218.1 - 1

(Adopted May 14, 1999)

RULE 218.1 CONTINUOUS EMISSION MONITORING PERFORMANCE

SPECIFICATIONS

(a) Definitions

(1) ANALYZER - the part of the continuous emission monitoring system

(CEMS) that analyzes the appropriate gaseous constituents of the

conditioned gaseous sample or measures stack gas volumetric flow and fuel 

flow rates, as applicable.

(A) Contaminant Analyzer - the part of the CEMS that detects the air

contaminant concentrations and represents those concentrations in

a signal output.

(B) Diluent Analyzer - the part of the CEMS that detects oxygen,

carbon dioxide or other diluent gas concentrations as represents

those concentrations in a signal output.

(C) Fuel Flowmeter - the part of the CEMS that detects the parameters 

of all essential measurement sub-systems (e.g., temperature,

pressure, differential pressure, frequency, gas density, gas

composition, heating value) and generates signal outputs which are 

a function of the fuel flow rate and all essential measurement subsystem parameters. 

(D) Stack Flowmeter -. the part of the CEMS that detects the

parameters from all essential measurement sub-systems (e.g.,

temperature, static and atmospheric pressure, gas density, gas

composition, molecular weight, gas moisture content) and

generates signal outputs which are a function of the stack gas

volumetric flow rate and all essential measurement sub-system 

parameters.

(2) CALIBRATION - a procedure performed to ensure that the CEMS

accurately measures and records the concentration of the specific air

contaminant or diluent gas, flow rate and other parameters necessary to

generate the required data, as evidenced by calibration checks and achieved 

by periodic manual or automatic adjustment.

(3) CALIBRATION CHECK - a procedure performed to determine CEMS

response to a given gaseous compound concentration by means of injecting 
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 2

a certified calibration gas mixture into the CEMS as close to the probe tip 

as practical.

(4) CALIBRATION DRIFT (CD) - change in the CEMS output or response

over a specific period of normal continuous operation when the air

contaminant or diluent gas concentration at the time of the measurements is 

the same known upscale value. CD is expressed as the sum of the absolute 

value of the mean difference and the absolute value of the confidence

coefficient of a series of tests, to the full span range, expressed as a

percentage as follows:

CD

d CC

FSR

=

+

×100

Where:

FSR = Full span range

CC = Absolute value of the 95% confidence coefficient 

d = Absolute value of the mean difference. The mean

difference, d , is calculated as:

d

n

i

i

n

= d

=

∑

1

1

Where:

i

i

n

d

=

∑

1

= Algebraic sum of the individual differences di

n = Number of data points

di =

The difference between the paired response values 

of the monitoring system

(5) CALIBRATION ERROR (CE)

(A) CALIBRATION ERROR , as applicable to Section (c), “Standards 

for Existing CEMS” - the ratio of the difference between the air

contaminant or diluent gas concentration indicated by the CEMS

and the known concentration of the calibration gas, to the known

concentration of the calibration gas. CE is calculated as the ratio of 

the sum of the absolute values of the mean difference and the 95
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 3

percent confidence coefficient of a series of tests, to the gas

concentration, expressed as a percentage, as follows:

CE

d CC

C

=

+

×100

Where:

C = Calibration gas concentration

CC = Absolute value of the 95% confidence coefficient 

d = Absolute value of the mean difference. The mean

difference is calculated as:

d

n

i

i

n

= d

=

∑

1

1

Where:

i

i

n

d

=

∑

1

= Algebraic sum of the individual differences di

n = Number of data pairs 

di = The difference between the paired monitoring

system response value and the known gas

concentration or the equivalent rating of the

reference method value, both in units of the

applicable standard

(B) CALIBRATION ERROR, as applicable to Section (b), “Standards

for New or Modified CEMS” - the ratio of the absolute value of the 

difference between the air contaminant or diluent gas concentration 

indicated by the CEMS and the known concentration of the

calibration gas, to the full span range, expressed as a percentage, 

as follows.

CE

C A

FSR

=

−

× 100

Where:

C = Calibration gas concentration

A = Actual response or the concentration indicated by the

monitoring system 
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 4

FSR = Full span range of the instrument

(6) CEMS AVAILABILITY PERCENTAGE - a percentage calculated as the 

ratio of the total unit operating hours for which the CEMS provided

quality-assured data, to the source total unit operating hours during a

specified period, excluding periods of calibration, maintenance, repair, or

audit, up to a maximum of 40 hours per month.

(7) CERTIFIED CEMS - a CEMS installed, tested, operated, maintained, and 

calibrated according to the applicable requirements of Rules 218 and 218.1; 

that has met the applicable performance specifications of Rule 218.1 and,

has received written approval and conditions thereto applying, from the

Executive Officer.

(8) CERTIFIED GAS MIXTURE - a gas mixture manufactured, analyzed and 

certified in accordance with the “EPA Traceability Protocol for Assay and 

Certification of Gaseous Calibration Standards” - EPA-600/R97/121, 

September 1997 Revision (EPA Traceability Protocol) or any subsequent

version published by EPA. This definition incorporates by reference EPA

Protocol.

(9) CONFIDENCE COEFFICIENT (CC) - the 2.5 percent error confidence

coefficient for the 95 percent confidence interval of a series of tests. The

CC is calculated as follows:

CC t0.975

Sd

n

=

Where:

Sd = Standard deviation

n = Number of data in a series of tests

t0.975 = t-value (see Table of t-Values below)

Table of t-Values*

n t0.975 n t0.975 n t0.975

2 12.706 7 2.447 12 2.201

3 4.303 8 2.365 13 2.179

4 3.182 9 2.306 14 2.160

5 2.776 10 2.262 15 2.145

6 2.571 11 2.228 16 2.131

* The t-values in this table are already corrected for n-1 degrees of 

freedom. Use n equal to the number of data points. 
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 5

(10) CONTINUOUS EMISSION MONITORING SYSTEM (CEMS) - the

total combined equipment and systems required to continuously determine

air contaminants and diluent gas concentrations and/or mass emission rate

of a source effluent (as applicable). The CEMS consists of three major

subsystems: sampling interface, analyzer and data acquisition system.

(11) CONTINUOUS MONITORING - a monitoring in which a minimum of

one measurement (e.g., concentration, mass emission, flow rate) is taken

and recorded each minute.

