.
- EPA’s Office of Research and Development (ORD) is working cooperatively with NIST to develop traceability protocols

## Status of Mercury Monitoring-Where Do We Go From Here ?

- Publication of alternative reference test methods for performing RATAs of Hg CEMS and sorbent trap monitoring systems
- These alternative methods are needed because the Ontario Hydro method is difficult to perform, expensive, and it takes days or weeks to find out the test results
- The Office of Air Quality Planning and Standards (OAQPS) plans to propose both an instrumental reference method and a sorbent–based method this spring