(12) DATA ACQUISITION SYSTEM (DAS) - the part of the CEMS that

processes data generated by the analyzer and records the results, thus

creating a permanent record of the output signal in terms of concentration, 

flow rate, and any other applicable parameter necessary to generate the

required data in units of applicable standard. The DAS consists of all 

equipment such as a computer required to convert the original recorded

values to any values required for reporting.

(13) DILUENT GAS - a gas present in a calibration gas mixture or in source

emissions that is present in quantities significantly larger than the air

contaminant.

(14 ) FULL SPAN RANGE - the full range of values or data display output that 

a monitor component is calibrated to measure.

(15) LINEARITY ERROR (LE) - the percentage error in linearity expressed in 

terms of the ratio of the absolute value of the difference between the

reference value and the mean CEMS response value, to the reference

value. LE is calculated as follows:

×100

−

=

R

R C

LE

Where:

C = Mean of the CEMS response values

R = Certified gas concentration as reference value

(16) MODIFICATION REQUIRING RECERTIFICATION - any change to the 

basic equipment, control equipment, contaminant concentration, interfering 

substances, or CEMS that is deemed by the Executive Officer to have a
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 6

potential for adversely affecting the ability of the CEMS to provide

accurate, precise and timely data representative of the stack emissions for

which the CEMS (or SCEMS) is required. 

(17) NINETY-FIVE PERCENT CONFIDENCE INTERVAL - the statistical

estimation denoting a range of values which is expected to include a true

value with a 95 percent probability.

(18) OPERATIONAL PERIOD - a minimum period of 168 continuous hours

during which the CEMS shall operate, according to the manufacturer's

written performance and equipment specifications, without unscheduled

maintenance, repair, or adjustment.

(19) QUALITY ASSURANCE/QUALITY CONTROL (QA/QC) PLAN - a

written document in which the specific procedures for the operation,

calibration and maintenance of a certified CEMS are described in detail,

including additional quality assurance assessments and the corrective action 

system. The purpose of this plan is to ensure that the CEMS generates,

collects and reports valid data that is precise, accurate, complete, and of a 

quality that meets the requirements, performance specifications, and

standards of Rules 218 and 218.1.

(20) REFERENCE METHOD (RM) - the official test method employed by the 

District to determine compliance with the rules or permit conditions. A list 

of reference methods is identified in Table 1.

(21) RELATIVE ACCURACY (RA) - the absolute mean difference between

the gas concentration or emission rate determined by the CEMS and the

value determined by the RM plus 2.5 percent error of confidence

coefficient of a series of tests, divided by the mean of the RM tests.

(22) RELATIVE ACCURACY AUDIT (RAA) - the RA test expressed in

terms of the ratio of the relative difference between the mean reference 

method value and the mean CEMS response value, to the mean value

determined by the reference method or applicable standard for

concentration, flow or mass emission rate. Unless otherwise specified, 

RAA shall have the same specifications and requirements as the Relative

Accuracy Test Audit (RATA), except that the RAA shall require a

minimum of three data sets. When a rule requires a correction of the air

contaminant concentration to a specific O2 or CO2 concentration, the RA

requirement shall apply to the corrected concentration value. The RA of a 

RAA data set is calculated and expressed as a percentage as follows:
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 7

RA r RM

RM

=

−

×100

Where:

RM = Mean of the values determined by the reference

method or applicable standard

r = Mean of the CEMS response values

(23) RELATIVE ACCURACY TEST AUDIT (RATA) - the RA test expressed 

in terms of the ratio of the sum of the absolute mean difference between the 

CEMS-generated data and the value determined by the applicable reference 

method or applicable standard and the absolute confidence coefficient, to 

the mean of the reference method or applicable standard value for

concentration, flow or mass emission rate. When a rule requires a

correction of the air contaminant concentration to a specific O2 or CO2

concentration, the relative accuracy requirement shall apply to the

corrected concentration value. The RA of a RATA data set is calculated

and expressed as a percentage as follows:

RA

d CC

RM

=

+

×100

Where:

d = Absolute value of the mean difference 

|CC| = Absolute value of the 95% confidence coefficient 

RM = Average RM value or applicable standard

The arithmetic mean of the difference, d, of a set of data is calculated as 

follows:

d

n

i

i

n

= d

=

∑

1

1

Where:

i

i

n

d

=

∑

1

= Algebraic sum of the individual differences di

di = The difference between the reference method value

and CEMS value, both in units of the applicable

standard

n = Number of data points
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 8

(24) RESPONSE TIME - the time interval from a step change in the air

contaminant or gas diluent concentration to the time when 95 percent of

the corresponding final value is reached as displayed on the CEMS data

recorder or acquisition system. The response time is determined by

introducing a certified gas mixture into the CEMS upstream of the

sampling interface and as close to the probe inlet as practicable.

(25) ROUTINE MAINTENANCE - preventive evaluation and repair (if

necessary) of CEMS performed at specified intervals to preclude system

failure. Routine maintenance may be performed as recommended by the

manufacturer or a documented standard operating procedure determined

through operating experience and approved by the Executive Officer. 

Repairs to a malfunctioning system are excluded from this definition.

(26) SAMPLING INTERFACE - that part of the CEMS that performs sample

acquisition using one or more of the following operations: extraction,

physical/chemical separation, transportation or conditioning of a

representative sample from a designated source.

(27) SEMI-CONTINUOUS EMISSION MONITORING SYSTEM (SCEMS) -

the total combined equipment and systems required to semi-continuously 

determine air contaminants and diluent gas concentrations and/or mass

emission rate of a source effluent (as applicable). The SCEMS consists of

three major subsystems: sampling interface, analyzer and data acquisition

system. This class of monitoring includes but is not limited to gas

chromatography, integrated sensitized tape analyzer, other sample

integration based technologies, and time-shared CEMS.

(28) SYSTEM BIAS - the difference between the gas concentrations exhibited 

by the CEMS when a calibration gas is introduced at a location upstream of 

the sampling interface, and as close to the sampling probe inlet as

practicable, and when the same calibration gas is introduced directly to the 

analyzer.

(29) SYSTEM FAILURE - inability of the CEMS to meet the requirements of

Rule 218.1.

(30) TIME-SHARING - a monitoring technique where an analyzer and possibly 

the associated sample conditioning system is used on more than one

source.
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 9

(31) ZERO CHECK- a procedure performed to determine the response of the

CEMS to a given zero gas standard by means of injecting the zero gas into 

the CEMS as close to the probe tip as practical.

(32) ZERO DRIFT (ZD) is the change in the monitoring system

output/response over a stated period of time of normal continuous

operation when the air contaminant or diluent gas concentration at the time 

of the measurements is zero. The values for ZD shall be expressed as the

ratio of the sum of the absolute value of the mean of the difference between 

paired instrument response values and the absolute value of the CC, to the 

full span range, calculated as a percentage as follows:

ZD

d CC

S

=

+

×100

Where:

S = Full span range

|CC| = Absolute value of the confidence coefficient 

d = Absolute value of the mean difference. The mean

difference is calculated as:

d

n

i

i

n

= d

=

∑

1

1

Where:

i

i

n

d

=

∑

1

= Algebraic sum of the individual differences di

n = Number of data pairs

di = The difference between a pair of instrument response

values

(33) ZERO GAS - a gas containing less than a specified amount of the

contaminant or diluent gas which, when periodically injected into the

CEMS, is used to check CEMS’ response to the absence of the air

contaminant or diluent gas.

(b) Standards for New or Modified CEMS

In order to be a Certified CEMS, a CEMS subject to the provisions of Rule 218

Sections (c)(1), (d)(1)(C), (d)(1)(D)(i), (d)(2)(C) and (d)(2)(D), as applicable,

shall meet the operational requirements, performance specifications, and standards 

as follows:
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 10

(1) Pre-Certification Testing Requirements for New or Modified CEMS

Before any certification or relative accuracy test is performed, the CEMS

shall meet the following standards:

(A) CEMS Location

The CEMS shall be installed at a location that enables 

measurements of air contaminant and diluent gas concentration, and 

flow rates can be made which are representative of the stack 

emissions of the source.

(B) Sampling Location

The monitoring system sampling probe tip and the reference 

method sampling port locations shall be determined according to 

District Method 1.1. The monitoring sampling probe shall be 

located where a sample may be obtained which is representative of 

the source emissions. Each probe shall not interfere with the other 

when in use. Other locations may be chosen subject to a written 

approval of the Executive Officer. If an alternate location is chosen 

which does not conform with District Method 1.1, the absence of 

flow disturbance shall be demonstrated using the District method in 

the source Test Manual, Chapter X, Section 1.4 - "Alternative Site 

Selection Method", or 40 CFR, Part 60, Appendix A, Method 1, 

Section 2.5 - "Alternative Measurement Site Selection Procedure", 

and, the absence of stratification shall be demonstrated using the 

District method in the source Test Manual, Chapter X, Section 13 -

"Determination of Gaseous Constituent Stratification". 

Alternatives to sampling site selection in the presence of 

stratification are presented in Rule 218.1(b)(3)(C)(ii).

(C) Full Span Range (FSR)

(i) The FSR for mass emission rate, air contaminant, diluent

and flow analyzers shall be set such that all data points are

within 10 to 95 percent of the range.

(ii) For air contaminant monitors, the FSR shall be set between 

150 and 200 percent of the concentration limit as specified

in the applicable rule or permit condition. The FSR may be 

set at a value other than that specified, but no lower than

120 percent, provided that the CEMS owner or operator

demonstrates to the satisfaction of the Executive Officer
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 11

that the FSR will not be exceeded. Such demonstrations

may include, but not limited to, historical emissions data,

historical process information, and historical operational

information. A written approval from the Executive Officer 

shall be obtained before the FSR may be modified outside of 

the 150 to 200 percent of the concentration limit.

(iii) For air contaminant monitors, a multiple-span-range may be 

required to satisfy the provisions of Sections C(i) and (ii)

above in situations where the normal concentration of the

air contaminant emitted is significantly less than the

allowable concentration limit. The CEMS shall have the

capability to automatically change from one range to the

other as appropriate to the monitor’s measured

concentration.

(iv) For diluent monitors, the FSR shall be set such that the full

range of oxygen and carbon dioxide concentrations can be

measured. The FSR shall be set at 25.0 percent O2

(maximum) and 1.0 percent CO2 (minimum)

concentrations, or at a value approved by the Executive

Officer.

(v) Should any data points fall below 10 percent of the FSR,

those data points shall be reported according the following, 

as applicable:

(I) For CEMS with certified multiple span ranges, the

owner shall report data that falls below 10.0 percent 

of the higher FSR and above 95 percent of the lower 

FSR, at the 10.0 percent value of the higher FSR, 

(II) In the event that any of the data points gathered by

the CEMS fall below 10.0 percent of the FSR, the

owner or operator may elect to report the

contaminant concentrations at the 10.0 percent FSR 

value, or, 

(III) In the event that any data points gathered fall below 

10.0 percent of the lowest vendor guaranteed FSR

for that CEMS (defined as the lowest FSR that the

vendor guarantees to be capable of meeting all
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 12

current certification requirements of Rule 218 and

Rule 218.1, as applicable) the owner or operator

may elect to use the following to measure and report 

contaminant concentrations:

(a) Report data at 10.0 percent FSR value, or, 

(b) Report data at actual measured value,

provided that the CEMS meets the

Supplemental and Alternative Performance 

Requirements in Attachment A.

(vi) Should any data points fall above 95 percent of FSR, the

value shall be invalid for quantification and the CEMS shall

be considered unavailable for the purposes of determining

CEMS availability percentage. All excursions above 95

percent of FSR and the duration of these excursions shall be 

reported in the CEMS summary report as prescribed under

Rule 218(f). 

(D) Strip Chart Recorder

(i) For CEMS where the strip chart recorder is used as the only 

means of data recording, the strip chart shall have a

minimum width of at least 10 inches, a readability of 0.5%

of the span, and a minimum of 100 chart divisions. 

(ii) For CEMS where the strip chart recorder is used as a backup system or for recording data from only a single

parameter, a strip chart of lesser size than specified in

Section (D)(i) above, may be proposed in the application.

(iii) For CEMS equipped with multiple-span ranges, the chart

recorder shall have the capability to automatically change

span, as appropriate.

(E) Data Acquisition System (DAS)

(i) The DAS shall maintain all recorded data in accordance

with Rule 218, Section (e).

(ii) For CEMS, DAS shall acquire data from monitored

parameters at least once every minute.

(iii) For SCEMS, DAS shall acquire data from monitored

parameters at least once every 15 minutes.
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 13

(iv) DAS acquisition rate shall be set at a constant rate such that 

the data points are equally spaced.

(v) All valid data points shall be used to determine compliance

with applicable limit(s), and, for certification testing and

RATA(s).

(vi) DAS sample acquisition rate during certification and

RATA(s) shall be the same as the DAS sample acquisition

rate during normal CEMS, or SCEMS, operation.

(F) Operational Period

The operational period before any certification tests shall be a 

minimum of 168 continuous hours.

(2) Certification Requirements and Performance Specifications for New or

Modified CEMS

Rule 218(c)(1) provides that a series of certification tests shall be 

performed to demonstrate the acceptability of CEMS performance. The 

requirements and specifications in conducting initial certification tests 

follow:

(A) Calibration Error (CE) Testing

The 24-Hour CE test shall be performed at the low and high ranges, 

namely 0 to 20 and 80 to 100 percent of FSR, respectively. CE 

specifications shall be less than or equal to: 

(i) 2.5 percent of the FSR for all analyzers, and

(ii) 3.0 percent of the FRS of the analyzer, for flow monitors,

when an electronic calibration check is applicable. 

The 24-hour CE test shall be performed once each day as close to 

24-hour intervals as practicable, with a total of eight (8) 

consecutive tests performed. The CE specifications shall not be 

exceeded on any of the tests during the entire testing period. 

(B) Analyzer Enclosure

(i) The analyzer shall be contained in an environmentally

controlled enclosure. An alarm and recording device shall be 

incorporated into the system to alert the operator to make

corrective action should the analyzer exceed the

manufacturer’s recommended specifications for temperature 

drift.
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 14

(ii) Alternatively, the owner or operator of the CEMS may

choose to perform the 2-hour CE tests in-lieu of meeting

the analyzer enclosure requirement in Section(b)(2)(B)(i).

The 2-hour CE test shall be performed once every two

hours as close to 2-hour intervals as practicable, with total

of thirteen consecutive tests performed. The 2-hr CE test

shall be performed when ambient temperature is expected to 

vary diurnally at least 30oF. The test shall be performed at 

the low and high ranges of FSR, namely 0 to 20 and 80 to 

100 percent, respectively. The specifications in Sections

(b)(2)(A)(i) and (ii) shall apply to 2-hour CE.

(iii) The owner or operator of the CEMS may qualify for an

exemption from Section(b)(2)(B)(i) to provide

environmental controls for the analyzer enclosure by

demonstrating, to the satisfaction of the Executive Officer,

that the CEMS is located:

(I) In a geographic area where seasonal high and low

temperatures do not exceed the operational

temperature specifications for the analyzer,

(II) In a geographic area where monthly maximum

temperature variation is less than 30oF for all months 

of the year, and

(III) The CEMS is located in a site that is protected from 

radiation and convection heating sources.

(C) Relative Accuracy

RATA shall be performed for raw contaminant concentration, and if 

applicable, for corrected concentration, emission rate, O2

concentration, CO2 concentration analyzers, and stack and fuel 

flow monitors. There shall be a minimum of nine sets of test data 

generated. If the number of tests exceeds nine sets, data may be 

discarded if it is identified as an outliers by the technical guidance 

set forth by the Executive Officer, or for valid reasons (e.g., 

process upsets, CEMS malfunction, etc.) which must be 

substantiated with appropriate documentation and subject to 

approval by the Executive Officer. All data collected shall be 

submitted to the Executive Officer.
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 15

The CEMS shall meet the following RA performance specifications:

(i) Less than or equal to 20.0 percent of the mean value of the 

reference method for pollutant concentrations, or the deminimus concentration as follows, whichever is greater:

Pollutant De minimus Concentration

NOx 1.0 ppm

SO2 2.0 ppm

CO 2.0 ppm

Reduced Sulfur Compounds 4.0 ppm

(ii) Less than or equal to 10.0 percent of the mean value of the 

reference method for diluent concentrations, or the de

minimus value of 1.0 percent O2, whichever is greater.

(iii) Less than or equal to 15.0 percent of the mean value of the

reference method for flow monitors, or the de minimus

value equivalent to a calculated volumetric flow rate based

on 2 feet per second stack gas velocity for cases where the

mean stack gas velocity obtained by the reference method

test is less than 15 feet per second.

(iv) Less than or equal to 20.0 percent of the mean value of the 

reference method for mass emission rates, or the de minimus 

value equivalent to a calculated mass emission rate based on 

2 feet per second stack gas velocity for cases where the

mean stack gas velocity obtained by the reference method

test is less than 15 feet per second.

The relative accuracy requirement may be met if the average 

of the differences between the CEMS measured data and

the reference method test data plus the confidence 

coefficient is less than or equal to the relative accuracy de

minimus value.

(3) Relative Accuracy Test Requirements for New or Modified CEMS 

Within fourteen days of, or during all relative accuracy tests, the CEMS 

shall meet the following requirements, except those that may be waived as 

allowed in Rule 218.1, Section (b)(4)(C):

(A) Response Time 

The response time for CO CEMS shall not exceed 1.5 minutes 

except where there is a technical limitation, in which case the 
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 16

response time shall be 5 minutes. The response time for all other 

CEMS and flow monitors, as applicable, shall not exceed 5 minutes.

(B) Calibration Error

The CE testing requirements are specified in Section (b)(2)(A).

(C) Concentration Stratification

(i) The owner or operator shall demonstrate the absence of

stratification through testing performed according to the

method in Chapter X, Section 13 - “Non-Standard Methods 

and Techniques”, of the District Source Testing Manual. 

The number of tests shall be determined as follows:

(I) Test(s) shall be conducted at one load level if the

owner or operator demonstrates to the satisfaction

of the Executive Officer that the equipment operates 

within a 20 percent load range for at least 80 percent 

of the time;

(II) Test(s) shall be conducted at two different load

levels if the owner or operator demonstrates to the

satisfaction of the Executive Officer that the

equipment operates within a 50 percent load range

for at least 80 percent of the time; or,

(III) Test(s) shall be conducted at three different load

levels if the equipment operates outside of the

criteria in Sections (b)(1)(C)(i)(I) and (II).

The absence of stratification is considered verified if

the difference between the highest measured

concentration (time normalized) and the lowest

measured concentration (time normalized) divided

by the average measured concentration (time

normalized), when expressed as a percentage, is less 

than or equal to 10 percent. Upon verification of the 

absence of stratification, the owner or operator may

position the CEMS sampling probe at any point

within the stack with the exception of those points

that are adjacent to the stack wall. The CEMS

sampling probe should be located in the stack at

least one-third of the stack diameter. The RM for
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 17

RATA may be conducted at a single point within the 

stack that is not adjacent to the stack wall and does

not interfere with the sampling and the operation of

the facility CEMS.

(ii) Should testing demonstrate the presence of stratification,

the owner or operator may elect one of the following

alternatives:

(I) If the stratification is greater than 10 percent but the 

difference between the highest measured

concentration (time normalized) and the lowest

measured concentration (time normalized) is less

than or equal to 1.0 ppmv:

(a) Then the CEMS sampling probe may be

located at any point within the stack except

any points that is adjacent to the stack or

adjacent to the highest measured

concentration (time normalized) and the

lowest measured concentration (time

normalized), or

(b) If it is not possible to avoid using a point

adjacent to either the highest measured

concentration (time normalized) or the

lowest measured concentration (time

normalized), then locate the CEMS sampling 

probe such that the placement minimizes the

difference between the concentration at the

proposed probe location and the

concentration at the point of highest

measured concentration (time normalized) or 

the lowest measured concentration (time

normalized).

(II) Determine a representative CEMS probe location 

such that the following criteria are met:

(a) all traverse point concentrations are within

10.0% of the average of all traverse point

concentrations (time normalized), or, the
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 18

difference is less than or equal to 1.0 ppm,

whichever is greater, and

(b) there exists at least one traverse point

concentration (Xr), not located next to the

stack or duct wall, that is less than or equal

to 10.0% each adjacent traverse point

concentration of Xr, or the difference is less

than or equal to 1.0 ppm, whichever is 

greater, and,

(c) the CEMS probe is located at (or as near as

practical) Xr with minimum adjacent traverse 

point concentration fluctuations as

determined in section (ii)(II)(b), above.

(III) Determine a representative multiple point sampling

configuration as approved by the Executive Officer, 

following the guidance document by Emission

Measurement Technical Information Center,

"Evaluation Procedure for Multi-Hole Sample

Probes" (EMTIC GD-031) 

(IV) Modify the stack and/or CEMS sampling probe

location and retest for the absence of stratification.

(D) Cyclonic Flow

The owner or operator shall perform tests to verify the absence of 

cyclonic flow for the CEMS and reference method sampling probes. 

The cyclonic flow test shall be required when measuring mass 

emission rates and shall be performed according to the District 

method in the Source Test Manual, Chapter X: Non-Standard 

Methods and Techniques following the testing conditions of 

Section (3)(C)(i)(I), (II) or (III), as applicable.

(E) Interference

The owner or operator shall perform tests to verify the absence of 

sampling, analytical and flow interference, as applicable.

(F) Linearity Error

LE tests shall be performed at the low, middle and high ranges of

concentration, namely 20 to 30, 50 to 60, and 80 to 100 percent. 

Each calibration gas shall be introduced into the CEMS three times. 
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 19

The same gas shall not be used twice in succession. LE shall be less 

than or equal to 5.0 percent of the calibration gas concentration.

(G) Multiple -Span-Range

For CEMS that have multiple- span range, all certification tests 

shall be performed at the lowest range. Except for RA and 

interference tests, all other certification tests shall be performed on 

other ranges.

(4) Operational Requirements and Performance Specifications for New or

Modified CEMS

After final approval, the CEMS shall be subsequently operated and 

maintained according to the following requirements and specifications:

(A) 24-Hour CE

CE tests shall be performed once each day as close to 24 hour 

intervals as practicable at the low (0 to 20 percent) and high (80 to 

100 percent) ranges of concentration. CE test results which are 

greater than the limits specified in Sections (b)(2)(A)(i) and (ii), but 

less than or equal to 5.0 percent of the full span range shall be 

addressed by QA/QC Plan remediation. The CEMS shall be 

deemed out-of-control during such period when any CE test result 

is greater than the specified limits and greater than 5.0 percent of 

the full span range, until the CE test meets the specifications. All 

data generated by the CEMS during an out-of-control period shall 

be deemed invalid but shall not be deleted or excluded from the 

records or database.

(B) System Bias Test

A system bias shall be conducted every 12 months in conjunction 

with relative accuracy audit required under Rule 218 Section 

(b)(4)(C). The CEMS system bias shall not exceed + 5.0 percent of 

the full span range for contaminant analyzers. In addition, the 

owner or operator shall include in the facility QA/QC Plan, criteria 

for excessive drift (e.g. control limits on cumulative drift) and 

appropriate diagnostic techniques to identify sources of analyzer 

drift and system bias when control limits are exceeded.

(C) Relative Accuracy Testing

RATA and RAA, as applicable, shall be performed at least once 

every 12 months. The test shall be completed annually no later than 
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 20

the end of the calendar quarter in which the date of the original 

certification test was performed. During any relative accuracy tests 

after CEMS certification, the owner or operator may request a 

waiver from stratification, cyclonic flow, and/or interference 

requirements in Sections (b)(3)(C), (D) and (E), respectively, by 

submitting to the Executive Officer, for approval, any applicable 

documentation or previous test or historical data that meets the 

stratification, cyclonic flow, and/or interference requirements.

(D) Cylinder Gas Audit (CGA)

A CGA shall be performed every calendar quarter but in no more 

than three quarters in succession. The CGA shall be conducted 

according to the provisions of 40 CFR 60, Appendix F. The audit 

gases shall be according to the certification requirements of Rule 

218.1.

(E) The Executive Officer may require recertification of the CEMS if

the annual availability percentage is below 95 percent. Annual

CEMS availability percentage calculations will be based on the year 

ending on the last day of the calendar quarter in which the CEMS

was originally certified.

(F) The owner or operator of a CEMS that requires moisture

correction in reporting flow and concentration shall measure and

monitor moisture in the stack gas used for emission data

calculations in accordance with the written technical guidance

document set forth by the Executive Officer. Alternatively, with

Executive Officer approval, for equipment whose moisture source

is only from fuel combustion, the operator may calculate the

moisture content using fuel properties and ambient air humidity

data or, for processes that saturate the exhaust gas with moisture,

such as a wet scrubber system, the operator may use the saturation 

temperature for moisture content data.

(c) Standards for Existing CEMS

In order to be a Certified CEMS, a CEMS subject to the provisions of Rule 218

Sections (d)(1) and (d)(2), shall meet the following operational requirements and 

performance specifications, and the standards of Rule 218.1 Section (d):

(1) Performance Specifications for Existing Gaseous Air Contaminant CEMS
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 21

Parameter Specifications

(A) Operational Period Greater than or equal to 168 hours

(B) Calibration Error Less than or equal to 5 percent of

the calibration gas value

(C) Response Time Less than or equal to 10 minutes

(D) Zero Drift (2-hour) Less than or equal to 2 percent of

FSR

(E) Zero Drift (24-hour) Less than or equal to 2 percent of

FSR

(F) Calibration Drift (2-hour) Less than or equal to 2 percent of

FSR

(G) Calibration Drift (24-hour) Less than or equal to 2.5 percent

of FSR.

(H) Relative Accuracy Less than or equal to 20 percent of 

the mean value of the RM test

data, or, less than or equal to 10

percent of the allowed

concentration, whichever is

greater

(2) Performance Specifications for Existing Diluent Gas CEMS

Parameter Specifications

(A) Operational Period Greater than or equal to 168 hours

(B) Calibration Error Less than or equal to 5 percent of

the calibration gas value

(C) Response Time Less than or equal to 10 minutes

(D) Zero Drift (2-hour) Less than or equal to 0.4 percent

CO2 or O2

(E) Zero Drift (24-hour) Less than or equal to 0.5 percent

CO2 or O2

(F) Calibration Drift (2-hour) Less than or equal to 0.4 percent

CO2 or O2

(G) Calibration Drift (24 hour) Less than or equal to 0.5 percent

CO2 or O2
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 22

(3) Full Span Range for Existing CEMS

The instrument FSR shall be equivalent to approximately 200 percent of 

the concentration limit as specified in the applicable rule, or at a value 

approved by the Executive Officer. Oxygen and carbon dioxide instrument 

full span readings shall be such that the full range of concentrations 

encountered can be measured.

(4) Cycle of Operation for Existing CEMS

The CEMS shall complete a minimum of one cycle of operation (sampling, 

analyzing and data recording), for each successive 15 minute period.

(d) Standards, Specifications and Requirements for New, Modified and Existing 

CEMS:

(1) Calibration Gas

(A) Calibration gas mixtures, as defined in Rule218.1 (a)(8), shall be

manufactured, analyzed and certified in accordance with the “EPA

Traceability Protocol for Assay and Certification of Gaseous

Calibration Standards” - EPA-600/R97/121, September 1997

Revision (EPA Protocol). The certification period and

recertification requirements, as applicable, shall be according to the 

EPA Protocol. 

(B) For gas calibration standards not explicitly covered by the EPA

Protocol, the CEMS owner or operator shall submit the gas

manufacturer's alternative certification protocol for the specific

compound or compounds. 

(i) The procedures of the EPA Protocol shall be used for gas

calibration standards not explicitly covered therein, except

that the gas manufacturer must identify a recertificaton

period and submit data documenting the applicability of this 

period. The gas manufacturer may submit alternative

performance standards for certification and recertification,

based on supporting technical data also provided by the

manufacturer. This alternative shall be subject to the

approval of Executive Officer.

(ii) If there is no existing National Institute of Standards and

Technology (NIST) standard for the measured parameter,

the gas manufacturer may submit an alternative reference
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 23

standard and the supporting technical data that define the

stability, accuracy, and precision of the alternative reference 

standard. This alternative shall be subject to the approval of 

Executive Officer.

(iii) The CEMS owner or operator may submit an alternative

protocol to the EPA Protocol, provided that the CEMS

owner or operator demonstrates through supporting

technical data that the procedures therein are not applicable 

to the constituent in the calibration gas standard being

certified. This alternative shall be subject to the approval of

Executive Officer.

(C) Compressed and/or filtered air, such as instrument air, may also be

used in lieu of oxygen span gas provided that the CEMS owner or 

operator demonstrates, to the satisfaction of the Executive Officer, 

that it is of equivalent quality to the calibration gas standards above. 

As part of such documentation, the owner or operator shall include 

in their QA/QC plan the process or operation in producing such

compressed and/or filtered air and periodically checking that

compressed air and/or filtered air continues to meet the calibration

gas standards.

(2) Zero Gas

Zero gases used shall meet the following criteria:

(A) For gaseous air contaminant monitors, the zero gas shall be

certified by the manufacturer to contain no more than 0.1 ppm of

the air contaminant analyzed by the subject monitor or 1.0 percent 

of the applicable standard, whichever is less.

(B) For carbon monoxide monitors, the zero gas shall be certified by

the manufacturer to contain less than 0.5 ppm carbon monoxide or 

1.0 percent of the applicable standard, whichever is less.

(C) For carbon dioxide and oxygen monitors, the zero gas shall be

certified by the manufacturer to contain less than 1.0 ppm carbon

dioxide or oxygen.

(D) Compressed and/or filtered air, such as instrument air, may also be

used in lieu of zero gas provided that the CEMS owner or operator 

demonstrates, to the satisfaction of the Executive Officer, that it is

of equivalent quality to the above zero gas standards. As part of
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 24

such documentation, the owner or operator shall include in their

QA/QC plan the process or operation in producing such

compressed and/or filtered air and periodically checking that

compressed air and/or filtered air continues to meet the zero gas

standards.

(3) Automatic Calibration Data

If automatic adjustments to the monitor settings are made, conduct the 

calibration tests in a way that the magnitude of the adjustments can be 

determined and recorded.

(4) F-Factors

The owner or operator shall use in the CEMS calculations the Fd factors 

listed in 40 CFR Part 60, Appendix A, Method 19, Table 19-1, as 

applicable. When alternative fuels are fired, the owner or operator shall 

submit data to develop Fd factors and obtain Executive Officer approval.

(5) NO2 to NO Conversion Efficiency 

The conversion efficiency tests shall be conducted according to the 

requirements of District Method 100.1. The value for the NO2 gas shall be 

greater than or equal to the maximum expected or recorded NO2 and 

greater than or equal to 20 percent of the FSR. 

(e) Time-Sharing Requirements

A time-shared CEMS for which an application is submitted after [date of adoption] 

shall meet all of the performance specifications as well as the following

requirements:

(1) All sources shall have mutually compatible range(s) of air contaminant

gases at all times.

(2) Each source shall have a data-reading period, at a minimum, equal to three 

times the longest response time of the system. For shared systems the

response time is measured at the input or probe at each source. A

demonstration of response time for each source shall be made during

certification testing. Data are not to be collected following a switch of

sample sources until a period of time equal to one response time has

passed.

(3) The CEMS shall be capable of performing and recording zero and span

calibrations at each source, including the calibration factors and correction 

values before and after every automatic calibration.
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 25
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 26

Table 1

REFERENCE METHODS

RULE 218.1

District Method 1.1 - Sample and Velocity Traverses for Stationary Sources

District Method 1.2 - Sample and Velocity Traverses for Stationary Sources with Small 

Stack or Ducts

District Method 2.1 - Determination of Stack Gas Velocity and Volumetric Flow Rate 

(S-type Pitot tube)

District Method 2.2 - Direct Measurement of Gas Volume through Pipes and Small Ducts

District Method 2.3 - Determination of Gas Velocity and Volumetric Flow Rate from 

Small Stacks or Ducts

District Method 3.1 - Gas Analysis for Dry Molecular Weight and Excess Air

District Method 4.1 - Determination of Moisture Content in Stack Gases

District Method 6.1 - Determination of Sulfuric Acid and Sulfur Oxides from Stationary 

Sources

District Method 7.1 - Determination of Nitrogen Oxide Emissions for Stationary Sources

District Method 100.1 - Instrumental Analyzer Procedures for Continuous Gaseous 

Emission Sampling

District Method 307.91 - Determination of Sulfur in a Gaseous Matrix

EPA Method 6 - Determination of Sulfur Dioxide Emissions from Stationary Sources

EPA Method 19 - Determination of Sulfur Dioxide Removal Efficiency and Particulate, 

Sulfur Dioxide and Nitrogen Oxides Emission Rates from Electric Utility Steam 

Generator (40 CFR Part 60 Appendix A)

ASTM Method D 4294 or D 2622-82 - Determination of Sulfur in Liquid Fuels
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 27

ATTACHMENT A

SUPPLEMENTAL AND ALTERNATIVE 

CEMS PERFORMANCE REQUIREMENTS 

A. Applicability of Supplemental and Alternative Performance Requirements 

The CEMS operator who elects (or who may be required) to measure

concentrations that fall below 10 percent of the lowest vendor guaranteed full scale

span range, shall satisfy the performance requirements as specified in Table A-1 

listed below. 

TABLE A-1 

Alternative Performance Requirement(s)

CEMS Certified per 

Rule 218.1

Performance Requirement(s)

Yes or No LLSR/BFD HLSR/BFD LLR/BFD LLCE

Yes x + x

No x x + x

1. + (plus) denotes an additional performance requirement that shall be conducted if 

the mandatory performance requirement(s) cannot be met. 

2. If the concentration of the CEMS is such that the specifications for the low level 

spike recovery/bias factor determination cannot be met, the Facility Permit

holder shall conduct a low level RATA/bias factor determination. 

3. Abbreviations used in this Attachment are:

Low Level Spike Recovery/Bias Factor Determination (LLSR/BFD) 

High Level Spike Recovery/Bias Factor Determination (HLSR/BFD) 

Low Level RATA/Bias Factor Determination (LLR/BFD) 

Low Level Calibration Error (LLCE) 

Relative Accuracy Test Audit (RATA) 

Relative Accuracy (RA) 

National Institute of Standards Traceability (NIST) 

B. Test Definitions, Performance Specifications and Test Procedures 

This section explains in detail how each performance requirement is to be conducted. 

1. Low Level Calibration Error

The low level calibration error test is defined as challenging the CEMS (from

probe to monitor) with certified calibration gases (e.g., NO in N2) at three levels 
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 28

in the 0-20 percent full span range. Since certified gas mixtures or standards may 

not be available at the concentrations required for this test, gas dilution systems

may be used, with District approval, if they are used according to either District 

or EPA protocols as specified in Rule 218.1, for the verification of gas dilution 

systems in the field. The CEMS high-level calibration gas may be diluted for the 

purpose of conducting the low level calibration error test.

a. Performance Specifications 

Introduce pollutant concentrations at approximately the 20 percent, 10

percent, and 5 percent of full span levels through the normal CEMS

calibration system. No low level calibration error shall exceed 2.5 percent of 

full scale span. 

b. Testing Procedures 

i. Perform a standard zero/span check; if zero or span check exceeds 2.5 

percent full span, adjust monitor and redo zero/span check. 

ii. After zero/span check allow the CEMS to sample stack gas for at least 

15 minutes. 

iii. Introduce any of the low level calibration error standards through the

CEMS calibration system. 

iv. Read the CEMS response to the calibration gas starting no later than

three system response times after introducing the calibration gas; the

CEMS response shall be averaged for at least three response times and 

for no longer than six response times. 

v. After the low level calibration error check allow the CEMS to sample

stack gas for at least 15 minutes. 

vi. Repeat steps iii through v until all three low level calibration error

checks are complete. 

vii. Conduct post test calibration and zero checks. 

2. Spike Recovery and Bias Factor Determinations

Spiking is defined as introducing known concentrations of the pollutant of

interest (e.g., gas standard to contain a mixture of NO and NO2 is representative 

of the ratio of NO and NO2 in stack gas) and an appropriate non-reactive, noncondensable and non-soluble tracer gas from a single cylinder (EPA Protocol as 

specified in Rule 218.1 or NIST traceable to 2 percent analytical accuracy if no 

EPA Protocol is available) near the probe and upstream of any sample

conditioning systems, at a flow rate not to exceed 10 percent of the total sample 

gas flow rate. The purpose of the 10 percent limitation is to ensure that the gas 
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 29

matrix (water, CO2, particulates, interferences) is essentially the same as the

stack gas alone. The tracer gas is monitored in real time and the ratio of the

monitored concentration to the certified concentration in the cylinder is the

dilution factor. The expected pollutant concentration (dilution factor times the

certified pollutant concentration in the cylinder) is compared to the monitored

pollutant concentration. 

3. High Level Spike Recovery/Bias Factor Determination 

The high level spike recovery/bias factor determination is used when it is

technologically not possible to certify the CEMS per the standard Rule 218.1

requirements. The spiking facility/interface shall be a permanently installed part 

of the CEMS sample acquisition system and accessible to the Executive Officer 

as well as the CEMS operator.

a. Performance Specifications 

The CEMS shall demonstrate a RA < 20 percent, where the spike value is

used in place of the reference method in the normal RA calculation, as

described below.

b. Testing Procedures 

i. Spike the sample to the CEMS with a calibration standard containing the 

pollutant of interest and CO or other non-soluble, non-reacting 

alternative tracer gas (alternative tracer gas) at a flow rate not to exceed 

10 percent of the CEMS sampling flow rate and of such concentrations

as to produce an expected 40-80 percent of full scale span for the

pollutant of interest and a quantifiable concentration of CO (or

alternative tracer gas) that is at least a factor of 10 higher than expected 

in the unspiked stack gas. The calibration standards for both pollutants

of interest and CO (or alternative tracer gas) must meet requirements

ii. Monitor the CO (or alternative tracer gas) using an appropriate

continuous (or semi-continuous if necessary) monitor meeting the

requirements of Method 100.1 and all data falling within the 10-95 

percent full scale span, and preferably within 30-70 percent full scale

span. 

iii. Alternate spiked sample gas and unspiked sample gas for a total of nine

runs of spiked sample gas and ten runs of unspiked sample gas. Sampling 

times should be sufficiently long to mitigate response time and averaging 

effects. 

iv. For each run, the average CEMS reading must be between 40 percent full 

scale span and 80 percent full scale span. If not, adjust spiking as

necessary and continue runs, but expected spike must represent at least 

50 percent of the total pollutant value read by the CEMS. 
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 30

v. Calculate the spike recovery for both the pollutant and the CO (or

alternative tracer gas) for each run by first averaging the pre- and postspike values for each run and subtracting that value from the spiked value 

to yield nine values for recovered spikes. 

vi. Using the CO (or alternative tracer gas) spike recovery values for each

run and the certified CO (or alternative tracer gas) concentration,

calculate the dilution ratio for each run. Multiply the certified pollutant 

concentration by the dilution factor for each run to determine the

expected diluted pollutant concentrations. Using the expected diluted

concentrations as the "reference method" value, calculate the Relative

Accuracy. The RA shall be < 20 percent.

4. Low Level Spike Recovery/Bias Factor Determination

The low-level spike recovery/bias factor determination is used to determine if a

significant bias exists at concentrations near the 10 percent full scale span level. 

The spiking facility/interface shall be a permanently installed part of the CEMS

sample acquisition system and accessible to the Executive Officer staff as well as 

the CEMS operator. 

a. Performance Specifications 

There are no pass/fail criteria with respect to the magnitude of the percent

relative accuracy. There are performance criteria for the range of

concentration on the CEMS the extent to which the spike must be greater

than the background pollutant level. 

b. Testing Procedures 

i. Spike the sample to the CEMS with a calibration standard containing the 

pollutant of interest and CO or other non-soluble, non-reacting 

alternative tracer gas (alternative tracer gas) at a flow rate not to exceed 

10 percent of the CEMS sampling flow rate and of such concentrations

as to produce an expected 10-25 percent of full scale span for the

pollutant of interest and a quantifiable concentration of CO (or

alternative tracer gas) that is at least a factor of 10 higher than expected 

in the unspiked stack gas. The calibration standards for both pollutants

of interest and CO (or alternative tracer gas) must meet Rule 218.1

requirements.

ii. Monitor the CO (or alternative tracer gas) using an appropriate

continuous (or semi-continuous if necessary) monitor meeting the

requirements of Method 100.1 and all data falling within the 10-95 

percent full scale span, and preferably within 30-70 percent full scale

span. 
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 31

iii. Alternate spiked sample gas and unspiked sample gas for a total of nine 

runs of spiked sample gas and ten runs of unspiked sample gas. Sampling 

times should be sufficiently long to mitigate response time and averaging 

effects. 

iv. For each run, the average CEMS reading must be below 25 percent full

scale span and > 10 percent full scale span. If not, adjust spiking as

necessary and continue runs; but expected spike must represent at least

50 percent of the total pollutant value read by the CEMS. 

v. Calculate the spike recovery for both the pollutant and the CO (or

alternative tracer gas) for each run by first averaging the pre- and postspike values for each run and subtracting that value from the spiked value 

to yield nine values for recovered spikes. 

vi. Using the CO (or alternative tracer gas) spike recovery values for each

run and the certified CO (or alternative tracer gas) concentration,

calculate the dilution ratio for each run. Multiply the certified pollutant 

concentration by the dilution factor for each run to determine the

expected diluted pollutant concentrations. Using the expected diluted

concentrations as the "reference method" value, calculate the Relative

Accuracy as specified in Rule 218.1. If the average difference is less than 

the confidence coefficient then no low level bias factor is applied. If the 

average difference is greater than the confidence coefficient and the

average expected spike is less than the average CEMS measured spike,

then no low level bias factor is applied. If the average difference is

greater than the confidence coefficient and the average expected spike is 

greater than the average CEMS measured spike, then a low level bias

factor equal to the absolute value of the average difference is added to

data reported at or below the 10 percent of full scale span. 

5. Low Level RATA/Bias Factor Determination using Enhanced Reference

Method 6.1

A low level RATA/bias factor determination is designed to determine if there

exists a statistically significant bias at low level concentrations. It consists of

nine test runs that measure the stack concentration and the CEMS

concentration concurrently. 

a. Performance Specifications 

There are no pass/fail criteria with respect to the magnitude of the percent 

relative accuracy. There are performance criteria for the special RATA

with respect to the reference method and range of concentration on the

CEMS. 
Rule 218.1 (Cont.) (Adopted May 14, 1999)

218.1 - 32

b. Testing Procedures 

The reference method for the low level RATA/bias factor determination is 

Method 100.1 

i. Perform a minimum of nine runs of low level RATA for CEMS versus 

the reference method at actual levels (unspiked). 

ii. The full scale span range for the reference method shall be such that all 

data falls with 20 - 95 percent of full scale span range. 

iii. The reference method shall meet all Method 100.1 performance

criteria. 

iv. Calculate the average difference (d = CEMS - reference method, ppm) 

and confidence coefficient (cc = statistical calculated, ppm). 

v. If d > 0 then the bias = 0 ppm; if d < 0 and |d| > cc then bias = d; if d < 

0 and |d| < cc then bias = 0 ppm. 

C. Testing Frequency 

For each CEMS, perform the aforementioned performance requirements once a year 

thereafter. These annual assessments shall be completed within six months of the

end of the calendar quarter in which the CEMS was originally certified.